The cell cycle. Many tumor suppressors work to regulate the cycle at specific checkpoints in order to prevent damaged cells from replicating.
A tumor suppressor gene (TSG), or anti-oncogene, is a gene that regulates a cell during cell division and replication. If the cell grows uncontrollably, it will result in cancer.
When a tumor suppressor gene is mutated, it results in a loss or
reduction in its function. In combination with other genetic mutations,
this could allow the cell to grow abnormally. The loss of function for these genes may be even more significant in the development of human cancers, compared to the activation of oncogenes.
TSGs can be grouped into the following categories: caretaker genes,
gatekeeper genes, and more recently landscaper genes. Caretaker genes
ensure stability of the genome via DNA repair and subsequently when
mutated allow mutations to accumulate. Meanwhile, gatekeeper genes directly regulate cell growth by either inhibiting cell cycle progression or inducing apoptosis. Lastly, landscaper genes regulate growth by contributing to the
surrounding environment, and when mutated, can cause an environment that
promotes unregulated proliferation. The classification schemes are evolving as medical advances are being made from fields including molecular biology, genetics, and epigenetics.
History
The discovery of oncogenes and their ability to deregulate cellular processes related to cell proliferation and development appeared first in the literature as opposed to the idea of tumor suppressor genes. However, the idea of genetic mutation leading to increased tumor growth gave way to another possible genetic idea of genes playing a role in decreasing cellular growth and development of cells. This idea was not solidified until experiments by Henry Harris were conducted with somatic cell hybridization in 1969.
Within Harris's experiments, tumor cells were fused with normal somatic cells to make hybrid cells. Each cell had chromosomes
from both parents and upon growth, a majority of these hybrid cells did
not have the capability of developing tumors within animals. The suppression of tumorigenicity in these hybrid cells prompted researchers to hypothesize that genes within the normal somatic cell had inhibitory actions to stop tumor growth. This initial hypothesis eventually lead to the discovery of the first classic tumor suppressor gene by Alfred Knudson, known as the Rb gene, which codes for the retinoblastoma tumor suppressor protein.
Alfred Knudson, a pediatrician and cancer geneticist, proposed that in order to develop retinoblastoma, two allelic mutations are required to lose functional copies of both the Rb genes to lead to tumorigenicity. Knudson observed that retinoblastoma often developed early in life for
younger patients in both eyes, while in some rarer cases retinoblastoma
would develop later in life and only be unilateral. This unique development pattern allowed Knudson and several other
scientific groups in 1971 to correctly hypothesize that the early
development of retinoblastoma was caused by inheritance of one loss of function mutation to an RB germ-line gene followed by a later de novo mutation on its functional Rb gene allele.
The more sporadic occurrence of unilateral development of
retinoblastoma was hypothesized to develop much later in life due to two
de novo mutations that were needed to fully lose tumor suppressor properties. This finding formed the basis of the two-hit hypothesis. In order to verify that the loss of function of tumor suppressor genes causes increased tumorigenicity, interstitial deletion experiments on chromosome 13q14 were conducted to observe the effect of deleting the loci for the Rb gene. This deletion caused increased tumor growth in retinoblastoma, suggesting that loss or inactivation of a tumor suppressor gene can increase tumorigenicity.
Two-hit hypothesis
Unlike oncogenes, tumor suppressor genes generally follow the two-hit hypothesis, which states both alleles that code for a particular protein must be affected before an effect is manifested. If only one allele for the gene is damaged, the other can still produce
enough of the correct protein to retain the appropriate function. In
other words, mutant tumor suppressor alleles are usually recessive, whereas mutant oncogene alleles are typically dominant.
Models of tumor suppressionIllustration of two-hit hypothesis
Proposed by A.G. Knudson for cases of retinoblastoma. He observed that 40% of U.S cases were caused by a mutation in the
germ-line. However, affected parents could have children without the
disease, but the unaffected children became parents of children with
retinoblastoma. This indicates that one could inherit a mutated germ-line but not
display the disease. Knudson observed that the age of onset of
retinoblastoma followed 2nd order kinetics,
implying that two independent genetic events were necessary. He
recognized that this was consistent with a recessive mutation involving a
single gene, but requiring bi-allelic mutation. Hereditary cases
involve an inherited mutation and a single mutation in the normal
allele. Non-hereditary retinoblastoma involves two mutations, one on each allele. Knudson also noted that hereditary cases often developed bilateral
tumors and would develop them earlier in life, compared to
non-hereditary cases where individuals were only affected by a single
tumor.
There are exceptions to the two-hit rule for tumor suppressors, such as certain mutations in the p53 gene product. p53 mutations can function as a dominant negative, meaning that a mutated p53 protein can prevent the function of the natural protein produced from the non-mutated allele. Other tumor-suppressor genes that do not follow the two-hit rule are those that exhibit haploinsufficiency, including PTCH in medulloblastoma and NF1 in neurofibroma. Another example is p27, a cell-cycle inhibitor, that when one allele is mutated causes increased carcinogen susceptibility.
Functions
The proteins encoded by most tumor suppressor genes inhibit cell proliferation or survival. Inactivation of tumor suppressor genes therefore leads to tumor development by eliminating negative regulatory proteins. In most cases, tumor suppressor proteins inhibit the same cell regulatory pathways that are stimulated by the products of oncogenes. While tumor suppressor genes have the same main function, they have
various mechanisms of action, that their transcribed products perform,
which include the following:
Intracellular proteins, that control gene expression of a specific stage of the cell cycle. If these genes are not expressed, the cell cycle does not continue, effectively inhibiting cell division. (e.g., pRB and p16)
Proteins that induce apoptosis.
If damage cannot be repaired, the cell initiates programmed cell death
to remove the threat it poses to the organism as a whole. (e.g., p53).
Proteins involved in repairing mistakes in DNA.
Caretaker genes encode proteins that function in repairing mutations in
the genome, preventing cells from replicating with mutations.
Furthermore, increased mutation rate from decreased DNA repair leads to
increased inactivation of other tumor suppressors and activation of
oncogenes. (e.g., p53 and DNA mismatch repair protein 2 (MSH2)).
Certain genes can also act as tumor suppressors and oncogenes.
Dubbed Proto-oncogenes with Tumor suppressor function, these genes act
as "double agents" that both positively and negatively regulate transcription. (e.g., NOTCH receptors, TP53 and FAS).
Epigenetic influences
Expression of genes, including tumor suppressors, can be altered through biochemical alterations known as DNA methylation. Methylation is an example of epigenetic modifications, which commonly
regulate expression in mammalian genes. The addition of a methyl group
to either histone
tails or directly on DNA causes the nucleosome to pack tightly together
restricting the transcription of any genes in this region. This process
not only has the capabilities to inhibit gene expression, it can also
increase the chance of mutations. Stephen Baylin observed that if
promoter regions experience a phenomenon known as hypermethylation, it
could result in later transcriptional errors, tumor suppressor gene
silencing, protein misfolding, and eventually cancer growth. Baylin et
al. found methylation inhibitors known as azacitidine and decitabine.
These compounds can actually help prevent cancer growth by inducing
re-expression of previously silenced genes, arresting the cell cycle of
the tumor cell and forcing it into apoptosis.
There are further clinical trials under current investigation
regarding treatments for hypermethylation as well as alternate tumor
suppression therapies that include prevention of tissue hyperplasia,
tumor development, or metastatic spread of tumors. The team working with Wajed have investigated neoplastic tissue
methylation in order to one day identify early treatment options for
gene modification that can silence the tumor suppressor gene. In addition to DNA methylation, other epigenetic modifications like histone deacetylation
or chromatin-binding proteins can prevent DNA polymerase from
effectively transcribing desired sequences, such as ones containing
tumor suppressor genes.
Clinical significance
Gene therapy
is used to reinstate the function of a mutated or deleted gene type.
When tumor suppressor genes are altered in a way that results in less or
no expression,
several severe problems can arise for the host. This is why tumor
suppressor genes have commonly been studied and used for gene therapy.
The two main approaches used currently to introduce genetic material
into cells are viral and non-viral delivery methods.
Viral methods
The viral method of transferring genetic material harnesses the power of viruses. By using viruses that are durable to genetic material alterations,
viral methods of gene therapy for tumor suppressor genes have shown to
be successful. In this method, vectors from viruses are used. The two most commonly used vectors are adenoviralvectors and adeno-associated vectors. In vitro genetic manipulation of these types of vectors is easy and in vivo application is relatively safe compared to other vectors.Before the vectors are inserted into the tumors of the host, they are prepared by having the parts of their genome that control replication either mutated or deleted. This makes them safer for insertion. Then, the desired genetic material is inserted and ligated to the vector. In the case with tumor suppressor genes, genetic material which encodes p53 has been used successfully, which after application, has shown reduction in tumor growth or proliferation.
Non-viral methods
The non-viral method of transferring genetic material is used less often than the viral method.However, the non-viral method is a more cost-effective, safer,
available method of gene delivery not to mention that non-viral methods
have shown to induce fewer host immune responses and possess no restrictions on size or length of the transferable genetic material. Non-viral gene therapy uses either chemical or physical methods to introduce genetic material to the desired cells. The chemical methods are used primarily for tumor suppressor gene
introduction and are divided into two categories which are naked plasmid or liposome-coated plasmids. The naked plasmid strategy has garnered interest because of its easy to use methods. Direct injection into the muscles
allows for the plasmid to be taken up into the cell of possible tumors
where the genetic material of the plasmid can be incorporated into the
genetic material of the tumor cells and revert any previous damage done
to tumor suppressor genes. The liposome-coated plasmid method has recently also been of interest since they produce relatively low host immune response and are efficient with cellular targeting. The positively charged capsule in which the genetic material is packaged helps with electrostatic attraction to the negatively charged membranes of the cells as well as the negatively charged DNA of the tumor cells. In this way, non-viral methods of gene therapy are highly effective in
restoring tumor suppressor gene function to tumor cells that have either
partially or entirely lost this function.
Limitations
The
viral and non-viral gene therapies mentioned above are commonly used
but each has some limitations which must be considered. The most
important limitation these methods have is the efficacy at which the
adenoviral and adeno-associated vectors, naked plasmids, or
liposome-coated plasmids are taken in by the host's tumor cells. If
proper uptake by the host's tumor cells is not achieved, re-insertion
introduces problems such as the host's immune system recognizing these
vectors or plasmids and destroying them which impairs the overall
effectiveness of the gene therapy treatment further.
Retinoblastoma protein (pRb). pRb was the first tumor-suppressor protein discovered in human retinoblastoma; however, recent evidence has also implicated pRb as a tumor-survival factor. RB1 gene is a gatekeeper gene that blocks cell proliferation, regulates cell division and cell death. Specifically pRb prevents the cell cycle progression from G1 phase into the S phase by binding to E2F and repressing the necessary gene transcription. This prevents the cell from replicating its DNA if there is damage.
p53.TP53, a caretaker gene, encodes the protein p53,
which is nicknamed "the guardian of the genome". p53 has many different
functions in the cell including DNA repair, inducing apoptosis,
transcription, and regulating the cell cycle. Mutated p53 is involved in many human cancers, of the 6.5 million
cancer diagnoses each year about 37% are connected to p53 mutations. This makes it a popular target for new cancer therapies. Homozygous
loss of p53 is found in 65% of colon cancers, 30–50% of breast cancers,
and 50% of lung cancers. Mutated p53 is also involved in the
pathophysiology of leukemias, lymphomas, sarcomas, and neurogenic
tumors. Abnormalities of the p53 gene can be inherited in Li-Fraumeni syndrome (LFS), which increases the risk of developing various types of cancers.
BCL2.BCL2 is a family of proteins that are involved in either inducing or inhibiting apoptosis.[31] The main function is involved in maintaining the composition of the mitochondria membrane, and preventing cytochrome c release into the cytosol. When cytochrome c is released from the mitochondria it starts a signaling cascade to begin apoptosis.
SWI/SNF. SWI/SNF is a chromatin remodeling complex, which is lost in about 20% of tumors. The complex consists of 10-15 subunits encoded by 20 different genes. Mutations in the individual complexes can lead to misfolding, which
compromises the ability of the complex to work together as a whole.
SWI/SNF has the ability move nucleosomes, which condenses DNA, allowing for transcription or block transcription from occurring for certain genes. Mutating this ability could cause genes to be turned on or off at the wrong times.
As the cost of DNA sequencing continues to diminish, more cancers can
be sequenced. This allows for the discovery of novel tumor suppressors
and can give insight on how to treat and cure different cancers in the
future. Other examples of tumor suppressors include pVHL, APC, CD95, ST5, YPEL3, ST7, and ST14, p16, BRCA2.
Genome editing was pioneered in the 1990s, before the advent of the common current nuclease-based gene-editing
platforms, but its use was limited by low efficiencies of editing.
Genome editing with engineered nucleases, i.e. all three major classes
of these enzymes—zinc finger nucleases (ZFNs), transcription
activator-like effector nucleases (TALENs) and engineered
meganucleases—were selected by Nature Methods as the 2011 Method of the Year. The CRISPR-Cas system was selected by Science as 2015 Breakthrough of the Year.
In May 2019, lawyers in China reported, in light of the purported creation by Chinese scientist He Jiankui of the first gene-edited humans (see Lulu and Nana controversy), the drafting of regulations that anyone manipulating the human genome by gene-editing techniques, like CRISPR, would be held responsible for any related adverse consequences. A cautionary perspective on the possible blind spots and risks of
CRISPR and related biotechnologies has been recently discussed, focusing on the stochastic nature of cellular control processes.
In February 2020, a US trial safely showed CRISPR gene editing on 3 cancer patients. In 2020 Sicilian Rouge High GABA, a tomato that makes more of an amino
acid said to promote relaxation, was approved for sale in Japan.
In 2021, England (not the rest of the UK) planned to remove restrictions on gene-edited plants and animals, moving from European Union-compliant
regulation to rules closer to those of the US and some other countries.
An April 2021 European Commission report found "strong indications"
that the current regulatory regime was not appropriate for gene editing. Later in 2021, researchers announced a CRISPR alternative, labelled
obligate mobile element–guided activity (OMEGA) proteins including IscB,
IsrB and TnpB as endonucleases found in transposons, and guided by small ωRNAs.
Background
Genetic engineering,
as method of introducing new genetic elements into organisms, has been
around since the 1970s. One drawback of this technology has been the
random nature with which the DNA is inserted into the host's genome,
which can impair or alter other genes within the organism. However,
several methods have been discovered that target the inserted genes to specific sites within an organism's genome. It has also enabled the editing of specific sequences within a genome,
as well as reduced off-target effects. This could be used for research
purposes, by targeting mutations to specific genes, and in gene therapy.
By inserting a functional gene into an organism, and targeting it to
replace the defective one, it could be possible to cure certain genetic diseases.
Gene targeting
Homologous recombination
Early methods to target genes to certain sites within a genome of an organism (called gene targeting) relied on homologous recombination (HR). By creating DNA constructs that contain a template that matches the
targeted genome sequence, it is possible that the HR processes within
the cell will insert the construct at the desired location. Using this
method on embryonic stem cells led to the development of transgenic mice with targeted genes knocked out. It has also been possible to knock in genes or alter gene expression patterns. In recognition of their discovery of how homologous recombination can
be used to introduce genetic modifications in mice through embryonic
stem cells, Mario Capecchi, Martin Evans and Oliver Smithies were awarded the 2007 Nobel Prize for Physiology or Medicine.
Conditional targeting
If a vital gene is knocked out, it can prove lethal to the organism. In order to study the function of these genes, site specific recombinases (SSR) were used. The two most common types are the Cre-LoxP and Flp-FRT systems. Cre recombinase
is an enzyme that removes DNA by homologous recombination between
binding sequences known as Lox-P sites. The Flip-FRT system operates in a
similar way, with the Flip recombinase recognising FRT sequences. By
crossing an organism containing the recombinase sites flanking the gene
of interest with an organism that express the SSR under control of tissue specific promoters,
it is possible to knock out or switch on genes only in certain cells.
These techniques were also used to remove marker genes from transgenic
animals. Further modifications of these systems allowed researchers to
induce recombination only under certain conditions, allowing genes to be
knocked out or expressed at desired times or stages of development.
A common form of genome editing relies on the concept of DNA double stranded break (DSB) repair mechanics. There are two major pathways that repair DSB; non-homologous end joining (NHEJ) and homology directed repair
(HDR). NHEJ uses a variety of enzymes to directly join the DNA ends,
while the more accurate HDR uses a homologous sequence as a template for
regeneration of missing DNA sequences at the break point. This can be
exploited by creating a vector with the desired genetic elements within a sequence that is homologous
to the flanking sequences of a DSB. This will result in the desired
change being inserted at the site of the DSB. While HDR based gene
editing is similar to the homologous recombination based gene targeting,
the rate of recombination is increased by at least three orders of
magnitude.
Engineered nucleases
Groups of engineered nucleases. Matching colors signify DNA recognition patterns
The key to genome editing is creating a DSB at a specific point
within the genome. Commonly used restriction enzymes are effective at
cutting DNA, but generally recognize and cut at multiple sites. To
overcome this challenge and create site-specific DSB, three distinct
classes of nucleases have been discovered and bioengineered to date.
These are the Zinc finger nucleases (ZFNs), transcription-activator like effector nucleases (TALEN), meganucleases and the clustered regularly interspaced short palindromic repeats (CRISPR/Cas9) system.
Meganucleases
Meganucleases, discovered in the late 1980s, are enzymes in the endonuclease family which are characterized by their capacity to recognize and cut large DNA sequences (from 14 to 40 base pairs). The most widespread and best known meganucleases are the proteins in the LAGLIDADG family, which owe their name to a conserved amino acid sequence.
Meganucleases, found commonly in microbial species, have the
unique property of having very long recognition sequences (>14bp)
thus making them naturally very specific.However, there is virtually no chance of finding the exact meganuclease
required to act on a chosen specific DNA sequence. To overcome this
challenge, mutagenesis and high throughput screening methods have been used to create meganuclease variants that recognize unique sequences. Others have been able to fuse various meganucleases and create hybrid enzymes that recognize a new sequence. Yet others have attempted to alter the DNA interacting aminoacids of
the meganuclease to design sequence specific meganucelases in a method
named rationally designed meganuclease. Another approach involves using computer models to try to predict as
accurately as possible the activity of the modified meganucleases and
the specificity of the recognized nucleic sequence.
A large bank containing several tens of thousands of protein
units has been created. These units can be combined to obtain chimeric
meganucleases that recognize the target site, thereby providing research
and development tools that meet a wide range of needs (fundamental
research, health, agriculture, industry, energy, etc.) These include the
industrial-scale production of two meganucleases able to cleave the
human XPC gene; mutations in this gene result in Xeroderma pigmentosum, a severe monogenic disorder that predisposes the patients to skin cancer and burns whenever their skin is exposed to UV rays.
Meganucleases have the benefit of causing less toxicity in cells than methods such as Zinc finger nuclease (ZFN), likely because of more stringent DNA sequence recognition; however, the construction of sequence-specific enzymes for all possible
sequences is costly and time-consuming, as one is not benefiting from
combinatorial possibilities that methods such as ZFNs and TALEN-based
fusions utilize.
Zinc finger nucleases
As
opposed to meganucleases, the concept behind ZFNs and TALEN technology
is based on a non-specific DNA cutting catalytic domain, which can then
be linked to specific DNA sequence recognizing peptides such as zinc
fingers and transcription activator-like effectors (TALEs). The first step to this was to find an endonuclease whose DNA
recognition site and cleaving site were separate from each other, a
situation that is not the most common among restriction enzymes. Once this enzyme was found, its cleaving portion could be separated
which would be very non-specific as it would have no recognition
ability. This portion could then be linked to sequence recognizing
peptides that could lead to very high specificity.
Zinc fingermotifs occur in several transcription factors.
The zinc ion, found in 8% of all human proteins, plays an important
role in the organization of their three-dimensional structure. In
transcription factors, it is most often located at the protein-DNA
interaction sites, where it stabilizes the motif. The C-terminal part of
each finger is responsible for the specific recognition of the DNA
sequence.
The recognized sequences are short, made up of around 3 base
pairs, but by combining 6 to 8 zinc fingers whose recognition sites have
been characterized, it is possible to obtain specific proteins for
sequences of around 20 base pairs. It is therefore possible to control
the expression of a specific gene. It has been demonstrated that this
strategy can be used to promote a process of angiogenesis in animals. It is also possible to fuse a protein constructed in this way with the
catalytic domain of an endonuclease in order to induce a targeted DNA
break, and therefore to use these proteins as genome engineering tools.
The method generally adopted for this involves associating two
DNA binding proteins – each containing 3 to 6 specifically chosen zinc
fingers – with the catalytic domain of the FokI
endonuclease which need to dimerize to cleave the double-strand DNA.
The two proteins recognize two DNA sequences that are a few nucleotides
apart. Linking the two zinc finger proteins to their respective
sequences brings the two FokI domains closer together. FokI requires
dimerization to have nuclease activity and this means the specificity
increases dramatically as each nuclease partner would recognize a unique
DNA sequence. To enhance this effect, FokI nucleases have been engineered that can only function as heterodimers.
Several approaches are used to design specific zinc finger
nucleases for the chosen sequences. The most widespread involves
combining zinc-finger units with known specificities (modular assembly).
Various selection techniques, using bacteria, yeast or mammal cells
have been developed to identify the combinations that offer the best
specificity and the best cell tolerance. Although the direct genome-wide
characterization of zinc finger nuclease activity has not been
reported, an assay that measures the total number of double-strand DNA
breaks in cells found that only one to two such breaks occur above
background in cells treated with zinc finger nucleases with a 24 bp
composite recognition site and obligate heterodimer FokI nuclease domains.
The heterodimer functioning nucleases would avoid the possibility
of unwanted homodimer activity and thus increase specificity of the
DSB. Although the nuclease portions of both ZFNs and TALEN constructs
have similar properties, the difference between these engineered
nucleases is in their DNA recognition peptide. ZFNs rely on Cys2-His2
zinc fingers and TALEN constructs on TALEs. Both of these DNA
recognizing peptide domains have the characteristic that they are
naturally found in combinations in their proteins. Cys2-His2 Zinc
fingers typically happen in repeats that are 3 bp apart and are found in
diverse combinations in a variety of nucleic acid interacting proteins
such as transcription factors.
Each finger of the Zinc finger domain is completely independent and the
binding capacity of one finger is impacted by its neighbor. TALEs on
the other hand are found in repeats with a one-to-one recognition ratio
between the amino acids and the recognized nucleotide pairs. Because
both zinc fingers and TALEs happen in repeated patterns, different
combinations can be tried to create a wide variety of sequence
specificities. Zinc fingers have been more established in these terms and approaches
such as modular assembly (where Zinc fingers correlated with a triplet
sequence are attached in a row to cover the required sequence), OPEN
(low-stringency selection of peptide domains vs. triplet nucleotides
followed by high-stringency selections of peptide combination vs. the
final target in bacterial systems), and bacterial one-hybrid screening
of zinc finger libraries among other methods have been used to make site
specific nucleases.
Zinc finger nucleases
are research and development tools that have already been used to
modify a range of genomes, in particular by the laboratories in the Zinc
Finger Consortium. The US company Sangamo BioSciences uses zinc finger nucleases to carry out research into the genetic engineering of stem cells and the modification of immune cells for therapeutic purposes. Modified T lymphocytes are currently undergoing phase I clinical trials to treat a type of brain tumor (glioblastoma) and in the fight against AIDS.
TALEN
General overview of the TALEN process
Transcription activator-like effector nucleases
(TALENs) are specific DNA-binding proteins that feature an array of 33
or 34-amino acid repeats. TALENs are artificial restriction enzymes
designed by fusing the DNA cutting domain of a nuclease to TALE domains,
which can be tailored to specifically recognize a unique DNA sequence.
These fusion proteins serve as readily targetable "DNA scissors" for
gene editing applications that enable to perform targeted genome
modifications such as sequence insertion, deletion, repair and
replacement in living cells. The DNA binding domains, which can be designed to bind any desired DNA sequence, comes from TAL effectors, DNA-binding proteins excreted by plant pathogenic Xanthomanos app.
TAL effectors consists of repeated domains, each of which contains a
highly conserved sequence of 34 amino acids, and recognize a single DNA
nucleotide within the target site. The nuclease can create double strand
breaks at the target site that can be repaired by error-prone non-homologous end-joining
(NHEJ), resulting in gene disruptions through the introduction of small
insertions or deletions. Each repeat is conserved, with the exception
of the so-called repeat variable di-residues (RVDs) at amino acid
positions 12 and 13. The RVDs determine the DNA sequence to which the
TALE will bind. This simple one-to-one correspondence between the TALE
repeats and the corresponding DNA sequence makes the process of
assembling repeat arrays to recognize novel DNA sequences
straightforward. These TALEs can be fused to the catalytic domain from a
DNA nuclease, FokI, to generate a transcription activator-like effector
nuclease (TALEN). The resultant TALEN constructs combine specificity
and activity, effectively generating engineered sequence-specific
nucleases that bind and cleave DNA sequences only at pre-selected sites.
The TALEN target recognition system is based on an easy-to-predict
code. TAL nucleases are specific to their target due in part to the
length of their 30+ base pairs binding site. TALEN can be performed
within a 6 base pairs range of any single nucleotide in the entire
genome.
TALEN constructs are used in a similar way to designed zinc
finger nucleases, and have three advantages in targeted mutagenesis: (1)
DNA binding specificity is higher, (2) off-target effects are lower, and (3) construction of DNA-binding domains is easier.
CRISPRs (Clustered Regularly Interspaced Short Palindromic Repeats) are genetic elements that bacteria use as a kind of acquired immunity
to protect against viruses. They consist of short sequences that
originate from viral genomes and have been incorporated into the
bacterial genome. Cas (CRISPR associated proteins) process these
sequences and cut matching viral DNA sequences. By introducing plasmids
containing Cas genes and specifically constructed CRISPRs into
eukaryotic cells, the eukaryotic genome can be cut at any desired
position.
Editing by nucleobase modification (Base editing)
One
of the earliest methods of efficiently editing nucleic acids employs
nucleobase modifying enzymes directed by nucleic acid guide sequences
was first described in the 1990s and has seen resurgence more recently. This method has the advantage that it does not require breaking the
genomic DNA strands, and thus avoids the random insertion and deletions
associated with DNA strand breakage. It is only appropriate for precise
editing requiring single nucleotide changes and has found to be highly
efficient for this type of editing.
ARCUT
ARCUT
stands for artificial restriction DNA cutter, it is a technique
developed by Komiyama. This method uses pseudo-complementary peptide
nucleic acid (pcPNA), for identifying cleavage site within the
chromosome. Once pcPNA specifies the site, excision is carried out by
cerium (CE) and EDTA (chemical mixture), which performs the splicing
function.
Precision and efficiency of engineered nucleases
Meganucleases
method of gene editing is the least efficient of the methods mentioned
above. Due to the nature of its DNA-binding element and the cleaving
element, it is limited to recognizing one potential target every 1,000
nucleotides. ZFN was developed to overcome the limitations of meganuclease. The
number of possible targets ZFN can recognise was increased to one in
every 140 nucleotides. However, both methods are unpredictable because of their DNA-binding
elements affecting each other. As a result, high degrees of expertise
and lengthy and costly validation processes are required.
TALE nucleases, being the most precise and specific method,
yields a higher efficiency than the previous two methods. It achieves
such efficiency because the DNA-binding element consists of an array of
TALE subunits, each of them having the capability of recognizing a
specific DNA nucleotide chain independently from others, resulting in a
higher number of target sites with high precision. New TALE nucleases
take about one week and a few hundred dollars to create, with specific
expertise in molecular biology and protein engineering.
CRISPR nucleases have a slightly lower precision when compared to
the TALE nucleases. This is caused by the need to have a specific
nucleotide at one end in order to produce the guide RNA that CRISPR uses
to repair the double-strand break it induces. It has been shown to be
the quickest and cheapest method, only costing less than two hundred
dollars and a few days of time. CRISPR also requires the least amount of expertise in molecular
biology, as the design lays in the guide RNA instead of the proteins.
One major advantage that CRISPR has over the ZFN and TALEN methods is
that it can be directed to target different DNA sequences using its
~80nt CRISPR sgRNAs, while both ZFN and TALEN methods required
construction and testing of the proteins created for targeting each DNA
sequence.
Because off-target activity
of an active nuclease would have potentially dangerous consequences at
the genetic and organismal levels, the precision of meganucleases, ZFNs,
CRISPR, and TALEN-based fusions has been an active area of research.
While variable figures have been reported, ZFNs tend to have more
cytotoxicity than TALEN methods or RNA-guided nucleases, while TALEN and
RNA-guided approaches tend to have the greatest efficiency and fewer
off-target effects. Based on the maximum theoretical distance between DNA binding and
nuclease activity, TALEN approaches result in the greatest precision.
Multiplex Automated Genomic Engineering (MAGE)
Synthetic
DNA is repeatedly introduced at multiple targeted areas of the
chromosome and/or loci and then is replicated producing cells
with/without mutations.
The methods for scientists and researchers wanting to study genomic
diversity and all possible associated phenotypes were very slow,
expensive, and inefficient. Prior to this new revolution, researchers
would have to do single-gene manipulations and tweak the genome one
little section at a time, observe the phenotype, and start the process
over with a different single-gene manipulation. Therefore, researchers at the Wyss Institute at Harvard University
designed the MAGE, a powerful technology that improves the process of in
vivo genome editing. It allows for quick and efficient manipulations of
a genome, all happening in a machine small enough to put on top of a
small kitchen table. Those mutations combine with the variation that
naturally occurs during cell mitosis creating billions of cellular
mutations.
Chemically combined, synthetic single-stranded DNA (ssDNA) and a
pool of oligonucleotides are introduced at targeted areas of the cell,
thereby creating genetic modifications. The cyclical process involves
transformation of ssDNA (by electroporation)
followed by outgrowth, during which bacteriophage homologous
recombination proteins mediate annealing of ssDNAs to their genomic
targets. Experiments targeting selective phenotypic markers are screened
and identified by plating the cells on differential medias. Each cycle
ultimately takes 2.5 hours to process, with additional time required to
grow isogenic cultures and characterize mutations. By iteratively
introducing libraries of mutagenic ssDNAs targeting multiple sites, MAGE
can generate combinatorial genetic diversity in a cell population.
There can be up to 50 genome edits, from single nucleotide base pairs to
whole genome or gene networks simultaneously with results in a matter
of days.
MAGE experiments can be divided into three classes, characterized
by varying degrees of scale and complexity: (i) many target sites,
single genetic mutations; (ii) single target site, many genetic
mutations; and (iii) many target sites, many genetic mutations. An example of class three was reflected in 2009, where Church and colleagues were able to program Escherichia coli
to produce five times the normal amount of lycopene, an antioxidant
normally found in tomato seeds and linked to anti-cancer properties.
They applied MAGE to optimize the 1-deoxy-D-xylulose 5-phosphate (DXP) metabolic pathway in Escherichia coli
to overproduce isoprenoid lycopene. It took them about 3 days and just
over $1,000 in materials. The ease, speed, and cost efficiency in which
MAGE can alter genomes can transform how industries approach the
manufacturing and production of important compounds in the
bioengineering, bioenergy, biomedical engineering, synthetic biology,
pharmaceutical, agricultural, and chemical industries.
Applications
Plants, animals and human genes that are successfully targeted using ZFN, which demonstrates the generality of this approach
As of 2012, efficient genome editing had been developed for a wide
range of experimental systems ranging from plants to animals, often
beyond clinical interest, and was becoming a standard experimental
strategy in research labs. The recent generation of rat, zebrafish, maize and tobacco
ZFN-mediated mutants and the improvements in TALEN-based approaches
testify to the significance of the methods, and the list is expanding
rapidly. Genome editing with engineered nucleases will likely contribute
to many fields of life sciences from studying gene functions in plants
and animals to gene therapy in humans. For instance, the field of synthetic biology
which aims to engineer cells and organisms to perform novel functions,
is likely to benefit from the ability of engineered nuclease to add or
remove genomic elements and therefore create complex systems. In addition, gene functions can be studied using stem cells with engineered nucleases.
Listed below are some specific tasks this method can carry out:
The
combination of recent discoveries in genetic engineering, particularly
gene editing and the latest improvement in bovine reproduction
technologies (e.g. in vitro embryo culture) allows for genome
editing directly in fertilised oocytes using synthetic highly specific
endonucleases. RNA-guided endonucleases:clustered regularly interspaced
short palindromic repeats associated Cas9 (CRISPR/Cas9) are a new tool,
further increasing the range of methods available. In particular
CRISPR/Cas9 engineered endonucleases allows the use of multiple guide
RNAs for simultaneous Knockouts (KO) in one step by cytoplasmic direct
injection (CDI) on mammalian zygotes.
Furthermore, gene editing can be applied to certain types of fish
in aquaculture such as Atlantic salmon. Gene editing in fish is
currently experimental, but the possibilities include growth, disease
resistance, sterility, controlled reproduction, and colour. Selecting
for these traits can allow for a more sustainable environment and better
welfare for the fish.
AquAdvantage salmon
is a genetically modified Atlantic salmon developed by AquaBounty
Technologies. The growth hormone-regulating gene in the Atlantic salmon
is replaced with the growth hormone-regulating gene from the Pacific
Chinook salmon and a promoter sequence from the ocean pout.
Thanks to the parallel development of single-cell
transcriptomics, genome editing and new stem cell models we are now
entering a scientifically exciting period where functional genetics is
no longer restricted to animal models but can be performed directly in
human samples. Single-cell gene expression analysis has resolved a
transcriptional road-map of human development from which key candidate
genes are being identified for functional studies. Using global
transcriptomics data to guide experimentation, the CRISPR based genome
editing tool has made it feasible to disrupt or remove key genes in
order to elucidate function in a human setting.
Targeted gene modification in plants
Overview of GEEN workflow and editing possibilities
Genome editing using Meganuclease, ZFNs, and TALEN provides a new strategy for genetic manipulation in
plants and are likely to assist in the engineering of desired plant
traits by modifying endogenous genes. For instance, site-specific gene
addition in major crop species can be used for 'trait stacking' whereby
several desired traits are physically linked to ensure their
co-segregation during the breeding processes. Progress in such cases have been recently reported in Arabidopsis thaliana and Zea mays. In Arabidopsis thaliana,
using ZFN-assisted gene targeting, two herbicide-resistant genes
(tobacco acetolactate synthase SuRA and SuRB) were introduced to SuR
loci with as high as 2% transformed cells with mutations. In Zea mays, disruption of the target locus was achieved by ZFN-induced
DSBs and the resulting NHEJ. ZFN was also used to drive
herbicide-tolerance gene expression cassette (PAT) into the targeted endogenous locus IPK1 in this case. Such genome modification observed in the regenerated plants has been
shown to be inheritable and was transmitted to the next generation. A potentially successful example of the application of genome editing
techniques in crop improvement can be found in banana, where scientists
used CRISPR/Cas9 editing to inactivate the endogenous banana streak virus in the B genome of banana (Musa spp.) to overcome a major challenge in banana breeding.
In addition, TALEN-based genome engineering has been extensively tested and optimized for use in plants. TALEN fusions have also been used by a U.S. food ingredient company, Calyxt, to improve the quality of soybean oil products and to increase the storage potential of potatoes.
Several optimizations need to be made in order to improve editing plant genomes using ZFN-mediated targeting. There is a need for reliable design and subsequent test of the
nucleases, the absence of toxicity of the nucleases, the appropriate
choice of the plant tissue for targeting, the routes of induction of
enzyme activity, the lack of off-target mutagenesis, and a reliable detection of mutated cases.
A common delivery method for CRISPR/Cas9 in plants is Agrobacterium-based transformation. T-DNA is introduced directly into the plant genome by a T4SS mechanism. Cas9 and gRNA-based expression cassettes are turned into Ti plasmids, which are transformed in Agrobacterium for plant application. To improve Cas9 delivery in live plants, viruses are being used more effective transgene delivery.
Research
Gene therapy
The ideal gene therapy
practice is one that replaces the defective gene with a normal allele
at its natural location. This is advantageous over a virally-delivered
gene, as there is no need to include the full coding sequences and
regulatory sequences when only a small proportion of the gene needs to
be altered, as is often the case. The expression of the partially replaced genes is also more consistent
with normal cell biology than full genes that are carried by viral
vectors.
The first clinical use of TALEN-based genome editing was in the treatment of CD19+ acute lymphoblastic leukemia in an 11-month old child in 2015. Modified donor T cells were engineered to attack the leukemia cells, to be resistant to Alemtuzumab, and to evade detection by the host immune system after introduction.
Extensive research has been done in cells and animals using
CRISPR-Cas9 to attempt to correct genetic mutations which cause genetic
diseases such as Down syndrome, spina bifida, anencephaly, and Turner
and Klinefelter syndromes.
Researchers have used CRISPR-Cas9 gene drives to modify genes associated with sterility in A. gambiae, the vector for malaria. This technique has further implications in eradicating other vector borne diseases such as yellow fever, dengue, and Zika.
The CRISPR-Cas9 system can be programmed to modulate the
population of any bacterial species by targeting clinical genotypes or
epidemiological isolates. It can selectively enable the beneficial
bacterial species over the harmful ones by eliminating pathogen, which
gives it an advantage over broad-spectrum antibiotics.
Antiviral applications for therapies targeting human viruses such
as HIV, herpes, and hepatitis B virus are under research. CRISPR can be
used to target the virus or the host to disrupt genes encoding the
virus cell-surface receptor proteins. In November 2018, He Jiankui announced that he had edited two human embryos, to attempt to disable the gene for CCR5, which codes for a receptor that HIV uses to enter cells. He said that twin girls, Lulu and Nana, had been born a few weeks earlier. He said that the girls still carried functional copies of CCR5 along with disabled CCR5 (mosaicism) and were still vulnerable to HIV. The work was widely condemned as unethical, dangerous, and premature.
In January 2019, scientists in China reported the creation of five identical cloned gene-edited monkeys, using the same cloning technique that was used with Zhong Zhong and Hua Hua – the first ever cloned monkeys - and Dolly the sheep, and the same gene-editing Crispr-Cas9 technique allegedly used by He Jiankui in creating the first ever gene-modified human babies Lulu and Nana. The monkey clones were made in order to study several medical diseases.
Prospects and limitations
In
the future, an important goal of research into genome editing with
engineered nucleases must be the improvement of the safety and
specificity of the nucleases action. For example, improving the ability to detect off-target events can
improve our ability to learn about ways of preventing them. In addition,
zinc-fingers used in ZFNs are seldom completely specific, and some may
cause a toxic reaction. However, the toxicity has been reported to be
reduced by modifications done on the cleavage domain of the ZFN.
In addition, research by Dana Carroll
into modifying the genome with engineered nucleases has shown the need
for better understanding of the basic recombination and repair machinery
of DNA. In the future, a possible method to identify secondary targets
would be to capture broken ends from cells expressing the ZFNs and to
sequence the flanking DNA using high-throughput sequencing.
Because of the ease of use and cost-efficiency of CRISPR,
extensive research is currently being done on it. There are now more
publications on CRISPR than ZFN and TALEN despite how recent the
discovery of CRISPR is. Both CRISPR and TALEN are favored to be the choices to be implemented
in large-scale productions due to their precision and efficiency.
Genome editing occurs also as a natural process without
artificial genetic engineering. The agents that are competent to edit
genetic codes are viruses or subviral RNA-agents.
Although GEEN has higher efficiency than many other methods in
reverse genetics, it is still not highly efficient; in many cases less
than half of the treated populations obtain the desired changes. For example, when one is planning to use the cell's NHEJ to create a
mutation, the cell's HDR systems will also be at work correcting the DSB
with lower mutational rates.
Traditionally, mice have been the most common choice for
researchers as a host of a disease model. CRISPR can help bridge the gap
between this model and human clinical trials by creating transgenic
disease models in larger animals such as pigs, dogs, and non-human
primates. Using the CRISPR-Cas9 system, the programmed Cas9 protein and the sgRNA
can be directly introduced into fertilized zygotes to achieve the
desired gene modifications when creating transgenic models in rodents.
This allows bypassing of the usual cell targeting stage in generating
transgenic lines, and as a result, it reduces generation time by 90%.
One potential that CRISPR brings with its effectiveness is the
application of xenotransplantation. In previous research trials, CRISPR
demonstrated the ability to target and eliminate endogenous
retroviruses, which reduces the risk of transmitting diseases and
reduces immune barriers. Eliminating these problems improves donor organ function, which brings this application closer to a reality.
In plants, genome editing is seen as a viable solution to the conservation of biodiversity. Gene drive are a potential tool to alter the reproductive rate of invasive species, although there are significant associated risks.
Many transhumanists see genome editing as a potential tool for human enhancement.Australian biologist and Professor of Genetics David Andrew Sinclair
notes that "the new technologies with genome editing will allow it to
be used on individuals (...) to have (...) healthier children" – designer babies. According to a September 2016 report by the Nuffield Council on
Bioethics in the future it may be possible to enhance people with genes
from other organisms or wholly synthetic genes to for example improve night vision and sense of smell. George Church has compiled a list of potential genetic modifications for possibly advantageous traits such as less need for sleep, cognition-related changes that protect against Alzheimer's disease, disease resistances and enhanced learning abilities along with some of the associated studies and potential negative effects.
The American National Academy of Sciences and National Academy of Medicine issued a report in February 2017 giving qualified support to human genome editing. They recommended that clinical trials for genome editing might one day
be permitted once answers have been found to safety and efficiency
problems "but only for serious conditions under stringent oversight."
Risks
In the 2016 Worldwide Threat Assessment of the US Intelligence Community statement United States Director of National Intelligence, James R. Clapper, named genome editing as a potential weapon of mass destruction,
stating that genome editing conducted by countries with regulatory or
ethical standards "different from Western countries" probably increases
the risk of the creation of harmful biological agents or products.
According to the statement the broad distribution, low cost, and
accelerated pace of development of this technology, its deliberate or
unintentional misuse might lead to far-reaching economic and national
security implications. For instance technologies such as CRISPR could be used to make "killer
mosquitoes" that cause plagues that wipe out staple crops.
According to a September 2016 report by the Nuffield Council on Bioethics, the simplicity and low cost of tools to edit the genetic code will allow amateurs – or "biohackers" –
to perform their own experiments, posing a potential risk from the
release of genetically modified bugs. The review also found that the
risks and benefits of modifying a person's genome – and having those
changes pass on to future generations – are so complex that they demand
urgent ethical scrutiny. Such modifications might have unintended
consequences which could harm not only the child, but also their future
children, as the altered gene would be in their sperm or eggs. In 2001 Australian researchers Ronald Jackson and Ian Ramshaw were criticized for publishing a paper in the Journal of Virology that explored the potential control of mice, a major pest in Australia, by infecting them with an altered mousepox virus that would cause infertility as the provided sensitive information could lead to the manufacture of biological weapons by potential bioterrorists who might use the knowledge to create vaccine resistant strains of other pox viruses, such as smallpox, that could affect humans. Furthermore, there are additional concerns about the ecological risks of releasing gene drives into wild populations.
Medicine has been practiced since prehistoric times, and for most of this time it was an art (an area of creativity and skill), frequently having connections to the religious and philosophical beliefs of local culture. For example, a medicine man would apply herbs and say prayers for healing, or an ancient philosopher and physician would apply bloodletting according to the theories of humorism. In recent centuries, since the advent of modern science, most medicine has become a combination of art and science (both basic and applied, under the umbrella of medical science). For example, while stitching technique for sutures is an art learned through practice, knowledge of what happens at the cellular and molecular level in the tissues being stitched arises through science.
Prescientific forms of medicine, now known as traditional medicine or folk medicine, remain commonly used in the absence of scientific medicine and are thus called alternative medicine. Alternative treatments outside of scientific medicine with ethical, safety and efficacy concerns are termed quackery.
Medical availability and clinical practice vary across the world due to regional differences in culture and technology. Modern scientific medicine is highly developed in the Western world, while in developing countries such as parts of Africa or Asia, the population may rely more heavily on traditional medicine with limited evidence and efficacy and no required formal training for practitioners.
In the developed world, evidence-based medicine
is not universally used in clinical practice; for example, a 2007
survey of literature reviews found that about 49% of the interventions
lacked sufficient evidence to support either benefit or harm.
In modern clinical practice, physicians and physician assistants personally assess patients to diagnose, prognose, treat, and prevent disease using clinical judgment. The doctor-patient relationship typically begins with an interaction with an examination of the patient's medical history and medical record, followed by a medical interview and a physical examination. Basic diagnostic medical devices (e.g., stethoscope, tongue depressor) are typically used. After examining for signs and interviewing for symptoms, the doctor may order medical tests (e.g., blood tests), take a biopsy, or prescribe pharmaceutical drugs or other therapies. Differential diagnosis
methods help to rule out conditions based on the information provided.
During the encounter, properly informing the patient of all relevant
facts is an important part of the relationship and the development of
trust. The medical encounter is then documented in the medical record,
which is a legal document in many jurisdictions. Follow-ups may be shorter but follow the same general procedure, and
specialists follow a similar process. The diagnosis and treatment may
take only a few minutes or a few weeks, depending on the complexity of
the issue.
The components of the medical interview and encounter are:
Chief complaint (CC): the reason for the current medical visit. These are the symptoms. They are in the patient's own words and are recorded along with the duration of each one. Also called chief concern or presenting complaint.
Current activity: occupation, hobbies, what the patient actually does.
Family history (FH): listing of diseases in the family that may impact the patient. A family tree is sometimes used.
History of present illness
(HPI): the chronological order of events of symptoms and further
clarification of each symptom. Distinguishable from history of previous
illness, often called past medical history (PMH). Medical history comprises HPI and PMH.
Past medical history (PMH/PMHx): concurrent medical problems, past hospitalizations and operations, injuries, past infectious diseases or vaccinations, history of known allergies.
Review of systems (ROS) or systems inquiry: a set of additional questions to ask, which may be missed on HPI: a general enquiry (have you noticed any weight loss, change in sleep quality, fevers, lumps and bumps? etc.), followed by questions on the body's main organ systems (heart, lungs, digestive tract, urinary tract, etc.).
Social history (SH): birthplace, residences, marital history, social and economic status, habits (including diet, medications, tobacco, alcohol).
The physical examination is the examination of the patient for
medical signs of disease that are objective and observable, in contrast
to symptoms that are volunteered by the patient and are not necessarily
objectively observable. The healthcare provider uses sight, hearing, touch, and sometimes smell (e.g., in infection, uremia, diabetic ketoacidosis). Four actions are the basis of physical examination: inspection, palpation (feel), percussion (tap to determine resonance characteristics), and auscultation (listen), generally in that order, although auscultation occurs prior to percussion and palpation for abdominal assessments.
It is to likely focus on areas of interest highlighted in the medical history and may not include everything listed above.
The treatment plan may include ordering additional medical laboratory tests and medical imaging studies, starting therapy, referral to a specialist, or watchful observation. A follow-up may be advised. Depending upon the health insurance plan and the managed care system, various forms of "utilization review", such as prior authorization of tests, may place barriers on accessing expensive services.
The medical decision-making (MDM) process includes the analysis
and synthesis of all the above data to come up with a list of possible
diagnoses (the differential diagnoses), along with an idea of what needs
to be done to obtain a definitive diagnosis that would explain the
patient's problem.
On subsequent visits, the process may be repeated in an
abbreviated manner to obtain any new history, symptoms, physical
findings, lab or imaging results, or specialist consultations.
Contemporary medicine is, in general, conducted within health care systems. Legal, credentialing,
and financing frameworks are established by individual governments,
augmented on occasion by international organizations, such as churches.
The characteristics of any given health care system have a significant
impact on the way medical care is provided.
From ancient times, Christian emphasis on practical charity gave
rise to the development of systematic nursing and hospitals, and the Catholic Church today remains the largest non-government provider of medical services in the world. Advanced industrial countries (with the exception of the United States)and many developing countries provide medical services through a system of universal health care that aims to guarantee care for all through a single-payer health care
system or compulsory private or cooperative health insurance. This is
intended to ensure that the entire population has access to medical care
on the basis of need rather than ability to pay. Delivery may be via
private medical practices, state-owned hospitals and clinics, or
charities, most commonly a combination of all three.
Most tribal
societies provide no guarantee of healthcare for the population as a
whole. In such societies, healthcare is available to those who can
afford to pay for it, have self-insured it (either directly or as part
of an employment contract), or may be covered by care financed directly
by the government or tribe.
Transparency of information is another factor defining a delivery
system. Access to information on conditions, treatments, quality, and
pricing greatly affects the choice of patients/consumers and, therefore,
the incentives of medical professionals. While the US healthcare system
has come under fire for its lack of openness, new legislation may encourage greater openness. There is a perceived
tension between the need for transparency on the one hand and such
issues as patient confidentiality and the possible exploitation of
information for commercial gain on the other.
Primary care medical services are provided by physicians, physician assistants, nurse practitioners, or other health professionals who have first contact with a patient seeking medical treatment or care. These occur in physician offices, medical practices, clinics, nursing homes,
schools, patients' homes, and in other places that are typically
geographically close to where patients live, work or study. About 90% of
medical visits can be satisfactorily and effectively dealt with by
primary care provider(s). Primary care visits might include treatment of minor, acute or chronic illnesses, preventive care, and health education. Primary care is directed to the health of entire populations and thus providers care for patients of all ages and sexes.
Secondary care medical services are provided by medical specialists
in their offices, practices or clinics, or at local community
hospitals, to patients referred by the primary care provider who first
diagnosed or treated the patient. 'Referrals' are made of those patients who required the particular
expertise of, or specific procedures performed by, specialists.
Secondary care services include both ambulatory care and inpatient services, emergency departments, some intensive care medicine, some surgeries and related services, physical therapy, labor and delivery, endoscopy units, diagnostic laboratory and medical imaging services, hospice
centers, and others depending on the health services systems within
which the care is being delivered. Some primary care providers may also
take care of hospitalized patients and deliver babies in a secondary
care setting.
Tertiary care
medical services are provided by specialist teams of providers in
larger, more specialised hospitals or regional medical centers, which
are equipped with diagnostic and treatment facilities not typically
available at local (often smaller) hospitals. This allows for the
treatment and care of patients with more complex or urgent or serious
medical conditions, which in turn may require more expertise (including
multi-disciplinary teams) and resources (facilities, staff, bed days) to
effectively treat. Tertiary care may include that provided at burn treatment or trauma centers, advanced neonatology unit services, organ transplants, high-risk pregnancy and child delivery, radiationoncology, and very many other forms of specialist and intensive care.
Modern medical care also depends on the keeping and use of
information, including about a particular patient—still kept in many
health care settings on paper 'medical records', but increasingly
nowadays by electronic means.
In low-income countries, modern healthcare is often too expensive
for the average person. International healthcare policy researchers
have advocated that "user fees" be removed in these areas to ensure
access; however, even with removal of patient fee obligations,
significant costs and barriers remain for the poor and the sick in
accessing sufficient care.
Separation of prescribing and dispensing is a practice in medicine and pharmacy in which the physician who provides a medical prescription is different from the pharmacist who provides the prescription drug
to the patient. In the Western world there are centuries of tradition
and practice differentiating pharmacists from physicians, and two quite
separate professions developed. In many Asian countries, on the other
hand, it is traditional for physicians to also deliver drugs directly to
patients, at least in some cases. This model is also being used increasingly in the west: especially for
simply-treated conditions (eg, those needing general antibiotics), in
remote locations, with vulnerable communities of patients, and in small
or integrated medical facilities.
Branches
Drawing by Marguerite Martyn (1918) of a visiting nurse in St. Louis, Missouri, with medicine and babies
The scope and sciences underpinning human medicine overlap many
other fields. A patient admitted to the hospital is usually under the
care of a specific team based on their main presenting problem, e.g.,
the cardiology team, who then may interact with other specialties, e.g., surgical, radiology, to help diagnose or treat the main problem or any subsequent complications/developments.
Physicians have many specializations and subspecializations into
certain branches of medicine, which are listed below. There are
variations from country to country regarding which specialties certain
subspecialties are in.
The main branches of medicine are:
Basic sciences of medicine; this is what every physician is educated in, and some return to in biomedical research.
Interdisciplinary fields, where different medical specialties are mixed to function in certain occasions.
Biostatistics is the application of statistics
to biological fields in the broadest sense. A knowledge of
biostatistics is essential in the planning, evaluation, and
interpretation of medical research. It is also fundamental to epidemiology and evidence-based medicine.
Cytology is the microscopic study of individual cells.
In the broadest meaning of "medicine", there are many different
specialties. In the UK, most specialities have their own body or
college, which has its own entrance examination. These are collectively
known as the Royal Colleges, although not all currently use the term
"Royal". The development of a speciality is often driven by new
technology (such as the development of effective anaesthetics) or ways
of working (such as emergency departments); the new specialty leads to
the formation of a unifying body of doctors and the prestige of
administering their own examination.
Within medical circles, specialities usually fit into one of two
broad categories: "Medicine" and "Surgery". "Medicine" refers to the
practice of non-operative medicine, and most of its subspecialties
require preliminary training in Internal Medicine. In the UK, this was
traditionally evidenced by passing the examination for the Membership of
the Royal College of Physicians
(MRCP) or the equivalent college in Scotland or Ireland. "Surgery"
refers to the practice of operative medicine, and most subspecialties in
this area require preliminary training in General Surgery, which in the
UK leads to membership of the Royal College of Surgeons of England
(MRCS). At present, some specialties of medicine do not fit easily into
either of these categories, such as radiology, pathology, or
anesthesia. Most of these have branched from one or other of the two
camps above; for example anaesthesia developed first as a faculty of the Royal College of Surgeons (for which MRCS/FRCS would have been required) before becoming the Royal College of Anaesthetists
and membership of the college is attained by sitting for the
examination of the Fellowship of the Royal College of Anesthetists
(FRCA).
Surgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate or treat a pathological condition such as disease or injury, to help improve bodily function or appearance or to repair unwanted ruptured areas (for example, a perforated ear drum).
Surgeons must also manage pre-operative, post-operative, and potential
surgical candidates on the hospital wards. In some centers, anesthesiology
is part of the division of surgery (for historical and logistical
reasons), although it is not a surgical discipline. Other medical
specialties may employ surgical procedures, such as ophthalmology and dermatology, but are not considered surgical sub-specialties per se.
Surgical training in the U.S. requires a minimum of five years of
residency after medical school. Sub-specialties of surgery often
require seven or more years. In addition, fellowships can last an
additional one to three years. Because post-residency fellowships can be
competitive, many trainees devote two additional years to research.
Thus in some cases surgical training will not finish until more than a
decade after medical school. Furthermore, surgical training can be very
difficult and time-consuming.
Surgical subspecialties include those a physician may specialize
in after undergoing general surgery residency training as well as
several surgical fields with separate residency training. Surgical
subspecialties that one may pursue following general surgery residency
training:
Internal medicine is the medical specialty dealing with the prevention, diagnosis, and treatment of adult diseases. According to some sources, an emphasis on internal structures is implied. In North America, specialists in internal medicine are commonly called "internists". Elsewhere, especially in Commonwealth nations, such specialists are often called physicians. These terms, internist or physician
(in the narrow sense, common outside North America), generally exclude
practitioners of gynecology and obstetrics, pathology, psychiatry, and
especially surgery and its subspecialities.
Because their patients are often seriously ill or require complex
investigations, internists do much of their work in hospitals.
Formerly, many internists were not subspecialized; such general physicians
would see any complex nonsurgical problem; this style of practice has
become much less common. In modern urban practice, most internists are
subspecialists: that is, they generally limit their medical practice to
problems of one organ system or to one particular area of medical
knowledge. For example, gastroenterologists and nephrologists specialize respectively in diseases of the gut and the kidneys.
In the Commonwealth of Nations and some other countries, specialist pediatricians and geriatricians are also described as specialist physicians
(or internists) who have subspecialized by age of patient rather than
by organ system. Elsewhere, especially in North America, general
pediatrics is often a form of primary care.
There are many subspecialities (or subdisciplines) of internal medicine:
Training in internal medicine (as opposed to surgical training), varies considerably across the world: see the articles on medical education
for more details. In North America, it requires at least three years of
residency training after medical school, which can then be followed by a
one- to three-year fellowship in the subspecialties listed above. In
general, resident work hours in medicine are less than those in surgery,
averaging about 60 hours per week in the US. This difference does not
apply in the UK where all doctors are now required by law to work less
than 48 hours per week on average.
Clinical neurophysiology
is concerned with testing the physiology or function of the central and
peripheral aspects of the nervous system. These kinds of tests can be
divided into recordings of: (1) spontaneous or continuously running
electrical activity, or (2) stimulus evoked responses. Subspecialties
include electroencephalography, electromyography, evoked potential, nerve conduction study and polysomnography.
Sometimes these tests are performed by techs without a medical degree,
but the interpretation of these tests is done by a medical professional.
Nuclear medicine
is concerned with studying human organ systems by administering
radiolabelled substances (radiopharmaceuticals) to the body, which can
then be imaged outside the body by a gamma camera
or a PET scanner. Each radiopharmaceutical consists of two parts: a
tracer that is specific for the function under study (e.g.,
neurotransmitter pathway, metabolic pathway, blood flow, or other), and a
radionuclide (usually either a gamma-emitter or a positron emitter).
There is a degree of overlap between nuclear medicine and radiology, as
evidenced by the emergence of combined devices such as the PET/CT
scanner.
The following are some major medical specialties that do not directly fit into any of the above-mentioned groups:
Anesthesiology (also known as anaesthetics):
concerned with the perioperative management of the surgical patient.
The anesthesiologist's role during surgery is to prevent derangement in
the vital organs' (i.e. brain, heart, kidneys) functions and
postoperative pain. Outside of the operating room, the anesthesiology
physician also serves the same function in the labor and delivery ward,
and some are specialized in critical medicine.
Emergency medicine is concerned with the diagnosis and treatment of acute or life-threatening conditions, including trauma, surgical, medical, pediatric, and psychiatric emergencies.
Family medicine, family practice, general practice or primary care
is, in many countries, the first port-of-call for patients with
non-emergency medical problems. Family physicians often provide services
across a broad range of settings including office based practices,
emergency department coverage, inpatient care, and nursing home care.
Medical genetics is concerned with the diagnosis and management of hereditary disorders.
Neurology is concerned with diseases of the nervous system. In the UK, neurology is a subspecialty of general medicine.
Obstetrics and gynecology (often abbreviated as OB/GYN (American English) or Obs & Gynae (British English)) are concerned respectively with childbirth and the female reproductive and associated organs. Reproductive medicine and fertility medicine are generally practiced by gynecological specialists.
Pediatrics (AE) or paediatrics
(BE) is devoted to the care of infants, children, and adolescents. Like
internal medicine, there are many pediatric subspecialties for specific
age ranges, organ systems, disease classes, and sites of care delivery.
Pharmaceutical medicine
is the medical scientific discipline concerned with the discovery,
development, evaluation, registration, monitoring and medical aspects of
marketing of medicines for the benefit of patients and public health.
Forensic medicine deals with medical questions in legal
context, such as determination of the time and cause of death, type of
weapon used to inflict trauma, reconstruction of the facial features
using remains of deceased (skull) thus aiding identification.
Gender-based medicine studies the biological and physiological differences between the human sexes and how that affects differences in disease.
Hospital medicine
is the general medical care of hospitalized patients. Physicians whose
primary professional focus is hospital medicine are called hospitalists in the United States and Canada. The term Most Responsible Physician (MRP) or attending physician is also used interchangeably to describe this role.
Laser medicine involves the use of lasers in the diagnostics or treatment of various conditions.
Nosokinetics is the science/subject of measuring and modelling the process of care in health and social care systems.
Nosology is the classification of diseases for various purposes.
Occupational medicine
is the provision of health advice to organizations and individuals to
ensure that the highest standards of health and safety at work can be
achieved and maintained.
Pain management (also called pain medicine, or algiatry) is the medical discipline concerned with the relief of pain.
Therapeutics
is the field, more commonly referenced in earlier periods of history,
of the various remedies that can be used to treat disease and promote
health.
Travel medicine or emporiatrics deals with health problems of international travelers or travelers across highly different environments.
Tropical medicine
deals with the prevention and treatment of tropical diseases. It is
studied separately in temperate climates where those diseases are quite
unfamiliar to medical practitioners and their local clinical needs.
Urgent care
focuses on delivery of unscheduled, walk-in care outside of the
hospital emergency department for injuries and illnesses that are not
severe enough to require care in an emergency department. In some
jurisdictions this function is combined with the emergency department.
Medical education and training varies around the world. It typically involves entry level education at a university medical school, followed by a period of supervised practice or internship, or residency.
This can be followed by postgraduate vocational training. A variety of
teaching methods have been employed in medical education, still itself a
focus of active research. In Canada and the United States of America, a
Doctor of Medicine degree, often abbreviated M.D., or a Doctor of Osteopathic Medicine
degree, often abbreviated as D.O. and unique to the United States, must
be completed in and delivered from a recognized university.
Since knowledge, techniques, and medical technology continue to evolve at a rapid rate, many regulatory authorities require continuing medical education. Medical practitioners upgrade their knowledge in various ways, including medical journals,
seminars, conferences, and online programs. A database of objectives
covering medical knowledge, as suggested by national societies across
the United States, can be searched at http://data.medobjectives.marian.edu/Archived 4 October 2018 at the Wayback Machine.
In most countries, it is a legal requirement for a medical doctor to
be licensed or registered. In general, this entails a medical degree
from a university and accreditation by a medical board or an equivalent
national organization, which may ask the applicant to pass exams. This
restricts the considerable legal authority of the medical profession to
physicians that are trained and qualified by national standards. It is
also intended as an assurance to patients and as a safeguard against charlatans
that practice inadequate medicine for personal gain. While the laws
generally require medical doctors to be trained in "evidence based",
Western, or Hippocratic Medicine, they are not intended to discourage different paradigms of health.
In the European Union, the profession of doctor of medicine is
regulated. A profession is said to be regulated when access and exercise
is subject to the possession of a specific professional qualification.
The regulated professions database contains a list of regulated
professions for doctor of medicine in the EU member states, EEA
countries and Switzerland. This list is covered by the Directive 2005/36/EC.
Doctors who are negligent or intentionally harmful in their care of patients can face charges of medical malpractice and be subject to civil, criminal, or professional sanctions.
Medical ethics is a system of moral principles that apply values and
judgments to the practice of medicine. As a scholarly discipline,
medical ethics encompasses its practical application in clinical
settings as well as work on its history, philosophy, theology, and
sociology. Six of the values that commonly apply to medical ethics
discussions are:
autonomy – the patient has the right to refuse or choose their treatment. (Latin: Voluntas aegroti suprema lex.)
beneficence – a practitioner should act in the best interest of the patient. (Latin: Salus aegroti suprema lex.)
justice – concerns the distribution of scarce health resources, and the decision of who gets what treatment (fairness and equality).
non-maleficence – "first, do no harm" (Latin: primum non-nocere).
respect for persons – the patient (and the person treating the patient) have the right to be treated with dignity.
Values such as these do not give answers as to how to handle a
particular situation, but provide a useful framework for understanding
conflicts. When moral values are in conflict, the result may be an
ethical dilemma
or crisis. Sometimes, no good solution to a dilemma in medical ethics
exists, and occasionally, the values of the medical community (i.e., the
hospital and its staff) conflict with the values of the individual
patient, family, or larger non-medical community. Conflicts can also
arise between health care providers, or among family members. For
example, some argue that the principles of autonomy and beneficence
clash when patients refuse blood transfusions, considering them life-saving; and truth-telling was not emphasized to a large extent before the HIV era.
Statuette of ancient Egyptian physician Imhotep, the first physician from antiquity known by name
Ancient world
Prehistoric medicine incorporated plants (herbalism), animal parts, and minerals. In many cases these materials were used ritually as magical substances by priests, shamans, or medicine men. Well-known spiritual systems include animism (the notion of inanimate objects having spirits), spiritualism (an appeal to gods or communion with ancestor spirits); shamanism (the vesting of an individual with mystic powers); and divination (magically obtaining the truth). The field of medical anthropology
examines the ways in which culture and society are organized around or
impacted by issues of health, health care and related issues.
In Egypt, Imhotep (3rd millennium BCE) is the first physician in history known by name. The oldest Egyptian medical text is the Kahun Gynaecological Papyrus from around 2000 BCE, which describes gynaecological diseases. The Edwin Smith Papyrus dating back to 1600 BCE is an early work on surgery, while the Ebers Papyrus dating back to 1500 BCE is akin to a textbook on medicine.
In China, archaeological evidence of medicine in Chinese dates back to the Bronze AgeShang dynasty, based on seeds for herbalism and tools presumed to have been used for surgery. The Huangdi Neijing,
the progenitor of Chinese medicine, is a medical text written beginning
in the 2nd century BCE and compiled in the 3rd century.
In India, the oldest known surgical text, the Sushruta Samhita written by the surgeon Sushruta, described numerous surgical operations, including the earliest forms of plastic surgery as well as methods of sterilization for surgical instruments. The earliest records of dedicated hospitals come from Mihintale in Sri Lanka where evidence of dedicated medicinal treatment facilities for patients are found.
In Greece, the ancient Greek physician Hippocrates, the "father of modern medicine", laid the foundation for a rational approach to medicine. Hippocrates introduced the Hippocratic Oath for physicians, which is still relevant and in use today, and was the first to categorize illnesses as acute, chronic, endemic and epidemic, and use terms such as, "exacerbation, relapse, resolution, crisis, paroxysm, peak, and convalescence". The Greek physician Galen
was also one of the greatest surgeons of the ancient world and
performed many audacious operations, including brain and eye surgeries.
After the fall of the Western Roman Empire and the onset of the Early Middle Ages, the Greek tradition of medicine went into decline in Western Europe, although it continued uninterrupted in the Eastern Roman (Byzantine) Empire.
Most of our knowledge of ancient Hebrew medicine during the 1st millennium BC comes from the Torah, i.e. the Five Books of Moses,
which contain various health related laws and rituals. The Hebrew
contribution to the development of modern medicine started in the Byzantine Era, with the physician Asaph the Jew.
The concept of hospital as institution to offer medical care and
possibility of a cure for the patients due to the ideals of Christian
charity, rather than just merely a place to die, appeared in the Byzantine Empire.
Although the concept of uroscopy
was known to Galen, he did not see the importance of using it to
localize the disease. It was under the Byzantines with physicians such
of Theophilus Protospatharius
that they realized the potential in uroscopy to determine disease in a
time when no microscope or stethoscope existed. That practice eventually
spread to the rest of Europe.
After 750 CE, the Muslim world had the works of Hippocrates, Galen and Sushruta translated into Arabic, and Islamic physicians engaged in some significant medical research. Notable Islamic medical pioneers include the Persian polymath, Avicenna, who, along with Imhotep and Hippocrates, has also been called the "father of medicine". He wrote The Canon of Medicine which became a standard medical text at many medieval European universities, considered one of the most famous books in the history of medicine. Others include Abulcasis, Avenzoar, Ibn al-Nafis, and Averroes. Persian physician Rhazes was one of the first to question the Greek theory of humorism, which nevertheless remained influential in both medieval Western and medieval Islamic medicine. Some volumes of Rhazes's work Al-Mansuri, namely "On Surgery" and "A General Book on Therapy", became part of the medical curriculum in European universities. Additionally, he has been described as a doctor's doctor, the father of pediatrics, and a pioneer of ophthalmology. For example, he was the first to recognize the reaction of the eye's pupil to light. The Persian Bimaristan hospitals were an early example of public hospitals.
In Europe, Charlemagne decreed that a hospital should be attached to each cathedral and monastery and the historian Geoffrey Blainey likened the activities of the Catholic Church in health care
during the Middle Ages to an early version of a welfare state: "It
conducted hospitals for the old and orphanages for the young; hospices
for the sick of all ages; places for the lepers; and hostels or inns
where pilgrims could buy a cheap bed and meal". It supplied food to the
population during famine and distributed food to the poor. This welfare
system the church funded through collecting taxes on a large scale and
possessing large farmlands and estates. The Benedictine
order was noted for setting up hospitals and infirmaries in their
monasteries, growing medical herbs and becoming the chief medical care
givers of their districts, as at the great Abbey of Cluny. The Church also established a network of cathedral schools and universities where medicine was studied. The Schola Medica Salernitana in Salerno, looking to the learning of Greek and Arab physicians, grew to be the finest medical school in medieval Europe.
Siena's Santa Maria della Scala Hospital,
one of Europe's oldest hospitals. During the Middle Ages, the Catholic
Church established universities to revive the study of sciences, drawing
on the learning of Greek and Arab physicians in the study of medicine.
However, the fourteenth and fifteenth century Black Death
devastated both the Middle East and Europe, and it has even been argued
that Western Europe was generally more effective in recovering from the
pandemic than the Middle East. In the early modern period, important early figures in medicine and anatomy emerged in Europe, including Gabriele Falloppio and William Harvey.
The major shift in medical thinking was the gradual rejection, especially during the Black Death
in the 14th and 15th centuries, of what may be called the "traditional
authority" approach to science and medicine. This was the notion that
because some prominent person in the past said something must be so,
then that was the way it was, and anything one observed to the contrary
was an anomaly (which was paralleled by a similar shift in European
society in general – see Copernicus's rejection of Ptolemy's theories on astronomy). Physicians like Vesalius
improved upon or disproved some of the theories from the past. The main
tomes used both by medicine students and expert physicians were Materia Medica and Pharmacopoeia.
Andreas Vesalius was the author of De humani corporis fabrica, an important book on human anatomy. Bacteria and microorganisms were first observed with a microscope by Antonie van Leeuwenhoek in 1676, initiating the scientific field microbiology. Independently from Ibn al-Nafis, Michael Servetus rediscovered the pulmonary circulation, but this discovery did not reach the public because it was written down for the first time in the "Manuscript of Paris" in 1546, and later published in the theological work for which he paid with his life in 1553. Later this was described by Renaldus Columbus and Andrea Cesalpino. Herman Boerhaave
is sometimes referred to as a "father of physiology" due to his
exemplary teaching in Leiden and textbook 'Institutiones medicae'
(1708). Pierre Fauchard has been called "the father of modern dentistry".
Veterinary medicine was, for the first time, truly separated from human medicine in 1761, when the French veterinarian Claude Bourgelat
founded the world's first veterinary school in Lyon, France. Before
this, medical doctors treated both humans and other animals.
Modern scientific biomedical research (where results are testable and reproducible)
began to replace early Western traditions based on herbalism, the Greek
"four humours" and other such pre-modern notions. The modern era really
began with Edward Jenner's discovery of the smallpox vaccine at the end of the 18th century (inspired by the method of variolation originated in ancient China), Robert Koch's discoveries around 1880 of the transmission of disease by bacteria, and then the discovery of antibiotics around 1900.
As science and technology developed, medicine became more reliant upon medications.
Throughout history and in Europe right until the late 18th century, not
only plant products were used as medicine, but also animal (including
human) body parts and fluids. Pharmacology developed in part from herbalism and some drugs are still derived from plants (atropine, ephedrine, warfarin, aspirin, digoxin, vinca alkaloids, taxol, hyoscine, etc.). Vaccines were discovered by Edward Jenner and Louis Pasteur.
The first antibiotic was arsphenamine (Salvarsan) discovered by Paul Ehrlich
in 1908 after he observed that bacteria took up toxic dyes that human
cells did not. The first major class of antibiotics was the sulfa drugs, derived by German chemists originally from azo dyes.
Pharmacology has become increasingly sophisticated; modern biotechnology
allows drugs targeted towards specific physiological processes to be
developed, sometimes designed for compatibility with the body to reduce side-effects. Genomics and knowledge of human genetics and human evolution is having increasingly significant influence on medicine, as the causative genes of most monogenic genetic disorders have now been identified, and the development of techniques in molecular biology, evolution, and genetics are influencing medical technology, practice and decision-making.
Evidence-based medicine is a contemporary movement to establish the most effective algorithms of practice (ways of doing things) through the use of systematic reviews and meta-analysis. The movement is facilitated by modern global information science,
which allows as much of the available evidence as possible to be
collected and analyzed according to standard protocols that are then
disseminated to healthcare providers. The Cochrane Collaboration
leads this movement. A 2001 review of 160 Cochrane systematic reviews
revealed that, according to two readers, 21.3% of the reviews concluded
insufficient evidence, 20% concluded evidence of no effect, and 22.5%
concluded positive effect.
Quality, efficiency, and access
Evidence-based medicine, prevention of medical error (and other "iatrogenesis"), and avoidance of unnecessary health care
are a priority in modern medical systems. These topics generate
significant political and public policy attention, particularly in the
United States where healthcare is regarded as excessively costly but population health metrics lag similar nations.
Globally, many developing countries lack access to care and access to medicines. As of 2015,
most wealthy developed countries provide health care to all citizens,
with a few exceptions such as the United States where lack of health
insurance coverage may limit access.
Telemedicine (also Telehealth) refers to preventive, promotive, and
curative care delivery, including remote clinical services, such as
diagnosis, monitoring, administration and provider education.The main categories of telehealth:
Telenursing
is experiencing significant growth globally due to factors such as the
need to reduce healthcare costs, an increasing aging and chronically ill
population, and expanded healthcare coverage to distant, rural, small,
or sparsely populated regions. Telenursing can help address nurse
shortages, reduce travel time and distances, and minimize hospital
admissions.
Telepalliative care
is a remote approach to optimising quality of life and relieving
suffering for people with serious, complex and often fatal illnesses.
The World Health Organization
(WHO) recommends integrating palliative care as early as possible for
any chronic and fatal illness. Telepalliative care typically utilizes
telecommunication technologies like video conferencing, messaging for
follow-ups, and digital symptom assessments through questionnaires that
generate alerts for healthcare professionals.
Telepharmacy
involves delivering pharmaceutical care via telecommunications to
patients in locations where direct contact with a pharmacist may not be
possible or difficult.
Telepsychiatry
(telemental health) uses telecommunications technology to provide
remote psychiatric care for individuals with mental health conditions.
Telepsychology is the use of communication technology for the remote administration of psychological tests and psychotherapy.
Teleneurotherapy utilizes computers and communications technology to deliver neurotherapy remotely. Research indicates that systematic physical stimuli from standard
electronic devices, such as tablets with headphones, may treat injured
nervous systems online by modulating neuronal plasticity. Evidence
suggests that teleneurotherapy could enhance neurological treatment if
it incorporates the therapeutic effect of a systematic abiotic impact of
physical forces with key parameters of mother-fetus interaction. Recent
research has shown therapeutic effects when implementing the APIN
method in the online treatment of patients with various neurological
conditions.
Telenutrition refers to the use of video conferencing or
telephony to provide online consultations by nutritionists or
dieticians.
Telerehabilitation
(or e-rehabilitation) is the delivery of rehabilitation services over
telecommunication networks and the Internet. Most services fall into two
categories: clinical assessment (evaluating the patient's functional
abilities in their environment) and clinical therapy.
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