Thiomersal and vaccines

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Thiomersal (or Thimerosal) is a mercury compound used as a preservative used in some vaccines. Anti-vaccination activists promoting the incorrect claim that vaccination causes autism, have asserted that the mercury in thiomersal is the cause. There is no scientific evidence to support this claim. The idea that thiomersal in vaccines might have detrimental effects originated with anti-vaccination activists and was sustained by them and especially through the action of plaintiffs' lawyers.

 

The potential impact of thiomersal on autism has been investigated extensively. Multiple lines of scientific evidence have shown that thiomersal does not cause autism. For example, the clinical symptoms of mercury poisoning differ significantly from those of autism. In addition, multiple population studies have found no association between thiomersal and autism, and rates of autism have continued to increase despite removal of thiomersal from vaccines. Thus, major scientific and medical bodies such as the Institute of Medicine and World Health Organization (WHO) as well as governmental agencies such as the Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) reject any role for thiomersal in autism or other neurodevelopmental disorders. In spite of the consensus of the scientific community, some parents and advocacy groups continue to contend that thiomersal is linked to autism and the claim is still stated as if it were fact in anti-vaccination propaganda, notably that of Robert F. Kennedy, Jr., through his group Children's Health Defense. Thiomersal is no longer used in most children's vaccines in the United States, with the exception of some types of flu shots. While exposure to mercury may result in damage to brain, kidneys, and developing fetus, the scientific consensus is that thiomersal has no such effects.

This controversy has caused harm due to parents attempting to treat their autistic children with unproven and possibly dangerous treatments, discouraging parents from vaccinating their children due to fears about thiomersal toxicity and diverting resources away from research into more promising areas for the cause of autism. Thousands of lawsuits have been filed in the U.S. to seek damages from alleged toxicity from vaccines, including those purportedly caused by thiomersal. US courts have ruled against multiple representative test cases involving thiomersal. A 2011 journal article described the vaccine-autism connection as "perhaps, the most damaging medical hoax of the last 100 years".

Outside of the United States, worries about thiomersal had not gained any significant traction as of 2009.

History

Thiomersal (also spelled thimerosal, especially in the United States) is an organomercury compound used as a preservative in vaccines to prevent bacterial and fungal contamination. Following a mandated review of mercury-containing food and drugs in 1999, the Centers for Disease Control and Prevention (CDC) and the American Academy of Pediatrics (AAP) asked vaccine makers to remove thiomersal from vaccines as quickly as possible as a precautionary measure, and it was rapidly phased out of most US and EU vaccines, but is still used in multi-dose vials of flu vaccines in both jurisdictions. In the context of perceived increased autism rates and increased number of vaccines in the childhood vaccination schedule, some parents believed the action to remove thiomersal was an indication that the preservative caused autism.

It was introduced as a preservative in the 1930s to prevent the growth of infectious organisms such as bacteria and fungi, and has been in use in vaccines and other products such as immunoglobulin preparations and ophthalmic and nasal solutions. Vaccine manufacturers have used preservatives to prevent microbial growth during the manufacturing process or when packaged as "multi-dose" products to allow for multiple punctures of the same vial to dispense multiple vaccinations with less fear of contamination. After the FDA Modernization Act of 1997 mandated a review and risk assessment of all mercury-containing food and drugs, vaccine manufacturers responded to FDA requests made in December 1998 and April 1999 to provide detailed information about the thiomersal content of their preparations.

A review of the data showed that while the vaccine schedule for infants did not exceed FDA, Agency for Toxic Substances and Disease Registry (ATSDR), or WHO guidelines on mercury exposure, it could have exceeded Environmental Protection Agency (EPA) standards for the first six months of life, depending on the vaccine formulation and the weight of the infant. The review also highlighted difficulty interpreting toxicity of the ethylmercury in thiomersal because guidelines for mercury toxicity were based primarily on studies of methylmercury, a different mercury compound with different toxicologic properties. Multiple meetings were scheduled among various government officials and scientists from multiple agencies to discuss the appropriate response to this evidence. There was a wide range of opinions on the urgency and significance of the safety of thiomersal, with some toxicologists suggesting there was no clear evidence that thiomersal was harmful and other participants like Neal Halsey, director of the Institute of Vaccine Safety at Johns Hopkins School of Public Health, strongly advocating removal of thiomersal from vaccines due to possible safety risks. In the process of forming the response to this information, the participants attempted to strike a balance between acknowledging possible harm from thiomersal and the risks involved if childhood vaccinations were delayed or stopped.

Upon conclusion of their review, the FDA, in conjunction with the other members of the US Public Health Service (USPHS), the National Institutes of Health (NIH), CDC and Health Resources and Services Administration (HRSA), in a joint statement with the AAP in July 1999 concluded that there was "no evidence of harm caused by doses of thimerosal found in vaccines, except for local hypersensitivity reactions."

Despite the lack of convincing evidence of toxicity of thiomersal when used as a vaccine preservative, the USPHS and AAP determined that thiomersal should be removed from vaccines as a purely precautionary measure. This action was based on the precautionary principle, which assumes that there is no harm in exercising caution even if it later turns out to be unnecessary. The CDC and AAP reasoned that despite the lack of evidence of significant harm in the use of thiomersal in vaccines, the removal of this preservative would increase the public confidence in the safety of vaccines. Although thiomersal was largely removed from routine infant vaccines by summer 2001 in the U.S., some vaccines continue to contain non-trace amounts of thiomersal, mainly in multi-dose vaccines targeted against influenza, meningococcal disease and tetanus.

In 2004 Quackwatch posted an article saying that chelation therapy has been falsely promoted as effective against autism, and that practitioners falsified diagnoses of metal poisoning to "trick" parents into having their children undergo the process. As of 2008, between 2–8% of children with autism had undergone the therapy.

Rationale for concern

Reports of autism cases per 1,000 children grew dramatically in the U.S. from 1996 to 2007. It is unknown how much, if any, growth came from changes in autism's prevalence.

 

Although intended to increase public confidence in vaccinations, the decision to remove thiomersal instead led to some parents suspecting thiomersal as a cause of autism. This concern over a vaccine-autism link grew from a confluence of several underlying factors. First, methylmercury had for decades been the subject of widespread environmental and media concern after two highly publicized episodes of poisonings in the 1950s and 1960s in Minamata Bay, Japan from industrial waste and in the 1970s in Iraq from fungicide contamination of wheat. These incidents led to new research on methylmercury safety and culminated in the publication of an array of confusing recommendations by public health agencies in the 1990s warning against methylmercury exposure in adults and pregnant women, which ensured a continued high public awareness of mercury toxicity. Second, the vaccine schedule for infants expanded in the 1990s to include more vaccines, some of which, including the Hib vaccine, DTaP vaccine and hepatitis B vaccine, could have contained thiomersal. Third, the number of diagnoses of autism grew in the 1990s, leading parents of these children to search for an explanation for the apparent rise in diagnoses, including considering possible environmental factors. The dramatic increase in reported cases of autism during the 1990s and early 2000s is largely attributable to changes in diagnostic practices, referral patterns, availability of services, age at diagnosis, and public awareness, and it is unknown whether autism's true prevalence increased during the period. Nevertheless, some parents believed that there was a growing "autism epidemic" and connected these three factors to conclude that the increase in number of vaccines, and specifically the mercury in thiomersal in those vaccines, was causing a dramatic increase in the incidence of autism.

Advocates of a thiomersal-autism link also relied on indirect evidence from the scientific literature, including analogy with neurotoxic effects of other mercury compounds, the reported epidemiologic association between autism and vaccine use, and extrapolation from in vitro experiments and animal studies. Studies conducted by Mark Geier and his son David Geier have been the most frequently cited research by parents advocating a link between thiomersal and autism. This research by Geier has received considerable criticism for methodological problems in his research, including not presenting methods and statistical analyses to others for verification, improperly analyzing data taken from Vaccine Adverse Event Reporting System, as well as either mislabelling or confusing fundamental statistical terms in his papers, leading to results that were "uninterpretable".

Publicity of concern

Several months after the recommendation to have thiomersal removed from vaccines was published, a speculative article was published in Medical Hypotheses, a non-peer-reviewed journal, by parents who launched the parental advocacy group SafeMinds to promote the theory that thiomersal caused autism. The controversy began to gain legitimacy in the eyes of the public and gained widening support within certain elements in the autism advocacy community as well as in the political arena, with U.S. Representative Dan Burton openly supporting this movement and holding a number of Congressional hearings on the subject.

Further support for the association between autism and thiomersal appeared in an article by Robert F. Kennedy, Jr. in the magazines Rolling Stone and Salon.com alleging a government conspiracy at a CDC meeting to conceal the dangers of thiomersal to protect the pharmaceutical industry, and a book written by David Kirby, Evidence of Harm, dramatizing the lives of parents of autistic children, with both authors participating in media interviews to promote their work and the controversy. Although the allegations by Kennedy were denied and a US Senate committee investigation later found no evidence to substantiate the most serious allegations, the story had already been well publicized by leveraging Kennedy's celebrity. Salon magazine subsequently amended Kennedy's article five times due to factual errors and later retracted it completely on January 16, 2011, stating that the works of critics of the article and evidence of the flaws in the science connecting autism and vaccines undermined the value of the article to the editors.

Meanwhile, during this time of increased media publicity of the controversy, public health officials and institutions did little to rebut the concerns and speculative theories being offered. Media attention and polarization of the debate has also been fueled by personal injury lawyers who took out full-page ads in prominent newspapers and offered financial support for expert witnesses who dissented from the scientific consensus that there is no convincing evidence for a link between thiomersal and autism. Paul Offit, a leading vaccine researcher and advocate, has said that the media has a tendency to provide false balance by perpetually presenting both sides of an issue even when only one side is supported by the evidence and thereby giving a platform for the spread of misinformation.

Despite the consensus from experts that there is no link between thiomersal and autism, many parents continue to believe that such a link exists. These parents share the viewpoint that autism is not just treatable, but curable through "biomedical" interventions and have been frustrated by the lack of progress from more "mainline" scientists in finding this cure. Instead, they have supported an alternative community of like-minded parents, physicians and scientists who promote this belief. This mindset has taught these parents to challenge the expertise from the mainstream scientific community. Parents have also been influenced by an extensive network of anti-vaccination organizations such as Robert F. Kennedy Jr.'s Children's Health Defense and a large number of online anti-vaccination websites that present themselves as an alternative source for evidence using pseudoscientific claims. These websites use emotional appeals to gather support and frame the controversy as an adversarial dispute between parents and a conspiracy of doctors and scientists. Advocates for a thiomersal-autism link have also relied on celebrities like model Jenny McCarthy and information presented on Don Imus' Imus in the Morning radio show to persuade the public to their cause, instead of relying only on "dry" scientific papers and scientists. McCarthy has published a book describing her personal experience with her autistic son and appeared on The Oprah Winfrey Show to promote the hypothesis of vaccines causing autism. Bitterness over this issue has led to numerous threats made against the CDC as well as researchers like Offit, with increased security placed by the CDC in response to these threats.

Scientific evaluation

Rationale for doubting link

Various lines of evidence undermine a proposed link between thiomersal and autism. For example, although advocates of a thiomersal-autism link consider autism a form of "mercury poisoning," the typical symptoms of mercury toxicity are significantly different from symptoms seen in autism. Likewise, the neuroanatomic and histopathologic features of the brains of patients who have mercury poisoning, both with methylmercury as well as ethylmercury, have significant differences from the brains of people with autism. Previous episodes of widespread mercury toxicity in a population such as in Minamata Bay, Japan would also be expected to lead to documentation of a significant rise in autism or autism-like behavior in children should autism be caused by mercury poisoning. However, research on several episodes of acute and chronic mercury poisoning have not documented any such rise in autism-like behavior. Although some parents cite an association between the timing of onset of autistic symptoms with the timing of vaccinations as evidence of an environmental cause such as thiomersal, this line of reasoning can be misleading. Associations such as these do not establish causation as the two occurring together may be only coincidental in nature. Also, genetic disorders that have no environmental triggers such as Rett syndrome and Huntington's disease nevertheless have specific ages when they begin to show symptoms, suggesting specific ages of onset of symptoms does not necessarily require an environmental cause.

Although the concern for a thiomersal-autism link was originally derived from indirect evidence based on the known potent neurotoxic effects of methylmercury, recent studies show these feared effects were likely overestimated. Ethylmercury, such as in thiomersal, clears much faster from the body after administration than methylmercury, suggesting total mercury exposure over time is much less with ethylmercury. Currently used methods of estimating brain deposition of mercury likely overestimates the amounts deposited due to ethylmercury, and ethylmercury also decomposes quicker in the brain than methylmercury, suggesting a lower risk of brain damage. These findings show that the assumptions that originally led to concern about the toxicity of ethylmercury, which were based on direct comparison to methylmercury, were flawed.

Population studies

Multiple studies have been performed on data from large populations of children to study the relationship between the use of vaccines containing thiomersal, and autism and other neurodevelopmental disorders. Almost all of these studies have found no association between thiomersal-containing vaccines (TCVs) and autism, and studies done after the removal of thiomersal from vaccines have nevertheless shown autism rates continuing to increase. The only epidemiologic research that has found a purported link between TCVs and autism has been conducted by Mark Geier, whose flawed research has not been given any weight by independent reviews.

In Europe, a cohort study of 467,450 Danish children found no association between TCVs and autism or autism spectrum disorders (ASDs), nor any dose-response relationship between thiomersal and ASDs that would be suggestive of toxic exposure. An ecological analysis that studied 956 Danish children diagnosed with autism likewise did not show an association between autism and thiomersal. A retrospective cohort study on 109,863 children in the United Kingdom found no association between TCVs and autism, but a possible increased risk for tics. Analysis in this study also showed a possible protective effect with respect to general developmental disorders, attention-deficit disorder, and otherwise unspecified developmental delay. Another UK study based on a prospective cohort of 13,617 children likewise found more associated benefits than risks from thiomersal exposure with respect to developmental disorders. Because the Danish and UK studies involved only diphtheria-tetanus-pertussis (DTP) or diphtheria-tetanus (DT) vaccines, they are less relevant for the higher thiomersal exposure levels that occurred in the U.S.

In North America, a Canadian study of 27,749 children in Quebec showed that thiomersal was unrelated to the increasing trend in pervasive developmental disorders (PDDs). In fact, the study noted that rates of PDDs were higher in the birth cohorts with no thiomersal when compared to those with medium or high levels of exposure. A study performed in the US which analyzed data from 78,829 children enrolled in HMOs taken from the Vaccine Safety Datalink (VSD) did not show any consistent association between TCVs and neurodevelopmental outcomes, noting different results from data in different HMOs. A study performed in California found that removal of thiomersal from vaccines did not decrease the rates of autism, suggesting that thiomersal could not be the primary cause of autism. A study on children from Denmark, Sweden and California likewise argued against TCVs being causally associated with autism.

Scientific consensus

In 2001 the Centers for Disease Control and Prevention and the National Institutes of Health asked the U.S. National Academy of Science's (NAS) Institute of Medicine to establish an independent expert committee to review hypotheses about existing and emerging immunization safety concerns. This initial report found that based on indirect and incomplete evidence available at the time, there was inadequate evidence to accept or reject a thiomersal-autism link, though it was biologically plausible.

Since this report was released, several independent reviews have examined the body of published research for a possible thiomersal-autism link by examining the theoretical mechanisms of thiomersal causing harm and by reviewing the in vitro, animal, and population studies that have been published. These reviews determined that no evidence exists to establish thiomersal as the cause of autism or other neurodevelopmental disorders.

The scientific consensus on the subject is reflected in a follow up report that was subsequently published in 2004 by the Institute of Medicine, which took into account new data that had been published since the 2001 report. The committee noted, in response to those who cite in vitro or animal models as evidence for the link between autism and thiomersal:

"However, the experiments showing effects of thimerosal on biochemical pathways in cell culture systems and showing abnormalities in the immune system or metal metabolism in people with autism are provocative; the autism research community should consider the appropriate composition of the autism research portfolio with some of these new findings in mind. However, these experiments do not provide evidence of a relationship between vaccines or thimerosal and autism. In the absence of experimental or human evidence that vaccination (either the MMR vaccine or the preservative thimerosal) affects metabolic, developmental, immune, or other physiological or molecular mechanisms that are causally related to the development of autism, the committee concludes that the hypotheses generated to date are theoretical only."

The committee concludes:

"Thus, based on this body of evidence, the committee concludes that the evidence favors rejection of a causal relationship between thimerosal-containing vaccines and autism." [bold in original]

Further evidence of the scientific consensus includes the rejection of a causal link between thiomersal and autism by multiple national and international scientific and medical bodies including the American Medical Association, the American Academy of Pediatrics, the American College of Medical Toxicology, the Canadian Paediatric Society, the U.S. National Academy of Sciences, the Food and Drug Administration, Centers for Disease Control and Prevention, the World Health Organization, the Public Health Agency of Canada, and the European Medicines Agency.

A 2011 journal article reflects this point of view and described the vaccine-autism connection as "the most damaging medical hoax of the last 100 years".

Consequences

The suggestion that thiomersal has contributed to autism and other neurodevelopmental disorders has had a number of effects. Public health officials believe fear driven by advocates of a thiomersal-autism link has caused parents to avoid vaccination or adopt "made up" vaccination schedules that expose their children to increased risk from preventable diseases such as measles and pertussis. Advocates of a thiomersal-autism link have also helped enact laws in six states (California, Delaware, Illinois, Missouri, New York and Washington) between 2004 and 2006 to limit the use of thiomersal given to pregnant women and children, although later attempts in 2009 in twelve other states failed to pass. These laws can be temporarily suspended, but vaccine advocates doubt their utility given the lack of evidence for danger with thiomersal in vaccines. Vaccine advocates are also concerned that passage of such laws help fuel a backlash against vaccination and contribute to doubts about the safety of vaccines that are unwarranted.

During the period of time of removal of thiomersal, the CDC and AAP asked doctors to delay the birth dose of hepatitis B vaccine in children not at risk for hepatitis. This decision, though following the precautionary principle, nevertheless sparked confusion, controversy and some harm. Approximately 10% of hospitals suspended the use of hepatitis B vaccine for all newborns, and one child born to a Michigan mother infected with hepatitis B virus died of it. Similarly, a study found that the number of hospitals who failed to properly vaccinate infants of hepatitis B seropositive mothers rose by over 6 times. This is a potential negative outcome given the high probability that infants who acquire hepatitis B infection at birth will develop the infection in a chronic form and possibly liver cancer.

The notion that thiomersal causes autism has led some parents to have their children treated with costly and potentially dangerous therapies such as chelation therapy, which is typically used to treat heavy metal poisoning, due to parental fears that autism is a form of "mercury poisoning". As many as 2 to 8% of autistic children in the U.S., numbering as many as several thousand children per year, receive mercury-chelating agents. Although critics of using chelation therapy as an autism treatment point to a lack of any evidence to support its use, hundreds of doctors prescribe these medications despite possible side effects including nutritional deficiencies as well as damage to the liver and kidney. The popularity of this therapy caused a "public health imperative" that led the U.S. National Institute of Mental Health (NIMH) to commission a study about chelation in autism by studying DMSA, a chelating agent used for lead poisoning, despite worries from critics that there would be no chance it would show positive results and it would be unlikely to convince parents to not use the therapy. Ultimately, the study was halted due to ethical concerns that there would be too much risk to children with autism who did not have toxic levels of mercury or lead due to a new animal study showing possible cognitive and emotional problems associated with DMSA. A 5-year-old autistic boy died from cardiac arrest immediately after receiving chelation therapy treatment using EDTA in 2005.

The notion has also diverted attention and resources away from efforts to determine the causes of autism. The 2004 Institute of Medicine report committee recommended that while it supported "targeted research that focuses on better understanding the disease of autism, from a public health perspective the committee does not consider a significant investment in studies of the theoretical vaccine-autism connection to be useful at this time." Alison Singer, a senior executive of Autism Speaks, resigned from the group in 2009 in a dispute over whether to fund more research on links between vaccination and autism, saying, "There isn't an unlimited pot of money, and every dollar spent looking where we know the answer isn't is one less dollar we have to spend where we might find new answers."

Court cases

From 1988 until August 2010, 5,632 claims relating to autism were made to Office of Special Masters of the U.S. Court of Federal Claims (commonly known as the "Vaccine Court") which oversees vaccine injury claims, of which one case has received compensation, 738 cases have been dismissed with no compensations made, and with the remaining cases pending. In the one case which received compensation, the U.S. government agreed to pay for injury to a child that had a pre-existing mitochondrial disorder who developed autism-like symptoms after multiple vaccinations, some of which included thiomersal. Citing the inability to rule out a role of these vaccinations in exacerbating her underlying mitochondrial disorder as the rationale for payment, CDC officials cautioned against generalizing this one case to all autism-related vaccine cases as most patients with autism do not have a mitochondrial disorder. In February 2009, this court also ruled on three autism-related cases, each exploring different mechanisms that plaintiffs proposed linked thiomersal-containing vaccines with autism. Three judges independently found no evidence that vaccines caused autism and denied the plaintiffs compensation. Since these same mechanisms formed the basis for the vast majority of remaining autism-related vaccine injury cases, the chance for compensation in any of these cases has significantly decreased. In March 2010, the court ruled in three other test cases that thiomersal-containing vaccines do not cause autism.

What’s Wrong with Moral Foundations Theory, and How to get Moral Psychology Right

By Oliver Scott Curry

March 26, 2019

Original link:  http://behavioralscientist.org/whats-wrong-with-moral-foundations-theory-and-how-to-get-moral-psychology-right/?fbclid=IwAR2FMsH20-sGW1WIoirXrNG8nmuw1miG4_o7rtigArM_l7i4tSe6Uw-_25c

 

Image: Antonio Marín Segovia/Flickr

Once the exclusive preserve of philosophy and theology, the study of morality has now become a thriving interdisciplinary endeavor, encompassing research in evolutionary theory, genetics, biology, animal behavior, psychology, and anthropology. The emerging consensus is that there is nothing mysterious about morality; it is merely a collection of biological and cultural traits that promote cooperation.

Best known among these accounts is Jonathan Haidt’s Moral Foundations Theory (MFT). According to MFT: “Moral systems are interlocking sets of values, virtues, norms, practices, identities, institutions, technologies, and evolved psychological mechanisms that work together to suppress or regulate selfishness and make cooperative social life possible.” And MFT proceeds to argue that, because humans face multiple social problems, they have multiple moral values—they rely on multiple “foundations” when making moral decisions. These foundations include: Care, Fairness, Loyalty, Authority, and Purity.

• Care: “The suffering of others, including virtues of caring and compassion.”
• Fairness: “Unfair treatment, cheating, and more abstract notions of justice and rights.”
• Loyalty: The “obligations of group membership” including “self-sacrifice, and vigilance against betrayal.”
• Authority: “Social order and the obligations of hierarchical relationships, such as obedience, respect, and the fulfillment of role-based duties.”
• Purity: “Physical and spiritual contagion, including virtues of chastity, wholesomeness, and control of desires.”

These moral foundations have been operationalized, and measured, by the Moral Foundations Questionnaire (MFQ; you can complete it here).

MFT and the questionnaire have had an enormous impact on moral psychology. The central papers have been cited hundreds of times. And there is now a huge literature applying MFT to bioethics, charity, environmentalism, psychopathy, religion, and especially politics. However, MFT has some serious problems, both theoretical and empirical.

The main theoretical problem is that MFT’s list of foundations is not based on any particular theory of cooperation, or on any explicit theory at all. Indeed, Haidt, has explicitly argued against taking what he calls an “a priori or principled” approach to moral psychology, and instead has advocated taking an “ad hoc” approach. The shortcomings of this ad hoc approach, however, are all too plain to see.

First, MFT’s list of foundations has critical omissions. Despite claiming to be an evolutionary-cooperative account of morality, MFT fails to include the four most well-established types of evolved cooperation: kin altruism, reciprocal altruism, competitive altruism, and respect for prior possession.

• Kin altruism has no dedicated foundation in MFT. Although MFT argues that Care originally motivated investment in offspring, it is now applied to nonkin; and MFT treats “family” as just another type of “group.” The questionnaire (MFQ) does have two items pertaining to family, but they appear under Fairness and Loyalty, not Care.
• Reciprocal altruism has no dedicated foundation in MFT. Instead, MFT conflates reciprocity—a solution to iterated prisoners’ dilemmas—with fairness—a solution to bargaining problems. And the MFQ has no items pertaining to reciprocity.
• Competitive altruism—that is, costly signals of status, such as bravery or generosity—has no dedicated foundation in MFT, and no items in the MFQ.
• Respect for prior possession—that is, property rights and the prohibition of theft—has no dedicated foundation in MFT. The MFQ’s only mention of property occurs in an item about inheritance, under Fairness.

Second, in addition to these omissions, MFT includes two foundations that are not distinct types of evolved cooperation: Care and Purity.

• Care—like “altruism” or “benevolence”—is a generic category, not a specific type of cooperation. It doesn’t distinguish between the various distinct types of cooperation—kin altruism, mutualism, reciprocal altruism, competitive altruism and their corresponding psychological mechanisms—all of which involve caring for different people (including family, friends, strangers) for different reasons.
• Purity is supposed to stem from the need to avoid “people w/ diseases, parasites [&] waste products.” But “avoiding pathogens” is not itself a cooperative problem, any more than, say, “avoiding predators.” And, indeed, MFT offers no connection between purity and cooperation. On the contrary, Purity is described as an “odd corner” of morality because it is not “concerned with how we treat other people.” Hence, categorizing Purity as a moral foundation is anomalous.

Thus, MFT’s theory-free approach results in egregious errors of omission, conflation, and commission. It misses some candidate moral domains, combines others, and includes noncooperative domains. Most egregiously, the lack of theory means that MFT cannot rectify these errors; it cannot make principled predictions about what (other) foundations there might be, thus it cannot make progress toward a cumulative science of morality.

MFT also has empirical problems. The main problem is that MFT’s five-factor model of morality has not been well supported by studies using the MFQ. Some of the original studies, as well as replications in Italy, New Zealand, Korea, Sweden, and Turkey, and also a 27 country study using the short-form MFQ, have found that MFT’s five-factor model falls short of the conventionally acceptable degree of model fit (CFIs less than 0.90). These studies typically find that a two-factor model—“Care-Fairness” and “Loyalty-Authority-Purity”—is a better fit. And so despite MFT promising five moral domains, the MFQ typically delivers only two. The MFQ does not distinguish domains dedicated to Fairness, Loyalty, or Authority; nor does it establish that Care and Purity are distinct moral domains. Simply put, it does not establish that there are five moral foundations. Other research has taken issue with specific foundations, especially Purity and the link between disgust and morality; but that’s a story for another time.

To their credit, proponents of MFT acknowledge these problems. They accept that the original list of foundations was “arbitrary,” based on a limited review of only “five books and articles,” and never intended to be “exhaustive.” And they have positively encouraged research that could “demonstrate the existence of an additional foundation, or show that any of the current five foundations should be merged or eliminated.”

And so that is what my colleagues and I have done. But we have not done so by making yet more “ad hoc” suggestions. We have gone back to first principles, to the theory that can provide a rigorous, systematic foundation for a cooperative theory of morality—the mathematics of cooperation, the theory of non-zero-sum games. We call this approach Morality-as-Cooperation (MAC).

According to MAC, morality consists of a collection of biological and cultural solutions to the problems of cooperation recurrent in human social life. For 50 million years humans and their ancestors have lived in social groups. During this time, they faced a range of different problems of cooperation, and they evolved and invented a range of different solutions to them. Together, these biological and cultural mechanisms provide the motivation for cooperative behavior; and they provide the criteria by which we evaluate the behavior of others. And, according to MAC, it is precisely this collection of cooperative traits—these instincts, intuitions, and institutions—that constitute human morality.

Which problems of cooperation do humans face? And how are they solved? That’s where game theory comes in. Game theory makes a principled distinction between zero-sum and non-zero-sum games. Zero-sum games are competitive interactions that have a winner and a loser; one’s gain is another’s loss. Non-zero-sum games are cooperative interactions that can have two winners; they are win-win situations. Game theory also distinguishes between different types of non-zero-sum games and the strategies used to play them. Thus, it delineates mathematically distinct types of cooperation.

A review of this literature suggests that there are (at least) seven well established types of cooperation: (1) the allocation of resources to kin; (2) coordination to mutual advantage; (3) social exchange; and conflict resolution through contests featuring (4) hawkish displays of dominance and (5) dove-ish displays of submission; (6) division of disputed resources; and (7) recognition of prior possession.

In my research, I have shown how each of these types of cooperation can be used to identify and explain a distinct type of morality.

(1) Kin selection explains why we feel a special duty of care for our families, and why we abhor incest. (2) Mutualism explains why we form groups and coalitions (there is strength and safety in numbers), and hence why we value unity, solidarity, and loyalty. (3) Social exchange explains why we trust others, reciprocate favors, feel gratitude and guilt, make amends, and forgive. And conflict resolution explains why we (4) engage in costly displays of prowess such as bravery and generosity, why we (5) express humility and defer to our superiors, why we (6) divide disputed resources fairly and equitably, and why we (7) respect others’ property and refrain from stealing.

Our research has shown that examples of these seven types of cooperative behavior—help your family, help your group, return favors, be brave, defer to your superiors, be fair, and respect others’ property—are considered morally good all around the world and are probably cross-cultural moral universals.

And we have used MAC’s framework to develop a new measure of moral values that promises, and delivers, seven moral domains: (1) Family, (2) Group, (3) Reciprocity, (4) Heroism, (5) Deference, (6) Fairness, and (7) Property. This new Morality-as-Cooperation Questionnaire (MAC-Q) introduces the four moral domains that were missing from MFT: Family, Reciprocity, Heroism, Property. And unlike the MFQ, it distinguishes Family from Group (Loyalty), Group (Loyalty) from Deference (Authority), and Reciprocity from Fairness.

So this principled approach to morality, grounded firmly in the underlying logic of cooperation, outperforms an unprincipled approach. MAC explains more types of morality than MFT. It can generate novel principled predictions about morality’s content and structure—predictions that have thus far been supported by psychological and anthropological research. And it leads to a more comprehensive and reliable measure of moral values.

Equipped with this new map of the moral landscape, we can now examine familiar ground in greater detail and survey previously unexplored territory. We can take a fresh look at the genetic basis, and the psychological architecture, of morality. We can reassess the relationship between morals and politics. And we can investigate how and why moral values vary around the world. Above all, by using a theory to generate new testable predictions, we can pave the way for a genuine science of morality.

Oliver Scott Curry

Oliver Scott Curry is a senior researcher at the Institute of Cognitive and Evolutionary Anthropology, University of Oxford. His research investigates the nature, content, and structure of human morality, using a range of techniques from philosophy, experimental and social psychology, and comparative anthropology.

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Understanding gene interactions holds key to personalized medicine

by University of Toronto

March 25, 2019 

Original link: https://medicalxpress.com/news/2019-03-gene-interactions-key-personalized-medicine.html?fbclid=IwAR3MxlnKkFlr5XNwwR0QYkxqgSaz0kU2-k4__w-suZUSBH34Ivc9HJjbQFk

When the Human Genome Project was completed, in 2003, it opened the door to a radical new idea of health—that of personalized medicine, in which disease risk and appropriate treatment would be gleaned from one's genetic makeup. As more people had their genomes sequenced, disease-related genes would start coming into view— and while this is true in many ways, things also turned out to be much more complicated.

Sixteen years on, tens of thousands of people have had their genomes sequenced yet it remains a major challenge to infer future health from genome information. Part of the reason may be that genes interact with each other to modify trait inheritance in ways that aren't totally clear, write Donnelly Centre researchers in an invited perspective for the leading biomedical journal Cell.

"All the genome sequencing data is highlighting the complexity of inheritance for the human genetics community," says Brenda Andrews, University Professor and Director of U of T's Donnelly Centre for Cellular and Biomolecular Research and a senior co-author, whose lab studies interactions between genes. "The simple idea of a single gene leading to a single disease is more likely to be an exception than a rule," she says.

Andrews and Charles Boone, who is also a senior co-author, are professors in U of T's Donnelly Centre and the Department of Molecular Genetics, as well as Senior Fellows of the Genetic Networks program at the Canadian Institute for Advanced Research, which Boone co-directs.

Genome wide association studies, or GWAS, which scan the genomes of patient populations and compare them to healthy controls, have unearthed thousands of mutations, or genetic variants, that are more prevalent in disease. Most variants are found in common diseases that affect large swathes of the world's population but their effects can be small and hard to see. Instead of there being a single gene for heart disease or schizophrenia, for example, there may be many combinations of subtle genetic changes scattered across the genome that tune up or down a person's susceptibility to these diseases.

Vast genetic diversity in the human population further influences trait inheritance while environmental effects, such as diet and upbringing, further complicate matters.

In some cases, a single gene variant can be extremely potent and cause a disease, as seen in cystic fibrosis, heamophilia and other inherited disorders. But even two people with the same disease variant can experience a wildly different disease severity which, presently, cannot be gleaned from their genomes. Even more astonishing, sequencing studies have identified people who carry damaging mutations but remain perfectly healthy, presumably protected by other, as yet unknown gene variants within their genomes.

"It would be a simpler problem if one particular mutation resulted in Disease X all of the time, but that's often not the case," says Michael Costanzo, Senior Research Associate in Boone's lab and one of the authors on the paper. "To understand the effect of combinations of variants is really difficult. We suspect it's particular sets of mutations that really impact what the disease outcome is going to be in a personal genome" says Costanzo. "How genes interact with each other is important and, given our current understanding of gene-gene interactions, it's not a problem that's easily solved by reading individual genome sequences."

It's a numbers game as most genome analysis methods lack the statistical power to confidently uncover multiple genes behind a disease. An often-cited calculation, by researchers at the Broad Institute in Boston, states that to identify a single pair of genes underlying a disease, on the order of half a million patients would have to have their genomes sequenced, with another half a million of healthy people as controls. "If most genetic diseases involve gene combinations, collecting enough patient data to find these interactions is a huge challenge," says Costanzo.

Genetic interactions—what are they and how can they be identified?

"The concept of genetic interaction is simple, but the physiological repercussions can be profound," write the authors. Two genes are said to interact if a combined outcome of their defects is bigger or lesser than expected from their individual outcomes. For example, a person carrying a mutation in either gene A or in gene B can be healthy, but if both A and B don't work, disease occurs.

Research in simple model organisms—most notably yeast—has mapped genome-wide genetic interactions revealing how thousands of genes organize into functional groups within a network. From this, basic principles emerged, allowing researchers to predict a gene's function and its relative importance for the cell's health based on its position in the network. Studies also revealed the identity of so-called "modifier genes" which can suppress the effect of damaging mutations and how genetic background influences trait inheritance.

These types of studies rest on the researchers' ability to switch off genes in precise combinations to find the ones that work together. For human genes, however, such tools did not exist until very recently.

That's all changed now thanks to the gene editing tool CRISPR with which human genes can be turned off in any combination with ease. Although no genome-wide map is yet available, early work indicates that the same principles uncovered in model organisms also apply to human genes. This is already helping reveal function of the less studied human genes and how they relate to disease. And with new computational approaches, it is becoming possible to integrate findings from model organisms with incoming human data to achieve an emerging glimpse of more meaningful insights about health from genome information.

Genetic interactions and cancer therapy

Freed from normal checks and balances, cancer cells stockpile mutations in their genomes and this sets them apart from healthy cells in a way that can be exploited for therapy. Knowing how genes interact in cancer holds promise for the development of selective drugs that kill only sick cells and leave healthy ones unharmed.

"Cancer is a genetic disease and ultimately the genetic wiring of a cancer cell is a product of mutations that occur its genome and we want to understand that," says Jason Moffat, a co-author on the paper and a professor of molecular genetics in the Donnelly Centre whose lab uses CRISPR to map genetic interactions in cancer cells. "With CRISPR, we can start to systematically map how genes interact in cancer cell lines in a similar fashion to how geneticists have mapped genetic interactions in yeast," he says.

This work has the potential to reveal distinct drug targets for different forms of disease. The goal is to find a drug that synergizes with a mutation that's only found in a type of cancer. The drug would then kill sick cells more precisely and with fewer side effects than chemotherapy or radiotherapy.

The knowledge of genetic interactions will also help shed light on why so many approved cancer drugs only work in some patients and not others.

"We can't think about genes in isolation anymore," says Boone. "We have to start looking at variants of multiple genes as a major component of genetic disease, because those combinations are going to be different for different people and these specific combinations may not only profoundly affect disease susceptibility, but they will likely dictate new personalized therapies."

Causes of autism

From Wikipedia, the free encyclopedia

This diagram shows the brain sections and how autism relates to them.

 

Many causes of autism have been proposed, but understanding of the theory of causation of autism and the other autism spectrum disorders (ASD) is incomplete. Research indicates that genetic factors predominate. The heritability of autism, however, is complex, and it is typically unclear which genes are responsible. In rare cases, autism is strongly associated with agents that cause birth defects. Many other causes have been proposed, such as childhood immunizations, but numerous epidemiological studies have shown no scientific evidence supporting any link between vaccinations and autism.

Related disorders

Autism involves atypical brain development which often becomes apparent in behavior and social development before a child is three years old. It can be characterized by impairments in social interaction and communication, as well as restricted interests and stereotyped behavior, and the characterization is independent of any underlying neurological defects. Other characteristics include repetitive-like tasks seen in their behavior and sensory interests. This article uses the terms autism and ASD to denote classical autism and the wider dispersion of symptoms and manifestations of autism, respectively. 

Autism's theory of causation is incomplete. It has long been presumed that there is a common cause at the genetic, cognitive, and neural levels for autism's characteristic triad of symptoms. However, there is increasing suspicion among researchers that autism does not have a single cause, but is instead a complex disorder with a set of core aspects that have distinct causes. Different underlying brain dysfunctions have been hypothesized to result in the common symptoms of autism, just as completely different brain problems result in intellectual disability. The terms autism or ASDs capture the wide range of disease processes at work. Although these distinct causes have been hypothesized to often co-occur, it has also been suggested that the correlation between the causes has been exaggerated. The number of people known to have autism has increased dramatically since the 1980s, at least partly due to changes in diagnostic practice. It is unknown whether prevalence has increased as well.

The consensus among mainstream autism researchers is that genetic factors predominate. Environmental factors that have been claimed to contribute to autism or exacerbate its symptoms, or that may be important to consider in future research, include certain foods, infectious disease, heavy metals, solvents, diesel exhaust, PCBs, phthalates and phenols used in plastic products, pesticides, brominated flame retardants, alcohol, smoking, illicit drugs, and vaccines. Among these factors, vaccines have attracted much attention, as parents may first become aware of autistic symptoms in their child around the time of a routine vaccination, and parental concern about vaccines has led to a decreasing uptake of childhood immunizations and an increasing likelihood of measles outbreaks. However, there is overwhelming scientific evidence showing no causal association between the measles-mumps-rubella (MMR) vaccine and autism, and there is no scientific evidence that the vaccine preservative thiomersal causes autism.

Genetics

Genetic factors may be the most significant cause for autism spectrum disorders. Early studies of twins had estimated heritability to be over 90%, meaning that genetics explains over 90% of whether a child will develop autism. However, this may be an overestimation, as new twin studies estimate the heritability at between 60–90%. Many of the non-autistic co-twins had learning or social disabilities. For adult siblings the risk for having one or more features of the broader autism phenotype might be as high as 30%.

However, in spite of the strong heritability, most cases of ASD occur sporadically with no recent evidence of family history. It has been hypothesized that spontaneous de novo mutations in the father's sperm or mother's egg contribute to the likelihood of developing autism. There are two lines of evidence that support this hypothesis. First, individuals with autism have significantly reduced fecundity, they are 20 times less likely to have children than average, thus curtailing the persistence of mutations in ASD genes over multiple generations in a family. Second, the likelihood of having a child develop autism increases with advancing paternal age, and mutations in sperm gradually accumulate throughout a man's life.

The first genes to be definitively shown to contribute to risk for autism were found in the early 1990s by researchers looking at gender-specific forms of autism caused by mutations on the X chromosome. An expansion of the CGG trinucleotide repeat in the promoter of the gene FMR1 in boys causes fragile X syndrome, and at least 20% of boys with this mutation have behaviors consistent with autism spectrum disorder. Mutations that inactivate the gene MECP2 cause Rett syndrome, which is associated with autistic behaviors in girls, and in boys the mutation is embryonic lethal.

Besides these early examples, the role of de novo mutations in ASD first became evident when DNA microarray technologies reached sufficient resolution to allow the detection of copy number variation (CNV) in the human genome. CNVs are the most common type of structural variation in the genome, consisting of deletions and duplications of DNA that range in size from a kilobase to a few megabases. Microarray analysis has shown that de novo CNVs occur at a significantly higher rate in sporadic cases of autism as compared to the rate in their typically developing siblings and unrelated controls. A series of studies have shown that gene disrupting de novo CNVs occur approximately four times more frequently in ASD than in controls and contribute to approximately 5–10% of cases. Based on these studies, there are predicted to be 130–234 ASD-related CNV loci. The first whole genome sequencing study to comprehensively catalog de novo structural variation at a much higher resolution than DNA microarray studies has shown that the mutation rate is approximately 20% and not elevated in autism compared to sibling controls. However, structural variants in individuals with autism are much larger and four times more likely to disrupt genes, mirroring findings from CNV studies.

CNV studies were closely followed by exome sequencing studies, which sequence the 1–2% of the genome that codes for proteins (the "exome"). These studies found that de novo gene inactivating mutations were observed in approximately 20% of individuals with autism, compared to 10% of unaffected siblings, suggesting the etiology of ASD is driven by these mutations in around 10% of cases. There are predicted to be 350-450 genes that significantly increase susceptibility to ASDs when impacted by inactivating de novo mutations. A further 12% of cases are predicted to be caused by protein altering missense mutations that change an amino acid but do not inactivate a gene. Therefore approximately 30% of individuals with autism have a spontaneous de novo large CNV that deletes or duplicates genes, or mutation that changes the amino acid code of an individual gene. A further 5–10% of cases have inherited structural variation at loci known to be associated with autism, and these known structural variants may arise de novo in the parents of affected children.

Tens of genes and CNVs have been definitively identified based on the observation of recurrent mutations in different individuals, and suggestive evidence has been found for over 100 others. The Simons Foundation Autism Research Initiative (SFARI) details the evidence for each genetic locus associated with autism.

These early gene and CNV findings have shown that the cognitive and behavioral features associated with each of the underlying mutations is variable. Each mutation is itself associated with a variety of clinical diagnoses, and can also be found in a small percentage of individuals with no clinical diagnosis. Thus the genetic disorders that comprise autism are not autism-specific. The mutations themselves are characterized by considerable variability in clinical outcome and typically only a subset of mutation carriers meet criteria for autism. This variable expressivity results in different individuals with the same mutation varying considerably in the severity of their observed particular trait.

The conclusion of these recent studies of de novo mutation is that the spectrum of autism is breaking up into quanta of individual disorders defined by genetics.

One gene that has been linked to autism is SHANK2. Mutations in this gene act in a dominant fashion. Mutations in this gene appear to cause hyperconnectivity between the neurons.

Epigenetics

Epigenetic mechanisms may increase the risk of autism. Epigenetic changes occur as a result not of DNA sequence changes but of chromosomal histone modification or modification of the DNA bases. Such modifications are known to be affected by environmental factors, including nutrition, drugs, and mental stress. Interest has been expressed in imprinted regions on chromosomes 15q and 7q.

Prenatal environment

The risk of autism is associated with several prenatal risk factors, including advanced age in either parent, diabetes, bleeding, and use of psychiatric drugs in the mother during pregnancy. Autism has been linked to birth defect agents acting during the first eight weeks from conception, though these cases are rare.

Infectious processes

Prenatal viral infection has been called the principal non-genetic cause of autism. Prenatal exposure to rubella or cytomegalovirus activates the mother's immune response and may greatly increase the risk for autism in mice. Congenital rubella syndrome is the most convincing environmental cause of autism. Infection-associated immunological events in early pregnancy may affect neural development more than infections in late pregnancy, not only for autism, but also for psychiatric disorders of presumed neurodevelopmental origin, notably schizophrenia.

Environmental agents

Teratogens are environmental agents that cause birth defects. Some agents that are theorized to cause birth defects have also been suggested as potential autism risk factors, although there is little to no scientific evidence to back such claims. These include exposure of the embryo to valproic acid, paracetamol, thalidomide or misoprostol. These cases are rare. Questions have also been raised whether ethanol (grain alcohol) increases autism risk, as part of fetal alcohol syndrome or alcohol-related birth defects. All known teratogens appear to act during the first eight weeks from conception, and though this does not exclude the possibility that autism can be initiated or affected later, it is strong evidence that autism arises very early in development.

Autoimmune and inflammatory diseases

Maternal inflammatory and autoimmune diseases can damage embryonic and fetal tissues, aggravating a genetic problem or damaging the nervous system.

Other maternal conditions

Thyroid problems that lead to thyroxine deficiency in the mother in weeks 8–12 of pregnancy have been postulated to produce changes in the fetal brain leading to autism. Thyroxine deficiencies can be caused by inadequate iodine in the diet, and by environmental agents that interfere with iodine uptake or act against thyroid hormones. Possible environmental agents include flavonoids in food, tobacco smoke, and most herbicides. This hypothesis has not been tested.

Diabetes in the mother during pregnancy is a significant risk factor for autism; a 2009 meta-analysis found that gestational diabetes was associated with a twofold increased risk. A 2014 review also found that maternal diabetes was significantly associated with an increased risk of ASD. Although diabetes causes metabolic and hormonal abnormalities and oxidative stress, no biological mechanism is known for the association between gestational diabetes and autism risk.

Maternal obesity during pregnancy may also increase the risk of autism, although further study is needed.

Maternal malnutrition during preconception and pregnancy influences fetal neurodevelopment. Intrauterine growth restriction is associated with ASD, in both term and preterm infants.

Other in utero

It has been hypothesized that folic acid taken during pregnancy could play a role in reducing cases of autism by modulating gene expression through an epigenetic mechanism. This hypothesis is supported by multiple studies.

Prenatal stress, consisting of exposure to life events or environmental factors that distress an expectant mother, has been hypothesized to contribute to autism, possibly as part of a gene-environment interaction. Autism has been reported to be associated with prenatal stress both with retrospective studies that examined stressors such as job loss and family discord, and with natural experiments involving prenatal exposure to storms; animal studies have reported that prenatal stress can disrupt brain development and produce behaviors resembling symptoms of autism. However, other studies have cast doubts on this association, notably population based studies in England and Sweden finding no link between stressful life events and ASD.

The fetal testosterone theory hypothesizes that higher levels of testosterone in the amniotic fluid of mothers pushes brain development towards improved ability to see patterns and analyze complex systems while diminishing communication and empathy, emphasizing "male" traits over "female", or in E-S theory terminology, emphasizing "systemizing" over "empathizing". One project has published several reports suggesting that high levels of fetal testosterone could produce behaviors relevant to those seen in autism.

Based in part on animal studies, diagnostic ultrasounds administered during pregnancy have been hypothesized to increase the child's risk of autism. This hypothesis is not supported by independently published research, and examination of children whose mothers received an ultrasound has failed to find evidence of harmful effects.

Some research suggests that maternal exposure to selective serotonin reuptake inhibitors during pregnancy is associated with an increased risk of autism, but it remains unclear whether there is a causal link between the two. There is evidence, for example, that this association may be an artifact of confounding by maternal mental illness.

Perinatal environment

Autism is associated with some perinatal and obstetric conditions. A 2007 review of risk factors found associated obstetric conditions that included low birth weight and gestation duration, and hypoxia during childbirth. This association does not demonstrate a causal relationship. As a result, an underlying cause could explain both autism and these associated conditions. There is growing evidence that perinatal exposure to air pollution may be a risk factor for autism, although this evidence suffers from methodological limitations, including a small number of studies and failure to control for potential confounding factors.

Postnatal environment

A wide variety of postnatal contributors to autism have been proposed, including gastrointestinal or immune system abnormalities, allergies, and exposure of children to drugs, vaccines, infection, certain foods, or heavy metals. The evidence for these risk factors is anecdotal and has not been confirmed by reliable studies.

Amygdala neurons

This theory hypothesizes that an early developmental failure involving the amygdala cascades on the development of cortical areas that mediate social perception in the visual domain. The fusiform face area of the ventral stream is implicated. The idea is that it is involved in social knowledge and social cognition, and that the deficits in this network are instrumental in causing autism.

Autoimmune disease

This theory hypothesizes that autoantibodies that target the brain or elements of brain metabolism may cause or exacerbate autism. It is related to the maternal infection theory, except that it postulates that the effect is caused by the individual's own antibodies, possibly due to an environmental trigger after birth. It is also related to several other hypothesized causes; for example, viral infection has been hypothesized to cause autism via an autoimmune mechanism.

Interactions between the immune system and the nervous system begin early during embryogenesis, and successful neurodevelopment depends on a balanced immune response. It is possible that aberrant immune activity during critical periods of neurodevelopment is part of the mechanism of some forms of ASD. A small percentage of autism cases are associated with infection, usually before birth. Results from immune studies have been contradictory. Some abnormalities have been found in specific subgroups, and some of these have been replicated. It is not known whether these abnormalities are relevant to the pathology of autism, for example, by infection or autoimmunity, or whether they are secondary to the disease processes. As autoantibodies are found in diseases other than ASD, and are not always present in ASD, the relationship between immune disturbances and autism remains unclear and controversial. A 2015 systematic review and meta-analysis found that children with a family history of autoimmune diseases were at a greater risk of autism compared to children without such a history.

When an underlying maternal autoimmune disease is present, antibodies circulating to the fetus could contribute to the development of autism spectrum disorders.

Gastrointestinal connection

Gastrointestinal problems are one of the most commonly associated medical disorders in people with autism. These are linked to greater social impairment, irritability, behavior and sleep problems, language impairments and mood changes, so the theory that they are an overlap syndrome has been postulated. Studies indicate that gastrointestinal inflammation, immunoglobulin E-mediated or cell-mediated food allergies, gluten-related disorders (celiac disease, wheat allergy, non-celiac gluten sensitivity), visceral hypersensitivity, dysautonomia and gastroesophageal reflux are the mechanisms that possibly link both.

A 2016 review concludes that enteric nervous system abnormalities might play a role in several neurological disorders, including autism. Neural connections and the immune system are a pathway that may allow diseases originated in the intestine to spread to the brain. A 2018 review suggests that the frequent association of gastrointestinal disorders and autism is due to abnormalities of the gut–brain axis.

The "leaky gut" hypothesis is popular among parents of children with autism. It is based on the idea that defects in the intestinal barrier produce an excessive increase of the intestinal permeability, allowing substances present in the intestine, including bacteria, environmental toxins and food antigens, to pass into the blood. The data supporting this theory are limited and contradictory, since both increased intestinal permeability and normal permeability have been documented in people with autism. Studies with mice provide some support to this theory and suggest the importance of intestinal flora, demonstrating that the normalization of the intestinal barrier was associated with an improvement in some of the ASD-like behaviours. Studies on subgroups of people with ASD showed the presence of high plasma levels of zonulin, a protein that regulates permeability opening the "pores" of the intestinal wall, as well as intestinal dysbiosis (reduced levels of Bifidobacteria and increased abundance of Akkermansia muciniphila, Escherichia coli, Clostridia and Candida fungi) that promotes the production of proinflammatory cytokines, all of which produces excessive intestinal permeability. This allows passage of bacterial endotoxins from the gut into the bloodstream, stimulating liver cells to secrete tumor necrosis factor alpha (TNFα), which modulates blood–brain barrier permeability. Studies on ASD people showed that TNFα cascades produce proinflammatory cytokines, leading to peripheral inflammation and activation of microglia in the brain, which indicates neuroinflammation. In addition, neuroactive opioid peptides from digested foods have been shown to leak into the bloodstream and permeate the blood–brain barrier, influencing neural cells and causing autistic symptoms.

After a preliminary 1998 study of three children with ASD treated with secretin infusion reported improved GI function and dramatic improvement in behavior, many parents sought secretin treatment and a black market for the hormone developed quickly. Later studies found secretin clearly ineffective in treating autism.

Endogenous opiate precursor theory

In 1979, Jaak Panksepp proposed a connection between autism and opiates, noting that injections of minute quantities of opiates in young laboratory animals induce symptoms similar to those observed among autistic children. The possibility of a relationship between autism and the consumption of gluten and casein was first articulated by Kalle Reichelt in 1991.

Opiate theory hypothesizes that autism is the result of a metabolic disorder in which opioid peptides gliadorphin (aka gluteomorphin) and casomorphin, produced through metabolism of gluten (present in wheat and related cereals) and casein (present in dairy products), pass through an abnormally permeable intestinal wall and then proceed to exert an effect on neurotransmission through binding with opioid receptors. It has been postulated that the resulting excess of opioids affects brain maturation, and causes autistic symptoms, including behavioural difficulties, attention problems, and alterations in communicative capacity and social and cognitive functioning.

Although high levels of these opioids are eliminated in the urine, it has been suggested that a small part of them cross into the brain causing interference of signal transmission and disruption of normal activity. Three studies have reported that urine samples of people with autism show an increased 24-hour peptide excretion. A study with a control group found no appreciable differences in opioid levels in urine samples of people with autism compared to controls. Two studies showed an increased opioid levels in cerebrospinal fluid of people with autism.

The theory further states that removing opiate precursors from a child's diet may allow time for these behaviors to cease, and neurological development in very young children to resume normally. As of 2014 there is no good evidence that a gluten-free diet is of benefit as a standard treatment for autism. Problems observed in studies carried out include the suspicion that there were transgressions of the diet because the participants asked for food containing gluten or casein to siblings and peers; and the lack of a washout period, that could diminish the effectiveness of the treatment if gluten or casein peptides have a long term residual effect, which is especially relevant in studies of short duration. In the subset of people who have gluten sensitivity there is limited evidence that suggests that a gluten-free diet may improve some autistic behaviors.

Lack of vitamin D

The hypothesis that vitamin D deficiency has a role in autism is biologically plausible, but not researched.

Lead

Lead poisoning has been suggested as a possible risk factor for autism, as the lead blood levels of autistic children has been reported to be significantly higher than typical. The atypical eating behaviors of autistic children, along with habitual mouthing and pica, make it hard to determine whether increased lead levels are a cause or a consequence of autism.

Locus coeruleus–noradrenergic system

This theory hypothesizes that autistic behaviors depend at least in part on a developmental dysregulation that results in impaired function of the locus coeruleus–noradrenergic (LC-NA) system. The LC-NA system is heavily involved in arousal and attention; for example, it is related to the brain's acquisition and use of environmental cues.

Mercury

This theory hypothesizes that autism is associated with mercury poisoning, based on perceived similarity of symptoms and reports of mercury or its biomarkers in some autistic children. This view has gained little traction in the scientific community as the typical symptoms of mercury toxicity are significantly different from symptoms seen in autism. The principal source of human exposure to organic mercury is via fish consumption and for inorganic mercury is dental amalgams. The evidence so far is indirect for the association between autism and mercury exposure after birth, as no direct test has been reported, and there is no evidence of an association between autism and postnatal exposure to any neurotoxicant. A meta-analysis published in 2007 concluded that there was no link between mercury and autism.

Oxidative stress

This theory hypothesizes that toxicity and oxidative stress may cause autism in some cases. Evidence includes genetic effects on metabolic pathways, reduced antioxidant capacity, enzyme changes, and enhanced biomarkers for oxidative stress; however, the overall evidence is weaker than it is for involvement oxidative stress with disorders such as schizophrenia. One theory is that stress damages Purkinje cells in the cerebellum after birth, and it is possible that glutathione is involved. Autistic children have lower levels of total glutathione, and higher levels of oxidized glutathione. Based on this theory, antioxidants may be a useful treatment for autism.

Viral infection

Many studies have presented evidence for and against association of autism with viral infection after birth. Laboratory rats infected with Borna disease virus show some symptoms similar to those of autism but blood studies of autistic children show no evidence of infection by this virus. Members of the herpes virus family may have a role in autism, but the evidence so far is anecdotal. Viruses have long been suspected as triggers for immune-mediated diseases such as multiple sclerosis but showing a direct role for viral causation is difficult in those diseases, and mechanisms whereby viral infections could lead to autism are speculative.

Social construct

The social construct theory says that the boundary between normal and abnormal is subjective and arbitrary, so autism does not exist as an objective entity, but only as a social construct. It further argues that autistic individuals themselves have a way of being that is partly socially constructed.

Asperger syndrome and high-functioning autism are particular targets of the theory that social factors determine what it means to be autistic. The theory hypothesizes that individuals with these diagnoses inhabit the identities that have been ascribed to them, and promote their sense of well-being by resisting or appropriating autistic ascriptions.

Discredited theories

Vaccines

Scientific studies have refuted a causal relationship between vaccinations and autism. Despite this, some parents believe that vaccinations cause autism and therefore delay or avoid immunizing their children, for example under the "vaccine overload" hypothesis that giving many vaccines at once may overwhelm a child's immune system and lead to autism, even though this hypothesis has no scientific evidence and is biologically implausible. Because diseases such as measles can cause severe disabilities and death, the risk of death or disability for an unvaccinated child is higher than the risk for a child who has been vaccinated. Despite all this, antivaccine activism continues. A developing tactic appears to be the "promotion of irrelevant research [as] an active aggregation of several questionable or peripherally related research studies in an attempt to justify the science underlying a questionable claim."

Refrigerator mother

Bruno Bettelheim believed that autism was linked to early childhood trauma, and his work was highly influential for decades both in the medical and popular spheres. 

Parents, especially mothers, of individuals with autism were blamed for having caused their child's condition through the withholding of affection. Leo Kanner, who first described autism, suggested that parental coldness might contribute to autism. Although Kanner eventually renounced the theory, Bettelheim put an almost exclusive emphasis on it in both his medical and his popular books. Treatments based on these theories failed to help children with autism, and after Bettelheim's death, it came out that his reported rates of cure (around 85%) were found to be fraudulent.

MMR vaccine

The MMR vaccine as a cause of autism is one of the most extensively debated hypotheses regarding the origins of autism. Andrew Wakefield et al. reported a study of 12 children who had autism and bowel symptoms, in some cases reportedly with onset after MMR. Although the paper, which was later retracted by the journal, concluded "We did not prove an association between measles, mumps, and rubella vaccine and the syndrome described," Wakefield nevertheless suggested during a 1998 press conference that giving children the vaccines in three separate doses would be safer than a single dose. 

In 2004, the interpretation of a causal link between MMR vaccine and autism was formally retracted by ten of Wakefield's twelve co-authors. The retraction followed an investigation by The Sunday Times, which stated that Wakefield "acted dishonestly and irresponsibly". The Centers for Disease Control and Prevention, the Institute of Medicine of the National Academy of Sciences, and the U.K. National Health Service have all concluded that there is no evidence of a link between the MMR vaccine and autism. 

In February 2010, The Lancet, which published Wakefield's study, fully retracted it after an independent auditor found the study to be flawed. In January 2011, an investigation published in the journal BMJ described the Wakefield study as the result of deliberate fraud and manipulation of data.

Thiomersal (thimerosal)

Perhaps the best-known hypothesis involving mercury and autism involves the use of the mercury-based compound thiomersal, a preservative that has been phased out from most childhood vaccinations in developed countries including US and the EU. Parents may first become aware of autistic symptoms in their child around the time of a routine vaccination. There is no scientific evidence for a causal connection between thiomersal and autism, but parental concern about the thiomersal controversy has led to decreasing rates of childhood immunizations and increasing likelihood of disease outbreaks. In 1999, due to concern about the dose of mercury infants were being exposed to, the U.S. Public Health Service recommended that thiomersal be removed from childhood vaccines, and by 2002 the flu vaccine was the only childhood vaccine containing more than trace amounts of thimerosal. Despite this, autism rates did not decrease after the removal of thimerosal, in the US or other countries that also removed thimerosal from their childhood vaccines.

A causal link between thimerosal and autism has been rejected by international scientific and medical professional bodies including the American Medical Association, the American Academy of Pediatrics, the American College of Medical Toxicology, the Canadian Paediatric Society, the U.S. National Academy of Sciences, the Food and Drug Administration, Centers for Disease Control and Prevention, the World Health Organization, the Public Health Agency of Canada, and the European Medicines Agency.