Genetics are significantly more responsible for driving autism spectrum disorders than maternal factors or environmental factors such as vaccines and chemicals, according to a massive new study involving more than 2 million people from five different countries.
The largest-of-its-kind study, published this week in the journal JAMA Psychiatry, found that around 80 percent of a person's risk of developing autism disorders stem from inherited genes, meaning that other factors not related to altering genetic DNA account for just 20 percent of the risk. Of these, only about 1 percent could be attributed to maternal factors such as a mother's weight and diet, or the method and time the baby was delivered. The researchers said many maternal factors, but not all, had a "nonexistent or minimal" impact. The other environmental factors were not specifically identified.
The researchers examined data in national medical records from 1998 to 2012 of people born in Denmark, Sweden, Finland, Israel and Australia until they were 16 years old. Of the 2 million total, more than 22,000 had developed some type of autism spectrum disorder. The researchers also looked at the histories of these individuals' family members, including siblings, cousins, parents and grandparents, comparing health outcomes with genetic connections and environmental factors they shared.
"Everywhere we looked, in five different samples, what we saw was that genetic factors were most important," lead author for the study Sven Sandin, an epidemiologist at Sweden's Karolinska Institutet, told HuffPost.
The findings are consistent with previous studies on the heritability of autism, many of which were limited to studying twins or siblings. But this study is the first and largest to show the significant extent to which genetic factors determine autism outcomes.
The study further contradicts a long-held ?— but unproven — popular belief that vaccines are a leading cause of autism, HealthDay News reported, noting that "long-discredited, fraudulent data" supporting that belief is still widely cited by a global anti-vaccine movement.
In an editorial published alongside the study, three Columbia University psychiatrists noted that environmental factors "often receive disproportionate attention from the public and the media, even when (as in the case of vaccine fears), they are debunked."
The anti-vaccine movement came to the forefront after medical journal The Lancet published a paper by a now-discredited British physician, Andrew Wakefield, which claimed to show a link between children developing autism and the measles, mumps and rubella vaccine. The research was repeatedly debunked and declared fraudulent, Wakefield was struck from the UK's medical register following six charges of professional misconduct, and The Lancet retracted the paper.
HealthDay News reported that the study could be a jumping off point for further research into how genetics specifically causes autism disorders, which affect 1 out of every 59 children in the U.S., according to the U.S. Centers for Disease Control and Prevention. But experts caution that environmental risk factors can't be totally overlooked.
"Environmental factors also play a smaller, but important, role," Dr. Andrew Adesman, who directs developmental and behavioral pediatrics at Cohen Children's Medical Center in New Hyde Park, New York, told HealthDay News. "This does not mean that we can completely ignore the environmental risk factors and their interaction with the genetic risk factors."
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