In The Politics of Autism, I discuss various ideas about what causes the condition. Here is just a partial list of correlates, risk factors, and possible causes that have been the subject of serious studies -- including one about grandparental age.
Nicholette Zeliadt at NYT:
In the past 50 years, scientists have compiled a short list of factors, including certain genes, premature birth, and some medications, that might contribute to autism. They have begun to understand which people have the greatest chances of having a child with autism, and they have identified a few things you can do to minimize those chances.
Until the 1970s, many experts subscribed to now-discredited notions about autism being caused by “cold” parenting styles or growing up in extreme isolation (as in the famous case of the Wild Boy of Aveyron in France in the late 1700s). Since then, studies have shown autism runs in families and have put its heritability at around 80 percent, or about as heritable as height or eye color.
So, autism is highly genetic, but that doesn’t mean environmental factors are unimportant, said Dr. Brian Lee, Ph.D., associate professor of epidemiology and biostatistics at the A.J. Drexel Autism Institute in Philadelphia. Height, for example, is influenced by environmental factors like malnutrition. “You can have a genetic underlying factor that puts you at risk, but there may need to be some sort of an environmental condition or trigger,” Lee said.
S.S.R.I.s are strong candidates for factors that could trigger autism. They act on the brain chemical serotonin, which is important for social function and is found at high levels in some autistic people, and many of them cross from a woman’s blood into the womb.
But Dr. Alan Brown, M.D., professor of psychiatry and epidemiology at Columbia University, said that it’s difficult to separate the effects of a medication from a pregnant woman’s reason for taking them — her underlying mental health condition. Several recent studies suggest that the autism risk associated with S.S.R.I. use is very small, perhaps nonexistent. “The literature is confusing on S.S.R.I.s and autism,” Brown said. “Some studies show the association, others don’t.”
Researchers also have looked into prenatal exposure to toxins, such as pesticides or air pollution, and have come up with similarly inconclusive results. They have found no increased autism risk related to prenatal smoking, cesarean section, fertility treatments or vaccines.