As for the overall rise, we can’t know whether there are more autistic children now than there were in previous generations, because we’re so much more aware of the disorder today than we’ve ever been. (Lord does not believe that autism is being overdiagnosed.) The criteria for autism didn’t change between 2008 and 2010 (though the criteria did change in 2013), and a 30 percent rise does seem like a lot to simply attribute to raised awareness.
Still, there is no indication that there’s a rise in severity. Just as they did in 2008, the numbers refer to everyone on the spectrum, which includes a huge range, from extremely mild to extremely severe. In 2008, 62 percent of children with ASD did not have an intellectual disability (which means an IQ over 70). In 2010, 69 percent of children did not have an intellectual disability. Lord compares the breadth of this study to one about people with sight problems, which included “both people who have to wear glasses when they’re 60 to read up close, up to people who are functionally blind. It is a very, very broad range.”
Aaron Carroll makes related points:
1) The definition of autism is evolving. It’s now a spectrum, and being identified in higher functioning individuals.
2) Awareness is increasing, leading more children to be labelled.
3) There are many areas where support for autism services are robust, but support for other disabilities are thin. Giving children the diagnosis of autism opens up doors for them that might otherwise be closed with respect to help.
4) Of course, the prevalence could be increasing as well.
Over the weekend, Sam Wang looked (NYT) at the various factors that increase the risk of autism. One of the more surprising ones:
A highly underappreciated prenatal risk is stress. For pregnant women who take the sometimes-wrenching step of emigrating to a new country, for example, the risk ratio is 2.3. In the fifth through ninth months of pregnancy, getting caught in a hurricane strike zone carries a risk ratio of about 3. Maternal post-traumatic stress disorder during pregnancy is associated with a similar effect. These events are likely to trigger the secretion of stress hormones, which can enter the fetus’s bloodstream and affect the developing brain for a lifetime. Stressors may also lead to maternal illness, the immune response to which may interfere with brain development.
Wang promotes the article at his blog:
In my article in the Sunday New York Times on how to think about autism risks, I apply meta-analytical techniques to autism research literature. It’s nearly impossible to get a good overall perspective from news reports. However, I provide a way to look at it all at once. My secret decoder ring takes the form of risk ratios. Check it out.