Article: Rise in Autism May Be Due to Semantics, Study Finds

Autism, autism-spectrum disorder, and Asperger's syndrome. 

A new study suggests the idea that more kids are being diagnosed with autism not because something catastrophic has happened to U.S. children, but rather because they're simply being classified and diagnosed differently.

Special education enrollment figures suggest 97 percent of the increase in autism seen between 2000 and 2010 could simply be accounted for by reclassification — at least among older kids — a team at Penn State University found. [And about 2/3 of the total increase.]

[snip] 

Santhosh Girirajan, an assistant professor of biochemistry and molecular biology and of anthropology at Penn State and colleagues looked at 11 years of special-education enrollment data covering more than 6 million children a year. They found that the increase in students designated as having autism could be offset by a nearly equal decrease in students diagnosed with other intellectual disabilities often seen along with autism.

Additionally, higher autism rates are found in children of teen parents and of older parents. Since there has been more of those two groups over the last 30 years or so, that could account for some of the rest of the increase. 

Also, there is a genetic factor at work as well. Parents who are detailed oriented tend to be at an increased risk of having children with autism. It used to be that men who were detailed oriented tended to end up certain occupations, such as engineering. Women in others. These men would tend to find spouses at church or in social organizations or in support staff where they worked. These women would be less likely to carry any autism related genes. 

Because detail-oriented women are being encouraged to move into engineering type occupations, detail oriented men and women are now  more likely to marry each other. This increases the risk of a "double dose" of the genes related to autism. 

If these three things are true, they probably account for close to 100% of the increase in the diagnosis of autism and its related syndromes.