Autism is more widespread, U.S. studies show, but why?

Autism is more widespread, U.S. studies show, but why? - A new government survey estimates that more U.S. children than ever have a diagnosed autism spectrum disorder. Overall, the prevalence was 110 out of every 10,000 children ages 3 to 17. But the rate varied by sex and racial or ethnic group:
Boys: 173 of 10,000
Girls: 43 of 10,000
Hispanic: 103 of 10,000
Non-Hispanic white: 125 of 10,000
Non-Hispanic black: 61 of 10,000
Non-Hispanic multiracial: 71 of 10,000
Non-Hispanic other single race: 66 of 10,000