Most of the genetic risk for autism comes from versions of genes that are common in the population rather than from rare variants or spontaneous glitches, researchers funded by the National Institutes of Health have found. Heritability also outweighed other risk factors in this largest study of its kind to date.
According to an article in the Morbidity and Mortality Weekly Report, a publication of the U.S. Centers for Disease Control and Prevention (CDC), the prevalence of autism spectrum disorder (ASD) is higher than ever . The CDC periodically surveys the prevalence of ASD, looking during each surveillance period at the percentage of 8-year-old children who have current ASD diagnoses. In 2000, a survey of children born in 1992 revealed that one in 150 had ASD. These numbers have been steadily climbing, such that the most recent survey — completed in 2008 and surveying children born in 2000 — indicates that one in 88 children has ASD. The numbers are even more disturbing for male children, who have an ASD prevalence of one in 54.
The largest and most rigorous twin study of its kind to date has found that shared environment influences susceptibility to autism more than previously thought.
The study, supported by the National Institutes of Health, found that shared environmental factors — experiences and exposures common to both twin individuals — accounted for 55% of strict autism and 58% of more broadly defined autism spectrum disorders (ASD). Genetic heritability accounted for 37% of autism and 38% of ASD. Random environmental factors not shared among twins play a much smaller role.