Environment plays part in autism liability

ENVIRONMENTAL factors play a greater role in the development of autism than previously believed, say researchers, in the wake of a study overturning decades-old dogma that genes contribute most of the liability.

US researchers looked at the rates of autism in 192 twin pairs where at least one twin had autism spectrum disorder (ASD). 

They found that while concordance rates of autism were 58–60% in monozygotic twins, the concordance rates for dizygotic twins were 21–27%, much higher than previously reported.

They calculated that genetic heritability contributed 37%, and a shared environmental variance contributed 55%, to the development of strict autism. For ASD, genetic heritability contributed 38%, and a shared environmental component 58%, to the condition. 

The study provided evidence that the rate of concordance in dizygotic twins may have been seriously underestimated, and the influence of genetic factors on