Harvard Mental Health Letter

In Brief: The genetics of autism

In Brief

The genetics of autism

The three main features of autism are impaired capacity for social interaction, impaired speech, and restricted, repetitive behavior and interests. A study by British researchers suggests that these characteristics are inherited separately, and autism must be broken down into its components for purposes of genetic research.

The parents of nearly 7,000 eight-year-old twins (about 2,300 fraternal and 1,100 identical pairs) answered a questionnaire called the Childhood Asperger Syndrome Test, which identifies symptoms along the autistic spectrum from severe autism to Asperger's syndrome. The 2% of children who scored highest for autistic symptoms were described as "at risk of autistic spectrum disorder." As expected, the vast majority (77%) were boys.

This study also confirmed the strongly genetic nature of autism: Shared environment — common home and family upbringing — had no influence on autistic spectrum disorders or autistic traits. Identical twins were much more likely than fraternal twins to have autistic symptoms in common. The heritability of being "at risk" was about 90%, and nearly the same high level of heritability (80%) was found all along the spectrum of symptoms from none to severe.

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