Twins reveal genetic risk for autism

The study of two million Swedish children showed that the relative recurrent risk – a measure of the risk of an autism diagnosis in the sibling of a child with ASD – was 10.3 for full siblings, 3.3 for maternal half-siblings, 2.9 for paternal half-siblings and 2.0 in cousins.

Non-shared environmental effects accounted for the balance of the autism risk, with shared environmental influences, reflecting non-genetic influences that contribute to similarity within pairs of siblings, having a negligible effect.