Bai D, Yip BHK, Windham GC, et al. - In this population-based, multinational cohort study, researchers estimated the additive genetic, maternal, and environmental influences in autism spectrum disorder (ASD). They analyzed 2,001,631 individuals from birth cohorts of children from Denmark, Finland, Sweden, Israel, and Western Australia. These were followed up to age 16 years. A diagnosis of ASD was received by 22,156 of the whole study sample. For ASD, the estimated heritability was nearly 80%, when population data from 5 countries were used. This suggests that inherited genetic influences are mostly responsible for the variation in ASD occurrence in the population, and maternal effects did not contribute. Across countries, the sources of ASD risk may vary modestly.