Bai D, et al. - Through a population-based, multinational cohort study that involved full birth cohorts of children from Denmark, Finland, Sweden, Israel, and Western Australia born between January 1, 1998 and December 31, 2011, experts assessed the additive genetic, maternal, and environmental impacts in autism spectrum disorder (ASD). They recruited 2,001,631 participants, out of which 22,156 were diagnosed with ASD. Ranging from 50.9% (Finland) to 86.8% (Israel), the median ASD heritability was 80.8% for country-specific point estimates. Heritability estimates ranged from 81.2% to 82.7% for the Nordic countries combined. The maternal effect was expected to range from 0.4% to 1.6%. Estimates of genetic, maternal, and environmental impacts for autistic disorder were comparable to ASD. Therefore, the heritability of ASD was assessed to be around 80%, indicating that the differences in ASD occurrence in the population was mostly owing to inherited genetic impacts; no support was seen for contributions from maternal influences in this study. Findings proposed possible modest variations in the sources of ASD risk among countries.