Autism Spectrum Disorder, 1: Genetic and Environmental Risk Factors

The global prevalence of autism spectrum disorder (ASD) has quadrupled during the past 3 decades; the reasons for this are many and include broadening of the diagnostic concept, increased awareness of the disorder, increased screening (including of adults and of girl children), and, possibly, increased exposure to environmental risk factors. This article examines genetic and especially environmental risk factors for ASD. Unsurprisingly, hundreds of potential genes have been identified, many of which overlap between ASD, schizophrenia, depression, and cardiometabolic disorders. Likewise, over a hundred environmental exposures have been associated with ASD risk. These include exposure to parental and family characteristics, exposure to maternal disorders arising during pregnancy, exposure to chronic maternal disorders present during pregnancy, exposure to fetal and other pregnancy-related problems/events, exposure to neonatal problems/events, exposure to maternal nutritional deficiencies during pregnancy, maternal exposure to substances during pregnancy, maternal exposure to pharmacological agents during pregnancy, in utero exposure to toxic substances, and early life exposure to toxic substances. Some of the risk factors identified may be causal, some may be markers of intermediary mechanisms, and some may be unrelated markers. About 40 of these risk factors have been confirmed in meta-analysis for association with ASD. Nearly 70 maternal diagnoses have also been associated with ASD, but, after correcting for false discovery error and shared risk, only 30 remain; and, of these 30, almost all may be explained by genetic and environmental risk factors shared between mother and child, judging from findings in discordant sibling pair and paternal negative control analyses. Caveats and nuances in the interpretation of risks are briefly discussed.