Parental Age and Autism Spectrum Disorders

PurposeWe sought to study the possible association between parental age and autism spectrum disorder (ASD) by using both a cohort design and a sibling design.MethodsOur cohort included all singleton births in Denmark from January 1, 1980, through December 31, 2003, a total of 1,311,736 children. Cases of ASDs were obtained from the Danish National Psychiatric Register using International Classification of Diseases (ICD)-8 and ICD-10.ResultsA total of 9556 children were diagnosed with an ASD. Both maternal and paternal age were associated with a greater risk of ASD in the offspring (hazard ratios ranging from 1.21 (1.10–1.34) to 1.65 (1.09–2.48) depending on combinations of parental age categories; <35, 35–39, and 40+ years). For mothers younger than 35 years, the risk of ASD increased with increasing father’s age group. For fathers younger than 35 years, the risk of ASD increased with increasing maternal age.ConclusionsWe found an association between parental age and ASD in the cohort study, but the combined underlying mechanisms through which paternal and maternal age impact ASD risk do not seem to act synergistically. The results of the sibling analysis suggest that the association between parental age and ASD found in the cohort study cannot be accounted for by common genetic and environmental factors.