Age, Race, and Ethnicity of Maternal Grandparents in Autism Spectrum Disorder, a California Multigenerational Study

We investigated associations between maternal grandparents' age and autism spectrum disorders (ASD) in grandchildren, exploring differences by race/ethnicity. In a multigenerational California birth cohort study including 1,743,998 and 1,630,722 mother-child pairs (with 27,975 and 25,816 ASD cases, respectively), we examined ASD risk by grandmother's and grandfather's age at the time when their daughter was born. Logistic regression was used to obtain odds ratios (ORs) and 95% CIs. The odds of ASD in grandchildren were higher among White grandmothers (OR, 1.14; 95% CI, 1.08-1.20) and grandfathers (OR, 1.18; 95% CI, 1.11-1.25) who had daughters at younger ages (18-24 years) compared to the 25-29 year reference, while inverse associations were observed for younger Black grandmothers (OR, 0.85; 95% CI, 0.78-0.94). At older ages (35-55 years), ASD risks were higher among Hispanic grandmothers (OR, 1.13; 95% CI, 1.06-1.21) and Hispanic (OR, 1.12; 95% CI, 1.06-1.18) and Black grandfathers (OR, 1.18; 95% CI, 1.05-1.32). The risk of ASD in grandchildren was higher among older grandparents of several races/ethnicities but among the youngest grandparents only among those of White race. Differences by race/ethnicity may imply different mechanisms operating in younger and older grandparents. Studies exploring the contributions of biological as well as social, occupational, and environmental factors on the influence of age at pregnancy with ASD are needed.