Social Demographic Change and Autism

Kayuet Liu, Columbia University
Noam Zerubavell, Columbia University
Peter S. Bearman, Columbia University

Parental age at child’s birth – which has increased for children born in the 1992-2000 birth cohorts is strongly associated with an increased risk of autism. By turning a social demographic lens on the historical patterning of concordance amongst twin pairs, we identify a central mechanism for this association -- de novo mutations -- changes in DNA in the germ cells that are not present in the parents’ DNA. We show that a demographic eye on the rising prevalence of autism gives rise to three major discoveries. The first is that we show that social demographic change can yield genetic changes that at the population level combine to contribute to the increased prevalence of autism. The second is that the estimated heritability of autism has been dramatically overstated. Third, we show that heritability estimates can change over remarkably short periods of time due to increases in germ-cell mutations.