The contribution of de novo tandem repeat mutations to autism spectrum disorders

Recent studies have demonstrated a strong contribution of germline mutations to autism spectrum disorders (ASD). Tandem repeats (TRs), consisting of repeated sequence motifs of 1-20bp, comprise one of the largest sources of human genetic variation. Yet, the contribution of TR mutations to ASD has not been assessed on a genome-wide scale. Here, we leverage novel bioinformatics tools and ~35× whole genome sequencing of ~1,600 families from the Simons Simplex Collection (SSC) to analyze germline TR mutations at nearly 1 million loci in ASD-affected and unaffected siblings. We identify an average of 54 high-confidence mutations per child at an estimated true positive rate of 90%. We find novel genome-wide TR mutation patterns, including a bias toward larger mutations from the maternal compared with paternal germlines. We demonstrate a significant genome-wide excess of TR mutations in ASD probands, which are significantly larger than in controls, enriched in promoters of fetal brain expressed genes, and more strongly predicted to alter expression during brain development. Overall, our results indicate a significant, but so far overlooked, contribution of repetitive regions to ASD.