The genetic architecture of obsessive-compulsive disorder: alleles across the frequency spectrum contribute liability to OCD

Objective: Obsessive-compulsive disorder (OCD) is known to be substantially heritable; however, the contribution of common genetic variation across the alleleic frequency spectrum to this heritability remains uncertain. We use two new, homogenous cohorts to estimate heritability of OCD from common genetic variation and contrast results with prior studies. Methods: The sample consisted of 2096 Swedish-born individuals diagnosed with OCD and 4609 controls, all genotyped for common genetic variants, specifically >400,000 single nucleotide polymorphisms (SNPs) with minor allele frequency (MAF) ≥ 0.01. Using genotypes of these SNPs to estimate distant familial relationships among individuals, we estimated heritability of OCD, both overall and partitioned according to MAF bins. Results: We estimated narrow-sense heritability of 28% (SE=4%). The estimate was robust, varying only modestly under different models. Contrary to an earlier study, however, SNPs with MAF between 0.01 and 0.05 accounted for 8% of heritability and estimated heritability per bin roughly follows expectations based on a simple model for SNP-based heritability. Conclusions: These results indicate that common inherited risk variation (MAF ≥ 0.01) accounts for most of the heritable variation in OCD. SNPs with low MAF contribute meaningfully to the heritability of OCD and the results are consistent with expectation under the "infinitesimal model," where risk is influenced by a large number of loci across the genome and across MAF bins.