Another interesting contrast is the evidence for heritability across chromosomes. Davis et al. observed essentially no heritability for OCD on chromosome 6, which encodes both the HLA and histone gene clusters, and extremely high heritability on chromosome 15. In discussing these results, the authors suggest that chromosome 15 has an outsized contribution to OCD risk and that the HLA locus is effectively excluded from OCD risk. Given the contrasting results in our study, and in our analyses combining results from both studies, we again conclude that the data are consistent with the infinitesimal model and that smaller sample sizes might account for results that diverge from expectation.
