The initial correlation between OCD heritability and chromosome length increased substantially after removal of chromosome 15 (Tables S5 and S6). This increase in correlation is quite similar to the increase in the correlation between chromosome length and heritability reported for multiple sclerosis (MS) [48] upon removal of chromosome 6 (r = 0.45), suggesting that chromosome 15 may contribute to the heritability of OCD much to the same degree that chromosome 6 contributes to the heritability of MS [48]. Regions of chromosome 15 have been identified as linkage signals for OCD across multiple populations [52], [53]. Additionally, genes within the imprinted genomic region chr15q11-13 have been reproducibly associated with repetitive behaviors, obsessive compulsive behaviors, and autism [54], [55], [56], [57]. Together these findings continue to implicate chromosome 15 in the development of OCD.
