Prior to the advent of dense genotyping, the heritability of a trait was typically estimated from its distribution within pedigrees. These kinds of studies continue to this day, in large part because they capture heritability due to both common and rare inherited genetic variation. It is thus interesting to compare our SNP-based heritability estimate from common variation, 29%, to that from Swedish families, 35–50% (1, 4). This comparison suggests that while the majority of inherited liability for OCD in Sweden traces to common genetic variation, rare variation contributes to OCD liability as well, but to a lesser degree, consistent with the findings to date regarding rare variation and risk for OCD (17–20).
