To date, four complex segregation analyses of OCD transmission in families ascertained through OCD probands have been reported.69-72 All studies provided evidence that the transmission of OCD within families is consistent with genetic transmission. However, the genetic model that best explained the transmission within families differed from study to study. Given the variability of recurrence risks observed in the family studies and the clinical heterogeneity that is evident in OCD, this result is not surprising. Nevertheless, it is noteworthy that the conclusions of the authors in all of these reports were that there are some genes of major effect important for the manifestation of OCD. Given the variability in the estimates of recurrence risks in the reported studies, it is quite likely that OCD is an oligogenic disorder (ie, a number of genes are important for the expression of the disorder).
