Parent-of-origin effect in transmission of bipolar disorder.

Recently, possible involvement of a parent-of-origin effect in the transmission of bipolar disorder has been suggested. We examined the possible contribution of parent-of-origin effect by using data from a large family and family history study of bipolar patients in the Collaborative Depression Study. In 276 probands with bipolar I disorder, family histories were examined using three diagnostic criteria: 1) bipolar I disorder, 2) bipolar I or bipolar II disorder, and 3) bipolar disorders or recurrent unipolar depression for parents and siblings. An excess of affected mothers was not observed when unipolar depression was excluded. Age-at-onset was significantly lower in probands having a father with bipolar disorders or recurrent unipolar depression than in probands with an affected mother. This difference was not observed when unipolar depression was excluded. There was no significant difference of prevalence rate in children of affected mothers and those with affected fathers. These data do not support the contribution of parent-of-origin effect in the transmission of bipolar disorder.