The effect of the proband's gender on the familial aggregation of psychiatric disorders has rarely been investigated. Consequently, the goals of the study were to assess the effect of the proband's gender on the familial aggregation of Major Depressive Disorder (MDD) and Bipolar-I Disorder (BP-I).

The present paper was based on data from a family study of 130 bipolar-I probands, 158 unipolar depressive probands and 97 normal controls as well as their adult first-degree relatives (n=1651). Diagnoses were made according to a best-estimate procedure based on a semi-structured interview (DIGS), medical records and family history information. Analyses were performed using logistic regression models.

The major findings were that the relatives of female probands with MDD had an almost doubled risk of suffering from recurrent MDD as compared to the those of male probands with MDD. Moreover, the relatives of female probands suffered from anxiety disorders and committed suicidal attempts more frequently than those of male probands. In contrast, the proband's gender was found to have no impact on the familial transmission of bipolar disorder. However, there was a two-times increased risk for alcohol dependence in the relatives of female as compared to male bipolar probands.

Our data provided support for the influence of the proband's gender on the familial aggregation of MDD, suggesting higher genetic loading in depressed females as compared to males. A similar effect of the proband's gender could not be observed for bipolar disorder.