The study investigated the effect of the parental age on the age-of-onset (AO) in bipolar I disorder (BPI) in connection with proband gender and family history for major psychoses in a directly interviewed sample of 530 BPI probands.

All 530 probands, 73.0% of their first-degree and 22.62% of their second-degree relatives were administered the DIGS and FIGS interviews. The family history (FH) method was used for unavailable relatives. The impact of parental age on proband early/late AO was evaluted through logistic regressions. The commingling analysis (SAGEv6.1-software) was used to determine the cut-off age separating the early/late AO.

We evidenced a significant influence of the paternal age ≥ 35 years on AO in BPI disorder in the total sample (p = 0.023) and in some subgroups defined by positive/negative FH for major psychoses: the sporadic group (p = 0.035) and the group with FH of recurrent unipolar major depression (Mdd-RUP) (p = 0.041). No effect of the paternal/maternal age on disease AO was found in patients with FH of bipolar/schizoaffective disorders/schizoprenia (BP/SA/SCZ). The global significant effect of the advancing paternal age on the decreasing proband AO was generated by female patients (p = 0.022). No effect of the paternal/maternal age on disease AO was found in male patients. Paternal age was older in fathers of sporadic cases and of cases with FH of Mdd-RUP than in cases with FH of BP/SA/SCZ (p = 0.011).

We evidenced a selective effect of the advancing paternal age on bipolar onset depending on offspring gender and type of FH for major psychoses.