Impact of birth weight and genetic liability on psychopathology in children of bipolar parents

Objective: To test different models for ways in which birth weight and familial loading influence the risk for psychopathology in bipolar offspring. Method: DSM-IV diagnoses of 140 bipolar offspring (12-21 years of age) were assessed with the K-SADS-PL. Parents were interviewed using the Family History-Research Diagnostic Criteria to determine familial loading of mood and substance use disorders. Parents reported the birth weight of their offspring. Age- and sex-adjusted hazard ratios were calculated. Results: Low birth weight was associated with mood and non-mood disorders in bipolar offspring (hazard ratio = 0.6, confidence interval = 0.4-0.8), even after controlling for familial loading of unipolar disorder, bipolar disorder, or substance use disorder. There were no significant interactions between birth weight and familial loading of unipolar disorder, familial loading of bipolar disorder, and familial loading of substance use disorder. Conclusions: Birth weight is associated with mood as well as non-mood disorders. This association is independent from the association of familial loading of mood and substance use disorder with mood- and non-mood disorders in bipolar offspring.