Familial transmission of parental mood disorders: unipolar and bipolar disorders in offspring.

OBJECTIVES: Offspring of depressed parents are at increased risk for psychiatric disorders. Although bipolar disorder (BD) and major depressive disorder (MDD) are both found in the same families, it is not clear whether transmission to offspring of BD or MDD tends to occur from parents with the same mood disorder subtype. Our primary hypothesis was that the offspring of parents with BD would be at increased risk for BD and other comorbid disorders common to BD, such as anxiety and substance use, relative to the offspring of parents with MDD. The offspring of parents with BD versus those with MDD were also hypothesized to be at greater risk for externalizing disorders (i.e., conduct disorder, attention-deficit hyperactivity disorder, or antisocial personality disorder).

METHODS: Parents (n = 320) with mood disorders and their offspring (n = 679) were studied. Adult offspring were administered the Structured Clinical Interview for DSM-IV Axis I Disorders to establish the presence of psychopathology. Offspring aged 10-18 years were assessed using the School Aged Schedule for Affective Disorders and Schizophrenia, Present and Lifetime version, and parents of children under the age of ten completed the Child Behavioral Checklist. Data were examined using Cox proportional hazard regression.

RESULTS: There was no difference in hazard of mood disorders in the offspring of parents with BD as compared to the offspring of parents with MDD. However, a number of other parent and offspring characteristics increased the risk of mood, anxiety, externalizing, and substance use disorders in the offspring, including self-reported childhood abuse in the parent or offspring, offspring impulsive aggression, and the age at onset of parental mood disorder.

CONCLUSIONS: Mood disorders are highly familial, a finding that appears independent of whether the parent's condition is unipolar or bipolar, suggesting considerable overlap in the heritability of MDD and BD. Although parental characteristics had a limited influence on the risk of offspring psychopathology, reported childhood adversity, be it in the parent or child, is a harbinger of negative outcomes. These risk factors extend previous findings, and are consistent with diathesis-stress conceptualizations.