Sibling resemblance for depression in a high-risk sample of adults

Numerous studies have shown that offspring of depressed parents are at heightened risk to develop depression themselves. However, most studies have not examined sibling resemblance for depression in high-risk samples, even though such samples generally may include more than one offspring per family. The present study analyzes sibling resemblance for depression and other psychiatric disorders in a sample of adults at high and low risk for depression (via psychiatric status of biological parents) participating in a 10-year follow-up study (the current age range is between 16 and 33 years). Sibling resemblance was assessed using the pairwise odds ratio, which is uniquely suited to the analysis of variable numbers of siblings in families. There was moderate sibling resemblance for depression in the high-risk sample, and virtually no sibling aggregation for other disorders. Overall, the results highlight the differential outcomes for siblings who grew up in the same family, even in a high-risk environment. Furthermore, our longitudinal data (spanning a 10-year interval) reveal that sibling resemblance decreases as siblings enter adulthood. Future work should move beyond family-wide explanations of intergenerational transmission of depression in order to consider the unique developmental trajectories of siblings at risk for affective disorders.