Sibling aggregation for psychiatric disorders in offspring at high and low risk for depression: 10-year follow-up

Background. A unique way of determining patterns of parent-offspring transmission of risk to affective disorders is to focus on aggregation within sibling pairs. We attempt to extend our previous finding that sibling aggregation is notable for anxiety disorders in a 10-year follow-up of siblings at high and low risk for depression, by virtue of parental diagnosis. Methods. The sample, which included 173 unique sibling pairs in the high risk cohort, and 83 pairs in the low risk cohort, had been assessed using semi-structured clinical interviews three times over a 10-year period, spanning from childhood to adulthood. Sibling aggregation was quantified using pairwise odds ratios. Results. Sibling aggregation in the high risk cohort was greater than aggregation in the low risk cohort for anxiety disorders, especially those that emerged in childhood, and later co-morbid disorders, especially major depressive disorder and suicide attempts. Conclusions. Familial liability to affective disorders may be reflected most strongly by a developmental sequence of anxiety disorders in childhood followed by later depressive and suicidal behaviour in adolescence and adulthood.