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Although many etiologically heterogeneous conditions are often lumped together as major depressive disorder, teasing apart these pathogenically discrete entities could be enlightening. In this largest-ever study, investigators conducted two analyses to assess the heritability of perinatal versus nonperinatal depression. The first study relied on Swedish Twin Registry data from some 1500 monozygotic and 1900 same-sex dizygotic female twins; the second employed a sibling design using Swedish population-based data from 314,000 full-sister pairs, 29,000 maternal half-sister pairs, 34,000 paternal half-sister pairs, and 2300 twin pairs.
Heritability of perinatal depression was estimated to be 54% in the twin analysis and 44% in the sibling analysis. Heritability of nonperinatal depression was an estimated 32% in the sibling analysis. Overall, 14% of the variance for perinatal depression was attributable to genetic factors unique to this condition, whereas 28% was due to genetic factors shared with nonperinatal depression. In separate analyses, heritability of antenatal and postnatal depression was estimated at 37% and 40%, respectively.
Viktorin A et al. Heritability of perinatal depression and genetic overlap with nonperinatal depression. Am J Psychiatry 2015 Sep 4; [e-pub]. (http://dx.doi.org/10.1176/appi.ajp.2015.15010085)
Comment
These major-scale studies suggest that about a third of genetic contributions to perinatal depression are not shared with those of nonperinatal depression. This finding provides a springboard for studies to seek unique genetic markers and, potentially, therapeutic targets. Other studies have shown that postpartum depression carries enhanced risk for subsequent bipolar disorder; thus, genetic factors associated with bipolar disorder might overlap and account for some of the variance observed here. Finally, these data can serve clinicians as they counsel patients and their families about possible genetic risks for depression.