Genes and environment: Limbic structure in young twins with depression

Early onset major depressive disorder (MDD) is highly heritable and has been associated with volumetric changes in prefrontal-limbic circuit structures. Here we examine if structural differences reported are related to genetic or environmental influences. Using a twin research design, we studied an epidemiologically ascertained sample of young female twin pairs ( 15-24 y.o.) where one or both twins have a lifetime history of MDD (34 pairs) and control twin pairs (17 pairs) with no lifetime history of MDD. Volumetric analyses of the subgenual prefrontal cortex SGPFC) and amygdala were based on high resolution 3D T1 weighted images using established image analysis methods with high reliability (ICC > 0.93). Left SGPFC volume was somewhat smaller in MDD vs control subjects but was significantly reduced in twins with MDD in comparison to their non-MDD cotwin (average 39% reduction, p=0.02). Right amygdala volume was significantly decreased in twins with MDD and their non-MDD cotwin in comparison to unrelated control twins (10% reduction, p=0.02). These results support that: 1) some structural changes in MDD are signifi-cantly influenced by environmental factors (left SGPFC), while other changes which are present in both MDD and at risk subjects (right amygdala) are under more direct genetic influence.