Molecular genetic analysis subdivided by adversity exposure suggests etiologic heterogeneity in major depression

Objective The extent to which major depression is the outcome of a single biological mechanism or represents a final common pathway of multiple disease processes remains uncertain. Genetic approaches can potentially identify etiologic heterogeneity in major depression by dividing patients on their experience of major adverse events. Method Data are from China, Oxford, and VCU Experimental Research on Genetic Epidemiology (CONVERGE), a study of Han Chinese women with recurrent major depression aimed at identifying genetic risk factors for major depression in a rigorously ascertained cohort carefully assessed for key environmental risk factors (n = 9599). To detect etiologic heterogeneity, genome-wide association studies (GWAS), heritability analyses, and gene-by-environment interaction analyses were performed. Results GWAS stratified by exposure to adversity revealed three novel loci associated with major depression only in subjects with no history of adversity. Significant GxE interactions were seen between adversity and genotype at all three loci and 13.2% of major depression liability can be attributed to genome-wide interaction with adversity exposure. The genetic risk in major depression for samples who reported major adverse life events (27%) was partially shared with that in samples who did not (73%) (genetic correlation = +0.64). Together with results from simulation studies, these findings suggest etiologic heterogeneity within major depression as a function of environmental exposures. Conclusions The genetic contributions to major depression in women may differ in those with and without major adverse life events. These results have implications for the molecular dissection of major depression and other complex psychiatric and biomedical diseases.