Finally, as expected, we found that major depression had modest hSNP2 (8.7%) as it is a complex malady with both genetic and environmental determinants. We found that major depression has a very high genetic correlation with proxy measures that can be briefly assessed. Lifetime major depressive disorder requires a constellation of signs and symptoms whose reliable scoring requires an extended interview with a trained clinician. However, the common variant genetic architecture of lifetime major depression in these seven cohorts (containing many subjects medically treated for MDD) has strong overlap with that of current depressive symptoms in general community samples. Similar relations of clinically-defined ADHD or autism with quantitative genetic variation in the population have been reported74,75. The “disorder versus symptom” relationship has been debated extensively76, but our data indicate that the common variant genetic overlap is very high. This finding has important implications.
