The genetics of depression and manic-depressive disorder.

Depressive disorders are more common in the relatives of depressed probands than in the population at large, and there is compelling evidence that the familial aggregation of bipolar disorder and severe unipolar depression is at least partly due to genetic factors. However, the evidence concerning 'non-endogenous' depression is less clear, and family environment probably plays a stronger role. Much current research is focused on two areas: firstly, the mode of inheritance of manic-depressive illness, with the use of molecular biological techniques to detect and localise major genes; and secondly, the ways in which familial predisposition and environmental insults combine to produce depressive disorder.