Exogenous and Endogenous Depressions?

Professor James Potash discusses the hypothesis that there are two forms of depression - one that results primarily from external factors (exogenous) and a second endogenous form.

For a long time there was this notion that there were two forms of depression, so-called endogenous and exogenous, or sometimes it was referred to endogenous and reactive. Certainly there are patients who seem to have everything going for them, and become depressed completely out of the blue. On the other hand, there are lots of patients who seem to get depressed in response to stressors. There is an awful lot that is not understood about that, but it makes a lot of sense to me that that might well relate to either differing levels or differing kinds of genetic susceptibility that people have.