Is there evidence that unipolar depression and bipolar depression are actually caused by different disease processes?
MANJI: Unipolar depression is a much broader category than bipolar depression. In some ways, unipolar depression is somewhat less specific, somewhat like fever. With fever, you can get there many ways-from viral infection, bacterial infection, a reaction to a drug, etc. Depression may be similar. In my opinion, a subgroup of what we see as unipolar depression probably belongs in the bipolar family. Most of the data suggest that in bipolar disorder, multiple genes are susceptible, and if you get enough of them, you have bipolar illness. It is not like Huntington’s disease, which arises from one gene. The older European studies are suggesting that in recurrent unipolar depression and bipolar disorder that run in families, treatment response is similar (i.e., they respond to lithium treatment), and this suggests that you have in recurrent unipolar depression many of the same genes as in bipolar disorder. More and more data are confirming this, including brain imaging studies, such as thos
