|1.4 The Unipolar – Bipolar Distinction, Related Comorbities, and Differential Diagnosis|
Although conceptually the distinction between unipolar and bipolar disorder was made in the 19th century by French and German physicians, it was not until the family studies of Angst (1966) and Perris (1966) that the first evidence that these are two different conditions was provided. The distinction came primarily from family studies that found that patients with bipolar disorder had a higher incidence of family relatives with bipolar disorder. Recent genetic studies have confirmed this finding and have highlighted the heritability of mania over depression, which has been estimated to be close to 85% (McGuffin, Rijsdijk et al. 2003).
However, whether the two conditions are separate or related remains an open debate. Some researchers argue that mania is a separate condition (Cuellar et al., 2005); (McGuffin, Rijsdijk et al. 2003) to depression, with the later being or not being comorbid with mania.
Angst, J. 1966. [On the etiology and nosology of endogenous depressive psychoses. A genetic, sociologic and clinical study]. Monogr Gesamtgeb Neurol Psychiatr, 112, 1-118.