All roads lead to depression: clinically homogeneous, etiologically heterogeneous.

Manias, and particularly depressions, are syndromes not disease. Considerable data support the fact that depressions, though similar clinically, are of heterogeneous etiologies. We can separate depressions generally into those that are endogenous/psychotic and those that occur in the context of marked emotional instability. Familial pure depressive disease is a specific example of the former, depression spectrum diseases a specific example of the latter. These are separable on the basis of personality, clinical, follow-up, familial and treatment variables.