Figure 1.

Study design. The figure illustrates pedigree models from the (a) high- and (b) low-risk families. In the high-risk families, the index proband was required to have a diagnosis of MDD (filled in shapes) with impairment; in the low-risk families, the index proband, as well as their spouse, had no lifetime history of major depression (open shapes). No requirements were imposed on the children (Generation 2) or grandchildren (Generation 3) of these probands.