This notion is further supported by the finding that depression in relatives of probands with AAD typically does not occur independently but only in combination with alcoholism. That is, the prevalence of major depression alone is not increased in those relatives. The prevalence of AAD, however, is increased twofold in relatives of probands with alcoholism plus depressive syndrome (i.e., 4.4 percent) and increased nearly fourfold in relatives of probands with alcoholism plus major depression (i.e., 8.4 percent) when compared with relatives of control subjects (i.e., 2.2 percent [see table 4]). Another analysis (not shown on the table) found that the prevalence of depression alone is not significantly increased in relatives of probands with alcoholism alone (19.6 percent) or with the AAD phenotype (21.2 percent) compared with relatives of control subjects (19.3 percent). The prevalence of the AAD phenotype, however, is increased in relatives of probands with alcoholism only (10.2 percent) and in relatives of probands with AAD (14.3 percent) compared with relatives of control subjects (3.4 percent). These findings argue for a model in which some families carry susceptibility factors
