UNIPOLAR RELATIVES IN BIPOLAR PEDIGREES - A SEARCH FOR ELUSIVE INDICATORS OF UNDERLYING BIPOLARITY

In an effort to identify features indicative of underlying bipolarity within the unipolar relatives of bipolar probands, we compared unipola r relatives of bipolars with unipolar relatives of controls. Using dat a from the Yale-NIMH Collaborative Study of Depression, we compared a number of demographic and clinical features individually, and then dev eloped a logistic regression model for the differences found. Unipolar relatives of bipolars were generally similar to relatives of controls , but they were older and more likely to suffer from more severe, even psychotic, depression, and somewhat less likely to report a brief tra nsition into their illness. A multiple logistic regression model for o bserved differences was highly statistically significant, but had limi ted ability to discriminate effectively between the two groups. These findings suggest that more stringent diagnostic criteria might be bene ficial if unipolar relatives are counted as affected in linkage studie s of bipolar disorder. The ability of this strategy to improve the ''c linical phenotype'' is limited, however, and other approaches may be n eeded to identify features of underlying bipolarity and thus to define ''caseness'' for unipolar relatives in linkage analyses of bipolar di sorder. (C) 1996 Wiley-Liss, Inc.