Association between family history of affective disorder and the depressive syndrome of Alzheimer's disease.

For each of 41 index patients with probable Alzheimer's disease and a first episode of major depression and 71 nondepressed Alzheimer's disease patients, two first-degree relatives were interviewed by a rater blind to presence or absence of depression in the proband. The depressed patients had significantly more first- and second-degree relatives with depression than did control subjects. The lifetime risk for major depression, adjusted for differences in age distribution, was significantly greater in first-degree relatives of index patients, suggesting that depression in Alzheimer's disease is genetically related to primary affective disorder. Alzheimer's disease may be useful for studying aspects of depressive pathophysiology.