Affective Illness in Veteran Twins: A Diagnostic Review
MARTIN G. ALLEN M.D.1,
STEPHEN COHEN M.D.2,
WILLIAM POLLIN M.D.3, , and
STANLEY I. GREENSPAN M.D.4
1 Assistant Professor of Psychiatry, Georgetown University School of Medicine, 3800 Reservoir Rd., N.W., Washington, D.C. 20007
2 Assistant Professor of Psychiatry, University of Vermont College of Medicine, Burlington, Vt.
3 Chief, Section on Twin and Sibling Studies, Adult Psychiatry Branch, National Institute of Mental Health, Bethesda, Md.
4 Research Psychiatrist, National Institute of Mental Health Study Center, Adelphi, Md.
The authors systematically reviewed diagnoses in the Veteran Twin Registry and found 62 pairs of twins (69 individuals) in which one or both had affective illness, a frequency of .22 percent (monozygotic [MZ] concordance = 33 percent, dizygotic [DZ] concordance = 0 percent, and MZ/DZ ratio 
11.5). In 40 of the 62 pairs, one or both twins had unipolar depression (MZ concordance = 40 percent, DZ concordance = 0 percent, and MZ/DZ ratio 8). Bipolar depression was present in 22 pairs (MZ concordance = 20 percent, DZ concordance = 0 percent, MZ/DZ ratio 3.2). The data indicate that both environmental and genetic factors are important in the etiology of affective illness and present evidence that unipolar and bipolar illness are separate entities.
