The (US) National Academy of Sciences Registry of aging twin veterans contains 15,924 pairs of white male twins born between 1917 and 1927. About 8,000 pairs are living today. In preparation for a study of Alzheimer's disease (AD) in this Registry, we investigated 829 members of pairs living in North and South Carolina, Virginia, in the District of Columbia, and Maryland. A brief telephone interview for cognitive symptoms was administered to 678 (91.4%) of 742 subjects located. Cognitive dysfunction was identified initially in 124 individuals (18.3%), whose clinical histories were then obtained over the telephone. Results suggested that 108 subjects did not have AD. Ten (62.5%) of the remaining 16 subjects underwent diagnostic evaluation for dementia. One had cerebrovascular disease with coincident depression. Two others with probable AD were a monozygotic (MZ) pair. The remaining 7 subjects had possible AD or a mild but progressive cognitive disorder suggestive of early AD. Upon subsequent examination, 3 of 4 MZ co-twins showed significant symptoms that had not been detected during screening procedures. None of 3 dizygotic co-twin showed any significant abnormality. These results suggest: (1) that a combination of mailed information, telephone interviews, and clinical examination provides a feasible means of detecting AD in the Registry, (2) that about 150 pairs with presumptive AD in 1 or both subjects will be identified in a full study of the Registry; (3) that concordance for AD in MZ pairs may exceed prior estimates, but (4) that such rates of concordance are apparent only upon detailed evaluation of apparently normal co-twins as well as their impaired brothers. Longitudinal observation of pairs with apparently affected individuals will be required for definitive conclusions.

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