Dementia of the Alzheimer type. Clinical genetics, natural history, and associated conditions.

Relatives of 125 probands, who had dementia of the Alzheimer type as proved by autopsy, were subjects of a genetic investigation. The relatives exhibited an excess of dementing illness consistent with genetic transmission. Risk to relatives decreased sharply as severity of the proband's illness decreased. Also, when compared with a control group and the general population, the relatives had excesses of Down's syndrome, lymphoma, and immune diatheses. These associated conditions also were more likely to be present when the proband had severe illness. Mortality at all ages was increased among the relatives.