Validity of family history for the diagnosis of dementia among siblings of patients with late-onset Alzheimer's disease.

We examined 180 siblings of 127 probands with probable or possible Alzheimer's dementia (AD) in a family study of AD. The overall sensitivity of a simple family history questionnaire was 64% and the specificity was 84%. Sensitivity improved 90-100% with minimal decline in specificity when we considered clinic-based vs. population survey patients. Higher education among informants and the availability of a spouse or a sibling as informant significantly increased sensitivity. Awareness of such factors may improve the yield of the family history in AD using a simple questionnaire.