The familial aggregation of Alzheimer's disease: an epidemiological review.

This report reviews current data on the familial aggregation of Alzheimer's disease (AD). Single pedigree reports indicate that in few families AD is inherited as an autosomal dominant single gene disorder. Family studies show that first-degree relatives of AD patients have a higher lifetime incidence of AD than the general population or groups of nondemented subjects. Case-control studies indicate that the risk of developing AD is significantly higher for subjects with family members affected by dementia than for those without. The concordance rate in monozygotic twin pairs was found to be much lower than expected from an autosomal dominant disease. These data are inconclusive; however, they suggest that in future etiologic studies 3 types of AD should be considered separately: autosomal dominant, familial, and sporadic. Subclassification of AD by type of occurrence generates groups of patients which are probably more homogeneous regarding etiology.