Molecular genetics of Alzheimer's disease.

Genetic studies have led to the identification of three genes which, when mutated, cause familial forms of Alzheimer's disease (AD): the beta-amyloid precursor protein gene (APP), presenilin 1 (PS-1) and presenilin 2 (PS-2). Association studies have also shown that the epsilon 4 allele of the apolipoprotein E (ApoE) gene increases risk for AD in a dose-dependent manner in both familial and sporadic forms of AD. It is likely that there are additional AD risk factors, both genetic and environmental, as 50% of sporadic AD cases have no ApoE epsilon 4 alleles, and families showing mendelian inheritance of AD exist in which there are no mutations in any of the known genes.