Abstract

The apolipoprotein E type 4 allele ( APOE -ε4) is genetically associated with the common late onset familial and sporadic forms of Alzheimer's disease (AD). Risk for AD increased from 20% to 90% and mean age at onset decreased from 84 to 68 years with increasing number of APOE -ε4 alleles in 42 families with late onset AD. Thus APOE -ε4 gene dose is a major risk factor for late onset AD and, in these families, homozygosity for APOE -ε4 was virtually sufficient to cause AD by age 80.