To the Editor. —Researchers at Duke University have shown that apolipoproteinE4(apo E) gene dosage correlates with increased risk of Alzheimer's disease (AD).1Their study included members of 42 families with late-onset AD (age at onset, >60 years) with known apo E genotype and used Kaplan-Meier survival analysis to estimate the age-of-onset curves for subjects with zero, one, and twoE4alleles. The resulting curves revealed a significant dosage effect, where each additionalE4allele shifted the onset to an earlier age. We have performed a similar study, which included members of 52 families with late-onset AD (age at onset, >60 years) with known apo E genotype and used Kaplan-Meier survival analysis to estimate the age-of-onset curves for subjects with zero, one, and twoE4alleles. Our study included 252 individuals with known age and apo E genotype; 38 were younger than 60 years,