"However, the ??4 allele frequency is not significantly different in the two cohorts (0.217 vs 0.218).6 Interestingly, the Yoruba have a lower incidence of both vascular disease and vascular risk factors including hypertension than did the African Americans. 15 Also, cholesterol and lipid levels are much lower in the Yoruba.This lack of association together with the low incidence rate of AD makes t" . . . . .