A common polymorphism of the gene encoding acyl-coenzyme A: cholesterol acyltransferase 1 (SOAT1), which is involved in the regulation of beta-amyloid peptide generation, is associated with low brain amyloid load (P=0.03) and with low cerebrospinal fluid levels of cholesterol (P=0.005). This polymorphism of SOAT1 is also associated with reduced risk for Alzheimer's disease in ethnically distinct populations (P=0.0001, odds ratio: 0.6, 95% confidence interval 0.4-0.8).