APOE and early-onset autosomal dominant Alzheimer disease: It has been shown that the prevalence of Alzheimer's disease (AD) is associated with the polymorphisms of genes related to cholesterol metabolism, including apolipoprotein E (apoE) [1-3], ATP-binding cassette transporter A1 (ABCA1) [4], and CYP46, the gene encoding cholesterol 24-hydroxylase [5,6].