We demonstrated that, in blood, AD-related DMRs exist in CpG island shores in three out of six AD-associated genes examined, CR1 (complement receptor 1), CLU (clusterin), and PICALM (phosphatidylinositol-binding clathrin assembly protein), and that with the combination of APOE (apolipoprotein E) genotypes, the methylation levels of CLU in blood may effectively differentiate AD patients from cognitive elderly with a high sensitivity and specificity. The gene discussed is CR1; the disease is Alzheimer disease.