APOE and early-onset autosomal dominant Alzheimer disease: The risk of developing Alzheimer’s disease increases with each copy of the APOE4 variant compared with the APOE3/APOE3 genotype: The odds ratio (OR) is 2.6 (APOE2/APOE4) and 3.2 (APOE3/APOE4) with one copy of the APOE4 allele, and the OR increases to 14.9 with two copies of the allele (APOE4/APOE4)10.