The APOE E4 allele is associated with an increased risk of developing Alzheimer’s disease (OR = 2–3 in heterozygosis; OR = 14.9 in homozygosis [24]), although the presence of the APOE E4 allele is not necessary or sufficient to develop Alzheimer’s disease. The gene discussed is APOE; the disease is early-onset autosomal dominant Alzheimer disease.