These include studies involving familial Alzheimer’s disease causing mutants of Presenilin-1 and − 2 and the amyloid precursor protein (APP), and studies on the effects of ε4 allele of apolipoprotein E (ApoE4) which is a major risk factor for Alzheimer’s disease [5, 26, 41, 92, 99]. The gene discussed is APOE; the disease is Alzheimer disease.