APOE has been extensively investigated in several diseases, since its three main alleles (ε4, ε3, and ε2) carry differential risk or protection for several conditions, such as AD, PD, cardiovascular disease, AMD, obesity, chronic airway obstruction, type 2 diabetes, gallbladder disease, and liver disease (36). The gene discussed is APOE; the disease is obesity due to melanocortin 4 receptor deficiency.