The human APOE gene is located on chromosome 19 at position q13.3 (Figures 2B,C) and encodes for a 299 amino acid protein (∼34 kDa) with multiple functions, particularly with cholesterol metabolism, lipid homeostasis, and innate immunity (Davignon et al., 1988), which are all likely to contribute to increased reproductive success and protection against infection load. Here, APOE is linked to infection.