Mutations in AP3S2, one of the optimal five proteins, were associated with type 2 diabetes mellitus (Kazakova, et al. 2017; Kooner et al. 2011; Mohlke and Boehnke 2015) and may be related to the hypothesized increase in type 2 diabetes mellitus due to COVID-19 (Rubino et al. 2020). This evidence concerns the gene AP3S2 and type 2 diabetes mellitus.