DPP4 and type 2 diabetes mellitus: The human DPP4-encoding gene, located on chromosome 2q24.2 with 28 exons, contains almost 35,000 polymorphic sites, a few of which are associated with clinical conditions such as T2DM, myocardial infarction, dyslipidemia and coronavirus disease 2019 (COVID-19) (14, 19–, 21).