DPP4 and diabetes mellitus: Abbreviations: SARS-CoV-2: the virus responsible for the illness COVID-19; PASC: Post-Acute Sequelae of CoV-2; T2D: type 2 diabetes mellitus; T1D: type 1 diabetes mellitus; BMI: body mass index; GLP-1: glucagon like peptide-1; DPP-4: dipeptidyl peptidase-4; TMPSSR2: transmembrane protease serine-2 precursor; PPARγ: peroxisome proliferator activated receptor gamma.