Based on the evidence that the DPP4 is the functional receptor for the virus responsible for Middle East Respiratory Syndrome (MERS), a potential role of DPP4 in patients with diabetes mellitus and COVID-19 infection has been hypothesized, suggesting a better course of the COVID-19 infection in patients with diabetes mellitus treated with DPP4 inhibitors [41]. Here, DPP4 is linked to Middle East respiratory syndrome.