ACE2 and diabetes mellitus: aimed to investigate the physiological roots of clinical findings relating diabetes to the severity and adverse effect of COVID-19, the communication between COVID-19 and the progressive loss of pancreatic beta cells that contributes to diabetes, and the association between serum levels of FBG in SARS-CoV-2 patients, showed that there are three main pathophysiological pathways: angiotensin-converting enzyme 2, liver dysfunction, and chronic inflammation.