ACE2 and diabetes mellitus: Given that cardiovascular diseases, hypertension, and diabetic mellitus are important comorbidity factors for COVID-19, it is not surprising that recently the ACE2 polymorphism has also been found to not only be associated with entry efficiency of SARS-CoV-2 [34, 35] but also with COVID-19 outcome [36], indicating that ACE2 polymorphism plays important roles in COVID pathogenesis.