ACE2 and COVID-19: As ACE2 is a receptor for SARS-CoV-2, which declines with age in some settings (this study) (34,41, 42, 43), and because age is the strongest predictor of fatal COVID-19, a paradox has emerged (45): SARS-CoV-2 receptor expression does not positively correlate with high-risk groups of severe COVID-19.