The co-expression of ACE2 and TMPRSS2 was reported in type 1 pneumocytes [195], alveolar macrophages [9, 192], lymphocytes [9], smooth muscle cells and enterocytes in the gastrointestinal tract [9, 195], vessel smooth muscle cells [9], cardiomyocytes [9, 192], hepatocytes [169], kidney cells [87], proximal tubule cells [114], and neurons [112], all of which are in line with the common clinical symptoms of COVID-19 [15, 19, 61, 151, 166, 183, 191, 197]. The gene discussed is ACE2; the disease is COVID-19.