A recent study performed in our laboratory comparing the ancestral, Wuhan-like strain USA-WA1/2020 and its derivative mouse-adapted MA10 strain in K18-hACE2, C57BL/6J, and BALB/c mice, demonstrated a decline in mouse Ace2 rather than hACE2 mRNA transcript abundance following infection (31). The gene discussed is ACE2; the disease is infection.