ACE2 and COVID-19: Finally, consistent with the notion that D614G mutation rapidly accelerated the viral SARS-CoV-2 transmission by increasing affinity between the receptor binding domain of S protein and ACE2, the G614 variant causes a statistically higher frequency (~6-fold) of anosmia than the D614 variant, further suggesting that the OD is a key diagnostic marker for COVID-19 pathogenesis 51.