ACE2 and COVID-19: Whether variations in ACE2 expression contribute to disease severity in humans remains uncertain, although it is intriguing to note that genetic polymorphisms in LZTFL1 (a ciliopathy BBsome protein) and SLC6A20 (an ACE2 coreceptor) are strongly associated with severe COVID-19 [59–63] and might influence the cell-surface, ciliary expression of ACE2.