NAT2*37 is assigned decreased function based on moderate evidence. NAT2*37 is characterized by the core SNVs c.590G>A (p.R197Q), c.638C>T (p.P213L) and c.803G>A. c.803G>A (p.R268K) defines NAT2*4, formerly considered the reference allele, which has repeatedly shown increased function in vivo and in vitro. There is no experimental evidence describing function for c.638C>T (p.P213L). Seven out of ten variant effect predictors tested by CPIC staff predict that c.638C>T (p.P213L) impairs protein function, which is supported by published in silico analysis (29273096). c.590G>A (p.R197Q) defines NAT2*6 which has been extensively studied, exhibiting decreased N-acetyltransferase activity both in vivo and in vitro. Similarly, seven out of ten variant effect predictors tested by CPIC staff predict that c.590G>A impairs protein function. Thus, NAT2*37 is assigned decreased function based on c.590G>A. Despite this, it remains unknown whether there are any combinatorial effects associated with c.638C>T and c.590G>A.