NAT2*38 is assigned decreased function based on moderate evidence. NAT2*38 is characterized by the core SNVs c.590G>A (p.R197Q), c.766A>G (p.K256E) and c.803G>A (p.R268K). c.803G>A (p.R268K) defines NAT2*4, formerly considered the reference allele, which has repeatedly shown increased function in vivo and in vitro. Published in silico modeling predicts that c.766A>G (p.K256E) does not alter protein function (19909761). Four out of nine variant effect predictors tested by CPIC staff predict that c.766A>G impairs protein function. 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 nine variant effect predictors tested by CPIC staff predict that c.590G>A impairs protein function. Thus, NAT2*38 is assigned decreased function based on c.590G>A. While c.766A>G is not predicted to impair protein function, it remains unknown whether there are any combinatorial effects associated with c.590G>A and c.766A>G.