NAT2*64 is assigned decreased function based on moderate evidence. NAT2*64 is characterized by the core SNVs c.590G>A (p.R197Q), c.796G>A (p.V266M) 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. There is no literature describing function for c.796G>A (p.V266M). Three out of nine variant effect predictors tested by CPIC staff predict c.796G>A (p.V266M) 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 (p.R197Q) impairs protein function. Thus, NAT2*64 is assigned decreased function based on c.590G>A. Despite this, the combinatorial effects associated with c.796G>A and c.590G>A are uncertain