NAT2*15 is assigned decreased function based on moderate evidence. The NAT gene nomenclature committee has historically assigned acetylation activity to alleles as either "rapid" or "slow", classifying the NAT2*15 allele as "slow" . Under the CPIC allele function terminology, slow acetylation alleles are categorized as "Decreased Function". NAT2*15 is characterized by the core SNVs c.191G>A (p.R64Q, defining NAT2*14) and c.590G>A (p.R197Q, defining NAT2*6) and c.803G>A (p.R268K). c.803G>A defines NAT2*4, formerly considered the reference allele, which has repeatedly exhibited increased function in vivo and in vitro. c.191G>A and c.590G>A have both repeatedly shown decreased NAT2 acetylation in numerous clinical and in vitro studies. An in vitro study using a bacterial expression system found that NAT2*15 exhibited significantly decreased N-acetyltransferase activity toward sulfamethazine and isoniazid and significantly decreased thermostability compared to the former reference NAT2*4 (28523442). Six and seven out of ten variant effect predictors tested by CPIC staff predict that c.191G>A (p.R64Q) and c.590G>A (p.R197Q) impair protein function, respectively. While c.191G>A and c.590G>A are both definitively attributed to decreased function individually, the combinatorial effects of having both variants present in the same allele are uncertain. Thus, NAT2*15 is assigned a moderate level of evidence.