NAT2*1 is assigned increased function based on definitive evidence. The NAT gene nomenclature committee has historically assigned acetylation activity to alleles as either "rapid" or "slow", classifying the reference NAT2*1 allele as "rapid". Under the CPIC allele function terminology, rapid acetylation alleles are categorized as "Increased Function". NAT2*1 corresponds to the NCBI reference sequence, NG_012246.1, containing no SNVs. NAT2*1 has been studied for more than 25 years and has shown rapid acetylation in numerous clinical studies with various substrates. Rapid acetylation activity has been demonstrated in individuals heterozygous for NAT2*1 using caffeine (9333101, 10744128, 15558239, 20801937, 24221535, 27223070), dapsone (10762005), sulfamethazine (21946899), and isoniazid (30149019). NAT2*1 is distinguished from NAT2*4 by the absence of the core SNV c.803G>A (p.R268K).