NAT2*57 is assigned unknown function based on a lack of evidence. NAT2*57 is characterized by the core SNVs c.321C>A (p.H107Q) 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 Eight out of ten variant effect predictors tested by CPIC staff predict that c.321C>A (p.H107Q) impairs protein function