NAT2*55 is assigned unknown function based on a lack of evidence. NAT2*55 is characterized by the core SNVs c.51C>G (p.N17K) 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.51C>G (p.N17K). Ten out of ten variant effect predictors tested by CPIC staff predict that c.51C>G (p.N17K) is neutral for protein function.