NAT2*10 is assigned uncertain function based on inadequate evidence. The NAT gene nomenclature committee has historically assigned acetylation activity to alleles as either "rapid" or "slow", classifying the NAT2*10 allele as "slow" and possibly substrate dependent. Under the CPIC allele function terminology, slow acetylation alleles are categorized as "Decreased Function". NAT2*10 is characterized by the core SNVs c.499G>A (p.E167K) 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.499G>A; p.E167K was shown to decrease N-acetylation activity toward sulfamethazine in vitro due to decreased protein levels (17434923). Published in silico modeling predicts that c.499G>A (p.E167K) decreases hydrogen bond capacity, decreases hydrophobicity, and alters protein charge (18680467). However, eight out of nine variant effect predictors tested by CPIC staff predict that c.499G>A is neutral/tolerated for protein function. The lack of in vivo evidence, along with the conflicting in vitro and computational evidence, results in the assignment of uncertain function.