Molecular Mechanism of Slow Acetylation of Drugs and Carcinogens in Humans

The acetylation polymorphism is one of the most common genetic variations in the transformation of drugs and chemicals. More than 50% of individuals in Caucasian populations are homozygous for a recessive trait and are of the "slow acetylator" phenotype. They are less efficient than "rapid acetylators" in the metabolism of numerous drugs and environmental and industrial chemicals. The acetylation polymorphism is associated with an increased risk of drug toxicity and with an increased frequency of certain cancers. We report the identification of the primary mutations in two alleles of the gene for the N-acetyltransferase (NAT; acetyl-CoA:arylamine N-acetyltransferase, EC 2.3.1.5) isozyme NAT2 associated with slow acetylation. These alleles, M1 and M2, account for more than 90% of slow acetylator alleles in the European population we have studied. M1 and M2 were identified by restriction fragment length polymorphisms with Kpn I and Msp I and subsequently cloned and sequenced. M1 and M2 each are characterized by a combination of two different point mutations, one causing an amino acid substitution (Ile-113 → Thr in M1, Arg-197 → Gln in M2), the other being silent (C 481 → T in M1, C 282 → T in M2). Functional expression of M1 and M2 and of chimeric gene constructs between mutant and wild-type NAT2 in COS-1 cells suggests that M1 causes a decrease of NAT2 protein in the liver by defective translation, whereas M2 produces an unstable enzyme. On the basis of the mutations described here and a rare mutant allele (M3) reported recently, we have developed a simple DNA amplification assay that allows the predictive genotyping of more than 95% of slow and rapid acetylator alleles and the identification of individuals at risk.