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Diverse point mutations in the human gene for polymorphic N-acetyltransferase
K P Vatsis1, K J Martell, W W Weber
1Department of Pharmacology, Medical School, University of Michigan, Ann Arbor 48109-0626.
Summary
Genetic variations in human N-acetyltransferase (NAT) activity, crucial for drug metabolism, are linked to the NAT2 gene. This study identifies specific mutations in NAT2 responsible for both rapid and slow acetylator phenotypes, clarifying genetic differences in drug processing.
Area of Science:
- Pharmacogenetics
- Molecular Biology
- Human Genetics
Background:
- Human acetylator status (rapid vs. slow) is determined by hereditary N-acetylation rates of various compounds.
- N-acetyltransferase (NAT) enzymes, encoded by NAT1 and NAT2 genes, are responsible for arylamine acetylation.
- While NAT1 is thought to be invariant, NAT2 is suspected to encode polymorphic NAT proteins.
Purpose of the Study:
- To identify the specific genetic variations within the NAT2 gene responsible for the polymorphic N-acetylation phenotype in humans.
- To characterize the molecular basis of rapid and slow acetylator phenotypes by analyzing NAT2 gene sequences.
Main Methods:
- Polymerase chain reaction (PCR) was used to amplify 1.9-kilobase human genomic EcoRI fragments encoding NAT2 from DNA of individuals with known acetylator phenotypes.
- Direct sequencing of the amplified NAT2 fragments was performed to identify point mutations.
- Analysis included DNA from seven subjects with homozygous and heterozygous acetylator phenotypes.
Main Results:
- Two distinct NAT2 variants with multiple point mutations in the coding region were identified.
- One variant, from a slow acetylator, had a silent mutation at codon 94 and an Arg-197 to Gln substitution (G-to-A at position 590).
- A second variant, from a low activity liver sample, had three nucleotide transitions, including a silent mutation at codon 161 and amino acid substitutions Ile-114 to Thr and Lys-268 to Arg.
- Heterozygosity was observed in three samples, including compound heterozygotes for both mutant alleles.
Conclusions:
- The genetically variant N-acetyltransferase (NAT) enzyme is conclusively encoded by the NAT2 gene.
- Specific point mutations and resulting amino acid substitutions in NAT2 directly explain the observed rapid and slow acetylator phenotypes.
- This finding provides a molecular basis for understanding genetic variability in drug metabolism and arylamine acetylation.