Genotype–phenotype correlation for histamine N-methyltransferase in a Chinese Han population

Abstract

Background: Two potential single-nucleotide polymorphisms (SNP) (C314T and A595G) exist in the gene for human histamine N-methyltransferase (HNMT). Methods: A radiochemical microassay was used to measure the erythrocyte HNMT activities, whereas the polymerase chain reaction–restriction fragment length polymorphism (PCR-RFLP) was employed to perform the genetic analysis in 247 unrelated Chinese Han subjects. Results: All subjects had detectable HNMT activity. The activity of HNMT was gender related (males>females, p<0.0001), with a 5.5-fold individual variation. The distribution of HNMT activity was compatible with a normal distribution. There were 28 heterozygotes for the variant T314 allele among the 247 subjects, whereas no A595G transition was observed. All heterozygotes for the T314 allele displayed an intermediate or low HNMT activity, with an average HNMT activity being 34.0% lower than those with wild-type genotype (623.1±136.0 vs. 944.8±249.3 U/ml red blood cells [RBC], p<0.0001). Conclusion: The C314T polymorphism was functionally important and contributes in part to phenotypic variance of HNMT activity in Chinese Han population. Additional unknown genetic or epigenetic factors should also play important roles in the regulation of HNMT activity.