Phenotyping and genotyping studies of thiopurine S-methyltransferase in Kazaks

Genetic analysis of thiopurine methyltransferase polymorphism in the Jordanian population

This study provides the first analysis of the TPMT mutant allele frequency in a sample of the Jordanian population and indicates that TPMT*3A is the most common allele in Jordanian subjects.

PURPOSE

thiopurine methyltransferase TPMT catalyses the S-methylation of thiopurine drugs such as 6-mercaptopurine, 6-thioguanine, and azathiopurine. Thiopurine methyltransferase (TPMT) polymorphisms are the major determinants of interindividual differences in the severe haematological toxicity of 6-mercaptopurine. Several variants in the TPMT gene have been identified that correlate with a low activity phenotype. Four variant alleles, TPMT*2, TPMT*3A, TPMT*3B and TPMT*3C, are responsible for over 80% of the low or undetectable enzyme activity. The allelic frequency of TPMT variants has been established in many populations.

METHODS

In this study, the frequencies of four (TPMT*2, TPMT*3A, TPMT*3B and TPMT*3C) variants were investigated in 169 healthy Jordanian men (18-45 years of age). Single nucleotide polymorphisms (SNPs) were genotyped using the Sequenom MassARRAY technology (Sequenom; San Diego, CA, USA).

RESULTS

TPMT*3A and TPMT*3C were the only deficiency alleles detected in the Jordanian population with an allele frequency of 0.59% and 0.30% respectively. The TPMT*3A allele frequency is found to be lower than in the European Caucasian population.

CONCLUSION

TPMT*3A and TPMT*3C were the only deficiency alleles detected in the Jordanian population with an allele frequency of 0.59% and 0.30% respectively. The TPMT*3A allele frequency is found to be lower than in the European Caucasian population.

Thiopurine S-methyltransferase alleles, TPMT(*)2, (*)3B and (*)3C, and genotype frequencies in an Indian population

Thiopurine S-methyltransferase (TPMT) catalyzes the S-methylation of aromatic and heterocyclic sulfhydryl compounds including thiopurine drugs such as 6-mercaptopurine, 6-thioguanine and azathioprine. TPMT activity exhibits genetic variation and shows tri-modal distribution with 89-94% of individuals possessing high activity, 6-11% intermediate activity and approximately 0.3% low activity. Patients with intermediate or deficient TPMT activity exposed to thiopurine drugs show severe hematopoietic toxicity. Three single nucleotide polymorphisms (SNPs) in TPMT (NM_000367.2:c.238G>C, NM_000367.2:c.460G>A and NM_000367.2:c.719A>G) define the most prevalent mutant alleles associated with loss of catalytic activity reported in several populations. The present study investigated, for the first time, the frequency distribution of these three SNPs of TPMT, their alleles and genotypes in a Southern Indian population. Peripheral blood was obtained from 326 individuals of a Southern Indian population, and genomic DNA was isolated from total peripheral white blood cells. The genotypes at the polymorphic loci were determined by allele-specific polymerase chain reaction, restriction fragment length polymorphism and confirmatory DNA sequencing. The estimated genotype frequency for homozygous TPMT(*)1/(*)1 was 97.24%, for heterozygous TPMT(*)1/(*)2 and TPMT(*)1/(*)3B, 0.61% each, and for heterozygous TPMT(*)1/(*)3C, 1.53%. The frequency of heterozygous mutants in the studied Indian population was 2.76%. This study demonstrated significant variations in TPMT gene polymorphisms in an Indian population in relation to other human populations and may help to predict both clinical efficacy and drug toxicity of thiopurine drugs.

Polymorphisms of the TPMT gene in the Czech healthy population and patients with inflammatory bowel disease

Genetic variation in thiopurine S-methyltransferase (TPMT) is a major factors for wide variation in the metabolism and safety of thiopurine drugs. We investigated the frequency of functional gene polymorphisms in 396 patients with inflammatory bowel disease and 300 healthy subjects. Frequencies of functionally deficient alleles TPMT*2, TPMT*3A, TPMT*3B, and TPMT*3B in the patient group were 0.1%, 4.3%, 0.1%, and 0.4%, respectively, and were similar to those of healthy subjects in the Czech population. Our results provide necessary information for pharmacoeconomic studies in the Czech Republic.

The low frequency of defective TPMT alleles in Turkish population: a study on pediatric patients with acute lymphoblastic leukemia

6-Mercaptopurine (6MP) is an essential anticancer drug used in the treatment of childhood acute lymphoblastic leukemia (ALL). Thiopurine methyltransferase (TPMT) polymorphisms are the major determinants of interindividual differences in the severe toxicity or efficacy of 6MP. Four variant alleles, TPMT*2, TPMT*3A, TPMT*3B, and TPMT*3C, are responsible over the 80% of low or undetectable enzyme activity. The frequencies of these variants were investigated among 106 children with ALL in Turkish population. TPMT*3A and TPMT*3C were the only deficiency alleles detected in Turkish population with an allele frequency of 0.9% for both. While *3C allele frequency in Turkish population was found to be very similar to Asian and other Caucasian populations, *3A allele frequency was significantly (P < 0.05) lower. So far, studies showed that the genetic polymorphisms of other drug metabolizing enzymes like CYP2E1, CYP1A1, GSTM1/ T1 in Turkish population were similar to Caucasian populations. However, we found that the distribution of TPMT polymorphisms in Turkish population was significantly lower than those in other Caucasians like British, French, and Italian whereas the distributions of TPMT variants were found to be very similar to Kazak population which is also Caucasian in ethnic origin. In this study, the clinical histories of the patients in the sample population were also examined, retrospectively. The patients with heterozygous or homozygous mutant genotypes had developed severe neutropenia and infection during 6MP therapy. The study provides the first data on the frequency of common TPMT variants in the Turkish population, based on analysis of pediatric patients with ALL.

Thiopurine S-Methyltransferase Pharmacogenetics: Genotype to Phenotype Correlation in the Slovenian Population

The toxicity of thiopurine drugs has been correlated to the activity of thiopurine S-methyltransferase (TPMT), whose interindividual variation is a consequence of genetic polymorphisms. We have herein investigated the relevance of some genetic markers for the prediction of thiopurine-related toxicities and to determine the genotype to phenotype correlation in the Slovenian population. The most prevalent mutant allele in the Slovenian population is TPMT*3A (4.1%), followed by TPMT*3C (0.5) and TPMT*3B (0.3), while the TPMT*2 allele was not found in any of the examined samples. TPMT enzyme activity distribution in the subgroup sample was bimodal and as such correlated with genetic data. Using a cutoff value of 9.82 pmol/10(7) RBC per h, the genetic data correctly predicted TPMT enzyme activity in 91.6% of the examined individuals. Pharmacogenetic TPMT analyses have therefore proved to have significant clinical implications for prediction of individuals' responses to treatment with thiopurine drugs in order to avoid possible life-threatening therapy-related toxicities.