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- Haglund, Sofie, et al.
(author)
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Pyrosequencing of TPMT Alleles in a General Swedish Population and in Patients with Inflammatory Bowel Disease
- 2004
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In: Clinical Chemistry. - : Oxford University Press (OUP). - 0009-9147 .- 1530-8561. ; 50:2, s. 288-295
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Journal article (peer-reviewed)abstract
- Background: Interindividual differences in therapeutic efficacy in patients treated with thiopurines might be explained by the presence of thiopurine S-methyltransferase (TPMT) alleles that encode for reduced TPMT enzymatic activity. It is therefore of value to know an individual's inherent capacity to express TPMT. Method: We developed a pyrosequencing method to detect 10 single-nucleotide polymorphisms (SNPs) in TPMT. A Swedish population (n = 800) was examined for TPMT*3A, TPMT*3B, TPMT*3C, and TPMT*2. Patients with inflammatory bowel disease (n = 24) and healthy volunteers (n = 6), selected on the basis of TPMT enzymatic activity, were investigated for all 10 SNPs to determine the relationship between TPMT genotype and phenotype. Results: In the general population we identified the following genotypes with nonfunctional alleles: TPMT*1/*3A (*3A allelic frequency, 3.75%), TPMT*1/*3C (*3C allelic frequency, 0.44%), TPMT*1/*3B (*3B allelic frequency, 0.13%), and TPMT*1/*2 (*2 allelic frequency, 0.06%). All nine individuals with normal enzymatic activity were wild-type TPMT*1/*1. Thirteen individuals with intermediate activity were either TPMT*1/*3A (n = 12) or TPMT*1/*2 (n = 1). Eight individuals with low enzymatic activity were TPMT*3A/*3A (n = 4), TPMT*3A/*3C (n = 2), or TPMT*1/*3A (n = 2). Conclusion: Next to wild type, the most frequent alleles in Sweden are TPMT*3A and TPMT*3C. A previously established phenotypic cutoff for distinguishing normal from intermediate metabolizers was confirmed. To identify the majority of cases (90%) with low or intermediate TPMT activity, it was sufficient to analyze individuals for only 3 of the 10 SNPs investigated. Nevertheless, this investigation indicates that other mutations might be of relevance for decreased enzymatic activity. © 2004 American Association for Clinical Chemistry.
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- Lindqvist Appell, Malin, 1976-, et al.
(author)
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Identification of two novel sequence variants affecting thiopurine methyltransferase enzyme activity
- 2004
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In: Pharmacogenetics. - : Ovid Technologies (Wolters Kluwer Health). - 0960-314X .- 1473-561X. ; 14:4, s. 261-265
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Journal article (peer-reviewed)abstract
- The polymorphic enzyme thiopurine methyltransferase (TPMT) is involved in the methylation of thiopurines. On comparing the phenotype with the genotype in Swedish patients with inflammatory bowel disease and healthy individuals, we found two discordant cases with low TPMT enzyme activity (0.3 and 0.4 U/ml packed red blood cells (pRBC). Genotyping by pyrosequencing revealed that they carried the nucleotide substitutions 460G>A and 719A>G, giving two possible genotypes (TPMT*1/*3A or TPMT*3B/ *3C). DNA sequencing of exon III to X was performed in the patients and their parents. We identified an A>G transition in the start codon (exon III, 1A>G, Met>Val, TPMT*14) in one of the patients and her father (6.3 U/ml pRBC). The mother in this family carried the 460G>A and 719A>G nucleotide substitutions (TPMT*3A, 5.0 U/ml pRBC). In the second family, sequencing revealed a G>A transition in the acceptor splice site in intron VII/exon VIII (IVS7 - 1G>A, TPMT*15) in the patient and his mother (6.9 U/ml pRBC). His father was genotyped as TPMT*1/*3A (6.0 U/ml pRBC). Hence, we report the identification of two novel sequence variants, present in highly conserved nucleotide positions of the human TPMT gene, resulting in a loss of enzyme activity.
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