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Detection of a Novel Single Nucleotide Polymorphism of the Human Thiopurine S-Methyltransferase Gene in a Chinese Individual
Drug Metab. Pharmacokinet. 27 (5): 559561 (2012).
Copyright © 2012 by the Japanese Society for the Study of Xenobiotics (JSSX)
SNP Communication Detection of a Novel Single Nucleotide Polymorphism of the Human Thiopurine S-Methyltransferase Gene in a Chinese Individual Chun Kiat L EE 1 , Tze Ping LOH 2, Soon Tee WONG 3 , Hong Kai L EE 4 , Pei Tee H UAN 1 , Lily-Lily C HIU 1 and Evelyn Siew-Chuan KOAY 1,4, * 1
Molecular Diagnosis Centre, Singapore, Singapore Division of Clinical Chemistry, Department of Laboratory Medicine, National University Hospital, Singapore, Singapore 3 Raffles Skin Centre, Raffles Hospital, Singapore, Singapore 4 Department of Pathology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
2
Full text of this paper is available at http://www.jstage.jst.go.jp/browse/dmpk Summary: A 62-year-old Chinese patient with recurrent pompholyx submitted his blood sample for pretreatment thiopurine S-methyltransferase (TPMT) pharmacogenetic profiling, and it was found to harbour a novel single nucleotide polymorphism (SNP). The novel SNP, detected by mRNA sequencing, was a c.2T>C (g.11018T>C) transition in the start codon, causing a Met1Thr amino acid change. This finding was confirmed on a subsequent blood sample from the same patient by DNA sequencing. The patient was genotyped as TPMT*1/*29, sequentially named as such following the latest TPMT SNP (TPMT*1/*28) at the time of writing. The novel SNP is expected to result in complete lack of protein translation, similar to the impact exerted by TPMT*14, another start codon SNP of the TPMT gene. Keywords: thiopurine S-methyltransferase; single nucleotide polymorphism; genetic polymorphism
able for this purpose. These methods may not detect other SNPs that are scattered throughout the TPMT gene, beyond the target regions of the assays.9¥ Complete genomic sequencing of the TPMT gene can overcome this limitation. An in-house mRNA-based TPMT sequencing assay, which covers the entire TPMT mRNA, was developed at the National University Hospital, Singapore. During routine application of this assay, a novel SNP was uncovered at the start codon of the TPMT mRNA of a patient, and this was confirmed by DNA sequencing, on a second sample. The discovery of the novel SNP underscores the importance of performing full genomic TPMT sequencing.
Introduction Thiopurine S-methyltransferase ¤TPMT¥ is a cytoplasmic enzyme involved in the S-methylation of thiopurine compounds, which include anti-proliferative drugs such as azathioprine, 6-mercaptopurine, and 6-thioguanine.1¥ Owing to the relatively narrow therapeutic indices of thiopurine drugs, patients with low TPMT enzyme activity ¤poor metabolizers¥ may suffer potentially life-threatening toxicity when given a standard dose. Conversely, patients with high TPMT enzyme activity ¤extensive metabolizers¥ may be under-treated when a similar dosage is applied.2¥ TPMT genotyping can provide predictive information about a personös TPMT enzyme activity and therefore the thiopurine drug metabolism profile.3®6¥ Supported by early evidence for its clinical utility,7,8¥ an increasing number of physicians are requesting pre-treatment TPMT testing to help determine the optimum thiopurine dose for their patients. Several PCR methods, which selectively target several common single nucleotide polymorphisms ¤SNPs¥, are avail-
Materials and Methods A 62-year-old Chinese man with diabetes and hypertension, which were satisfactorily controlled by oral medications, presented with recurrent pompholyx affecting his hands and feet. Initially, he was treated with oral prednisolone, to which he responded well. As there was concern about the impact of chronic steroid use on the patientös diabetes and hypertension control, topical triam-
Received January 17, 2012; Accepted March 8, 2012 J-STAGE Advance Published Date: March 22, 2012, doi:10.2133/dmpk.DMPK-12-SC-008 *To whom correspondence should be addressed: Evelyn Siew-Chuan KOAY, Ph.D., FAACB, FRCPath, Molecular Diagnosis Centre, Department of Laboratory Medicine, Level 3, NUH Main Building, 5 Lower Kent Ridge Road, Singapore 119074, Singapore. Tel. +65- 67724564, Fax. +6567751757, E-mail: [email protected] 559
560
Chun Kiat LEE, et al. Table 1. Primer sequences used for the analysis of the thiopurine S-methyltransferase gene Targeted region
Forward primer sequence ¤5$®3$¥
Nucleotide position
Reverse primer sequence ¤5$®3$¥
Nucleotide position
Amplicon size ¤bp¥
Exons 2®7a Exons 4®9a Start codonb
GAA GAC ATA TGC TTG TGA GAC CGA AAT TCC TGG AAC CAA AGT GAA GAC ATA TGC TTG TGA GAC
117®137 494®514 10978®10998
GAA AGA ACA CAC AGG AGA TAC CTA GCA ATC TGC AAG ACA CAT GTT CCT GAT GAA AAG CAG TC
692®712 1140®1160 11127®11146
596 667 169
a
Based on a Homo sapiens thiopurine S-methyltransferase mRNA, GenBank accession: NMð000367.2. Based on Homo sapiens thiopurine S-methyltransferase ¤TPMT¥ gene, RefSeqGene on chromosome 6, GenBank accession: NGð012137.1.
b
cinolone was given as an alternative. It did not adequately control his symptoms. Azathioprine was considered as next-line therapy and a pre-treatment TPMT genotyping was undertaken for this patient. During analysis of his specimen, a novel TPMT SNP located at the start codon was detected. Total RNA was extracted from 3 mL of whole blood. cDNA, reverse transcribed from the extracted mRNA, served as the template for PCR amplification. Two sets of primers flanking exons 2 to 9, in 2 overlapping fragments, were designed to contain a single base mismatch at the 3$ end to discriminate against the TPMT pseudogene, using GenBank: NMð000367.2 as reference ¤Table 1¥. The amplification was performed using HotStarTaq PCR reagents ¤Qiagen, Hilden, Germany¥, on the GeneAmp¬ PCR thermal cycler ¤Applied Biosystems, Foster City, CA, USA¥. Cycling conditions included an initial denaturation step ¤95ôC, 15 min¥, followed by 40 cycles of the amplification step at 94ôC for 10 s, 58ôC for 1 min, 72ôC for 45 s, followed by a final extension step ¤72ôC, 7 min¥. The amplified products were sequenced bi-directionally with the amplification primers ¤Table 1¥, using the BigDye¬ Terminator v3.1 cycle sequencing kit ¤Applied Biosystems¥. The DNA sequence of the purified product was analyzed on the ABI 3130xl genetic analyzer ¤Applied Biosystems¥, according to the manufacturerös instructions. In order to confirm the above finding of the novel mutation, an additional blood sample was obtained from the patient to perform direct DNA sequencing. A new set of primers flanking the start codon of the TPMT gene were designed using GenBank: NGð012137.1 as reference ¤Table 1¥. These primers were designed to contain mismatches at the 3$ end to prevent amplification of the TPMT pseudogene. The reverse primer was also used as the sequencing primer. The extracted genomic DNA was amplified and sequenced using the amplification/sequencing protocols described earlier. This study received exemption from the Institution Review Board of the National University Hospital, Singapore. Written informed consent was provided by the patient. Results and Discussion We found the novel SNP: SNP: 110607LeeCK001; GENE NAME: TPMT; ACCESSION NUMBER: NGð012137.1; LENGTH: 25 bases; OBSERVED: T/C; 5$-TCTCTGAAACTAT/CGGATGGTACAAG-3$.
Fig. 1. Electropherograms of the heterozygous index case containing the novel g.11018ThC, TPMT*29 sequence variant by mRNA and DNA sequencing (top and middle panels, respectively) compared with a homozygous TPMT*1 wild type (bottom panel)
The TPMT gene carries a g.11018ThC transition in the start codon, resulting in a Met1Thr amino acid change, first discovered using an mRNA sequencing approach. To authenticate the finding of this mutation, it was confirmed by direct DNA sequencing in a follow-up sample received at a later date. The electropherograms of the novel TPMT SNP by mRNA and DNA sequencing are shown in Figure 1. This novel SNP was named TPMT*29, following the last described TPMT mutation ¤TPMT*28¥ at the time of writing.10¥ The 62-year-old Chinese patient carrying the novel TPMT mutation was genotyped as TPMT*1/*29. This represents the second start codon SNP to be described in the TPMT gene, the first being TPMT*14.11¥ In an in-vitro functional study, TPMT*14 was associated with complete absence of TPMT enzyme expression.6¥ It is likely that the novel start codon mutation, TPMT*29, would display a similar lack of protein translation. Being heterozygous for the novel mutation, the patient probably has intermediate TPMT enzyme activity as described previously in a heterozygous TPMT*1/*14 individual.11¥ The likely thiopurine metabolic profile of a patient can be assessed by functional or genetic studies. TPMT enzyme activity is currently the more popular choice for pre-
Copyright © 2012 by the Japanese Society for the Study of Xenobiotics (JSSX)
Novel Start Codon TPMT Mutation
treatment testing.7,8¥ However, it is susceptible to interference from blood transfusion12¥ and anaemia,13¥ as well as alteration of enzyme activity following certain medications.14,15¥ In one report, a patient with apparently normal TPMT enzyme activity developed myelotoxicity as a consequence of a hidden mutation uncovered with subsequent genotyping.14¥ TPMT genotype testing can circumvent some of the limitations of the functional study. This case highlights the advantage of our proposed mRNA sequencing approach, which provides full coverage of all coding exons of the TPMT gene, and detects cryptic or hitherto unreported mutations that otherwise may be missed by targeted genotyping, with possible adverse clinical consequences.12,13¥ Moreover, this method minimizes the number of PCRs performed; although, precautions should be taken to avoid amplification of the TPMT pseudogene. While TPMT phenotyping and genotyping tests are useful diagnostic tools, they should not supersede routine monitoring of myelotoxicity by simple complete blood count. Finally, physicians should familiarize themselves with the non-TPMT causes of thiopurine toxicity.
6¥
7¥
8¥
9¥
10¥
11¥
References 1¥ Lennard, L.: Clinical implications of thiopurine methyltransferaseoptimization of drug dosage and potential drug interactions. Ther. Drug Monit., 20: 527®531 ¤1998¥. 2¥ Srikumar, S., Danny, H. and Sandip, R.: Clinical pharmacology and pharmacogenetics of thiopurines. Eur. J. Clin. Pharmacol., 64: 753® 767 ¤2008¥. 3¥ Schaeffeler, E., Fischer, C., Brockmeier, D., Wernet, D., Moerike, K., Eichelbaum, M., Zanger, U. M. and Schwab, M.: Comprehensive analysis of thiopurine S-methyltransferase phenotype-genotype correlation in a large population of GermanCaucasians and identification of novel TPMT variants. Pharmacogenetics, 14: 407®417 ¤2004¥. 4¥ Milek, M., Murn, J., Jaksic, Z., Lukac Bajalo, J., Jazbec, J. and Mlinaric Rascan, I.: Thiopurine S-methyltransferase pharmacogenetics: genotype to phenotype correlation in the Slovenian population. Pharmacology, 77: 105®114 ¤2006¥. 5¥ Kham, S. K., Soh, C. K., Liu, T. C., Chan, Y. H., Ariffin, H.,
12¥ 13¥
14¥
15¥
561
Tan, P. L. and Yeoh, A. E.: Thiopurine S-methyltransferase activity in three major Asian populations: a population-based study in Singapore. Eur. J. Clin. Pharmacol., 64: 373®379 ¤2008¥. Ujiie, S., Sasaki, T., Mizugaki, M., Ishikawa, M. and Hiratsuka, M.: Functional characterization of 23 allelic variants of thiopurine S-methyltransferase gene ¤TPMT*2-*24¥. Pharmacogenet. Genomics, 18: 887®893 ¤2008¥. van den Akker-van Marle, M. E., Gurwitz, D., Detmar, S. B., Enzing, C. M., Hopkins, M. M., Gutierrez de Mesa, E. and Ibarreta, D.: Cost-effectiveness of pharmacogenomics in clinical practice: a case study of thiopurine methyltransferase genotyping in acute lymphoblastic leukemia in Europe. Pharmacogenomics, 7: 783® 792 ¤2006¥. Gurwitz, D., Rodríguez-Antona, C., Payne, K., Newman, W., Gisbert, J. P., de Mesa, E. G. and Ibarreta, D.: Improving pharmacovigilance in Europe: TPMT genotyping and phenotyping in the UK and Spain. Eur. J. Hum. Genet., 17: 991®998 ¤2009¥. Wood, N., Fraser, A., Bidwell, J. and Standen, G.: RT-PCR permits simultaneous genotyping of thiopurine S-methyltransferase allelic variants by multiplex induced heteroduplex analysis. Hum. Mutat., 24: 93®99 ¤2004¥. Appell, M. L., Wennerstrand, P., Peterson, C., Hertervig, E. and Mårtensson, L. G.: Characterization of a novel sequence variant, TPMT*28, in the human thiopurine methyltransferase gene. Pharmacogenet. Genomics, 20: 700®707 ¤2010¥. Lindqvist, M., Haglund, S., Almer, S., Peterson, C., Taipalensu, J., Hertervig, E., Lyrenäs, E. and Söderkvist, P.: Identification of two novel sequence variants affecting thiopurine methyltransferase enzyme activity. Pharmacogenetics, 14: 261®265 ¤2004¥. Cheung, S. T. and Allan, R. N.: Mistaken identity: misclassification of TPMT phenotype following blood transfusion. Eur. J. Gastroenterol. Hepatol., 15: 1245®1247 ¤2003¥. Barlow, N. L., Graham, V. and Berg, J. D.: Expressing thiopurine S-methyltransferase activity as units per litre of whole-blood overcomes misleading high results in patients with anaemia. Ann. Clin. Biochem., 47: 408®414 ¤2010¥. Leung, M., Piatkov, I., Rochester, C., Boyages, S. C. and Leong, R. W.: Normal thiopurine methyltransferase phenotype testing in a Crohn disease patient with azathioprine induced myelosuppression. Intern. Med. J., 39: 121®126 ¤2009¥. Schaeffeler, E., Stanulla, M., Greil, J., Schrappe, M., Eichelbaum, M., Zanger, U. M. and Schwab, M.: A novel TPMT missense mutation associated with TPMT deficiency in a 5-year-old boy with ALL. Leukemia, 17: 1422®1424 ¤2003¥.
Copyright © 2012 by the Japanese Society for the Study of Xenobiotics (JSSX)
Copyright © 2012 by the Japanese Society for the Study of Xenobiotics (JSSX)
SNP Communication Detection of a Novel Single Nucleotide Polymorphism of the Human Thiopurine S-Methyltransferase Gene in a Chinese Individual Chun Kiat L EE 1 , Tze Ping LOH 2, Soon Tee WONG 3 , Hong Kai L EE 4 , Pei Tee H UAN 1 , Lily-Lily C HIU 1 and Evelyn Siew-Chuan KOAY 1,4, * 1
Molecular Diagnosis Centre, Singapore, Singapore Division of Clinical Chemistry, Department of Laboratory Medicine, National University Hospital, Singapore, Singapore 3 Raffles Skin Centre, Raffles Hospital, Singapore, Singapore 4 Department of Pathology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
2
Full text of this paper is available at http://www.jstage.jst.go.jp/browse/dmpk Summary: A 62-year-old Chinese patient with recurrent pompholyx submitted his blood sample for pretreatment thiopurine S-methyltransferase (TPMT) pharmacogenetic profiling, and it was found to harbour a novel single nucleotide polymorphism (SNP). The novel SNP, detected by mRNA sequencing, was a c.2T>C (g.11018T>C) transition in the start codon, causing a Met1Thr amino acid change. This finding was confirmed on a subsequent blood sample from the same patient by DNA sequencing. The patient was genotyped as TPMT*1/*29, sequentially named as such following the latest TPMT SNP (TPMT*1/*28) at the time of writing. The novel SNP is expected to result in complete lack of protein translation, similar to the impact exerted by TPMT*14, another start codon SNP of the TPMT gene. Keywords: thiopurine S-methyltransferase; single nucleotide polymorphism; genetic polymorphism
able for this purpose. These methods may not detect other SNPs that are scattered throughout the TPMT gene, beyond the target regions of the assays.9¥ Complete genomic sequencing of the TPMT gene can overcome this limitation. An in-house mRNA-based TPMT sequencing assay, which covers the entire TPMT mRNA, was developed at the National University Hospital, Singapore. During routine application of this assay, a novel SNP was uncovered at the start codon of the TPMT mRNA of a patient, and this was confirmed by DNA sequencing, on a second sample. The discovery of the novel SNP underscores the importance of performing full genomic TPMT sequencing.
Introduction Thiopurine S-methyltransferase ¤TPMT¥ is a cytoplasmic enzyme involved in the S-methylation of thiopurine compounds, which include anti-proliferative drugs such as azathioprine, 6-mercaptopurine, and 6-thioguanine.1¥ Owing to the relatively narrow therapeutic indices of thiopurine drugs, patients with low TPMT enzyme activity ¤poor metabolizers¥ may suffer potentially life-threatening toxicity when given a standard dose. Conversely, patients with high TPMT enzyme activity ¤extensive metabolizers¥ may be under-treated when a similar dosage is applied.2¥ TPMT genotyping can provide predictive information about a personös TPMT enzyme activity and therefore the thiopurine drug metabolism profile.3®6¥ Supported by early evidence for its clinical utility,7,8¥ an increasing number of physicians are requesting pre-treatment TPMT testing to help determine the optimum thiopurine dose for their patients. Several PCR methods, which selectively target several common single nucleotide polymorphisms ¤SNPs¥, are avail-
Materials and Methods A 62-year-old Chinese man with diabetes and hypertension, which were satisfactorily controlled by oral medications, presented with recurrent pompholyx affecting his hands and feet. Initially, he was treated with oral prednisolone, to which he responded well. As there was concern about the impact of chronic steroid use on the patientös diabetes and hypertension control, topical triam-
Received January 17, 2012; Accepted March 8, 2012 J-STAGE Advance Published Date: March 22, 2012, doi:10.2133/dmpk.DMPK-12-SC-008 *To whom correspondence should be addressed: Evelyn Siew-Chuan KOAY, Ph.D., FAACB, FRCPath, Molecular Diagnosis Centre, Department of Laboratory Medicine, Level 3, NUH Main Building, 5 Lower Kent Ridge Road, Singapore 119074, Singapore. Tel. +65- 67724564, Fax. +6567751757, E-mail: [email protected] 559
560
Chun Kiat LEE, et al. Table 1. Primer sequences used for the analysis of the thiopurine S-methyltransferase gene Targeted region
Forward primer sequence ¤5$®3$¥
Nucleotide position
Reverse primer sequence ¤5$®3$¥
Nucleotide position
Amplicon size ¤bp¥
Exons 2®7a Exons 4®9a Start codonb
GAA GAC ATA TGC TTG TGA GAC CGA AAT TCC TGG AAC CAA AGT GAA GAC ATA TGC TTG TGA GAC
117®137 494®514 10978®10998
GAA AGA ACA CAC AGG AGA TAC CTA GCA ATC TGC AAG ACA CAT GTT CCT GAT GAA AAG CAG TC
692®712 1140®1160 11127®11146
596 667 169
a
Based on a Homo sapiens thiopurine S-methyltransferase mRNA, GenBank accession: NMð000367.2. Based on Homo sapiens thiopurine S-methyltransferase ¤TPMT¥ gene, RefSeqGene on chromosome 6, GenBank accession: NGð012137.1.
b
cinolone was given as an alternative. It did not adequately control his symptoms. Azathioprine was considered as next-line therapy and a pre-treatment TPMT genotyping was undertaken for this patient. During analysis of his specimen, a novel TPMT SNP located at the start codon was detected. Total RNA was extracted from 3 mL of whole blood. cDNA, reverse transcribed from the extracted mRNA, served as the template for PCR amplification. Two sets of primers flanking exons 2 to 9, in 2 overlapping fragments, were designed to contain a single base mismatch at the 3$ end to discriminate against the TPMT pseudogene, using GenBank: NMð000367.2 as reference ¤Table 1¥. The amplification was performed using HotStarTaq PCR reagents ¤Qiagen, Hilden, Germany¥, on the GeneAmp¬ PCR thermal cycler ¤Applied Biosystems, Foster City, CA, USA¥. Cycling conditions included an initial denaturation step ¤95ôC, 15 min¥, followed by 40 cycles of the amplification step at 94ôC for 10 s, 58ôC for 1 min, 72ôC for 45 s, followed by a final extension step ¤72ôC, 7 min¥. The amplified products were sequenced bi-directionally with the amplification primers ¤Table 1¥, using the BigDye¬ Terminator v3.1 cycle sequencing kit ¤Applied Biosystems¥. The DNA sequence of the purified product was analyzed on the ABI 3130xl genetic analyzer ¤Applied Biosystems¥, according to the manufacturerös instructions. In order to confirm the above finding of the novel mutation, an additional blood sample was obtained from the patient to perform direct DNA sequencing. A new set of primers flanking the start codon of the TPMT gene were designed using GenBank: NGð012137.1 as reference ¤Table 1¥. These primers were designed to contain mismatches at the 3$ end to prevent amplification of the TPMT pseudogene. The reverse primer was also used as the sequencing primer. The extracted genomic DNA was amplified and sequenced using the amplification/sequencing protocols described earlier. This study received exemption from the Institution Review Board of the National University Hospital, Singapore. Written informed consent was provided by the patient. Results and Discussion We found the novel SNP: SNP: 110607LeeCK001; GENE NAME: TPMT; ACCESSION NUMBER: NGð012137.1; LENGTH: 25 bases; OBSERVED: T/C; 5$-TCTCTGAAACTAT/CGGATGGTACAAG-3$.
Fig. 1. Electropherograms of the heterozygous index case containing the novel g.11018ThC, TPMT*29 sequence variant by mRNA and DNA sequencing (top and middle panels, respectively) compared with a homozygous TPMT*1 wild type (bottom panel)
The TPMT gene carries a g.11018ThC transition in the start codon, resulting in a Met1Thr amino acid change, first discovered using an mRNA sequencing approach. To authenticate the finding of this mutation, it was confirmed by direct DNA sequencing in a follow-up sample received at a later date. The electropherograms of the novel TPMT SNP by mRNA and DNA sequencing are shown in Figure 1. This novel SNP was named TPMT*29, following the last described TPMT mutation ¤TPMT*28¥ at the time of writing.10¥ The 62-year-old Chinese patient carrying the novel TPMT mutation was genotyped as TPMT*1/*29. This represents the second start codon SNP to be described in the TPMT gene, the first being TPMT*14.11¥ In an in-vitro functional study, TPMT*14 was associated with complete absence of TPMT enzyme expression.6¥ It is likely that the novel start codon mutation, TPMT*29, would display a similar lack of protein translation. Being heterozygous for the novel mutation, the patient probably has intermediate TPMT enzyme activity as described previously in a heterozygous TPMT*1/*14 individual.11¥ The likely thiopurine metabolic profile of a patient can be assessed by functional or genetic studies. TPMT enzyme activity is currently the more popular choice for pre-
Copyright © 2012 by the Japanese Society for the Study of Xenobiotics (JSSX)
Novel Start Codon TPMT Mutation
treatment testing.7,8¥ However, it is susceptible to interference from blood transfusion12¥ and anaemia,13¥ as well as alteration of enzyme activity following certain medications.14,15¥ In one report, a patient with apparently normal TPMT enzyme activity developed myelotoxicity as a consequence of a hidden mutation uncovered with subsequent genotyping.14¥ TPMT genotype testing can circumvent some of the limitations of the functional study. This case highlights the advantage of our proposed mRNA sequencing approach, which provides full coverage of all coding exons of the TPMT gene, and detects cryptic or hitherto unreported mutations that otherwise may be missed by targeted genotyping, with possible adverse clinical consequences.12,13¥ Moreover, this method minimizes the number of PCRs performed; although, precautions should be taken to avoid amplification of the TPMT pseudogene. While TPMT phenotyping and genotyping tests are useful diagnostic tools, they should not supersede routine monitoring of myelotoxicity by simple complete blood count. Finally, physicians should familiarize themselves with the non-TPMT causes of thiopurine toxicity.
6¥
7¥
8¥
9¥
10¥
11¥
References 1¥ Lennard, L.: Clinical implications of thiopurine methyltransferaseoptimization of drug dosage and potential drug interactions. Ther. Drug Monit., 20: 527®531 ¤1998¥. 2¥ Srikumar, S., Danny, H. and Sandip, R.: Clinical pharmacology and pharmacogenetics of thiopurines. Eur. J. Clin. Pharmacol., 64: 753® 767 ¤2008¥. 3¥ Schaeffeler, E., Fischer, C., Brockmeier, D., Wernet, D., Moerike, K., Eichelbaum, M., Zanger, U. M. and Schwab, M.: Comprehensive analysis of thiopurine S-methyltransferase phenotype-genotype correlation in a large population of GermanCaucasians and identification of novel TPMT variants. Pharmacogenetics, 14: 407®417 ¤2004¥. 4¥ Milek, M., Murn, J., Jaksic, Z., Lukac Bajalo, J., Jazbec, J. and Mlinaric Rascan, I.: Thiopurine S-methyltransferase pharmacogenetics: genotype to phenotype correlation in the Slovenian population. Pharmacology, 77: 105®114 ¤2006¥. 5¥ Kham, S. K., Soh, C. K., Liu, T. C., Chan, Y. H., Ariffin, H.,
12¥ 13¥
14¥
15¥
561
Tan, P. L. and Yeoh, A. E.: Thiopurine S-methyltransferase activity in three major Asian populations: a population-based study in Singapore. Eur. J. Clin. Pharmacol., 64: 373®379 ¤2008¥. Ujiie, S., Sasaki, T., Mizugaki, M., Ishikawa, M. and Hiratsuka, M.: Functional characterization of 23 allelic variants of thiopurine S-methyltransferase gene ¤TPMT*2-*24¥. Pharmacogenet. Genomics, 18: 887®893 ¤2008¥. van den Akker-van Marle, M. E., Gurwitz, D., Detmar, S. B., Enzing, C. M., Hopkins, M. M., Gutierrez de Mesa, E. and Ibarreta, D.: Cost-effectiveness of pharmacogenomics in clinical practice: a case study of thiopurine methyltransferase genotyping in acute lymphoblastic leukemia in Europe. Pharmacogenomics, 7: 783® 792 ¤2006¥. Gurwitz, D., Rodríguez-Antona, C., Payne, K., Newman, W., Gisbert, J. P., de Mesa, E. G. and Ibarreta, D.: Improving pharmacovigilance in Europe: TPMT genotyping and phenotyping in the UK and Spain. Eur. J. Hum. Genet., 17: 991®998 ¤2009¥. Wood, N., Fraser, A., Bidwell, J. and Standen, G.: RT-PCR permits simultaneous genotyping of thiopurine S-methyltransferase allelic variants by multiplex induced heteroduplex analysis. Hum. Mutat., 24: 93®99 ¤2004¥. Appell, M. L., Wennerstrand, P., Peterson, C., Hertervig, E. and Mårtensson, L. G.: Characterization of a novel sequence variant, TPMT*28, in the human thiopurine methyltransferase gene. Pharmacogenet. Genomics, 20: 700®707 ¤2010¥. Lindqvist, M., Haglund, S., Almer, S., Peterson, C., Taipalensu, J., Hertervig, E., Lyrenäs, E. and Söderkvist, P.: Identification of two novel sequence variants affecting thiopurine methyltransferase enzyme activity. Pharmacogenetics, 14: 261®265 ¤2004¥. Cheung, S. T. and Allan, R. N.: Mistaken identity: misclassification of TPMT phenotype following blood transfusion. Eur. J. Gastroenterol. Hepatol., 15: 1245®1247 ¤2003¥. Barlow, N. L., Graham, V. and Berg, J. D.: Expressing thiopurine S-methyltransferase activity as units per litre of whole-blood overcomes misleading high results in patients with anaemia. Ann. Clin. Biochem., 47: 408®414 ¤2010¥. Leung, M., Piatkov, I., Rochester, C., Boyages, S. C. and Leong, R. W.: Normal thiopurine methyltransferase phenotype testing in a Crohn disease patient with azathioprine induced myelosuppression. Intern. Med. J., 39: 121®126 ¤2009¥. Schaeffeler, E., Stanulla, M., Greil, J., Schrappe, M., Eichelbaum, M., Zanger, U. M. and Schwab, M.: A novel TPMT missense mutation associated with TPMT deficiency in a 5-year-old boy with ALL. Leukemia, 17: 1422®1424 ¤2003¥.
Copyright © 2012 by the Japanese Society for the Study of Xenobiotics (JSSX)