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Characterization of a novel sequence variant, TPMT*28, in the human thiopurine methyltransferase gene

Appell, Malin Lindqvist; Wennerstrand, Patricia; Peterson, Curt; Hertervig, Erik LU and Martensson, Lars-Goran (2010) In Pharmacogenetics & Genomics 20(11). p.700-707
Abstract
Background The activity of the human enzyme thiopurine methyltransferase (TPMT) varies greatly between individuals because of genetic polymorphism. TPMT is involved in the detoxification and activation of thiopurines such as 6-mercaptopurine, 6-thioguanine, and azathioprine. These drugs are used in the treatment of acute lymphoblastic leukemia and inflammatory bowel disease. A total of 29 sequence variants have been identified so far in the TPMT gene. However, most of these variants are rare and not fully characterized. Methods and results In this study, we describe the identification and characterization of a novel TPMT sequence variant, originally found in a Swedish man of Italian origin. Sequencing of the variable number tandem repeats... (More)
Background The activity of the human enzyme thiopurine methyltransferase (TPMT) varies greatly between individuals because of genetic polymorphism. TPMT is involved in the detoxification and activation of thiopurines such as 6-mercaptopurine, 6-thioguanine, and azathioprine. These drugs are used in the treatment of acute lymphoblastic leukemia and inflammatory bowel disease. A total of 29 sequence variants have been identified so far in the TPMT gene. However, most of these variants are rare and not fully characterized. Methods and results In this study, we describe the identification and characterization of a novel TPMT sequence variant, originally found in a Swedish man of Italian origin. Sequencing of the variable number tandem repeats region of the TPMT promoter and exons III-X revealed a T-to-C transition at nucleotide 611, causing an amino acid substitution from isoleucine to threonine at amino acid 204, positioned in an alpha-helix, approximately 16A from the active site. This new variant was found in the patient and in his son. Both had intermediate enzyme activity (8.1 U/ml packed red blood cells and 8.8 U/ml packed red blood cells, respectively) and neither carried other variants in the coding region of the gene. To be able to study this variant in more detail, the TPMT*28 variant was expressed in Escherichia coli, and an in-vitro characterization of the variant revealed that the protein was destabilized and showed a stronger tendency towards degradation at 37 degrees C than the wild-type protein. The individuals carrying the TPMT*28 variant had less TPMT protein and lower TPMT activity in both red and white blood cells compared with a wild-type control. Conclusions We present a detailed in-vivo and in-vitro characterization of a novel TPMT sequence variant (TPMT*28) causing decreased TPMT activity. Individuals carrying TPMT*28 might have an increased risk for developing severe side effects if treated with conventional doses of thiopurines. Pharmacogenetics and Genomics 20: 700-707 (C) 2010 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
single nucleotide polymorphism, right-angle light scattering, pharmacogenetics, protein stability, thiopurine methyltransferase
in
Pharmacogenetics & Genomics
volume
20
issue
11
pages
700 - 707
publisher
Lippincott Williams & Wilkins
external identifiers
  • wos:000282965100005
  • scopus:78049296472
ISSN
1744-6872
DOI
10.1097/FPC.0b013e3283402ee4
language
English
LU publication?
yes
id
2fd9896d-646e-458f-bfea-f7df8353e360 (old id 1725518)
date added to LUP
2010-12-03 12:21:48
date last changed
2018-05-29 11:31:28
@article{2fd9896d-646e-458f-bfea-f7df8353e360,
  abstract     = {Background The activity of the human enzyme thiopurine methyltransferase (TPMT) varies greatly between individuals because of genetic polymorphism. TPMT is involved in the detoxification and activation of thiopurines such as 6-mercaptopurine, 6-thioguanine, and azathioprine. These drugs are used in the treatment of acute lymphoblastic leukemia and inflammatory bowel disease. A total of 29 sequence variants have been identified so far in the TPMT gene. However, most of these variants are rare and not fully characterized. Methods and results In this study, we describe the identification and characterization of a novel TPMT sequence variant, originally found in a Swedish man of Italian origin. Sequencing of the variable number tandem repeats region of the TPMT promoter and exons III-X revealed a T-to-C transition at nucleotide 611, causing an amino acid substitution from isoleucine to threonine at amino acid 204, positioned in an alpha-helix, approximately 16A from the active site. This new variant was found in the patient and in his son. Both had intermediate enzyme activity (8.1 U/ml packed red blood cells and 8.8 U/ml packed red blood cells, respectively) and neither carried other variants in the coding region of the gene. To be able to study this variant in more detail, the TPMT*28 variant was expressed in Escherichia coli, and an in-vitro characterization of the variant revealed that the protein was destabilized and showed a stronger tendency towards degradation at 37 degrees C than the wild-type protein. The individuals carrying the TPMT*28 variant had less TPMT protein and lower TPMT activity in both red and white blood cells compared with a wild-type control. Conclusions We present a detailed in-vivo and in-vitro characterization of a novel TPMT sequence variant (TPMT*28) causing decreased TPMT activity. Individuals carrying TPMT*28 might have an increased risk for developing severe side effects if treated with conventional doses of thiopurines. Pharmacogenetics and Genomics 20: 700-707 (C) 2010 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.},
  author       = {Appell, Malin Lindqvist and Wennerstrand, Patricia and Peterson, Curt and Hertervig, Erik and Martensson, Lars-Goran},
  issn         = {1744-6872},
  keyword      = {single nucleotide polymorphism,right-angle light scattering,pharmacogenetics,protein stability,thiopurine methyltransferase},
  language     = {eng},
  number       = {11},
  pages        = {700--707},
  publisher    = {Lippincott Williams & Wilkins},
  series       = {Pharmacogenetics & Genomics},
  title        = {Characterization of a novel sequence variant, TPMT*28, in the human thiopurine methyltransferase gene},
  url          = {http://dx.doi.org/10.1097/FPC.0b013e3283402ee4},
  volume       = {20},
  year         = {2010},
}