Comprehensive screening of the thiopurine methyltransferase polymorphisms by denaturing high-performance liquid chromatography.
The drug-metabolizing enzyme thiopurine S-methyltransferase (TPMT) catalyzes the S-methylation of thiopurines such as 6-mercaptopurine, 6-thioguanine, and azathiopurine, which are used as immunosuppressants and in the treatment of acute lymphoblastic leukemia and rheumatoid arthritis. TPMT enzymatic activity is a polymorphic trait, and poor metabolizers may develop life-threatening bone marrow failure. To avoid such adverse effects, the TPMT enzymatic activity in patients' red blood cells (RBCs) is routinely measured prior to thiopurine administration in a limited number of oncology clinics. In the present study, we took advantage of a highly sensitive and specific automated denaturing high-performance liquid chromatography (dHPLC) technique that not only detects known polymorphic alleles, but also identifies previously uncharacterized sequence variants. We developed a dHPLC-based protocol to analyze the entire coding region and validated the protocol to detect all 16 previously described variant alleles. We further analyzed the entire coding region of the TPMT gene in 288 control samples collected worldwide and identified two novel amino acid substitutions Arg163Cys (487C>T) and Arg226Gln (677G>A) within exons 7 and 10, respectively. The clinical application of this comprehensive screening system for examining the entire TPMT gene would help to identify patients at risk for bone marrow failure prior to 6-mercaptopurine therapy.
Udaka
Toru
T
Department of Pediatrics, Keio University School of Medicine, Tokyo 160-8582, Japan.
Torii
Chiharu
C
Takahashi
Daisuke
D
Mori
Tetsuya
T
Aramaki
Michihiko
M
Kosaki
Rika
R
Tanigawara
Yusuke
Y
Takahashi
Takao
T
Kosaki
Kenjiro
K
D002851:Chromatography, High Pressure Liquid; D005091:Exons; D006801:Humans; D008780:Methyltransferases / Q000737:chemistry / Q000235:genetics*; D016297:Mutagenesis, Site-Directed; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic
D008780:Methyltransferases; C022745:thiopurine methyltransferase