Thiopurine methyltransferase pharmacogenetics: alternative molecular diagnosis and preliminary data from Northern Portugal.
The thiopurine methyltransferase (TPMT) genetic polymorphism has been shown to have a highly significant clinical impact, namely in the therapeutic efficiency of thiopurine drugs used in the treatment of a wide range of diseases. Available diagnostic methods, although reproducible and sensitive, are relatively laborious. Thus population studies are still very scarce. In this work we describe a new polymerase chain reaction-single strand confirmational analysis based protocol for TPMT specific detection which introduces a substantial technical simplification avoiding the use of restriction enzyme treatment after polymerase chain reaction amplification. Additionally, the use of this protocol allows the simultaneous detection of a T474 to C substitution, a frequent silent mutation in the North Portuguese population (TPMT*1S = 0.215). In a sample of 310 unrelated Northern Portuguese individuals, 15 were found to be heterozygous for the TPMT*3A allele (defined by the presence of two transitions, G460 to A and A719 to G) which is associated with TPMT enzymatic deficiency; the corresponding gene frequency estimate was 0.024. We also attempted to evaluate the relationship between the molecular TPMT genotype and the reaction to treatments involving thiopurine drugs by analysing a sample of 24 children submitted to curative therapy of acute lymphoblastic leukaemia. Four of them were shown to be heterozygous for the TPMT*3A allele. An examination of their clinical histories showed that all four patients exhibited signs of severe hepatic toxicity during treatment.
Alves
S
S
IPATIMUP, Faculdade de Ciências da Universidade do Porto, Portugal.
Prata
M J
MJ
Ferreira
F
F
Amorim
A
A
D000970:Antineoplastic Agents / Q000009:adverse effects / Q000378:metabolism / Q000627:therapeutic use; D001483:Base Sequence; D002648:Child; D017931:DNA Primers; D006579:Heterozygote; D006801:Humans; D008780:Methyltransferases / Q000235:genetics*; D010597:Pharmacogenetics; D012150:Polymorphism, Restriction Fragment Length; D011174:Portugal; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000188:drug therapy / Q000201:enzymology; D011687:Purines / Q000009:adverse effects / Q000378:metabolism* / Q000627:therapeutic use
D000970:Antineoplastic Agents; D017931:DNA Primers; D011687:Purines; D008780:Methyltransferases; C022745:thiopurine methyltransferase