ABSTRACT
BACKGROUND: Thiopurines are widely used for the treatment of inflammatory bowel disease, but are associated with the development of side effects. It has been suggested that the enzyme inosine triphosphate pyrophosphatase (ITPA) plays a role in the digestion of thiopurines and that defective activity resulting from polymorphisms in the inosine triphosphate pyrophosphatase encoding genes may be associated with thiopurine-induced side effects. Current studies are controversial regarding this hypothesis. AIM: To perform a meta-analysis and gain more insight into a possible correlation between thiopurine-induced side effects and ITPA polymorphisms. METHODS: We explored Medline for articles on ITPA polymorphisms and thiopurine toxicity. Studies that compared ITPA polymorphism frequencies among thiopurine-tolerant and -intolerant adult inflammatory bowel disease patients were included in this meta-analysis. RESULTS: Nine published studies investigated associations between ITPA polymorphisms and thiopurine toxicity. Six studies (with 751 patients included) met our inclusion criteria and were processed in the meta-analysis. This analysis demonstrates that the ITPA 94C-->A polymorphism, is not significantly associated with any of the studied side effect parameters. CONCLUSIONS: This meta-analysis does not prove a correlation between the development of thiopurine toxicity and the ITPA 94C-->A polymorphism. This implies that there is no clinical relevance to determine ITPA polymorphisms in thiopurine-treated patients.
Subject(s)
Inflammatory Bowel Diseases/drug therapy , Methyltransferases/genetics , Mutation/genetics , Polymorphism, Genetic/genetics , Pyrophosphatases/adverse effects , Cohort Studies , Cross-Sectional Studies , Female , Humans , Inflammatory Bowel Diseases/enzymology , Inflammatory Bowel Diseases/genetics , Male , Methyltransferases/administration & dosage , Methyltransferases/adverse effects , Methyltransferases/metabolism , Pharmacogenetics , Inosine TriphosphataseABSTRACT
AIM: To evaluate the polymorphisms of several genes involved in the azathioprine and mercaptopurine metabolism, in an attempt to explain their toxicity and efficacy in Crohn's disease and ulcerative colitis. METHODS: In 422 consecutive patients (250 with Crohn's disease and 172 with ulcerative colitis) and 245 healthy controls, single nucleotide polymorphisms of thiopurine methyltransferase, inosine triphosphate pyrophosphatase and hypoxanthine phosphoribosyl transferase (HPRT1) genes were related to the occurrence of adverse drug reactions (ADRs) and efficacy of therapy. RESULTS: Seventy-three patients reported 81 episodes of ADRs; 45 patients did not respond to therapy. Frequency of thiopurine methyltransferase risk haplotypes was significantly increased in patients with leucopenia (26% vs. 5.7% in patients without ADRs, and 4% of controls) (P < 0.001); no correlation with other ADRs and efficacy of therapy was found. Conversely, the frequency of inosine triphosphate pyrophosphatase and HPRT1 risk genotypes was not significantly different in patients with ADRs (included leucopenia). Non-responders had an increased frequency of inosine triphosphate pyrophosphatase risk genotypes (P = 0.03). CONCLUSIONS: The majority of azathioprine/mercaptopurine-induced ADRs and efficacy of therapy are not explained by the investigated gene polymorphisms. The combined evaluation of all three genes enhanced the correlation with leucopenia (43.5% vs. 23% in controls) (P = 0.008), at the expense of a reduced accuracy (60%).