title: ITPA
text: # ITPA
  
  Inosine triphosphate pyrophosphatase is an enzyme that in humans is encoded by the ITPA gene, by the rdgB gene in bacteria E.coli and the HAM1 gene in yeast S. cerevisiae; the protein is also encoded by some RNA viruses of the Potyviridae family. Two transcript variants encoding two different isoforms have been found for this gene. Also, at least two other transcript variants have been identified which are probably regulatory rather than protein-coding.
  
  ## Function
  
  The protein encoded by this gene hydrolyzes inosine triphosphate and deoxyinosine triphosphate to the monophosphate nucleotide and diphosphate. The enzyme possesses a multiple substrate-specificity and acts on other nucleotides including xanthosine triphosphate and deoxyxanthosine triphosphate. The encoded protein, which is a member of the HAM1 NTPase protein family, is found in the cytoplasm and acts as a homodimer.
  
  ## Clinical significance
  
  Defects in the encoded protein can result in inosine triphosphate pyrophosphorylase deficiency. The enzyme ITPase dephosphorylates ribavirin triphosphate in vitro to ribavirin monophosphate, and ITPase reduced enzymatic activity present in 30 % of humans potentiates mutagenesis in hepatitis C virus. Gene variants predicting reduced predicted ITPase activity have been associated with decreased risk of ribavirin-induced anemia, increased risk of thrombocytopenia, lower ribavirin concentrations, as well as a ribavirin-like reduced relapse risk following interferon-based therapy for hepatitis C virus (HCV) genotype 2 or 3 infection.
  
  ## Reading
  
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  * Marinaki AM, Duley JA, Arenas M, et al. (2005). "Mutation in the ITPA gene predicts intolerance to azathioprine". Nucleosides Nucleotides Nucleic Acids. 23 (8–9): 1393–7. doi:10.1081/NCN-200027639. PMID 15571265. S2CID 86308163.
  * Marinaki AM, Sumi S, Arenas M, et al. (2005). "Allele frequency of inosine triphosphate pyrophosphatase gene polymorphisms in a Japanese population". Nucleosides Nucleotides Nucleic Acids. 23 (8–9): 1399–401. doi:10.1081/NCN-200027641. PMID 15571266. S2CID 36126159.
  * Maeda T, Sumi S, Ueta A, et al. (2005). "Genetic basis of inosine triphosphate pyrophosphohydrolase deficiency in the Japanese population". Mol. Genet. Metab. 85 (4): 271–9. doi:10.1016/j.ymgme.2005.03.011. PMID 15946879.
  * Breen DP, Marinaki AM, Arenas M, Hayes PC (2005). "Pharmacogenetic association with adverse drug reactions to azathioprine immunosuppressive therapy following liver transplantation". Liver Transpl. 11 (7): 826–33. doi:10.1002/lt.20377. PMID 15973722. S2CID 9301778.
  * Porta J, Kolar C, Kozmin SG, et al. (2006). "Structure of the orthorhombic form of human inosine triphosphate pyrophosphatase". Acta Crystallographica Section F. 62 (Pt 11): 1076–81. doi:10.1107/S1744309106041790. PMC 2225220. PMID 17077483.
  * Arenas M, Duley J, Sumi S, et al. (2007). "The ITPA c.94C>A and g.IVS2+21A>C sequence variants contribute to missplicing of the ITPA gene". Biochim. Biophys. Acta. 1772 (1): 96–102. doi:10.1016/j.bbadis.2006.10.006. PMID 17113761.
  * Stenmark P, Kursula P, Flodin S, et al. (2007). "Crystal structure of human inosine triphosphatase. Substrate binding and implication of the inosine triphosphatase deficiency mutation P32T". J. Biol. Chem. 282 (5): 3182–7. doi:10.1074/jbc.M609838200. PMID 17138556.
  * Atanasova S, Shipkova M, Svinarov D, et al. (2007). "Analysis of ITPA phenotype-genotype correlation in the Bulgarian population revealed a novel gene variant in exon 6". Therapeutic Drug Monitoring. 29 (1): 6–10. doi:10.1097/FTD.0b013e3180308554. PMID 17304144. S2CID 7286658.
  