THPM2 is associated with severe hematopoietic toxicity when patients are treated with standard doses of thiopurines, a class of antineoplastic/immunosuppressant agents that consists of mercaptopurine, thioguanine, and azathioprine. Thiopurines are prodrugs that require extensive metabolism in order to exert their cytotoxic action. Thiopurines are converted into cytotoxic thioguanine nucleotides (TG), which are incorporated into DNA and cause cell death. NUDT15 inactivates thiopurine metabolites and negatively regulates cytotoxicity (summary by Moriyama et al., 2016). The NUDT15 deficiency trait follows an additive genetic mode of inheritance, with the severity of the phenotype proportional to the cumulative number of risk alleles in NUDT15.
For a discussion of genetic heterogeneity of poor thiopurine metabolism, see THPM1 (610460). [from OMIM]
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