Nonsynonymous Polymorphism in Guanine Monophosphate Synthetase Is a Risk Factor for Unfavorable Thiopurine Metabolite Ratios in Patients With Inflammatory Bowel Disease

Rebecca L. Roberts, Mary C. Wallace, Margien L. Seinen, Adriaan A. van Bodegraven, Krupa Krishnaprasad, Gregory T. Jones, Andre M. van Rij, Angela Baird, Ian C. Lawrance, Ruth Prosser, Peter Bampton, Rachel Grafton, Lisa A. Simms, Corrie Studd, Sally J. Bell, Martin A. Kennedy, Jacob Halliwell, Richard B. Gearry, Graham Radford-Smith, Jane M. AndrewsPatrick C. McHugh, Murray L. Barclay

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Background: Up to 20% of patients with inflammatory bowel disease (IBD) who are refractory to thiopurine therapy preferentially produce 6-methylmercaptopurine (6-MMP) at the expense of 6-thioguanine nucleotides (6-TGN), resulting in a high 6-MMP:6-TGN ratio (>20). The objective of this study was to evaluate whether genetic variability in guanine monophosphate synthetase (GMPS) contributes to preferential 6-MMP metabolizer phenotype. Methods: Exome sequencing was performed in a cohort of IBD patients with 6-MMP:6-TGN ratios of >100 to identify nonsynonymous single nucleotide polymorphisms (nsSNPs). In vitro assays were performed to measure GMPS activity associated with these nsSNPs. Frequency of the nsSNPs was measured in a cohort of 530 Caucasian IBD patients. Results: Two nsSNPs in GMPS (rs747629729, rs61750370) were detected in 11 patients with very high 6-MMP:6-TGN ratios. The 2 nsSNPs were predicted to be damaging by in silico analysis. In vitro assays demonstrated that both nsSNPs resulted in a significant reduction in GMPS activity (P < 0.05). The SNP rs61750370 was significantly associated with 6-MMP:6-TGN ratios ≥100 (odds ratio, 5.64; 95% confidence interval, 1.01-25.12; P < 0.031) in a subset of 264 Caucasian IBD patients. Conclusions: The GMPS SNP rs61750370 may be a reliable risk factor for extreme 6MMP preferential metabolism.
Original languageEnglish
Pages (from-to)2606-2612
JournalInflammatory Bowel Diseases
Issue number12
Publication statusPublished - 2018

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