NUDT15 C415T variant compared with TPMT genotyping in predicting azathioprine-induced leucopenia: prospective analysis of 1014 inflammatory bowel disease patients in India
Background: Recent studies reported that Nudix Hydrolase 15(NUDT 15) gene variant (C415T) can better predict thiopurine induced leucopenia in Asian patients with inflammatory bowel disease (IBD) than thiopurine S-methyl transferase (TPMT).
Aim: To evaluate the role of the NUDT variant compared with TPMT in predicting azathioprine induced leucopenia in Indian IBD patients.
Methods: Prospectively collected data of consecutive patients treated with azathioprine from a large IBD registry were analysed for side effects, discontinuation time, and initial and maximum dose tolerated. Genotyping of NUDT15 C415T (rs116855232; p.R139C) was carried out retrieving blood samples from bio-repository employing real time polymerase chain reaction with age and sex-matched healthy volunteers. The association of NUDT15 C415T with leucopenia (<3 × 109 /L) and neutropenia (<1.5 × 109 /L) was evaluated. TPMT genotyping was done in patients who developed leucopenia.
Results: Among 1014 patients (mean age 35.84 ± 12.74 years; 61% males; 54% ulcerative colitis, 44% Crohn's disease and 2% IBD-unclassified), 79 were excluded due to inadequate blood samples. Of the remaining 935, 81 (9%) developed leucopenia and 70 (7.5%) developed neutropenia. The variant "T" allele [heterozygous (CT) and homozygous (TT) versus wild type (CC)] was associated with a 19-fold higher odds (OR19.35, 95% CI11.55-32.42; P < 0.0001) of leucopenia and 21-fold higher odds of neutropenia (OR21.41, 95% CI12.25-37.41). There was significant difference in median dose tolerated between CC, CT and TT (1.35, 1.38 and 0.92 mg/kg body weight, respectively) (P = 0.037) and median duration of therapy (18, 15 and 10 months for CC/CT/TT) (P = 0.003). NUDT15 genotype was an independent risk factor for leucopenia (hazard ratio (HR): CT 11.31, 95% CI6.85-18.03, P < 0.0001 and TT 31.283, 95% CI14.76-66.30 compared to CC) and neutropenia (HR: CT 13.04, 95% CI7.65-22.22, P < 0.0001 and TT 43.39, 95% CI20.21-92.68 compared to CC). The sensitivities for predicting leucopenia and neutropenia by number of mutant NUDT 15 alleles based on additive predictive model were 66.67% and 70% with a receptor operator characteristic curve area under curve value of 0.791 and 0.807, respectively. Among patients with leucopenia, only 6.2% were heterozygous and none were homozygous for TPMT variants.
Conclusion: NUDT15 variant genotyping appears to be a better predictor for azathioprine-induced leucopenia in an Indian population than TPMT with high accuracy and can be useful in optimizing azathioprine dosage.