Genetic variants at the ITPA locus protect against ribavirin-induced hemolytic anemia and dose reduction in an HCV G2/G3 cohort

OBJECTIVES: Two functional genetic variants in the inosine triphosphatase (ITPA) gene have been shown to be strongly associated with protection from ribavirin (RBV)-induced hemolysis. We aimed at evaluating this finding in a chronic hepatitis C genotype 2/3 cohort with a predominance of genotype 3 patients where available data are scarce. A second objective was to determine whether a protective association translated into the need for RBV reduction and hence a possible impact on treatment response. METHODS: Overall, 457 patients were recruited from two trials of genotype 2/3 patients treated with pegylated interferon α-2b and weight-based RBV. rs1127354 and rs7270101 were genotyped and a composite ITPAase deficiency variable was graded according to the two single nucleotide polymorphisms. The primary endpoints were hemoglobin (Hb) decline from baseline and Hb decline of more than 3 g/dl at week 4. RESULTS: Both single nucleotide polymorphisms and the composite ITPAase deficiency variable were strongly and independently associated with protection from a decline in Hb at week 4 in multivariate linear regression models (Prs1127354=7.0×10, Prs7270101=0.0036, PITPase deficiency variable =6.3×10). Patients with any degree of reduced ITPAase activity were less likely to have their RBV dose reduced (odds ratio 0.39, 95% confidence interval 0.16-0.96, P=0.040), although this did not translate into increased rapid viral response or sustained viral response (Prvr=0.93, Psvr=0.22). CONCLUSION: We have confirmed a strong association between functional ITPA variants and RBV-induced hemolysis and showed protection from RBV dose reduction, although this did not translate into increased rapid viral response or sustained viral response.