Predictive factors of anemia during sofosbuvir and ribavirin therapy for genotype 2 chronic hepatitis C patients.

AIM: Sofosbuvir (SOF) and ribavirin (RBV) combination therapy has improved the sustained virologic response (SVR) rate and shortened the treatment duration for patients with chronic hepatitis C virus (HCV) genotype 2 infection. Ribavirin-induced hemolytic anemia is one of the most troublesome side-effects of SOF/RBV therapy; however, factors associated with this condition have not been fully elucidated. We aimed to identify a safer way to complete treatment with SOF/RBV therapy by examining factors related to RBV-induced hemolytic anemia and identifying patients who did not develop anemia. METHODS: Two hundred and one patients with genotype 2 chronic hepatitis C treated with SOF/RBV therapy were studied. Significant factors associated with the decline in hemoglobin (Hb) levels from the baseline were analyzed. RESULTS: The SVR rate was 96.5% (194 out of 201 patients) based on intent-to-treat analysis. In multivariate analysis, inosine triphosphatase (ITPA) gene variation (P < 0.0001) and estimated glomerular filtration rate (eGFR) (0.001) were significantly associated with a decrease in Hb levels less than 2 g/dL. All patients were divided into four groups by ITPA and eGFR at baseline, and we identified patients with ITPA CA/AA and eGFR >75 as a group that did not develop anemia. CONCLUSIONS: The results presented here suggest that patients with ITPA CA/AA and eGFR >75 had no reduction in Hb levels during the treatment with SOF/RBV in HCV genotype 2-infected patients. Adding RBV to direct-acting antiviral therapy might not be problematic in certain patients, at least in terms of the occurrence of anemia.

ITPA gene variation and ribavirin-induced anemia in patients with genotype 2 chronic hepatitis C treated with sofosbuvir plus ribavirin.

AIM: Sofosbuvir (SOF) and ribavirin (RBV) combination therapy produces a sustained response in many patients with genotype 2 chronic hepatitis C. However, RBV-induced anemia is a troublesome side-effect that may limit this treatment. Genetic variation leading to inosine triphosphatase (ITPA) deficiency is known to protect against RBV-induced hemolytic anemia. This study aimed to evaluate the relationships between the efficacy and safety of SOF/RBV treatment and ITPA gene variants. METHODS: Ninety patients with genotype 2 chronic hepatitis C treated with SOF/RBV were studied. The relationships among genetic polymorphisms of ITPA and the decline in hemoglobin levels from baseline, RBV dose reduction, and sustained virological response (SVR) rates were analyzed. RESULTS: Overall SVR at 12 weeks was 94.4% (85/90). Patients with the ITPA CA/AA genotypes had a lower degree of anemia throughout the therapy than those with the ITPA CC genotype. The percentage of patients requiring RBV dose reduction was significantly lower for those with the ITPA CA/AA variation, a difference even more apparent when the pretreatment hemoglobin level was <12 g/dL. The dose reduction of RBV and serum albumin level were significantly associated with SVR. CONCLUSIONS: Patients with the ITPA CA/AA genotype were less likely to develop anemia than those with the ITPA CC genotype and were more likely to complete SOF/RBV therapy. These results may provide a valuable pharmacogenetic diagnostic tool to predict drug-induced adverse events, particularly in patients with pre-existing anemia.

Correlation between polymorphism in the inosine triphosphatase and the reductions in hemoglobin concentration and ribavirin dose during sofosbuvir and ribavirin therapy.

BACKGROUND AND AIM: It is unclear whether polymorphism in the inosine triphosphatase (ITPA) gene correlates to the reduction in hemoglobin (Hb) concentrations during sofosbuvir (SOF) and ribavirin (RBV) therapy. This study investigated the effects of the ITPA polymorphism on Japanese patients with chronic hepatitis C virus genotype 2 infection treated with SOF/RBV therapy. METHODS: In 106 patients treated with SOF/RBV therapy, this study assessed the effects of the ITPA polymorphism (rs1127354) on anemia, RBV dose reduction, and sustained virological response. RESULTS: Of the 106 patients, 80 had the CC genotype, whereas 26 had a non-CC genotype in ITPA. Patients with the CC genotype had significantly larger reductions in Hb concentrations than those with a non-CC genotype throughout the treatment course. RBV dose reduction was required in 18/106 (17.0%) patients, with a significantly higher frequency in patients with the CC genotype than in those with a non-CC genotype (P = 0.010). In multivariate analysis, age ≥ 65 years (P = 0.011) and the ITPA CC genotype (P < 0.0001) were factors significantly associated with anemia throughout the treatment course. Sustained virological response was achieved in 99.0% of all patients: 98.7% of patients with the CC genotype and 100% of patients with a non-CC genotype. CONCLUSIONS: Inosine triphosphatase polymorphism appeared to correlate with anemia incidence and RBV dose reduction during SOF/RBV therapy, but not the clinical outcome. Careful monitoring of Hb concentrations and prompt adjustment of RBV doses are required for successful treatment, particularly in patients harboring the ITPA CC genotype or age ≥ 65 years.

Prevalence of abnormal glycometabolism in treatment-naive patients with hepatitis C virus infection in a Chinese Han population.

BACKGROUND AND AIM: The hepatitis C virus (HCV) may promote pancreatic ß-cell apoptosis-like cell death through a caspase 3-dependent pathway, initiating the onset of type 2 diabetes mellitus (T2DM); however, the risk factors for development of T2DM and other abnormal glycometabolic factors in HCV patients of the Chinese Han ethnicity have been poorly explored. METHODS: A total of 947 patients Chinese Han patients with confirmed HCV infection were enrolled in a multicenter study in order to examine the genetic and physiological parameters associated with the onset of abnormal glycometabolic conditions, including T2DM and prediabetes. RESULTS: HCV genotype 1b and host interleukin-28B CC genotype were most commonly observed. A total of 145 (15.3%) patients were diagnosed with T2DM and prediabetes. Elevated age, waist circumference, smoking duration, and systolic and diastolic blood pressure were shown to increase risks for abnormal glycometabolism. Liver dysfunction was shown to have positive correlations with abnormal glycometabolism in HCV patients. Genome-wide association studies indicated that certain genetic encoding inosine triphosphatase polymorphs (rs6051702) were associated with elevated risks for abnormal glycometabolism. Coupled with previous research data, it is likely that abnormal glycometabolism may be a useful predictor of risk for poor response to antiviral therapies and treatment-induced complications, such as anemia, in treatment naïve patients. CONCLUSIONS: Abnormal glycometabolism and other such complications of HCV and HCV treatment may share critical metabolic and genetic pathways, providing potentially novel targets for future antiviral therapies for treatment resistant HCV genotypes.

Comparative safety study on severe anemia by simeprevir versus telaprevir-based triple therapy for chronic hepatitis C.

BACKGROUND AND AIM: The addition of hepatitis C virus (HCV) NS3/4A protease inhibitors to the pegylated interferon (PEG-IFN) α and ribavirin combination regimen (triple therapy) has dramatically improved treatment outcome. Unfortunately, anemia remains a common adverse effect. This study was done to compare the development of severe anemia during simeprevir- or telaprevir-based triple therapy. METHODS: This retrospective multicenter study consisted of 837 consecutive Japanese HCV genotype 1 patients treated in a real-world clinical setting, 811 of whom were enrolled (simeprevir 281, telaprevir 530). The inosine triphosphate pyrophosphatase (ITPA) genotype at rs1127354 was determined for all studied patients. Logistic regression was done after propensity score matching to assess the risk of development of severe anemia. RESULTS: Propensity score matching of the entire study population yielded 266 matched pairs. Severe anemia (nadir hemoglobin < 9.0 g/dL) was developed during the treatment period by 81 (30.5%) and 144 (54.1%) patients treated with simeprevir and telaprevir, respectively. Treatment with simeprevir was independently associated with a lower risk of severe anemia (odds ratio 0.25, 95% confidence interval 0.16-0.38, P < 0.0001). Moreover, ITPA genotype, age, hemoglobin level, and estimated glomerular filtration rate at baseline were also independent factors associated with the development of severe anemia. CONCLUSIONS: Patients treated with simeprevir-based triple therapy have a lower risk of the development of severe anemia than those treated with telaprevir. Moreover, ITPA genotype and age may be useful for individualizing treatment to reduce the risk of anemia-related adverse effects.

Administration of low-dose epoetin-alpha facilitates adherence to ribavirin in triple therapy with pegylated interferon-alpha-2b and telaprevir.

AIM: Anemia frequently develops in patients given pegylated interferon, ribavirin (RBV), telaprevir (TVR) triple therapy and restricts treatment by forcing reduction or discontinuation of RBV administration. We investigated whether erythropoietin (EPO) could alleviate RBV-induced anemia to help maintain the RBV dose during the first 12 weeks, the triple therapy phase. METHODS: Twenty-two patients with hepatitis C virus (HCV) genotype 1 were enrolled. Hemoglobin (Hb) concentration was measured every week. If Hb reduction from the baseline was 2 g/dL or more, 12 000 IU of epoetin-α was administrated. When further reduction (≥3 g/dL) was observed, 24 000 IU of epoetin-α was used. Inosine triphosphatase (ITPA) single nucleotide polymorphism (rs1127354) was genotyped for all patients. RESULTS: Among the 22 patients enrolled in this study, three required RBV dose reduction due to anemia, two had to discontinue or reduce TVR and RBV due to creatinine elevation. The remaining 17 patients completed the treatment during the triple therapy phase without reduction of the RBV dose or adverse events attributable to EPO. Regardless of ITPA genotype, Hb decline was well controlled by EPO administration, whereas the total EPO dose tended to be higher in the CC genotype group. The average adherence to RBV during the triple therapy phase was 97.5%. SVR was achieved in 17 patients; two patients had viral breakthrough and three patients had relapse of HCV RNA. CONCLUSION: EPO can be a favorable alternative to reduction of RBV to facilitate the adherence of patients on TVR-based triple therapy.

Clinical milestones for the prediction of severe anemia by chronic hepatitis C patients receiving telaprevir-based triple therapy.

BACKGROUND & AIMS: Anemia is a common adverse effect of telaprevir (TVR) in combination with pegylated interferon (PegIFN)α and ribavirin (RBV) therapy. It occurs at a higher incidence with the TVR relative to PegIFNα and RBV alone. We herein evaluate the baseline and on-treatment predictors of the development of severe anemia by chronic hepatitis C virus (HCV) patients receiving TVR-based triple therapy. METHODS: This prospective, multicenter study consisted of 292 patients (median age: 62 years) infected with HCV genotype 1. All received 12 weeks of TVR in combination with 24 weeks of PegIFNα2b and RBV. The definition of severe anemia during antiviral treatment is hemoglobin (Hb)<85 g/L. RESULTS: 101 (34.6%) patients developed severe anemia during the treatment period. Multivariable logistic regression analysis of possible pretreatment predictors of the development of severe anemia extracted baseline Hb < 135 g/L (Hazard ratio [HR], 2.53; p = 0.0013), estimated glomerular filtration rate <80 ml/min/1.73 m(2) (HR, 1.83; p = 0.0265), and inosine triphosphatase (ITPA) CC genotype (rs1127354) (HR, 2.91; p = 0.0024). For patients with ITPA CC (n = 227), multivariable logistic regression analysis of possible pretreatment and on-treatment predictors of the development of severe anemia extracted Hb level at week 2 (HR, 0.96; p = 0.0085) and the initial four weeks of weight-adjusted TVR (HR, 1.05; p = 0.0281). CONCLUSIONS: Anemia remains a risk for all patients treated with TVR-based triple therapy. However, ITPA polymorphism (rs1127354) is useful for predicting the development of severe anemia and will be helpful in the management of treatment.

Inosine triphosphatase deficiency helps predict anaemia, anaemia management and response in chronic hepatitis C therapy.

Anaemia frequently complicates peginterferon/ribavirin therapy for chronic hepatitis C infection. Better prediction of anaemia, ribavirin dose reduction or erythropoietin (EPO) need, may enhance patient management. Inosine triphosphatase (ITPA) genetic variants are associated with ribavirin-induced anaemia and dose reduction; however, their impact in real-life clinic patient cohorts remains to be defined. We studied 193 clinic patients with chronic hepatitis C infection of mixed viral genotype (genotype 1/4 n = 123, genotype 2/3, n = 70) treated with peginterferon/ribavirin. Patients were genotyped for ITPA polymorphisms rs1127354 and rs7270101 using Taqman primers. Hardy-Weinberg equilibrium was present. Estimated ITPA deficiency was graded on severity (0-3, no deficiency/mild/moderate/severe, n = 126/40/24/3, respectively). Multivariable models tested the association with anaemia at 4 weeks of treatment [including decline in haemoglobin (g/dL); haemoglobin <10 g/dL and haemoglobin decline >3 g/dL]; ribavirin dose reduction and EPO use and explored sustained viral response (SVR) to peginterferon/ribavirin. More severe ITPA deficiency was associated with less reduction in haemoglobin level (P <0.001; R(2) = 0.34), less ribavirin dose reduction (OR 0.42; (95% CI = 0.23-0.77); P = 0.005) and less EPO use [OR 0.53; (0.30-0.94); P = 0.029]. ITPA deficiency was associated with SVR [OR: 1.70; (1.02-2.83); P = 0.041] independently of clinical covariates (adjusted R(2) = 0.31). In this clinical cohort, ITPA deficiency helped predict the risk of on-treatment anaemia, ribavirin dose reduction, need for EPO support and was associated with SVR. For patients on HCV regimens including peginterferon/ribavirin, testing for ITPA deficiency may have clinical utility.

NUDT15 is a key genetic factor for prediction of hematotoxicity in pediatric patients who received a standard low dosage regimen of 6-mercaptopurine.

6-Mercaptopurine (6-MP) is commonly used for treatment of acute lymphoblastic leukemia (ALL). The incidence of hematotoxicity caused by this drug is quite high in Asians even using a standard low dosage regimen. The present study was aimed to elucidate the impact of thiopurine S-methyltransferase (TPMT), a nucleoside diphosphate-linked moiety X-type motif 15 (NUDT15), inosine triphosphatase (ITPA) and ATP Binding Cassette Subfamily C Member 4 (ABCC4) polymorphisms on hematotoxicity in pediatric patients who received a standard low starting dose of 6-MP. One hundred and sixty-nine pediatric patients were enrolled and their genotypes were determined. Patients who carried NUDT15∗3 and NUDT15∗2 genotypes were at a 10-15 fold higher risk of severe neutropenia than those of the wild-type during the early months of the maintenance phase. Risk of neutropenia was not significantly increased in patients with other NUDT15 variants as well as in patients with TPMT, ITPA or ABCC4 variants. These results suggest that NUDT15 polymorphisms particularly, NUDT15∗3 and NUDT15∗2, play major roles in 6-MP-induced severe hematotoxicity even when using a standard low dosage of 6-MP and genotyping of these variants is necessary in order to obtain precise tolerance doses and avoid severe hematotoxicity in pediatric patients.

Induction of inosine triphosphatase activity during ribavirin treatment for chronic hepatitis C.

BACKGROUND: Ribavirin (RBV) is an antiviral agent and the primary component for chronic hepatitis C (CHC) therapy. Hemolytic anemia is limitation for RBV treatment. Inosine triphosphatase (ITPA) activity has been associated with severity of RBV-induced anemia. However, changes in ITPA activity during CHC therapy are unknown. The aim of this study was to measure the time-dependent change in ITPA activity over the RBV treatment. METHODS: Forty-two patients with CHC were evaluated for ITPA activity over the course of RBV treatment. RESULTS: The median value of ITPA activity at start of RBV treatment was 134.2 µmol/h/g hemoglobin (Hb; range, 26.3-251.0 µmol/h/g Hb). The ITPA activity values at 4, 8, and 12 weeks during RBV treatment were 143.2, 202.2, and 225.7 µmol/h/g Hb, respectively, and these ITPA values were significantly elevated compared with the start of treatment (p < 0.001). In patients with ITPA variants, patients with anemia (Hb < 10 g/dL) had greater elevated ITPA activities compared with patients without anemia at 12 weeks. CONCLUSION: Our findings indicate that ITPA activities are elevated with RBV therapy, and this elevation may be a risk of anemia in late therapeutic phase in patients that began with low ITPA activity.

Role of TPMT and ITPA variants in mercaptopurine disposition.

PURPOSE: To explore the levels of thioguanine incorporated into DNA (DNA-TG), and erythrocyte levels of 6-thioguanine nucleotides (Ery-TGN) and methylated metabolites (Ery-MeMP) during 6-mercaptopurine (6MP)/Methotrexate (MTX) therapy of childhood acute lymphoblastic leukemia (ALL) and the relation to inosine triphosphatase (ITPA) and thiopurine methyltransferase (TPMT) gene variants. METHODS: Blood samples were drawn during 6MP/MTX maintenance therapy from 132 children treated for ALL at Rigshospitalet, Copenhagen. The samples were analysed for thiopurine metabolites and compared to TPMT (rs1800460 and rs1142345) and ITPA (rs1127354) genotypes. RESULTS: Median DNA-TG (mDNA-TG) levels were higher in TPMT and ITPA low-activity patients as compared to wildtype patients (TPMTLA 549 vs. 364 fmol/µg DNA, p = 0.007, ITPALA 465 vs. 387 fmol/µg DNA, p = 0.04). mDNA-TG levels were positively correlated to median Ery-TGN (mEry-TGN)(rs = 0.37, p = 0.001), but plateaued at higher mEry-TGN levels. DNA-TG indices (mDNA-TG/mEry-TGN) were 42% higher in TPMTWT patients as compared to TPMTLA patients but no difference in DNA-TG indices was observed between ITPAWT and ITPALA patients (median 1.7 vs. 1.6 fmol/µg DNA/ nmol/mmol Hb, p = 0.81). DNA-TG indices increased with median Ery-MeMP (mEry-MeMP) levels (rs = 0.25, p = 0.001). CONCLUSIONS: TPMT and ITPA genotypes significantly influence the metabolism of 6MP. DNA-TG may prove to be a more relevant pharmacokinetic parameter for monitoring 6MP treatment intensity than cytosolic metabolites. Prospective trials are needed to evaluate the usefulness of DNA-TGN for individual dose adjustments in childhood ALL maintenance therapy.

Clinical utility of pharmacogenomics in the management of hepatitis C.

Hepatitis C virus (HCV) was identified for the first time more than 20 years ago. Since then, several studies have highlighted the complicated aspects of this viral infection in relation to its worldwide prevalence, its clinical presentation, and its therapeutic response. Recently, two landmark scientific breakthroughs have moved us closer to the successful eradication of chronic HCV infection. First, response rates in treatment-naïve patients and in prior non-responders to pegylated-interferon-α and ribavirin therapy are increasing as a direct consequence of the development of direct-acting antiviral drugs. Secondly, the discovery of single-nucleotide polymorphisms near the interleukin 28B gene significantly related to spontaneous and treatment-induced HCV clearance represents a milestone in the HCV therapeutic landscape. The implementation of this pharmacogenomics finding as a routine test for HCV-infected patients has enhanced our understanding of viral pathogenesis, has encouraged the design of ground-breaking antiviral treatment regimens, and has become useful for pretreatment decision making. Nowadays, interleukin 28B genotyping is considered to be a key diagnostic tool for the management of HCV-infected patients and will maintain its significance for new combination treatment schemes using direct-acting antiviral agents and even in interferon-free regimens. Such pharmacogenomics insights represent a challenge to clinicians, researchers, and health administrators to transform this information into knowledge with the aim of elaborating safer and more effective therapeutic strategies specifically designed for each patient. In conclusion, the individualization of treatment regimens for patients with hepatitis C, that may lead to a universal cure in future years, is becoming a reality due to recent developments in biomarker and genomic medicine. In light of these advances, we review the scientific evidence and clinical implications of recent findings related to host genetic factors in the management of HCV infection.

Individualization of chronic hepatitis C treatment according to the host characteristics.

Hepatitis C virus (HCV) infection is a global health problem that affects more than 170 million people worldwide. It is a major cause of cirrhosis and hepatocellular carcinoma, making the virus the most common cause of liver failure and transplantation. The standard-of-care treatment for chronic hepatitis C (CHC) has been changed during the last decade and direct acting antiviral drugs have already been used. Besides, understanding of the pathogenesis of CHC has evolved rapidly during the last years and now several host factors are known to affect the natural history and response to treatment. Recent genome-wide association studies have shown the important role of interleukin-28B and inosine triphosphatase in HCV infection. The present review article attempts to summarize the current knowledge on the role of host factors towards individualization of HCV treatment.

Association of ITPA polymorphism with outcomes of peginterferon-α plus ribavirin combination therapy.

AIM: To analyzed the association between inosine triphosphatase (ITPA) (rs1127354) genotypes and sustained virological response (SVR) rates in peginterferon (Peg-IFN)α + ribavirin (RBV) treatment. METHODS: Patients who underwent Peg-IFNα + RBV combination therapy were enrolled (n = 120) and they had no history of other IFN-based treatments. Variation in hemoglobin levels during therapy, cumulative reduction of RBV dose, frequency of treatment withdrawal, and SVR rates were investigated in each ITPA genotype. RESULTS: In patients with ITPA CC genotype, hemoglobin decline was significantly greater and the percentage of patients in whom total RBV dose was < 60% of standard and/or treatment was withdrawn was significantly higher compared with CA/AA genotype. However, SVR rates were equivalent between CC and CA/AA genotypes, and within a subset of patients with Interleukin 28B (IL28B) (rs8099917) TT genotype, SVR rates tended to be higher in patients with ITPA CC genotype, although the difference was not significant. CONCLUSION: ITPA CC genotype was a disadvantageous factor for Peg-IFNα + RBV treatment in relation to completion rates and RBV dose. However, CC genotype was not inferior to CA/AA genotype for SVR rates. When full-length treatment is accomplished, it is plausible that more SVR is achieved in patients with ITPA CC variant, especially in a background of IL28B TT genotype.

Association of ITPA gene variation and serum ribavirin concentration with a decline in blood cell concentrations during pegylated interferon-alpha plus ribavirin therapy for chronic hepatitis C.

BACKGROUND: Genetic variation leading to inosine triphosphatase (ITPA) deficiency protects chronic hepatitis C patients receiving ribavirin against hemolytic anemia. The relationship between ITPA gene variation and serum ribavirin concentration was analyzed in association with a reduction in blood cells and dose reduction of pegylated interferon (PEG-IFN) or ribavirin. PATIENTS AND METHODS: A total of 300 hepatitis C patients treated with PEG-IFN plus ribavirin were analyzed. Genetic polymorphisms were determined in ITPA and the quantitative reduction in blood cells from the baseline was analyzed every 4 weeks for the duration of treatment and after the end of therapy. The decline in hemoglobin (Hb) or platelet (PLT) level at week 4 compared to baseline was also assessed according to ribavirin concentrations. RESULTS: Patients with the ITPA-CA/AA genotypes showed a lower degree of Hb reduction throughout therapy than those with the ITPA-CC genotype and a marked difference in mean Hb reduction was found at week 4 (CA/AA -1.0 vs. CC -2.8, p < 0.001). The ITPA-CC genotype had significantly less reduction in the mean platelet count than the ITPA-CA/AA genotypes early during treatment (p < 0.001 for weeks 4 and 8). Patients with the ITPA-CA/AA genotypes were less likely to develop anemia, regardless of the concentration of ribavirin. Patients with baseline PLT counts below 130 × 10(3)/µl had a significantly lower tendency to achieve sustained virological response (SVR), especially those with the ITPA-CA/AA genotypes. ITPA gene variation was not extracted by multivariable analysis as an important predictor of SVR. CONCLUSIONS: Despite the fact that ITPA variants were less likely to develop anemia, patients with low baseline PLT counts were difficult to treat, especially those with the ITPA-CA/AA genotype. These results may give a valuable pharmacogenetic diagnostic tool for the tailoring of dosing to minimize drug-induced adverse events.

Association of ITPA polymorphisms rs6051702/rs1127354 instead of rs7270101/rs1127354 as predictor of ribavirin-associated anemia in chronic hepatitis C treated patients.

Functional variants rs7270101 and rs1127354 of inosine triphosphatase (ITPA) were recently found to protect against ribavirin (RBV)-induced hemolytic anemia. However, no definitive data are yet available on the role of no functional rs6051702 polymorphism. Since a simultaneous evaluation of the three ITPA SNPs for hemolytic anemia has not yet been investigated, we aimed to understand the contribution of each SNPs and its potential clinical use to predict anemia in HCV treated patients. A retrospective analysis included 379 HCV treated patients. The ITPA variants rs6051702, rs7270101 and rs1127354 were genotyped and tested for association with achieving anemia at week 4. We also investigated, using multivariate logistic regression, the impact of each single and paired associated polymorphism on anemia onset. All SNPs were associated with Hb decrease. The carrier of at least one variant allele in the functional ITPA SNPs was associated with a lower decrement of Hb, as compared to patients without a variant allele. In multivariate logistic regression analyses the carrier of a variant allele in the rs6051702/rs1127354 association (OR=0.11, p=1.75×10(-5)) and Hb at baseline (OR=1.51, p=1.21×10(-4)) were independently associated with protection against clinically significant anemia at week 4. All ITPA polymorphisms considered were shown to be significantly associated with anemia onset. A multivariate regression model based on ITPA genetic polymorphisms was developed for predicting the risk of anemia. Considering the characterization of pre-therapy anemia predictors, rs6051702 SNP in association to rs1127354 is more informative in order to avoid this relevant adverse event.

Beyond TPMT: genetic influences on thiopurine drug responses in inflammatory bowel disease.

Azathioprine and 6-mercaptopurine are widely used in the management of inflammatory bowel disease (IBD). However, approximately 25% of IBD patients experience toxicity, and up to 10% show resistance to these thiopurine drugs. The importance of genetic variability in determining thiopurine toxicity was first recognized over 25 years ago with the discovery of the thiopurine S-methyltransferase (TPMT) polymorphism and the occurrence of azathioprine-induced myelosuppression in TPMT-deficient patients. In the intervening period, TPMT has become the foremost example of pharmacogenetics, and TPMT deficiency represents one of the few pharmacogenetic phenomena that have successfully made the transition from the research laboratory to diagnostics. While TPMT activity predicts some cases of myelosuppression, deficiency in this enzyme is neither predictive of other adverse drug reactions, nor resistance to thiopurine therapy. As myelosuppression only accounts for approximately 2.5% of adverse reactions in IBD patients, researchers are increasingly turning their attention to other enzymes involved in thiopurine metabolism to find molecular explanations for intolerance and resistance to azathioprine and 6-mercaptopurine. In this review, we summarize the current state of knowledge with regards to TPMT, and also explore genetic variability, beyond TPMT, that may contribute to thiopurine response in IBD patients.

Typing TPMT and ITPase to detect azathioprine toxicity.

Genetic variation in thiopurine methyltransferase (TPMT) enzyme activity strongly predicts adverse effects in patients treated with the thiopurine drugs, azathioprine and 6-mercaptopurine, and is one of the classic examples of pharmacogenetics in clinical practice. Recently, polymorphic variation in the gene encoding the enzyme inosine triphosphatase (ITPase) has also been associated with risk of thiopurine-related toxicity. This article reviews the evidence for the role of TPMT and ITPase deficiency as predictors of thiopurine toxicity and makes recommendations for clinical and laboratory practice.