Pediatric Transplants

Glutathione S-transferase gene variations influence BU pharmacokinetics and outcome of hematopoietic SCT in pediatric patients

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Abstract

BU is a key compound of conditioning regimens in children undergoing hematopoietic SCT (HSCT). Inter-individual differences in BU pharmacokinetics (PKs) might affect BU efficacy and toxicity. As BU is mainly metabolized by glutathione S-transferase (GST), we investigated the relationship between GSTA1, GSTM1 and GSTP1 genotypes with first-dose BU PKs, and the relationship with HSCT outcomes in 69 children receiving myeloablative conditioning regimen. GSTM1 null genotype correlated with higher BU exposure and lower clearance in patients older than 4 years (P0.04). In accordance with the suggested functional role, GSTA1*A2 haplotype was associated with lower drug levels and higher drug clearance (P0.03). Gene-dosage effect was also observed (P0.007). GSTA1 haplotypes were associated with HSCT outcomes. Patients with two copies of haplotype *A2 had better event free survival (P=0.03). In contrast, homozygous individuals for haplotypes *B and *B1 had higher occurrence of veno-occlusive disease (P=0.009). GSTM1 null individuals older than 4 years had more frequently graft versus host disease (P=0.03). In conclusion, we showed that GST gene variants influence BU PK and outcomes of HSCT in children. A model for the dosage adjustment with the inclusion of genetic and non-genetic factors should be evaluated in a future prospective validation cohort.

Introduction

BU is a key component of myeloablative regimens given before hematopoietic SCT (HSCT).1 Inter-individual variation in BU plasma levels is observed even when BU is administered by the i.v. route.2, 3 There is no consensus on the optimal therapeutic window of i.v. BU in pediatric patients; although studies have shown improved outcomes at steady-state concentrations (Css) of 600–900 ng/mL, when a conventional dosing schedule is followed.3, 4, 5, 6 There is an increased incidence of adverse events such as veno-occlusive disease (VOD), pulmonary toxicity and graft versus host disease (GVHD) at higher concentrations and graft failure or disease relapse at lower concentrations in pediatric and adult patients.4, 7, 8 To decrease the occurrence of toxicity and to improve efficacy, therapeutic drug monitoring is performed to adjust BU dose based on the first-dose pharmacokinetics (PKs).6, 8 In addition to the PK-guided dosing of BU, prediction of inter-individual variability in BU levels before its administration would be helpful in individualizing BU treatment.

BU is primarily metabolized by liver glutathione S-transferase enzymes (GST), predominantly by GSTA1.9, 10 GSTM1 and GSTP1 are also involved in BU metabolism but to a lesser extent.9, 11 BU metabolism is affected by GST enzyme activity, which is influenced by age, disease condition and co-medication.2, 12, 13, 14 Body weight and body surface area have been also shown to contribute to PK variability.15, 16, 17, 18, 19 Nevertheless, a large proportion of BU variability remains unexplained20 and could be due to GST polymorphisms influencing GST activity21, 22, 23, 24, 25 (Table 1). Although some studies have shown that GSTA1 genotypes influence the PK of oral and i.v. BU in both adults and children;17, 26, 27, 28, 29, 30 others did not find this association.15, 31, 32 In a small pilot study, we have shown that polymorphisms in GSTM1 might influence the PK of BU.15 The present work was undertaken to confirm this finding and to allow more detailed insight into GST variants in a larger cohort.

Table 1 Common genetic variants of GSTA1, GSTM1 and GSTP1 selected for the study

Materials and methods

Patients

This study comprises 69 consecutive patients (including 28 from earlier study15; 32 men, 37 women, median age 6.5) who underwent allogeneic HSCT with i.v. BU at CHU Sainte-Justine, between May 2000 and August 2010. The review board approved the study and all patients/parents provided informed consent. The demographic characteristics of the patients, details of disease and transplantation are given in Table 2.

Table 2 Demographic characteristics, details of diseases and transplantation in study subjects (n=69)

Treatment regimen

I.v. BU (Busulfex, Otsuka Pharmaceuticals, Saint-Laurent, Montreal, QC, Canada). was administered as a 2-h infusion every 6 h from day −9 to −6. BU first dose was based on the age of the patient (infants3 months and 1 year of age and children4 years old received 0.8 mg/kg dose, children1 year and 4 years old received 1 mg/kg dose) and PK-guided dose adjustment was performed from the fifth dose onward.15 All the patients received 16 doses of BU followed by, i.v. CY (200 mg/kg total dose; n=62; Table 2). Cyclosporine was given as GVHD prophylaxis, and MTX or steroids were added for BM/peripheral blood and cord blood transplantation, respectively (Table 2). G-CSF was used after cord blood transplantation only. Prophylaxis for seizure included midazolam lorazepam or phenytoin. Fluconazole, acyclovir and trimethoprim/sulfamethoxazole were given as anti-infectious prophylaxis and acid ursodeoxycholic as VOD prophylaxis.

Definition of clinical outcomes

Diagnostic criteria for adverse events are detailed elsewhere.15 In brief, VOD was diagnosed according to the Seattle criteria33 and acute (a)GVHD was based on the 1994 Consensus Conference.34 Neutrophil and platelet recoveries were defined as absolute count 0.5 × 109/L for the first 3 consecutive days and 50 × 109/L without transfusion for the first 10 consecutive days from the day of transplant, respectively. Overall survival (OS) was the time between day of transplant and death because of any cause, whereas event free survival (EFS) was the time from day of transplant to the day of occurrence of any event that is, death, relapse or graft failure, whichever is seen first. OS was 83% at 1 year and EFS was 69% at 1 year. Details are also provided in the Table 3a.

Table 3A Clinical outcomes observed in the study subjects

PK analysis and genotyping

Five blood samples were collected after the first-dose infusion and were used for estimation of BU levels using an established analytical method.35 The PK parameters were estimated from the first dose using non-compartmental analysis (WinNonlin, version 3.1, Pharsight, Montreal, QC, Canada) and further doses from fifth dose onward were adjusted to achieve BU Css of 600–900 ng/mL. PK data are represented in terms of maximum concentration (Cmax), area under the curve (AUC), Css and clearance (CL; Table 3b).

Table 3B BU pharmacokinetic parameters observed in the study subjects (n=69)

Patients were genotyped for the common polymorphisms (Table 1) in GSTA1 and GSTP1 by allele-specific oligonucleotide hybridization.15 GSTM1 null allele was detected by gel electrophoresis.36

Statistical analysis

BU PK parameters (Cmax, AUC, Css and CL) and dose adjustment were compared across genotypes of GSTA1, GSTP1 and GSTM1 or between carriers and non-carriers of particular GSTA1 haplotype subtypes using non-parametric tests. Depending on the results obtained, appropriate genetic models (dominant, recessive or additive) for particular genotypes–haplotypes were subsequently derived. Non-parametric or χ2-tests were used to test differences in gender and age between different genotype groups. Linear regression was used to test gene-dosage effect and to assess the effect of genotypes on Cmax, AUC, Css and CL in a multivariate model with the inclusion of other covariates (age, gender, weight and BU dose). Survival (OS and EFS) was estimated using Kaplan–Meier curves and log-rank test was used to compare the differences between genotype groups in univariate analysis. EFS analysis for particular genotype was also performed when the event and follow-up were truncated to 1-year post HSCT. The cumulative incidence of engraftment or HSCT-related toxicity (VOD, aGVHD grades 1–4, lung toxicity, hemorrhagic cystitis, or any of these toxicities, whichever was seen first) in relation to the GST genotypes was estimated by one-survival curves using Kaplan–Meier analysis and log-rank test. Frequency of all toxic events between particular genotype groups was compared by χ2-test. Univariate Cox regression analysis was used to estimate hazard ratio (HR) with 95% confidence interval (CI); multivariate Cox regression was used to estimate the impact of genotypes on clinical outcomes in the presence of other covariates (same as above). Logistic regression was used to estimate percentage of variability in clinical outcomes because of genetic/non-genetic factors. Kaplan–Meier functions were used to assess relationship between PK data (categorical variable with four different categories corresponding to quartile distribution) and clinical outcomes. All PK parameters showed similar results; Css is used to present the data. Haplotypes were resolved using PHASE (version 2.1).37 Statistical analyses were performed using IBM SPSS statistics (version 19, SPSS Inc., New York, NY, USA).

Results

Genetic variants of GSTA1, M1, P1 and BU PKs

Overall PK distribution is given in Table 3b. The minor allele frequencies and GSTA1 haplotypes of patients analyzed are given in Table 4 and that of GSTM1 and GSTP1 in Supplementary Table 1.

Table 4 GSTA1 haplotypes and minor allele frequencies in the study population (n=69)

The GSTA1*A and *B haplotypes, defined by the 69C>T substitution, are further subdivided based on the presence or absence of minor alleles at positions –631, −1142 and −531 (Table 4). No significant association of GSTA1 genotypes with BU PK was observed when each GSTA1 polymorphism was analyzed individually. However, when haplotype-based analysis was performed, significant differences (P0.03) for each PK parameter analyzed (Cmax, Css, AUC and CL) was noted between the carriers and non-carriers of GSTA1*A2 haplotype (Figure 1a). Carriers had significantly lower AUC, Cmax and Css and higher CL compared with non-carriers. Similar differences were seen between two groups when the PK parameters (Cmax, Css and AUC) were normalized with BU first dose (mg/kg, P0.03, data not shown). The gene-dose effect of GSTA1*A2 haplotype was also observed (Figure 1b). Decrease in BU levels represented by Css (P=0.007) and increase in CL (P=0.005) correlated with the number of GSTA1*A2 haplotypes, being highest in individuals homozygous for that haplotype. No other GSTA1 haplotype correlated with BU PK.

Figure 1
figure1

Influence of GSTA1*A2 haplotypes on BU PKs. (a) Cmax, Css and AUC in GSTA1*A2 haplotype carriers (+, n=28) and non-carriers (−, n=41). Median (interquartile range) for Cmax, Css and AUC are 810 (684.25–863.25), 544.5 (494.75–631.75) and 184 973 (164 193–215 396) for *A2 carriers, respectively. Respective values for *A2 non-carriers are 855 (786–1045.5), 616 (538–723) and 210 607 (180 729–249 128). The units of measurements are given on the respective plot. (b) Gene-dose effect of GSTA1*A2 on BU first-dose PKs. 0, 1 and 2 refer to number of GSTA1*A2 haplotypes. The mean±s.d. for Css is 652.9±187.3 in group (0), 578.8±129.5 in group (1) and 490±100.7 in group (2). The mean±s.d. for CL is 3.9±1.0 in group (0), 4.49±1.1 in group (1) and 5.0±1.2 in group (2). The number of individuals represented for each haplotype group as well as P-values for the change across groups is given on each plot.

BU levels adjusted by dose (mg/kg) differed significantly (P0.001, data not shown) between individuals below (n=26) and above 4 years of age (n=43), suggesting the influence of age along with the genetic parameters studied. Similarly, Cmax distribution differed between males and females (P=0.04, data not shown). This prompted us to further investigate the association between GST genotype and BU PK on stratification by gender or age. In accordance with our previous report,15 GSTM1 association with PK was apparent in individuals above 4 years of age receiving uniform BU dose (0.8 mg/kg). The patients with GSTM1 null genotype had higher Cmax (P=0.02), and lower CL (P=0.04) compared with those with non-null genotype. A trend was observed for Css (P=0.07) and AUC (P=0.06), with null individuals having higher values compared with non-null individuals (Figure 2). The association of GSTA1 haplotype *A2 was particularly apparent in females (Supplementary Figure 1). No age-dependent correlation between PK and GSTA1 genotypes or gender-dependent GSTM1-PK correlation was noted. Finally, no correlation between GSTM1 and GSTA*A2 genotypes and age or gender of patients was seen.

Figure 2
figure2

Influence of GSTM1 genotypes on BU first-dose PKs in children older than 4 years. The PK parameters of BU measured in patients4 years and grouped based on GSTM1 genotypes: +: patients with GSTM1 null genotype (n=16); −: patients with non-null genotype (n=27). The median values with (interquartile range) for Cmax, Css, AUC and CL for GSTM1 null individuals are 894.7 (820.75–1075.75), 632 (555.5–772.5), 219 442 (187 341–267 710) and 3.6 (2.9–4.16). The respective values for non-null individuals are 798 (705–930), 575 (497–671), 196 086 (167 148–233 873) and 4.09 (3.37–4.46).

In a multivariate regression model that included age, gender, BU dose and weight as covariates, genotypes remained associated with BU PK (CL, P=0.03 for GSTA1*A2 and 0.04 for GSTM1 null; Css, P=0.04 for both genotypes; AUC, P=0.02 for both genotypes; Cmax, P=0.01 for GSTA1*A2 and 0.007 for GSTM1 null). The model with both genotypes and non-genetic covariates explained 47–54% of variability in PK with genetic factors contributing to 14–17% of this variability.

The ratio of adjusted dose to initial dose was used to compare the increment or decrement of dose according to genotype. GSTM1 null individuals received lower BU dose compared with GSTM1 non-null individuals (P=0.03; Figure 3a). Patients who are homozygous for GSTA*A2 haplotype had a higher increase in dose compared with remaining individuals (P=0.02, Figure 3a). In spite of dose adjustment, Css after eighth dose (available for 50 patients), although within the target range, was still significantly lower in *A2 carriers, compared with non-carriers (P=0.007, Figure 3b). No such relationship was seen for GSTM1 genotype. No correlation between GSTP1 genotypes and PK was observed.

Figure 3
figure3

BU dose adjustment and Css values following PK-guided dose adjustment and relation to GST genotype. (a) Dose adjustment in individuals with GSTA1*A2*A2 and GSTM1 null genotype calculated as ratio between adjusted and non-adjusted dose. Median ratio with (interquartile range (IQR)) for *A2*A2 carriers is 1.5 (1.2–1.9) and for non-carriers is 1.2 (1.0–1.4). Median ratio with (IQR) for GSTM1 null individuals is 1.1 (1.0–1.3) and for non-null individuals is 1.3 (1.1–1.6). (b) Css following eighth BU dose in carriers and non-carriers of GSTA1*A2 haplotype. Median ratio with (IQR) for *A2 carriers is 721.9 (634.6–842.8) and for non-carriers is 849 (771.2-906.5). ‘+’ and ‘−’, presence and absence of indicated haplotype–genotype, respectively; number of individuals represented by each genotype group and P-value for the difference between groups is given on each plot.

Genetic variants of GSTA1, M1, P1 and clinical outcomes of HSCT

Details of clinical outcomes are given in Table 3a. Patients with two copies of haplotype GSTA1*A2 had better EFS (100% vs 54%, P=0.03, Figure 4a). No event occurred in *A2 homozygotes (n=8), whereas events occurred in 26 out of the remaining 61 individuals. Gene-dosage effect was seen for EFS only at 1 year after HSCT (P=0.03, data not shown). Reduction of toxicity was observed in *A2 homozygotes; only one patient had VOD and none had hemorrhagic cystitis, lung toxicity or aGVHD (P=0.01 for number of all toxic events combined and P=0.06 for cumulative incidence of any toxicity). To verify whether these associations are due to *A2–PK relationship, we analyzed an association between Css and EFS and between Css and toxic events. Similar to our previous study,38 lower Css was associated with better EFS (P<0.0005, data not shown); higher Css correlated with higher cumulative incidence of any toxicity (P=0.005, data not shown) and with each individual toxicity (aGVHD, lung toxicity and hemorrhagic cystitis, P0.03) except VOD.

Figure 4
figure4

Association of GST1A1 haplotypes with EFS, the risk of VOD and acute GVHD (aGVHD). (a) Association of GST1A1 haplotypes with EFS. The number of patients in each curve representing the patients with or without indicated genotype, number of individuals with an event (in the parenthesis), as well as the p value, estimated by log-rank test for the survival differences between the patients groups, are indicated on the plot. (b, c) Association of GST1A1 genotypes with the risk of VOD. The number of patients in each curve with and without *B*B (b, left panel and c) and with and without *B1*B1 haplotype pair (right panel in b), number of individuals with VOD (given in the parenthesis), as well as the P-value, estimated by log-rank test for the cumulative VOD incidence between the haplotype groups, are indicated on each plot. Results in b include all patients, and in c are limited to females only. Risk of VOD associated with the *B*B (represented by −69TT) and *B1*B1 (represented by −1142GG genotype) expressed as HR with 95% CI, is indicated below respective plots. (d) Association of GSTM1 null genotype with the risk of aGVHD. The number of patients in each curve with and without GSTM1 null genotype, number of individuals with aGVHD (given in the parenthesis), as well as the P-value, estimated by log-rank test for the cumulative aGVHD (grades 1–4) incidence between the genotype groups, are indicated on each plot. The analyses are limited to the patients above 4 years of age.

Association analyses between GST genotypes and HSCT-related toxicities indicated that homozygous GSTA1 −69 TT and −1142 GG patients had higher occurrence of VOD. As shown in Table 4, the T allele of −69C>T defines haplotype *B (all haplotypes *B combined) and G allele of −1142C>G defines haplotype *B1, therefore the same results are obtained with these haplotypes. VOD was seen in 43% homozygous *B or *B1 individuals compared with 9.6% in remaining patients (HR=5.3, 95% CI= 1.3–21.5, P=0.009; Figure 4b). The effect seems to be modulated by gender, being more apparent in girls than in boys (75% vs 12.5%, HR=9.6; 95% CI=2.0–45.1, P=0.001; Figure 4c). GSTM1 null individual above age of 4 had more frequently aGVHD (grades 1–4, 44% vs 17%, HR=3.8, 95% CI=1.1–13.7, P=0.03; Figure 4d). Genotypes remained significantly associated with clinical outcomes in multivariate models that included age, gender, BU dose and weight as covariates. Genetic and non-genetic factors explained 26% of EFS variability (with 11% of GSTA1*A2 contribution, P=0.05), 26% of VOD variability (with 19% of GSTA1*B contribution, P=0.04) and 32% of aGVHD variability (with 10% of GSTM1 null contribution). No other significant association between GST genotypes–haplotypes and HSCT clinical outcomes was seen.

Discussion

GST genetic variants and BU PK variability

Analysis of GSTA1 genotypes–haplotypes revealed significant associations with BU exposure. An increase in BU CL and reduction in drug levels following the first dose was seen in individuals with GSTA1*A2 haplotype. Gene-dosage effect was also noted. Our observation is in accordance with the functional studies suggesting higher GSTA activity in GSTA1*A carriers10, 22, 24 and is also supported by several previous reports.17, 26, 27, 28, 29, 30 Decreased CL following oral BU was seen in adults and children with GSTA*B haplotype;17, 29, 31 a significant decrease in CL following i.v. BU was observed in pediatric GSTA1*B patients;21, 22 and accordingly increased BU CL correlated with GSTA1*A haplotype.17, 39 However, a few studies conducted in adults and children15, 31, 32 failed to show such an association, which might be due to low sample size,15 different BU dosing schedules,31, 32 dose adjustment, or varying proportions of non-malignant diseases.15, 31, 32 Use of phenytoin31 or different methods of estimating BU PK might also have contributed to the conflicting observations. Our study included patients receiving only myeloablative conditioning regimen with i.v. BU in a conventional dosing schedule with a small proportion of hemoglobinopathy (<15%) and only three patients that received phenytoin for seizure prevention. Patients were also categorized into specific subtypes of GSTA1*A/*B haplotypes allowing more detailed insight into the GSTA1 gene effect. We also noted a gender-dependent effect of GSTA1 genotype. GSTA1*A haplotype influence on BU metabolism might be more prominent in females as they were shown to have lower cytosolic GST activity compared with males.40

We confirmed our previous findings on association of GSTM1 genotypes with BU exposure.15 GSTM1 null genotypes were significantly associated with higher BU levels and lower BU CL in individuals older than 4 years, which can be explained, to a certain extent, by increased GSTM1 involvement of BU metabolism in older children with moderate or reduced GSTA activity.6 Observations from our study are not in agreement with a report by Srivastava et al.,41 who showed enhanced CL and low Css of oral BU in thalassemia children carrying GSTM1 null genotype. Another study conducted in adult patients found reduced i.v. BU CL in individuals with combined GSTM1 and GSTT1 null genotypes, but not in individuals with GSTM1 null genotype alone,39 whereas others reported absence of such association.17, 26, 27, 30, 31, 32 The compensatory action of other GST isoforms to defective enzyme activity has been also demonstrated.39 We did not find clear combined effect or interaction between GSTM1 and GSTA1 genotypes. However, it is worth noting that the distribution of the genotypes was not completely random. All individuals that were GSTA*A2 carriers also had GSTM1 non-null genotype, that is, there was no individuals that had GSTA*A2 and GSTM1 null genotype combination; hence the combined GSTA1/GSTM1 effect cannot be ruled out.

Multiple linear regression analysis showed that genetic factors contribute to 14–17% of the variability in BU PK compared with non-genetic factors alone (30%). This is similar to studies conducted in adults that have reported that GSTA1 polymorphisms could account for 15–18% of the variability in first-dose BU CL, and in line with the unexplained variability of BU CL among pediatric patients reported in a recent meta-analysis.16, 30, 39

Homozygous GSTA1*A2 individuals had an augmentation of BU dose, owing to increased CL of BU. Although reaching the target level, *A2 carriers had still lower Css after the eighth dose as compared with non-carriers, which may suggest the need to reduce the BU dose in patient without *A2 haplotype. Wide ranges in the requirement of BU dose was nevertheless seen in individuals with no GSTA1*A2 homozygosity, which might be due to age, presence of single GSTA1*A2 copy, GSTM1 or other genotypes. GSTM1 null individuals had subsequently received lower BU doses than non-null individuals explained by lower CL in GSTM1 null patients.

No significant association of GSTP1 genotypes with BU exposure was found confirming our previous observation15 and is in agreement with earlier studies.15, 17, 26, 30, 32

GST genetic variants and clinical outcomes of HSCT

Better EFS was seen in homozygous GSTA1*A2 patients, which is likely due to a significantly lower BU levels seen in these individuals. Indeed, lower Css correlated with better EFS, which is in accordance with our observation38 and with previous reports.19 It is worth noting that Css in GSTA1*A2 carriers following dose adjustment, was on average in the target range but did not exceed the target concentrations and was significantly lower than in individuals without this haplotype, which might resulted in lower toxicity. Indeed, overall reduction in toxicity was noted for homozygous GSTA1*A2 patients, further supported by correlation between lower Css and less frequent toxicity. This finding might support previous observation of decreased incidence of GVHD in GSTA1*A/*A patients.28

We have also shown that individuals that are homozygous for either haplotype *B or *B1, respectively, had higher incidence of VOD. Haplotype *B was reported to confer decreased GSTA1 activity,22 suggesting higher BU level in such individuals. Higher AUC levels were indeed reported to correlate with VOD.42 We have not, however, found either significant association between Css and VOD or between *B (*B1) haplotype and PK, which can be due to low VOD and/or genotype numbers, but also involvement of BU-independent mechanism. For example, liver toxicity could be influenced by CY, including time of its administration relative to BU.43, 44 Higher levels of toxic metabolites of CY in GSTA*B homozygotes can also contribute to VOD development, in which case administration of CY after BU would be detrimental. This finding is nevertheless contrary to the hypothesis that increased activity of GSTA in GSTM1 null individuals might deplete GSH causing damage to liver and occurrence of VOD.41 None of the few studies that looked into an association between GST genotypes and clinical outcomes17, 28, 32 reported correlation between GSTA1 genotypes and EFS or VOD, which may be due to the low incidence of VOD, inclusion of patients on non-myeloablative regimen, other events, non-investigated factors that may potentiate GSTA1 effect (for example, gender), dose adjustment or low sample size. We did not observe any association of VOD with GSTM1 genotypes, in agreement with previous studies15, 17, 28 and contrary to a report on higher VOD incidence in GSTM1 null carriers, which could be attributed to the different patient population.41 And finally, our finding of higher GVHD frequency in GSTM1 null individuals in agreement with previous report.17. This could be explained by observed GSTM1 nullPK relationship, further supported by an association between higher Css and higher incidence of aGVHD.

In conclusion, we showed that GST gene variants influence BU PK and outcomes of HSCT in children. A model for the dosage adjustment with the inclusion of genetic and non-genetic factors should be evaluated in a future prospective validation cohort. Predicting BU dose before initiation of therapy will be helpful to achieve better clinical outcomes in pediatric patients and pave the way for individualized BU treatment according to the individual patient’s genetic profile.

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Acknowledgements

We are thankful to all patients and their parents for consenting to participate in this study. This investigation was supported by grants provided by the Geneva Cancer League, CANSEARCH, Hans Wilsdorf, Telemaque and Charles Bruneau foundations. We thank the Swiss Oncology Group as our sponsor and the European Blood and Marrow Transplantation Pediatric (EBMT) working disease group for their support and for labeling this study as an EBMT trial. This study has been fully registered in a public trials registry as part of an ongoing prospective EBMT multicentric study (register at Clinical Trials.gov, NCT01257854). It is submitted on behalf of the Pediatric Disease Working Parties of the European Blood and Marrow Transplant group and is an EBMT label study (EudraCT number: 2009-018105-41).

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Correspondence to M Ansari or M Krajinovic.

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The authors declare no conflict of interest.

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Supplementary Information accompanies the paper on Bone Marrow Transplantation website

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Ansari, M., Rezgui, M., Théoret, Y. et al. Glutathione S-transferase gene variations influence BU pharmacokinetics and outcome of hematopoietic SCT in pediatric patients. Bone Marrow Transplant 48, 939–946 (2013) doi:10.1038/bmt.2012.265

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Keywords

  • Busulfan
  • hematopoietic SCT
  • pharmacokinetics
  • children
  • GST
  • pharmacogenetics

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