A Hypomorphic PALB2 Allele Gives Rise to an Unusual Form of FA-N Associated with Lymphoid Tumour Development.

Patients with biallelic truncating mutations in PALB2 have a severe form of Fanconi anaemia (FA-N), with a predisposition for developing embryonal-type tumours in infancy. Here we describe two unusual patients from a single family, carrying biallelic PALB2 mutations, one truncating, c.1676_1677delAAinsG;(p.Gln559ArgfsTer2), and the second, c.2586+1G>A; p.Thr839_Lys862del resulting in an in frame skip of exon 6 (24 amino acids). Strikingly, the affected individuals did not exhibit the severe developmental defects typical of FA-N patients and initially presented with B cell non-Hodgkin lymphoma. The expressed p.Thr839_Lys862del mutant PALB2 protein retained the ability to interact with BRCA2, previously unreported in FA-N patients. There was also a large increased chromosomal radiosensitivity following irradiation in G2 and increased sensitivity to mitomycin C. Although patient cells were unable to form Rad51 foci following exposure to either DNA damaging agent, U2OS cells, in which the mutant PALB2 with in frame skip of exon 6 was induced, did show recruitment of Rad51 to foci following damage. We conclude that a very mild form of FA-N exists arising from a hypomorphic PALB2 allele.

Parallel targeted next generation sequencing of childhood and adult acute myeloid leukemia patients reveals uniform genomic profile of the disease.

The age-specific differences in the genetic mechanisms of myeloid leukemogenesis have been observed and studied previously. However, NGS technology has provided a possibility to obtain a large amount of mutation data. We analyzed DNA samples from 20 childhood (cAML) and 20 adult AML (aAML) patients, using NGS targeted sequencing. The average coverage of high-quality sequences was 2981 × per amplicon. A total of 412 (207 cAML, 205 aAML) variants in the coding regions were detected; out of which, only 122 (62 cAML and 60 aAML) were potentially protein-changing. Our results confirmed that AML contains small number of genetic alterations (median 3 mutations/patient in both groups). The prevalence of the most frequent single gene AML associated mutations differed in cAML and aAML patient cohorts: IDH1 (0 % cAML, 5 % aAML), IDH2 (0 % cAML, 10 % aAML), NPM1 (10 % cAML, 35 % aAML). Additionally, potentially protein-changing variants were found in tyrosine kinase genes or genes encoding tyrosine kinase associated proteins (JAK3, ABL1, GNAQ, and EGFR) in cAML, while among aAML, the prevalence is directed towards variants in the methylation and histone modifying genes (IDH1, IDH2, and SMARCB1). Besides uniform genomic profile of AML, specific genetic characteristic was exclusively detected in cAML and aAML.

Functional Analysis of an (A)γ-Globin Gene Promoter Variant (HBG1: g.-225_-222delAGCA) Underlines Its Role in Increasing Fetal Hemoglobin Levels Under Erythropoietic Stress.

Hereditary persistence of fetal hemoglobin (HPFH) is a condition characterized by persistent γ-globin gene expression and synthesis of high levels of fetal hemoglobin (Hb F; α2γ2) during adult life. It is usually caused by promoter variants or large deletions affecting the human fetal globin (HBG1 and HBG2) genes. Some of these HPFH-causing variants, such as HBG2: g.-158 C > T, exert their effect only under conditions of erythropoietic stress, typical for ß-thalassemia (ß-thal) patients. Namely, the presence of HBG2: g.-158 C > T favors a higher Hb F response, while it has little effect in healthy individuals. We analyzed a previously reported deletion residing in the promoter region of the HBG1 gene (HBG1: g.-225_-222delAGCA), both in normal conditions and under conditions of erythropoietic stress. Our results indicate that this deletion is responsible for decreased HBG1 gene expression. Specifically, this deletion was shown to result in drastically reduced reporter gene expression in K562 cells, compared to the wild-type sequence but only under conditions of erythropoietic stress, mimicked by introduction of erythropoietin (EPO) into the cell culture. Also, electrophoretic mobility shift analysis showed that the HBG1: g.-225_-222delAGCA deletion creates additional transcriptional factors' binding sites, which, we propose, bind a transcriptional repressor, thus decreasing the HBG1 gene promoter activity. These results are consistent with in silico analysis, which indicated that this deletion creates a binding site for GATA1, known to be a repressor of the γ-globin gene expression. These data confirm the regulatory role of the HBG1: g.-225_-222 region that exerts its effect under conditions of erythropoietic stress characteristic for ß-thal patients.

Functional analysis of a novel KLF1 gene promoter variation associated with hereditary persistence of fetal hemoglobin.

Hereditary persistence of fetal hemoglobin (HPFH) is a rare hereditary condition resulting in elevated levels of fetal hemoglobin (HbF) in adults. Typical HPFH is associated with promoter mutations or large deletions affecting the human fetal globin (HBG1 and HBG2) genes, while genetic defects in other genes involved in human erythropoiesis, e.g. KLF1, also result in atypical HPFH. Here, we report the first KLF1 gene promoter mutation (KLF1:g.-148G > A) that is associated with increased HbF level. This mutation was shown to result in drastically reduced CAT reporter gene expression in K562 cells, compared to the wild-type sequence (p = 0.009) and also in reduced KLF1 gene expression in vivo. Furthermore, consistent with in silico analysis, electrophoretic mobility shift analysis showed that the KLF1:g.-148G > A mutation resides in a Sp1 binding site and further that this mutation leads to the ablation of Sp1 binding in vitro. These data suggest that the KLF1:g-148G > A mutation could play a role in increasing HbF levels in adults and further underlines the role of KLF1 as one of the key transcription factors involved in human fetal globin gene switching.

Colon carcinoma in a child treated with oxaliplatin and antiangiogenic treatment regimens.

Colorectal carcinoma is an extremely rare tumor in childhood. Therefore, the role of adjuvant chemotherapy has not been adequately evaluated in children leading to limited data on safety profile and treatment response after application of novel drugs and novel targeted agents. In this report, we describe a case of colon adenocarcinoma in a 13-year-old girl treated with standard adult treatment as well as novel targeted therapy. This case report illustrates initial good disease control with FOLFOX therapy. On the other hand, targeted therapy revealed no improvement in disease control and good safety profile without significant adverse effects.

Pediatric non-Hodgkin lymphoma: a retrospective 14-year experience with Berlin-Frankfurt-Münster (BFM) protocols from a tertiary care hospital in Serbia.

Use of current intensive chemotherapy protocols in pediatric non-Hodgkin lymphoma (NHL) in high-income countries resulted in event-free survival (EFS) rates ranging from 80 to 90%. The results are inferior in less privileged countries with limited resources for medical care. There are no reports about comprehensive data analysis in pediatric NHL in Serbia. A retrospective study was carried out at University Children's Hospital, Belgrade, in children aged less than 18 years diagnosed with non-Hodgkin lymphoma from 1997 to 2011. Fifty-seven children were eligible for analysis. Fourteen were diagnosed with lymphoblastic lymphoma, 38 with mature B-cell NHL (B-NHL), and 5 with anaplastic large-cell lymphoma. Mean age at diagnosis was 9.2 years, with male to female ratio 2.35:1. Children were treated according to Berlin-Frankfurt-Münster (BFM) protocols. With median follow-up of 59.3 months, 5-year probability of EFS was 84.1% for all patients, whereas overall survival was 93%. These results with BFM protocol administration, although inferior to leading international groups, reflect good treatment outcome in our patients. To the best of the authors' knowledge, this article presents the first results regarding treatment and survival of childhood NHL in Serbia.

Thalassemia syndromes in Serbia: an update.

Thalassemia syndromes constitute a group of genetic disorders, widespread throughout the world. The present study contains data on thalassemia syndromes and their chromosomal environment obtained in Serbia over a period of 10 years. Ten different ß-thalassemia (ß-thal) mutations and two hemoglobin (Hb) variants were detected in 127 members of 68 families. Hb Lepore-Boston-Washington (Lepore-BW) (δ87Gln-ß-IVS-II-8), a thalassemic Hb variant, was shown to be the most common cause of thalassemia in Serbia. Haplotype analyses of the ß-globin gene clusters of healthy individuals as well as of individuals affected with ß-thal showed that haplotype I was the most frequent haplotype in the Serbian population, followed by haplotypes II and IX. Two novel haplotypes were detected. Haplotype analyses showed the association between certain haplotypes and the most common thalassemic mutations. Results presented in this paper will update the Serbian national mutation database and contribute to a better understanding of genographic history of South European and Balkan populations.

Late vitamin K deficiency bleeding in an infant with choledochal cyst.

Infantile choledochal cyst (CC) usually presents as jaundice, vomiting, acholic stools, and hepatomegaly, and it can resemble biliary atresia. Although bleeding tendency is a rare clinical presentation of CC, it can be the first symptom, especially in infants less than 12 months of age. We report a case of a two-month-old infant with choledochal cyst presenting as late vitamin K deficiency bleeding (VKDB). Early recognition of diseases predisposing to VKDB and immediate investigation and treatment of warning bleeds help to prevent the worst consequences. Late VKDB is often the presenting feature of a serious underlying disease that may be recognized early. The sudden onset of bleeding tendency in infants with congenital liver or biliary tract disease may suggest not only biliary atresia but also, although extremely rare, CC. Early vitamin K administration leads to rapid normalization of hemostatic parameters, which enables major liver surgery.

Pharmacogenomic Markers of Methotrexate Response in the Consolidation Phase of Pediatric Acute Lymphoblastic Leukemia Treatment.

Methotrexate (MTX) is one of the staples of pediatric acute lymphoblastic leukemia (ALL) treatment. MTX targets the folate metabolic pathway (FMP). Abnormal function of the enzymes in FMP, due to genetic aberrations, leads to adverse drug reactions. The aim of this study was to investigate variants in pharmacogenes involved in FMP and their association with MTX pharmacokinetics (MTX elimination profile) and toxicity in the consolidation therapy phase of pediatric ALL patients. Eleven variants in the thymidylate synthetase (TYMS), methylenetetrahydrofolate reductase (MTHFR), dihydrofolate reductase (DHFR), SLC19A1 and SLCO1B genes were analyzed in 148 patients, using PCR- and sequencing-based methodology. For the Serbian and European control groups, data on allele frequency distribution were extracted from in-house and public databases. Our results show that the A allele of SLC19A1 c.80 variant contributes to slow MTX elimination. Additionally, the AA genotype of the same variant is a predictor of MTX-related hepatotoxicity. Patients homozygous for TYMS 6bp deletion were more likely to experience gastrointestinal toxicity. No allele frequency dissimilarity was found for the analyzed variants between Serbian and European populations. Statistical modelling did not show a joint effect of analyzed variants. Our results indicate that SLC19A1 c.80 variant and TYMS 6bp deletion are the most promising pharmacogenomic markers of MTX response in pediatric ALL patients.

Application of targeted next generation sequencing for the mutational profiling of patients with acute lymphoblastic leukemia.

BACKGROUND: Acute lymphoblastic leukemia (ALL) is the most common cancer in children, whereas it is less common in adults. Identification of cytogenetic aberrations and a small number of molecular abnormalities are still the most important risk and therapy stratification methods in clinical practice today. Next generation sequencing (NGS) technology provides a large amount of data contributing to elucidation of mutational landscape of childhood (cALL) and adult ALL (aALL). METHODS: We analyzed DNA samples from 34 cALL and aALL patients, using NGS targeted sequencing TruSeq Amplicon - Cancer Panel (TSACP) which targets mutational hotspots in 48 cancer related genes. RESULTS: We identified a total of 330 variants in the coding regions, out of which only 95 were potentially protein-changing. Observed in individual patients, detected mutations predominantly disrupted Ras/RTK pathway (STK11, KIT, MET, NRAS, KRAS, PTEN). Additionally, we identified 5 patients with the same mutation in HNF1A gene, disrupting both Wnt and Notch signaling pathway. In two patients we detected variants in NOTCH1 gene. HNF1A and NOTCH1 variants were mutually exclusive, while genes involved in Ras/RTK pathway exhibit a tendency of mutation accumulation. CONCLUSIONS: Our results showed that ALL contains low number of mutations, without significant differences between cALL and aALL (median per patient 2 and 3, respectively). Detected mutations affect few key signaling pathways, primarily Ras/RTK cascade. This study contributes to knowledge of ALL mutational landscape, leading to better understanding of molecular basis of this disease.

Pharmacogenomic and Pharmacotranscriptomic Profiling of Childhood Acute Lymphoblastic Leukemia: Paving the Way to Personalized Treatment.

Personalized medicine is focused on research disciplines which contribute to the individualization of therapy, like pharmacogenomics and pharmacotranscriptomics. Acute lymphoblastic leukemia (ALL) is the most common malignancy of childhood. It is one of the pediatric malignancies with the highest cure rate, but still a lethal outcome due to therapy accounts for 1%⁻3% of deaths. Further improvement of treatment protocols is needed through the implementation of pharmacogenomics and pharmacotranscriptomics. Emerging high-throughput technologies, including microarrays and next-generation sequencing, have provided an enormous amount of molecular data with the potential to be implemented in childhood ALL treatment protocols. In the current review, we summarized the contribution of these novel technologies to the pharmacogenomics and pharmacotranscriptomics of childhood ALL. We have presented data on molecular markers responsible for the efficacy, side effects, and toxicity of the drugs commonly used for childhood ALL treatment, i.e., glucocorticoids, vincristine, asparaginase, anthracyclines, thiopurines, and methotrexate. Big data was generated using high-throughput technologies, but their implementation in clinical practice is poor. Research efforts should be focused on data analysis and designing prediction models using machine learning algorithms. Bioinformatics tools and the implementation of artificial i Lack of association of the CEP72 rs924607 TT genotype with intelligence are expected to open the door wide for personalized medicine in the clinical practice of childhood ALL.

Influence of variants in folate metabolism genes on 6-mercaptopurine induced toxicity during treatment for childhood acute lymphocytic leukemia.

PURPOSE: To analyze influence of variants in TYMS, MTHFR, SLC19A1 and DHFR genes on 6-mercaptopurine (MP) induced toxicity during maintenance phase of treatment for childhood acute lymphocytic leukemia (ALL). METHODS: One-hundred twenty-seven children with ALL that received maintenance therapy were involved in this study. All patients were treated according to Berlin-Frankfurt-Muenster (BFM) based protocols. Myelotoxicity and hepatotoxicity were evaluated using surrogate markers (median 6-MP dose, number of leukopenic episodes and levels of bilirubin and transaminases on each visit). RESULTS: Higher number of leukopenic episodes, as a surrogate marker of 6-MP myelotoxicity, was found in carriers of TYMS 3R3R and 3R4R genotypes (p=0.067) as well as in TYMS 3R6bp+ (28bp VNTR, 6bp indel) haplotype carriers (p=0.015). Carriers of DHFR CATAG (-680, -675, -556, -464, -317) haplotype were also found to have higher number of leukopenic episodes (p=0.070). SLC19A1 c.80A allele (p=0.079) and TYMS 2R6bp+ (5'UTR VNTR, 6bp indel) haplotype carriers (p=0.078) had fewer leukopenic episodes. No difference in genotype frequencies between the control group of volunteered blood donors and childhood ALL patients was found. CONCLUSIONS: Variants in TYMS, SLC19A1 and DHFR genes are potential biomarkers of myelotoxicity and could be used for 6-MP therapy individualization in maintenance phase of childhood ALL treatment, alongside with well-established TPMT variants.

Expression Pattern of Long Non-coding RNA Growth Arrest-specific 5 in the Remission Induction Therapy in Childhood Acute Lymphoblastic Leukemia.

BACKGROUND: Long non-coding RNA growth arrest-specific 5 (GAS5) is deregulated in many cancers because of its role in cell growth arrest and apoptosis. Additionally, GAS5 interacts with glucocorticoid receptor, making it a potential pharmacotranscription marker of glucocorticoid (GC) therapy. In this study, we aimed at analysing GAS5 expression in the remission induction therapy phase of childhood acute lymphoblastic leukemia (ALL), in which GCs are mandatorily used, and to correlate it with therapy response. METHODS: GAS5 expression was measured in peripheral blood mononuclear cells taken from 29 childhood ALL patients at diagnosis, on day 15 and day 33 of remission induction therapy using RT-qPCR methodology. RESULTS: Our results have shown interindividual differences in GAS5 expression at all time points. For each ALL patient, GAS5 expression was higher on day 15 in comparison to its level at diagnosis (p<0.0005). On day 33, the level of GAS5 expression decreased in comparison with day 15 (p<0.0005), but it was still significantly higher than at diagnosis for the majority of patients (p=0.001). Patients whose number of blasts on day 8 was below 100 per µL of peripheral blood had a higher GAS5 expression at diagnosis (p=0.016), and lower ratio day 15/diagnosis (p=0.009). CONCLUSIONS: Our results suggest that the expression level of GAS5 could be a potential marker of therapy response in remission induction therapy of childhood ALL.

Bone marrow findings in juvenile idiopathic arthritis.

The diagnosis of juvenile idiopathic arthritis (JIA) is an exclusion one due to heterogeneous clinical presentation and lack of specific laboratory tests. The authors investigated bone marrow of 25 untreated children with JIA at the onset of the disease. Bone marrow smears were evaluated for cell populations as well as myelodysplastic features and compared to two control groups. The characteristic of bone marrow in JIA was myeloid hyperplasia and elevated plasmocyte count. There was no difference between JIA patients and control groups in terms of myelodysplastic features. These findings can be helpful in explaining hematological alterations in JIA.

Variants in TPMT, ITPA, ABCC4 and ABCB1 Genes As Predictors of 6-mercaptopurine Induced Toxicity in Children with Acute Lymphoblastic Leukemia.

BACKGROUND: Acute lymphoblastic leukemia is the most common childhood malignancy. Optimal use of anti leukemic drugs has led to less toxicity and adverse reactions, and a higher survival rate. Thiopurine drugs, including 6-mercaptopurine, are mostly used as antileukemic medications in the maintenance phase of treatment for children with acute lymphoblastic leukemia. For those patients, TPMT genotype- tailored 6-mercaptopurine therapy is already implemented in the treatment protocols. We investigated the role of TPMT, ITPA, ABCC4 and ABCB1 genetic variants as predictors of outcome and 6-mercaptopurine induced toxicity during the maintenance phase of treatment in pediatric acute lymphoblastic leukemia. METHODS: Sixty-eight children with acute lymphoblastic leukemia were enrolled in this study. Patients have been treated according to ALL IC-BFM 2002 or ALL IC-BFM 2009 protocols. Toxicity and adverse events have been monitored via surrogate markers (off-therapy weeks, episodes of leu - ko penia and average 6-mercaptopurine dose) and a prob- abilistic model was employed to predict overall 6-mercaptopurine related toxicity. RESULTS: We confirmed that patients with acute lymphoblastic leukemia that carry inactive TPMT allele(s) require 6- mercaptopurine dose reduction. ITPA and ABCC4 genetic variants failed to show an association with 6-mercapto - purine induced toxicity during the maintenance phase. Carriers of ABCB1 variant allele experienced greater hepatotoxicity. The probabilistic model Neural net which considered all the analysed genetic variants was assessed to be the best prediction model. It was able to discriminate ALL patients with good and poor 6-mercaptopurin tolerance in 71% of cases (AUC=0.71). CONCLUSIONS: This study contributes to the design of a panel of pharmacogenetic markers for predicting thiopurineinduced toxicity in pediatric ALL.

Pharmacogenomic markers of glucocorticoid response in the initial phase of remission induction therapy in childhood acute lymphoblastic leukemia.

Background Response to glucocorticoid (GC) monotherapy in the initial phase of remission induction treatment in childhood acute lymphoblastic leukemia (ALL) represents important biomarker of prognosis and outcome. We aimed to study variants in several pharmacogenes (NR3C1, GSTs and ABCB1) that could contribute to improvement of GC response through personalization of GC therapy. Methods Retrospective study enrolling 122 ALL patients was carried out to analyze variants of NR3C1 (rs33389, rs33388 and rs6198), GSTT1 (null genotype), GSTM1 (null genotype), GSTP1 (rs1695 and rs1138272) and ABCB1 (rs1128503, rs2032582 and rs1045642) genes using PCR-based methodology. The marker of GC response was blast count per microliter of peripheral blood on treatment day 8. We carried out analysis in which cut-off value for GC response was 1000 (according to Berlin-Frankfurt-Munster [BFM] protocol), as well as 100 or 0 blasts per microliter. Results Carriers of rare NR3C1 rs6198 GG genotype were more likely to have blast count over 1000, than the non-carriers (p = 0.030). NR3C1 CAA (rs33389-rs33388-rs6198) haplotype was associated with blast number below 1000 (p = 0.030). GSTP1 GC haplotype carriers were more likely to have blast number below 1000 (p = 0.036), below 100 (p = 0.028) and to be blast negative (p = 0.054), while GSTP1 GT haplotype and rs1138272 T allele carriers were more likely to be blasts positive (p = 0.034 and p = 0.024, respectively). ABCB1 CGT (rs1128503-rs2032582-rs1045642) haplotype carriers were more likely to be blast positive (p = 0.018). Conclusions Our results have shown that NR3C1 rs6198 variant and GSTP1 rs1695-rs1138272 haplotype are the most promising pharmacogenomic markers of GC response in ALL patients.

Myeloid sarcoma presenting with bilateral proptosis and kidney infiltration.

The authors describe a male infant with a history of transient pancytopenia who developed progressive bilateral proptosis associated with diffuse infiltration of the kidney and normal bone marrow. The histopathological examination of the kidney revealed diffuse infiltration of cells of myeloid origin with monocytic differentiation. Although orbital involvement by myeloid sarcoma, with or without concurrent acute myeloid leukemia, is well known, there are distinctive features in this patient that are not reported in the literature, namely bilateral proptosis and simultaneous presence of bilateral kidney infiltration, which enabled diagnosis.

Lymphoblastic lymphomas in children ­ A single-center experience from Serbia.

Introduction: Intensive treatment protocols used for non-Hodgkin lymphoma in children lead to eventfree survival rates ranging from 80% to 90%. However, the results are less successful in developing countries. Lymphoblastic lymphoma (LBL) is the second most frequent type of lymphoma in children, contributing with about one third to all non-Hodgkin lymphoma in childhood. Objective: The aim of the study was to evaluate the results of LBL treatment in University Children's Hospital (UCH), Belgrade. Methods: A retrospective analysis of patient records at UCH from 1997 to 2015 was carried out in patients aged 0­18 years, in whom the diagnosis of LBL had been established. Twenty-two children were included in the analysis. Results: Mean age at diagnosis was 10 years, with preponderance of male patients. All patients were treated according to Berlin-Frankfurt-Münster-based chemotherapy protocols. With median follow-up of 91.5 months, five-year probability of event-free survival was 79.5% for all patients, while overall survival was 81.8%. Conclusion: Our results, although slightly inferior to those of leading international groups, reflect a good treatment outcome in our patients.

Extreme Hypertriglyceridemia in an Infant with Hemophagocytic Lymphohistiocytosis and Hydroxycobalamin Deficiency.

INTRODUCTION: Hemophagocytic lymphohistiocytosis (HLH) is a severe hyperinflammatory condition characterized by fever, cytopenias, hepatosplenomegaly and hemophagocytosis. HLH may be primary or secondary to infection, autoimmune disease or malignancy. Hypertriglyceridemia is a common abnormality in HLH and one of the HLH-2004 diagnostic criteria. CASE OUTLINE: We present an infant with severe hypotonia and hypoproteinemic edema who also had extreme hypertriglyceridemia (21 mmol/l) and was diagnosed with HLH based on six of eight HLH-2004 criteria (fever, hepatosplenomegaly, bicytopenia, hypertriglyceridemia with hypofibrinogenemia, slL-2R > 2400 IU/ml, hemophagocytosis). The presence of IgM antibodies to Epstein-Barr virus and cytomegalovirus indicated a probable infectious trigger. The child was cured by the HLH-2004 protocol for secondary HLH (consisting of dexamethasone and cyclosporine). He was also found to have low serum hydroxycobalamin levels, promptly corrected upon hydroxycobalamin administration. CONCLUSION: The presented case history underlines the need to ascertain the presence or absence of each of the eight HLH-2004 criteria in any patient suspected to suffer from HLH.

TPMT gene expression is increased during maintenance therapy in childhood acute lymphoblastic leukemia patients in a TPMT gene promoter variable number of tandem repeat-dependent manner.

AIMS: 6-mercaptopurine influences in vitro TPMT gene expression in a TPMT promoter variable number of tandem repeats (VNTR)-dependent manner. We studied TPMT expression following 6-mercaptopurine and methotrexate administration in childhood acute lymphoblastic leukemia (ALL) patients and the pharmacogenomic potential of the VNTR architecture. MATERIALS & METHODS: TPMT gene expression was determined in childhood ALL patients at diagnosis (n = 57) and during the maintenance therapy (n = 27). RESULTS: A threefold increase of TPMT gene expression was obtained during maintenance therapy, modulated by the architecture of the VNTR region. CONCLUSION: The TPMT promoter genetic variants need to be considered at the very beginning of the maintenance therapy for childhood ALL patients. The TPMT promoter VNTR region may serve as a pharmacogenomic biomarker when introducing thiopurine therapy.