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 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.

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.

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.

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.

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.

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.

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.

Non-Hodgkin lymphomas in childhood: how to move on?

Non-Hodgkin lymphomas of childhood represent a diverse group of neoplasms with different clinical, pathological, immunophenotypical and genetic features. A vast majority of childhood non-Hodgkin lymphomas could be classified into one of the three major histological subgroups: mature B-cell neoplasms, lymphoblastic lymphomas or anaplastic large cell lymphomas. Modern therapeutic strategies lead to cure in more than 80% of patients. Conversely, refractory diseases, as well as disease relapse convey a dismal prognosis. This fact requires much better stratification based on prognostic markers which would ideally recognize distinct groups of patients requiring different therapeutic regimens. Defining novel diagnostic and prognostic markers should improve diagnosis and prognosis as well as patient follow-up. It should also allow introduction of individually tailored treatment regimens in selected groups of patients with non-Hodgkin lymphomas, with the main goal of improving treatment results and decreasing short- and long-term complications.

Hemophagocytic lymphohistiocytosis arising in a child with Langerhans cell histiocytosis.

Langerhans cell histiocytosis (LCH) is characterized by the proliferation of clonal dendritic cells, while hemophagocytic lymphohistiocytosis (HLH) is an extreme inflammatory process sustained by the uncontrolled activation of macrophages. HLH can be primary or secondary, the latter arising in infectious, autoimmune or neoplastic disorders. We hereby present a young girl who developed secondary HLH while being treated for relapsed multisystem LCH under the LCH III Protocol. She fulfilled 5 of 8 HLH-2004 criteria (fever, splenomegaly, pancytopenia, ferritin level >500 µ/l and sIL-2R >2400 IU/ml) and was successfully treated by the HLH-2004 Protocol for secondary HLH. She remains in good health, apart from insipid diabetes she developed as a complication of LCH. Considering that the occurrence of HLH in LCH patients has been reported before, the case history presented here yields additional support for the hypothesis that the pathogenesis of the two histiocytoses--LCH and HLH--may indeed overlap to a considerable extent.

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.

[Clinical characteristics and disease course in children with haemophagocytic lymphohistiocytosis treated at the University Children's Hospital in Belgrade].

INTRODUCTION: Haemophagocytic lymphohistiocytosis (HLH) is a disorder characterised by long-standing fever, splenomegaly and bicytopoenia or pancytopoenia. Lymphadenopathy, jaundice and neurological symptoms mayalsooccur. HLH may ensue in various forms of innate or acquired immunodeficiency with impaired cytotoxic lymphocyte function resulting in excessive macrophage activation. OBJECTIVE: To describe and analyse clinical characteristics of patients treated for HLH at the University Children's Hospital of Belgrade from August 2000 to August 2010. METHODS: Retrospective analysis of medical records. RESULTS: Diagnosis of HLH was established in 13 children (five boys and eight girls) aged from one month to 14 years. In six children HLH was secondary (to visceral leishmaniasis in two, Ebstein-Barr virus infection in one, Langerhans' cell histiocytosis in one and systemic juvenile rheumatoid arthritis in two). Of the remaining seven patients, genes for perforin and syntaxin 11 were examined in two and no mutations were found. Of the remaining seven patients, genes encoding perforin and syntaxin 11 were analyzed in two, but no mutations were found. All children had fever, splenomegaly, cytopoenias, hyperferritinaemia and hypertriglyceridaemia, but haemophagocytosis was seen in only six (46.1%). Six children were cured (four with secondary HLH and two with primary HLH).Two children are undergoing treatment, while five succumbed (three before treatment could be administered and two due to complications). In four of the six cured children, HLH arose in the first year of life. Cure rate in those who underwent haematopoietic stem cell transplantation was 2/3. CONCLUSION: Results underscore the importance of timely diagnosis and treatment of HLH, warranting that in all children with fever, splenomegaly and/or cytopoenias, with or without haemophagocytosis, HLH be actively sought.

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.

6-mercaptopurine influences TPMT gene transcription in a TPMT gene promoter variable number of tandem repeats-dependent manner.

AIM: TPMT activity is characterized by a trimodal distribution, namely low, intermediate and high methylator. TPMT gene promoter contains a variable number of GC-rich tandem repeats (VNTRs), namely A, B and C, ranging from three to nine repeats in length in an A(n)B(m)C architecture. We have previously shown that the VNTR architecture in the TPMT gene promoter affects TPMT gene transcription. MATERIALS, METHODS & RESULTS: Here we demonstrate, using reporter assays, that 6-mercaptopurine (6-MP) treatment results in a VNTR architecture-dependent decrease of TPMT gene transcription, mediated by the binding of newly recruited protein complexes to the TPMT gene promoter, upon 6-MP treatment. We also show that acute lymphoblastic leukemia patients undergoing 6-MP treatment display a VNTR architecture-dependent response to 6-MP. CONCLUSION: These data suggest that the TPMT gene promoter VNTR architecture can be potentially used as a pharmacogenomic marker to predict toxicity due to 6-MP treatment in acute lymphoblastic leukemia patients.

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.

Incidence of FLT3 and nucleophosmin gene mutations in childhood acute myeloid leukemia: Serbian experience and the review of the literature.

Mutations in the fms-like tyrosine kinase 3 (FLT3) gene (internal tandem duplication (ITD) and point mutation in the tyrosine kinase domain, FLT3/D835) as well as the nucleophosmin (NPM1) gene are the most common abnormalities in adult acute myeloid leukemia (AML). Their significance in pediatric AML is still unclear. In this study we evaluated the frequency of FLT3 and NPM1 mutations in childhood AML. We also examined clinical features and outcome of these patients. FLT3 and NPM1 mutations were analysed in 42 and 37 childhood AML patients, respectively, using polymerase chain reaction (PCR) and direct sequencing. FLT3 mutations were detected in 4/42 patients (9.5%). The frequencies of FLT3/ITD and FLT3/D835 were the same, 2/42 (4.7%). NMP1 mutations were found in 1/37 patients (2.7%). FLT3 gene mutations were correlated with induction failure. Here we report the results of the study of FLT3 and NPM1 gene mutations in childhood AML patients in Serbia. Low frequencies of these molecular markers point out that these abnormalities are rare in this cohort of patients. Comparative study of data on NPM1 mutations in childhood AML revealed that various NPM1 gene mutation types are associated with childhood AML. Our findings as well as previously reported data, contributes to a hypothesis of different biology and etiology of adult and childhood AML. More extensive studies of NPM1 and FLT3 mutations in childhood AML are needed to determine their biological and clinical importance.

[Immunoglobulin genes and T-cell receptors as molecular markers in children with acute lymphoblastic leukaemia]. / Geni za imunoglobulin i T-celijski receptor kao molekularni markeri kod dece s akutnom limfoblastnom leukemijom.

INTRODUCTION: Acute lymphoblastic leukaemia (ALL) is a malignant clonal disease, one of the most common malignancies in childhood. Contemporary protocols ensure high remission rate and long term free survival. The ability of molecular genetic methods help to establish submicroscopic classification and minimal residual disease (MRD) follow up, in major percent responsible for relapse. OBJECTIVE: The aim of the study was to detect the frequency of IgH and TCR gene rearrangements and their correlation with clinical parameters. METHODS: Forty-one children with ALL were enrolled in the study group, with initial diagnosis of IgH and TCR gene rearrangements by polimerase chain reaction (PCR). MRD follow-up was performed in induction phase when morphological remission was expected, and after intensive chemiotherapy. RESULTS: In the study group IgH rearrangement was detected in 82.9% of children at the diagnosis, while TCR rearrangement was seen in 56.1%. On induction day 33, clonal IgH rearrangements persisted in 39% and TCR rearrangements in 36.5% of children. CONCLUSION: Molecular analysis of genetic alterations and their correlation with standard prognostic parameters show the importance of risk stratification revision which leads to new therapy intensification approach. MRD stands out as a precise predictive factor for the relapse of disease.

[Hyper-IgM syndrome in a boy with recurrent pneumonia and hepatosplenomegaly].

INTRODUCTION: We present a boy diagnosed at age 14 years with hyper-immunoglobulin (Ig) M syndrome, a congenital immunodeficiency characterized by reduced plasma concentrations of IgA, IgE and IgG, with normal or elevated concentrations of IgM. This syndrome is caused by a defect of CD40 ligand (CD40L) on T-helper lymphocytes, impeding the "second signal" during activation of B lymphocytes and interactions of T cells with dendritic cells and macrophages, resulting in the absence of secondary immune response (class switching, affinity maturation, immune memory), as well as responses to T-dependent antigens, with an impairment of cellular immunity. CASE OUTLINE: The history of the presented patient was dominated by frequent lower respiratory infections and failure to thrive. Physical examination demonstrated severe hepatosplenomegaly. The suspicion of hyper-IgM syndrome was raised by low plasma IgA (0.36 g/l) with high plasma IgM (35.5 g/l), while the concentration of IgG was within the normal range (12.1 g/l). The diagnosis was confirmed by flow cytometry, which demonstrated the absence of expression of CD40L on lymphocytes following stimulation by phorbolmyristylacetate and calcium ionophore. Since the time of diagnosis, intravenous immunoglobulin therapy has led to catch-up growth, recession of hepatosplenomegaly and reduction in the frequency of respiratory infections. CONCLUSION: Our report emphasizes the importance for the primary healthcare paediatrician to be well informed about the clinical presentation and pathogenesis of hyper-IgM syndrome, in order to provide early detection and increase the likelihood of success in treating this rare immunodeficiency. To the best of our knowledge, this is the first case of hyper-IgM syndrome reported in the Republic of Serbia.