A pediatric approach to the WHO classification of myelodysplastic and myeloproliferative diseases

Characteristics and outcomes of children, adolescent, and young adult patients with myelodysplastic neoplasms: A single-center retrospective analysis

Myelodysplastic syndrome, or myelodysplastic neoplasms, are a rare finding in pediatric, adolescent, and young adult (AYA) patients. More literature is needed to highlight trends of survival or treatment resistance in subpopulations to improve treatment. Here we report a single center retrospective analysis of pediatric and AYA patients from 2000 to 2022 including molecular and cytogenetic data. Using the IPSS-R and IPSS-M, which have been reported exclusively in adults, and excluding patients with bone marrow failure syndromes, we analyzed 119 pediatric and AYA patients with myelodysplastic neoplasms. Therapy-related myelodysplastic neoplasms were present in 36 % of patients, and 31 % of patients developed acute myeloid leukemia. The 5-year overall survival (OS) rate for the entire cohort was 45 %. Contrary to young adults and older adults, mutations were not common in pediatrics. Those who underwent stem cell transplant (SCT)(at any time) had significantly longer median OS. Although SCT at any time improved OS in the de novo myelodysplastic neoplasm group, the choice of the initial treatment with intensive chemotherapy, hypomethylating agents, or SCT did not significantly alter OS. Median OS was shorter in the pediatric group (<18 years old) and longer for those with isolated deletion of 5q or TET2 mutation, but these were not significant findings. Median OS was significantly shorter in those with monosomy 7 or 7q deletion and those with therapy-related myelodysplastic neoplasms. These findings build on previously reported findings and encourage the use of SCT along with molecular and cytogenetic analysis.

Observation and Management of Juvenile Myelomonocytic Leukemia and Noonan Syndrome-Associated Myeloproliferative Disorder: A Real-World Experience

Juvenile Myelomonocytic Leukemia (JMML) is a rare and clonal hematopoietic disorder of infancy and early childhood with myeloproliferative/myelodysplastic features resulting from germline or somatic mutations in the RAS pathway. Treatment is not uniform, with management varying from observation to stem cell transplant. The aim of our retrospective review is to describe the treatment and outcomes of a cohort of patients with JMML or Noonan Syndrome-associated Myeloproliferative Disorder (NS-MPD) to provide management guidance for this rare and heterogeneous disease. We report on 22 patients with JMML or NS-MPD managed at three institutions in the Texas Medical Center. Of patients with known genetic mutations and cytogenetics, 6 harbored germline mutations, 12 had somatic mutations, and 9 showed cytogenetic abnormalities. Overall, 14/22 patients are alive. Spontaneous clinical remission occurred in one patient with somatic NRAS mutation, as well as two with germline PTPN11 mutations with NS-MPD, and two others with germline PTPN11 mutations and NS-MPD remain under surveillance. Patients with NS-MPD were excluded from treatment analysis as none required chemotherapeutic intervention. All patients (5/5) treated with 5-azacitidine alone and one of the four treated with 6-mercaptopurine monotherapy had a reduction in mutant variant allele frequency. Transformation to acute myeloid leukemia was seen in two patients who both died. Among patients who received transplants, 7/13 are alive, and relapse post-transplant occurred in 3/13 with a median time to relapse of 3.55 months. This report provides insight into therapy responses and long-term outcomes across different genetic subsets of JMML and lends insight into the expected time to spontaneous resolution in patients with NS-MPD with germline PTPN11 mutations.

Landscape of driver mutations and their clinical effects on Down syndrome-related myeloid neoplasms

ABSTRACT

Transient abnormal myelopoiesis (TAM) is a common complication in newborns with Down syndrome (DS). It commonly progresses to myeloid leukemia (ML-DS) after spontaneous regression. In contrast to the favorable prognosis of primary ML-DS, patients with refractory/relapsed ML-DS have poor outcomes. However, the molecular basis for refractoriness and relapse and the full spectrum of driver mutations in ML-DS remain largely unknown. We conducted a genomic profiling study of 143 TAM, 204 ML-DS, and 34 non-DS acute megakaryoblastic leukemia cases, including 39 ML-DS cases analyzed by exome sequencing. Sixteen novel mutational targets were identified in ML-DS samples. Of these, inactivations of IRX1 (16.2%) and ZBTB7A (13.2%) were commonly implicated in the upregulation of the MYC pathway and were potential targets for ML-DS treatment with bromodomain-containing protein 4 inhibitors. Partial tandem duplications of RUNX1 on chromosome 21 were also found, specifically in ML-DS samples (13.7%), presenting its essential role in DS leukemia progression. Finally, in 177 patients with ML-DS treated following the same ML-DS protocol (the Japanese Pediatric Leukemia and Lymphoma Study Group acute myeloid leukemia -D05/D11), CDKN2A, TP53, ZBTB7A, and JAK2 alterations were associated with a poor prognosis. Patients with CDKN2A deletions (n = 7) or TP53 mutations (n = 4) had substantially lower 3-year event-free survival (28.6% vs 90.5%; P < .001; 25.0% vs 89.5%; P < .001) than those without these mutations. These findings considerably change the mutational landscape of ML-DS, provide new insights into the mechanisms of progression from TAM to ML-DS, and help identify new therapeutic targets and strategies for ML-DS.

Myelodysplastic neoplasms evolving from inherited bone marrow failure syndromes / germline predisposition syndromes: Back under the microscope

Inherited bone marrow failure syndromes and germline predisposition syndromes (IBMFS/GPS) are associated with increased risk for hematologic malignancies, particularly myeloid neoplasms, such as myelodysplastic neoplasms (MDS) and acute myeloid leukemia (AML). The diagnosis of MDS in these syndromes poses difficulty due to frequent bone marrow hypocellularity and the presence of some degree of dysplastic features related to the underlying germline defect causing abnormal maturation of one or more cell lines. Yet, the diagnosis of MDS is usually associated with a worse outcome in several IBMFS/GPS. Criteria for the diagnosis of MDS in IBMFS/GPS have not been standardized with some authors suggesting a mixture of morphologic, cytogenetic, and genetic criteria. This review highlights these challenges and suggests a more standardized approach to nomenclature and diagnostic criteria.

Childhood Myelodysplastic Syndrome

Myelodysplastic syndrome (MDS) in children is rare, accounting for < 5% of all childhood hematologic malignancies. With the advent of next-generation sequencing, the etiology of many childhood MDS (cMDS) cases has been elucidated with the finding of predisposing germline mutations in one-quarter to one-third of cases; somatic mutations have also been identified, indicating that cMDS is different than adult MDS. Herein, cMDS classification schema, clinical presentation, laboratory values, bone marrow histology, differential diagnostic considerations, and the recent molecular findings of cMDS are described.

The Role of BCL-2 and PD-1/PD-L1 Pathway in Pathogenesis of Myelodysplastic Syndromes

Myelodysplastic syndromes (MDSs) belong to a group of clonal bone marrow malignancies. In light of the emergence of new molecules, a significant contribution to the understanding of the pathogenesis of the disease is the study of the B-cell CLL/lymphoma 2 (BCL-2) and the programmed cell death receptor 1 (PD-1) protein and its ligands. BCL-2-family proteins are involved in the regulation of the intrinsic apoptosis pathway. Disruptions in their interactions promote the progression and resistance of MDSs. They have become an important target for specific drugs. Bone marrow cytoarchitecture may prove to be a predictor of response to its use. The challenge is the observed resistance to venetoclax, for which the MCL-1 protein may be largely responsible. Molecules with the potential to break the associated resistance include S63845, S64315, chidamide and arsenic trioxide (ATO). Despite promising in vitro studies, the role of PD-1/PD-L1 pathway inhibitors has not yet been established. Knockdown of the PD-L1 gene in preclinical studies was associated with increased levels of BCL-2 and MCL-1 in lymphocytes T, which could increase their survival and promote tumor apoptosis. A trial (NCT03969446) is currently underway to combine inhibitors from both groups.

Anemia in the pediatric patient

The World Health Organization estimates that approximately a quarter of the world's population suffers from anemia, including almost half of preschool-age children. Globally, iron deficiency anemia is the most common cause of anemia. Other important causes of anemia in children are hemoglobinopathies, infection, and other chronic diseases. Anemia is associated with increased morbidity, including neurologic complications, increased risk of low birth weight, infection, and heart failure, as well as increased mortality. When approaching a child with anemia, detailed historical information, particularly diet, environmental exposures, and family history, often yield important clues to the diagnosis. Dysmorphic features on physical examination may indicate syndromic causes of anemia. Diagnostic testing involves a stepwise approach utilizing various laboratory techniques. The increasing availability of genetic testing is providing new mechanistic insights into inherited anemias and allowing diagnosis in many previously undiagnosed cases. Population-based approaches are being taken to address nutritional anemias. Novel pharmacologic agents and advances in gene therapy-based therapeutics have the potential to ameliorate anemia-associated disease and provide treatment strategies even in the most difficult and complex cases.

Chronic myeloid leukemia: a type of MPN

This review article classifies chronic myeloid leukemia (CML) based on cytogenetic analyses and different mutations detected in CML patients. The use of advanced technologies, such as karyotyping, fluorescent in situ hybridization, and comparative genomic hybridization, has allowed us to study CML in detail and observe the different biochemical changes that occur in different CML types. This review also highlights the different types of receptor and signaling pathway mutations that occur in CML.

The effect of decitabine-combined minimally myelosuppressive regimen bridged allo-HSCT on the outcomes of pediatric MDS from 10 years' experience of a single center

Background

Myelodysplastic syndrome (MDS) is a rare disease in children and the treatment option before the allogeneic hematopoietic stem cell transplantation (allo-HSCT) is rarely reported. Our main objective was to report our single-center experience with the DNA-hypomethylating agent, decitabine-combined minimally myelosuppressive regimen (DAC + MMR) bridged allo-HSCT in children with MDS.

Methods

Twenty-eight children with de novo MDS who underwent allo-HSCT between 2011 and 2020 were enrolled. Patients were divided into subgroups (refractory cytopenia of childhood [RCC] and advanced MDS [aMDS]) and treated by HSCT alone or pre-transplant combination treatment based on risk stratification. The patients’ clinical characteristics, treatment strategies and outcomes were retrospectively evaluated.

Results

Twenty patients with aMDS had received pre-transplant treatment (three were treated with decitabine alone, thirteen with DAC + MMR, and four with acute myeloid leukemia type [AML-type] induction therapy). DAC + MMR was well tolerated and the most common adverse events were myelosuppression and gastrointestinal reaction. DAC + MMR had shown an improved marrow complete remission (mCR) compared with AML-type chemotherapy (13/13, 100% versus 2/4, 50%, P = 0.044). The median follow-up for total cohort was 53.0 months (range, 2.3-127.0 months) and the 4-year overall survival (OS) was 71.4 ± 8.5%. In the subgroup of aMDS, pretreatment of DAC + MMR resulted in a much better survival rate than AML-type chemotherapy (84.6 ± 10.0% versus 0.0 ± 0.0%, P < 0.001).

Conclusions

The DAC + MMR bridged allo-HSCT may be recommended as a novel and effective approach.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12887-022-03376-1.

A Summary of the Inaugural WHO Classification of Pediatric Tumors: Transitioning from the Optical into the Molecular Era

Pediatric tumors are uncommon, yet are the leading cause of cancer-related death in childhood. Tumor types, molecular characteristics, and pathogenesis are unique, often originating from a single genetic driver event. The specific diagnostic challenges of childhood tumors led to the development of the first World Health Organization (WHO) Classification of Pediatric Tumors. The classification is rooted in a multilayered approach, incorporating morphology, IHC, and molecular characteristics. The volume is organized according to organ sites and provides a single, state-of-the-art compendium of pediatric tumor types. A special emphasis was placed on "blastomas," which variably recapitulate the morphologic maturation of organs from which they originate. SIGNIFICANCE: In this review, we briefly summarize the main features and updates of each chapter of the inaugural WHO Classification of Pediatric Tumors, including its rapid transition from a mostly microscopic into a molecularly driven classification systematically taking recent discoveries in pediatric tumor genomics into account.

CRLF1 and CLCF1 in Development, Health and Disease

Cytokines and their receptors have a vital function in regulating various processes such as immune function, inflammation, haematopoiesis, cell growth and differentiation. The interaction between a cytokine and its specific receptor triggers intracellular signalling cascades that lead to altered gene expression in the target cell and consequent changes in its proliferation, differentiation, or activation. In this review, we highlight the role of the soluble type I cytokine receptor CRLF1 (cytokine receptor-like factor-1) and the Interleukin (IL)-6 cytokine CLCF1 (cardiotrophin-like cytokine factor 1) during development in physiological and pathological conditions with particular emphasis on Crisponi/cold-induced sweating syndrome (CS/CISS) and discuss new insights, challenges and possibilities arising from recent studies.

Case report: Venetoclax therapy in a boy with acute myeloid leukemia in Shwachman Diamond syndrome

Shwachman-Diamond syndrome (SDS) is a rare bone marrow failure syndrome characterized by exocrine pancreatic insufficiency, bone abnormalities, progressive cytopenia, and predispositions to myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). AML, in these patients, is associated with a poor prognosis and with an increased risk of organ toxicity and infectious complications from chemotherapy and hematopoietic stem cell transplantation (HSCT), thus leading to high rates of treatment-related morbidity and mortality. The BCL-2 inhibitor venetoclax has revolutionized the treatment of AML in elderly adults, especially for treatment-naive elderly patients who are ineligible for intensive chemotherapy. There is limited evidence on the use of venetoclax in pediatric patients with SDS-related MDS or AML. Here, we report a case of a 14-year-old boy with SDS with AML arising from MDS. The patient was treated with two cycles of conventional chemotherapy with fludarabine and cytarabine with an initial good response but immediate relapse and substantial toxicity. Treatment with venetoclax and azacitidine was started, with a substantial reduction of leukemic burden (good response on peripheral leukemic infiltration and partial response in the bone marrow after one course). However, it was followed by multiple infectious complications and worsening of the general condition not allowing treatment to be continued, and the patient eventually died from multiorgan failure. With the limitations of observation of a single patient, our experience suggests that venetoclax/azacitidine combination therapy may represent a therapeutic possibility for patients with SDS and AML, even though it may be associated with significant toxicity.

Prospective validation of the provisional entity of refractory cytopenia of childhood, proposed by the World Health Organization

In 2008, the World Health Organization proposed a new entity of childhood myelodysplastic syndrome (MDS), which was referred to as refractory cytopenia of childhood (RCC). However, whether this morphological classification reflects clinical outcomes remains unclear. We performed a prospective evaluation of bone marrow morphology in 252 children with acquired bone marrow failure between 2009 and 2013. Of 252 patients, 63 were diagnosed with aplastic anaemia (AA), 131 with RCC without multilineage dysplasia (RCC-w/o-MLD) and 58 with RCC with MLD (RCC-MLD). One patient with AA, three with RCC-w/o-MLD and nine with RCC-MLD presented with chromosomal abnormalities at diagnosis (P = 0·001). The response rates to immunosuppressive therapy (IST) at 6 months and the cumulative incidence of clonal evolution at 5 years did not significantly differ among the three groups. A multivariate analysis revealed that the morphological classification of RCC-MLD was a significant risk factor for secondary graft failure after haematopoietic cell transplantation (HCT) (P = 0·003). In view of these findings, RCC could be divided into two categories, RCC-w/o-MLD and RCC-MLD, because children with this condition exhibited a distinct morphology, frequent chromosomal abnormalities at diagnosis and a high frequency of secondary graft failure after HCT.

Pediatric myelodysplastic syndrome with inflammatory manifestations: Diagnosis, genetics, treatment, and outcome

BACKGROUND

Inflammatory manifestations (IM) are well described in adult patients with myelodysplastic syndrome (MDS), but the presentation is highly variable and no standardized treatment exists. This phenomenon is rarely reported in children. As more pediatric patients are hematopoietic stem cell transplantation (HSCT) candidates, the role of anti-inflammatory treatment in relation to HSCT should be defined.

PROCEDURE

Here, we report a series of five children from a tertiary center. We describe the clinical presentation, molecular findings, and treatment options.

RESULTS

All patients presented with advanced MDS with blast percentages ranging 10-30%, all had severe IM. One patient had MDS secondary to severe congenital neutropenia, the other four patients had presumably primary MDS. All four were found to harbor a PTPN11 gene driver mutation, which is found in 35% of cases of juvenile myelomonocytic leukemia (JMML). The mutation was present in the myeloid lineage but not in T lymphocytes. Three had symptoms of Behcet's-like disease with trisomy 8 in their bone marrow. All patients were treated with anti-inflammatory medications (mainly systemic steroids) in an attempt to bring them to allogeneic HSCT in a better clinical condition. All demonstrated clinical improvement as well as regression in their MDS status post anti-inflammatory treatment. All have recovered from both MDS and their inflammatory symptoms post HSCT.

CONCLUSION

Primary pediatric MDS with IM is driven in some cases by PTPN11 mutations, and might be on the clinical spectrum of JMML. Anti-inflammatory treatment may reverse MDS progression and improve the outcome of subsequent HSCT.

Prognostic value of the revised International Prognostic Scoring System five-group cytogenetic abnormality classification for the outcome prediction of hematopoietic stem cell transplantation in pediatric myelodysplastic syndrome

Cytogenetic abnormalities are a major risk factor for relapse after hematopoietic stem cell transplantation (HSCT) for myelodysplastic syndrome (MDS). We aimed to evaluate the value of the five-group cytogenetic classification according to the revised International Prognostic Scoring System (R-IPSS) for predicting the outcome after HSCT in pediatric patients with MDS. We retrospectively analyzed the Japanese registration data of 242 pediatric patients with MDS. According to the R-IPSS classification, 112 (45.5%) patients had good, 55 (22.7%) had intermediate, 64 (26.4%) had poor, and 11 (4.6%) had very poor cytogenetics. The 5-year overall survival (5yOS) was 72%, 69%, 59%, and 30% in the good, intermediate, poor, and very poor cytogenetic subgroups (p = 0.026), respectively. The very good, good, and intermediate subgroups were grouped into a "standard" subgroup and reclassified into three subgroups (standard, poor, and very poor). Patients with very poor risk had worse 5yOS (hazard ratio 2.17, 95% confidence interval (CI) 1.02-4.61; p = 0.04) and a much higher 5yCIR (hazard ratio 2.52, 95% CI 1.05-6.04; p = 0.04) than those of patients in the standard group in the multivariate analysis, indicating that very poor risk cytogenetic characteristics independently predicted worse outcome after HSCT in pediatric patients with MDS.

Functional and epigenetic phenotypes of humans and mice with DNMT3A Overgrowth Syndrome

Germline pathogenic variants in DNMT3A were recently described in patients with overgrowth, obesity, behavioral, and learning difficulties (DNMT3A Overgrowth Syndrome/DOS). Somatic mutations in the DNMT3A gene are also the most common cause of clonal hematopoiesis, and can initiate acute myeloid leukemia (AML). Using whole genome bisulfite sequencing, we studied DNA methylation in peripheral blood cells of 11 DOS patients and found a focal, canonical hypomethylation phenotype, which is most severe with the dominant negative DNMT3AR882H mutation. A germline mouse model expressing the homologous Dnmt3aR878H mutation phenocopies most aspects of the human DOS syndrome, including the methylation phenotype and an increased incidence of spontaneous hematopoietic malignancies, suggesting that all aspects of this syndrome are caused by this mutation.

Leukemia Risk in a Cohort of 3.9 Million Children with and without Down Syndrome

OBJECTIVE

To assess leukemia risks among children with Down syndrome in a large, contemporary cohort.

STUDY DESIGN

Retrospective cohort study including 3 905 399 children born 1996-2016 in 7 US healthcare systems or Ontario, Canada, and followed from birth to cancer diagnosis, death, age 15 years, disenrollment, or December 30, 2016. Down syndrome was identified using International Classification of Diseases, Ninth and Tenth Revisions, diagnosis codes. Cancer diagnoses were identified through linkages to tumor registries. Incidence and hazard ratios (HRs) of leukemia were estimated for children with Down syndrome and other children adjusting for health system, child's age at diagnosis, birth year, and sex.

RESULTS

Leukemia was diagnosed in 124 of 4401 children with Down syndrome and 1941 of 3 900 998 other children. In children with Down syndrome, the cumulative incidence of acute myeloid leukemia (AML) was 1405/100 000 (95% CI 1076-1806) at age 4 years and unchanged at age 14 years. The cumulative incidence of acute lymphoid leukemia in children with Down syndrome was 1059/100 000 (95% CI 755-1451) at age 4 and 1714/100 000 (95% CI 1264-2276) at age 14 years. Children with Down syndrome had a greater risk of AML before age 5 years than other children (HR 399, 95% CI 281-566). Largest HRs were for megakaryoblastic leukemia before age 5 years (HR 1500, 95% CI 555-4070). Children with Down syndrome had a greater risk of acute lymphoid leukemia than other children regardless of age (<5 years: HR 28, 95% CI 20-40, ≥5 years HR 21, 95% CI 12-38).

CONCLUSIONS

Down syndrome remains a strong risk factor for childhood leukemia, and associations with AML are stronger than previously reported.

A Case of Myelofibrosis and Myelodysplasia Identified Following Exposure to Isotretinoin

A 15-year-old male individual treated with isotretinoin for acne vulgaris presented with persistent pancytopenia and circulating myeloblasts after discontinuation of the drug. Marrow assessment revealed myelofibrosis (MF) and myeloblasts exhibiting monosomy 7, diagnostic of myelodysplastic syndrome (MDS). Although a popular website seems to associate isotretinoin with MF, no published cases of MF or MDS attributable to this drug were identified. Although we expect that he would eventually have developed MDS and MF, this patient was perhaps identified sooner due to cytopenias accelerated by isotretinoin. This case illustrates that patients exhibiting cytopenias persisting following isotretinoin therapy merit evaluation for underlying hematopoietic disorders.

Unmanipulated haploidentical hematopoietic stem cell transplantation for children with myelodysplastic syndrome

Myelodysplastic syndrome (MDS) is a heterogeneous group of clonal disorders and is rare in children. Allogeneic hematopoietic stem cell transplantation (HSCT) is commonly used in children with MDS with excess blasts and in patients with refractory cytopenia of childhood (RCC) associated with monosomy 7, complex karyotype, severe neutropenia, or transfusion dependence. We recruited 27 children with MDS who received haploidentical hematopoietic stem cell transplantation (haplo-HSCT). At transplantation, 10 patients had RCC, 12 patients had advanced MDS (RAEB and RAEB-T), and 5 patients had myelodysplasia-related acute myeloid leukemia (MDR-AML). All patients received granulocyte colony-stimulating factor (G-CSF)-mobilized bone marrow cells and peripheral blood stem cells. At a median follow-up of 24.1 months (range: 2.0-74.5 months) after HSCT, the estimated probabilities of 3-year disease-free survival (DFS) and overall survival (OS) were both 81.9% (95% CI, 66.8-100.0%). The estimated 3-year incidences of relapse (CIR) and non-relapse mortality (NRM) were both 7.4% (95% CI, 1.2%-21.4%). The 100-day cumulative incidence of grade II-IV aGVHD was 52.6% (95% CI, 42.9-62.3%), while that of grade III-IV aGVHD was 11.1% (95% CI, 5.1-17.1%). The 3-year cumulative incidences of overall and extensive cGVHD were 42.3% (95% CI, 19.8%-57.5%) and 21.1% (95% CI, 2.5%-63.2%), respectively. Univariate analysis showed that chronic GVHD significantly affected OS and DFS. Haploidentical HSCT may be an effective treatment option with easier donor availability for pediatric patients with MDS.

Reduction of Extramedullary Complications in Patients With Acute Myeloid Leukemia/Myelodysplastic Syndrome Treated With Azacitidine

The distinction between myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) often relies on an arbitrary marrow blast cutoff of 30% in pediatrics and 20% in adults. There is little data about the treatment of children with extramedullary myeloid malignancy that has features of both, MDS and AML. Herein, we report for the first time 2 patients MDS/AML (1 with Shwachman-Diamond syndrome and 1 with idiopathic MDS and monosomy 7) who presented with extramedullary complications, received treatment with azacitidine, achieved complete remission and subsequently underwent hematopoietic stem cell transplantation.

Cellular and molecular architecture of hematopoietic stem cells and progenitors in genetic models of bone marrow failure

Inherited bone marrow failure syndromes, such as Fanconi anemia (FA) and Shwachman-Diamond syndrome (SDS), feature progressive cytopenia and a risk of acute myeloid leukemia (AML). Using deep phenotypic analysis of early progenitors in FA/SDS bone marrow samples, we revealed selective survival of progenitors that phenotypically resembled granulocyte-monocyte progenitors (GMP). Whole-exome and targeted sequencing of GMP-like cells in leukemia-free patients revealed a higher mutation load than in healthy controls and molecular changes that are characteristic of AML: increased G>A/C>T variants, decreased A>G/T>C variants, increased trinucleotide mutations at Xp(C>T)pT, and decreased mutation rates at Xp(C>T)pG sites compared with other Xp(C>T)pX sites and enrichment for Cancer Signature 1 (X indicates any nucleotide). Potential preleukemic targets in the GMP-like cells from patients with FA/SDS included SYNE1, DST, HUWE1, LRP2, NOTCH2, and TP53. Serial analysis of GMPs from an SDS patient who progressed to leukemia revealed a gradual increase in mutational burden, enrichment of G>A/C>T signature, and emergence of new clones. Interestingly, the molecular signature of marrow cells from 2 FA/SDS patients with leukemia was similar to that of FA/SDS patients without transformation. The predicted founding clones in SDS-derived AML harbored mutations in several genes, including TP53, while in FA-derived AML the mutated genes included ARID1B and SFPQ. We describe an architectural change in the hematopoietic hierarchy of FA/SDS with remarkable preservation of GMP-like populations harboring unique mutation signatures. GMP-like cells might represent a cellular reservoir for clonal evolution.

Improved outcomes of allogeneic hematopoietic stem cell transplantation including haploidentical transplantation for childhood myelodysplastic syndrome

This retrospective study aimed to investigate the outcomes of allogeneic hematopoietic stem cell transplantation (HSCT) for childhood myelodysplastic syndrome (MDS). Thirty-six patients (low-grade MDS, 24; advanced MDS, 12) received HSCT at the Asan Medical Center over two decades (early period, 1997-2007; recent period, 2008-2017). The transplantation outcomes were analyzed according to disease status, conditioning regimen, various donor types, and period of HSCT. During a median follow-up of 5.6 (range, 1.4-21.1) years, the probability of overall survival (OS) and failure-free survival was 77% and 69%, respectively. The cumulative incidence of transplantation-related mortality (TRM) was 12%. Significantly reduced TRM and improved OS were observed in patients who received HSCT during the recent period vs. the early period (TRM, 4% vs. 30%, P = 0.021; OS, 87% vs. 50%, P = 0.006). Comparable outcomes were observed for HSCT from haploidentical family donors vs. HLA-identical donors (TRM, 10% vs. 14%, P= 0.837; OS, 86% vs. 79%, P = 0.625). This study identified the improved outcomes of allogeneic HSCT for childhood MDS over time, in addition, the feasible outcomes of haploidentical HSCT suggested its use as an attractive alternative in the future procedures.

Clinical implications of immune-mediated diseases in children with Down syndrome

Children with Down syndrome have changes in their innate and adaptive immunity, which contribute to increased rates of infections, autoimmune diseases, and haematological malignancies. While improved care for congenital heart disease has decreased mortality and morbidity, complications related to immune-mediated diseases continue to limit the life expectancy in Down syndrome. Infectious diseases are common and have a significant effect on development, behaviour and quality of life. Infection frequency and severity are influenced by various anatomical and physiological alterations in addition to immunological changes in Down syndrome. Thus, prevention of respiratory tract infections requires a multifactorial approach. This could include additional active and/or passive immunizations, prophylactic antibiotics, immunoglobulin replacement and ear, nose and throat surgical interventions. Autoimmune conditions like coeliac disease, type I diabetes mellitus and thyroid disease are classically mentioned in the context of Down syndrome. However, autoinflammatory conditions are more prevalent as well. Screening for autoimmune diseases is required and immunosuppression has to be used with caution. Future studies should address optimal screening programmes for immune-mediated diseases in individuals with Down syndrome, as well as the effect of immune modulation, to further decrease morbidity and mortality, and improve the quality of life of individuals with Down syndrome.

Expression Profiles of DNA Methylation and Demethylation Machinery Components in Pediatric Myelodysplastic Syndrome: Clinical Implications

Purpose

The aim of this study was to analyse the expression profiles of DNMT1, DNMT3A, DNMT3B (components of DNA methylation machinery), TET2 and APOBEC3B (components of DNA demethylation machinery) in pediatric MDS patients and investigate their associations with MDS subtypes, cytogenetics, evolution to acute myeloid leukemia (AML) and p15^INK4B methylation level.

Patients and Methods

The expressions of DNMT1, DNMT3A, DNMT3B, TET2, and APOBEC3B were evaluated in 39 pediatric MDS patients by real-time quantitative PCR (qPCR). The quantification of p15^INK4B methylation levels (MtL) was performed in 20 pediatric MDS patients by pyrosequencing. Mann–Whitney test was used to evaluate possible differences between the expression levels of selected in patients and donors, according to MDS subtypes, karyotypes, evolution to AML and p15^INK4B MtL. The correlations between the expression levels of the different genes were assessed by Spearman rank correlation coefficient.

Results

We found that DNMTs expression levels were higher in pediatric MDS compared to donors [DNMT1 (p<0.03), DNMT3A (p<0.03), DNMT3B (p<0.02)]. TET2 and APOBEC3B expression levels did not show a statistically significant difference between pediatric patients and donors. Considering MDS subtypes, patients at initial stage presented DNMT1 overexpression (p<0.01), while DNMT3A (p<0.02) and DNMT3B (p<0.007) were overexpressed in advanced subtypes. TET2 and APOBEC3B expression did not differ in MDS subtypes. DNMT1 (p<0.03), DNMT3B (p<0.03), and APOBEC3B (p<0.04) expression was higher in patients with normal karyotypes, while patients with abnormal karyotypes showed higher DNMT3A expression (p<0.03). Karyotypes had no association with TET2 expression. DNMTs overexpression was observed in patients who showed disease evolution. A positive correlation was found between DNMTs expression and between APOBEC3B and DNMT3A/DNMT3B. However, TET2 expression was not correlated with DNMTs or APOBEC3B. p15^INK4B MtL was higher in pediatric MDS patients compared with donors (p<0.03) and its hypermethylation was associated with increased DNMT1 expression (p<0.009).

Conclusion

Our results suggest that the overexpression of DNMTs and an imbalance between the expressions of the DNA methylation/demethylation machinery components play an important role in MDS development and evolution to AML. These results have clinical implications indicating the importance of DNMTs inhibitors for preventing or delaying the progression to leukemia in pediatric MDS patients.

Aberrant Expression of EZH2 in Pediatric Patients with Myelodysplastic Syndrome: A Potential Biomarker of Leukemic Evolution

Pediatric myelodysplastic syndrome (MDS) is an uncommon disease and little is known about the molecular alterations of its development and evolution to acute myeloid leukemia (AML). The Enhancer of Zeste Homolog 2 (EZH2) is the catalytic subunit of Polycomb repressive complex 2 (PCR2). It is a histone methyltransferase, that targets lysine 27 of histone 3. This methylated H3–K27 is usually associated with the silencing of genes that are involved in fundamental cellular processes, such as cell proliferation and differentiation. There are only few studies showing the status of EZH2 expression in patients with MDS and they were performed in adult MDS patients. The aim of this study was to analyze the EZH2 expression in pediatric patients with MDS and its association with karyotypes and evolution to acute myeloid leukemia (AML). We conducted the first study of EZH2 expression in pediatric patients with MDS. Considering the EZH2 expression levels in 42 patients and 17 healthy pediatric donors, it was possible to define three groups of expression in patients: low, intermediate, and high. The intermediate level encompassed patients with normal karyotypes, low level included patients with monosomy 7 and del(7q) and high level included patients with trisomy 8 and del(11q) (p < 0.0001). Comparing the leukemic evolution, the low expression group presented disease evolution in 100% (8/8) of the cases, the intermediate expression group showed disease evolution in 4.34% (1/23) and in the high expression group, 63.63% (7/11) patients showed evolution from MDS to AML (p < 0.0001). It is important to note that low and high EZH2 expression are associated with leukemic evolution, however low expression showed a stronger association with evolution from MDS to AML than the high expression. Our results suggest a scale of measure for EZH2 expression in pediatric MDS, where aberrant EZH2 expression may be a potential biomarker of disease evolution.

ZRSR2 mutation in a child with refractory macrocytic anemia and Down Syndrome

Here we report a case of refractory macrocytic anemia with a spliceosomal point mutation involving the ZRSR2 gene in a child with Down syndrome (DS). Such mutations have been shown to cause refractory macrocytic anemia and myelodysplastic syndrome (MDS) in elderly individuals. We report the hematological indices of a child with DS and a ZRSR2 spliceosomal mutation. DS is known to produce macrocytic anemia but does not lead to transfusion dependence. In this case, the ZRSR2 mutation was the likely implicating factor for severe transfusion-dependent anemia in a child with DS. The clinical implication of a ZRSR2 mutation in a child with DS has not been previously described and warrants close surveillance to detect potential insidious transformation to MDS.

Spontaneous Remission of Monosomy 7 Six Years After Diagnosis

Monosomy 7 may be a poor prognostic indicator in pediatric myelodysplastic syndrome. There are case reports of children with monosomy 7 who undergo spontaneous remission 2 to 24 months after diagnosis. We report a case of a child with bone marrow failure and monosomy 7 who underwent spontaneous remission 75 months after diagnosis. The patient had no exposure to chemotherapeutic or immunosuppressive agents. The patient did not receive chemotherapy or other treatment during the 75 months. Despite remaining positive for monosomy 7, he never developed myelodysplasia or acute myeloid leukemia. Spontaneous remission of monosomy 7 may occur years after diagnosis in some patients.

Identification of long non-coding RNA competing interactions and biological pathways associated with prognosis in pediatric and adolescent cytogenetically normal acute myeloid leukemia

Background

LncRNAs can regulate miRNAs and mRNAs by sequestering and binding them. Indeed, many researchers have reported lncRNA mediated-competing endogenous RNAs (ceRNAs) could regulate the progression of solid tumors. However, the roles of ceRNA in acute myeloid leukemia (AML), especially in pediatric and adolescent AML, were not completely expounded.

Materials and methods

27 cytogenetically normal acute myeloid leukemia (CN-AML) patients under 18 years old with corresponding clinical data were selected from the cancer genome atlas (TCGA), which was a large sample sequencing database of RNA sequencing. We constructed a survival specific ceRNA network, and investigated its associations with patients' clinical information by analyzing the data from TCGA.

Results

We identified survival specific lncRNAs, miRNAs and mRNAs, and constructed a survival specific ceRNA network of CN-AML patients and a weighted correlation network. Furthermore, we identified 4 biological pathways associated with OS and selected the most enriched pathway 'Transcriptional misregulation in cancer' to verify that it could accurately predict younger CN-AML patients' prognosis to guide treatment.

Conclusions

We successfully constructed a survival specific ceRNA network which could provide a new approach to lncRNA research in younger CN-AML. Importantly, we constructed a weighted correlation network to overcome the difficulty in biological interpretation of individual genes.

Molecular profile of inflammatory and megakaryocytic factors in pediatric myelodysplastic syndrome with acute myelofibrosis

Pediatric fibrotic myelodysplastic syndromes (ped-MDS-MF) and pediatric primary myelofibrosis (ped-PMF) are rare, and the molecular changes which mediate fibrosis have never been investigated. Histology and gene expression profile of 119 fibrosis/angiogenesis/inflammation/megakaryopoiesis-related factors in bone marrow biopsies were performed (two ped-MDS-MF and one ped-PMF). In one progressive ped-MDS, comparison of MF grade 0 (no myelofibrosis) and MF grade 2 (dense network of reticulin fibres) after 4 months showed that expression of fibrosis-related transcripts increased and dysplastic megakaryocytes formed a dense net of CD42b⁺ proplatelets. These changes were not observed in another ped-MDS-MF, whereas ped-PMF showed a similar proplatelet pattern. These findings indicate that fibrotic changes in ped-MDS may involve proplatelet-related and unrelated pathways.

Down syndrome associated childhood myeloid leukemia with yet unreported acquired chromosomal abnormalities and a new potential adverse marker: dup(1)(q25q44)

Background

Children with constitutional trisomy 21, i.e. Down syndrome (DS, OMIM #190685) have a 10 to 20-fold increased risk for a hematopoietic malignancy. They may suffer from acute lymphoblastic leukemia or acute myeloid leukemia (AML). AML referred to as myeloid leukemia of Down syndrome (ML-DS) is observed especially after birth at an early gestational age and characterized by enhanced white blood cell count, failure of spontaneous remission, liver fibrosis or liver dysfunction, and is significantly associated with early death. There are only few studies yet focusing on the clonal cytogenetic changes during evolution of ML-DS.

Case presentation

In a 1.4-year-old boy with DS an immunophenotype consistent with AML-M1 according to French-American-British (FAB) classification was diagnoses. Cytogenetic and molecular cytogenetic analyses revealed, besides constitutional free trisomy 21, an unbalanced translocation as der(16)t(1;16)(q25.3;q24), plus a balanced translocation t(3;20)(q25;q13.1). A poor clinical outcome was observed here.

Conclusions

To the best of our knowledge, an ML-DS case associated with identical acquired chromosomal abnormalities was not previously reported. Our findings suggest that especially partial trisomy 1q25 to 1q44 may be indicative for a poor prognosis in ML-DS.

Somatic mutations activating Wiskott-Aldrich syndrome protein concomitant with RAS pathway mutations in juvenile myelomonocytic leukemia patients

The WAS gene product is expressed exclusively in the cytoplasm of hematopoietic cells and constitutional genetic abrogation of WASP leads to Wiskott-Aldrich syndrome (WAS). Moreover, mutational activation of WASP has been associated with X-linked neutropenia. Although studies reported that patients with constitutional WAS mutations affecting functional WASP expression may present juvenile myelomonocytic leukemia (JMML)-like features, confounding differential diagnosis above all in the copresence of mutated RAS, an activating somatic mutation of WASP has not been previously described in JMML patients. In our ongoing studies on JMML genomics, we at first detected a somatic WAS mutation in a major clone found at two consecutive relapses in one of two twins with JMML. Both twins were treated with hematopoietic stem cell transplantation after diagnosis of JMML. The somatic WAS mutation detected here displayed an activating WASP phenotype. Screening of 46 sporadic JMML patients at disease onset for mutations in the same PBD domain of WAS revealed two additional singleton patients carrying minor mutated clones. This is the first study to associate somatically acquired WASP mutations with a hematopoietic malignancy and increases insight in the complexity of the genomic landscape of JMML that shows low recurrent mutations concomitant with general hyperactivation of RAS pathway signaling.

Familial Myelodysplastic/Acute Leukemia Syndromes-Myeloid Neoplasms with Germline Predisposition

Although most cases of myeloid neoplasms are sporadic, a small subset has been associated with germline mutations. The 2016 revision of the World Health Organization classification included these cases in a myeloid neoplasm group with a predisposing germline mutational background. These patients must have a different management and their families should get genetic counseling. Cases identification and outline of the major known syndromes characteristics will be discussed in this text.

A unique set of complex chromosomal abnormalities in an infant with myeloid leukemia associated with Down syndrome

Background

Children with Down syndrome (DS) have an enhanced risk of developing acute leukemia, with the most common subtype being acute megakaryoblastic leukemia (AMKL). Myeloid leukemia in Down syndrome (ML-DS) is considered a disease with distinct clinical and biological features. There are few studies focusing on the clonal cytogenetic changes during evolution of ML-DS.

Case presentation

Here, we describe a complex karyotype involving a previously unreported set of chromosomal abnormalities acquired during progression of ML-DS in an infant boy: derivative der(1)t(1;15)(q24;q23), translocation t(4;5)(q26;q33) and derivative der(15)t(7;15)(p21;q23). Different molecular cytogenetic probes and probesets including whole chromosome painting (WCP) and locus specific probes, as well as, multicolor-FISH and multicolor chromosome banding (MCB) were performed in order to characterize the chromosomal abnormalities involved in this complex karyotype. The patient was treated according to the acute myeloid leukemia-Berlin-Frankfurt-Munich-2004 (AML-BFM 2004) treatment protocol for patients with Down syndrome; however, he experienced a poor clinical outcome.

Conclusion

The molecular cytogenetic studies performed, allowed the characterization of novel chromosomal abnormalities in ML-DS and possible candidate genes involved in the leukemogenic process. Our findings suggest that the complex karyotype described here was associated with the poor prognosis.

Down syndrome, RASopathies, and other rare syndromes

In this article we discuss the occurrence of myeloid neoplasms in patients with a range of syndromes that are due to germline defects of the RAS signaling pathway and in patients with trisomy 21. Both RAS mutations and trisomy 21 are common somatic events contributing to leukemogenis. Thus, the increased leukemia risk observed in children affected by these conditions is biologically highly plausible. Children with myeloid neoplasms in the context of these syndromes require different treatments than children with sporadic myeloid neoplasms and provide an opportunity to study the role of trisomy 21 and RAS signaling during leukemogenesis and development.

CRISPR/Cas9-Directed Reassignment of the GATA1 Initiation Codon in K562 Cells to Recapitulate AML in Down Syndrome

Using a CRISPR/Cas9 system, we have reengineered a translational start site in the GATA1 gene in K562 cells. This mutation accounts largely for the onset of myeloid leukemia in Down syndrome (ML-DS). For this reengineering, we utilized CRISPR/Cas9 to generate mammalian cell lines that express truncated versions of the Gata1s protein similar to that seen in ML-DS, as determined by analyzing specific genetic alterations resulting from CRISPR/Cas9 cleavage. During this work, 73 cell lines were clonally expanded, with allelic variance analyzed. Using Tracking of Indels by DEcomposition (TIDE) and Sanger sequencing, we defined the DNA sequence and variations within each allele. We found significant heterogeneity between alleles in the same clonally expanded cell, as well as among alleles from other clonal expansions. Our data demonstrate and highlight the importance of the randomness of resection promoted by non-homologous end joining after CRISPR/Cas9 cleavage in cells undergoing genetic reengineering. Such heterogeneity must be fully characterized to predict altered functionality inside target tissues and to accurately interpret the associated phenotype. Our data suggest that in cases where the objective is to rearrange specific nucleotides to redirect gene expression in human cells, it is imperative to analyze genetic composition at the individual allelic level.

Characteristics of the phenotypic abnormalities of bone marrow cells in childhood myelodysplastic syndromes and juvenile myelomonocytic leukemia

BACKGROUND

Immunophenotyping of bone marrow (BM) hemopoietic precursors is useful for diagnosis of adult myelodysplastic syndrome (MDS), but data concerning pediatric patients are limited. We analyzed immunophenotypic features of BM cells at diagnosis of children who were referred to the Brazilian Pediatric Cooperative Group of Myelodysplastic Syndromes.

METHODS

Diagnosis was based on clinical information, peripheral blood counts, BM cytology and cytogenetics. Patients with Down syndrome were excluded. Children with deficiency anemias or transitory neutropenias were used as controls (CTRLs). Immunophenotyping was performed on an eight-color antibody platform evaluating myelomonocytic maturation and progenitor cells.

RESULTS

A total of 32 patients were examined: 6 refractory cytopenia of childhood [RCC]; 5 refractory anemia with excess of blasts [RAEB]; 8 refractory anemia with excess of blasts in transformation [RAEB-t]; 13 juvenile myelomonocytic leukemia [JMML] and 10 CTRLs. Median age was 66 months (RCC), 68 months (RAEB/RAEB-t), 29 months (JMML) and 70 months (CTRLs). Median number of phenotypic alterations was 4 (range 1-6) in RCC; 6 (range 2-11) in RAEB/RAEB-t and 6 (range 2-11) in JMML (P = 0.004). The percentage of CD34⁺ /CD117⁺ /CD13⁺ cells was 0.5% (range 0.1-2.8) in RCC; 4.2% (range 0.3-10.1) in RAEB/RAEB-t and 3.7 % (range 0.5-8.6) in JMML cases, compared with 0.7% (0.5-1.2) in CTRLs (P < 0.0005). Aberrancies in antigen expression of myeloid progenitors were seen in 63% of JMML and in 45% of RAEB/RAEB-t. CD34⁺ /CD19⁺ /CD10⁺ cells were decreased or absent in patients compared with age-matched controls. T lymphocytes were decreased in JMML.

CONCLUSIONS

Phenotypic abnormalities were similar to those found in adult MDS. A decrease in B-cell precursors was observed especially in RAEB/RAEB-t. JMML and RAEB showed a similar pattern.

Juvenile Myelomonocytic Leukemia in Turkey: A Retrospective Analysis of Sixty-five Patients

OBJECTIVE

This study aimed to define the status of juvenile myelomonocytic leukemia (JMML) patients in Turkey in terms of time of diagnosis, clinical characteristics, mutational studies, clinical course, and treatment strategies.

MATERIALS AND METHODS

Data including clinical and laboratory characteristics and treatment strategies of JMML patients were collected retrospectively from pediatric hematology-oncology centers in Turkey.

RESULTS

Sixty-five children with JMML diagnosed between 2002 and 2016 in 18 institutions throughout Turkey were enrolled in the study. The median age at diagnosis was 17 months (min-max: 2-117 months). Splenomegaly was present in 92% of patients at the time of diagnosis. The median white blood cell, monocyte, and platelet counts were 32.9x109/L, 5.4x109/L, and 58.3x109/L, respectively. Monosomy 7 was present in 18% of patients. JMML mutational analysis was performed in 32 of 65 patients (49%) and PTPN11 was the most common mutation. Hematopoietic stem cell transplantation (HSCT) could only be performed in 28 patients (44%), the majority being after the year 2012. The most frequent reason for not performing HSCT was the inability to find a suitable donor. The median time from diagnosis to HSCT was 9 months (min-max: 2-63 months). The 5-year cumulative survival rate was 33% and median estimated survival time was 30±17.4 months (95% CI: 0-64.1) for all patients. Survival time was significantly better in the HSCT group (log-rank p=0.019). Older age at diagnosis (>2 years), platelet count of less than 40x109/L, and PTPN11 mutation were the factors significantly associated with shorter survival time.

CONCLUSION

Although there has recently been improvement in terms of definitive diagnosis and HSCT in JMML patients, the overall results are not satisfactory and it is necessary to put more effort into this issue in Turkey.

Myelodysplastic and myeloproliferative disorders of childhood

Myelodysplastic syndrome (MDS) and myeloproliferative disorders are rare in children; they are divided into low-grade MDS (refractory cytopenia of childhood [RCC]), advanced MDS (refractory anemia with excess blasts in transformation), and juvenile myelomonocytic leukemia (JMML), each with different characteristics and management strategies. Underlying genetic predisposition is recognized in an increasing number of patients. Germ line GATA2 mutation is found in 70% of adolescents with MDS and monosomy 7. It is challenging to distinguish RCC from aplastic anemia, inherited bone marrow failure, and reactive conditions. RCC is often hypoplastic and may respond to immunosuppressive therapy. In case of immunosuppressive therapy failure, hypercellular RCC, or RCC with monosomy 7, hematopoietic stem cell transplantation (HSCT) using reduced-intensity conditioning regimens is indicated. Almost all patients with refractory anemia with excess blasts are candidates for HSCT; children age 12 years or older have a higher risk of treatment-related death, and the conditioning regimens should be adjusted accordingly. Unraveling the genetics of JMML has demonstrated that JMML in patients with germ line PTPN11 and CBL mutations often regresses spontaneously, and therapy is seldom indicated. Conversely, patients with JMML and neurofibromatosis type 1, somatic PTPN11, KRAS, and most of those with NRAS mutations have a rapidly progressive disease, and early HSCT is indicated. The risk of relapse after HSCT is high, and prophylaxis for graft-versus-host disease and monitoring should be adapted to this risk.

Transient Abnormal Myelopoiesis and AML in Down Syndrome: an Update

Children with constitutional trisomy 21 (Down syndrome (DS)) have a unique predisposition to develop myeloid leukaemia of Down syndrome (ML-DS). This disorder is preceded by a transient neonatal preleukaemic syndrome, transient abnormal myelopoiesis (TAM). TAM and ML-DS are caused by co-operation between trisomy 21, which itself perturbs fetal haematopoiesis and acquired mutations in the key haematopoietic transcription factor gene GATA1. These mutations are found in almost one third of DS neonates and are frequently clinically and haematologcially 'silent'. While the majority of cases of TAM undergo spontaneous remission, ∼10 % will progress to ML-DS by acquiring transforming mutations in additional oncogenes. Recent advances in the unique biological, cytogenetic and molecular characteristics of TAM and ML-DS are reviewed here.

The Differencies in Adult and Pediatric Myelodysplastic Syndrome: A Review

Myelodysplastic syndrome (MDS) represent very heterogenous group of clonal stem cell bone marrow disorders with ineffective haematopoesis leading to cytopenias in peripheral blood and increased risk of blastic transformation and evolution of acute myeloid leukemia. MDS is a disease of older age mostly, in children it seems to be very rare. There are several significant morphological, cytogenetic and prognostic differencies of the disease in adults and in children. Adult MDS patients most commonly manifest with symptoms of anemia, bleeding and infection are uncommon. In childhood, MDS manifests predominantly by neutropenia and thrombocytopenia. In addition, some pediatric MDS patients present also with constitutional disease’s signs and symptoms. Early and correct diagnosis in both age groups is essential for the choice of appropriate therapy and also for next life of patients. However, the diagnosis of MDS is challenging, complex and requiring close correlation of clinical symptoms, laboratory parameters and standardized examination of BM biopsies. The authors present an overview focused on biology of MDS in adults and children, on the differences in the incidence, clinical presentation and treatment. They summarize the possibilities and limits of histopathological diagnosis and differential diagnosis of the disease in different age groups. A major problem in the morphological diagnosis of MDS remains the determination, whether the myelodysplasia is due to clonal disorder. It might result also from some other factors, as significant dysplasia can also occur in reactive conditions, and vice versa, only discrete dysplasia is sometimes observed in MDS patients. Although histomorphological and immunohistochemical analysis of BM biopsy is invasive and time-consuming examination, it has its value in the diagnosis, differential diagnosis and evaluation of therapeutic effect.