Transient leukaemia--a benign form of leukaemia in newborn infants with trisomy 21

The hematopoietic microenvironment of the fetal liver and transient abnormal myelopoiesis associated with Down syndrome: A review

Transient abnormal myelopoiesis (TAM) in neonates with Down syndrome is a distinct form of leukemia or preleukemia that mirrors the hematological features of acute megakaryoblastic leukemia. However, it typically resolves spontaneously in the early stages. TAM originates from fetal liver (FL) hematopoietic precursor cells and emerges due to somatic mutations in GATA1 in utero. In TAM, progenitor cells proliferate and differentiate into mature megakaryocytes and granulocytes. This process occurs both in vitro, aided by hematopoietic growth factors (HGFs) produced in the FL, and in vivo, particularly in specific anatomical sites like the FL and blood vessels. The FL's hematopoietic microenvironment plays a crucial role in TAM's pathogenesis and may contribute to its spontaneous regression. This review presents an overview of current knowledge regarding the unique features of TAM in relation to the FL hematopoietic microenvironment, focusing on the functions of HGFs and the pathological features of TAM.

Transient abnormal myelopoiesis requiring advanced neonatal intensive care treatment

AIM

Five to thirty percent of neonates with trisomy 21 develop transient abnormal myelopoiesis (TAM) with a high mortality rate. The aim of the study was to identify contributing factors that determine mortality and need for chemotherapy in this patient group.

METHODS

Six-year, single-centre, retrospective study of neonatal TAM cases requiring admission to intensive care. Data were collected from electronic patient records, laboratory and genetic results. The odds ratio was calculated to assess the likelihood of neonates with certain clinical characteristics having short-term mortality and needing chemotherapy.

RESULTS

Twenty-one neonates were studied with a mortality rate of 28%. Neonates requiring inotropic support (OR 19, 95% CI: 0.9-399, p = 0.05) and inhaled nitric oxide (iNO) (OR 13, 95% CI: 1.4-124.3, p = 0.03) were less likely to survive to discharge. Neonates needing mechanical ventilation (OR 14, 95% CI: 1.1-185.5, p = 0.04), or a white cell count >50 × 109/L (OR 27, 95% CI: 1.2-605.7, p = 0.04) were more likely to receive chemotherapy.

CONCLUSION

A high mortality rate was identified in TAM neonates with symptomatic pulmonary hypertension (PH) needing active treatment strategies, such as inotropes and iNO. The presence of PH should be considered in the clinical management, prognosis and parental counselling.

Down syndrome and leukemia: An insight into the disease biology and current treatment options

Children with Down syndrome (DS) have a 10- to 20-fold greater predisposition to develop acute leukemia compared to the general population, with a skew towards myeloid leukemia (ML-DS). While ML-DS is known to be a subtype with good outcome, patients who relapse face a dismal prognosis. Acute lymphocytic leukemia in DS (DS-ALL) is considered to have poor prognosis. The relapse rate is high in DS-ALL compared to their non-DS counterparts. We have a better understanding about the mutational spectrum of DS leukemia. Studies using animal, embryonic stem cell- and induced pluripotent stem cell-based models have shed light on the mechanism by which these mutations contribute to disease initiation and progression. In this review, we list the currently available treatment strategies for DS-leukemias along with their outcome with emphasis on challenges with chemotherapy-related toxicities in children with DS. We focus on the mechanisms of initiation and progression of leukemia in children with DS and highlight the novel molecular targets with greater success in preclinical trials that have the potential to progress to the clinic.

Chromosomal abnormalities associated with fetal pleural effusion (II): Specific and non-specific chromosome aberrations

Fetal pleural effusion has been reported to be associated with chromosomal abnormalities, genetic syndromes, obstructive uropathy, lymphatic vessel abnormalities such as Noonan syndrome, RASopathy and congenital lymphatic anomalies, thoracic cavity defects, Rh or ABO incompatibility, non-immune hydrops fetalis, infections, congenital cardiac anomalies, metabolic diseases and hematologic diseases such as α-thalassemia. This review provides a comprehensive view of specific and non-specific chromosome aberrations associated with fetal pleural effusion which is useful for genetic counseling and fetal therapy at prenatal diagnosis of fetal pleural effusion.

How I diagnose myeloid neoplasms with germline predisposition

OBJECTIVES

Pathologists play a crucial role in the initial diagnosis of germline predisposition to myeloid neoplasia and subsequent surveillance for disease progression. The diagnostic workup can be challenging, particularly if clinical history, laboratory testing, or genetic studies are incomplete or unavailable.

METHODS

Through case-based examples, we illustrate common diagnostic challenges and pitfalls encountered during bone marrow examination of patients being evaluated for myeloid malignancy with potential germline predisposition to myeloid neoplasia.

RESULTS

Lack of familial disease, the absence of syndromic manifestations, and late-onset hematologic malignancy do not exclude an underlying germline predisposition syndrome. Targeted myeloid sequencing panels can help identify potential germline alterations but may not detect large deletions or insertions, noncoding, or novel variants. Confirmation of the germline nature of an alteration detected in the peripheral blood or bone marrow ideally requires genetic testing using nonhematopoietic germline DNA to definitively distinguish between germline and somatic alterations. The ideal tissue source for germline testing is cultured skin fibroblasts. Certain germline predisposition syndromes can contain characteristic baseline bone marrow dysplastic-appearing features associated with cytopenias without constituting myelodysplastic syndrome.

CONCLUSION

Recognizing germline predisposition to myeloid neoplasia is critical for proper disease management. This recognition is particularly important for patients who will undergo hematopoietic stem cell transplantation to screen potential related donors. Integration of the clinical history, bone marrow findings, cytogenetic studies, and specialized laboratory and molecular genetic testing is often essential for accurate diagnosis and subsequent disease monitoring.

Transient abnormal myelopoiesis in Down syndrome: Experience of long term follow up from a single tertiary center in Thailand

Transient abnormal myelopoiesis (TAM) is a unique disease occurring in Down syndrome (DS) infants from which most patients have spontaneous remission. This study aimed to evaluate the incidence and outcomes of TAM in a tertiary center in Thailand. We reviewed the records of 997 DS patients diagnosed between June 1993 and October 2019. From the 997 DS patients, 32 had been diagnosed with TAM. The incidence of TAM was 3.2% and an overall survival rate of 87.5%. A total of 2/28 who survived (7.1%) subsequently developed AML-DS at the ages of 2.1 and 4.5 years, respectively. The risk factors related with death included maternal multiparity, sepsis, skin bleeding, subcutaneous nodules, high WBC count, low hemoglobin, and elevated AST level.Abbreviations.

Leukemogenesis in infants and young children with trisomy 21

Children with Down syndrome (DS) have a greater than 100-fold increased risk of developing acute myeloid leukemia (ML) and an approximately 30-fold increased risk of acute lymphoblastic leukemia (ALL) before their fifth birthday. ML-DS originates in utero and typically presents with a self-limiting, neonatal leukemic syndrome known as transient abnormal myelopoiesis (TAM) that is caused by cooperation between trisomy 21-associated abnormalities of fetal hematopoiesis and somatic N-terminal mutations in the transcription factor GATA1. Around 10% of neonates with DS have clinical signs of TAM, although the frequency of hematologically silent GATA1 mutations in DS neonates is much higher (~25%). While most cases of TAM/silent TAM resolve without treatment within 3 to 4 months, in 10% to 20% of cases transformation to full-blown leukemia occurs within the first 4 years of life when cells harboring GATA1 mutations persist and acquire secondary mutations, most often in cohesin genes. By contrast, DS-ALL, which is almost always B-lineage, presents after the first few months of life and is characterized by a high frequency of rearrangement of the CRLF2 gene (60%), often co-occurring with activating mutations in JAK2 or RAS genes. While treatment of ML-DS achieves long-term survival in approximately 90% of children, the outcome of DS-ALL is inferior to ALL in children without DS. Ongoing studies in primary cells and model systems indicate that the role of trisomy 21 in DS leukemogenesis is complex and cell context dependent but show promise in improving management and the treatment of relapse, in which the outcome of both ML-DS and DS-ALL remains poor.

Sensitive detection of GATA1 mutations using complementary DNA-based analysis for transient abnormal myelopoiesis associated with the Down syndrome

INTRODUCTION

GATA1 mutation plays an important role in initiating transient abnormal myelopoiesis (TAM) and in the clonal evolution towards acute megakaryoblastic leukaemia (AMKL) associated with Down syndrome (DS). This study aimed to develop and validate the clinical utility of a complementary DNA (cDNA) analysis in parallel with the conventional genomic DNA (gDNA) Sanger sequencing (Ss), as an initial screening test for GATA1 mutations.

METHODS

GATA1 mutations were evaluated using both gDNA and cDNA in 14 DS patients using Ss and fragment analysis (FA), respectively.

RESULTS

The detection sensitivity of conventional gDNA sequencing was limited in low blast percentage TAM (LBP-TAM); however, cDNA-based Ss readily detected all the pathognomonic GATA1 mutations. The cDNA-based FA readily detected GATA1 frameshift mutation with a reliable sensitivity ranging from 0.005% to 0.01% of clonal cells.

CONCLUSIONS

GATA1 mutations are heterogeneous; therefore, we would like to propose a dual cDNA and gDNA analysis as a standard diagnostic approach, especially for LBP-TAM. cDNA-based FA promises an excellent sensitivity for detecting frameshift GATA1 mutations in the longitudinal clonal evolution towards AMKL without using a patient specific primer.

The Mutational Landscape of Myeloid Leukaemia in Down Syndrome

Children with Down syndrome (DS) are particularly prone to haematopoietic disorders. Paediatric myeloid malignancies in DS occur at an unusually high frequency and generally follow a well-defined stepwise clinical evolution. First, the acquisition of mutations in the GATA1 transcription factor gives rise to a transient myeloproliferative disorder (TMD) in DS newborns. While this condition spontaneously resolves in most cases, some clones can acquire additional mutations, which trigger myeloid leukaemia of Down syndrome (ML-DS). These secondary mutations are predominantly found in chromatin and epigenetic regulators-such as cohesin, CTCF or EZH2-and in signalling mediators of the JAK/STAT and RAS pathways. Most of them are also found in non-DS myeloid malignancies, albeit at extremely different frequencies. Intriguingly, mutations in proteins involved in the three-dimensional organization of the genome are found in nearly 50% of cases. How the resulting mutant proteins cooperate with trisomy 21 and mutant GATA1 to promote ML-DS is not fully understood. In this review, we summarize and discuss current knowledge about the sequential acquisition of genomic alterations in ML-DS.

Increased risk of leukaemia in children with Down syndrome: a somatic evolutionary view

Children show a higher incidence of leukaemia compared with young adolescents, yet their cells are less damaged because of their young age. Children with Down syndrome (DS) have an even higher risk of developing leukaemia during the first years of life. The presence of a constitutive trisomy of chromosome 21 (T21) in DS acts as a genetic driver for leukaemia development, however, additional oncogenic mutations are required. Therefore, T21 provides the opportunity to better understand leukaemogenesis in children. Here, we describe the increased risk of leukaemia in DS during childhood from a somatic evolutionary view. According to this idea, cancer is caused by a variation in inheritable phenotypes within cell populations that are subjected to selective forces within the tissue context. We propose a model in which the increased risk of leukaemia in DS children derives from higher rates of mutation accumulation, already present during fetal development, which is further enhanced by changes in selection dynamics within the fetal liver niche. This model could possibly be used to understand the rate-limiting steps of leukaemogenesis early in life.

Congenital acute myeloid leukemia: challenges and lessons. A 15-year experience from the UK

Congenital Acute Myeloid leukemia (CAML) is a rare leukemia diagnosed within the first 28 days of life. Dismal survival rates of approximately 25% at two years from diagnosis have not improved despite multiple treatment protocols, and there lacks international consensus for optimal management of these vulnerable patients. We report a retrospective analysis of our fifteen-year experience from a large UK tertiary pediatric center, focusing on treatment modalities and outcomes, including late therapeutic toxicities. To our knowledge, this is the first UK series of congenital leukemia patients reported. Twelve patients with a median age of 16.4 days (1-60) were diagnosed with CAML in fifteen years. All patients presented unwell; 92% demonstrating skin involvement. 10 (83%) received chemotherapy; with 1 death at presentation and 1 spontaneous remission. 5 (42%) received subsequent stem cell transplant. Only 4 (33%) remain alive, with 5 (42%) dying in disease remission with treatment-related mortality. Documented cardiotoxicity was observed in 3 (25%) patients, with a further 2 (17%) suspected but not receiving postmortem. Treatment of congenital AML raises challenging diagnostic, therapeutic and ethical questions and requires multi-center, international collaboration to see improvements.

Transient abnormal myelopoiesis in pediatrics with trisomy 21

Transient abnormal myelopoiesis is common among Down syndrome patients. Although no therapeutic measures are required, close monitoring of comorbidities such as gastrointestinal bleeding is required. Long-term follow-up is promising for a healthy future and reduced requirement of unnecessary therapeutic measures including chemotherapy and remission of the pathology.

Genetic predisposition in pediatric oncology

Identifying patients with a genetic predisposition for developing malignant tumors has a significant impact on both the patient and family. Recognition of genetic predisposition, before diagnosing a malignant pathology, may lead to early diagnosis of a neoplasia. Recognition of a genetic predisposition syndrome after the diagnosis of neoplasia can result in a change of treatment plan, a specific follow-up of adverse treatment effects and, of course, a long-term follow-up focusing on the early detection of a second neoplasia.

Responsible for genetic syndromes that predispose individuals to malignant pathology are germline mutations. These mutations are present in all cells of conception, they can be inherited or can occur de novo.

Several mechanisms of inheritance are described: Mendelian autosomal dominant, Mendelian autosomal recessive, X-linked patterns, constitutional chromosomal abnormality and non-Mendelian inheritance.

In the following review we will present the most important genetic syndromes in pediatric oncology.

Transient Abnormal Myelopoeisis and Mosaic Down Syndrome in a Phenotypically Normal Newborn

Transient abnormal myelopoiesis (TAM) is a common and potentially fatal neonatal complication of newborn babies with Down syndrome (DS). Children born with mosaic DS are also at risk of developing TAM. However, due to their variable phenotypes, early identification of patients with mosaic DS may be difficult; thus, early diagnosis of TAM is just as challenging. In this report, we describe a case of a phenotypically normal newborn who presented with concerns for neonatal leukemia. The diagnosis of mosaic DS and TAM was confirmed with abnormal GATA1 mutation testing, highlighting the importance of early GATA1 mutation testing in newborn leukemia with high suspicion for TAM.

Clinical, cytogenetic, and molecular analyses of 17 neonates with transient abnormal myelopoiesis and nonconstitutional trisomy 21

BACKGROUND

Transient abnormal myelopoiesis (TAM) is a unique myeloproliferative disorder that occurs in neonates with constitutional trisomy 21/Down syndrome (DS). Although TAM also develops in neonates without constitutional trisomy 21, the clinical, cytogenetic, and molecular characteristics of those patients are not fully understood.

PROCEDURE

We retrospectively evaluated the clinical and cytogenetic findings and GATA1 mutation status of 17 neonates with TAM and nonconstitutional trisomy 21 tested for GATA1 mutations at our institute, and compared the findings with those of 64 neonates with TAM and constitutional trisomy 21/DS.

RESULTS

DS clinical features were observed in five of the 17 (29%) patients. In all patients, both trisomy 21 and GATA1 mutations were detected in diagnostic samples. Over a median follow-up of 33 (range, 0-139) months, early death (< 6 months of age) occurred in four patients (24%). Overall and event-free survivals were not significantly different between the patients with TAM and nonconstitutional trisomy 21 and those with TAM and constitutional trisomy 21/DS (five-year overall survival: 76% ± 10% vs 53% ± 13%, P = 0.40; five-year event-free survival: 55% ± 13% vs 48% ± 12%, P = 0.90). The five-year cumulative incidence of progression to myeloid leukemia of DS was also similar between the groups (21% vs 24%, P = 0.80).

CONCLUSIONS

Patients with TAM and nonconstitutional trisomy 21 exhibited similar biology and outcomes to those with TAM and constitutional trisomy 21/DS. The possibility of TAM should be considered even in phenotypically normal neonates with TAM symptoms, for appropriate management.

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.

Two Novel GATA1 Mutations in Transient Abnormal Myelopoiesis of Thai Neonates with Down Syndrome

Children with Down syndrome (DS) are 150 times more likely to develop acute myeloid leukemia (ML-DS), compared with those without. One risk factor is transient abnormal myelopoiesis (TAM). Somatic truncating GATA1 mutations are found in most TAM patients and are markers for future ML-DS. We identified two novel frameshift mutations in our seven newborns with DS and TAM: a heterozygous mutation of 17 nucleotide duplication (c.154_170 dup) and a heterozygous 9-nucleotide deletion combined with a 2-nucleotide insertion (c.150_158delins CT). Both mutations introduced a truncated GATA1 protein. Thus, neonates with DS and TAM require frequent ML-DS monitoring.

Transient leukemia of Down syndrome

Childhood leukemia is mostly a "developmental accident" during fetal hematopoiesis and may require multiple prenatal and postnatal "hits". The World Health Organization defines transient leukemia of Down syndrome (DS) as increased peripheral blood blasts in neonates with DS and classifies this type of leukemia as a separate entity. Although it was shown that DS predisposes children to myeloid leukemia, neither the nature of the predisposition nor the associated genetic lesions have been defined. Acute myeloid leukemia of DS is a unique disease characterized by a long pre-leukemic, myelodysplastic phase, unusual chromosomal findings and a high cure rate. In the present manuscript, we present a comprehensive review of the literature about clinical and biological findings of transient leukemia of DS (TL-DS) and link them with the genetic discoveries in the field. We address the manuscript to the pediatric generalist and especially to the next generation of pediatric hematologists.

Backtracked analysis of preleukemic fusion genes and DNA repair foci in umbilical cord blood of children with acute leukemia

The first event in origination of many childhood leukemias is a specific preleukemic fusion gene (PFG) that arises, often in utero, in hematopoietic stem/progenitor cells (HSPC) from misrepaired DNA double strand break (DSB). An immanently elevated level of DSB and impaired apoptosis may contribute to origination and persistence of PFG and donor cell-derived leukemia in recipients of allogeneic transplantation of umbilical cord blood (UCB). We investigated DSB, apoptosis and PFG in the backtracked UCB cells of leukemic patients. RNA from UCB of three patients with acute lymphoblastic leukemia, patient with acute megakaryoblastic leukemia and Down syndrome, and four healthy children was screened for common PFG by RT-qPCR. Presence of PFG was validated by sequencing. Endogenous γH2AX and 53BP1 DNA repair foci, cell populations, and apoptosis were analyzed in UCB CD34+/- cells with imaging and standard flow cytometry. We found MLL₂-AF4 and BCR-ABL (p190) fusion genes in UCB of two out from four pediatric patients, apparently not detected at diagnosis, while UCB cells of TEL-AML1+ ALL patient were tested negative for this PFG and no PFG were detected in UCB cells of healthy children. No significant difference in DNA damage and apoptosis between UCB CD34+/- cells from healthy children and leukemic patients was observed, while Down syndrome trisomy increased DNA damage and resulted in distribution of cell populations resembling transient abnormal myelopoiesis. Our findings indicate increased genetic instability in UCB HSPC of leukemic patients and may be potentially used for diagnostics and exclusion of possibly affected UCB from transplantation.

A novel role of CKIP-1 in promoting megakaryocytic differentiation

Casein kinase 2-interacting protein-1 (CKIP-1) is a known regulator of cardiomyocytes and macrophage proliferation. In this study, we showed that CKIP-1 was involved in the process of megakaryocytic differentiation. During megakaryocytic differentiation of K562 cells, CKIP-1 was dramatically upregulated and this upregulation induced by PMA was mediated through downregulation of transcription factor GATA-1. By transient transfection, oligonucleotide-directed mutagenesis and chromatin immunoprecipitation assays, we identified the transcriptional regulation of CKIP-1 by GATA-1. Overexpression of CKIP-1 initiated events of spontaneous megakaryocytic differentiation in K562 cells. Conversely, knockdown of CKIP-1 in cell lines suppressed megakaryocytic differentiation. Mechanistically, overexpression of CKIP-1 changed the expression levels of transcription factors that have been shown to be critical in erythro-megakaryocytic differentiation such as Fli-1, c-Myb and c-Myc. In vivo analysis confirmed that CKIP-1^−/− mice had decreased number of CD41⁺ cells harvested from bone marrow, and lower platelet levels when compared to wild-type littermates. This is the first direct evidence suggesting that CKIP-1 is a novel regulator of megakaryocytic differentiation.

GATA1 mutations in a cohort of Malaysian children with Down syndrome-associated myeloid disorder

INTRODUCTION

Children with Down syndrome (DS) are at increased risk of developing distinctive clonal myeloid disorders, including transient abnormal myelopoiesis (TAM) and myeloid leukaemia of DS (ML-DS). TAM connotes a spontaneously resolving congenital myeloproliferative state observed in 10%-20% of DS newborns. Following varying intervals of apparent remission, a proportion of children with TAM progress to develop ML-DS in early childhood. Therefore, TAM and ML-DS represent a biological continuum. Both disorders are characterised by recurring truncating somatic mutations of the GATA1 gene, which are considered key pathogenetic events.

METHODS

We herein report, to our knowledge, the first observation on the frequency and nature of GATA1 gene mutations in a cohort of Malaysian children with DS-associated TAM (n = 9) and ML-DS (n = 24) encountered successively over a period of five years at a national referral centre.

RESULTS

Of the 29 patients who underwent GATA1 analysis, GATA1 mutations were observed in 15 (51.7%) patients, including 6 (75.0%) out of 8 patients with TAM, and 9 (42.9%) of 21 patients with ML-DS. All identified mutations were located in exon 2 and the majority were sequence-terminating insertions or deletions (66.7%), including several hitherto unreported mutations (12 out of 15).

CONCLUSION

The low frequency of GATA1 mutations in ML-DS patients is unusual and potentially indicates distinctive genomic events in our patient cohort.

Distinct GATA1 Point Mutations in Monozygotic Twins With Down Syndrome and Transient Abnormal Myelopoiesis From a Triplet Pregnancy: A Case Report and Review of Literature

OBJECTIVES

Down syndrome (DS)-associated transient abnormal myelopoiesis (TAM) or acute megakaryoblastic leukemia (AMKL) in monozygotic twins is exceedingly rare and has not been well characterized.

METHODS

We describe a unique case of monozygotic twins with simultaneous TAM from a triplet pregnancy at 34 weeks' gestation. Previously reported cases of TAM and DS-AMKL in monozygotic twins have been reviewed to compare with our cases. The current concept of a sequential multistep process in leukemogenesis and disease evolution of TAM into DS-AMKL through the collaboration among trisomy 21, GATA1, and other gene mutations is also reviewed.

RESULTS

Distinct GATA1 mutations are identified in our neonate twins with TAM from a triplet pregnancy, whereas precisely identical GATA1 mutations have been detected in all three monozygotic DS twins reported in the literature.

CONCLUSIONS

Identical GATA1 mutations in cases of monozygotic twins are likely derived from twin-twin transmission. Distinct GATA1 mutations identified in our neonate twins with TAM provide unequivocal evidence of independent intra-utero GATA1 mutations, a completely different mechanism of development of TAM in monozygotic twins from previously reported cases. Interaction of trisomy 21 and GATA1 mutation produces TAM, but additional gene mutations are required for TAM to transform into DS-AMKL.

[Infant acute leukemia]

If acute leukemia is the most frequent cancer in childhood (33%), it remains a very rare diagnosis in infants less than one year old, e.g. less than 5% of cases. At this age, the frequency of acute lymphoblastic leukemia (ALL) (almost all of B-lineage) is quite similar to the one of myeloblastic forms (AML). Infant leukemia frequently presents with high hyperleucocytosis, major tumoral burden and numerous extra-hematological features, especially in central nervous system and skin. Whatever the lineage, the leukemic cell is often very immature cytologically and immunologically. Rearrangements of the Mixed Lineage Leukemia (MLL) gene, located on band 11q23, are the hallmark of these immature leukemias and confer a particular resistance to conventional approaches, corticosteroids and chemotherapy. The immaturity of infants less than 1-year-old is associated to a decrease of the tolerable dose-intensity of some drugs (anthracyclines, alkylating agents) or asks questions about some procedures like radiotherapy or high dose conditioning regimen, responsible of inacceptable acute and late toxicities. The high level of severe infectious diseases and other high-grade side effects limits also the capacity to cure these infants. The survival of infants less than 1-year-old with AML is only 50% but similar to older children. On the other hand, survival of those with ALL is the same, then quite limited comparing the 80% survival in children over one year. Allogeneic stem cell transplantations are indicated in high-risk subgroups of infant ALL (age below 6 months, high hyperleucocytosis >300.10(9)/L, MLL-rearrangement, initial poor prednisone response). However, morbidity and mortality remain very important and these approaches cannot be extended to all cases. During the neonatal period, the dismal prognosis linked to the high number of primary failures or very early relapses and uncertainties about the late toxicities question physicians about ethics. It is an emergency to propose different strategies (targeted therapies) to these infants with acute leukemia as conventional trials failed to improve outcome.

Extensive placental choriovascular infiltration by maturing myeloid cells in down syndrome-associated transient abnormal myelopoiesis

Transient abnormal myelopoiesis (TAM), a clonal proliferation of predominantly megakaryocytic precursor cells, affects 4%-10% of newborns with Down syndrome. Approximately 20%-30% of TAM survivors are at risk of development of acute myeloid leukemia (myeloid leukemia associated with Down syndrome, ML-DS). We report unusual placental findings in a female infant with trisomy 21 born at 38 weeks of gestation. In line with previous descriptions of placental pathology in infants with TAM, abundant blast-like cells were present in the lumen of chorionic and stem villous vessels. In addition, there was multifocal extensive infiltration of the wall of chorionic vessels by maturing myeloid cells in a pattern reminiscent of TAM- or leukemia-associated systemic infiltration. The clinical significance of this unusual choriovascular involvement of the placenta in TAM is undetermined.

Acute megakaryoblastic leukemia with acquired trisomy 21 and GATA1 mutations in phenotypically normal children

GATA1 mutations are found almost exclusively in children with myeloid proliferations related to Down syndrome (DS). Here, we report two phenotypically and cytogenetically normal children with acute megakaryoblastic leukemia (AMKL) whose blasts had both acquired trisomy 21 and GATA1 mutation. Patient 1 was diagnosed with transient abnormal myelopoiesis in the neonatal period. Following spontaneous improvement of the disease, leukemic blasts increased 7 months later. He received less intensive chemotherapy, and he is now 6 years old in complete remission. Patient 2 was diagnosed with AMKL at the age of 18 months. Although he received intensive chemotherapy and a cord blood transplantation, he died without gaining remission. In both cases, trisomy 21 and GATA1 mutation were detected only in leukemic blasts, but not in germline samples. Based on a literature review, we identified reports describing 14 non-DS AMKL with GATA1 mutation and acquired trisomy 21. Of those, 12 cases were diagnosed during the neonatal period, whereas the remaining 2 cases were diagnosed at the age of 22 and 31 months, respectively.

CONCLUSION

These cases suggest that GATA1 mutation may cooperate with the additional chromosome 21 in developing myeloid proliferations even in non-DS patients.

Down syndrome preleukemia and leukemia

Children with Down syndrome (DS) and acute leukemias acute have unique biological, cytogenetic, and intrinsic factors that affect their treatment and outcome. Myeloid leukemia of Down syndrome (ML-DS) is associated with high event-free survival (EFS) rates and frequently preceded by a preleukemia condition, the transient abnormal hematopoiesis (TAM) present at birth. For acute lymphoblastic leukemia (ALL), their EFS and overall survival are poorer than non-DS ALL, it is important to enroll them on therapeutic trials, including relapse trials; investigate new agents that could potentially improve their leukemia-free survival; and strive to maximize the supportive care these patients need.

Fetal liver stromal cells support blast growth in transient abnormal myelopoiesis in Down syndrome through GM-CSF

Transient abnormal myelopoiesis (TAM) in neonates with Down syndrome, which spontaneously resolves within several weeks or months after birth, may represent a very special form of leukemia arising in the fetal liver (FL). To explore the role of the fetal hematopoietic microenvironment in the pathogenesis of TAM, we examined the in vitro influences of stromal cells of human FL and fetal bone marrow (FBM) on the growth of TAM blasts. Both FL and FBM stromal cells expressed mesenchymal cell antigens (vimentin, α-smooth muscle actin, CD146, and nestin), being consistent with perivascular cells/mesenchymal stem cells that support hematopoietic stem cells. In addition, a small fraction of the FL stromal cells expressed an epithelial marker, cytokeratin 8, indicating that they could be cells in epithelial-mesenchymal transition (EMT). In the coculture system, stromal cells of the FL, but not FBM, potently supported the growth of TAM blast progenitors, mainly through humoral factors. High concentrations of hematopoietic growth factors were detected in culture supernatants of the FL stromal cells and a neutralizing antibody against granulocyte-macrophage colony-stimulating factor (GM-CSF) almost completely inhibited the growth-supportive activity of the culture supernatants. These results indicate that FL stromal cells with unique characteristics of EMT cells provide a pivotal hematopoietic microenvironment for TAM blasts and that GM-CSF produced by FL stromal cells may play an important role in the pathogenesis of TAM.

Haematopoietic development and leukaemia in Down syndrome

Children with constitutional trisomy 21 (cT21, Down Syndrome, DS) are at a higher risk for both myeloid and B-lymphoid leukaemias. The myeloid leukaemias are often preceded by a transient neonatal pre-leukaemic syndrome, Transient Abnormal Myelopoiesis (TAM). TAM is caused by cooperation between cT21 and acquired somatic N-terminal truncating mutations in the key haematopoietic transcription factor GATA1. These mutations, which are not leukaemogenic in the absence of cT21, are found in almost one-third of neonates with DS. Analysis of primary human fetal liver haematopoietic cells and of human embryonic stem cells demonstrates that cT21 itself substantially alters human fetal haematopoietic development. Consequently, many haematopoietic developmental defects are observed in neonates with DS even in the absence of TAM. Although studies in mouse models have suggested a pathogenic role of deregulated expression of several chromosome 21-encoded genes, their role in human leukaemogenesis remains unclear. As cT21 exists in all embryonic cells, the molecular basis of cT21-associated leukaemias probably reflects a complex interaction between deregulated gene expression in haematopoietic cells and the fetal haematopoietic microenvironment in DS.

The prenatal origins of cancer

The concept that some childhood malignancies arise from postnatally persistent embryonal cells has a long history. Recent research has strengthened the links between driver mutations and embryonal and early postnatal development. This evidence, coupled with much greater detail on the cell of origin and the initial steps in embryonal cancer initiation, has identified important therapeutic targets and provided renewed interest in strategies for the early detection and prevention of childhood cancer.

Morphologic and GATA1 sequencing analysis of hematopoiesis in fetuses with trisomy 21

Trisomy 21 alters fetal liver hematopoiesis and, in combination with somatic globin transcription factor 1 (GATA1) mutations, leads to development of transient myeloproliferative disease in newborns. However, little is known about the morphological hematopoietic changes caused by trisomy 21 in the fetus, and to date, the exact onset of GATA1 mutations remains uncertain. Therefore, we analyzed fetal liver hematopoiesis from second trimester pregnancies in trisomy 21 and screened for GATA1 mutations. We examined 57 formalin-fixed and paraffin-embedded fetal liver specimens (49 harboring trisomy 21 and 8 controls) by immunohistochemistry for CD34, CD61, factor VIII, and glycophorin A. GATA1 exon 2 was sequenced in fetal livers and corresponding nonhematologic tissue. Cell counts of megakaryocytes (P = .022), megakaryocytic precursors (P = .021), and erythroid precursors were higher in trisomy 21 cases. CD34-positive hematopoietic blasts showed no statistically significant differences. No mutation was detected by GATA1 exon 2 sequencing in fetal livers from 12 to 25 weeks of gestation. Our results suggest that GATA1 exon 2 mutations occur late in trisomy 21 fetal hematopoiesis. However, trisomy 21 alone provides a proliferative stimulus of fetal megakaryopoiesis and erythropoiesis. CD34-positive precursor cells are not increased in trisomy 21 fetal livers.

GATA1-mutant clones are frequent and often unsuspected in babies with Down syndrome: identification of a population at risk of leukemia

Transient abnormal myelopoiesis (TAM), a preleukemic disorder unique to neonates with Down syndrome (DS), may transform to childhood acute myeloid leukemia (ML-DS). Acquired GATA1 mutations are present in both TAM and ML-DS. Current definitions of TAM specify neither the percentage of blasts nor the role of GATA1 mutation analysis. To define TAM, we prospectively analyzed clinical findings, blood counts and smears, and GATA1 mutation status in 200 DS neonates. All DS neonates had multiple blood count and smear abnormalities. Surprisingly, 195 of 200 (97.5%) had circulating blasts. GATA1 mutations were detected by Sanger sequencing/denaturing high performance liquid chromatography (Ss/DHPLC) in 17 of 200 (8.5%), all with blasts >10%. Furthermore low-abundance GATA1 mutant clones were detected by targeted next-generation resequencing (NGS) in 18 of 88 (20.4%; sensitivity ∼0.3%) DS neonates without Ss/DHPLC-detectable GATA1 mutations. No clinical or hematologic features distinguished these 18 neonates. We suggest the term "silent TAM" for neonates with DS with GATA1 mutations detectable only by NGS. To identify all babies at risk of ML-DS, we suggest GATA1 mutation and blood count and smear analyses should be performed in DS neonates. Ss/DPHLC can be used for initial screening, but where GATA1 mutations are undetectable by Ss/DHPLC, NGS-based methods can identify neonates with small GATA1 mutant clones.

Development of acute megakaryoblastic leukemia in Down syndrome is associated with sequential epigenetic changes

Acute megakaryoblastic leukemia (AMKL) is more frequently observed in Down syndrome (DS) patients, in whom it is often preceded by a transient myeloproliferative disorder (TMD). The development of DS-TMD and DS-AMKL requires not only the presence of the trisomy 21 but also that of GATA1 mutations. Despite extensive studies into the genetics of DS-AMKL, the importance of epigenetic deregulation in this disease has been unexplored. We performed DNA methylation profiling at different stages of development of DS-AMKL and analyzed the dynamics of the epigenetic program. Early genome-wide DNA methylation changes can be detected in trisomy 21 fetal liver mononuclear cells, prior to the acquisition of GATA1 mutations. These early changes are characterized by marked loss of DNA methylation at genes associated with developmental disorders, including those affecting the cardiovascular, neurological, and endocrine systems. This is followed by a second wave of changes detected in DS-TMD and DS-AMKL, characterized by gains of methylation. This new wave of hypermethylation targets a distinct set of genes involved in hematopoiesis and regulation of cell growth and proliferation. These findings indicate that the final epigenetic landscape of DS-AMKL is the result of sequential and opposing changes in DNA methylation occurring at specific times in the disease development.

Direct protein interactions are responsible for Ikaros-GATA and Ikaros-Cdk9 cooperativeness in hematopoietic cells

Ikaros (Ik) is a critical regulator of hematopoietic gene expression. Here, we established that the Ik interactions with GATA transcription factors and cyclin-dependent kinase 9 (Cdk9), a component of the positive transcription elongation factor b (P-TEFb), are required for transcriptional activation of Ik target genes. A detailed dissection of Ik-GATA and Ik-Cdk9 protein interactions indicated that the C-terminal zinc finger domain of Ik interacts directly with the C-terminal zinc fingers of GATA1, GATA2, and GATA3, whereas the N-terminal zinc finger domain of Ik is required for interaction with the kinase and T-loop domains of Cdk9. The relevance of these interactions was demonstrated in vivo in COS-7 and primary hematopoietic cells, in which Ik facilitated Cdk9 and GATA protein recruitment to gene promoters and transcriptional activation. Moreover, the oncogenic isoform Ik6 did not efficiently interact with Cdk9 or GATA proteins in vivo and perturbed Cdk9/P-TEFb recruitment to Ik target genes, thereby affecting transcription elongation. Finally, characterization of a novel nuclear Ik isoform revealed that Ik exon 6 is dispensable for interactions with Mi2 and GATA proteins but is essential for the Cdk9 interaction. Thus, Ik is central to the Ik-GATA-Cdk9 regulatory network, which is broadly utilized for gene regulation in hematopoietic cells.

Blast cell deficiency of CD11a as a marker of acute megakaryoblastic leukemia and transient myeloproliferative disease in children with and without Down syndrome

BACKGROUND

The classification of acute myeloid leukemia (AML) FAB subtype M7 relies on immunophenotypic assessment. CD41 is expressed throughout all stages of maturation of megakaryocytes and has therefore been described as a specific blast cell marker in AML M7 as well as in transient myeloproliferative disease (TMD) of patients with Down syndrome (DS). However, technical difficulties underlie the need for new markers for these entities.

METHODS

We evaluated the expression of human lymphocyte function-associated antigen 1 (CD11a) in a large cohort of pediatric AML and TMD patients (n = 91) of the Austrian AML-BFM 98 and 2004 studies.

RESULTS

We found a consistent deficiency of CD11a as assessed by mean fluorescence intensity in all patients with non-DS AML M7 (n = 8) and M6 (n = 1), all cases of classical DS-AML (n = 12) as well as TMD (n = 15) that was statistically significant in comparison to non-DS AML M0-M5 patients (n = 55; P < 0.001, sensitivity 100%). Only three of 55 Non-DS M0-5 patients were CD11a deficient (specificity 95%). Monocytic leukemias (M4/5) and normal monocytes typically showed a high CD11a expression, FAB types M1/2 and normal neutrophils an intermediate expression level, while all M3 leukemias were rather low in CD11a expression.

CONCLUSIONS

We conclude, that deficiency of CD11a expression should be added to the diagnostic criteria of AML-M7, classical DS-AML and TMD.

Concise review: preleukemic stem cells: molecular biology and clinical implications of the precursors to leukemia stem cells

Recent experimental evidence has shown that acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) arise from transformed immature hematopoietic cells following the accumulation of multiple stepwise genetic and epigenetic changes in hematopoietic stem cells and committed progenitors. The series of transforming events initially gives rise to preleukemic stem cells (pre-LSC), preceding the formation of fully transformed leukemia stem cells (LSC). Despite the established use of poly-chemotherapy, relapse continues to be the most common cause of death in AML and MDS. The therapeutic elimination of all LSC, as well as pre-LSC, which provide a silent reservoir for the re-formation of LSC, will be essential for achieving lasting cures. Conventional sequencing and next-generation genome sequencing have allowed us to describe many of the recurrent mutations in the bulk cell populations in AML and MDS, and recent work has also focused on identifying the initial molecular changes contributing to leukemogenesis. Here we review recent and ongoing advances in understanding the roles of pre-LSC, and the aberrations that lead to pre-LSC formation and subsequent LSC transformation.

Transient Myeloproliferative Disorder and Down Syndrome: Is there a link?

An extremely premature male neonate presented with an unusual multisystem dysfunction within the first 24 to 48 hours of life. The unfolding of clinical events and investigations revealed a transient myeloproliferative disorder (TMD). TMD was the main indication for karyotyping of this premature infant without clinical symptoms of Down syndrome. The awareness of TMD in a newborn warrants karyotype analysis to look for trisomy 21 and a close surveillance because of its potential progression to true leukaemia.

Acute leukemias in children with Down syndrome

Children with Down syndrome (DS) often present with hematopoietic abnormalities, and are at increased risk of developing leukemia. Specifically, 3-10% of newborns with DS are diagnosed with transient myeloproliferative disease, and children with DS are 500 times more likely to develop acute megakaryoblastic leukemia (AMKL) and 20 times more likely to develop acute lymphoblastic leukemia (ALL) than typical children. This review examines the characteristics of these leukemias and their development in the unique genetic background of trisomy 21. A discussion is also provided for areas of future research and potential therapeutic development.