Natural history of transient myeloproliferative disorder clinically diagnosed in Down syndrome neonates: a report from the Children's Oncology Group Study A2971

Eosinophilia in a Neonate With Trisomy 21, Transient Abnormal Myelopoiesis, and Neurofibromatosis Type 1

Transient abnormal myelopoiesis is a syndrome that causes excess proliferation of immature myeloid cells and occurs in 10% to 15% of neonates with trisomy 21. Transient abnormal myelopoiesis usually resolves spontaneously but occasionally requires treatment with chemotherapy. The disorder is not typically associated with eosinophilia. We report on a neonate with trisomy 21 and transient abnormal myelopoiesis characterized by leukocytosis with marked eosinophilia. The patient required 2 cycles of cytarabine for adequate myeloproliferative control. Furthermore, this patient was subsequently also diagnosed with neurofibromatosis type 1, which has no known association with trisomy 21 or transient abnormal myelopoiesis.

Trisomy 21 and Congenital Heart Disease: Impact on Health and Functional Outcomes From Birth Through Adolescence: A Scientific Statement From the American Heart Association

Due to improvements in recognition and management of their multisystem disease, the long-term survival of infants, children, and adolescents with trisomy 21 and congenital heart disease now matches children with congenital heart disease and no genetic condition in many scenarios. Although this improved survival is a triumph, individuals with trisomy 21 and congenital heart disease have unique and complex care needs in the domains of physical, developmental, and psychosocial health, which affect functional status and quality of life. Pulmonary hypertension and single ventricle heart disease are 2 known cardiovascular conditions that reduce life expectancy in individuals with trisomy 21. Multisystem involvement with respiratory, endocrine, gastrointestinal, hematological, neurological, and sensory systems can interact with cardiovascular health concerns to amplify adverse effects. Neurodevelopmental, psychological, and functional challenges can also affect quality of life. A highly coordinated interdisciplinary care team model, or medical home, can help address these complex and interactive conditions from infancy through the transition to adult care settings. The purpose of this Scientific Statement is to identify ongoing cardiovascular and multisystem, developmental, and psychosocial health concerns for children with trisomy 21 and congenital heart disease from birth through adolescence and to provide a framework for monitoring and management to optimize quality of life and functional status.

Down syndrome-associated leukaemias: current evidence and challenges

Children with Down syndrome (DS) are at increased risk of developing haematological malignancies, in particular acute megakaryoblastic leukaemia and acute lymphoblastic leukaemia. The microenvironment established by abnormal haematopoiesis driven by trisomy 21 is compounded by additional genetic and epigenetic changes that can drive leukaemogenesis in patients with DS. GATA-binding protein 1 (GATA1) somatic mutations are implicated in the development of transient abnormal myelopoiesis and the progression to myeloid leukaemia of DS (ML-DS) and provide a model of the multi-step process of leukaemogenesis in DS. This review summarises key genetic drivers for the development of leukaemia in patients with DS, the biology and treatment of ML-DS and DS-associated acute lymphoblastic leukaemia, late effects of treatments for DS-leukaemias and the focus for future targeted therapy.

Cytokine profiling in 128 patients with transient abnormal myelopoiesis: a report from the JPLSG TAM-10 trial

ABSTRACT

Transient abnormal myelopoiesis (TAM) occurs in 10% of neonates with Down syndrome (DS). Although most patients show spontaneous resolution of TAM, early death occurs in ∼20% of cases. Therefore, new biomarkers are needed to predict early death and determine therapeutic interventions. This study aimed to determine the association between clinical characteristics and cytokine levels in patients with TAM. A total of 128 patients with DS with TAM enrolled in the TAM-10 study conducted by the Japanese Pediatric Leukemia/Lymphoma Study Group were included in this study. Five cytokine levels (interleukin-1b [IL-1b], IL-1 receptor agonist, IL-6, IL-8, and IL-13) were significantly higher in patients with early death than in those with nonearly death. Cumulative incidence rates (CIRs) of early death were significantly associated with high levels of the 5 cytokines. Based on unsupervised consensus clustering, patients were classified into 3 cytokine groups: hot-1 (n = 37), hot-2 (n = 42), and cold (n = 49). The CIR of early death was significantly different between the cytokine groups (hot-1/2, n = 79; cold, n = 49; hot-1/2 CIR, 16.5% [95% confidence interval (CI), 7.9-24.2]; cold CIR, 2.0% [95% CI, 0.0-5.9]; P = .013). Furthermore, cytokine groups (hot-1/2 vs cold) were independent poor prognostic factors in the multivariable analysis for early death (hazard ratio, 15.53; 95% CI, 1.434-168.3; P = .024). These results provide valuable information that cytokine level measurement was useful in predicting early death in patients with TAM and might help to determine the need for therapeutic interventions. This trial was registered at UMIN Clinical Trials Registry as #UMIN000005418.

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.

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.

[SFCE harmonization workshops: Neonatal acute myeloid leukemia]

Neonatal acute myeloid leukemias (AML) occurred within the first 28 days of life and constitute only a small proportion of all AL. They are distinguished from leukemias of older children by their clinical presentation, which frequently includes cutaneous localizations ("blueberry muffin rash syndrome") and a leukocytosis above 50 ×109/L. This proliferation may be transient, causing a transient leukemoid reaction in a background of constitutional trisomy 21 ("Transient Abnormal Myelopoieseis" or TAM) or Infantile Myeloproliferative Disease in the absence of constitutional trisomy 21 ("Infantile Myeloproliferative Disease" or IMD). In cases of true neonatal AML, the prognosis of patients is poor. Overall survival is around 35 % in the largest historical series. This poor prognosis is mainly due to the period of onset of this pathology making the use of chemotherapy more limited and involving many considerations, both ethical and therapeutic. The objective of this work is to review this rare pathology by addressing the clinical, biological, therapeutic and ethical particularities of patients with true neonatal AML or transient leukemoid reactions occurring in a constitutional trisomy 21 (true TAM) or somatic background (IMD).

Survival outcomes of myeloid leukemia associated with Down syndrome and de novo acute myeloid leukemia in children: Experience from a single tertiary center in Thailand

Few studies have reported the survival outcomes of myeloid leukemia associated with Down syndrome (DS) in resource-limited countries. This study aimed to compare characteristics and survival outcomes of children with acute myeloid leukemia (AML) between those with and without DS in Thailand. The medical records of AML patients aged 0-15 years treated in a major tertiary center in Southern Thailand between October 1978 and December 2019 were reviewed retrospectively. The overall (OS) and event-free survivals (EFS) rates were calculated using the Kaplan-Meier method. A total of 362 AML patients were included, of which 41 (11.3%) had DS. The mean age at diagnosis of the DS patients was 2.5 ± 1.9 years and most of them (90.2%) were under the age of five. The DS patients had lower initial white blood cell counts and peripheral blasts compared to the non-DS patients. The AML-M7 subtype was more common in the DS than in the non-DS patients (80.5% vs. 9.1%, p < 0.01, respectively). The 5-year OS and EFS rates of the DS patients were lower compared to the non-DS patients (12.9% vs. 20.5%, p = 0.05 and 13.7% vs. 18.4%, p = 0.03, respectively). DS patients had a significantly higher rate of early and treatment-related deaths compared to non-DS patients (30.3% vs. 13.5%, p < 0.01 and 39.4% vs. 19.5%, p = 0.02, respectively). Over the study period, there were a decrease in early death rate and an increase in survival rates of DS patients, which suggests that chemotherapy regimens and supportive care have improved over time.

Transient Abnormal Myelopoiesis: An Abnormal Course and the Efficacy of Delayed Treatment

Transient abnormal myelopoiesis (TAM) is observed in a few neonates with Down syndrome. While a large proportion undergo complete remission without any treatment, some of them can develop myeloid leukemia of Down syndrome (ML-DS) in the future. Without proper treatment, mortality can be high. Here we have described an interesting and difficult-to-treat case of a neonatal with Down syndrome who presented with anemia, thrombocytopenia, and 75% blasts. We came across multiple challenges in treatment due to severe pneumonia.

Tumour lysis syndrome in a neonate with transient abnormal myelopoiesis

BACKGROUND

Tumor lysis syndrome (TLS) is an oncological emergency associated with hematological malignancies or highly proliferative solid tumors, commonly after chemotherapy. It is rarely associated with transient abnormal myelopoiesis.

OBSERVATION

We report a rare case of a neonate with transient abnormal myelopoiesis and tumor lysis syndrome, complicated with concomitant heart failure due to an underlying atrioventricular septal defect. Hyperhydration was contraindicated due to heart failure. The patient was managed conservatively with full recovery.

CONCLUSION

Tumor lysis syndrome should be suspected in neonates with transient abnormal myelopoiesis with electrolyte abnormalities. Treatment options should be considered carefully for their risks and benefits.

GATA1 in Normal and Pathologic Megakaryopoiesis and Platelet Development

GATA1 is a highly conserved hematopoietic transcription factor (TF), essential for normal erythropoiesis and megakaryopoiesis, that encodes a full-length, predominant isoform and an amino (N) terminus-truncated isoform GATA1s. It is consistently expressed throughout megakaryocyte development and interacts with its target genes either independently or in association with binding partners such as FOG1 (friend of GATA1). While the N-terminus and zinc finger have classically been demonstrated to be necessary for the normal regulation of platelet-specific genes, murine models, cell-line studies, and human case reports indicate that the carboxy-terminal activation domain and zinc finger also play key roles in precisely controlling megakaryocyte growth, proliferation, and maturation. Murine models have shown that disruptions to GATA1 increase the proliferation of immature megakaryocytes with abnormal architecture and impaired terminal differentiation into platelets. In humans, germline GATA1 mutations result in variable cytopenias, including macrothrombocytopenia with abnormal platelet aggregation and excessive bleeding tendencies, while acquired GATA1s mutations in individuals with trisomy 21 (T21) result in transient abnormal myelopoiesis (TAM) and myeloid leukemia of Down syndrome (ML-DS) arising from a megakaryocyte-erythroid progenitor (MEP). Taken together, GATA1 plays a key role in regulating megakaryocyte differentiation, maturation, and proliferative capacity. As sequencing and proteomic technologies expand, additional GATA1 mutations and regulatory mechanisms contributing to human diseases of megakaryocytes and platelets are likely to be revealed.

Too many white cells-TAM, JMML, or something else?

Leukocytosis is a common finding in pediatric patients, and the differential diagnosis can be broad, including benign reactive leukocytosis and malignant myeloproliferative disorders. Transient abnormal myelopoiesis is a myeloproliferative disorder that occurs in young infants with constitutional trisomy 21 and somatic GATA1 mutations. Most patients are observed, but outcomes span the spectrum from spontaneous resolution to life-threatening complications. Juvenile myelomonocytic leukemia is a highly aggressive myeloproliferative disorder associated with altered RAS-pathway signaling that occurs in infants and young children. Treatment typically involves hematopoietic stem cell transplantation, but certain patients can be observed. Early recognition of these and other myeloproliferative disorders is important and requires a clinician to be aware of these diagnoses and have a clear understanding of their presentations. This paper discusses the presentation and evaluation of leukocytosis when myeloproliferative disorders are part of the differential and reviews different concepts regarding treatment strategies.

Survival outcomes of children with relapsed or refractory myeloid leukemia associated with Down syndrome

Children with Down syndrome (DS) are at a significantly higher risk of developing acute myeloid leukemia, also termed myeloid leukemia associated with DS (ML-DS). In contrast to the highly favorable prognosis of primary ML-DS, the limited data that are available for children who relapse or who have refractory ML-DS (r/r ML-DS) suggest a dismal prognosis. There are few clinical trials and no standardized treatment approach for this population. We conducted a retrospective analysis of international study groups and pediatric oncology centers and identified 62 patients who received treatment with curative intent for r/r ML-DS between year 2000 to 2021. Median time from diagnosis to relapse was 6.8 (range, 1.1-45.5) months. Three-year event-free survival (EFS) and overall survival (OS) were 20.9 ± 5.3% and 22.1 ± 5.4%, respectively. Survival was associated with receipt of hematopoietic stem cell transplantation (HSCT) (hazard ratio [HR], 0.28), duration of first complete remission (CR1) (HR, 0.31 for > 12 months) and attainment of remission after relapse (HR, 4.03). Patients who achieved complete remission (CR) before HSCT, had an improved OS and EFS of 56.0 ± 11.8% and 50.5 ± 11.9%, respectively compared to those who underwent HSCT without CR (3-year OS and EFS of 10.0 ± 9.5%). Treatment failure after HSCT was predominantly because of disease recurrence (52%) followed by treatment-related mortality (10%). The prognosis of r/r ML-DS remains dismal even in the current treatment period and serve as a reference point for current prognostication and future interventional studies. Clinical trials aimed at improving the survival of patients with r/r ML-DS are needed.

Prenatal diagnosis of Down syndrome combined with transient abnormal myelopoiesis in foetuses with a GATA1 gene variant: two case reports

BACKGROUND

Down syndrome myeloid hyperplasia includes transient abnormal myelopoiesis (TAM) and the myeloid leukemia associated with Down syndrome (ML-DS). The mutation of GATA1 gene is essential in the development of Down syndrome combined with TAM or ML-DS. Some patients with TAM are asymptomatic and may also present with severe manifestations such as hepatosplenomegaly and hydrops.

CASE PRESENTATION

We report two cases of prenatally diagnosed TAM. One case was a rare placental low percentage 21 trisomy mosiacism, resulting in the occurrence of a false negative NIPT. The final diagnosis was made at 36 weeks of gestation when ultrasound revealed significant enlargement of the foetal liver and spleen and an enlarged heart; the foetus eventually died in utero. We detected a placenta with a low percentage (5-8%) of trisomy 21 mosiacism by Copy Number Variation Sequencing (CNV-seq) and Fluorescence in situ hybridization (FISH). In another case, foetal oedema was detected by ultrasound at 31 weeks of gestation. Two foetuses were diagnosed with Down syndrome by chromosomal microarray analysis via umbilical vein puncture and had significantly elevated cord blood leucocyte counts with large numbers of blasts. The GATA1 Sanger sequencing results suggested the presence of a [NM_002049.4(GATA1):c.220G > A (p. Val74Ile)] hemizygous variant and a [NM_002049.4(GATA1):c.49dupC(p. Gln17ProfsTer23)] hemizygous variant of the GATA1 gene in two cases.

CONCLUSION

It seems highly likely that these two identified mutations are the genetic cause of prenatal TAM in foetuses with Down syndrome.

Congenital leukemia: A case report and review of literature

BACKGROUND

Acute leukemia in newborns is also known as neonatal or congenital leukemia (CL) and is a rare disease with an incidence rate of 1-5 per 1000000 live births. After birth, infants with CL exhibit infiltrative cutaneous nodules, hepatosplenomegaly, thrombocytopenia, and immature leukocytes in the peripheral blood. These symptoms are frequently accompanied by congenital abnormalities including trisomy 21, trisomy 9, trisomy 13, or Turner syndrome. Despite significant advances in disease management, the survival rate is approximately 25% at 2 years.

CASE SUMMARY

Here, we document a case of trisomy 21-related acute myeloid leukemia (AML) in a female neonate. The baby was sent to the neonatal intensive care unit because of anorexia, poor responsiveness, and respiratory distress. She was diagnosed with AML based on bone marrow aspiration and immunophenotyping. Genetic sequencing identified a mutation in the GATA1 gene. After receiving the diagnosis, the parents decided against medical care for their child, and the baby died at home on day 9 after birth.

CONCLUSIONS

The newborn infant was diagnosed with trisomy 21-related AML. Genetic sequencing identified a mutation in the GATA1 gene. The parents abandoned medical treatment for their infant after receiving the diagnosis, and the infant died at home on the 9th day after birth.

Management of Down Syndrome-Associated Leukemias: A Review

Importance

Down syndrome (DS), caused by an extra copy of material from chromosome 21, is one of the most common genetic conditions. The increased risk of acute leukemia in DS (DS-AL) has been recognized for decades, consisting of an approximately 150-fold higher risk of acute myeloid leukemia (AML) before age 4 years, and a 10- to 20-fold higher risk of acute lymphoblastic leukemia (ALL), compared with children without DS.

Observations

A recent National Institutes of Health-sponsored conference, ImpacT21, reviewed research and clinical trials in children, adolescents, and young adults (AYAs) with DS-AL and are presented herein, including presentation and treatment, clinical trial design, and ethical considerations for this unique population. Between 10% to 30% of infants with DS are diagnosed with transient abnormal myelopoiesis (TAM), which spontaneously regresses. After a latency period of up to 4 years, 20% to 30% develop myeloid leukemia associated with DS (ML-DS). Recent studies have characterized somatic mutations associated with progression from TAM to ML-DS, but predicting which patients will progress to ML-DS remains elusive. Clinical trials for DS-AL have aimed to reduce treatment-related mortality (TRM) and improve survival. Children with ML-DS have better outcomes compared with non-DS AML, but outcomes remain dismal in relapse. In contrast, patients with DS-ALL have inferior outcomes compared with those without DS, due to both higher TRM and relapse. Management of relapsed leukemia poses unique challenges owing to disease biology and increased vulnerability to toxic effects. Late effects in survivors of DS-AL are an important area in need of further study because they may demonstrate unique patterns in the setting of chronic medical conditions associated with DS.

Conclusions and Relevance

Optimal management of DS-AL requires specific molecular testing, meticulous supportive care, and tailored therapy to reduce TRM while optimizing survival. There is no standard approach to treatment of relapsed disease. Future work should include identification of biomarkers predictive of toxic effects; enhanced clinical and scientific collaborations; promotion of access to novel agents through innovative clinical trial design; and dedicated studies of late effects of treatment.

Transient abnormal myelopoiesis with extramedullary involvement in a down syndrome preemie leading to an unresponsive course despite chemotherapy

INTRODUCTION

Transient abnormal myelopoiesis (TAM) is a transient, clonal myeloproliferative disorder unique to Down Syndrome (DS) babies. It is characterized by increased peripheral blasts and presence of GATA1 mutation. The clinical spectrum ranges from jaundice and hepatosplenomegaly to multi-organ failure and death. Here we present a case of a premature baby with DS diagnosed to have TAM with extramedullary involvement at birth who had a fatal outcome.

CASE REPORT

A 30.3-week-old female fetus with DS had leukocytosis (WBC: 187.82 K/uL) with neutrophilia (ANC 27.65 K/uL), macrocytic anemia (RBC: 2.41 m/uL, Hb 8.8 g/dL, MCV 108.3, MCH 36.5, MCHC 33.7) and thrombocytosis (platelet count 361 K/uL) at birth. Liver panels demonstrated normal bilirubin levels with elevated liver enzymes (AST = 239 U/L, ALT = 216 U/L).

RESULTS

Peripheral smear showed marked leukocytosis with increased blasts (70%), nucleated RBCs, giant platelets, and megakaryocytic elements. Flow cytometry demonstrated two populations of cells: 20% myeloblasts and 26% dim CD45 CD34- cells. GATA1 mutation was present. Based on these findings a diagnosis of TAM with extramedullary hematopoiesis was made. She received two cycles of cytarabine chemotherapy. Though her WBC levels reached a low of 18.93 K/uL, she developed multi-organ failure, eventually leading to death on day 45.

DISCUSSION

TAM is a transient condition resulting in disease resolution in around 80% of cases. Death is reported in 10% of cases. Risk factors associated with early death include prematurity, hyperleukocytosis, elevated bilirubin levels. Management of high-risk babies with chemotherapy is recommended to improve survival.

Myeloid Leukemia of Down Syndrome

Myeloid leukemia of Down syndrome (ML-DS) is characterized by a distinct natural history and is classified by the World Health Organization (WHO) as an independent entity, occurring with unique clinical and molecular features. The presence of a long preleukemic, myelodysplastic phase, called transient abnormal myelopoiesis (TAM), precedes the initiation of ML-DS and is defined by unusual chromosomal findings. Individuals with constitutional trisomy 21 have a profound dosage imbalance in the hematopoiesis-governing genes located on chromosome 21 and thus are subject to impaired fetal as well as to neonatal erythro-megakaryopoiesis. Almost all neonates with DS develop quantitative and morphological hematological abnormalities, yet still only 5-10% of them present with one of the preleukemic or leukemic conditions of DS. The acquired mutations in the key hematopoietic transcription factor gene GATA1, found solely in cells trisomic for chromosome 21, are considered to be the essential step for the selective growth advantage of leukemic cells. While the majority of cases of TAM remain clinically 'silent' or undergo spontaneous remission, the remaining 20% to 30% of them progress into ML-DS until the age of 4 years. The hypersensitivity of ML-DS blasts to chemotherapeutic agents, including but not limited to cytarabine, and drugs' increased infectious and cardiac toxicity have necessitated the development of risk-adapted treatment protocols for children with ML-DS. Recent advances in cytogenetics and specific molecular mechanisms involved in the evolution of TAM and ML-DS are reviewed here, as well as their integration in the improvement of risk stratification and targeted management of ML-DS.

Low-Level Germline 48,XYY,+21 Mosaicism Associated with Transient Abnormal Myelopoiesis in a Phenotypically Normal Neonate

Transient abnormal myelopoiesis (TAM) is a unique neonatal leukemoid reaction caused by a pathognomonic GATA1 mutation in conjunction with the gene dosage effect of trisomy 21, which is either of germline or somatic origin. We encountered a 48,XYY,+21 phenotypically normal neonate with Down syndrome who developed TAM due to cryptic germline mosaicism. Quantification of the mosaic ratio was complicated by an overestimation bias of hyperproliferating TAM within the germline component. To establish a workflow for such a clinical scenario, we analyzed the cytogenetic findings of neonates with TAM associated with somatic or low-level germline mosaicism. We showed that multistep diagnostic procedures (i.e., paired cytogenetic analyses of peripheral blood specimens in culture with or without phytohemagglutinin; serial cytogenetic studies of more than one tissue, such as the buccal membrane; and complementary DNA-based GATA1 mutation screening) can verify the specificity of cytogenetic testing for phenotypically normal neonates with TAM suspected of mosaicism.

Layered immunity and layered leukemogenicity: Developmentally restricted mechanisms of pediatric leukemia initiation

Hematopoietic stem cells (HSCs) and multipotent progenitor cells (MPPs) arise in successive waves during ontogeny, and their properties change significantly throughout life. Ontological changes in HSCs/MPPs underlie corresponding changes in mechanisms of pediatric leukemia initiation. As HSCs and MPPs progress from fetal to neonatal, juvenile and adult stages of life, they undergo transcriptional and epigenetic reprogramming that modifies immune output to meet age-specific pathogenic challenges. Some immune cells arise exclusively from fetal HSCs/MPPs. We propose that this layered immunity instructs cell fates that underlie a parallel layered leukemogenicity. Indeed, some pediatric leukemias, such as juvenile myelomonocytic leukemia, myeloid leukemia of Down syndrome, and infant pre-B-cell acute lymphoblastic leukemia, are age-restricted. They only present during infancy or early childhood. These leukemias likely arise from fetal progenitors that lose competence for transformation as they age. Other childhood leukemias, such as non-infant pre-B-cell acute lymphoblastic leukemia and acute myeloid leukemia, have mutation profiles that are common in childhood but rare in morphologically similar adult leukemias. These differences could reflect temporal changes in mechanisms of mutagenesis or changes in how progenitors respond to a given mutation at different ages. Interactions between leukemogenic mutations and normal developmental switches offer potential targets for therapy.

Bullous eruptions in transient abnormal myelopoiesis with normal phenotype

Cutaneous lesions are common manifestation of congenital leukaemia especially myeloid type with incidence of 25%-50% in reported cases. It is relatively rare in transient abnormal myelopoiesis (TAM) seen in trisomy 21 (~10%). The rashes seen in leukaemia and TAM are different. We report a case with a rare presentation of confluent bullous eruption in a phenotypically normal neonate with trisomy 21 restricted to haematopoietic blast cells. This rash resolved rapidly after low-dose cytarabine therapy with normalisation of total white cell counts. The risk of Down syndrome-associated myeloid leukaemia in such cases is still high (19%-23%) in first 5 years and rare thereafter.

Myeloid Proliferations Associated with Down Syndrome: Clinicopathologic Characteristics of Forty Cases from Five Large Academic Institutions

INTRODUCTION

The incidence of myelodysplastic syndrome and acute myeloid leukemia is significantly increased in children with Down syndrome (DS). Within the revised 2016 WHO edition, these entities are jointly classified as myeloid leukemia associated with DS (ML-DS). Additionally, infants with DS may develop transient abnormal myelopoiesis (TAM) which is histomorphologically similar to ML-DS. While TAM is self-limiting, it is associated with an increased risk of subsequently developing ML-DS. Differentiating TAM and ML-DS is challenging but clinically critical.

METHODS

We performed a retrospective review of ML-DS and TAM cases collected from five large academic institutions in the USA. We assessed clinical, pathological, immunophenotypical, and molecular features to identify differentiating criteria.

RESULTS

Forty cases were identified: 28 ML-DS and 12 TAM. Several features were diagnostically distinct, including younger age in TAM (p < 0.05), as well as presentation with clinically significant anemia and thrombocytopenia in ML-DS (p < 0.001). Dyserythropoiesis was unique to ML-DS, as well as structural cytogenetic abnormalities aside from the constitutional trisomy 21. Immunophenotypic characteristics of TAM and ML-DS were indistinguishable, including the aberrant expression of CD7 and CD56 by the myeloid blasts.

DISCUSSION

The findings of the study confirm marked biological similarities between TAM and ML-DS. At the same time, several significant clinical, morphological, and genetic differences were observed between TAM and ML-DS. The clinical approach and the differential diagnosis between these entities are discussed in detail.

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.

A rare case of hepatic sinusoidal occlusive syndrome in a premature neonate with trisomy 21

Trisomy 21 (Down Syndrome) may lead to multiple hematological and hepatobiliary manifestations including the development of transient abnormal myelopoiesis. While many cases resolve, transient abnormal myelopoiesis may lead to significant morbidity and mortality in a small percentage of patients. This condition may present a diagnostic challenge for physicians and currently there is only limited data on effective treatments, particularly with low blast percent transient abnormal myelopoiesis. We present a case of a neonate with trisomy 21 and multiple congenital anomalies who consequently developed hepatic failure with evidence of non-cirrhotic portal hypertension likely due to transient abnormal myelopoiesis. This clinical scenario highlights the need for additional evaluation for transient abnormal myelopoiesis associated hepatic disorder and possibly hepatic sinusoidal occlusive syndrome among trisomy 21 neonates particularly with low blast percentage.

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.

Pediatric Germline Predisposition to Myeloid Neoplasms

PURPOSE OF REVIEW

Advances in the understanding of germline predisposition to pediatric cancers, particularly myeloid neoplasms, have increased rapidly over the last 20 years. Here, we highlight the most up-to-date knowledge regarding known pathogenic germline variants that contribute to the development of myeloid neoplasms in children.

RECENT FINDINGS

This discussion enumerates the most notable myeloid neoplasm-causing germline mutations. These mutations may be organized based on their molecular underpinnings-transcriptional control, splicing and signal transduction control, and a group of heterogeneous bone marrow failure syndromes. We review recent findings related to the biochemical mechanisms that predispose to malignant transformation in each condition. Key genetic discoveries such as novel mutations, degrees of penetrance, principles of the two-hit hypothesis, and co-occurrence of multiple mutations are shared. Clinical pearls, such as information regarding epidemiology, natural history, or prognosis, are also discussed. Germline mutations predisposing to pediatric myeloid neoplasms are frequent, but underrecognized. They hold major clinical implications regarding prognosis, treatment strategies, and screening for other malignancies. Further research is warranted to better characterize each of these conditions, as well as identify additional novel germline pathogenic variants of interest.

Fetal Distress and Neonatal Death After Thoracoamniotic Shunting Therapy Due to Hydrops Associated With Transient Abnormal Myelopoiesis

We present the case of a pregnant woman who developed fetal bradycardia, which required an emergency cesarean delivery immediately after thoracoamniotic shunting (TAS), resulting in neonatal death four hours after birth due to hemodynamic deterioration. A 35-year-old Japanese female was referred to our hospital at 30⁺⁰ weeks of gestation due to fetal hydrops. Blood and ultrasonography examinations suggested that transient abnormal myelopoiesis (TAM) due to trisomy 21 could contribute to the development of hydrops fetalis. We performed thoracocentesis and TAS replacement as well as chromosomal testing of the amniotic fluid. However, the fetus developed persistent bradycardia soon after the treatment, and a sonographic examination revealed a recurrence of fluid retention in the thoracic cavity. A 1,558-g male neonate received life-saving resuscitation after being born via emergency surgery. Blood analysis revealed the occurrence of TAM in utero. At autopsy, there were no injuries to the intrathoracic organs. The G-banded karyotype revealed trisomy 21 (47, XY, +21). Our case offers new perspectives on providing prenatal information about potential complications to family members and selecting fetuses for TAS in the case of trisomy 21 complicated with TAM.

Clonal Myeloproliferative Disorders in Patients with Down Syndrome-Treatment and Outcome Results from an Institution in Argentina

Children with Down syndrome (DS) are at an increased risk of developing clonal myeloproliferative disorders. The balance between treatment intensity and treatment-related toxicity has not yet been defined. We analyzed this population to identify risk factors and optimal treatment. This single-center retrospective study included 78 DS patients <16 years-old with Transient Abnormal Myelopoiesis (TAM, n = 25), Acute Myeloblastic Leukemia (DS-AML, n = 41) of which 35 had classical Myeloid Leukemia associated with DS (ML-DS) with megakaryoblastic immunophenotype (AMKL) and 6 sporadic DS-AML (non-AMKL). Patients with DS-AML were treated according to four BFM-based protocols. Classical ML-DS vs. non-DS-AMKL were compared and the outcome of ML-DS was analyzed according to treatment intensity. Only four patients with TAM required cytoreduction with a 5-year Event-Free Survival probability (EFSp) of 74.4 (±9.1)%. DS-AML treatment-related deaths were due to infections, with a 5-year EFSp of 60.6 (±8.2)%. Megakaryoblastic immunophenotype was the strongest good-prognostic factor in univariate and multivariate analysis (p = 0.000). When compared ML-DS with non-DS-AMKL, a better outcome was associated with a lower relapse rate (p = 0.0002). Analysis of administered treatment was done on 32/33 ML-DS patients who achieved CR according to receiving or not high-dose ARA-C block (HDARA-C), and no difference in 5-year EFSp was observed (p = 0.172). TAM rarely required treatment and when severe manifestations occurred, early intervention was effective. DS-AML good outcome was associated with AMKL with a low relapse-rate. Even if treatment-related mortality is still high, our data do not support the omission of HDARA-C in ML-DS since we observed a trend to detect a higher relapse rate in the arm without HDARA-C.

The Paradox of Myeloid Leukemia Associated with Down Syndrome

Children with Down syndrome constitute a distinct genetic population who has a greater risk of developing acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML) compared to their non-Down syndrome counterparts. The risk for developing solid tumors is also distinct from the non-Down syndrome population. In the case of myeloid leukemias, the process of leukemogenesis in Trisomy 21 begins in early fetal life where genetic drivers including GATA1 mutations lead to the development of the preleukemic condition, transient abnormal myelopoiesis (TAM). Various other mutations in genes encoding cohesin, epigenetic regulators and RAS pathway can result in subsequent progression to Myeloid Leukemia associated with Down Syndrome (ML-DS). The striking paradoxical feature in the Down syndrome population is that even though there is a higher predisposition to developing AML, they are also very sensitive to chemotherapy agents, particularly cytarabine, thus accounting for the very high cure rates for ML-DS compared to AML in children without Down syndrome. Current clinical trials for ML-DS attempt to balance effective curative therapies while trying to reduce treatment-associated toxicities including infections by de-intensifying chemotherapy doses, if possible. The small proportion of patients with relapsed ML-DS have an extremely poor prognosis and require the development of new therapies.

Hematological disorders in children with Down syndrome

INTRODUCTION

Hematological abnormalities are common in children with down syndrome (DS), mainly during childhood.

AREAS COVERED

DS newborns can develop hematological benign conditions that resolve spontaneously within 1 -2 months. However, about 10% of them can present transient abnormal myelopoiesis (TAM), characterized by the presence of circulating blasts. About 80% of DS neonates with TAM undergo spontaneous resolution of both clinical and laboratory abnormalities within 3-6 months after birth. However, some newborns with TAM may develop acute myeloid leukemia associated with DS (ML-DS), usually after an interval without signs of leukemia. GATA1 mutations are stable molecular markers that may monitor the presence of minimal residual disease (MRD) after TAM resolution. Moreover, DS children have a 10-20-fold increased risk of developing acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML). The predisposition to develop leukemia occurs both in children with complete trisomy 21 and in those with mosaic trisomy, suggesting an important role of chromosome 21 in leukemogenesis.

EXPERT OPINION

In contrast to the excellent prognosis of ML-DS obtained likewise with low doses of chemotherapy, DS-ALL patients show worse outcomes than non-DS children, therefore advances and risk-stratified treatment adjustments are mandatory for this particular set of patients.

High-dose AraC is essential for the treatment of ML-DS independent of postinduction MRD: results of the COG AAML1531 trial

Myeloid leukemia in children with Down syndrome (ML-DS) is associated with young age and somatic GATA1 mutations. Because of high event-free survival (EFS) and hypersensitivity of the leukemic blasts to chemotherapy, the prior Children's Oncology Group protocol ML-DS protocol (AAML0431) reduced overall treatment intensity but lacking risk stratification, retained the high-dose cytarabine course (HD-AraC), which was highly associated with infectious morbidity. Despite high EFS of ML-DS, survival for those who relapse is rare. AAML1531 introduced therapeutic risk stratification based on the previously identified prognostic factor, measurable residual disease (MRD) at the end of the first induction course. Standard risk (SR) patients were identified by negative MRD using flow cytometry (<0.05%) and did not receive the historically administered HD-AraC course. Interim analysis of 114 SR patients revealed a 2-year EFS of 85.6% (95% confidence interval [CI], 75.7-95.5), which was significantly lower than for MRD- patients treated with HD-AraC on AAML0431 (P = .0002). Overall survival at 2 years was 91.0% (95% CI, 83.8-95.0). Twelve SR patients relapsed, mostly within 1 year from study entry and had a 1-year OS of 16.7% (95% CI, 2.7-41.3). Complex karyotypes were more frequent in SR patients who relapsed compared with those who did not (36% vs 9%; P = .0248). MRD by error-corrected sequencing of GATA1 mutations was piloted in 18 SR patients and detectable in 60% who relapsed vs 23% who did not (P = .2682). Patients with SR ML-DS had worse outcomes without HD-AraC after risk classification based on flow cytometric MRD.

Clinical and biological aspects of myeloid leukemia in Down syndrome

Children with Down syndrome are at an elevated risk of leukemia, especially myeloid leukemia (ML-DS). This malignancy is frequently preceded by transient abnormal myelopoiesis (TAM), which is self-limited expansion of fetal liver-derived megakaryocyte progenitors. An array of international studies has led to consensus in treating ML-DS with reduced-intensity chemotherapy, leading to excellent outcomes. In addition, studies performed in the past 20 years have revealed many of the genetic and epigenetic features of the tumors, including GATA1 mutations that are arguably associated with all cases of both TAM and ML-DS. Despite these advances in understanding the clinical and biological aspects of ML-DS, little is known about the mechanisms of relapse. Upon relapse, patients face a poor outcome, and there is no consensus on treatment. Future studies need to be focused on this challenging aspect of leukemia in children with DS.

Using the in vitro drug sensitivity test to identify candidate treatments for transient abnormal myelopoiesis

Approximately 20% of patients with transient abnormal myelopoiesis (TAM) die due to hepatic or multiorgan failure. To identify potential new treatments for TAM, we performed in vitro drug sensitivity testing (DST) using the peripheral blood samples of eight patients with TAM. DST screened 41 agents for cytotoxic properties against TAM blasts. Compared with the reference samples of healthy subjects, TAM blasts were more sensitive to glucocorticoids, the mitogen-activated protein kinase kinase (MAP2K) inhibitor trametinib, and cytarabine. Our present results support the therapeutic potential of glucocorticoids and the role of the RAS/MAP2K signalling pathway in TAM pathogenesis.

Transient myeloproliferative disorder as the presenting feature for mosaic trisomy 21

Trisomy 21 is a common congenital disorder with well-documented clinical manifestations, including an increased risk for the transient myeloproliferative disorder as a neonate and leukemia in childhood and adolescence. Transient myeloproliferative disorder is only known to occur in hematopoietic cells with trisomy 21. Children with mosaic trisomy 21 also have a risk for hematological malignancies. We present a nondysmorphic neonate, with a negative noninvasive prenatal screening of maternal blood for trisomy 21, who came to medical attention because of ruddy skin. He was found to have mild polycythemia, thrombocytopenia, and developed peripheral blasts. His clinical presentation was consistent with transient myeloproliferative disorder, which is only seen with trisomy 21. Cytogenetic studies of peripheral blood are positive for mosaic trisomy 21.

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.

Dermatologic conditions in Down syndrome

Down syndrome (DS) is the most common chromosomal condition and affects many organs including the skin. Dermatologists are an integral part of the DS care team. This is a review of both common and rare dermatologic conditions in DS. We provide practical strategies for a successful dermatology interview and examination. We explore the downstream effects of trisomy of chromosome 21, in particular on the immune system, and how these insights may enhance our pathophysiologic understanding of their cutaneous conditions.

Modeling genetic platelet disorders with human pluripotent stem cells: mega-progress but wanting more on our plate(let)

PURPOSE OF REVIEW

Megakaryocytes are rare hematopoietic cells that play an instrumental role in hemostasis, and other important biological processes such as immunity and wound healing. With the advent of cell reprogramming technologies and advances in differentiation protocols, it is now possible to obtain megakaryocytes from any pluripotent stem cell (PSC) via hematopoietic induction. Here, we review recent advances in PSC-derived megakaryocyte (iMK) technology, focusing on platform validation, disease modeling and current limitations.

RECENT FINDINGS

A comprehensive study confirmed that iMK can recapitulate many transcriptional and functional aspects of megakaryocyte and platelet biology, including variables associated with complex genetic traits such as sex and race. These findings were corroborated by several pathological models in which iMKs revealed molecular mechanisms behind inherited platelet disorders and assessed the efficacy of novel pharmacological interventions. However, current differentiation protocols generate primarily embryonic iMK, limiting the clinical and translational potential of this system.

SUMMARY

iMK are strong candidates to model pathologic mutations involved in platelet defects and develop innovative therapeutic strategies. Future efforts on generating definitive hematopoietic progenitors would improve current platelet generation protocols and expand our capacity to model neonatal and adult megakaryocyte disorders.

Infant Acute Leukemia

Infant acute leukemia is a rare but aggressive disease. Although infant acute leukemia is cytologically and histologically similar to acute leukemia seen in older children and adults, it displays unique and characteristic clinical and genetic characteristics. The features, as well as the extremely young age of the patients, present multiple challenges for treatment. This review focuses on the unique pathology of acute leukemia of infancy, including the genetic characteristics that are specific for these diseases.

Recommendations for Diagnosis and Treatment of Children with Transient Abnormal Myelopoiesis (TAM) and Myeloid Leukemia in Down Syndrome (ML-DS)

Children with Down syndrome are at a high risk of developing transient abnormal myelopoiesis (TAM; synonym: TMD) or myeloid leukemia (ML-DS). While most patients with TAM are asymptomatic and go into spontaneous remission without a need for therapy, around 20% of patients die within the first six months due to TAM-related complications. Another 20-30% of patients progress from TAM to ML-DS. ML-DS patients are particularly vulnerable to therapy-associated toxicity, but the prognosis of relapsed ML-DS is extremely poor - thus, ML-DS therapy schemata must strive for a balance between appropriate efficacy (to avoid relapses) and treatment-related toxicity. This guideline presents diagnostic and therapeutic strategies for TAM and ML-DS based on the experience and results of previous clinical studies from the BFM working group, which have helped reduce the risk of early death in symptomatic TAM patients using low-dose cytarabine, and which have achieved excellent cure rates for ML-DS using intensity-reduced treatment protocols.

Mapping the cellular origin and early evolution of leukemia in Down syndrome

Children with Down syndrome have a 150-fold increased risk of developing myeloid leukemia, but the mechanism of predisposition is unclear. Because Down syndrome leukemogenesis initiates during fetal development, we characterized the cellular and developmental context of preleukemic initiation and leukemic progression using gene editing in human disomic and trisomic fetal hematopoietic cells and xenotransplantation. GATA binding protein 1 (GATA1) mutations caused transient preleukemia when introduced into trisomy 21 long-term hematopoietic stem cells, where a subset of chromosome 21 microRNAs affected predisposition to preleukemia. By contrast, progression to leukemia was independent of trisomy 21 and originated in various stem and progenitor cells through additional mutations in cohesin genes. CD117+/KIT proto-oncogene (KIT) cells mediated the propagation of preleukemia and leukemia, and KIT inhibition targeted preleukemic stem cells.

Clinical impact of genomic characterization of 15 patients with acute megakaryoblastic leukemia-related malignancies

Acute megakaryoblastic leukemia (AMKL) is a rare subtype of acute myeloid leukemia but is approximately 500 times more likely to develop in children with Down syndrome (DS) through transformation of transient abnormal myelopoiesis (TAM). This study investigates the clinical significance of genomic heterogeneity of AMKL in children with and without DS and in children with TAM. Genomic evaluation of nine patients with DS-related TAM or AMKL, and six patients with non-DS AMKL, included conventional cytogenetics and a comprehensive next-generation sequencing panel for single-nucleotide variants/indels and copy-number variants in 118 genes and fusions involving 110 genes. Recurrent gene fusions were found in all patients with non-DS, including two individuals with complex genomes and either a NUP98–KDM5A or a KMT2A–MLLT6 fusion, and the remaining harbored a CBFA2T3–GLIS2 fusion, which arose from both typical and atypical cytogenetic mechanisms. These fusions guided treatment protocols and resulted in a change in diagnosis in two patients. The nine patients with DS had constitutional trisomy 21 and somatic GATA1 mutations, and those with DS-AMKL had two to four additional clinically significant somatic mutations. Comprehensive genomic characterization provides critical information for diagnosis, risk stratification, and treatment decisions for patients with AMKL. Continued genetic and clinical characterization of these rare cancers will aid in improving patient management.

Pluripotent stem cell model of early hematopoiesis in Down syndrome reveals quantitative effects of short-form GATA1 protein on lineage specification

Children with Down syndrome (DS) are susceptible to two blood disorders, transient abnormal myelopoiesis (TAM) and Down syndrome-associated acute megakaryocytic leukemia (DS-AMKL). Mutations in GATA binding protein 1 (GATA1) have been identified as the cause of these diseases, and the expression levels of the resulting protein, short-form GATA1 (GATA1s), are known to correlate with the severity of TAM. On the other hand, despite the presence of GATA1 mutations in almost all cases of DS-AMKL, the incidence of DS-AMKL in TAM patients is inversely correlated with the expression of GATA1s. This discovery has required the need to clarify the role of GATA1s in generating the cells of origin linked to the risk of both diseases. Focusing on this point, we examined the characteristics of GATA1 mutant trisomy-21 pluripotent stem cells transfected with a doxycycline (Dox)-inducible GATA1s expression cassette in a stepwise hematopoietic differentiation protocol. We found that higher GATA1s expression significantly reduced commitment into the megakaryocytic lineage at the early hematopoietic progenitor cell (HPC) stage, but once committed, the effect was reversed in progenitor cells and acted to maintain the progenitors. These differentiation stage-dependent reversal effects were in contrast to the results of myeloid lineage, where GATA1s simply sustained and increased the number of immature myeloid cells. These results suggest that although GATA1 mutant cells cause the increase in myeloid and megakaryocytic progenitors regardless of the intensity of GATA1s expression, the pathways vary with the expression level. This study provides experimental support for the paradoxical clinical features of GATA1 mutations in the two diseases.

Molecular Mechanisms of the Genetic Predisposition to Acute Megakaryoblastic Leukemia in Infants With Down Syndrome

Individuals with Down syndrome are genetically predisposed to developing acute megakaryoblastic leukemia. This myeloid leukemia associated with Down syndrome (ML–DS) demonstrates a model of step-wise leukemogenesis with perturbed hematopoiesis already presenting in utero, facilitating the acquisition of additional driver mutations such as truncating GATA1 variants, which are pathognomonic to the disease. Consequently, the affected individuals suffer from a transient abnormal myelopoiesis (TAM)—a pre-leukemic state preceding the progression to ML–DS. In our review, we focus on the molecular mechanisms of the different steps of clonal evolution in Down syndrome leukemogenesis, and aim to provide a comprehensive view on the complex interplay between gene dosage imbalances, GATA1 mutations and somatic mutations affecting JAK-STAT signaling, the cohesin complex and epigenetic regulators.