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.

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.

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.

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.

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.

"TAM"ing of the shrew-challenges in the diagnosis of Neonatal leukemia with Down's syndrome -A case report with literature review.

The latest WHO (2017) classification describes the hematological abnormalities of Down's syndrome as a separate entity under 'Myeloid proliferations associated with Down's syndrome'. It includes Transient Abnormal Myelopoiesis and Myeloid leukemia of Down's syndrome. Here we report a case of a 3 days old neonate with Down's syndrome, presenting with a leukemic blood picture. The baby had icterus, fever and hepatosplenomagaly. Peripheral blood showed megakaryoblasts and giant platelets. A diagnosis of transient abnormal myelopoiesis was made by confirming with karyotyping and immunophenotyping. We attempt to address all the diagnostic challenges faced by a clinician and pathologist same, upon encountering such a case,by following an algorithmic approach. The mandatory need for follow up and cytogenetic studies in identifying high risk cases that will become myeloid leukemia of Down's syndrome are stressed. Our case also throws light upon the significance of identification of GATA1 mutation in diagnosing and prognostication of such cases.

A sensitive and inexpensive high-resolution melting-based testing algorithm for diagnosis of transient abnormal myelopoiesis and myeloid leukemia of Down syndrome.

Patients with Down syndrome (DS) are commonly affected by a pre-leukemic disorder known as transient abnormal myelopoiesis (TAM). This condition usually undergoes spontaneous remission within the first 2 months after birth; however, in children under 5, 20%-30% of cases evolve to myeloid leukemia of Down syndrome (ML-DS). TAM and ML-DS are caused by co-operation between trisomy 21 and acquired mutations in the GATA1 gene. Currently, only next-generation sequencing (NGS)-based methodologies are sufficiently sensitive for diagnosis in samples with small GATA1 mutant clones (≤10% blasts). Alternatively, this study presents research on a new, fast, sensitive, and inexpensive high-resolution melting (HRM)-based diagnostic approach that allows the detection of most cases of GATA1 mutations, including silent TAM. The algorithm first uses flow cytometry for blast count, followed by HRM and Sanger sequencing to search for mutations on exons 2 and 3 of GATA1. We analyzed 138 samples of DS patients: 110 of asymptomatic neonates, 10 suspected of having TAM, and 18 suspected of having ML-DS. Our algorithm enabled the identification of 33 mutant samples, among them five cases of silent TAM (5/110) and seven cases of ML-DS (7/18) with blast count ≤10%, in which GATA1 alterations were easily detected by HRM. Depending on the type of genetic variation and its location, our methodology reached sensitivity similar to that obtained by NGS (0.3%) at a considerably reduced time and cost, thus making it accessible worldwide.

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.

Trisomy 21, transposition of the great arteries and abnormal myelopoiesis.

Down syndrome is a well-recognised genetic condition associated with several comorbidities. Although CHD is common in Down syndrome, transposition of the great arteries is exceptionally rare. We describe a neonate with Down syndrome who presented with transient abnormal myelopoiesis and transposition of the great arteries. Down syndrome may accelerate pulmonary hypertension in transposition of the great arteries and is associated with poor outcomes.

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.

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.

A Case of Novel GATA-1 Mutation-positive Transient Abnormal Myelopoiesis With Life-threatening Complications in a Neonate With Down Syndrome.

Transient abnormal myelopoiesis is a transient myeloproliferative disorder seen in ∼15% to 20% of infants with Down syndrome. These infants are usually asymptomatic, requiring only monitoring, but they can have variable severity of symptoms up to multisystemic dysfunction requiring chemotherapy. GATA-1 somatic mutations acquired in utero are pathognomic of this entity and present nearly in all cases. Herein, we present a case of Down syndrome in a neonate who presented within her first week of life with life-threatening features of transient abnormal myelopoiesis requiring chemotherapy support. In addition, next-generation sequencing revealed a small mutant clone (8%) positive for a novel frameshift GATA-1 mutation.

Complete blood count differences in a cohort of Down syndrome neonates with transient abnormal myelopoiesis screened for GATA1 pathogenic variants.

Transient abnormal myelopoiesis (TAM) raises the risk for acute myeloid leukemia of Down syndrome (DS) (ML-DS), and both are related to GATA1 pathogenic variants. Here, we analyzed which findings on complete blood count (CBC) are associated with TAM in a cohort of neonates with DS screened for GATA1 pathogenic variants. The CBCs were compared among 70 newborns with DS, including 16 patients (22.9%) with TAM (cases), and 54 patients (77.1%) without TAM (controls). TAM was defined as peripheral circulating blasts (PCBs) ≥ 1%. PCR and direct sequencing were used to screen DNA samples from peripheral blood for GATA1 exon 2 mutations. Multivariate logistic regression analyses determined that the mean count of lymphocytes was significantly higher in DS infants with TAM (p = .035) and that lymphocytosis confers a risk for TAM (adjusted odds ratio = 7.23, 95% confidence intervals: 2.02-25.92). Pathogenic variants of GATA1 were identified in 2 of 70 analyzed DS neonates (2.9%), of which one had ML-DS and another had an asymptomatic TAM. Among those DS infants with TAM, the GATA1 pathogenic variant detection was 12.5%. Our results indicated that lymphocytosis is associated with TAM in neonates with DS. However, since not all infants with an abnormal CBC had TAM, and not all infants with TAM had GATA1 pathogenic variants, we emphasize that only the search for GATA1 pathogenic variants allows the proper identification of the subgroup of DS infants with a real increasing in risk for ML-DS.