Germline bi-allelic SH2B3/LNK alteration predisposes to a neonatal juvenile myelomonocytic leukemia-like disorder.

Juvenile myelomonocytic leukemia (JMML) is a rare, generally aggressive myeloproliferative neoplasm affecting young children. It is characterized by granulomonocytic expansion, with monocytosis infiltrating peripheral tissues. JMML is initiated by mutations upregulating RAS signaling. Approximately 10% of cases remain without an identified driver event. Exome sequencing of 2 unrelated cases of familial JMML of unknown genetics and analysis of the French JMML cohort identified 11 patients with variants in SH2B3, encoding LNK, a negative regulator of the JAK-STAT pathway. All variants were absent from healthy population databases, and mutation spectrum was consistent with a loss of function of the LNK protein. A stoploss variant was shown to affect both protein synthesis and stability. The other variants were either truncating or missense, the latter affecting the SH2 domain that interacts with activated JAK. Of the 11 patients, 8 from 5 families inherited pathogenic bi-allelic SH2B3 germline variants from their unaffected heterozygous parents. These children represent half of the cases with no identified causal mutation in the French cohort. They displayed typical clinical and hematological JMML features with neonatal onset and marked thrombocytopenia. They were characterized by absence of additional genetic alterations and a hypomethylated DNA profile with fetal characteristics. All patients showed partial or complete spontaneous clinical resolution. However, progression to thrombocythemia and immunity-related pathologies may be of concern later in life. Bi-allelic SH2B3 germline mutations thus define a new condition predisposing to a JMML-like disorder, suggesting that the JAK pathway deregulation is capable of initiating JMML, and opening new therapeutic options.

Next generation sequencing (NGS) interest in deciphering erythrocyte molecular defects' association in red cell disorders: Clinical and erythrocyte phenotypes of patients with mutations inheritance in PIEZO1, Spectrin ß1, RhAG and SLC4A1.

We report here an instructive case referred at 16 months-old for exploration of hemolysis without anemia (compensated anemia with reticulocytosis). The biology tests confirmed the hemolysis with increased total and indirect bilirubin. The usual hemolysis diagnosis tests were normal (DAT, G6PD, PK, Hb electrophoresis) except cytology and ektacytometry suggesting an association of multiple red blood cell (RBC) membrane disorders. This led us to propose a molecular screening analysis using targeted-Next Generation Sequencing (t-NGS) with a capture technique on 93 genes involved in RBC and erythropoiesis defects. We identified 4 missense heterozygous allelic variations, all of them were described without any significance (VUS) in the SLC4A1, RhAG, PIEZO1 and SPTB genes. The study of the familial cosegregation and research functional tests allowed to decipher the role of at least two by two genes in the phenotype and the hemolytic disease of this young patient. Specialized t-NGS panel (or virtual exome/genome sequencing) in a disease-referent laboratory and the motivated collaboration of clinicians, biologists and scientists should be the gold standard for improving the diagnosis of the patients affected with RBC diseases or rare inherited anemias.

Clonal hematopoiesis driven by chromosome 1q/MDM4 trisomy defines a canonical route toward leukemia in Fanconi anemia.

Fanconi anemia (FA) patients experience chromosome instability, yielding hematopoietic stem/progenitor cell (HSPC) exhaustion and predisposition to poor-prognosis myeloid leukemia. Based on a longitudinal cohort of 335 patients, we performed clinical, genomic, and functional studies in 62 patients with clonal evolution. We found a unique pattern of somatic structural variants and mutations that shares features of BRCA-related cancers, the FA-hallmark being unbalanced, microhomology-mediated translocations driving copy-number alterations. Half the patients developed chromosome 1q gain, driving clonal hematopoiesis through MDM4 trisomy downmodulating p53 signaling later followed by secondary acute myeloid lukemia genomic alterations. Functionally, MDM4 triplication conferred greater fitness to murine and human primary FA HSPCs, rescued inflammation-mediated bone marrow failure, and drove clonal dominance in FA mouse models, while targeting MDM4 impaired leukemia cells in vitro and in vivo. Our results identify a linear route toward secondary leukemogenesis whereby early MDM4-driven downregulation of basal p53 activation plays a pivotal role, opening monitoring and therapeutic prospects.

Perls' Stain Guidelines from the French-Speaking Cellular Hematology Group (GFHC).

In order to standardize cellular hematology practices, the French-speaking Cellular Hematology Group (Groupe Francophone d'Hématologie Cellulaire, GFHC) focused on Perls' stain. A national survey was carried out, leading to the proposal of recommendations on insoluble iron detection and quantification in bone marrow. The criteria presented here met with a "strong professional agreement" and follow the suggestions of the World Health Organization's classification of hematological malignancies.

When Ring Sideroblasts on Bone Marrow Smears Are Inconsistent with the Diagnosis of Myelodysplastic Neoplasms.

Ring sideroblasts are commonly seen in myelodysplastic neoplasms and are a key condition for identifying distinct entities of myelodysplastic neoplasms according to the WHO classification. However, the presence of ring sideroblasts is not exclusive to myelodysplastic neoplasms. Ring sideroblasts are as well either encountered in non-clonal secondary acquired disorders, such as exposure to toxic substances, drug/medicine, copper deficiency, zinc overload, lead poison, or hereditary sideroblastic anemias related to X-linked, autosomal, or mitochondrial mutations. This review article will discuss diseases associated with ring sideroblasts outside the context of myelodysplastic neoplasms. Knowledge of the differential diagnoses characterized by the presence of ring sideroblasts in bone marrow is essential to prevent any misdiagnosis, which leads to delayed diagnosis and subsequent management of patients that differ in the different forms of sideroblastic anemia.

GATA-1 Defects in Diamond-Blackfan Anemia: Phenotypic Characterization Points to a Specific Subset of Disease.

Diamond−Blackfan anemia (DBA) is one of the inherited bone marrow failure syndromes marked by erythroid hypoplasia. Underlying variants in ribosomal protein (RP) genes account for 80% of cases, thereby classifying DBA as a ribosomopathy. In addition to RP genes, extremely rare variants in non-RP genes, including GATA1, the master transcription factor in erythropoiesis, have been reported in recent years in patients with a DBA-like phenotype. Subsequently, a pivotal role for GATA-1 in DBA pathophysiology was established by studies showing the impaired translation of GATA1 mRNA downstream of the RP haploinsufficiency. Here, we report on a patient from the Dutch DBA registry, in which we found a novel hemizygous variant in GATA1 (c.220+2T>C), and an Iranian patient with a previously reported variant in the initiation codon of GATA1 (c.2T>C). Although clinical features were concordant with DBA, the bone marrow morphology in both patients was not typical for DBA, showing moderate erythropoietic activity with signs of dyserythropoiesis and dysmegakaryopoiesis. This motivated us to re-evaluate the clinical characteristics of previously reported cases, which resulted in the comprehensive characterization of 18 patients with an inherited GATA-1 defect in exon 2 that is presented in this case-series. In addition, we re-investigated the bone marrow aspirate of one of the previously published cases. Altogether, our observations suggest that DBA caused by GATA1 defects is characterized by distinct phenotypic characteristics, including dyserythropoiesis and dysmegakaryopoiesis, and therefore represents a distinct phenotype within the DBA disease spectrum, which might need specific clinical management.

Case Report: Targeting 2 Antigens as a Promising Strategy in Mixed Phenotype Acute Leukemia: Combination of Blinatumomab With Gemtuzumab Ozogamicin in an Infant With a KMT2A-Rearranged Leukemia.

Mixed phenotype acute leukemia (MPAL) accounts for 2-5% of leukemia in children. MPAL are at higher risk of induction failure. Lineage switch (B to M or vice versa) or persistence of only the lymphoid or myeloid clone is frequently observed in biphenotypic/bilineal cases, highlighting their lineage plasticity. The prognosis of MPAL remains bleak, with an event-free survival (EFS) of less than 50% in children. A lymphoid-type therapeutic approach appears to be more effective but failures to achieve complete remission (CR) remain significant. KMT2A fusions account for 75-80% of leukemia in infants under one year of age and remains a major pejorative prognostic factor in the Interfant-06 protocol with a 6 years EFS of only 36%. The search for other therapeutic approaches, in particular immunotherapies that are able to eradicate all MPAL clones, is a major issue. We describe here the feasibility and tolerance of the combination of two targeted immunotherapies, blinatumomab and Gemtuzumab Ozogamicin, in a 4-year-old infant with a primary refractory KTM2A-rearranged MPAL. Our main concern was to determine how to associate these two immunotherapies and we describe how we decided to do it with the parents' agreement. The good MRD response on the two clones made it possible to continue the curative intent with a hematopoietic stem cell transplant at 9 months of age. Despite a relapse at M11 post-transplant because of the recurrence of a pro-B clone retaining the initial lymphoid phenotype, the child is now 36 months old, in persistent negative MRD CR2 for 12 months after a salvage chemotherapy and an autologous CAR T cells infusion, with no known sequelae to date. This case study can thus lead to the idea of a sequential combination of two immunotherapies targeting two distinct leukemic subclones (or even a single biphenotypic clone), as a potential one to be tested prospectively in children MPAL and even possibly all KMT2A-rearranged infant ALL.

Infant Acute Myeloid Leukemia: A Unique Clinical and Biological Entity.

Infant acute myeloid leukemia (AML) is a rare subgroup of AML of children <2 years of age. It is as frequent as infant acute lymphoblastic leukemia (ALL) but not clearly distinguished by study groups. However, infant AML demonstrates peculiar clinical and biological characteristics, and its prognosis differs from AML in older children. Acute megakaryoblastic leukemia (AMKL) is very frequent in this age group and has raised growing interest. Thus, AMKL is a dominant topic in this review. Recent genomic sequencing has contributed to our understanding of infant AML. These data demonstrated striking features of infant AML: fusion genes are able to induce AML transformation without additional cooperation, and unlike AML in older age groups there is a paucity of associated mutations. Mice modeling of these fusions showed the essential role of ontogeny in the infant leukemia phenotype compared to older children and adults. Understanding leukemogenesis may help in developing new targeted treatments to improve outcomes that are often very poor in this age group. A specific diagnostic and therapeutic approach for this age group should be investigated.