Chemotherapy induces canalization of cell state in childhood B-cell precursor acute lymphoblastic leukemia.

Comparison of intratumor genetic heterogeneity in cancer at diagnosis and relapse suggests that chemotherapy induces bottleneck selection of subclonal genotypes. However, evolutionary events subsequent to chemotherapy could also explain changes in clonal dominance seen at relapse. We, therefore, investigated the mechanisms of selection in childhood B-cell precursor acute lymphoblastic leukemia (BCP-ALL) during induction chemotherapy where maximal cytoreduction occurs. To distinguish stochastic versus deterministic events, individual leukemias were transplanted into multiple xenografts and chemotherapy administered. Analyses of the immediate post-treatment leukemic residuum at single-cell resolution revealed that chemotherapy has little impact on genetic heterogeneity. Rather, it acts on extensive, previously unappreciated, transcriptional and epigenetic heterogeneity in BCP-ALL, dramatically reducing the spectrum of cell states represented, leaving a genetically polyclonal but phenotypically uniform population with hallmark signatures relating to developmental stage, cell cycle and metabolism. Hence, canalization of cell state accounts for a significant component of bottleneck selection during induction chemotherapy.

Chronic neutropenia: how best to assess severity and approach management?

INTRODUCTION: Neutropenia is a relatively common finding in medical practice and the medical approach requires a gradual and pertinent diagnostic procedure as well as adapted management. AREAS COVERED: The area of chronic neutropenia remains fragmented between diverse diseases or situations. Here physicians involved in different aspects of chronic neutropenia gather both the data from medical literature till the end of May 2021 and their experience to offer a global approach for the diagnosis of chronic neutropenia as well as their medical care. EXPERT OPINION: In most cases, the neutropenia is transient, frequently related to a viral infection, and not harmful. However, neutropenia can be chronic (i.e. >3 months) and related to a number of etiologies, some clinically benign, such as so-called 'ethnic' neutropenia. Autoimmune neutropenia is the common form in young children, whereas idiopathic/immune neutropenia is a frequent etiology in young females. Inherited neutropenia (or congenital neutropenia) is exceptional, with approximately 30 new cases per 106 births and 30 known subtypes. Such patients have a high risk of invasive bacterial infections, and oral infections. Supportive therapy, which is primarily based on daily administration of an antibiotic prophylaxis and/or treatment with granulocyte-colony stimulating factor (G-CSF), contributes to avoiding recurrent infections.

MECOM-associated syndrome: a heterogeneous inherited bone marrow failure syndrome with amegakaryocytic thrombocytopenia.

Heterozygous mutations in MECOM (MDS1 and EVI1 complex locus) have been reported to be causative of a rare association of congenital amegakaryocytic thrombocytopenia and radioulnar synostosis. Here we report on 12 patients with congenital hypomegakaryocytic thrombocytopenia caused by MECOM mutations (including 10 novel mutations). The mutations affected different functional domains of the EVI1 protein. The spectrum of phenotypes was much broader than initially reported for the first 3 patients; we found familial as well as sporadic cases, and the clinical spectrum ranged from isolated radioulnar synostosis with no or mild hematological involvement to severe bone marrow failure without obvious skeletal abnormality. The clinical picture included radioulnar synostosis, bone marrow failure, clinodactyly, cardiac and renal malformations, B-cell deficiency, and presenile hearing loss. No single clinical manifestation was detected in all patients affected by MECOM mutations. Radioulnar synostosis and B-cell deficiency were observed only in patients with mutations affecting a short region in the C-terminal zinc finger domain of EVI1. We propose the term MECOM-associated syndrome for this heterogeneous hereditary disease and inclusion of MECOM sequencing in the diagnostic workup of congenital bone marrow failure.

Stem cell transplantation in severe congenital neutropenia: an analysis from the European Society for Blood and Marrow Transplantation.

Allogeneic hematopoietic stem cell transplantation (HSCT) is the only curative treatment of severe congenital neutropenia (SCN), but data on outcome are scarce. We report on the outcome of 136 SCN patients who underwent HSCT between 1990 and 2012 in European and Middle East centers. The 3-year overall survival (OS) was 82%, and transplant-related mortality (TRM) was 17%. In multivariate analysis, transplants performed under the age of 10 years, in recent years, and from HLA-matched related or unrelated donors were associated with a significantly better OS. Frequency of graft failure was 10%. Cumulative incidence (day +90) of acute graft-versus-host disease (GVHD) grade 2-4 was 21%. In multivariate analysis, HLA-matched related donor and prophylaxis with cyclosporine A and methotrexate were associated with lower occurrence of acute GVHD. Cumulative incidence (1 year) of chronic GVHD was 20%. No secondary malignancies occurred after a median follow-up of 4.6 years. These data show that the outcome of HSCT for SCN from HLA-matched donors, performed in recent years, in patients younger than 10 years is acceptable. Nevertheless, given the TRM, a careful selection of HSCT candidates should be undertaken.

Nutritional status in children with Shwachman-diamond syndrome.

OBJECTIVE: In Shwachman-Diamond syndrome (SDS), pancreatic insufficiency can lead to malabsorption of fat-soluble vitamins and trace elements. The aim of this study was to assess the serum concentrations of vitamins A and E, zinc, copper, and selenium and their deficiencies. METHODS: This retrospective review was performed in 21 children (12 were male; median age, 7.8 years) with genetically confirmed SDS at a tertiary pediatric hospital. Pancreatic enzyme replacement therapy (PERT) and vitamin or trace elements supplements were documented. RESULTS: Twenty patients (95%) had pancreatic insufficiency receiving PERT, 10 (47%) had a combined vitamin and trace element deficiency, 6 (29%) had an isolated vitamin deficiency, and 4 (19%) had an isolated trace element deficiency. Vitamins A and E deficiency occurred in 16 (76%) and 4 (19%) of 21, respectively. Low serum selenium was found in 10 (47%), zinc deficiency in 7 (33%), and copper deficiency in 5 (24%). Eleven patients (52%) were on multivitamin supplementation, and 2 (10%) on zinc and selenium supplements. No statistical differences were found between repeated measurements for all micronutrients. CONCLUSIONS: More than 50% of the children had vitamin A and selenium deficiencies despite adequate supplementation of PERT and supplements. Micronutrients should be routinely measured in SDS patients to prevent significant complications.

GATA2 mutations in sporadic and familial acute myeloid leukaemia patients with CEBPA mutations.

GATA2 mutations have recently been reported in acute myeloid leukaemia (AML) patients with CEBPA-double mutations. To explore their impact on this favourable-risk disease, we determined GATA2 status in 153 sporadic AML patients and three members of a germ-line CEBPA-mutant family at AML presentation. Overall, 27% (15/55) CEBPA-double, 16% (7/43) CEBPA-single and 0% (0/55) normal karyotype/CEBPA-wild-type patients were GATA2-mutant. All familial AML patients acquired both a second CEBPA and a GATA2 mutation. CEBPA and GATA2 mutant levels indicated that both mutations were likely to be early events in leukaemogenesis. GATA2 status did not impact on the favourable outcome of CEBPA-double/FLT3-inernal tandem duplication-negative patients.

Recent advances in the understanding of genetic defects of neutrophil number and function.

Neutrophils are amongst the first immune cells to arrive at sites of infection and play an important role as the host's first line of defence against invading pathogens. Defects of neutrophil number or function are usually recognized clinically by recurrent infections that often are life-threatening. Over the last few years, a number of genetic mutations have been discovered to be the basis for congenital neutropenia, adding to our understanding of the molecular basis of these diseases. While many genetic mutations that cause severe congenital neutropenia result in a differentiation block at the promyelocyte stage, defects of neutrophil function are more heterogeneous on clinical, genetic and mechanistic levels. In this review we discuss recent advances in our understanding of the genetic and molecular basis of human neutrophil disorders.

Homozygous HAX1 mutations in severe congenital neutropenia patients with sporadic disease: a novel mutation in two unrelated British kindreds.

Patients with autosomal dominant (AD), sporadic and X-linked severe congenital neutropenia (SCN) may have mutations in the elastase 2 (ELA2) or Wiskott-Aldrich syndrome (WAS) genes. Homozygous mutations in the HAX1 gene have recently been reported in autosomal recessive (AR) cases of primarily Middle-Eastern descent and the original Kostmann family. We screened 109 predominantly Caucasian SCN kindreds for mutations in these genes; 33 (30%) had 24 different ELA2 mutations, five of them novel, two kindreds (2%) had WAS mutations and four kindreds (4%) had three different HAX1 mutations, two of them novel. One HAX1 mutation (p.Ser43LeufsX11) was found in an AR Ashkenazi Jewish kindred, the other (p.Glu31LysfsX54) in two unrelated British patients with sporadic disease. Microsatellite analysis of the HAX1 locus revealed a common haplotype (maximum distance 4.1 Megabases) for the p.Glu31LysfsX54 patients, suggesting a possible ancestral founder. In functional assays, the level of spontaneous and staurosporine-induced apoptosis was increased in neutrophils from both p.Ser43LeufsX11 patients but not a p.Glu31LysfsX54 patient, suggesting the possible presence of modifying factors. The low incidence of HAX1 mutations in our study suggests that the frequency may vary between racial groups but suggests that irrespective of inheritance or racial origin, SCN patients should be screened for HAX1 mutations.

Notch-1 mutations are secondary events in some patients with T-cell acute lymphoblastic leukemia.

PURPOSE: Activating Notch-1 mutations are frequent in T-cell acute lymphoblastic leukemia (T-ALL), occurring in >50% of patients. In murine models of T-ALL, Notch-1 activation can both directly initiate leukemia and cooperate secondarily to other primary events. Whether acquisition of Notch-1 mutations is an early initiating event or a secondary event in the pathogenesis of human T-ALL is unclear. EXPERIMENTAL DESIGN: We used denaturing high-performance liquid chromatography, sequencing, and fragment analysis to analyze Notch-1 mutational status and mutant level in 62 patients at presentation as well as 16 matched presentation-relapse samples. RESULTS: We detected Notch-1 mutations in 47 patients (76%). Seven of these were low-level mutations (quantified at < or =10%), despite high blast counts, suggesting that they were acquired as a secondary event in a subclone. Of 16 matched presentation-relapse samples studied, 7 were wild-type at both presentation and relapse. Five of nine mutant-positive patients at presentation relapsed with the same mutation(s) at the same high level. Four patients had evidence of a change in mutant at relapse. One lost a PEST mutation and became wild-type. Two others lost mutations at relapse but acquired different mutations, despite unchanged T-cell receptor rearrangements, suggesting that the latter event predated the acquisition of the Notch-1 mutation. One relapsed with a secondary T-cell leukemia and different Notch mutation. CONCLUSIONS: These results suggest that Notch-1 mutations can sometimes be acquired as secondary events in leukemogenesis and must be used cautiously as solitary minimal residual disease markers.

Unregulated actin polymerization by WASp causes defects of mitosis and cytokinesis in X-linked neutropenia.

Specific mutations in the human gene encoding the Wiskott-Aldrich syndrome protein (WASp) that compromise normal auto-inhibition of WASp result in unregulated activation of the actin-related protein 2/3 complex and increased actin polymerizing activity. These activating mutations are associated with an X-linked form of neutropenia with an intrinsic failure of myelopoiesis and an increase in the incidence of cytogenetic abnormalities. To study the underlying mechanisms, active mutant WASp(I294T) was expressed by gene transfer. This caused enhanced and delocalized actin polymerization throughout the cell, decreased proliferation, and increased apoptosis. Cells became binucleated, suggesting a failure of cytokinesis, and micronuclei were formed, indicative of genomic instability. Live cell imaging demonstrated a delay in mitosis from prometaphase to anaphase and confirmed that multinucleation was a result of aborted cytokinesis. During mitosis, filamentous actin was abnormally localized around the spindle and chromosomes throughout their alignment and separation, and it accumulated within the cleavage furrow around the spindle midzone. These findings reveal a novel mechanism for inhibition of myelopoiesis through defective mitosis and cytokinesis due to hyperactivation and mislocalization of actin polymerization.

Two novel activating mutations in the Wiskott-Aldrich syndrome protein result in congenital neutropenia.

Severe congenital neutropenia (SCN) is characterized by neutropenia, recurrent bacterial infections, and maturation arrest in the bone marrow. Although many cases have mutations in the ELA2 gene encoding neutrophil elastase, a significant proportion remain undefined at a molecular level. A mutation (Leu270Pro) in the gene encoding the Wiskott-Aldrich syndrome protein (WASp) resulting in an X-linked SCN kindred has been reported. We therefore screened the WAS gene in 14 young SCN males with wild-type ELA2 and identified 2 with novel mutations, one who presented with myelodysplasia (Ile294Thr) and the other with classic SCN (Ser270Pro). Both patients had defects of immunologic function including a generalized reduction of lymphoid and natural killer cell numbers, reduced lymphocyte proliferation, and abrogated phagocyte activity. In vitro culture of bone marrow progenitors demonstrated a profound reduction in neutrophil production and increased levels of apoptosis, consistent with an intrinsic disturbance of normal myeloid differentiation as the cause of the neutropenia. Both mutations resulted in increased WASp activity and produced marked abnormalities of cytoskeletal structure and dynamics. Furthermore, these results also suggest a novel cause of myelodysplasia and that male children with myelodysplasia and disturbance of immunologic function should be screened for such mutations.

Ectopic thymus presenting as a subglottic mass: diagnostic and management dilemmas.

The commonest subglottic mass in infants is a congenital haemangioma, which is usually managed conservatively without a histological diagnosis. Ectopic cervical thymus is rare and usually presents as a cervical mass, with only one case of subglottic ectopic thymus reported to date. Due to its rarity, the diagnosis in most cases relies on surgical excision and histological examination. However, histological diagnosis may not always be easily reached, as is demonstrated in this case report. In this article, an infant with congenital stridor secondary to a subglottic mass is described and the clinical and diagnostic difficulties in its management are discussed.

Neutrophil elastase mutations in congenital neutropenia.

Severe congenital neutropenia (SCN) was originally described as an autosomal recessive disorder. Autosomal dominant and sporadic forms of the disease have subsequently been recognized. All forms of the disease are manifest by persistent severe neutropenia and recurrent bacterial infection. Cyclical neutropenia (CyN) is characterized by periodic neutropenia inter-spaced with (near) normal neutrophil counts. Recently, heterozygous mutations in the ELA2 gene encoding neutrophil elastase (NE) have been described in the majority of cases of CyN and sporadic and autosomal dominant SCN. A case of paternal mosaicism has provided genetic "proof" of the pathogenicity of such mutations, but the exact pathogenic mechanism remains elusive. This review will focus on the mosaic proof and examine possible pathogenic mechanisms. The lack of obvious associations and indeed overlap between the mutations that cause the two diseases will also be discussed. Clinically to date, the discovery of an elastase mutation has been of limited value to individual patients. However, it is hoped that further genotype/phenotype studies may improve assessment of patient prognosis.

Long-term follow-up of granulocyte colony-stimulating factor receptor mutations in patients with severe congenital neutropenia: implications for leukaemogenesis and therapy.

Severe congenital neutropenia (SCN) is characterized by profound neutropenia, recurrent severe bacterial infections and maturation arrest in the myeloid lineage. Granulocyte colony-stimulating factor (G-CSF) treatment results in clinical improvement in over 90% of cases. Point mutations of the G-CSF receptor (G-CSFR) have been implicated in the progression of SCN to acute myeloid leukaemia (AML). Data are presented here on the 9-year follow-up of seven patients and the further screening of 18 other cases. One of the two original cases with a G-CSFR mutation has improved clinically; nevertheless, mutant DNA could still be detected at a very low level > 8 years after identification. The second child with a mutation progressed to myelodysplasia/AML 5 years after her mutation was detected. No mutations were found in the 18 new cases. One of three transformed cases had a G-CSFR mutation. This work is in agreement with the suggestion that G-CSFR mutations may provide a survival advantage to haemopoietic stem cells, but argues against the inevitability of leukaemic progression in their presence. Furthermore, the low frequency of G-CSFR mutations in SCN and the importance of regular screening and close clinical and laboratory follow-up if a mutation is found were demonstrated.

Paternal mosaicism proves the pathogenic nature of mutations in neutrophil elastase in severe congenital neutropenia.

Heterozygous mutations in neutrophil elastase have been detected in many sporadic cases of congenital neutropenia. However, a convincing pathogenetic mechanism has not been established, and it is unclear whether the effects of the mutant enzyme occur within the cell of production or are paracrine in nature. The healthy father of a patient was demonstrated to be mosaic for his daughter's Cys42Arg elastase mutation. Using semiquantitative polymerase chain reaction, approximately half of his T cells were shown to carry the mutation in contrast to less than 10% of neutrophils. Individual hematopoietic colonies grown from peripheral blood were heterozygous for the mutation or were homozygous wild type. These results demonstrate that precursors containing the mutation are selectively lost during myelopoiesis or fail to develop into neutrophils. This is the first in vivo confirmation of the pathogenic nature of elastase mutations in humans. The normal neutrophil count in the father suggests that the mutant elastase does not have paracrine effects.