Mosaicism of an ELANE mutation in an asymptomatic mother in a familial case of cyclic neutropenia

Clonal hematopoiesis in children with predisposing conditions

Clonal hematopoiesis in children and young adults differs from that occuring in the older adult population. A variety of stressors drive this phenomenon, sometimes independent of age-related processes. For the purposes of this review, we adopt the term clonal hematopoiesis in predisposed individuals (CHIPI) to differentiate it from classical, age-related clonal hematopoiesis of indeterminate potential (CHIP). Stress-induced CHIPI selection can be extrinsic, such as following immunologic, infectious, pharmacologic, or genotoxic exposures, or intrinsic, involving germline predisposition from inherited bone marrow failure syndromes. In these conditions, clonal advantage relates to adaptations allowing improved cell fitness despite intrinsic defects affecting proliferation and differentiation. In certain contexts, CHIPI can improve competitive fitness by compensating for germline defects; however, the downstream effects of clonal expansion are often unpredictable - they may either counteract the underlying pathology or worsen disease outcomes. A more complete understanding of how CHIPI arises in young people can lead to the definition of preleukemic states and strategies to assess risk, surveillance, and prevention to leukemic transformation. Our review summarizes current research on stress-induced clonal dynamics in individuals with germline predisposition syndromes.

The European Guidelines on Diagnosis and Management of Neutropenia in Adults and Children: A Consensus Between the European Hematology Association and the EuNet-INNOCHRON COST Action

Neutropenia, as an isolated blood cell deficiency, is a feature of a wide spectrum of acquired or congenital, benign or premalignant disorders with a predisposition to develop myelodysplastic neoplasms/acute myeloid leukemia that may arise at any age. In recent years, advances in diagnostic methodologies, particularly in the field of genomics, have revealed novel genes and mechanisms responsible for etiology and disease evolution and opened new perspectives for tailored treatment. Despite the research and diagnostic advances in the field, real world evidence, arising from international neutropenia patient registries and scientific networks, has shown that the diagnosis and management of neutropenic patients is mostly based on the physicians' experience and local practices. Therefore, experts participating in the European Network for the Innovative Diagnosis and Treatment of Chronic Neutropenias have collaborated under the auspices of the European Hematology Association to produce recommendations for the diagnosis and management of patients across the whole spectrum of chronic neutropenias. In the present article, we describe evidence- and consensus-based guidelines for the definition and classification, diagnosis, and follow-up of patients with chronic neutropenias including special entities such as pregnancy and the neonatal period. We particularly emphasize the importance of combining the clinical findings with classical and novel laboratory testing, and advanced germline and/or somatic mutational analyses, for the characterization, risk stratification, and monitoring of the entire spectrum of neutropenia patients. We believe that the wide clinical use of these practical recommendations will be particularly beneficial for patients, families, and treating physicians.

A patient with severe congenital neutropenia harbors a missense ELANE mutation due to paternal germline mosaicism

BACKGROUND

Clinical and genetic characteristics of ELANE mutation of a 3-year-old male who had a severe congenital neutropenia (SCN) were examined. We then investigated whether CRISPR/Cas9-mediated gene editing could correct the mutation.

PROCEDURE

The proband underwent extensive clinical assessments, such as exome sequencing and bioinformatics analysis, so that pathogenic genes could be identified. Sanger sequencing was also utilized for confirmation. The cell line, 293-ELANE, harboring ELANE mutation was generated, and the mutation was then corrected by CRISPR/Cas9-mediated homology-directed repair (HDR).

RESULTS

The ELANE gene test in the proband unveiled a heterozygous de novo missense mutation: c. 248T > A (p.V83D), which was not detected in his asymptomatic parents who had provided peripheral blood samples. We found that 46.01% of his father's sperm cells had the same mutation. These results demonstrate that the proband inherited the ELANE mutation from his father, who had an average neutrophil count but had a germline mosaicism. The highest repair efficiency of CRISPR/Cas9-mediated HDR for 293-ELANE is 4.43%.

CONCLUSIONS

We identified a missense mutation (p.V83D) in ELANE that causes SCN. This is the first report on paternal semen mosaicism of an ELANE mutation. Our study paves the way for preimplantation genetic diagnosis (PGD) based on ELANE mutation prevention and clinical treatment of congenital disabilities.

Somatic mosaicism in inherited bone marrow failure syndromes

Inherited bone marrow failure syndromes (IBMFS) are a heterogenous group of diseases caused by pathogenic germline variants in key pathways associated with haematopoiesis and genomic stability. Germline variants in IBMFS-related genes are known to reduce the fitness of hematopoietic stem and progenitor cells (HSPC), which has been hypothesized to drive clonal selection in these diseases. In many IBMFS, somatic mosaicism predominantly impacts cells by two distinct mechanisms, with contrasting effects. An acquired variation can improve cell fitness towards baseline levels, providing rescue of a deleterious phenotype. Alternatively, somatic mosaicism may result in a fitness advantage that results in malignant transformation. This review will describe these phenomena in IBMFS and delineate their relevance for diagnosis and clinical management. In addition, we will discuss which samples and methods can be used for detection of mosaicism according to clinical phenotype, type of mosaicism, and sample availability.

Dissecting ELANE neutropenia pathogenicity by human HSC gene editing

Severe congenital neutropenia (SCN) is a life-threatening disorder most often caused by dominant mutations of ELANE that interfere with neutrophil maturation. We conducted a pooled CRISPR screen in human hematopoietic stem and progenitor cells (HSPCs) that correlated ELANE mutations with neutrophil maturation potential. Highly efficient gene editing of early exons elicited nonsense-mediated decay (NMD), overcame neutrophil maturation arrest in HSPCs from ELANE-mutant SCN patients, and produced normal hematopoietic engraftment function. Conversely, terminal exon frameshift alleles that mimic SCN-associated mutations escaped NMD, recapitulated neutrophil maturation arrest, and established an animal model of ELANE-mutant SCN. Surprisingly, only -1 frame insertions or deletions (indels) impeded neutrophil maturation, whereas -2 frame late exon indels repressed translation and supported neutrophil maturation. Gene editing of primary HSPCs allowed faithful identification of variant pathogenicity to clarify molecular mechanisms of disease and encourage a universal therapeutic approach to ELANE-mutant neutropenia, returning normal neutrophil production and preserving HSPC function.

Two paternal mosaicism of mutation in ELANE causing severe congenital neutropenia exhibit normal neutrophil morphology and ROS production

Severe congenital neutropenia caused by ELANE gene mutation is a rare disease. To date, only four families were reported with mosaicism. Here we examined the morphology and function of granulocytes isolated from two patients and their mosaic fathers. Analysis of granulocytes isolated from the fathers revealed no genetic mutations. DNA extracted from fractionated peripheral blood mononuclear cells (PBMCs) and fingernails obtained from both fathers did harbor the mutation, suggesting mosaicism. Granulocytes isolated from the patients displayed significantly weaker ionomycin-induced intracellular reactive oxygen species (ROS) responses than those isolated from the fathers. Both patients showed increased expression of neutrophil elastase, whereas the mosaic fathers showed normal expression. Taken together, the results suggest that granulocytes from these SCN patients are immunocompromised, whereas those from the mosaic fathers are normal. These findings may provide new insight into disease diagnosis, prognosis, therapy and genetic counseling.

Mosaicism of an ELANE Mutation in an Asymptomatic Mother

PURPOSE

We report normal neutrophil count in a mother, who carries the same ELANE mutation as her daughter with severe congenital neutropenia. We hypothesized that the mother possessed wild- and mutant-type clones and the wild-type clones could generate neutrophils, whereas the mutant clones could not.

METHODS

We confirmed mutant variant ratio by sequence signals and measured the frequency of the mutant allele by subcloning in various cell types. We established the ELANE-mutated and non-mutated induced pluripotent stem cells (iPSCs) from the mother's T cells and compared granulopoiesis between these iPSCs.

RESULTS

In the sequence analysis of isolated peripheral blood (PB), nail and hair, the mutant variant was detected in approximately 40-60% of lymphocytes, monocytes, hematopoietic progenitor cells, and hair as well as in a small percentage of nail, but in none of the neutrophils. In the subcloning analysis of extracted DNA from CD3⁺ and CD34⁺ cells, the mutant allele was identified in 37.5% and 38.1%, respectively. We reprogrammed the mother's PB cells and established the ELANE-mutated and non-mutated iPSCs. Granulopoiesis from mutated iPSCs revealed little sensitivity to granulocyte colony-stimulating factor in comparison with non-mutated iPSCs.

CONCLUSIONS

These observations strongly suggest that mutant-carrying neutrophils did not appear in the mother's PB because mutated clones could not differentiate into neutrophils. The mother's normal hematological phenotype could be explained by the perseverance of normal, non-mutated granulopoiesis.

Spectrum of ELANE mutations in congenital neutropenia: a single-centre study in patients of Indian origin

AIMS

Congenital and cyclical neutropenia are rare inherited diseases that result in recurrent life-threatening bacterial infections due to a deficiency of mature neutrophils. Cyclical neutropenia is usually caused by heterozygous ELANE mutations while congenital neutropenia is genetically heterogeneous with mutations in genes like ELANE, HAX-1, G6PC3 and GFI1. The presence of ELANE mutation aids in the establishment of diagnosis and rules out other secondary causes of neutropenia such as autoimmune cytopenia and evolving aplasia. Further, patients with ELANE mutations are also at a high risk of developing myelodysplasia or acute myeloid leukaemia. Hence it is important to screen for these mutations in patients presenting with neutropenia early in life.

METHODS

The study included 52 patients who were evaluated for inherited neutropenia. Genomic DNA was extracted from peripheral blood leucocytes and mutation analysis was done by bidirectional Sanger sequencing.

RESULTS

Ten different missense, frameshift or splice site variants in ELANE gene were identified in 11 patients: c.125C>T (p.Pro42Leu), c.164G>A (p.Cys55Tyr), c.169G>A (p.Ala57Thr), c.179T>C (p.Ile60Thr), c.770C>T (p.Pro257Leu), c.367-8C>A, c.597+1G>A along with three novel mutations c.302T>A (p.Val101Glu), c.468G>T (p.Try156Cys) and c.596delT (Phe199Ser fs*13). Family studies were available for three patients and, in all three instances, the mutation had a de novo origin.

CONCLUSION

The widespread distribution of mutations suggests the need to screen all the exons in ELANE gene for proper characterisation of the genotype.

Both Granulocytic and Non-Granulocytic Blood Cells Are Affected in Patients with Severe Congenital Neutropenia and Their Non-Neutropenic Family Members: An Evaluation of Morphology, Function, and Cell Death

Objective:

To examine granulocytic and non-granulocytic cells in children with severe congenital neutropenia (SCN) and their non-neutropenic parents.

Materials and Methods:

Fifteen patients with SCN and 21 non-neutropenic parents were evaluated for a) CD95, CD95 ligand, annexin V, propidium iodide, cell cycle, and lymphocyte subsets by flow cytometry; b) rapid cell senescence (of leukocytes) by senescence-associated β-galactosidase stain; c) aggregation tests by aggregometer; d) in vitro bleeding time by PFA-100 instrument; e) mepacrine-labeled dense granule number of thrombocytes by fluorescence microscope; and f) hematomorphology by light and electron microscope. HAX1, ELANE, G6PC3, CSF3R, and JAGN1 mutations associated with SCN were studied in patients and several parents.

Results:

Significant increase in apoptosis and secondary necrosis in monocytes, lymphocytes, and granulocytes of the patients and parents was detected, irrespective of the mutation type. CD95 and CD95 ligand results implied that apoptosis was non-CD95-mediated. Leukocytes of 25%, 12.5%, and 0% of patients, parents, and controls showed rapid cell senescence. The cell cycle analysis testable in four cases showed G1 arrest and apoptosis in lymphocytes of three. The patients had HAX1 (n=6), ELANE (n=2), G6PC3 (n=2), and unidentified (n=5) mutations. The CD3, CD4, and NK lymphocytes were below normal levels in 16.6%, 8.3%, and 36.4% of the patients and in 0%, 0%, and 15.4% of the parents (controls: 0%, 0%, 5.6%). The thrombocytes aggregated at low rates, dense granule number/thrombocyte ratio was low, and in vitro bleeding time was prolonged in 37.5%-66.6% of patients and 33.3%-63.2% of parents (vs. 0% in controls). Under electron and/or light microscope, the neutrophils, monocytes, lymphocytes, and thrombocytes in the peripheral blood of both patients and parents were dysplastic and the bone marrow of patients revealed increased phagocytic activity, dysmegakaryopoiesis, and necrotic and apoptotic cells. Ultrastructurally, thrombocyte adhesion, aggregation, and release were inadequate.

Conclusion:

In cases of SCN, patients’ pluripotent hematopoietic stem cells and their non-neutropenic parents are both affected irrespective of the genetic defect.

ELANE gene mutation-induced cyclic neutropenia manifesting as recurrent fever with oral mucosal ulcer: A case report

BACKGROUND

Cyclic neutropenia (CyN) is a rare hematological disease. Herein, a CyN girl, aged 3 years and 2 months, with recurrent fever and oral mucosal ulcer caused by neutrophil elastase (ELANE) gene mutation is reported.

CASE PRESENTATION

A 3 years and 2 months old girl presented with recurrent fever and oral mucosal ulcer for 1 year. Routine blood test revealed that her absolute neutrophil count repeatedly decreased (minimum 0. 04 × 10/L) every 21 days on an average. Gene testing showed that the patient suffered from ELANE gene heterozygous mutation (c.197T>G) (exon2) (p.M66R). She was finally diagnosed as CyN. The patient's symptoms were relieved after infection prevention and treatment as well as granulocyte-colony stimulating factor (G-CSF) therapy. Her condition continues to remain stable.

CONCLUSION

Active prevention and treatment of infection as well as G-CSF therapy can successfully control CyN.