Genetic and molecular diagnosis of severe congenital neutropenia

The monogenic landscape of human infectious diseases

The spectrum of known monogenic inborn errors of immunity is growing, with certain disorders underlying a specific and narrow range of infectious diseases. These disorders reveal the core mechanisms by which these infections occur in various settings, including inherited and acquired immunodeficiencies, thereby delineating the essential mechanisms of protective immunity to the corresponding pathogens. These findings also have medical implications, facilitating diagnosis and improving the management of individuals at risk of disease.

Case report: Granulocyte-macrophage colony-stimulating factor sargramostim did not rescue the neutrophil phenotype in two patients with JAGN1-mutant severe congenital neutropenia

Background

Homozygous or compound heterozygous mutations in JAGN1 cause severe congenital neutropenia. JAGN1-mutant patients present with severe early-onset bacterial infections and most have been described as low-responders to recombinant granulocyte colony-stimulating factor (G-CSF) therapy. In a murine, hematopoietic JAGN1 knockout model, which displays susceptibility to Candida albicans infection in the absence of neutropenia, treatment with granulocyte-macrophage-CSF (GM-CSF) was able to restore the functional defect of neutrophils.

Patients

We present two unrelated patients with biallelic JAGN1 mutations, who were both treated with subcutaneous GM-CSF (sargramostim) after treatment failure to G-CSF. The first patient was an 18-year-old pregnant woman who received GM-CSF at 12 weeks of gestation up to a dose of 10 µg/kg/d for 7 days. The second patient was a 5-month-old girl who received GM-CSF for a total of 9 days at a dose of up to 20 µg/kg/d. GM-CSF did not increase neutrophil counts in our patients. Treatment was stopped when neutrophil numbers declined further, no beneficial effect was noticed, and patients presented with infections. No adverse effects were observed in either patient and the fetus. Both patients ultimately underwent successful hematopoietic stem cell transplantation.

Discussion

Both patients showed a high recurrence rate of severe infections on G-CSF treatment. GM-CSF therapy did not ameliorate the clinical phenotype, in contrast to the improvement of neutrophil function observed in the JAGN1 mouse model. No major additional extra-hematopoietic manifestations were evident in our patients.

Conclusion

In two unrelated patients, GM-CSF did not have any beneficial effect on neutrophil counts. Patients with JAGN1-mutant SCN with reduced G-CSF responsiveness and elevated infection rate should be evaluated early for stem cell transplantation.

Primary immunodeficiency diseases in the newborn

The normal neonate’s immune system is anatomically completed but antigenically inexperienced and shows somewhat decreased role of a number of immunological pathways. Aside from anatomic characteristics (e.g., thin skin and mucosal barriers) of newborn, weakened pro-inflammatory and T-helper cell type 1 cytokine release and lessened cell-mediated immunity predispose the neonate more susceptible to all types of infections. Furthermore, many types of primary immunodeficiency diseases (PIDs) that present in neonatal period are potentially life threatening. However, most of the newborns stand this period without sickness due to complete innate immunity with other adaptive immune system mechanisms and transferred maternal immunoglobulin G. Besides unique immunity of the preterm and normal newborns; risk factors, clinical features, and laboratory evaluation of most common PIDs in newborn are told in this article. The range of PIDs is growing, and the diagnosis and management of these disorders continues to increase in complexity. The most common PID types of the newborn including antibody deficiencies, cellular/combined immunodeficiencies, phagocytic diseases, complement deficiencies, and innate immune system and other disorders are briefly mentioned here as well.

Human MALT1 deficiency and predisposition to infections

Human germline MALT1 deficiency is an inborn error of immunity characterized by recurrent bacterial, viral, and fungal infections, periodontal disease, enteropathy, dermatitis, and failure to thrive. The number of identified MALT1-deficient patients have greatly increased in the past two years, which has significantly improved our understanding of the clinical features of this disorder. Patients frequently experience infections affecting the respiratory, skin, gastrointestinal, and blood systems. The most frequently detected pathogens are Staphylococcus aureus, Candida albicans, and cytomegalovirus. Enhanced susceptibility to S. aureus and C. albicans is likely due to impaired Th17 immunity, similar to STAT3 and IL-17 pathway deficiencies.

The genetic basis of pneumococcal and staphylococcal infections: inborn errors of human TLR and IL-1R immunity

Many bacteria can cause pyogenic lesions in humans. Most of these bacteria are harmless in most individuals, but they, nevertheless, cause significant morbidity and mortality worldwide. The inherited and acquired immunodeficiencies underlying these pyogenic infections differ between bacteria. This short review focuses on two emblematic pyogenic bacteria: pneumococcus (Streptococcus pneumoniae) and Staphylococcus, both of which are Gram-positive encapsulated bacteria. We will discuss the contribution of human genetic studies to the identification of germline mutations of the TLR and IL-1R pathways.

Zebrafish Granulocyte Colony-Stimulating Factor Receptor Maintains Neutrophil Number and Function throughout the Life Span

Granulocyte colony-stimulating factor receptor (G-CSFR), encoded by the CSF3R gene, represents a major regulator of neutrophil production and function in mammals, with inactivating extracellular mutations identified in a cohort of neutropenia patients unresponsive to G-CSF treatment. This study sought to elucidate the role of the zebrafish G-CSFR by generating mutants harboring these inactivating extracellular mutations using genome editing. Zebrafish csf3r mutants possessed significantly decreased numbers of neutrophils from embryonic to adult stages, which were also functionally compromised, did not respond to G-CSF, and displayed enhanced susceptibility to bacterial infection. The study has identified an important role for the zebrafish G-CSFR in maintaining the number and functionality of neutrophils throughout the life span and created a bona fide zebrafish model of nonresponsive neutropenia.

Clinical, Laboratory, and Molecular Characteristics and Remission Status in Children With Severe Congenital and Non-congenital Neutropenia

Objectives: Severe congenital neutropenia (SCN) is a primary immunodeficiency disease characterized by the early onset of recurrent infections and persistent severe neutropenia, with or without genetic defect. We aimed to study the different clinical features and hematological and bone marrow characteristics of patients with SCN and the non-congenital form of severe neutropenia (SN) with unknown etiology. Methods: Thirty-nine Chinese children with severe neutropenia for longer than 6 months unrelated to virus infection or autoimmune diseases were enrolled in the study to analyse the clinical, laboratory, and molecular characteristics. They were followed clinically to observe their remission status. Results: Seven patients were found to have SCN mutations, including ELANE and G6PC3. Among 26 patients with close follow-up, one died for an unknown reason, and 10 resolved spontaneously with a median neutropenia duration of 14.5 months; these patients were designated as having recovered SN. The demographic characteristics of both groups were similar, with a median infection rate of 5 times/year. SCN patients had more frequent infection than recovered SN patients (4 times/year, P = 0.039). The median absolute neutrophil count (ANC) was 0.40 × 10⁹/L in SCN patients, which was significantly higher than 0.2 × 10⁹/L in SN with unknown etiology and 0.21 × 10⁹/L in recovered SN patients (P = 0.021, P = 0.017). The median monocyte count was 1.60 × 10⁹/L in SCN patients, which was also significantly higher than 0.57 × 10⁹/L in SN of unknown etiology and 0.55 × 10⁹/L in recovered SN patients (P = 0.018, P = 0.001). Bone marrow examinations demonstrated myeloid maturation arrest at the myelocyte-metamyelocyte stage in SCN patients and normal findings in SN with unknown etiology and recovered SN patients. Conclusions: Patients with severe neutropenia due to gene mutations demonstrate more serious symptoms than patients with unknown etiology. Patients with relatively higher ANC and monocyte counts are more likely to have known gene mutations. Future studies should focus on more detailed laboratory investigation, prolonged follow-up and advanced molecular biology tools to facilitate accurate diagnosis and effective treatment.

Relationship between paediatric CT scans and subsequent risk of leukaemia and brain tumours: assessment of the impact of underlying conditions

BACKGROUND

We previously reported evidence of a dose-response relationship between ionising-radiation exposure from paediatric computed tomography (CT) scans and the risk of leukaemia and brain tumours in a large UK cohort. Underlying unreported conditions could have introduced bias into these findings.

METHODS

We collected and reviewed additional clinical information from radiology information systems (RIS) databases, underlying cause of death and pathology reports. We conducted sensitivity analyses excluding participants with cancer-predisposing conditions or previous unreported cancers and compared the dose-response analyses with our original results.

RESULTS

We obtained information from the RIS and death certificates for about 40% of the cohort (n∼180 000) and found cancer-predisposing conditions in 4 out of 74 leukaemia/myelodysplastic syndrome (MDS) cases and 13 out of 135 brain tumour cases. As these conditions were unrelated to CT exposure, exclusion of these participants did not alter the dose-response relationships. We found evidence of previous unreported cancers in 2 leukaemia/MDS cases, 7 brain tumour cases and 232 in non-cases. These previous cancers were related to increased number of CTs. Exclusion of these cancers reduced the excess relative risk per mGy by 15% from 0.036 to 0.033 for leukaemia/MDS (P-trend=0.02) and by 30% from 0.023 to 0.016 (P-trend<0.0001) for brain tumours. When we included pathology reports we had additional clinical information for 90% of the cases. Additional exclusions from these reports further reduced the risk estimates, but this sensitivity analysis may have underestimated risks as reports were only available for cases.

CONCLUSIONS

Although there was evidence of some bias in our original risk estimates, re-analysis of the cohort with additional clinical data still showed an increased cancer risk after low-dose radiation exposure from CT scans in young patients.

Primary immunodeficiency in the neonate: Early diagnosis and management

Many primary immunodeficiencies (PIDs) manifest in the neonatal period but can be challenging to diagnose and manage optimally. In part, the difficulty stems from the natural immaturity of the neonatal immune system that may mask immune deficits and/or complicate interpretation of clinical findings and laboratory assays. The great diversity of PIDs--from innate immune system defects to those that impact the humoral and/or cellular components of the adaptive immune system--and the rapid rate at which new PIDs are being discovered makes it challenging for practitioners to stay current. Moreover, recent appreciation for immune deficiencies that lead to autoinflammation and autoimmunity have broadened the spectrum of neonatal PID, adding additional complexity to an already intricate field. This article serves to highlight the deficiencies in the neonatal immune system, while providing a review of the more common PIDs that present in the neonate and guidelines for diagnosis and supportive care.

Aggressive forms of periodontitis secondary to systemic disorders

A number of systemic disorders increase a patient's susceptibility to destructive periodontitis and have impacts on periodontal disease progression and severity. The underlying factors are usually genetic and are mainly related to alterations in the immune response and in certain endocrine functions, leading to various syndromes in which periodontitis and/or early tooth loss are secondary manifestations. Neutrophils are important immune defense cells that play a significant role in controlling the spread of microbial plaque infections in the dentogingival region. This review focuses on a selected group of systemic disorders that are associated with alterations in either neutrophil counts (quantitative disorders) or function (qualitative disorders), and defects in the mineralization of bone and dental tissues. In most of these diseases controlling the periodontal disease progression is very challenging. Proper diagnosis is a prerequisite for proper management of the periodontal problem. Future advances in research, including gene targeting and the resolution of enzyme deficiencies, may bring about remedies of the underlying systemic disorders and may significantly improve the outcome of periodontal treatment in these patients.

Genetic analysis and clinical picture of severe congenital neutropenia in Israel

BACKGROUND

The relative frequency of mutated genes among patients with severe congenital neutropenia (SCN) may differ between various ethnic groups. To date, few population-based genetic studies have been reported. This study describes the genetic analysis of 32 Israeli patients with SCN.

PROCEDURES

Clinical data were retrieved from the prospective Israeli Inherited Bone Marrow Failure Registry. Recruitment included living and deceased patients who were diagnosed between 1982 and 2012, for whom molecular diagnosis was performed. ELANE, HAX1 and G6PC3 genes were sequenced in all patients, and GFI-1 and WAS genes were sequenced if other genes were wildtype.

RESULTS

Eleven patients (34%) had heterozygous mutations in ELANE (10 kindreds), eight (25%) had homozygous mutations in G6PC3 (5 kindreds) and 13 (41%) had no detected mutations. No patients had mutations in HAX1 or WAS. Four of the eight patients with G6PC3 mutations had congenital anomalies. The probability of survival for all patients was 50% at age of 18. Deaths were mainly due to sepsis (5 patients, 4/5 not responding to G-CSF, none with G6PC3 mutation). Two patients developed acute myelogenous leukemia (AML) and one myelodysplastic syndrome (MDS), none with G6PC3 mutation.

CONCLUSIONS

We found a unique pattern of SCN mutations in Israel with homozygous G6PC3 mutations in eight (25%) patients, the highest frequency described so far. HAX1 mutations, reported mainly in Sweden and Iran, were absent. Patients with G6PC3 mutations had congenital anomalies, appeared to have a better response to G-CSF, and so far have not developed AML or MDS.

Granulocyte colony-stimulating factor receptor mutations in myeloid malignancy

Granulocyte colony-stimulating factor is a cytokine able to stimulate both myelopoiesis and hematopoietic stem cell mobilization, which has seen it used extensively in the clinic to aid hematopoietic recovery. It acts specifically via the homodimeric granulocyte colony-stimulating factor receptor (G-CSFR), which is principally expressed on the surface of myeloid and hematopoietic progenitor cells. A number of pathogenic mutations have now been identified in CSF3R, the gene encoding G-CSFR. These fall into distinct classes, each of which is associated with a particular spectrum of myeloid disorders, including malignancy. This review details the various CSF3R mutations, their mechanisms of action, and contribution to disease, as well as discussing the clinical implications of such mutations.

Spectrum of bone marrow failures of myeloid series: new report of neutropenic patients from a referral pediatric center in Iran

Neutropenia is a reduction of the absolute neutrophil count (ANC), which could be seen in different conditions, while its association with a number of primary immunodeficiency diseases has been reported. This study was performed in all neutropenic patients who were admitted in a referral pediatric hospital during a 6-year period (2006-2011). One hundred and forty patients with ANC of below 1500/mm(3) were investigated in this study. The most common causes of neutropenia were severe congenital neutropenia (41%), aplastic anemia (19%), cyclic neutropenia (11%), hyperimmunoglobulin M syndrome (9%), and fanconi anemia (7%). The patients experienced their first manifestation at a median age of 1 year, while the median diagnostic age was 21 months. Parental consanguinity was present in about half of the cases. The most common clinical manifestations of the patients were sinusitis (62 cases), periodontitis (51 cases), acute diarrhea (39 cases), pneumonia (38 cases), abscess (36 cases), skin rashes (35 cases), and otitis media (31 cases). Twenty two patients (16%) died during the study period. Considering the differential diagnosis of neutropenia, making the diagnosis and appropriate treatments are the keys in management of patients with neutropenia to avoid further complications.

Molecular mechanisms regulating NETosis in infection and disease

Neutrophils are the foot soldiers of the immune system. They home in to the site of infection and kill pathogens by phagocytosis, degranulation, and the release of web-like structures called neutrophil extracellular traps (NETs) that trap and kill a variety of microbes. NETs have been shown to play a multitude of additional roles in immunity but have also been implicated in inflammatory and autoimmune disease. Here, we discuss the role of NETs in these various contexts with a particular emphasis on the molecular mechanisms that regulate NET release and clearance. We highlight the comprehensive concepts and explore the important open questions in the field.

Hematopoietic stem cell transplantation for severe congenital neutropenia

PURPOSE OF REVIEW

Hematopoietic stem cell transplantation (HCT) is the only curative option for patients with severe congenital neutropenia (SCN). Transplant success is dependent on identifying at-risk patients and proceeding to transplant before the development of severe infections or malignant transformation. This review focuses on recent advancements in risk stratification of SCN patients, indications for HCT, and review of published transplant studies.

RECENT FINDINGS

Patients with poor neutrophil response despite high doses of granulocyte colony-stimulating factor (G-CSF) are at greatest risk for malignant transformation. Other studies demonstrate elevated risk with mutations in the G-CSF receptor gene and a specific mutation in the ELANE gene. These patients are at high-risk of sepsis or leukemia development and should proceed to transplant with best available donor. As recent published studies demonstrate, HCT is highly successful in patients without leukemia and, therefore, may be considered in selected low-risk patients given the life-long risk of malignancy and infection.

SUMMARY

The decision whether to proceed to HCT in healthy patients maintained on G-CSF is difficult. As transplant-related mortality continues to decrease, the role of transplant in SCN is likely to expand to more patients.

Relato de um caso de neutropenia congênita grave em um lactente jovem

OBJETIVO: Relatar um caso de neutropenia congênita grave e alertar os pediatras sobre tal diagnóstico em pacientes jovens, com infecções recorrentes. DESCRIÇÃO DO CASO: Lactente jovem com 45 dias de vida, com história de febre alta, letargia, recusa alimentar e hemogramas repetidos com leucopenia importante à custa de polimorfonucleares. A hipótese diagnóstica foi confirmada pelo aspirado de medula óssea, que mostrou hipoplasia de série granulocítica e completa ausência de neutrófilos maduros. Foi introduzida antibioticoterapia de largo espectro e estimulador da formação de colônias de granulócitos. O paciente evoluiu para óbito em decorrência de complicações infecciosas após 21 dias de internação. COMENTÁRIOS: Trata-se de um lactente jovem, portador de uma rara desordem congênita que leva à intensa neutropenia, deixando-o vulnerável a infecções graves e potencialmente fatais. À internação, o paciente apresentava sinais e sintomas sugestivos de sepse, sendo introduzido antibioticoterapia de amplo espectro, necessária por se tratar de lactente jovem, neutropênico e febril. A hipótese diagnóstica se baseou na história clínica e nos leucogramas alterados, sendo posteriormente confirmada pelo aspirado de medula óssea. Foi introduzido o estimulador da formação de colônias de granulócitos, que geralmente é efetivo, porém, nesse caso, não houve sucesso e o paciente evoluiu para óbito devido à grave infecção.

[Severe congenital neutropenia: analysis of clinical features, diagnostic methods, treatment and long-term outcome]

INTRODUCTION

Severe congenital neutropenia (SCN), a heterogeneous condition with onset at early ages, is characterised by primary myelopoiesis failure with an absolute neutrophil count (ANC) < 0.5 x10(9)/L, severe infections and risk of leukaemic transformation.

OBJECTIVE

The aim of the study was to ascertain the long term outcome of patients with SCN.

MATERIAL AND METHODS

The clinical features, diagnostic methods, treatment and outcome of 11 patients with SCN were analysed.

RESULTS

The median age at diagnosis was 4 months (range: 3 days-12 years). The primary clinical manifestation was severe infection. Median ANC at diagnosis: 0.2 x 10(9)/L (range: 0-0.37). Bone marrow aspirate showed maturation arrest at promyelocyte stage in all cases. Genetic studies revealed 3 mutations, two in ELA-2 gene and 1 in G6PC3 gene, showing a correlation between genotype and phenotype. Granulocyte Colony Stimulating Factor (G-CSF) was the first-line treatment in 9 patients; six of whom showed a good response at doses between 5 and 15 μg/kg/day for 3-7 days/week. The remaining 3 patients failed to respond to G-CSF and allogeneic stem cell transplantation (SCT) was indicated. Furthermore, SCT was the treatment of choice in two cases. Median follow-up of the cohort was 5 years (range: 1-10 years) with 100% survival and no cases of leukaemic transformation.

CONCLUSIONS

We conclude that genetic study is useful for establishing a correlation between genotype and phenotype. The treatment of choice for SCN is G-CSF to which 2/3 of patients should respond; while SCT is reserved for cases of poor response or those evolving to myelodysplastic syndrome (MDS) or leukaemia; thus close follow-up of this condition is essential.

Severe congenital neutropenia, a genetically heterogeneous disease group with an increased risk of AML/MDS

OVER THE PAST DECADE, ENORMOUS PROGRESS HAS BEEN MADE IN THE UNDERSTANDING OF SEVERE CONGENITAL NEUTROPENIA (SCN), BY IDENTIFICATION OF SEVERAL CAUSAL GENE MUTATIONS: in ELANE, GFI1, HAX1, WAS and G3PC3. SCN is a preleukemic condition, independent of the genetic subtype. Acquired CSF3R mutations are specific for SCN and are strongly associated with malignant progression. In this review, we describe the known genetic subtypes of SCN, their molecular basis and clinical presentation and summarize the available evidence on CSF3R mutations and monosomy 7 in malignant conversion.

SerpinB1 protects the mature neutrophil reserve in the bone marrow

SerpinB1 is among the most efficient inhibitors of neutrophil serine proteases--NE, CG, and PR-3--and we investigated here its role in neutrophil development and homeostasis. We found that serpinB1 is expressed in all human bone marrow leukocytes, including stem and progenitor cells. Expression levels were highest in the neutrophil lineage and peaked at the promyelocyte stage, coincident with the production and packaging of the target proteases. Neutrophil numbers were decreased substantially in the bone marrow of serpinB1(-/-) mice. This cellular deficit was associated with an increase in serum G-CSF levels. On induction of acute pulmonary injury, neutrophils were recruited to the lungs, causing the bone marrow reserve pool to be completely exhausted in serpinB1(-/-) mice. Numbers of myeloid progenitors were normal in serpinB1(-/-) bone marrow, coincident with the absence of target protease expression at these developmental stages. Maturation arrest of serpinB1(-/-) neutrophils was excluded by the normal CFU-G growth in vitro and the normal expression in mature neutrophils of early and late differentiation markers. Normal absolute numbers of proliferating neutrophils and pulse-chase kinetic studies in vivo showed that the bone marrow deficit in serpinB1(-/-) mice was largely restricted to mature, postmitotic neutrophils. Finally, upon overnight culture, apoptosis and necrosis were greater in purified bone marrow neutrophils from serpinB1(-/-) compared with WT mice. Collectively, these findings demonstrate that serpinB1 sustains a healthy neutrophil reserve that is required in acute immune responses.

Severe congenital neutropenia resulting from G6PC3 deficiency with increased neutrophil CXCR4 expression and myelokathexis

Mutations in more than 15 genes are now known to cause severe congenital neutropenia (SCN); however, the pathologic mechanisms of most genetic defects are not fully defined. Deficiency of G6PC3, a glucose-6-phosphatase, causes a rare multisystem syndrome with SCN first described in 2009. We identified a family with 2 children with homozygous G6PC3 G260R mutations, a loss of enzymatic function, and typical syndrome features with the exception that their bone marrow biopsy pathology revealed abundant neutrophils consistent with myelokathexis. This pathologic finding is a hallmark of another type of SCN, WHIM syndrome, which is caused by gain-of-function mutations in CXCR4, a chemokine receptor and known neutrophil bone marrow retention factor. We found markedly increased CXCR4 expression on neutrophils from both our G6PC3-deficient patients and G6pc3(-/-) mice. In both patients, granulocyte colony-stimulating factor treatment normalized CXCR4 expression and neutrophil counts. In G6pc3(-/-) mice, the specific CXCR4 antagonist AMD3100 rapidly reversed neutropenia. Thus, myelokathexis associated with abnormally high neutrophil CXCR4 expression may contribute to neutropenia in G6PC3 deficiency and responds well to granulocyte colony-stimulating factor.