Neurodevelopmental abnormalities associated with severe congenital neutropenia due to the R86X mutation in the HAX1 gene

Discerning clinicopathological features of congenital neutropenia syndromes: an approach to diagnostically challenging differential diagnoses

The congenital neutropenia syndromes are rare haematological conditions defined by impaired myeloid precursor differentiation or function. Patients are prone to severe infections with high mortality rates in early life. While some patients benefit from granulocyte colony-stimulating factor treatment, they may still face an increased risk of bone marrow failure, myelodysplastic syndrome and acute leukaemia. Accurate diagnosis is crucial for improved outcomes; however, diagnosis depends on familiarity with a heterogeneous group of rare disorders that remain incompletely characterised. The clinical and pathological overlap between reactive conditions, primary and congenital neutropenias, bone marrow failure, and myelodysplastic syndromes further clouds diagnostic clarity.We review the diagnostically useful clinicopathological and morphological features of reactive causes of neutropenia and the most common primary neutropenia disorders: constitutional/benign ethnic neutropenia, chronic idiopathic neutropenia, cyclic neutropenia, severe congenital neutropenia (due to mutations in ELANE, GFI1, HAX1, G6PC3, VPS45, JAGN1, CSF3R, SRP54, CLPB and WAS), GATA2 deficiency, Warts, hypogammaglobulinaemia, infections and myelokathexis syndrome, Shwachman-Diamond Syndrome, the lysosomal storage disorders with neutropenia: Chediak-Higashi, Hermansky-Pudlak, and Griscelli syndromes, Cohen, and Barth syndromes. We also detail characteristic cytogenetic and molecular factors at diagnosis and in progression to myelodysplastic syndrome/leukaemia.

HAX1: A versatile, intrinsically disordered regulatory protein

HAX1 is a relatively small, ubiquitously expressed, predominantly mitochondrial, intrinsically disordered protein. It has been implicated in the regulation of apoptosis, cell migration, calcium cycling, proteostasis, angiogenesis, autophagy and translation. A wide spectrum of functions, numerous interactions and still elusive molecular mechanisms of action make HAX1 an intriguing subject of research. Moreover, HAX1 is involved in the pathogenesis of diseases; its deficiency leads to neutropenia and its overexpression is associated with cancer. In this review we aim to describe the characteristics of HAX1 gene and protein, and comprehensively discuss its multiple functions, highlighting the emerging role of HAX1 in protection from stress and apoptosis through maintaining cellular proteostasis and homeostasis.

HAX1-related congenital neutropenia: Long-term observation in paediatric and adult patients enrolled in the European branch of the Severe Chronic Neutropenia International Registry (SCNIR)

HAX1-related congenital neutropenia (HAX1-CN) is a rare autosomal recessive disorder caused by pathogenic variants in the HAX1 gene. HAX1-CN patients suffer from bone marrow failure as assessed by a maturation arrest of the myelopoiesis revealing persistent severe neutropenia from birth. The disorder is strongly associated with severe bacterial infections and a high risk of developing myelodysplastic syndrome or acute myeloid leukaemia. This study aimed to describe the long-term course of the disease, the treatment, outcome and quality of life in patients with homozygous HAX1 mutations reported to the European branch of the Severe Chronic Neutropenia International Registry. We have analysed a total of 72 patients with different types of homozygous (n = 68), compound heterozygous (n = 3), and digenic (n = 1) HAX1 mutations. The cohort includes 56 paediatric (<18 years) and 16 adult patients. All patients were initially treated with G-CSF with a sufficient increase in absolute neutrophil counts. Twelve patients required haematopoietic stem cell transplantation for leukaemia (n = 8) and non-leukaemic indications (n = 4). While previous genotype-phenotype reports documented a striking correlation between two main transcript variants and clinical neurological phenotypes, our current analysis reveals novel mutation subtypes and clinical overlaps between all genotypes including severe secondary manifestations, e.g., high incidence of secondary ovarian insufficiency.

A Novel Intronic Mutation Reduces HAX1 Level and is Associated With Severe Congenital Neutropenia

Severe congenital neutropenia (SCN) is a rare disease. Autosomal recessive forms of SCN are more frequent in countries where consanguineous marriages are common. In this report, we describe a 54-day-old female with neutropenia who presented with ecthyma gangrenosum. Clinical exome sequencing was used to identify the mutation. HAX1 messenger RNA and isoforms were examined by real-time quantitative and conventional polymerase chain reaction. Bone marrow aspiration was stained by hematoxylin and eosin. Granulocytes were tested for apoptosis upon H2O2 exposure. T-cell proliferation was tested by flow cytometry. Clinical exome sequencing revealed a novel homozygous acceptor splice site mutation in intron 3 of HAX1 (c.505-1G>C), which reduced both isoforms A and B of HAX1 messenger RNA. The Western blot studies showed a complete absence of HAX1 protein. The purified neutrophils from the patient showed increased apoptosis upon H2O2 exposure, whereas T-cell proliferative responses to various stimuli were intact. The patient was treated with combined antibiotics, filgrastim, and placed on antibiotics prophylaxis. To the best of our knowledge, our data provide the first experimental evidence for HAX1 deficiency because of a splice site mutation. Although 3 other splice site variants have been deposited in databases, functional studies were missing. This novel variant of HAX1 may explain the SCN and secondary infections in our patients.

Nonsense Suppression Therapy: New Hypothesis for the Treatment of Inherited Bone Marrow Failure Syndromes

Inherited bone marrow failure syndromes (IBMFS) are a group of cancer-prone genetic diseases characterized by hypocellular bone marrow with impairment in one or more hematopoietic lineages. The pathogenesis of IBMFS involves mutations in several genes which encode for proteins involved in DNA repair, telomere biology and ribosome biogenesis. The classical IBMFS include Shwachman–Diamond syndrome (SDS), Diamond–Blackfan anemia (DBA), Fanconi anemia (FA), dyskeratosis congenita (DC), and severe congenital neutropenia (SCN). IBMFS are associated with high risk of myelodysplastic syndrome (MDS), acute myeloid leukemia (AML), and solid tumors. Unfortunately, no specific pharmacological therapies have been highly effective for IBMFS. Hematopoietic stem cell transplantation provides a cure for aplastic or myeloid neoplastic complications. However, it does not affect the risk of solid tumors. Since approximately 28% of FA, 24% of SCN, 21% of DBA, 20% of SDS, and 17% of DC patients harbor nonsense mutations in the respective IBMFS-related genes, we discuss the use of the nonsense suppression therapy in these diseases. We recently described the beneficial effect of ataluren, a nonsense suppressor drug, in SDS bone marrow hematopoietic cells ex vivo. A similar approach could be therefore designed for treating other IBMFS. In this review we explain in detail the new generation of nonsense suppressor molecules and their mechanistic roles. Furthermore, we will discuss strengths and limitations of these molecules which are emerging from preclinical and clinical studies. Finally we discuss the state-of-the-art of preclinical and clinical therapeutic studies carried out for IBMFS.

Kostmann Syndrome With Neurological Abnormalities: A Case Report and Literature Review

Background: Severe congenital neutropenia (SCN), also known as Kostmann syndrome, is a rare heterogeneous group of diseases characterized by arrested neutrophil maturation in the bone marrow. Case Presentation: We report a case of Kostmann syndrome and review previously reported SCN cases with neurological abnormalities. A 10-year-old boy had a history of recurrent, once a month, infection starting at 6 months of age. He had neutropenia for more than 9 years, as well as intellectual disability. He was homozygous for the exon 3 c.430dupG mutation of the HAX1 gene NM-006118. After treatment of antibiotics and G-CSF, his symtoms were relieved and was 3 months free of infection. The search revealed 29 articles related to Kostmann syndrome caused by HAX1 gene mutation; they were screened, and the main clinical features of 13 cases of Kostmann syndrome with neurological abnormalities were summarized and analyzed. Conclusions: Kostmann syndrome has three main characteristics: severe neutropenia (<0.2 × 10⁹/L), maturation arrest of granulopoiesis at the promyelocyte stage, and death due to infections. HAX1 gene mutations affecting both isoforms A and B are associated with additional neurological symptoms. G-CSF can improve and maintain neutrophil counts, and improve prognosis and quality of life. At present, hematopoietic stem cell transplantation is the only cure.

Management of tooth extraction in a patient with ELANE gene mutation-induced cyclic neutropenia: A case report

INTRODUCTION

Cyclic neutropenia (CyN) is a rare hematological disease, and patients with CyN often experience an early onset of severe periodontitis and are forced to undergo tooth extraction. Here, we report a case of a patient with CyN who showed different periodicity and oscillations of neutrophil count compared with her mother, despite sharing the same novel genetic mutation.

PATIENT CONCERNS

A 17-year-old Japanese girl who had been diagnosed with CyN shortly after birth presented to our hospital with a complaint of mobility of her teeth and gingivitis. Upon presentation, an intraoral examination was performed and revealed redness and swelling of the marginal and attached gingiva. Radiographs revealed extreme resorption of the alveolar bone and apical lesions in her mandibular lateral incisors. The patient's hematologic data demonstrated a lack of blood neutrophils (0/μL). The patient had no history of dental extraction, and her mother also had a history of CyN.

DIAGNOSES

The patient was diagnosed with severe periodontitis that was associated with CyN. Gene testing showed a novel heterozygous mutation in exon 4 of the ELANE gene (c.538delC, p.Leu180Ser fsX11).

INTERVENTIONS

Based on the clinical findings, we planned to extract the patient's mandibular lateral incisors. Although the tooth extraction was scheduled considering the cyclic variation in neutrophil count, the patient's neutrophil count was 0/μL on the day before the planned extraction. Therefore, granulocyte-colony stimulating factor (G-CSF) was administered to increase the patient's neutrophil count. On the day of the patient's admission for the tooth extraction, she presented with fever (body temperature, 38.5°C), tonsillitis, and stomatitis. The extraction was subsequently delayed, and the patient was administered antibiotics and G-CSF for 4 days. At this time, the neutrophil count increased to 750/μL, and the tooth extraction was carried out safely.

OUTCOMES

The postoperative course was uneventful, and the healing process at the extraction site was excellent.

CONCLUSION

There is a possibility that the periodicity and oscillations of neutrophil count may change with growth in patients with CyN. Therefore, it is important to frequently examine and treat patients with fluctuating neutrophil levels for the management of invasive dental treatment in patients with CyN.

HAX1 is associated with neuronal apoptosis and astrocyte proliferation after spinal cord injury

HS1-associated protein X-1 (HAX1) is a class of multifunctional protein, participated in various physiological processes such as cell apoptosis, proliferation and motility. However, the HAX1 expression and function in the spinal cord injury (SCI) pathological process have not been investigated. In our current research, the rat model of SCI was established, and then we explored the possible role of HAX1 after SCI. The results of western blot indicated that HAX1 was present in sham operated control group and significantly elevated at 3 days post SCI, then declined gradually. Immunohistochemical studies indicated HAX1 expression was enhanced significantly in white and gray matter at 3 days post SCI compared with sham operated group. Double immunofluorescence staining showed the proportion of cells, double-labeled HAX1 and neurons, astrocytes, increased significantly at 3 days post SCI. In addition, co-localization of HAX1/active caspase-3 and HAX1/PCNA was tested in cells. Furthermore, over-expression of HAX1 inhibited neuronal apoptosis in vitro, and in astrocytes HAX1 silencing could down-regulate PCNA expression post LPS treatment. Meanwhile, CCK8 assay showed that knockdown of HAX1 could inhibit the astrocyte proliferation. In summary, our data indicated that HAX1 might play significant roles in pathological process of neuronal apoptosis and astrocyte proliferation during SCI.

Cyclic manner of neutropenia in a patient with HAX-1 mutation

Introduction: Severe congenital neutropenia (SCN) includes a group of genetic disorders which cause to arrest of neutrophil maturation. SCN can be associated with heterogenous group of genetic defects in ELANE, GFI1, HAX1, G6PC3, JAGN1, VPS45 or activating mutations in the Wiskott-Aldrich syndrome (WAS) gene. Aim: Here we report a patient who has a HAX1 mutation presented with cyclic manner. Case Report: A 6 year old female patients was admitted with recurrent apthous stomatitis. We followed the patient as cyclic neutropenia according to complete blood count results 2 times for 6 weeks. After persistant neutropenia developed during a severe varicella infection, we analysed HAX1 mutation, the result was interesting and incompatible with reported cyclic neutropenia patients. Conclusion: We suggest that HAX1 deficiency should be thought in patients who have normal neutrophil counts in the between of infections.

Human genetics of infectious diseases: Unique insights into immunological redundancy

For almost any given human-tropic virus, bacterium, fungus, or parasite, the clinical outcome of primary infection is enormously variable, ranging from asymptomatic to lethal infection. This variability has long been thought to be largely determined by the germline genetics of the human host, and this is increasingly being demonstrated to be the case. The number and diversity of known inborn errors of immunity is continually increasing, and we focus here on autosomal and X-linked recessive traits underlying complete deficiencies of the encoded protein. Schematically, four types of infectious phenotype have been observed in individuals with such deficiencies, each providing information about the redundancy of the corresponding human gene, in terms of host defense in natural conditions. The lack of a protein can confer vulnerability to a broad range of microbes in most, if not all patients, through the disruption of a key immunological component. In such cases, the gene concerned is of low redundancy. However, the lack of a protein may also confer vulnerability to a narrow range of microbes, sometimes a single pathogen, and not necessarily in all patients. In such cases, the gene concerned is highly redundant. Conversely, the deficiency may be apparently neutral, conferring no detectable predisposition to infection in any individual. In such cases, the gene concerned is completely redundant. Finally, the lack of a protein may, paradoxically, be advantageous to the host, conferring resistance to one or more infections. In such cases, the gene is considered to display beneficial redundancy. These findings reflect the current state of evolution of humans and microbes, and should not be considered predictive of redundancy, or of a lack of redundancy, in the distant future. Nevertheless, these observations are of potential interest to present-day biologists testing immunological hypotheses experimentally and physicians managing patients with immunological or infectious conditions.

Kv3 Channels: Enablers of Rapid Firing, Neurotransmitter Release, and Neuronal Endurance

The intrinsic electrical characteristics of different types of neurons are shaped by the K+ channels they express. From among the more than 70 different K+ channel genes expressed in neurons, Kv3 family voltage-dependent K+ channels are uniquely associated with the ability of certain neurons to fire action potentials and to release neurotransmitter at high rates of up to 1,000 Hz. In general, the four Kv3 channels Kv3.1-Kv3.4 share the property of activating and deactivating rapidly at potentials more positive than other channels. Each Kv3 channel gene can generate multiple protein isoforms, which contribute to the high-frequency firing of neurons such as auditory brain stem neurons, fast-spiking GABAergic interneurons, and Purkinje cells of the cerebellum, and to regulation of neurotransmitter release at the terminals of many neurons. The different Kv3 channels have unique expression patterns and biophysical properties and are regulated in different ways by protein kinases. In this review, we cover the function, localization, and modulation of Kv3 channels and describe how levels and properties of the channels are altered by changes in ongoing neuronal activity. We also cover how the protein-protein interaction of these channels with other proteins affects neuronal functions, and how mutations or abnormal regulation of Kv3 channels are associated with neurological disorders such as ataxias, epilepsies, schizophrenia, and Alzheimer's disease.

Delayed Puberty and Gonadal Failure in Patients with HAX1 Mutation

PURPOSE

Homozygous mutations in the HAX1 gene cause an autosomal recessive form of severe congenital neutropenia (SCN). There are limited data on cases of gonadal insufficiency that involve the HAX1 gene mutation. We aimed to evaluate the pubertal development and gonadal functions of our patients with a p.Trp44X mutation in the HAX1 gene.

METHOD

Pubertal development, physical and laboratory findings of one male and seven female patients with HAX1 deficiency were evaluated.

RESULTS

The age of the patients was between 13 and 25 years. All female patients were diagnosed with primary ovarian insufficiency (POI) based on amenorrhea and elevated gonadotropins. The ovary volumes in female patients were determined to be smaller than normal for their age through sonographic studies. Short stature associated with gonadal insufficiency was also observed in three patients.

CONCLUSION

The HAX1 gene is important for ovarian development, in which a p.Trp44X mutation may cause POI in female patients. It is crucial to follow up and evaluate the gonadal functions of female patients in such cases.

4R-Cembranoid Improves Outcomes after 6-Hydroxydopamine Challenge in Both In vitro and In vivo Models of Parkinson's Disease

(1S, 2E, 4R, 6R,-7E, 11E)-2, 7, 11-cembratriene-4, 6-diol (4R) is one of the cembranoids found in tobacco leaves. Previous studies have found that 4R protected acute rat hippocampal slices against neurotoxicity induced by N-methyl-D-aspartate (NMDA) and against the toxic organophosphorus compounds paraoxon and diisopropylfluorophosphate (DFP). Furthermore, in vivo, 4R reduced the infarct size in a rodent ischemic stroke model and neurodegeneration caused by DFP. The present study expanded our previous study by focusing on the effect of 4R in Parkinson's disease (PD) and elucidating its underlying mechanisms using 6-hydroxydopamine (6-OHDA)-induced injury models. We found that 4R exhibited significant neuroprotective activity in the rat unilateral 6-OHDA-induced PD model in vivo. The therapeutic effect was evident both at morphological and behavioral levels. 4R (6 and 12 mg/kg) treatments significantly improved outcomes of 6-OHDA-induced PD in vivo as indicated by reducing forelimb asymmetry scores and corner test scores 4 weeks after injection of 6-OHDA (p < 0.05). The therapeutic effect of 4R was also reflected by decreased depletion of tyrosine hydroxylase (TH) in the striatum and substantia nigra (SN) on the side injected with 6-OHDA. TH expression was 70.3 and 62.8% of the contralateral side in striatum and SN, respectively, after 6 mg/kg 4R treatment; furthermore, it was 80.1 and 79.3% after treatment with 12 mg/kg of 4R. In the control group, it was 51.9 and 23.6% of the contralateral striatum and SN (p < 0.05). Moreover, 4R also protected differentiated neuro-2a cells from 6-OHDA-induced cytotoxicity in vitro. The activation of p-AKT and HAX-1, and inhibition of caspase-3 and endothelial inflammation, were involved in 4R-mediated protection against 6-OHDA-induced injury. In conclusion, the present study indicates that 4R shows a therapeutic effect in the rat 6-OHDA-induced PD model in vivo and in 6-OHDA-challenged neuro-2a cells in vitro.

Case Reports of Severe Congenital Neutropenia Treated With Unrelated Cord Blood Transplantation With Reduced-intensity Conditioning

Allogeneic stem cell transplantation is a curative treatment for severe congenital neutropenia (SCN). However, a standard conditioning regimen and donor source have not been established. We report 3 consecutive cases of SCN who were successfully treated by cord blood transplantation (CBT) with reduced-intensity conditioning consisting of fludarabine, melphalan, and low-dose total body irradiation. All cases achieved complete donor chimerism without severe infectious complications and have maintained normal neutrophil counts for between 3 and 9 years after CBT. These results suggest that CBT with reduced-intensity conditioning can be an alternative therapy for SCN when human leukocyte antigen-matched bone marrow donor is unavailable.

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

PURPOSE

To confirm and characterize mosaicism of the cyclic neutropenia (CyN)-related mutation in the ELANE gene identified in the asymptomatic mother of patients with CyN.

METHODS

We identified sibling cases with CyN due to a novel heterozygous splicing site mutation, IVS4 +5SD G>T, in the ELANE gene, resulting in an internal in-frame deletion of 30 nucleotides (corresponding to a ten amino acid deletion, V161-F170). The mutated allele was also detected in their asymptomatic mother but at low frequency. We measured the frequency of the mutant allele from peripheral blood leukocytes (PBLs) by subcloning, and confirmed the allelic frequency of mosaicism in various cell types by massively parallel DNA sequencing (MPS) analysis.

RESULTS

In the subcloning analysis, the mutant allele was identified in 21.36 % of PBLs from the asymptomatic mother, compared with 54.72 % of PBLs from the CyN patient. In the MPS analysis, the mutant allele was observed in approximately 30 % of mononuclear cells, CD3(+) T cells, CD14(+) monocytes and the buccal mucosa. Conversely, it was detected in low frequency in polymorphonuclear leukocytes (PLMLs) (3-4 %) and CD16(+) granulocytes (2-3 %).

CONCLUSIONS

Mosaicism of the ELANE mutation has only previously been identified in one confirmed and one unconfirmed case of SCN. This is the first report of mosaicism of the ELANE mutation in a case of CyN. The MPS results suggest that this de novo mutation occurred during the two-cell stage of embryogenesis. PLMLs expressing the ELANE mutation were found to be actively undergoing apoptosis.

Neurological findings and genetic alterations in patients with Kostmann syndrome and HAX1 mutations

OBJECTIVES

To describe the clinical profile and the prevalence of severe congenital neutropenia (SCN) and HAX1 mutations, so-called Kostmann syndrome, in France.

STUDY DESIGN

Two pedigrees were identified from the French registry.

RESULTS

The study included five subjects (three males), which represent 0.7% of the 759 SCN cases registered in France. The age at diagnosis was 0.3 years (range: 0.1-1.2 years) and the median age at the last follow-up was 7.3 years (range: 1.2-17.8 years). A novel large homozygous deletion of the HAX1 gene (exons 2-5) was found in one pedigree; while, a homozygous frameshift mutation was identified in exon 3 (c.430dupG, p.Val144fs) in the second pedigree. Severe bacterial infections were observed in four patients, including two cases of sepsis, one case of pancolitis, a lung abscess, and recurrent cellulitis and stomatitis. During routine follow-up, the median neutrophil value was 0.16 × 10(9)/L, associated with monocytosis (2 × 10(9)/L). Bone marrow (BM) smears revealed a decrease of the granulocytic lineage with no mature myeloid cells above the myelocytes. One patient died at age 2 from neurological complications, while two other patients, including one who underwent a hematopoietic stem cell transplantation (HSCT) at age 5, are living with very severe neurological retardation.

CONCLUSIONS

SCN with HAX1 mutations, is a rare sub type of congenital neutropenia, mostly observed in population from Sweden and Asia minor, associating frequently neurological retardation, when the mutations involved the B isoform of the protein.

Genetic correction of HAX1 in induced pluripotent stem cells from a patient with severe congenital neutropenia improves defective granulopoiesis

HAX1 was identified as the gene responsible for the autosomal recessive type of severe congenital neutropenia. However, the connection between mutations in the HAX1 gene and defective granulopoiesis in this disease has remained unclear, mainly due to the lack of a useful experimental model for this disease. In this study, we generated induced pluripotent stem cell lines from a patient presenting for severe congenital neutropenia with HAX1 gene deficiency, and analyzed their in vitro neutrophil differentiation potential by using a novel serum- and feeder-free directed differentiation culture system. Cytostaining and flow cytometric analyses of myeloid cells differentiated from patient-derived induced pluripotent stem cells showed arrest at the myeloid progenitor stage and apoptotic predisposition, both of which replicated abnormal granulopoiesis. Moreover, lentiviral transduction of the HAX1 cDNA into patient-derived induced pluripotent stem cells reversed disease-related abnormal granulopoiesis. This in vitro neutrophil differentiation system, which uses patient-derived induced pluripotent stem cells for disease investigation, may serve as a novel experimental model and a platform for high-throughput screening of drugs for various congenital neutrophil disorders in the future.

Epidemiology of congenital neutropenia

Epidemiologic investigations of congenital neutropenia aim to determine several important indicators related to the disease, such as incidence at birth, prevalence, and outcome in the population, including the rate of severe infections, leukemia, and survival. Genetic diagnosis is an important criterion for classifying patients and reliably determining the epidemiologic indicators. Patient registries were developed in the 1990s. The prevalence today is probably more than 10 cases per million inhabitants. The rate of infection and leukemia risk can now be calculated. Risk factors for leukemia seem to depend on both the genetic background and cumulative dose of granulocyte colony stimulating factor.

Ovarian failure in HAX1-deficient patients: is there a gender-specific difference in pubertal development in severe congenital neutropenia or Kostmann disease?

AIM

Severe congenital neutropenia (SCN) is a rare disorder of myelopoiesis characterized by neutropenia, recurrent bacterial infections and a maturation arrest of the myelopoiesis in the bone marrow. Homozygous mutations in the HAX1 gene were described in patients with autosomal recessive SCN or Kostmann disease. Some of these patients display neurological disease. We noted, during the course of clinical management of patients with Kostmann disease, insufficient pubertal development in female patients, but not in our male patients. The study objective was to provide a detailed account of this phenotype and its possible relation to HAX1 mutations.

METHODS

Detailed clinical histories and laboratory investigations of three patients with Kostmann disease belonging to the original kindred in northern Sweden described by Rolf Kostmann are reported.

RESULTS

We report one male patient with normal puberty and two female patients with insufficient pubertal development. Elevated levels of LH and FSH were recorded in both patients. All three patients harbour the same p.Glu190X mutation in the HAX1 gene.

CONCLUSIONS

We show for the first time that female patients with Kostmann disease display primary gonadal insufficiency. This suggests a possible role for HAX1 in the development and/or function of the human ovary.

Hax-1 is rapidly degraded by the proteasome dependent on its PEST sequence

BACKGROUND

HS-1-associated protein X-1 (Hax-1), is a multifunctional protein that has sequence homology to Bcl-2 family members. HAX-1 knockout animals reveal that it plays an essential protective role in the central nervous system against various stresses. Homozygous mutations in the HAX-1 gene are associated with autosomal recessive forms of severe congenital neutropenia along with neurological symptoms. The protein level of Hax-1 has been shown to be regulated by cellular protease cleavage or by transcriptional suppression upon stimulation.

RESULTS

Here, we report a novel post-translational mechanism for regulation of Hax-1 levels in mammalian cells. We identified that PEST sequence, a sequence rich in proline, glutamic acid, serine and threonine, is responsible for its poly-ubiquitination and rapid degradation. Hax-1 is conjugated by K48-linked ubiquitin chains and undergoes a fast turnover by the proteasome system. A deletion mutant of Hax-1 that lacks the PEST sequence is more resistant to the proteasomal degradation and exerts more protective effects against apoptotic stimuli than wild type Hax-1.

CONCLUSION

Our data indicate that Hax-1 is a short-lived protein and that its PEST sequence dependent fast degradation by the proteasome may contribute to the rapid cellular responses upon different stimulations.

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.

Genetic defects in severe congenital neutropenia: emerging insights into life and death of human neutrophil granulocytes

The discovery of genetic defects causing congenital neutropenia has illuminated mechanisms controlling differentiation, circulation, and decay of neutrophil granulocytes. Deficiency of the mitochondrial proteins HAX1 and AK2 cause premature apoptosis of myeloid progenitor cells associated with dissipation of the mitochondrial membrane potential, whereas mutations in ELA2/ELANE and G6PC3 are associated with signs of increased endoplasmic reticulum stress. Mutations in the transcriptional repressor GFI1 and the cytoskeletal regulator WASP also lead to defective neutrophil production. This unexpected diversity of factors suggests that multiple pathways are involved in the pathogenesis of congenital neutropenia.

Congenital neutropenia: diagnosis, molecular bases and patient management

The term congenital neutropenia encompasses a family of neutropenic disorders, both permanent and intermittent, severe (<0.5 G/l) or mild (between 0.5-1.5 G/l), which may also affect other organ systems such as the pancreas, central nervous system, heart, muscle and skin. Neutropenia can lead to life-threatening pyogenic infections, acute gingivostomatitis and chronic parodontal disease, and each successive infection may leave permanent sequelae. The risk of infection is roughly inversely proportional to the circulating polymorphonuclear neutrophil count and is particularly high at counts below 0.2 G/l.When neutropenia is detected, an attempt should be made to establish the etiology, distinguishing between acquired forms (the most frequent, including post viral neutropenia and auto immune neutropenia) and congenital forms that may either be isolated or part of a complex genetic disease.Except for ethnic neutropenia, which is a frequent but mild congenital form, probably with polygenic inheritance, all other forms of congenital neutropenia are extremely rare and have monogenic inheritance, which may be X-linked or autosomal, recessive or dominant.About half the forms of congenital neutropenia with no extra-hematopoietic manifestations and normal adaptive immunity are due to neutrophil elastase (ELANE) mutations. Some patients have severe permanent neutropenia and frequent infections early in life, while others have mild intermittent neutropenia.Congenital neutropenia may also be associated with a wide range of organ dysfunctions, as for example in Shwachman-Diamond syndrome (associated with pancreatic insufficiency) and glycogen storage disease type Ib (associated with a glycogen storage syndrome). So far, the molecular bases of 12 neutropenic disorders have been identified.Treatment of severe chronic neutropenia should focus on prevention of infections. It includes antimicrobial prophylaxis, generally with trimethoprim-sulfamethoxazole, and also granulocyte-colony-stimulating factor (G-CSF). G-CSF has considerably improved these patients' outlook. It is usually well tolerated, but potential adverse effects include thrombocytopenia, glomerulonephritis, vasculitis and osteoporosis. Long-term treatment with G-CSF, especially at high doses, augments the spontaneous risk of leukemia in patients with congenital neutropenia.

HAX1 mutations causing severe congenital neuropenia and neurological disease lead to cerebral microstructural abnormalities documented by quantitative MRI

Biallelic mutations in the gene encoding HCLS-associated protein X-1 (HAX1) cause autosomal recessive severe congenital neutropenia (SCN). Some of these patients have neurological abnormalities including developmental delay, cognitive impairment, and/or epilepsy. Recent genotype-phenotype studies have shown that mutations in HAX1 affecting transcripts A (NM_006118.3) and B (NM_001018837.1) cause the phenotype of SCN with neurological impairment, while mutations affecting isoform A but not B lead to SCN without neurological aberrations. In this study, we identified a consanguineous family with two patients suffering from SCN and neurological disease caused by a novel, homozygous genomic deletion including exons 4-7 of the HAX1 gene. Quantitative MRI analyses showed generalized alterations in cerebral proton density in both of the patients, as well as in an additional unrelated patient with another HAX1 mutation (Arg86X) known to be associated with neurological manifestations. This study provides first in vivo evidence of aberrant neuroimaging findings associated with HAX1 deficiency in SCN patients.

[Molecular analysis of two cases of severe congenital neutropenia]

Severe congenital neutropenia is a rare hematological disease characterized by a selective decrease in circulating neutrophils, maturation arrest of granulocytic precursors at the promyelocyte stage, and recurrence of infections. A 2-month-old male infant (patient A) and a 14-month-old female child (patient B) were referred to our hospital due to severe neutropenia. Sequencing analysis of ELA2 and HAX1 genes was performed. Two single nucleotide polymorphisms of HAX1 gene were found. They were 5,104T-->G point mutation of exon 1 and 5,474A-->G point mutation of intron 1 in HAX1 gene. The mutation of ELA2 gene was not found. The patient A showed a good response to granulocyte colony-stimulating factor (G-CSF) treatment and the absolute neutrophil count recovered to 1,195/microL. But the patient B showed a partial response to G-CSF treatment and experienced several episodes of herpetic gingivostomatitis, oral ulcer, acute pharyngotonsillitis and otitis media during follow-up.

A novel HAX1 gene mutation in severe congenital neutropenia (SCN) associated with neurological manifestations

Autosomal recessive severe congenital neutropenia (SCN) results from a maturation arrest of granulopoiesis at the level of promyelocytes and apoptosis of myeloid cells. In SCN patients, mutations have been described in the HAX1 gene. Most of the SCN patients who carry nonsense mutations that are common to both transcript variants of the HAX1 gene also exhibit neurological deficits. This study describes an SCN patient with neurological manifestations including daily episodes of atonic seizures, learning disabilities, and developmental delay. Sequencing of the HAX1 gene of this SCN patient identified a novel nonsense c.463_464insC homozygous mutation in exon 3, which is common to both transcript variants of the gene. This mutation encodes for a p.Gln155ProfsX14 change and causes premature truncation of the HAX1 protein. Neutrophils isolated from the patient exhibited spontaneous apoptosis and loss of inner mitochondrial membrane potential, which were further enhanced upon treatment with hydrogen peroxide. This study adds to the spectrum of novel HAX1 gene mutations and disease manifestations in ethnically distinct SCN patients. Our report describes the only nonsense mutation in the HAX1 gene present in SCN patients of Arab origin.

Genetic insights into congenital neutropenia

Congenital neutropenia syndromes comprise a heterogeneous group of disorders leading to increased susceptibility to bacterial infections. Recent work has elucidated the molecular basis of several congenital neutropenia syndromes such as mutations in ELA2, HAX1, GF11, and WAS. In addition, a number of complex clinical syndromes associating congenital neutropenia have been recognized and elucidated on a genetic level, e.g. p14-deficiency or G6PC3-deficiency. The clinical and genetic findings of various neutropenia syndromes are being discussed.

Compound heterozygous HAX1 mutations in a Swedish patient with severe congenital neutropenia and no neurodevelopmental abnormalities

Kostmann disease or severe congenital neutropenia (SCN) is an autosomal recessive disorder of neutrophil production. Homozygous HAX1 mutations were recently identified in SCN patients belonging to the original family in northern Sweden described by Kostmann. Moreover, recent studies have suggested an association between neurological dysfunction and HAX1 deficiency. Here we describe a patient with a compound heterozygous HAX1 mutation consisting of a nonsense mutation (c.568C > T, p.Glu190X) and a frame-shift mutation (c.91delG, p.Glu31LysfsX54) resulting in a premature stop codon. The patient has a history of neutropenia and a propensity for infections, but has shown no signs of neurodevelopmental abnormalities.

Prevalence of mutations in ELANE, GFI1, HAX1, SBDS, WAS and G6PC3 in patients with severe congenital neutropenia

Severe congenital neutropenia (SCN) is a genetically heterogeneous syndrome associated with mutations of ELANE (ELA2), HAX1, GFI1, WAS, CSF3R or G6PC3. We investigated the prevalence of mutations of ELANE in a cohort of 162 SCN patients for whom blood or bone marrow samples were submitted to the North American Severe Chronic Neutropenia Tissue Repository. Mutations of ELANE were found in 90 of 162 patients (55.6%). Subsequently, we conducted an analysis of a subset of 73 of these cases utilising a high throughput sequencing approach to determine the prevalence of other mutations associated with SCN. Among the 73 patients, mutations of ELANE were detected in 28. In the remaining 45 patients with wild type ELANE alleles, five patients had mutations: GFI1 (1), SBDS (1), WAS (1) and G6PC3 (2); no mutations of HAX1 were detected. In approximately 40% of our cases, the genetic basis of SCN remains unknown. These data suggest that for genetic diagnosis of SCN, ELANE genotyping should first be performed. In patients without ELANE mutations, other known SCN-associated gene mutations will be found rarely and genotyping can be guided by the clinical features of each patient.

HAX-1: a multifunctional protein with emerging roles in human disease

HS-1-associated protein X-1 (HAX-1) was identified more than 10 years ago as a novel protein with ubiquitous tissue expression and a predominantly mitochondrial localization at the subcellular level. Recent studies have shown that homozygous mutations in the HAX1 gene are associated with autosomal recessive forms of severe congenital neutropenia (also known as Kostmann disease), and results from studies in mice and men are beginning to unravel a prominent role for HAX-1 in apoptosis signaling not only in the hematopoietic compartment, but also in the central nervous system. Moreover, several different cellular and viral binding partners of HAX-1 have been identified thus pointing toward a complex and multifunctional role of this protein. HAX-1 has also been shown to bind to the 3' untranslated regions of certain mRNAs and could therefore contribute to the regulation of transport and/or stability of such transcripts. The present review discusses the emerging and divergent roles of HAX-1, including its involvement in cell migration, apoptosis signaling, and mRNA surveillance. The importance of HAX-1 in human disease is also highlighted and outstanding questions that remain to be addressed are identified.

Ela2 mutations and clinical manifestations in familial congenital neutropenia

PURPOSE

Three familial cases of each of severe congenital neutropenia (SCN) and cyclic neutropenia (CN) in addition to 3 sporadic cases of SCN were analyzed for neutrophil elastase (Ela2) gene mutation. The contents of the neutrophil-specific granule proteins cathelicidin antimicrobial peptide and neutrophil gelatinase-associated lipocalin were also analyzed in SCN.

METHODS

Genomic DNA was extracted from the patients' peripheral blood or bone marrow, and the coding sequence of the Ela2 gene was amplified by polymerase chain reaction and subjected to direct sequencing. The contents of antimicrobial peptides were analyzed by flow cytometry.

RESULTS

Three cases of familial SCN (P13L, R52P, and S97L), 2 of familial CN (W212stop and P110L), and 1 of sporadic SCN (V72M) were shown to have heterozygous mutations in the Ela2 gene. W212stop found in a familial CN case was a novel mutation of Ela2. Prophylactic treatment for growth factors or antibiotic prophylaxis against bacterial infection was useful for lowering the frequency of infectious episodes. Adult patients tended to have less frequent infections compared with minors in the same family. The contents of both cathelicidin antimicrobial peptide and neutrophil gelatinase-associated lipocalin were significantly reduced in SCN compared with healthy controls.

CONCLUSIONS

Prophylaxis by growth factor or antibiotics is useful for decreasing risks of bacterial infections in SCN and CN. Adults were likely to have less frequent infections than children in familial cases of SCN and CN with the same mutation of Ela2.

Clinical implications of ELA2-, HAX1-, and G-CSF-receptor (CSF3R) mutations in severe congenital neutropenia

Congenital Neutropenia (CN) is a heterogeneous bone marrow failure syndrome characterized by a maturation arrest of myelopoiesis at the level of the promyelocyte/myelocyte stage with peripheral blood absolute neutrophil counts below 0.5 x 10(9)/l. There are two major subtypes of CN as judged by inheritance: an autosomal dominant subtype, e.g. defined by neutrophil elastase mutations (approximately 60% of patients) and an autosomal recessive subtype (approximately 30% of patients), both presenting with the same clinical and morphological phenotype. Different mutations have been described (e.g. HAX1, p14 etc) in autosomal recessive CN, with HAX1 mutations in the majority of these patients. CN in common is considered as a preleukemic syndrome, since the cumulative incidence for leukemia is more than 25% after 20 years of observation. Leukemias occur in both, the autosomal dominant and recessive subtypes of CN. The individual risk for each genetic subtype needs to be further evaluated. Numbers of patients tested for the underlying genetic defect are still limited. Acquired G-CSFR (CSF3R) mutations are detected in approximately 80% of CN patients who developed acute myeloid leukemia independent of the ELA2 or HAX1 genetic subtype, suggesting that these mutations are involved in leukemogenesis. As the majority of patients benefit from G-CSF administration, HSCT should be restricted to non-responders and patients with leukaemic transformation.