Genetic analysis and clinical picture of severe congenital neutropenia in Israel

Clinical and Laboratory Characteristics of Pediatric Patients With ACKR1/DARC-Associated Neutropenia

BACKGROUND

ACKR1/DARC-associated neutropenia (ADAN), resulting from homozygosity for a single nucleotide polymorphism (SNP) in the ACKR1/DARC gene (rs2814778), is a common cause of benign neutropenia that primarily affects individuals of African and Jewish Yemenite descent. We aimed to characterize ADAN in pediatric patients in Israel, given its ethnically diverse population.

PROCEDURE

We assessed children with isolated neutropenia treated during 2018-2023 at one pediatric center, for the ACKR1/DARC polymorphism, using Sanger sequencing or targeted next-generation sequencing.

RESULTS

Of 115 patients evaluated, 49 (42.6%) were diagnosed with ADAN; of these, 29 (59%) had absolute neutrophil counts in the severe range (0-0.5 × 109/L) at diagnosis. The allele distribution revealed 37% of Muslim Arab and 61% of Jewish origin. Yemenite, Ethiopian, Mediterranean, Asian, and European ancestry were included; 59% had a family history of neutropenia. The median age at the first neutropenia detection was 1.2 years; 91.8% were identified during routine blood counts. The median absolute neutrophil count at diagnosis was 0.5 × 109/L (interquartile range: 0.3). An increased susceptibility to infections was not found either before or during the median follow-up period of 2.5 years (interquartile range: 1.54) after the diagnosis of ADAN. In 34 patients (72.3%), neutrophil counts were in the normal range during febrile illnesses.

CONCLUSIONS

We identified ADAN in individuals of variable ethnicities, almost half with severe neutropenia. We recommend testing for ADAN in all children with isolated neutropenia without severe infections. Homozygosity for the ACKR1/DARC rs2814778 SNP may obviate the need for further investigation, follow-up, or treatment in specific clinical scenarios.

A large cohort from an immunology reference center and an algorithm for the follow-up of chronic neutropenia

Chronic neutropenia causes involve nutritional deficiencies and inborn errors of immunity(IEI), such as severe congenital neutropenia. To classify common chronic neutropenia causes in a pediatric immunology unit. We enrolled 109 chronic neutropenia patients admitted to a pediatric immunology department between 2002-2022. We recorded clinical/laboratory features and genetic characteristics. The male/female ratio was 63/46. Fifty-eight patients had parental consanguinity(57.4%). 26.6% (n = 29) patients had at least one individual in their family with neutropenia. Common symtpoms at presentation were upper respiratory tract infections(URTI)(31.1%), oral aphthae(23.6%), skin infections(23.6%), pneumonia(20.8%), and recurrent abscesses(12.3%). Common infections during follow-up were URTI(56.8%), pneumonia(33%), skin infections(25.6%), gastroenteritis(18.3%), and recurrent abscesses(14,6%). Common long-term complications were dental problems(n = 51), osteoporosis(n = 22), growth retardation(n = 14), malignancy(n = 16)[myelodysplastic syndrome(n = 10), large granulocytic leukemia(n = 1), acute lymphoblastic leukemia(n = 1), Hodgkin lymphoma(n = 1), EBV-related lymphoma(n = 1), leiomyosarcoma(n = 1), and thyroid neoplasm(n = 1)]. We performed a genetic study in 86 patients, and 69(71%) got a genetic diagnosis. Common gene defects were HAX-1(n = 26), ELA-2 (ELANE)(n = 10), AP3B1(n = 4), and ADA-2(n = 4) gene defects. The IEI ratio(70.6%) was high. GCSF treatment(93.4%), immunoglobulin replacement therapy(18.7%), and HSCT(15.9%) were the treatment options. The mortality rate was 12.9%(n = 14). The most common long term complications were dental problems that is three times more common in patients with known genetic mutations. We prepared an algorithm for chronic neutropenia depending on the present cohort. An important rate of inborn errors of immunity, especially combined immunodeficiency(11.9%) was presented in addition to congenital phagocytic cell defects. Early diagnosis will allow us tailor the disease-specific treatment options sooner, preventing irreversible consequences.

Genetic backgrounds and clinical characteristics of congenital neutropenias in Israel

BACKGROUND

Congenital neutropenias are characterized by severe infections and a high risk of myeloid transformation; the causative genes vary across ethnicities. The Israeli population is characterized by an ethnically diverse population with a high rate of consanguinity.

OBJECTIVE

To evaluate the clinical and genetic spectrum of congenital neutropenias in Israel.

METHODS

We included individuals with congenital neutropenias listed in the Israeli Inherited Bone Marrow Failure Registry. Sanger sequencing was performed for ELANE or G6PC3, and patients with wild-type ELANE/G6PC3 were referred for next-generation sequencing.

RESULTS

Sixty-five patients with neutropenia were included. Of 51 patients with severe congenital neutropenia, 34 were genetically diagnosed, most commonly with variants in ELANE (15 patients). Nine patients had biallelic variants in G6PC3, all of consanguineous Muslim Arab origin. Other genes involved were SRP54, JAGN1, TAZ, and SLC37A4. Seven patients had cyclic neutropenia, all with pathogenic variants in ELANE, and seven had Shwachman-Diamond syndrome caused by biallelic SBDS variants. Eight patients (12%) developed myeloid transformation, including six patients with an unknown underlying genetic cause. Nineteen (29%) patients underwent hematopoietic stem cell transplantation, mostly due to insufficient response to treatment with granulocyte-colony stimulating factor or due to myeloid transformation.

CONCLUSIONS

The genetic spectrum of congenital neutropenias in Israel is characterized by a high prevalence of G6PC3 variants and an absence of HAX1 mutations. Similar to other registries, for 26% of the patients, a molecular diagnosis was not achieved. However, myeloid transformation was common in this group, emphasizing the need for close follow-up.

Severe congenital neutropenia due to G6PC3 deficiency: early and delayed phenotype of a patient

BACKGROUND

Severe Congenital Neutropenia type 4 (SCN4), is a rare autosomal recessive condition, due to mutations in the G6PC3 gene. The phenotype comprises neutropenia of variable severity and accompanying anomalies.

CASE PRESENTATION

We report a male patient with confirmed G6PC3 deficiency presented with recurrent bacterial infections and multi-systemic complications. Our case was the first with a novel homozygous frameshift mutation in G6PC3. The patient demonstrated large platelets on his peripheral blood smear which is a rare presentation of this disease.

CONCLUSION

As SCN4 patients could be easily missed, it is recommended to consider G6PC3 mutation for any case of congenital, unexplained neutropenia.

Heterogeneous genetic landscape of congenital neutropenia in Korean patients revealed by whole exome sequencing: genetic, phenotypic and histologic correlations

Congenital neutropenia (CN) is a hematological disease heterogeneous in its genetic, phenotypic and histologic aspects. We aimed to identify the genetic etiology of Korean CN patients in the context of bone marrow (BM) histology and clinical phenotype. Whole-exome sequencing (WES) or targeted sequencing was performed on the BM or peripheral blood specimens of 16 patients diagnosed with CN based on BM exam from 2009 to 2018. Absolute count of myeloperoxidase (MPO)-positive cells was calculated using ImageJ software. Semi-quantitation of MPO-positive cells in BM sections was performed by MPO grading (grades 0-3). Comprehensive retrospective review on real-world data of 345 pediatric patients with neutropenia including 16 patients in this study during the same period was performed. Seven disease-causing variants were identified in ELANE, G6PC3 and CXCR4 in 7 patients. A novel homozygous G6PC3 variant (K72fs) of which the mechanism was copy-neutral loss of heterozygosity was detected in two brothers. A low myeloid-to-erythroid ratio (0.5-1.5) was consistently observed in patients with ELANE mutations, while MPO-positive cells (40%-50%) with MPO grade 1 or 2 were detected in myelokathexis caused by G6PC3 and CXCR4 mutations. Meanwhile, disease-causing variants were detected in ELANE, TAZ and SLC37A4 in 5 patients by retrospective review of medical records. Our results suggest that following the immunological study and BM exam, WES or an expanded next generation sequencing panel that covers genes related to immunodeficiency and other inherited bone marrow failures as well as CN is recommended for neutropenia patient diagnosis.

Efficacy of Low-Dose rhGM-CSF Treatment in a Patient With Severe Congenital Neutropenia Due to CSF3R Deficiency: Case Report of a Novel Biallelic CSF3R Mutation and Literature Review

This study reports the clinical manifestations, genetics, and efficacy of treatment with the efficacy of recombinant human granulocyte macrophage colony-stimulating factor (rhGM-GSF) of a 2-year-old female patient with severe congenital neutropenia (SCN) type 7 (SCN7) caused by novel biallelic mutations in the colony-stimulating factor 3 receptor (CSF3R) gene. Genetic diagnosis of the patient was performed by whole-exome and Sanger sequencing. Expression of the CSF3R gene in the peripheral neutrophils of the patient was detected by real-time PCR and Western blotting. The patient presented with recurrent suppurative tonsillitis and decreased absolute neutrophil count <0.5 × 10⁹/L. Novel heterozygous mutations were found to be inherited from each parent (maternal c.690delC [p.met231Cysfs^*32] and paternal c.64+5G>A). The patient's neutrophils had lower CSF3R mRNA and protein levels than those of the parents. Low-dose rhGM-CSF (3 μg/kg/day once a week) prevented recurrent infection in the patient. These results demonstrate that the clinical manifestations of SCN7 with biallelic CSF3R mutations and downregulated CSF3R can be effectively treated with rhGM-CSF.

Clinical and molecular characteristics of Thai patients with ELANE-related neutropaenia

AIMS

Congenital neutropaenia is a rare inherited disorder that mainly affects neutrophils causing severe infection. Mutations in several genes have been implicated in the disease pathogenesis. The genetic defects may vary in different populations, influenced by ethnicity and geographical location. Here we describe the clinical and genotypic characteristics of seven unrelated Thai cases with congenital neutropaenia.

METHODS

Seven unrelated patients with congenital neutropaenia were enrolled (5 female and 2 male) at King Chulalongkorn Memorial Hospital, Bangkok, Thailand. Clinical and laboratory data were collected. Whole exome sequencing (WES) analysis was performed in all cases.

RESULTS

WES successfully identified disease-causing mutations in the ELANE gene in all cases, including two novel ones: a heterozygous 12 base pair (bp) inframe insertion (c.289_300dupCAGGTGTTCGCC; p.Q97_A100dup) and a heterozygous 18 bp inframe deletion (c.698_715delCCCCGGTGGCACAGTTTG; p.A233_F238delAPVAQF). Five other previously described ELANE mutations (p.Arg103Pro, p.Gly214Arg, p.Trp241X, p.Ser126Leu and p.Leu47Arg) were also detected.

CONCLUSIONS

All Thai patients with congenital neutropaenia in this study harboured causative mutations in the ELANE gene, suggesting it the most common associated with the disease. Two novel mutations were also identified, expanding the genotypic spectrum of ELANE.

CRISPR-Cas9-Mediated ELANE Mutation Correction in Hematopoietic Stem and Progenitor Cells to Treat Severe Congenital Neutropenia

Severe congenital neutropenia (SCN) is a monogenic disorder. SCN patients are prone to recurrent life-threatening infections. The main causes of SCN are autosomal dominant mutations in the ELANE gene that lead to a block in neutrophil differentiation. In this study, we use CRISPR-Cas9 ribonucleoproteins and adeno-associated virus (AAV)6 as a donor template delivery system to repair the ELANEL172P mutation in SCN patient-derived hematopoietic stem and progenitor cells (HSPCs). We used a single guide RNA (sgRNA) specifically targeting the mutant allele, and an sgRNA targeting exon 4 of ELANE. Using the latter sgRNA, ∼34% of the known ELANE mutations can in principle be repaired. We achieved gene correction efficiencies of up to 40% (with sgELANE-ex4) and 56% (with sgELANE-L172P) in the SCN patient-derived HSPCs. Gene repair restored neutrophil differentiation in vitro and in vivo upon HSPC transplantation into humanized mice. Mature edited neutrophils expressed normal elastase levels and behaved normally in functional assays. Thus, we provide a proof of principle for using CRISPR-Cas9 to correct ELANE mutations in patient-derived HSPCs, which may translate into gene therapy for SCN.

Evaluation of periodontal status and cytokine/chemokine profile of GCF in patients with severe congenital neutropenia

Severe congenital neutropenia (SCN) is a primary immunodeficiency characterized by defect in neutrophil count. Increased risk of infections in addition to periodontal problems, such as ulcerations of oral mucosa, gingival inflammation, and rapid loss of attachment are common in the course of the disease. The aim of the present study is to define the causal relationship between the severity of periodontal inflammation and severe congenital neutropenia through identification of cytokine profile in gingival crevicular fluid (GCF). A case-control study was performed in patients diagnosed with SCN and healthy controls. Demographic data, the molecular defect, laboratory work-up were gathered from the hospital registry. Periodontal indices were recorded and GCF samples were analyzed using multiplex analysis for the simultaneous measurements of the particular cytokines and chemokines. The present study included 14 patients and 22 control subjects. Both groups were comparable in terms of age and sex. Severity of gingival inflammation measured by the criteria of Löe was higher in the SCN cases (p < 0.05). Moreover, GCF levels of IFN-α, TNF-α, IL-10, IL-13, IL-15, IL-17, IL-2, IL-7, IL-33, IP-10, MIG, MIP-1β were significantly higher in the controls. Decreased cytokine secretion seems to correlate with the decrease in neutrophil counts. The severity of gingival inflammation in SCN patients may be due to the bacterial overgrowth and the change in the content of the oral flora due to the decreased neutrophil counts. Therefore, regular periodontal examinations, the motivation of oral hygiene as well as the compliance with therapy in SCN patients contribute to the periodontal health.

Hypothesis: A Novel Neuroprotective Role for Glucose-6-phosphatase (G6PC3) in Brain-To Maintain Energy-Dependent Functions Including Cognitive Processes

The isoform of glucose-6-phosphatase in liver, G6PC1, has a major role in whole-body glucose homeostasis, whereas G6PC3 is widely distributed among organs but has poorly-understood functions. A recent, elegant analysis of neutrophil dysfunction in G6PC3-deficient patients revealed G6PC3 is a neutrophil metabolite repair enzyme that hydrolyzes 1,5-anhydroglucitol-6-phosphate, a toxic metabolite derived from a glucose analog present in food. These patients exhibit a spectrum of phenotypic characteristics and some have learning disabilities, revealing a potential linkage between cognitive processes and G6PC3 activity. Previously-debated and discounted functions for brain G6PC3 include causing an ATP-consuming futile cycle that interferes with metabolic brain imaging assays and a nutritional role involving astrocyte-neuron glucose-lactate trafficking. Detailed analysis of the anhydroglucitol literature reveals that it competes with glucose for transport into brain, is present in human cerebrospinal fluid, and is phosphorylated by hexokinase. Anhydroglucitol-6-phosphate is present in rodent brain and other organs where its accumulation can inhibit hexokinase by competition with ATP. Calculated hexokinase inhibition indicates that energetics of brain and erythrocytes would be more adversely affected by anhydroglucitol-6-phosphate accumulation than heart. These findings strongly support the paradigm-shifting hypothesis that brain G6PC3 removes a toxic metabolite, thereby maintaining brain glucose metabolism- and ATP-dependent functions, including cognitive processes.

Management of a Patient With Congenital Biallelic CSF3R Mutation With GM-CSF

Severe Congenital Neutropenia (SCN) is a rare inherited disease characterized by an absolute neutrophil count (ANC) lower than 500/μL. Genetic heterogeneity and biallelic CSF3R mutation has rarely been identified as an underlying genetic defect in SCN. The majority of SCN patients respond to granulocyte colony stimulating factor treatment; however, in patients with inherited CSF3R mutation, ANC cannot generally be increased with granulocyte colony stimulating factor treatment. In such cases, granulocyte macrophage colony stimulating factor presents as an effective treatment option. Herein, we report a case of a 5-year-old SCN girl with homozygous c610-611 del ins AG (p.Q204R) mutation in the CSF3R gene, who was successfully treated with granulocyte macrophage colony stimulating factor.

HSCT may lower leukemia risk in ELANE neutropenia: a before-after study from the French Severe Congenital Neutropenia Registry

ELANE neutropenia is associated with myelodysplasia and acute leukemia (MDS–AL), and severe infections. Because the MDS–AL risk has also been shown to be associated with exposure to GCSF, since 2005, in France, patients receiving high daily GCSF doses (>15 μg/kg/day) are eligible for HSCT, in addition to classic indications (MDS–AL or GCSF refractoriness). We analyzed the effect of this policy. Among 144 prospectively followed ELANE-neutropenia patients enrolled in the French Severe Congenital Neutropenia Registry, we defined two groups according to period: “before 2005” for those born before 2005 and followed until 31/12/2004 (1588 person-years); and “after 2005” comprised of those born after 2005 or born before 2005 but followed after 2005 until 31/03/2019 (1327 person-years). Sixteen of our cohort patients underwent HSCT (14 long-term survivors) and six developed MDS–ALs. Six leukemic transformations occurred in the before-2005 group and none after 2005 (respective frequencies 3.8 × 10^–3 vs. 0; P < 0.01), while four HSCTs were done before 2005 and 12 since 2005 (respective HSCT rates increased 2.5 × 10^–3 vs. 9 × 10^–3; P < 0.01). Our results support early HSCT for patients with ELANE mutations who received high GCSF doses, as it might lower the risk of leukemic transformation.

CDG and immune response: From bedside to bench and back

Glycosylation is an essential biological process that adds structural and functional diversity to cells and molecules, participating in physiological processes such as immunity. The immune response is driven and modulated by protein-attached glycans that mediate cell-cell interactions, pathogen recognition and cell activation. Therefore, abnormal glycosylation can be associated with deranged immune responses. Within human diseases presenting immunological defects are congenital disorders of glycosylation (CDG), a family of around 130 rare and complex genetic diseases. In this review, we have identified 23 CDG with immunological involvement, characterized by an increased propensity to-often life-threatening-infection. Inflammatory and autoimmune complications were found in 7 CDG types. CDG natural history(ies) and the mechanisms behind the immunological anomalies are still poorly understood. However, in some cases, alterations in pathogen recognition and intracellular signaling (eg, TGF-β1, NFAT, and NF-κB) have been suggested. Targeted therapies to restore immune defects are only available for PGM3-CDG and SLC35C1-CDG. Fostering research on glycoimmunology may elucidate the involved pathophysiological mechanisms and open new therapeutic avenues, thus improving CDG patients' quality of life.

MiR-608 Exerts Anti-inflammatory Effects by Targeting ELANE in Monocytes

miR-608 has been indicated to play an important role in the pathogenesis of various inflammation-related diseases, including sepsis and several types of cancers. However, there is little information about the underlying mechanism, especially in inflammatory cells. In this study, an hsa-miR-608-inhibition cell model was constructed in U937 cells using a lentivirus, and gene expression profiles were determined by a cDNA microarray. Altogether, 682 genes showed a difference greater than 1.2-fold, including 184 genes downregulated and 498 genes upregulated. Among these genes, one potential miR-608-target gene, ELANE, was further investigated. A positive relationship between the expression of miR-608 and that of ELANE was found both in vivo and in vitro. In addition, decreased expression of miR-608 resulted in overexpression of ELANE at both the mRNA and protein levels. Cotransfection of HEK293T cells with a miR-608 mimic inhibited reporter activity, and mutation of the miRNA seed sequences abolished the repression of reporter activity. These results suggest that miR-608 is an important posttranscriptional regulator of ELANE expression in human monocytes and may play an important role in the process of inflammation. miR-608 and neutrophil elastase may be novel targets for the diagnosis or treatment of sepsis.

Homozygous c.130-131 ins A (pW44X) mutation in the HAX1 gene as the most common cause of congenital neutropenia in Turkey: Report from the Turkish Severe Congenital Neutropenia Registry

BACKGROUND

Severe congenital neutropenia is a rare disease, and autosomal dominantly inherited ELANE mutation is the most frequently observed genetic defect in the registries from North America and Western Europe. However, in eastern countries where consanguineous marriages are common, autosomal recessive forms might be more frequent.

METHOD

Two hundred and sixteen patients with severe congenital neutropenia from 28 different pediatric centers in Turkey were registered.

RESULTS

The most frequently observed mutation was HAX1 mutation (n = 78, 36.1%). A heterozygous ELANE mutation was detected in 29 patients (13.4%) in our cohort. Biallelic mutations of G6PC3 (n = 9, 4.3%), CSF3R (n = 6, 2.9%), and JAGN1 (n = 2, 1%) were also observed. Granulocyte colony-stimulating factor treatment was given to 174 patients (80.6%). Two patients died with infectious complications, and five patients developed myelodysplastic syndrome/acute myeloblastic leukemia. The mean (± mean standard error) follow-up period was 129.7 ± 76.3 months, and overall survival was 96.8% (CI, 94.4-99.1%) at the age of 15 years. In Turkey, severe congenital neutropenia mostly resulted from the p W44X mutation in the HAX1 gene.

CONCLUSION

In Turkey, mutation analysis should be started with HAX1, and if this is negative, ELANE and G6PC3 should be checked. Because of the very high percentage of consanguineous marriage, rare mutations should be tested in patients with a negative mutation screen.

Congenital Neutropenia Patient With Hypomorphic Biallelic CSF3R Mutation Responding to GCSF

Congenital neutropenia (CN) is a rare disorder, and the most common gene responsible for CN is ELANE. Furthermore, the mutations of HAX1, G6PC3, and JAGN1 genes may cause CN. These patients generally find great benefit from subcutaneous administration of Granulocyte Colony Stimulating Factor (GCSF). In recent years, Biallelic Colony Stimulating Factor 3 Receptor (CSF3R) mutations have been described as an underlying defect of CN in several children. In contrast to the previous group, the patients who have a CSF3R mutation do not respond to GCSF treatment. Here, we present a CN patient with hypomorphic biallelic CSF3R mutation responding to GCSF.

Severe congenital neutropenias

Severe congenital neutropenias are a heterogeneous group of rare haematological diseases characterized by impaired maturation of neutrophil granulocytes. Patients with severe congenital neutropenia are prone to recurrent, often life-threatening infections beginning in their first months of life. The most frequent pathogenic defects are autosomal dominant mutations in ELANE, which encodes neutrophil elastase, and autosomal recessive mutations in HAX1, whose product contributes to the activation of the granulocyte colony-stimulating factor (G-CSF) signalling pathway. The pathophysiological mechanisms of these conditions are the object of extensive research and are not fully understood. Furthermore, severe congenital neutropenias may predispose to myelodysplastic syndromes or acute myeloid leukaemia. Molecular events in the malignant progression include acquired mutations in CSF3R (encoding G-CSF receptor) and subsequently in other leukaemia-associated genes (such as RUNX1) in a majority of patients. Diagnosis is based on clinical manifestations, blood neutrophil count, bone marrow examination and genetic and immunological analyses. Daily subcutaneous G-CSF administration is the treatment of choice and leads to a substantial increase in blood neutrophil count, reduction of infections and drastic improvement of quality of life. Haematopoietic stem cell transplantation is the alternative treatment. Regular clinical assessments (including yearly bone marrow examinations) to monitor treatment course and detect chromosomal abnormalities (for example, monosomy 7 and trisomy 21) as well as somatic pre-leukaemic mutations are recommended.

How I manage children with neutropenia

Neutropenia, usually defined as a blood neutrophil count <1·5 × 10⁹ /l, is a common medical problem for children and adults. There are many causes for neutropenia, and at each stage in life the clinical pattern of causes and consequences differs significantly. I recommend utilizing the age of the child and clinical observations for the preliminary diagnosis and primary management. In premature infants, neutropenia is quite common and contributes to the risk of sepsis with necrotizing enterocolitis. At birth and for the first few months of life, neutropenia is often attributable to isoimmune or alloimmune mechanisms and predisposes to the risk of severe bacterial infections. Thereafter when a child is discovered to have neutropenia, often associated with relatively minor symptoms, it is usually attributed to autoimmune disorder or viral infection. The congenital neutropenia syndromes are usually recognized when there are recurrent infections, the neutropenia is severe and there are congenital anomalies suggesting a genetic disorder. This review focuses on the key clinical finding and laboratory tests for diagnosis with commentaries on treatment, particularly the use of granulocyte colony-stimulating factor to treat childhood neutropenia.

From cytopenia to leukemia: the role of Gfi1 and Gfi1b in blood formation

The DNA-binding zinc finger transcription factors Gfi1 and Gfi1b were discovered more than 20 years ago and are recognized today as major regulators of both early hematopoiesis and hematopoietic stem cells. Both proteins function as transcriptional repressors by recruiting histone-modifying enzymes to promoters and enhancers of target genes. The establishment of Gfi1 and Gfi1b reporter mice made it possible to visualize their cell type-specific expression and to understand their function in hematopoietic lineages. We now know that Gfi1 is primarily important in myeloid and lymphoid differentiation, whereas Gfi1b is crucial for the generation of red blood cells and platelets. Several rare hematologic diseases are associated with acquired or inheritable mutations in the GFI1 and GFI1B genes. Certain patients with severe congenital neutropenia carry mutations in the GFI1 gene that lead to the disruption of the C-terminal zinc finger domains. Other mutations have been found in the GFI1B gene in families with inherited bleeding disorders. In addition, the Gfi1 locus is frequently found to be a proviral integration site in retrovirus-induced lymphomagenesis, and new, emerging data suggest a role of Gfi1 in human leukemia and lymphoma, underlining the role of both factors not only in normal hematopoiesis, but also in a wide spectrum of human blood diseases.