A patient with glycogen storage disease type Ib presenting with acute myeloid leukemia (AML) bearing monosomy 7 and translocation t(3;8)(q26;q24) after 14 years of treatment with granulocyte colony-stimulating factor (G-CSF): a case report

Treatment recommendations for glycogen storage disease type IB- associated neutropenia and neutrophil dysfunction with empagliflozin: Consensus from an international workshop

Glycogen storage disease type Ib (GSD Ib, biallelic variants in SLC37A4) is a rare disorder of glycogen metabolism complicated by neutropenia/neutrophil dysfunction. Since 2019, the SGLT2-inhibitor empagliflozin has provided a mechanism-based treatment option for the symptoms caused by neutropenia/neutrophil dysfunction (e.g. mucosal lesions, inflammatory bowel disease). Because of the rarity of GSD Ib, the published evidence on safety and efficacy of empagliflozin is still limited and does not allow to develop evidence-based guidelines. Here, an international group of experts provides 14 best practice consensus treatment recommendations based on expert practice and review of the published evidence. We recommend to start empagliflozin in all GSD Ib individuals with clinical or laboratory signs related to neutropenia/neutrophil dysfunction with a dose of 0.3-0.4 mg/kg/d given as a single dose in the morning. Treatment can be started in an outpatient setting. The dose should be adapted to the weight and in case of inadequate clinical treatment response or side effects. We strongly recommend to pause empagliflozin immediately in case of threatening dehydration and before planned longer surgeries. Discontinuation of G-CSF therapy should be attempted in all individuals. If available, 1,5-AG should be monitored. Individuals who have previously not tolerated starches should be encouraged to make a new attempt to introduce starch in their diet after initiation of empagliflozin treatment. We advise to monitor certain safety and efficacy parameters and recommend continuous, alternatively frequent glucose measurements during the introduction of empagliflozin. We provide specific recommendations for special circumstances like pregnancy and liver transplantation.

Three novel SLC37A4 variants in glycogen storage disease type 1b and a literature review

Glycogen storage disease type 1b (GSD1b) is a rare genetic disorder, resulting from mutations in the SLC37A4 gene located on chromosome 11q23.3. Although the SLC37A4 gene has been identified as the pathogenic gene for GSD1b, the complete variant spectrum of this gene remains to be fully elucidated. In this study, we present three patients diagnosed with GSD1b through genetic testing. We detected five variants of the SLC37A4 gene in these three patients, with three of these mutations (p. L382Pfs*15, p. G117fs*28, and p. T312Sfs*13) being novel variants not previously reported in the literature. We also present a literature review and general overview of the currently reported SLC37A4 gene variants. Our study expands the mutation spectrum of SLC37A4, which may help enable genetic testing to facilitate prompt diagnosis, appropriate intervention, and genetic counseling for affected families.

Patient-reported outcomes on empagliflozin treatment in glycogen storage disease type Ib: An international questionnaire study

In patients with glycogen storage disease type Ib (GSD Ib), quality of life is severely hampered by neutropenia and neutropenia-associated symptoms. SGLT2 inhibitors are a new treatment option and have shown improved medical outcomes in more than 120 patients so far. The aim of this international questionnaire study was to assess patient-reported outcomes of this new treatment in GSD Ib patients. Patients and caregivers of pediatric patients were invited to complete a web-based questionnaire. This was designed to evaluate treatment effects of the SGLT2 inhibitor empagliflozin on clinical symptoms and important aspects of daily life including physical performance, sleep, social and work life, traveling, socioeconomic aspects, and quality of life. The questionnaire was completed by 73 respondents from 17 different countries. The mean duration of treatment was 15 months, the cumulative treatment time was 94.8 years. More than 80% of patients reported an improved quality of life. The number of hospitalizations was reduced (66% of patients), as well as the number of days absent from school or work. Granulocyte colony-stimulating factor (G-CSF) treatment could be stopped in 49% of patients and reduced in another 42%. Clear improvement of neutropenia and all neutropenia-associated symptoms was reported by the majority of patients. Additionally, patients or caregivers reported positive effects on appetite (63%), level of activity (75%), overall well-being (96%), and sleep (63%). Empagliflozin positively impacts many aspects of daily life including work and social life and thereby significantly improves quality of life of patients and caregivers.

Improved inflammatory bowel disease, wound healing and normal oxidative burst under treatment with empagliflozin in glycogen storage disease type Ib

Background

Glycogen storage disease type Ib (GSD Ib) is a rare inborn error of glycogen metabolism due to mutations in SLC37A4. Besides a severe form of fasting intolerance, the disorder is usually associated with neutropenia and neutrophil dysfunction causing serious infections, inflammatory bowel disease, oral, urogenital and perianal lesions as well as impaired wound healing. Recently, SGLT2 inhibitors such as empagliflozin that reduce the plasma levels of 1,5-anhydroglucitol have been described as a new treatment option for the neutropenia and neutrophil dysfunction in patients with GSD Ib.

Results

We report on a 35-year-old female patient with GSD Ib who had been treated with G-CSF for neutropenia since the age of 9. She had a large chronic abdominal wound as a consequence of recurrent operations due to complications of her inflammatory bowel disease. Treatment with 20 mg empagliflozin per day resulted in normalisation of the neutrophil count and neutrophil function even after termination of G-CSF. The chronic abdominal wound that had been unchanged for 2 years before the start of empagliflozin nearly closed within 12 weeks. No side effects of empagliflozin were observed.

Conclusion

SGLT2 inhibitors are a new and probably safe treatment option for GSD Ib-associated neutropenia and neutrophil dysfunction. We hypothesize that restoration of neutrophil function and normalisation of neutrophil apoptosis leads to improvement of wound healing and ameliorates symptoms of inflammatory bowel disease.

Neutropenia in glycogen storage disease Ib: outcomes for patients treated with granulocyte colony-stimulating factor

PURPOSE OF REVIEW

Glycogen storage disease Ib (GSD Ib) is characterized by hepatomegaly, hypoglycemia, neutropenia, enterocolitis and recurrent bacterial infections. It is attributable to mutations in G6PT1, the gene for the glucose-6-phosphate transporter responsible for transport of glucose into the endoplasmic reticulum. Neutropenia in GSD Ib is now frequently treated with granulocyte colony-stimulating factor (G-CSF). We formed a cooperative group to review outcomes of the long-term treatment of GSD Ib patients treated with G-CSF.

RECENT FINDINGS

The study enrolled 103 patients (48 men and 55 women), including 47 currently adult patients. All of these patients were treated with G-CSF, starting at a median age of 3.8 years (range 0.04-33.9 years) with a median dose of 3.0 mcg/kg/day (range 0.01-93.1 mcg/kg/day) for a median of 10.3 years (range 0.01-29.3 years). Neutrophils increased in response to G-CSF in all patients (median values before G-CSF 0.2 × 10/l, on G-CSF 1.20 x 10/l). Treatment increased spleen size (before G-CSF, 47%, on treatment on G-CSF 76%), and splenomegaly was the dose-limiting adverse effect of treatment (pain and early satiety). Clinical observations and records attest to reduce frequency of infectious events and the severity of inflammatory bowel symptoms, but fever and recurrent infections remain a significant problem. In the cohort of patients followed carefully through the Severe Chronic Neutropenia International Registry, four patients have developed myelodysplasia or acute myeloid leukemia and we are aware of four other cases, (altogether seven on G-CSF, one never treated with G-CSF). Liver transplantation in five patients did not correct neutropenia. Four patients had hematopoietic stem cell transplantation; two adults and two children were transplanted; one adult and one child survived.

SUMMARY

GSD Ib is a complex disorder of glucose metabolism causing severe chronic neutropenia. G-CSF is effective to raise blood neutrophil counts and reduce fevers and infections in most patients. In conjunction with other therapies (salicylates, mesalamine sulfasalazine and prednisone), G-CSF ameliorates inflammatory bowel symptoms, but doses must be limited because it increases spleen size associated with abdominal pain.

A case of secondary acute myeloid leukemia on a background of glycogen storage disease with chronic neutropenia treated with granulocyte colony stimulating factor

Congenital neutropenias due to mutations in ELANE, SBDS or HAX1 or in the setting of glycogen storage disease (GSD) which is caused by SLC37A4 mutation, often require prolonged granulocyte colony stimulating factor (G-CSF) therapy to prevent recurrent infections and hospital admission. There has been emerging evidence that prolonged exposure to G-CSF in cases with congenital neutropenia other than GSD is associated with transformation to myelodysplastic syndrome/acute myeloid leukemia.

Molecular biology and gene therapy for glycogen storage disease type Ib

Glycogen storage disease type Ib (GSD-Ib) is caused by a deficiency in the ubiquitously expressed glucose-6-phosphate (G6P) transporter (G6PT or SLC37A4). The primary function of G6PT is to translocate G6P from the cytoplasm into the lumen of the endoplasmic reticulum (ER). Inside the ER, G6P is hydrolyzed to glucose and phosphate by either the liver/kidney/intestine-restricted glucose-6-phosphatase-α (G6Pase-α) or the ubiquitously expressed G6Pase-β. A deficiency in G6Pase-α causes GSD type Ia (GSD-Ia) and a deficiency in G6Pase-β causes GSD-I-related syndrome (GSD-Irs). In gluconeogenic organs, functional coupling of G6PT and G6Pase-α is required to maintain interprandial blood glucose homeostasis. In myeloid tissues, functional coupling of G6PT and G6Pase-β is required to maintain neutrophil homeostasis. Accordingly, GSD-Ib is a metabolic and immune disorder, manifesting impaired glucose homeostasis, neutropenia, and neutrophil dysfunction. A G6pt knockout mouse model is being exploited to delineate the pathophysiology of GSD-Ib and develop new clinical treatment options, including gene therapy. The safety and efficacy of several G6PT-expressing recombinant adeno-associated virus pseudotype 2/8 vectors have been examined in murine GSD-Ib. The results demonstrate that the liver-directed gene transfer and expression safely corrects metabolic abnormalities and prevents hepatocellular adenoma (HCA) development. However, a second vector system may be required to correct myeloid and renal dysfunction in GSD-Ib. These findings are paving the way to a safe and efficacious gene therapy for entering clinical trials.

Prolonged granulocyte colony stimulating factor use in glycogen storage disease type 1b associated with acute myeloid leukemia and with shortened telomere length

Glycogen storage disease (GSD) type 1 is a rare autosomal recessive inherited condition. The 1b subtype comprises the minority of cases, with an estimated prevalence of 1 in 500,000 children. Patients with glycogen storage disease type 1b are often treated with granulocyte colony stimulating factor (G-CSF) for prolonged periods to improve symptoms of inflammatory bowel disease (IBD) and in the face of severe neutropenia to decrease risk of infection. Long-term G-CSF treatment may result in an increased risk of myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML) possibly due to increased marrow stress resulting in telomere shortening. To our knowledge, there have been two published cases of AML in GSD type 1b patients following long-term G-CSF exposure. Here, we report two further cases of AML/MDS-related changes in patients GSD type 1b treated with G-CSF. One patient developed AML with complex karyotype after 20 years of G-CSF treatment. The second patient was found to have short telomeres after 10 years of G-CSF exposure, but no evidence of acute leukemia at present. The third patient developed AML/MDS after 25 years of G-CSF use, with short telomeres prior to bone marrow transplant. Together these cases suggest that GSD type 1b patients with prolonged G-CSF exposure may be at an increased risk of MDS/AML states associated with G-CSF-induced shortened telomeres. We recommend that any GSD1b patients with prolonged G-CSF should have routine telomere assessments with monitoring for MDS if telomere shortening is observed, and with particular attention warranted if there is unexplained loss of G-CSF responsiveness.

A Third Case of Glycogen Storage Disease IB and Giant Cell Tumour of the Mandible: A Disease Association or Iatrogenic Complication of Therapy

We report the third case of Glycogen Storage Disease type 1b (GSD 1b) with Giant Cell Tumour (GCT) of the mandible, associated with Granulocyte Colony Stimulating Factor (G-CSF) use. G-CSF in GSD 1b is indicated for persistent neutropaenia, sepsis, inflammatory bowel disease and severe diarrhoea. Our patient was 12 years old at GCT diagnosis and had been treated with G-CSF from 5 years of age. He underwent therapy with interferon followed by local resection which was successful in initial control of the disease. Histology demonstrated spindle shaped stromal cells together with numerous interspersed multinuclear osteoclastic giant cells. G-CSF has been hypothesized to induce osteoclastic differentiation and thus may be involved in the pathogenesis of GCT formation. At age 19 years he required a repeat operation for local recurrence. He currently continues on G-CSF and was commenced on denosumab for control of the GCT with no recurrence to date. A cause and effect relationship between G-CSF therapy and the development of GCT in GSD type 1b remains to be established.

Therapy-related myelodysplastic syndrome: a case study

We present a case of therapy-related myelodyspastic syndrome in which the t(3;8)(q26;q24) translocation appeared, even though no chromosomal abnormalities were found at the initial diagnosis of acute myeloid leukemia. To the best of our knowledge, there have only been around 20 reported cases of myeloid malignancies involving t(3;8)(q26;q24). We discuss the characteristics of t(3;8)(q26;q24) along with a review of literature.

Clinical spectrum and long-term follow-up of 14 cases with G6PC3 mutations from the French Severe Congenital Neutropenia Registry

Background

The purpose of this study was to describe the natural history of severe congenital neutropenia (SCN) in 14 patients with G6PC3 mutations and enrolled in the French SCN registry.

Methods

Among 605 patients included in the French SCN registry, we identified 8 pedigrees that included 14 patients with autosomal recessive G6PC3 mutations.

Results

Median age at the last visit was 22.4 years. All patients had developed various comordibities, including prominent veins (n = 12), cardiac malformations (n = 12), intellectual disability (n = 7), and myopathic syndrome with recurrent painful cramps (n = 1). Three patients developed Crohn’s disease, and five had chronic diarrhea with steatorrhea. Neutropenia was profound (<0.5 × 10⁹/l) in almost all cases at diagnosis and could marginally fluctuate. The bone marrow smears exhibited mild late-stage granulopoeitic defects. One patient developed myelodysplasia followed by acute myelogenous leukemia with translocation (18, 21) at age 14 years, cured by chemotherapy and hematopoietic stem cell transplantation. Four deaths occurred, including one from sepsis at age 5, one from pulmonary late-stage insufficiency at age 19, and two from sudden death, both at age 30 years. A new homozygous mutation (c.249G > A /p.Trp83*) was detected in one pedigree.

Conclusions

Severe congenital neutropenia with autosomal recessive G6PC3 mutations is associated with considerable clinical heterogeneity. This series includes the first described case of malignancy in this neutropenia.

Inborn errors of metabolism underlying primary immunodeficiencies

A number of inborn errors of metabolism (IEM) have been shown to result in predominantly immunologic phenotypes, manifesting in part as inborn errors of immunity. These phenotypes are mostly caused by defects that affect the (i) quality or quantity of essential structural building blocks (e.g., nucleic acids, and amino acids), (ii) cellular energy economy (e.g., glucose metabolism), (iii) post-translational protein modification (e.g., glycosylation) or (iv) mitochondrial function. Presenting as multisystemic defects, they also affect innate or adaptive immunity, or both, and display various types of immune dysregulation. Specific and potentially curative therapies are available for some of these diseases, whereas targeted treatments capable of inducing clinical remission are available for others. We will herein review the pathogenesis, diagnosis, and treatment of primary immunodeficiencies (PIDs) due to underlying metabolic disorders.

Hemophagocytic lymphohistiocytosis complicating erythroleukemia in a child with monosomy 7: a case report and review of the literature

Herein, the first case of childhood erythrophagocytosis following chemotherapy for erythroleukemia in a child with monosomy 7 is reported. A 5-year-old boy presented with anemia, thrombocytopenia, and hepatosplenomegaly in whom erythroleukemia was diagnosed. Prolonged pancytopenia accompanied by persistent fever and huge splenomegaly and hepatomegaly became evident after 2 courses of chemotherapy. On bone marrow aspiration, macrophages phagocytosing erythroid precursors were observed and the diagnosis of HLH was established; additionally, monosomy 7 was detected on bone marrow cytogenetic examination. In conclusion, monosomy 7 can lead to erythrophagocytosis associated with erythroid leukemia and should be considered among the chromosomal abnormalities contributing to the association.

The SLC37 family of phosphate-linked sugar phosphate antiporters

The SLC37 family consists of four sugar-phosphate exchangers, A1, A2, A3, and A4, which are anchored in the endoplasmic reticulum (ER) membrane. The best characterized family member is SLC37A4, better known as the glucose-6-phosphate (G6P) transporter (G6PT). SLC37A1, SLC37A2, and G6PT function as phosphate (Pi)-linked G6P antiporters catalyzing G6P:Pi and Pi:Pi exchanges. The activity of SLC37A3 is unknown. G6PT translocates G6P from the cytoplasm into the lumen of the ER where it couples with either glucose-6-phosphatase-α (G6Pase-α) or G6Pase-β to hydrolyze intraluminal G6P to glucose and Pi. The functional coupling of G6PT with G6Pase-α maintains interprandial glucose homeostasis and the functional coupling of G6PT with G6Pase-β maintains neutrophil energy homeostasis and functionality. A deficiency in G6PT causes glycogen storage disease type Ib, an autosomal recessive disorder characterized by impaired glucose homeostasis, neutropenia, and neutrophil dysfunction. Neither SLC37A1 nor SLC37A2 can functionally couple with G6Pase-α or G6Pase-β, and there are no known disease associations for them or SLC37A3. Since only G6PT matches the characteristics of the physiological ER G6P transporter involved in blood glucose homeostasis and neutrophil energy metabolism, the biological roles for the other SLC37 proteins remain to be determined.

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.

Extended spectrum of human glucose-6-phosphatase catalytic subunit 3 deficiency: novel genotypes and phenotypic variability in severe congenital neutropenia

OBJECTIVE

To delineate the phenotypic and molecular spectrum of patients with a syndromic variant of severe congenital neutropenia (SCN) due to mutations in the gene encoding glucose-6-phosphatase catalytic subunit 3 (G6PC3).

STUDY DESIGN

Patients with syndromic SCN were characterized for associated malformations and referred to us for G6PC3 mutational analysis.

RESULTS

In a cohort of 31 patients with syndromic SCN, we identified 16 patients with G6PC3 deficiency including 11 patients with novel biallelic mutations. We show that nonhematologic features of G6PC3 deficiency are good predictive indicators for mutations in G6PC3. Additionally, we demonstrate genetic variability in this disease and define novel features such as growth hormone deficiency, genital malformations, disrupted bone remodeling, and abnormalities of the integument. G6PC3 mutations may be associated with hydronephrosis or facial dysmorphism. The risk of transition to myelodysplastic syndrome/acute myeloid leukemia may be lower than in other genetically defined SCN subgroups.

CONCLUSIONS

The phenotypic and molecular spectrum in G6PC3 deficiency is wider than previously appreciated. The risk of transition to myelodysplastic syndrome or acute myeloid leukemia may be lower in G6PC3 deficiency compared with other subgroups of SCN.

Congenital and acquired neutropenias consensus guidelines on therapy and follow-up in childhood from the Neutropenia Committee of the Marrow Failure Syndrome Group of the AIEOP (Associazione Italiana Emato-Oncologia Pediatrica)

The management of congenital and acquired neutropenias presents some differences according to the type of the disease. Treatment with recombinant human granulocyte-colony stimulating factor (G-CSF) is not standardized and scanty data are available on the best schedule to apply. The frequency and the type of longitudinal controls in patients affected with neutropenias are not usually discussed in the literature. The Neutropenia Committee of the Marrow Failure Syndrome Group (MFSG) of the Associazione Italiana di Emato-Oncologia Pediatrica (AIEOP) elaborated this document following design and methodology formerly approved by the AIEOP board. The panel of experts reviewed the literature on the topic and participated in a conference producing a document that includes recommendations on neutropenia treatment and timing of follow-up.

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.

Glycogen storage disease type I and G6Pase-β deficiency: etiology and therapy

Glycogen storage disease type I (GSD-I) consists of two subtypes: GSD-Ia, a deficiency in glucose-6-phosphatase-α (G6Pase-α) and GSD-Ib, which is characterized by an absence of a glucose-6-phosphate (G6P) transporter (G6PT). A third disorder, G6Pase-β deficiency, shares similarities with this group of diseases. G6Pase-α and G6Pase-β are G6P hydrolases in the membrane of the endoplasmic reticulum, which depend on G6PT to transport G6P from the cytoplasm into the lumen. A functional complex of G6PT and G6Pase-α maintains interprandial glucose homeostasis, whereas G6PT and G6Pase-β act in conjunction to maintain neutrophil function and homeostasis. Patients with GSD-Ia and those with GSD-Ib exhibit a common metabolic phenotype of disturbed glucose homeostasis that is not evident in patients with G6Pase-β deficiency. Patients with a deficiency in G6PT and those lacking G6Pase-β display a common myeloid phenotype that is not shared by patients with GSD-Ia. Previous studies have shown that neutrophils express the complex of G6PT and G6Pase-β to produce endogenous glucose. Inactivation of either G6PT or G6Pase-β increases neutrophil apoptosis, which underlies, at least in part, neutrophil loss (neutropenia) and dysfunction in GSD-Ib and G6Pase-β deficiency. Dietary and/or granulocyte colony-stimulating factor therapies are available; however, many aspects of the diseases are still poorly understood. This Review will address the etiology of GSD-Ia, GSD-Ib and G6Pase-β deficiency and highlight advances in diagnosis and new treatment approaches, including gene therapy.

Neutropenia in type Ib glycogen storage disease

PURPOSE OF REVIEW

Glycogen storage disease type Ib, characterized by disturbed glucose homeostasis, neutropenia, and neutrophil dysfunction, is caused by a deficiency in a ubiquitously expressed glucose-6-phosphate transporter (G6PT). G6PT translocates glucose-6-phosphate (G6P) from the cytoplasm into the lumen of the endoplasmic reticulum, in which it is hydrolyzed to glucose either by a liver/kidney/intestine-restricted glucose-6-phosphatase-alpha (G6Pase-alpha) or by a ubiquitously expressed G6Pase-beta. The role of the G6PT/G6Pase-alpha complex is well established and readily explains why G6PT disruptions disturb interprandial blood glucose homeostasis. However, the basis for neutropenia and neutrophil dysfunction in glycogen storage disease type Ib is poorly understood. Recent studies that are now starting to unveil the mechanisms are presented in this review.

RECENT FINDINGS

Characterization of G6Pase-beta and generation of mice lacking either G6PT or G6Pase-beta have shown that neutrophils express the G6PT/G6Pase-beta complex capable of producing endogenous glucose. Loss of G6PT activity leads to enhanced endoplasmic reticulum stress, oxidative stress, and apoptosis that underlie neutropenia and neutrophil dysfunction in glycogen storage disease type Ib.

SUMMARY

Neutrophil function is intimately linked to the regulation of glucose and G6P metabolism by the G6PT/G6Pase-beta complex. Understanding the molecular mechanisms that govern energy homeostasis in neutrophils has revealed a previously unrecognized pathway of intracellular G6P metabolism in neutrophils.