SGLT5 is the renal transporter for 1,5-anhydroglucitol, a major player in two rare forms of neutropenia.

Neutropenia and neutrophil dysfunction in glycogen storage disease type 1b (GSD1b) and severe congenital neutropenia type 4 (SCN4), associated with deficiencies of the glucose-6-phosphate transporter (G6PT/SLC37A4) and the phosphatase G6PC3, respectively, are the result of the accumulation of 1,5-anhydroglucitol-6-phosphate in neutrophils. This is an inhibitor of hexokinase made from 1,5-anhydroglucitol (1,5-AG), an abundant polyol in blood. 1,5-AG is presumed to be reabsorbed in the kidney by a sodium-dependent-transporter of uncertain identity, possibly SGLT4/SLC5A9 or SGLT5/SLC5A10. Lowering blood 1,5-AG with an SGLT2-inhibitor greatly improved neutrophil counts and function in G6PC3-deficient and GSD1b patients. Yet, this effect is most likely mediated indirectly, through the inhibition of the renal 1,5-AG transporter by glucose, when its concentration rises in the renal tubule following inhibition of SGLT2. To identify the 1,5-AG transporter, both human and mouse SGLT4 and SGLT5 were expressed in HEK293T cells and transport measurements were performed with radiolabelled compounds. We found that SGLT5 is a better carrier for 1,5-AG than for mannose, while the opposite is true for human SGLT4. Heterozygous variants in SGLT5, associated with a low level of blood 1,5-AG in humans cause a 50-100% reduction in 1,5-AG transport activity tested in model cell lines, indicating that SGLT5 is the predominant kidney 1,5-AG transporter. These and other findings led to the conclusion that (1) SGLT5 is the main renal transporter of 1,5-AG; (2) frequent heterozygous mutations (allelic frequency > 1%) in SGLT5 lower blood 1,5-AG, favourably influencing neutropenia in G6PC3 or G6PT deficiency; (3) the effect of SGLT2-inhibitors on blood 1,5-AG level is largely indirect; (4) specific SGLT5-inhibitors would be more efficient to treat these neutropenias than SGLT2-inhibitors.

Human Genetics of Atrial Septal Defect.

Although atrial septal defects (ASD) can be subdivided based on their anatomical location, an essential aspect of human genetics and genetic counseling is distinguishing between isolated and familiar cases without extracardiac features and syndromic cases with the co-occurrence of extracardiac abnormalities, such as developmental delay. Isolated or familial cases tend to show genetic alterations in genes related to important cardiac transcription factors and genes encoding for sarcomeric proteins. By contrast, the spectrum of genes with genetic alterations observed in syndromic cases is diverse. Currently, it points to different pathways and gene networks relevant to the dysregulation of cardiomyogenesis and ASD pathogenesis. Therefore, this chapter reflects the current knowledge and highlights stable associations observed in human genetics studies. It gives an overview of the different types of genetic alterations in these subtypes, including common associations based on genome-wide association studies (GWAS), and it highlights the most frequently observed syndromes associated with ASD pathogenesis.

DBS are suitable for 1,5-anhydroglucitol monitoring in GSD1b and G6PC3-deficient patients taking SGLT2 inhibitors to treat neutropenia.

Glycogen storage disease type Ib (GSD1b) and G6PC3-deficiency are rare autosomal recessive diseases caused by inactivating mutations in SLC37A4 (coding for G6PT) and G6PC3, respectively. Both diseases are characterized by neutropenia and neutrophil dysfunction due to the intracellular accumulation of 1,5-anhydroglucitol-6-phosphate (1,5-AG6P), a potent inhibitor of hexokinases. We recently showed that the use of SGLT2 inhibitor therapy to reduce tubular reabsorption of its precursor, 1,5-anhydroglucitol (1,5-AG), a glucose analog present in blood, successfully restored the neutropenia and neutrophil function in G6PC3-deficient and GSD1b patients. The intra-individual variability of response to the treatment and the need to adjust the dose during treatment, especially in pediatric populations, can only be efficiently optimized if the concentration of 1,5-AG in blood is monitored during treatment, together with the patients' clinical signs and symptoms. Monitoring the 1,5-AG levels would be greatly simplified if it could be performed on dry blood spots (DBS) which are easy to collect, store and transport. The challenge is to know if a suitable method can be developed to perform accurate and reproducible assays for 1,5-AG using DBS. Here, we describe and validate an assay that quantifies 1,5-AG in DBS using isotopic dilution quantitation by LC-MS/MS that should greatly facilitate patients' follow-up. 1,5-AG levels measured in plasma and DBS give comparable values. This assay was used to monitor the levels of 1,5-AG in DBS from 3 G6PC3-deficient and 6 GSD1b patients during treatment with SGLT2 inhibitors. We recommend this approach to verify the adequate therapeutical response and compliance to the treatment in G6PC3-deficient and GSD1b patients treated with SGLT2 inhibitors.

SLGT2 Inhibitor Rescues Myelopoiesis in G6PC3 Deficiency.

The energy metabolism of myeloid cells depends primarily on glycolysis. 1,5-Anhydroglucitol (1,5AG), a natural monosaccharide, is erroneously phosphorylated by glucose-phosphorylating enzymes to produce 1,5-anhydroglucitol-6-phosphate (1,5AG6P), a powerful inhibitor of hexokinases. The endoplasmic reticulum transporter (SLC37A4/G6PT) and the phosphatase G6PC3 cooperate to dephosphorylate 1,5AG6P. Failure to eliminate 1,5AG6P is the mechanism of neutrophil dysfunction and death in G6PC3-deficient mice. Sodium glucose cotransporter 2 (SLGT2) inhibitor reduces 1,5AG level in the blood and restores the neutrophil count in G6PC3-deficient mice. In the investigator-initiated study, a 30-year-old G6PC3-deficient woman with recurrent infections, distressing gastrointestinal symptoms, and multi-lineage cytopenia was treated with an SLGT2-inhibitor. A significant increase in all the hematopoietic cell lineages and substantial improvement in the quality of life was observed.

Severe congenital neutropenia due to G6PC3 deficiency: Case series of five patients and literature review.

BACKGROUND AND OBJECTIVES: Glucose-6-phosphate catalytic subunit 3 (G6PC3) deficiency is characterized by severe congenital neutropenia with recurrent pyogenic infections, a prominent superficial venous pattern and cardiovascular and urogenital malformations caused by an alteration of glucose homeostasis, with increased endoplasmic reticulum stress and cell apoptosis. METHODS: We reviewed our patients with G6PC3 deficiency diagnosed along the last decade in Mexico; we also searched the PubMed/Medline database for the terms ('G6PC3 deficiency' OR 'Dursun syndrome' OR 'Severe congenital neutropenia type 4'), and selected articles published in English from 2009 to 2020. RESULTS: We found 89 patients reported from at least 14 countries in 4 continents. We describe five new cases from Mexico. Of the 94 patients, 56% are male, 48% from Middle East countries and none of them had adverse reactions to live vaccines; all presented with at least 1 severe infection prior to age 2. Seventy-five per cent had syndromic features, mainly atrial septal defect in 55% and prominent superficial veins in 62%. CONCLUSIONS: With a total of 94 patients reported in the past decade, we delineate the most frequent laboratory and genetic features, their treatment and outcomes, and to expand the knowledge of syndromic and non-syndromic phenotypes in these patients.

Successful use of empagliflozin to treat neutropenia in two G6PC3-deficient children: Impact of a mutation in SGLT5.

Neutropenia and neutrophil dysfunction found in deficiencies in G6PC3 and in the glucose-6-phosphate transporter (G6PT/SLC37A4) are due to accumulation of 1,5-anhydroglucitol-6-phosphate (1,5-AG6P), an inhibitor of hexokinase made from 1,5-anhydroglucitol (1,5-AG), an abundant polyol present in blood. Lowering blood 1,5-AG with an SGLT2 inhibitor greatly improved neutrophil counts and function in G6PC3-deficient mice and in patients with G6PT-deficiency. We evaluate this treatment in two G6PC3-deficient children. While neutropenia was severe in one child (PT1), which was dependent on granulocyte cololony-stimulating factor (GCSF), it was significantly milder in the other one (PT2), which had low blood 1,5-AG levels and only required GCSF during severe infections. Treatment with the SGLT2-inhibitor empagliflozin decreased 1,5-AG in blood and 1,5-AG6P in neutrophils and improved (PT1) or normalized (PT2) neutrophil counts, allowing to stop GCSF. On empagliflozin, both children remained infection-free (>1 year - PT2; >2 years - PT1) and no side effects were reported. Remarkably, sequencing of SGLT5, the gene encoding the putative renal transporter for 1,5-AG, disclosed a rare heterozygous missense mutation in PT2, replacing the extremely conserved Arg401 by a histidine. The higher urinary clearance of 1,5-AG explains the more benign neutropenia and the outstanding response to empagliflozin treatment found in this child. Our data shows that SGLT2 inhibitors are an excellent alternative to treat the neutropenia present in G6PC3-deficiency.

Severe Congenital Neutropenia Type 4: A Rare Disease Harboring a G6pc3 Gene Pathogenic Variant Particular to the Mexican Population.

Background: Severe congenital neutropenia type 4 (SCN4) is a rare autosomal recessive granulopoiesis disorder caused by G6PC3 gene pathogenic variants. The estimated prevalence is 1/10,000,000 people. Over 90% of patients present a syndromic form with variable multisystemic involvement, including congenital heart defects, increased visibility of superficial veins (IVSV), inflammatory bowel disease, and congenital urogenital defects as prominent symptoms. Objectives: The objective of the study was to study non-hematological phenotypic findings that suggest a clinical diagnosis of SCN4. Methods: We examined medical records of patients diagnosed with neutropenia from January 2000 to December 2020, selecting cases with non-hematologic manifestations for phenotypic description and G6PC3 gene sequencing. Results: We found 11 cases with non-hematologic features: congenital heart defects in 8, IVSV in 6, inflammatory bowel disease in 4, urogenital defects in 4, and similar facial appearance. In addition, Sanger sequencing confirmed 3 homozygous cases for the c.210delC variant, a compound heterozygous harboring this variant, and a c.199_218+1 deletion. Conclusions: Our findings of the c.210delC variant in very close geographical settings, to date, have only been reported among Mexicans, and a mutual uncommon surname in two families strongly supports a founder effect for the variant in the studied population. Furthermore, the described non-hematologic symptoms in patients with severe primary neutropenia should be explored, confirming SCN4 by investigating G6PC3 gene mutations.

Clinical and Mutation Description of the First Iranian Cohort of Infantile Inflammatory Bowel Disease: The Iranian Primary Immunodeficiency Registry (IPIDR).

We describe a cohort of 25 Iranian patients with infantile inflammatory bowel disease (IBD), 14 (56%) of whom had monogenic defects. After proper screening, patients were referred for whole exome sequencing (WES). Four patients had missense mutations in the IL10 RA, and one had a large deletion in the IL10 RB. Four patients had mutations in genes implicated in host:microbiome homeostasis, including TTC7A deficiency, and two patients with novel mutations in the TTC37 and NOX1. We found a novel homozygous mutation in the SRP54 in a deceased patient and the heterozygous variant in his sibling with a milder phenotype. Three patients had combined immunodeficiency: one with ZAP-70 deficiency (T+B+NK-), and two with atypical SCID due to mutations in RAG1 and LIG4. One patient had a G6PC3 mutation without neutropenia. Eleven of the 14 patients with monogenic defects were results of consanguinity and only 4 of them were alive to this date.

The Transplantation Resistance of Type II Diabetes Mellitus Adipose-Derived Stem Cells Is Due to G6PC and IGF1 Genes Related to the FoxO Signaling Pathway.

In cases of patients with rapidly progressive diabetes mellitus (DM), autologous stem cell transplantation is considered as one of the regenerative treatments. However, whether the effects of autonomous stem cell transplantation on DM patients are equivalent to transplantation of stem cells derived from healthy persons is unclear. This study revealed that adipose-derived mesenchymal stem cells (ADSC) derived from type II DM patients had lower transplantation efficiency, proliferation potency, and stemness than those derived from healthy persons, leading to a tendency to induce apoptotic cell death. To address this issue, we conducted a cyclopedic mRNA analysis using a next-generation sequencer and identified G6PC3 and IGF1, genes related to the FoxO signaling pathway, as the genes responsible for lower performance. Moreover, it was demonstrated that the lower transplantation efficiency of ADSCs derived from type II DM patients might be improved by knocking down both G6PC3 and IGF1 genes. This study clarified the difference in transplantation efficiency between ADSCs derived from type II DM patients and those derived from healthy persons and the genes responsible for the lower performance of the former. These results can provide a new strategy for stabilizing the quality of stem cells and improving the therapeutic effects of regenerative treatments on autonomous stem cell transplantation in patients with DM.

Inborn errors of metabolite repair.

It is traditionally assumed that enzymes of intermediary metabolism are extremely specific and that this is sufficient to prevent the production of useless and/or toxic side-products. Recent work indicates that this statement is not entirely correct. In reality, enzymes are not strictly specific, they often display weak side activities on intracellular metabolites (substrate promiscuity) that resemble their physiological substrate or slowly catalyse abnormal reactions on their physiological substrate (catalytic promiscuity). They thereby produce non-classical metabolites that are not efficiently metabolised by conventional enzymes. In an increasing number of cases, metabolite repair enzymes are being discovered that serve to eliminate these non-classical metabolites and prevent their accumulation. Metabolite repair enzymes also eliminate non-classical metabolites that are formed through spontaneous (ie, not enzyme-catalysed) reactions. Importantly, genetic deficiencies in several metabolite repair enzymes lead to 'inborn errors of metabolite repair', such as L-2-hydroxyglutaric aciduria, D-2-hydroxyglutaric aciduria, 'ubiquitous glucose-6-phosphatase' (G6PC3) deficiency, the neutropenia present in Glycogen Storage Disease type Ib or defects in the enzymes that repair the hydrated forms of NADH or NADPH. Metabolite repair defects may be difficult to identify as such, because the mutated enzymes are non-classical enzymes that act on non-classical metabolites, which in some cases accumulate only inside the cells, and at rather low, yet toxic, concentrations. It is therefore likely that many additional metabolite repair enzymes remain to be discovered and that many diseases of metabolite repair still await elucidation.

Susceptibility to type 2 diabetes may be modulated by haplotypes in G6PC2, a target of positive selection.

BACKGROUND: The endoplasmic reticulum enzyme glucose-6-phosphatase catalyzes the common terminal reaction in the gluconeogenic/glycogenolytic pathways and plays a central role in glucose homeostasis. In most mammals, different G6PC subunits are encoded by three paralogous genes (G6PC, G6PC2, and G6PC3). Mutations in G6PC and G6PC3 are responsible for human mendelian diseases, whereas variants in G6PC2 are associated with fasting glucose (FG) levels. RESULTS: We analyzed the evolutionary history of G6Pase genes. Results indicated that the three paralogs originated during early vertebrate evolution and that negative selection was the major force shaping diversity at these genes in mammals. Nonetheless, site-wise estimation of evolutionary rates at corresponding sites revealed weak correlations, suggesting that mammalian G6Pases have evolved different structural features over time. We also detected pervasive positive selection at mammalian G6PC2. Most selected residues localize in the C-terminal protein region, where several human variants associated with FG levels also map. This region was re-sequenced in ~560 subjects from Saudi Arabia, 185 of whom suffering from type 2 diabetes (T2D). The frequency of rare missense and nonsense variants was not significantly different in T2D and controls. Association analysis with two common missense variants (V219L and S342C) revealed a weak but significant association for both SNPs when analyses were conditioned on rs560887, previously identified in a GWAS for FG. Two haplotypes were significantly associated with T2D with an opposite effect direction. CONCLUSIONS: We detected pervasive positive selection at mammalian G6PC2 genes and we suggest that distinct haplotypes at the G6PC2 locus modulate susceptibility to T2D.

Functional analysis of mutations in a severe congenital neutropenia syndrome caused by glucose-6-phosphatase-ß deficiency.

Glucose-6-phosphatase-ß (G6Pase-ß or G6PC3) deficiency is characterized by neutropenia and dysfunction in both neutrophils and macrophages. G6Pase-ß is an enzyme embedded in the endoplasmic reticulum membrane that catalyzes the hydrolysis of glucose-6-phosphate (G6P) to glucose and phosphate. To date, 33 separate G6PC3 mutations have been identified in G6Pase-ß-deficient patients but only the p.R253H and p.G260R missense mutations have been characterized functionally for pathogenicity. Here we functionally characterize 16 of the 19 known missense mutations using a sensitive assay, based on a recombinant adenoviral vector-mediated expression system, to demonstrate pathogenicity. Fourteen missense mutations completely abolish G6Pase-ß enzymatic activity while the p.S139I and p.R189Q mutations retain 49% and 45%, respectively of wild type G6Pase-ß activity. A database of residual enzymatic activity retained by the G6Pase-ß mutations will serve as a reference for evaluating genotype-phenotype relationships.

A novel G6PC3 gene mutation in severe congenital neutropenia: pancytopenia and variable bone marrow phenotype can also be part of this syndrome.

Glucose-6-phosphatase catalytic subunit 3 (G6PC3) deficiency is a newly described syndrome characterized by severe congenital neutropenia associated with multiple organ abnormalities including cardiac and urogenital malformations. The underlying pathophysiology of increased apoptosis of myeloid cells and of neutrophil dysfunction in G6PC3 deficiency involves disturbed glucose metabolism, increased endoplasmic reticulum stress and deficient protein folding. Here, we report a new case of G6PC3 deficiency caused by a novel homozygous G6PC3 gene mutation p.Trp59Arg. The patient showed pancytopenia and a variable bone marrow phenotype with maturation arrest and vacuolization in myeloid lineage cells and a normocellular marrow, respectively. She also showed persistent lymphopenia with low CD4 T- and CD19 B-cell counts. Lymphopenia and even pancytopenia as well as a variable bone marrow phenotype can be part of this syndrome. These clinical findings in a patient with chronic neutropenia should alert the clinician to consider a diagnosis of G6PC3 deficiency.

Molecular and clinical characterization of a founder mutation causing G6PC3 deficiency.

G6PC3 deficiency is a monogenic immunometabolic disorder that causes syndromic congenital neutropenia. Patients display heterogeneous extra-hematological manifestations, contributing to delayed diagnosis. Here, we investigated the origin and functional consequence of the G6PC3 c.210delC variant found in patients of Mexican origin. Based on the shared haplotypes amongst carriers of the c.210delC mutation, we estimated that this variant originated from a founder effect in a common ancestor. Furthermore, by ancestry analysis, we concluded that it originated in the indigenous Mexican population. At the protein level, we showed that this frameshift mutation leads to an aberrant protein expression in overexpression and patient-derived cells. G6PC3 pathology is driven by the intracellular accumulation of the metabolite 1,5-anhydroglucitol-6-phosphate (1,5-AG6P) that inhibits glycolysis. We characterized how the variant c.210delC impacts glycolysis by performing extracellular flux assays on patient-derived cells. When treated with 1,5-anhydroglucitol (1,5-AG), the precursor to 1,5-AG6P, patient-derived cells exhibited markedly reduced engagement of glycolysis. Finally, we compared the clinical presentation of patients with the mutation c.210delC and all other G6PC3 deficient patients reported in the literature to date, and we found that c.210delC carriers display all prominent clinical features observed in prior G6PC3 deficient patients. In conclusion, G6PC3 c.210delC is a loss-of-function mutation that arose from a founder effect in the indigenous Mexican population. These findings may facilitate the diagnosis of additional patients in this geographical area. Moreover, the in vitro 1,5-AG-dependent functional assay used in our study could be employed to assess the pathogenicity of additional G6PC3 variants.

[Correction of the pathogenic mutation in the G6PC3 gene by adenine base editing in mutant embryos].

Objective: To determine whether the adenine base editor (ABE7.10) can be used to fix harmful mutations in the human G6PC3 gene. Methods: To investigate the safety of base-edited embryos, off-target analysis by deep sequencing was used to examine the feasibility and editing efficiency of various sgRNA expression vectors. The human HEK293T mutation models and human embryos were also used to test the feasibility and editing efficiency of correction. Results: ①The G6PC3(C295T) mutant cell model was successfully created. ②In the G6PC3(C295T) mutant cell model, three distinct Re-sgRNAs were created and corrected, with base correction efficiency ranging from 8.79% to 19.56% . ③ ABE7.10 could successfully fix mutant bases in the human pathogenic embryo test; however, base editing events had also happened in other locations. ④ With the exception of one noncoding site, which had a high safety rate, deep sequencing analysis revealed that the detection of 32 probable off-target sites was <0.5% . Conclusion: This study proposes a new base correction strategy based on human pathogenic embryos; however, it also produces a certain nontarget site editing, which needs to be further analyzed on the PAM site or editor window.

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.

A molecular signature for the G6PC3/SLC37A2/SLC37A4 interactors in glioblastoma disease progression and in the acquisition of a brain cancer stem cell phenotype.

Background: Glycogen plays an important role in glucose homeostasis and contributes to key functions related to brain cancer cell survival in glioblastoma multiforme (GBM) disease progression. Such adaptive molecular mechanism is dependent on the glycogenolytic pathway and intracellular glucose-6-phosphate (G6P) sensing by brain cancer cells residing within those highly hypoxic tumors. The involvement of components of the glucose-6-phosphatase (G6Pase) system remains however elusive. Objective: We questioned the gene expression levels of components of the G6Pase system in GBM tissues and their functional impact in the control of the invasive and brain cancer stem cells (CSC) phenotypes. Methods: In silico analysis of transcript levels in GBM tumor tissues was done by GEPIA. Total RNA was extracted and gene expression of G6PC1-3 as well as of SLC37A1-4 members analyzed by qPCR in four human brain cancer cell lines and from clinically annotated brain tumor cDNA arrays. Transient siRNA-mediated gene silencing was used to assess the impact of TGF-ß-induced epithelial-to-mesenchymal transition (EMT) and cell chemotaxis. Three-dimensional (3D) neurosphere cultures were generated to recapitulate the brain CSC phenotype. Results: Higher expression in G6PC3, SLC37A2, and SLC37A4 was found in GBM tumor tissues in comparison to low-grade glioma and healthy tissue. The expression of these genes was also found elevated in established human U87, U251, U118, and U138 GBM cell models compared to human HepG2 hepatoma cells. SLC37A4/G6PC3, but not SLC37A2, levels were induced in 3D CD133/SOX2-positive U87 neurospheres when compared to 2D monolayers. Silencing of SLC37A4/G6PC3 altered TGF-ß-induced EMT biomarker SNAIL and cell chemotaxis. Conclusion: Two members of the G6Pase system, G6PC3 and SLC37A4, associate with GBM disease progression and regulate the metabolic reprogramming of an invasive and CSC phenotype. Such molecular signature may support their role in cancer cell survival and chemoresistance and become future therapeutic targets.

Altered Functions of Neutrophils in Two Chinese Patients With Severe Congenital Neutropenia Type 4 Caused by G6PC3 Mutations.

Background: SCN4 is an autosomal recessive disease caused by mutations in the G6PC3 gene. The clinical, molecular, and immunological features; function of neutrophils; and prognosis of patients with SCN4 have not been fully elucidated. Methods: Two Chinese pediatric patients with G6PC3 mutations were enrolled in this study. Clinical data, genetic and immunologic characteristics, and neutrophil function were evaluated in patients and controls before and after granulocyte colony-stimulating factor (G-CSF) treatment. Results: Both patients had histories of pneumonia, inguinal hernia, cryptorchidism, and recurrent oral ulcers. Patient 1 also had asthma and otitis media, and patient 2 presented with prominent ectatic superficial veins and inflammatory bowel disease. DNA sequencing demonstrated that both patients harbored heterozygous G6PC3 gene mutations. Spontaneous and FAS-induced neutrophil apoptosis were significantly increased in patients, and improved only slightly after G-CSF treatment, while neutrophil respiratory burst and neutrophil extracellular traps production remained impaired in patients after G-CSF treatment. Conclusion: G-CSF treatment is insufficient for patients with SCN4 patients, who remain at risk of infection. Where possible, regular G-CSF treatment, long-term prevention of infection, are the optimal methods for cure of SCN4 patients. It is important to monitor closely for signs of leukemia in SCN4 patients. Once leukemia occurs in SCN4 patients, hematopoietic stem cell transplantation is the most important choice of treatment.

Novel G6PC3 Mutations in Patients with Congenital Neutropenia: Case Reports and Review of the Literature.

BACKGROUND: Severe congenital neutropenia (SCN4) caused by mutations in glucose-6- phosphatase catalytic subunit 3 (G6PC3) is characterized by recurrent infections due to severe neutropenia, may be accompanied by other extra-hematopoietic manifestations; including structural heart defects, urogenital abnormalities, prominent superficial venous markings, growth retention, and inflammatory bowel diseases with rare incidence. The homozygous or compound heterozygous mutations of G6PC3 are responsible for most cases of autosomal recessive SCN4. Herein, we present two cases of SCN4 affected by novel mutations in the G6PC3, in addition to a summarized list of variants in G6PC3 gene that are reported as pathogenic and related to the SCN4 phenotype. CASE PRESENTATION: Herein, we present two cases of SCN4; the first case was a three-months old boy with severe neutropenia and prior history of hospitalization due to umbilical separation, umbilical herniation, omphalitis, and pyelonephritis; and the second case was an eight-year-old with a history of neutropenia, recurrent and severe episodes of intractable diarrhea, refractory rectovaginal and rectoperineal fistula, congenital inguinal hernia, and ASD type 2. Whole exome sequencing was performed for both cases, which revealed two novel homozygous missense mutations in G6PC3 that were predicted to be deleterious; c.337G>A, p. Gly113Arg in the first case and c.479C>T; P. Ser160Leu in the second case. To our knowledge, both of these two mutations have not been reported in the G6PDC3 gene. CONCLUSION: In patients with severe neutropenia with varying extra hematopoietic syndrome, mutation of G6PC3 should be suspected after ruling out other mutations related to neutropenia. This study pointed toward novel G6PC3 mutations that should be considered in order to diagnose patients with severe congenital neutropenia.

The SGLT2-inhibitor dapagliflozin improves neutropenia and neutrophil dysfunction in a mouse model of the inherited metabolic disorder GSDIb.

Glycogen Storage Disease type 1b (GSDIb) is a genetic disorder with long term severe complications. Accumulation of the glucose analog 1,5-anhydroglucitol-6-phosphate (1,5AG6P) in neutrophils inhibits the phosphorylation of glucose in these cells, causing neutropenia and neutrophil dysfunctions. This condition leads to serious infections and inflammatory bowel disease (IBD) in GSDIb patients. We show here that dapagliflozin, an inhibitor of the renal sodium-glucose co-transporter-2 (SGLT2), improves neutrophil function in an inducible mouse model of GSDIb by reducing 1,5AG6P accumulation in myeloid cells.