GSD Ib Patients Research Articles

Clinical spectrum, over 12-year follow-up and experience of SGLT2 inhibitors treatment on patients with glycogen storage disease type Ib: a single-center retrospective study

BackgroundGlycogen storage disease type Ib (GSD Ib) is a rare disorder characterized by impaired glucose homeostasis caused by mutations in the SLC37A4 gene. It is a severe inherited metabolic disease associated with hypoglycemia, hyperlipidemia, lactic acidosis, hepatomegaly, and neutropenia. Traditional treatment consists of feeding raw cornstarch which can help to adjust energy metabolism but has no positive effect on neutropenia, which is fatal for these patients. Recently, the pathophysiologic mechanism of the neutrophil dysfunction and neutropenia in GSD Ib has been found, and the treatment with the SGLT2 inhibitor empaglifozin is now well established. In 2020, SGLT2 inhibitor empagliflozin started to be used as a promising efficient remover of 1,5AG6P in neutrophil of GSD Ib patients worldwide. However, it is necessary to consider long-term utility and safety of a novel treatment.ResultsIn this study, we retrospectively examined the clinical manifestations, biochemical examination results, genotypes, long-term outcomes and follow-up of thirty-five GSD Ib children who visited our department since 2009. Fourteen patients among them underwent empagliflozin treatment since 2020. This study is the largest cohort of pediatric GSD Ib patients in China as well as the largest cohort of pediatric GSD Ib patients treated with empagliflozin in a single center to date. The study also discussed the experience of long-term management on pediatric GSD Ib patients.ConclusionEmpagliflozin treatment for pediatric GSD Ib patients is efficient and safe. Increase of urine glucose is a signal for pharmaceutical effect, however attention to urinary infection and hypoglycemia is suggested.

Current understanding on pathogenesis and effective treatment of glycogen storage disease type Ib with empagliflozin: new insights coming from diabetes for its potential implications in other metabolic disorders.

Glycogen storage type Ib (GSDIb) is a rare inborn error of metabolism caused by glucose-6-phosphate transporter (G6PT, SLC37A4) deficiency. G6PT defect results in excessive accumulation of glycogen and fat in the liver, kidney, and intestinal mucosa and into both glycogenolysis and gluconeogenesis impairment. Clinical features include hepatomegaly, hypoglycemia, lactic acidemia, hyperuricemia, hyperlipidemia, and growth retardation. Long-term complications are liver adenoma, hepatocarcinoma, nephropathy and osteoporosis. The hallmark of GSDIb is neutropenia, with impaired neutrophil function, recurrent infections and inflammatory bowel disease. Alongside classical nutritional therapy with carbohydrates supplementation and immunological therapy with granulocyte colony-stimulating factor, the emerging role of 1,5-anhydroglucitol in the pathogenesis of neutrophil dysfunction led to repurpose empagliflozin, an inhibitor of the renal glucose transporter SGLT2: the current literature of its off-label use in GSDIb patients reports beneficial effects on neutrophil dysfunction and its clinical consequences. Surprisingly, this glucose-lowering drug ameliorated the glycemic and metabolic control in GSDIb patients. Furthermore, numerous studies from big cohorts of type 2 diabetes patients showed the efficacy of empagliflozin in reducing the cardiovascular risk, the progression of kidney disease, the NAFLD and the metabolic syndrome. Beneficial effects have also been described on peripheral neuropathy in a prediabetic rat model. Increasing evidences highlight the role of empagliflozin in regulating the cellular energy sensors SIRT1/AMPK and Akt/mTOR, which leads to improvement of mitochondrial structure and function, stimulation of autophagy, decrease of oxidative stress and suppression of inflammation. Modulation of these pathways shift the oxidative metabolism from carbohydrates to lipids oxidation and results crucial in reducing insulin levels, insulin resistance, glucotoxicity and lipotoxicity. For its pleiotropic effects, empagliflozin appears to be a good candidate for drug repurposing also in other metabolic diseases presenting with hypoglycemia, organ damage, mitochondrial dysfunction and defective autophagy.

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.

Cytokine profiling in patients with hepatic glycogen storage disease: Are there clues for unsolved aspects?

Hepatic Glycogen Storage Diseases (GSD) are rare genetic disorders in which the gluconeogenesis pathway is impaired. Cytokines control virtually every aspect of physiology and may help to elucidate some unsolved questions about phenotypes presented by GSD patients. This was an exploratory study in which 27 GSD patients on treatment (Ia=16, Ib=06, III=02, IXα=03) and 24 healthy age- and sex-matched subjects had plasma samples tested for a panel of 20 cytokines (G-CSF,GM-CSF, IL-1α,IL-1β, IL-4, IL-6, IL-8, IL-10, IL-13, IL-17A, GRO, IP-10/CXCL10, MCP-1/CCL2, MIP-1α/CCL3, MIP-1β/CCL4, MDC/CCL22, IFN-γ, TNF-α, TNF-β, VEGF) through a multiplex kit and analyzed in comparison to controls and among patients, regarding to clinical features as anemia, hepatic adenocarcinoma and triglyceride levels. Patients (GSD-Ia/III/IX) presented reduced levels of IL-4 (p=0.040), MIP-1α/CCL3 (p=0.003), MDC/CCL22 (p<0.001), TNF-β (p=0.045) and VEGF (p=0.043) compared to controls. When different types of GSD were compared, G-CSF was higher in GSD-Ib than -Ia (p<0.001) and than -III/IX (p=0.033) patients; IL-10 was higher in GSD-Ib than in GSD-Ia patients (p=0.019); and GSD-III/IX patients had increased levels of IP-10/CXCL10 than GSD-Ib patients (p=0.019). When GSD-I patients were gathered into the same group and compared with GSD-III/IX patients, IP10/CXCL10 and MCP-1 were higher in the latter group (p=0.005 and p=0.013, respectively). GSD-I patients with anemia presented higher levels of IL-4 and MIP-1α in comparison with patients who had not. Triglyceride level was correlated with neutrophil count and MDC levels on GSD-Ia patients without HCA. Altogether, altered levels of cytokines in GSD-I patients reflect an imbalance in immunoregulation process. This study also indicates that neutrophils and some cytokines are affected by triglyceride levels, and future studies on the theme should consider this variable.

Molecular mechanism underlying impaired hepatic autophagy in glycogen storage disease type Ib.

Type Ib glycogen storage disease (GSD-Ib) is caused by a deficiency in the glucose-6-phosphate (G6P) transporter (G6PT) that translocates G6P from the cytoplasm into the endoplasmic reticulum lumen, where the intraluminal G6P is hydrolyzed to glucose by glucose-6-phosphatase-α (G6Pase-α). Clinically, GSD-Ib patients manifest a metabolic phenotype of impaired blood glucose homeostasis and a long-term risk of hepatocellular adenoma/carcinoma (HCA/HCC). Studies have shown that autophagy deficiency contributes to hepatocarcinogenesis. In this study, we show that G6PT deficiency leads to impaired hepatic autophagy evident from attenuated expression of many components of the autophagy network, decreased autophagosome formation and reduced autophagy flux. The G6PT-deficient liver displayed impaired sirtuin 1 (SIRT1) and AMP-activated protein kinase (AMPK) signaling, along with reduced expression of SIRT1, forkhead boxO3a (FoxO3a), liver kinase B-1 (LKB1) and the active p-AMPK. Importantly, we show that overexpression of either SIRT1 or LKB1 in G6PT-deficient liver restored autophagy and SIRT1/FoxO3a and LKB1/AMPK signaling. The hepatosteatosis in G6PT-deficient liver decreased SIRT1 expression. LKB1 overexpression reduced hepatic triglyceride levels, providing a potential link between LKB1/AMPK signaling upregulation and the increase in SIRT1 expression. In conclusion, downregulation of SIRT1/FoxO3a and LKB1/AMPK signaling underlies impaired hepatic autophagy which may contribute to HCA/HCC development in GSD-Ib. Understanding this mechanism may guide future therapies.

The overall benefits of empagliflozin treatment in adult siblings with glycogen storage disease type Ib: one year experience.

IntroductionRecently published case reports suggest the benefit of empagliflozin use in subjects with glycogen storage disease Ib (GSD Ib).MethodsWe present the clinical and laboratory data of 2 adult brothers with GSD Ib treated with empagliflozin for 12 months.ResultsThere was no severe infection during administration of empagliflozin. The improvement of clinical symptoms of inflammatory bowel disease and arthritis along with reduction in serum CRP levels and urinary albumin excretion was noted. Neutrophil count increased, allowing for reduction or temporary withdrawal of G-CSF treatment.ConclusionsEmpagliflozin may be a new safe treatment in GSD Ib patients with an advanced stage of the disease.

Understanding the role of SGLT2 inhibitors in glycogen storage disease type Ib: the experience of one UK centre

BackgroundGlycogen storage disease type Ib (GSD Ib) is a severe disorder of carbohydrate metabolism due to bi-allelic variants in SLC37A4. It is associated with neutropaenia and neutrophil dysfunction, which has recently been attributed to the accumulation of 1,5-anhydroglucitol-6-phosphate (1,5AG6P) within neutrophils. Treatment with sodium-glucose co-transporter-2 (SGLT2) inhibitors, such as empagliflozin, is a novel therapy that reduces 1,5-anhydroglucitol (1,5AG) in plasma.ResultsWe report our experience in treating 8 paediatric GSD Ib patients with empagliflozin with a cumulative treatment time greater than 12 years. Treatment with a median dose of 5 mg (0.22 mg/kg height weight) of empagliflozin resulted in improvement in bowel health, growth, and laboratory parameters. Plasma 1,5AG levels reduced by a median of 78%. Baseline 1,5AG levels in our cohort were higher than in adult patients with GSD Ib. Hypoglycaemia on empagliflozin treatment occurred in 50% of our cohort.ConclusionWe report the largest single centre cohort of GSD Ib patients treated with empagliflozin to date. Treatment with SGLT2 inhibitors is a novel and favourable treatment option for neutropaenia and neutrophil dysfunction in GSD Ib. We suggest a low starting dose of empagliflozin with careful titration due to the risk of hypoglycaemia. The interpretation of 1,5AG levels and their role in treatment monitoring is yet to be established, and requires ongoing research.

Crohn disease-like enterocolitis remission after empagliflozin treatment in a child with glycogen storage disease type Ib: a case report

BackgroundBesides major clinical/biochemical features, neutropenia and inflammatory bowel disease (IBD) constitute common complications of Glycogen storage disease type Ib (GSD Ib). However, their management is still challenging. Although previous reports have shown benefit of empagliflozin administration on neutropenia, no follow-up data on bowel (macro/microscopic) morphology are available. We herein present for the first time longitudinal assessment of bowel morphology in a GSD Ib child suffering from Crohn disease-like enterocolitis treated with empagliflozin.Case presentationA 14-year-old boy with GSD Ib and severe IBD was (off-label) treated with empagliflozin (20 mg/day) after informed oral and written consent was obtained from the patient’s parents. No adverse events were noted. Clinical symptoms and stool frequency improved within the first week of treatment. Pediatric Crohn disease activity index (PCDAI) normalised within the first month of treatment. Abdomen magnetic resonance imaging (MRI) performed 3 months after treatment initiation showed dramatic decrease in disease activity and length. Similar findings were reported on histology at 5.5 months. At 7.5 months hemoglobin levels normalised and fecal calprotectin almost normalised. Improved neutrophil count, metabolic control and quality of life were also noted. G-CSF dose was decreased by 33% and the patient was partly weaned from tube feeding.ConclusionsThis is the first report presenting extensive gastrointestinal morphology follow-up in a GSD Ib patient receiving empagliflozin. The present case suggests that empagliflozin can be safe and effective in inducing IBD remission in GSD Ib patients and can even postpone surgery. Future studies are required to confirm its effect over time and assess its benefit in various disease stages. The development of an international collaborating networks for systematic data collection is worthy.

MO036DAPAGLIFLOZIN RESCUES THE RENAL PHENOTYPE OF GLYCOGEN STORAGE DISEASE TYPE IB

Abstract Background and Aims Glycogenosis I type b (GsdI-b) is a rare metabolic disease and immune disorder characterized by hepato-renal glycogen accumulation caused by a deficiency in the Glucose-6-phosphate transporter (G6PT). G6PT transports glucose-6-phosphate (G6P) from cytoplasm to endoplasmic reticulum (ER) where a G6Pase catalyses the hydrolysis of G6P in glucose and phosphate. G6PT deficiency lead to impaired glucose homeostasis, myeloid disfunction and long-term risk of hepatocellular adenomas. No causal therapy is so far available for GSDI-b patients besides a dietary approach to control glycemia and the use of Granulocyte Colony-Stimulating Factor (GCSF) to improve neutropenia. Over time, these supports increase the chronicity of GSDI-b with some complications. A mouse model recapitulating the GDSI-b has been recently generated by inducing G6PT suppression after tamoxifen injection. Here, we characterized the renal phenotype of TM-G6PT-/- mice model focusing on the molecular mechanisms that lead to renal dysfunction. Finally, we evaluated the efficiency of Dapagliflozin, a selective inhibitor of SGLT2, on kidney functions in terms of therapeutic effect. Method Machine learning approach to computer based evaluation of renal morphology was used to analyze the renal sections from TM-G6PT-/- treated with or without dapagliflozin. Results: G6PT is expressed in all renal zones and a severe downregulation of G6PT mRNA expression in whole kidney of TM-G6PT-/- mice can be observed. TM-G6PT-/- mice show tubular vacuolization and overall cellular dysfunction of PT due to a high glycogen accumulation. TM-G6PT-/- mice manifest glycosuria, phosphaturia and polyuria associated with a down regulation of main transporters of PT cells. The urine concentrating defect is due to a primarily role of G6PT in CNT/CD cells confirmed by a downregulation of AQP2, main water channel along CD segments. This mouse model recapitulates the human GSD-Ib renal phenotype characterized by a disfunction of PT but also CNT/CD cells. In order to evaluate whether targeting the glucose metabolism would improve the renal phenotype of these mice we limited glucose flux across the apical membrane of PT cells, applying the SGLT2-inhibitor dapagliflozin to reduce new glycogen formation. After one month of treatment, Dapagliflozin prevents glycogen accumulation in TM-G6PT-/- mice and ameliorates the main dysregulated markers of PT function. This finding was paralleled by an improvement of the histological features of kidney morphology in dapagliflozin treated TM-G6PT-/- mice. Conclusion Our data provide evidence that treatment with dapagliflozin ameliorates intracellular glycogen storage and improves the renal functions in TM-G6PT-/- mice.

Imbalanced cortisol concentrations in glycogen storage disease type I: evidence for a possible link between endocrine regulation and metabolic derangement

BackgroundGlycogen storage disease type I (GSDI) is an inborn error of carbohydrate metabolism caused by mutations of either the G6PC gene (GSDIa) or the SLC37A4 gene (GSDIb). Glucose 6-phosphate (G6P) availability has been shown to modulate 11β-hydroxysteroid dehydrogenase type 1 (11βHSD1), an ER-bound enzyme catalyzing the local conversion of inactive cortisone into active cortisol. Adrenal cortex assessment has never been performed in GSDI. The aim of the current study was to evaluate the adrenal cortex hormones levels in GSDI patients.MethodsSeventeen GSDI (10 GSDIa and 7 GSDIb) patients and thirty-four age and sex-matched controls were enrolled. Baseline adrenal cortex hormones and biochemical markers of metabolic control serum levels were analyzed. Low dose ACTH stimulation test was also performed.ResultsBaseline cortisol serum levels were higher in GSDIa patients (p = 0.042) and lower in GSDIb patients (p = 0.041) than controls. GSDIa patients also showed higher peak cortisol response (p = 0.000) and Cortisol AUC (p = 0.029). In GSDIa patients, serum cholesterol (p = 0.000), triglycerides (p = 0.000), lactate (p = 0.000) and uric acid (p = 0.008) levels were higher and bicarbonate (p = 0.000) levels were lower than controls. In GSDIb patients, serum cholesterol levels (p = 0.016) were lower and lactate (p = 0.000) and uric acid (p = 0.000) levels were higher than controls. Baseline cortisol serum levels directly correlated with cholesterol (ρ = 0.65, p = 0.005) and triglycerides (ρ = 0.60, p = 0.012) serum levels in GSDI patients.ConclusionsThe present study showed impaired cortisol levels in GSDI patients, with opposite trend between GSDIa and GSDIb. The otherwise preserved adrenal cortex function suggests that this finding might be secondary to local deregulation rather than hypothalamo-pituitary-adrenal axis dysfunction in GSDI patients. We hypothesize that 11βHSD1 might represent the link between endocrine regulation and metabolic derangement in GSDI, constituting new potential therapeutic target in GSDI patients.

Impact of genotype on neutropenia in a large cohort of Serbian patients with glycogen storage disease type Ib

BackgroundGlycogen storage disease type Ib (GSD-Ib) is an inherited metabolic disorder caused by autosomal recessive mutations in SLC37A4 coding for the glucose-6-phosphate transporter. Neutropenia represents major feature of GSD-Ib along with metabolic disturbances. Previous research in GSD-Ib patients did not reveal significant genotype-phenotype correlation. Our objective was to explore the frequency and severity of neutropenia and it's complications in relation to genotype of GSD-Ib patients. MethodsWe estimated cumulative incidence of neutropenia and severe neutropenia, relation of genotype to absolute neutrophil count (ANC), and dynamics of ANC during serious bacterial infections (SBI) in a cohort of Serbian GSD Ib patients. Impact of genotype on GSD Ib-related inflammatory bowel disease (IBD) was also assessed. ResultsAbsolute neutrophil count (ANC) < 1500/mm3 was present in all 33 patients, with severe neutropenia (ANC<500/mm3) occurring in 60.6% of patients. The median age at neutropenia onset was 24 months, while severe neutropenia developed at median of 4.5 years. The ANC was elevated during 90.5% episodes of SBI. Genotypes c.81T>A/c.785G>A and c.81T>A/c.1042_1043delCT are associated with earlier onset of neutropenia. Patients carrying c.785G>A mutation express a higher capacity for ANC increase during SBI. Inflammatory bowel disease was diagnosed in 8 patients (24.2% of total) with median age of onset at 7 years. Risk for IBD occurrence was not significantly affected by gender, genotype and severity of neutropenia. ConclusionsWe may conclude that certain mutations in SLC37A4 influence the risk for severe neutropenia occurrence but also affect the capacity to increase ANC during SBI.

CRISPR/Cas9 genome editing of SLC37A4 gene elucidates the role of molecular markers of endoplasmic reticulum stress and apoptosis in renal involvement in glycogen storage disease type Ib

Glycogen storage disease type Ib (GSD Ib) is an autosomal recessive disorder, caused by a deficiency of ubiquitously expressed SLC37A4 protein. Deficiency of SLC37A4 leads to abnormal storage of glycogen in the liver and kidneys, resulting in long-term complications of renal disease and hepatocellular adenomas, whose mechanisms are poorly understood. Molecular markers of the adaptive responses to the metabolic stress caused by a deficiency of SLC37A4, such as markers related to the endoplasmic reticulum (ER) stress and unfolded protein response (UPR), have not been extensively studied. The aim of this study was to investigate the expression of molecular markers of the UPR response and apoptosis related to a deficiency of SLC37A4 in kidney cells. For that purpose, we intended to establish a human kidney cell model system for GSD Ib. The novel variant c.248G>A, found in GSD Ib patients, was introduced into the Flp-In™T-REx™-293 cell line using CRISPR/Cas9-mediated precise gene editing method, resulting in significant decrease of SLC37A4 gene expression. In this model system we used RT-qPCR analysis to investigate the expression of molecular markers of the UPR response (ATF4, DDIT3, HSPA5, and XBP1s) and apoptosis (BCL2, BAX). We demonstrated that under chronic metabolic stress conditions caused by SLC37A4 deficiency, the ER stress-induced UPR was triggered, resulting in suppression of the UPR molecular markers and cell survival promotion (decreased expression levels of ATF4, DDIT3, HSPA5, with the exception of XBP1s). However, persistent metabolic stress overrides an adaptation and induces apoptosis through increased expression of pro-apoptotic markers (decreased ratio of BCL2/BAX genes). We established a cellular model system characterized by a deficiency of SLC37A4, which presents pathological manifestations of GSD Ib in the kidney. Expression analysis in a novel model system supports the hypothesis that renal dysfunction in the GSD Ib is partly due to the ER stress and increased apoptosis.

Insulin-resistance in glycogen storage disease type Ia: linking carbohydrates and mitochondria?

Glycogen storage disease type I (GSDI) is an inborn error of carbohydrate metabolism caused by mutations of either the G6PC gene (GSDIa) or the SLC37A4 gene (GSDIb). GSDIa patients are at higher risk of developing insulin-resistance (IR). Mitochondrial dysfunction has been implicated in the development of IR. Mitochondrial dysfunction can demonstrate abnormalities in plama acylcarnitines (ACs) and urine organic acids (UOA). The aim of the study was to investigate the presence of mitochondrial impairment in GSDI patients and its possible connection with IR. Fourteen GSDIa, seven GSDIb patients, 28 and 14 age and sex-matched controls, were enrolled. Plasma ACs, UOA, and surrogate markers of IR (HOMA-IR, QUICKI, ISI, VAI) were measured. GSDIa patients showed higher short-chain ACs and long-chain ACs levels and increased urinary excretion of lactate, pyruvate, 2-ketoglutarate, 3-methylglutaconate, adipate, suberate, aconitate, ethylmalonate, fumarate, malate, sebacate, 4-octenedioate, 3OH-suberate, and 3-methylglutarate than controls (p < 0.05). GSDIb patients showed higher C0 and C4 levels and increased urinary excretion of lactate, 3-methylglutarate and suberate than controls (p < 0.05). In GSDIa patients C18 levels correlated with insulin serum levels, HOMA-IR, QUICKI, and ISI; long-chain ACs levels correlated with cholesterol, triglycerides, ALT serum levels, and VAI. Increased plasma ACs and abnormal UOA profile suggest mitochondrial impairment in GSDIa. Correlation data suggest a possible connection between mitochondrial impairment and IR. We hypothesized that mitochondrial overload might generate by-products potentially affecting the insulin signaling pathway, leading to IR. On the basis of the available data, the possible pathomechanism for IR in GSDIa is proposed.

Type I glycogen storage diseases: disorders of the glucose-6-phosphatase/glucose-6-phosphate transporter complexes.

Disorders of the glucose-6-phosphatase (G6Pase)/glucose-6-phosphate transporter (G6PT) complexes consist of three subtypes: glycogen storage disease type Ia (GSD-Ia), deficient in the liver/kidney/intestine-restricted G6Pase-α (or G6PC); GSD-Ib, deficient in a ubiquitously expressed G6PT (or SLC37A4); and G6Pase-β deficiency or severe congenital neutropenia syndrome type 4 (SCN4), deficient in the ubiquitously expressed G6Pase-β (or G6PC3). G6Pase-α and G6Pase-β are glucose-6-phosphate (G6P) hydrolases with active sites lying inside the endoplasmic reticulum (ER) lumen and as such are dependent upon the G6PT to translocate G6P from the cytoplasm into the lumen. The tissue expression profiles of the G6Pase enzymes dictate the disease's phenotype. A functional G6Pase-α/G6PT complex maintains interprandial glucose homeostasis, while a functional G6Pase-β/G6PT complex maintains neutrophil/macrophage energy homeostasis and functionality. G6Pase-β deficiency is not a glycogen storage disease but biochemically it is a GSD-I related syndrome (GSD-Irs). GSD-Ia and GSD-Ib patients manifest a common metabolic phenotype of impaired blood glucose homeostasis not shared by GSD-Irs. GSD-Ib and GSD-Irs patients manifest a common myeloid phenotype of neutropenia and neutrophil/macrophage dysfunction not shared by GSD-Ia. While a disruption of the activity of the G6Pase-α/G6PT complex readily explains why GSD-Ia and GSD-Ib patients exhibit impaired glucose homeostasis, the basis for neutropenia and myeloid dysfunction in GSD-Ib and GSD-Irs are only now starting to be understood. Animal models of all three disorders are now available and are being exploited to both delineate the disease more precisely and develop new treatment approaches, including gene therapy.

Molecular mechanisms of neutrophil dysfunction in glycogen storage disease type Ib

AbstractGlycogen storage disease type Ib (GSD-Ib) is an autosomal-recessive syndrome characterized by neutropenia and impaired glucose homeostasis resulting from a deficiency in the glucose-6-phosphate (G6P) transporter (G6PT). The underlying cause of GSD-Ib neutropenia is an enhanced neutrophil apoptosis, but patients also manifest neutrophil dysfunction of unknown etiology. Previously, we showed G6PT interacts with the enzyme glucose-6-phosphatase-β (G6Pase-β) to regulate the availability of G6P/glucose in neutrophils. A deficiency in G6Pase-β activity in neutrophils impairs both their energy homeostasis and function. We now show that G6PT-deficient neutrophils from GSD-Ib patients are similarly impaired. Their energy impairment is characterized by decreased glucose uptake and reduced levels of intracellular G6P, lactate, adenosine triphosphate, and reduced NAD phosphate, whereas functional impairment is reflected in reduced neutrophil respiratory burst, chemotaxis, and calcium mobilization. We further show that the mechanism of neutrophil dysfunction in GSD-Ib arises from activation of the hypoxia-inducible factor-1α/peroxisome-proliferators–activated receptor-γ pathway.

Adeno-associated virus gene therapy prevents hepatocellular adenoma in murine model of glycogen storage disease type Ia

Adeno-associated virus gene therapy prevents hepatocellular adenoma in murine model of glycogen storage disease type Ia

Mutation in the SLC37A4 gene of glycogen storage disease type Ib in 15 families of the mainland of China

Glycogen storage disease type Ib (GSDIb, MIM: 232220) is an autosomal recessive inborn error of metabolism caused by deficiency of the glucose-6-phosphate translocase. The clinical manifestations include symptoms and signs of both the typical GSDIa, including hepatomegaly, fasting hypoglycemia, lactic acidemia and hyperlipidemia, and the dysfunction of neutrophils of recurrent infection and neutropenia. More than 84 mutations have been identified since the discovery of the SLC37A4 gene as the disease causing gene. Up to date, 5 mutations in 4 Chinese patients were reported from Hong Kang and Taiwan. In order to see the spectrum of the SLC37A4 gene mutations and the correlation between genotype and phenotype in patients with GSDIb of the mainland of China, the authors investigated 17 GSDIb patients from 15 families in this study. Data of 17 patients from 12 provinces, 11 male and 6 female, aged 6 months to 35 years, were collected from the genetic clinics of Peking Union Medical College Hospital from Oct. 2006 to Mar. 2009. All of them were Han Chinese in ethnicity. Consanguineous status was confirmed in 2 unrelated patients. All patients were presented with hepatomegaly, fasting hypoglycemia, lactic acidemia, hyperlipidemia and neutropenia with variable frequency of infections. The full coding exons, their relevant exon-intron boundaries, and the 5'- and 3'-flanking regions of the SLC37A4 gene were amplified and directly sequenced. RT-PCR was performed to verify the effect of the 2 novel splicing mutations. A total of 11 mutations were identified in 15 families. Four mutations, p.Gly149Glu, p.Pro191Leu, p.Arg415X and c.1042_1043 del CT, were previously reported, and seven mutations, p. Leu23Arg, p.Gly115Arg, p.Gly281Val, p.Arg415Gly, c.784 + 1G > A, c.870 + 5G > A and c.1014_1120del107, were novel. The frequent mutations are p.Pro191Leu, p.Gly149Glu and c.870 + 5G > A, accounting for 37%, 15% and 11% of mutant alleles respectively. RT-PCR analysis of novel mutation c.784 + 1G > A confirmed the splicing of exon 5 of 159 bp, causing inframe deletion. While mutation c.870 + 5G > A was proved to cause exon 6, 86 bp, deletion causing frame-shift. Among 15 families, 12 genotypes were identified, including 3 with homozygous mutation and 9 with compound heterozygous mutations. Homozygous p.Pro191Leu mutation was the only genotype detected in more than 1 family and was found in 4 unrelated families, including 1 patient from consanguineous marriage. A total of 11 SLC37A4 gene mutations were identified in 15 families of the mainland of China. The frequent mutations are p.Pro191Leu, p.Gly149Glu and c.870 + 5G > A. The number of Chinese SLC37A4 gene mutations was extended from 5 to 14.

Neutrophil stress and apoptosis underlie myeloid dysfunction in glycogen storage disease type Ib

AbstractGlycogen storage disease type Ib (GSD-Ib) is caused by a deficiency in the glucose-6-phosphate (G6P) transporter (G6PT) that works with a liver/kidney/intestine–restricted glucose-6-phosphatase-α (G6Pase-α) to maintain glucose homeostasis between meals. Clinically, GSD-Ib patients manifest disturbed glucose homeostasis and neutrophil dysfunctions but the cause of the latter is unclear. Neutrophils express the ubiquitously expressed G6PT and G6Pase-β that together transport G6P into the endoplasmic reticulum (ER) lumen and hydrolyze it to glucose. Because we expected G6PT-deficient neutrophils to be unable to produce endogenous glucose, we hypothesized this would lead to ER stress and increased apoptosis. Using GSD-Ib mice, we showed that GSD-Ib neutrophils exhibited increased production of ER chaperones and oxidative stress, consistent with ER stress, increased annexin V binding and caspase-3 activation, consistent with an increased rate of apoptosis. Bax activation, mitochondrial release of proapoptotic effectors, and caspase-9 activation demonstrated the involvement of the intrinsic mitochondrial pathway in these processes. The results demonstrate that G6P translocation and hydrolysis are required for normal neutrophil functions and support the hypothesis that neutrophil dysfunction in GSD-Ib is due, at least in part, to ER stress and increased apoptosis.

Myasthenia gravis in a patient affected by glycogen storage disease type Ib: A further manifestation of an increased risk for autoimmune disorders?

Glycogen storage disease type Ib (GSD Ib, OMIM 232220) is an inborn disorder of glucose metabolism, caused by mutations in the G6PT gene, encoding a glucose 6-phosphate transporter (G6PT). GSD Ib is mainly associated with fasting hypoglycaemia and hepatomegaly. Most GSD Ib patients also show neutropenia and neutrophil dysfunction and therefore are at risk of developing severe infections and inflammatory bowel disease (IBD). An increased risk for autoimmune disorders, such as thyroid autoimmunity and Crohn-like disease, has also been demonstrated, but no systematic study on the prevalence of autoimmune disorders in GSD Ib patients has ever been performed. We describe a 25-year-old patient affected by GSD Ib who developed 'seronegative' myasthenia gravis (MG), presenting with bilateral eyelid ptosis, diplopia, dysarthria, severe dysphagia, dyspnoea and fatigue. The repetitive stimulation of peripheral nerves test showed signs of exhaustion of neuromuscular transmission, particularly evident in the cranial area. Even in the absence of identifiable anti-acetylcholine receptor antibodies, seronegative MG is considered an autoimmune disorder and may be related to the disturbed immune function observed in GSD Ib patients.

Type I Glycogen Storage Diseases: Disorders of the Glucose-6- Phosphatase Complex

Glycogen storage disease type I (GSD-I) is a group of autosomal recessive disorders with an incidence of 1 in 100,000. The two major subtypes are GSD-Ia (MIM232200), caused by a deficiency of glucose-6-phosphatase (G6Pase), and GSD-Ib (MIM232220), caused by a deficiency in the glucose-6-phosphate transporter (G6PT). Both G6Pase and G6PT are associated with the endoplasmic reticulum (ER) membrane. G6PT translocates glucose-6-phosphate (G6P) from the cytoplasm into the lumen of the ER, where G6Pase hydrolyses the G6P into glucose and phosphate. Together G6Pase and G6PT maintain glucose homeostasis. G6Pase is expressed in gluconeogenic tissues, the liver, kidney, and intestine. However G6PT, which transports G6P efficiently only in the presence of G6Pase, is expressed ubiquitously. This suggests that G6PT may play other roles in tissues lacking G6Pase. Both GSD-Ia and GSD-Ib patients manifest phenotypic G6Pase deficiency, characterized by growth retardation, hypoglycemia, hepatomegaly, nephromegaly, hyperlipidemia, hyperuricemia, and lactic academia and the current treatment is a dietary therapy. GSD-Ib patients also suffer from chronic neutropenia and functional deficiencies of neutrophils and monocytes, which is treated with granulocyte colony stimulating factor to restore myeloid function. The GSD-Ia and GSD-Ib genes have been cloned. To date, 76 G6Pase and 69 G6PT mutations have been identified in GSD-I patients. A database of the residual enzymatic activity retained by the G6Pase missense mutants is facilitating the correlation of the disease phenotype with the patients' genotype. While the molecular basis for the GSD-I disorders are now known and symptomatic therapies are available, many aspects of the diseases are still poorly understood, and there are no cures. Recently developed animal models of the disorders are now being exploited to delineate the disease more precisely and develop new, more causative therapies.