Glycogen storage diseases: New perspectives

Metabolic myopathies: functional evaluation by different exercise testing approaches

Metabolic myopathies are a clinically and etiologically heterogeneous group of disorders due to defects in muscular energy metabolism. They include glycogen storage diseases, fatty acid oxidation defects, and mitochondrial disorders. The typical manifestations of a metabolic myopathy are exercise-induced myalgias, exercise intolerance, and cramps. Evaluating subjects with such symptoms is not easy because of the frequent lack of clinical features. Exercise tests are, therefore, reliable screening tools. Here, we discuss the possible role of such exercise testing techniques in the diagnostic approach of a patient with suspected metabolic myopathy.

Targeted deletion of liver glucose-6 phosphatase mimics glycogen storage disease type 1a including development of multiple adenomas

BACKGROUND AND AIMS

Glycogen storage disease type 1a (GSD1a) is an inherited disease caused by a deficiency in the catalytic subunit of the glucose-6 phosphatase enzyme (G6Pase). GSD1a is characterized by hypoglycaemia, hyperlipidemia, and lactic acidosis with associated hepatic (including hepatocellular adenomas), renal, and intestinal disorders. A total G6pc (catalytic subunit of G6Pase) knock-out mouse model has been generated that mimics the human pathology. However, these mice rarely live longer than 3 months and long-term liver pathogenesis cannot be evaluated. Herein, we report the long-term characterization of a liver-specific G6pc knock-out mouse model (L-G6pc(-/-)).

METHODS

We generated L-G6pc(-/-) mice using an inducible CRE-lox strategy and followed up the development of hepatic tumours using magnetic resonance imaging.

RESULTS

L-G6pc(-/-) mice are viable and exhibit normoglycemia in the fed state. They develop hyperlipidemia, lactic acidosis, and uricemia during the first month after gene deletion. However, these plasmatic parameters improved after 6 months. L-G6pc(-/-) mice develop hepatomegaly with glycogen accumulation and hepatic steatosis. Using an MRI approach, we could detect hepatic nodules with diameters of less than 1 mm, 9 months after induction of deficiency. Hepatic nodules (1 mm) were detected in 30-40% of L-G6pc(-/-) mice at 12 months. After 18 months, all L-G6pc(-/-) mice developed multiple hepatocellular adenomas of 1-10 mm diameter.

CONCLUSIONS

This is the first report of a viable animal model of the hepatic pathology of GSD1a, including the late development of hepatocellular adenomas.

Glycogen storage disease type Ia in canines: a model for human metabolic and genetic liver disease

A canine model of Glycogen storage disease type Ia (GSDIa) is described. Affected dogs are homozygous for a previously described M121I mutation resulting in a deficiency of glucose-6-phosphatase-α. Metabolic, clinicopathologic, pathologic, and clinical manifestations of GSDIa observed in this model are described and compared to those observed in humans. The canine model shows more complete recapitulation of the clinical manifestations seen in humans including “lactic acidosis”, larger size, and longer lifespan compared to other animal models. Use of this model in preclinical trials of gene therapy is described and briefly compared to the murine model. Although the canine model offers a number of advantages for evaluating potential therapies for GSDIa, there are also some significant challenges involved in its use. Despite these challenges, the canine model of GSDIa should continue to provide valuable information about the potential for generating curative therapies for GSDIa as well as other genetic hepatic diseases.

Perinatal gene transfer to the liver

The liver acts as a host to many functions hence raising the possibility that any one may be compromised by a single gene defect. Inherited or de novo mutations in these genes may result in relatively mild diseases or be so devastating that death within the first weeks or months of life is inevitable. Some diseases can be managed using conventional medicines whereas others are, as yet, untreatable. In this review we consider the application of early intervention gene therapy in neonatal and fetal preclinical studies. We appraise the tools of this technology, including lentivirus, adenovirus and adeno-associated virus (AAV)-based vectors. We highlight the application of these for a range of diseases including hemophilia, urea cycle disorders such as ornithine transcarbamylase deficiency, organic acidemias, lysosomal storage diseases including mucopolysaccharidoses, glycogen storage diseases and bile metabolism. We conclude by assessing the advantages and disadvantages associated with fetal and neonatal liver gene transfer.

Adeno-associated virus-mediated correction of a canine model of glycogen storage disease type Ia

Glycogen storage disease type Ia (GSDIa; von Gierke disease; MIM 232200) is caused by a deficiency in glucose-6-phosphatase-alpha. Patients with GSDIa are unable to maintain glucose homeostasis and suffer from severe hypoglycemia, hepatomegaly, hyperlipidemia, hyperuricemia, and lactic acidosis. The canine model of GSDIa is naturally occurring and recapitulates almost all aspects of the human form of disease. We investigated the potential of recombinant adeno-associated virus (rAAV) vector-based therapy to treat the canine model of GSDIa. After delivery of a therapeutic rAAV2/8 vector to a 1-day-old GSDIa dog, improvement was noted as early as 2 weeks posttreatment. Correction was transient, however, and by 2 months posttreatment the rAAV2/8-treated dog could no longer sustain normal blood glucose levels after 1 hr of fasting. The same animal was then dosed with a therapeutic rAAV2/1 vector delivered via the portal vein. Two months after rAAV2/1 dosing, both blood glucose and lactate levels were normal at 4 hr postfasting. With more prolonged fasting, the dog still maintained near-normal glucose concentrations, but lactate levels were elevated by 9 hr, indicating that partial correction was achieved. Dietary glucose supplementation was discontinued starting 1 month after rAAV2/1 delivery and the dog continues to thrive with minimal laboratory abnormalities at 23 months of age (18 months after rAAV2/1 treatment). These results demonstrate that delivery of rAAV vectors can mediate significant correction of the GSDIa phenotype and that gene transfer may be a promising alternative therapy for this disease and other genetic diseases of the liver.

Glycogen storage disease type III with hypoketosis

A rare case of glycogen storage disease type III with unusually absent ketone body production during hypoglycemia is presented. A 10-month-old boy presented with asymptomatic hepatomegaly. GOT/GPT 2555/1160 IU/L, CK 302 IU/L, triglycerides 1223 mg/dL, cholesterol 702 mg/dL and uric acid 7.9 mg/dL. After a 9-hour fast, glucose was 27 mg/dL and adequate lipolysis without ketogenesis was observed (total/free carnitine 34.5/20 micromol/L, free fatty acids 1620 micromol/L and beta-hydroxybutyrate 172 micromol/L). Result of MCT (medium-chain triglycerides) load test: basal hydroxybutyrate 29 micromol/L rose to 5748 micromol/L. Treatment with a fat-restricted diet supplemented with formula containing MCT was initiated and the patient presented a satisfactory initial evolution. Three months later, CK were 3000 IU/L. Muscle biopsy was diagnostic of glycogenosis. Enzymatic activity in skin fibroblasts was 0% for amylo-1,6-glucosidase. The diagnosis of glycogenosis type III was established. Echocardiography performed at that time showed non-obstructive ventricular hypertrophy. Until now hypoketosis during hypoglycemia has only been described in glycogenosis type I.

[Glycogenosis type IV (Andersen disease). Clinical data, pathology, and genetics in a fatal perinatal case]

Here we report the case of a newborn with glycogenosis type IV (Andersen disease), who died shortly after birth. The diagnosis was established in the first instance by light microscopy and histochemistry, and subsequently ultrastructurally. DNA could be extracted from a fibroblast cell culture by sequencing the causative GBE1 gene (glycogen branching enzyme 1). Two compound heterozygous mutations in the gene were identified. The differential diagnosis should include Lafora disease as well as polyglucosan body disease. Since there is no effective therapy for glycogenosis type IV to date, prenatal diagnosis is mandatory.

Impaired glucose tolerance and predisposition to the fasted state in liver glycogen synthase knock-out mice

Conversion to glycogen is a major fate of ingested glucose in the body. A rate-limiting enzyme in the synthesis of glycogen is glycogen synthase encoded by two genes, GYS1, expressed in muscle and other tissues, and GYS2, primarily expressed in liver (liver glycogen synthase). Defects in GYS2 cause the inherited monogenic disease glycogen storage disease 0. We have generated mice with a liver-specific disruption of the Gys2 gene (liver glycogen synthase knock-out (LGSKO) mice), using Lox-P/Cre technology. Conditional mice carrying floxed Gys2 were crossed with mice expressing Cre recombinase under the albumin promoter. The resulting LGSKO mice are viable, develop liver glycogen synthase deficiency, and have a 95% reduction in fed liver glycogen content. They have mild hypoglycemia but dispose glucose less well in a glucose tolerance test. Fed, LGSKO mice also have a reduced capacity for exhaustive exercise compared with mice carrying floxed alleles, but the difference disappears after an overnight fast. Upon fasting, LGSKO mice reach within 4 h decreased blood glucose levels attained by control floxed mice only after 24 h of food deprivation. The LGSKO mice maintain this low blood glucose for at least 24 h. Basal gluconeogenesis is increased in LGSKO mice, and insulin suppression of endogenous glucose production is impaired as assessed by euglycemic-hyperinsulinemic clamp. This observation correlates with an increase in the liver gluconeogenic enzyme phosphoenolpyruvate carboxykinase expression and activity. This mouse model mimics the pathophysiology of glycogen storage disease 0 patients and highlights the importance of liver glycogen stores in whole body glucose homeostasis.

New loci associated with kidney function and chronic kidney disease

Chronic kidney disease (CKD) is a significant public health problem, and recent genetic studies have identified common CKD susceptibility variants. The CKDGen consortium performed a meta-analysis of genome-wide association data in 67,093 individuals of European ancestry from 20 predominantly population-based studies in order to identify new susceptibility loci for reduced renal function as estimated by serum creatinine (eGFRcrea), serum cystatin c (eGFRcys) and CKD (eGFRcrea < 60 ml/min/1.73 m(2); n = 5,807 individuals with CKD (cases)). Follow-up of the 23 new genome-wide-significant loci (P < 5 x 10(-8)) in 22,982 replication samples identified 13 new loci affecting renal function and CKD (in or near LASS2, GCKR, ALMS1, TFDP2, DAB2, SLC34A1, VEGFA, PRKAG2, PIP5K1B, ATXN2, DACH1, UBE2Q2 and SLC7A9) and 7 loci suspected to affect creatinine production and secretion (CPS1, SLC22A2, TMEM60, WDR37, SLC6A13, WDR72 and BCAS3). These results further our understanding of the biologic mechanisms of kidney function by identifying loci that potentially influence nephrogenesis, podocyte function, angiogenesis, solute transport and metabolic functions of the kidney.

Prolonged Inhibition of Glycogen Phosphorylase in Livers of Zucker Diabetic Fatty Rats Models Human Glycogen Storage Diseases

The preclinical efficacy and safety of GPi921, a glycogen phosphorylase inhibitor, was assessed following twenty-eight days of administration to Zucker Diabetic Fatty (ZDF) rats. The ZDF rat is an animal model of type 2 diabetes mellitus (TTDM) which develops severe hyperglycemia. Inhibition of glycogen phosphorylase throughout the duration of the study was demonstrated by reductions in twenty-four-hour glucose profiles and glycated hemoglobin levels. In addition, progression towards hyperglycemia was halted in treated but not control animals, which developed hyperglycemia over the twenty-eight days of the study. Biochemical and histopathological analysis revealed large increases in hepatic glycogen, which closely paralleled the development of hepatomegaly and ultimately resulted in increases in hepatic lipids. Furthermore, prolonged glycogen phosphorylase inhibition resulted in an increased incidence and severity of other adverse pathological findings in the liver, such as inflammation, fibrosis, hemorrhage, and necrosis. The observed biochemical and histopathological phenotype of the liver closely resembled that seen in severe cases of human glycogen storage diseases (GSD) and hepatic glycogenosis in poorly controlled diabetes mellitus. These findings revealed that although glycogen phosphorylase inhibitors are efficacious agents for the control of hyperglycemia, prolonged treatment might have the potential to cause significant clinical hepatic complications that resemble those seen in GSD and hepatic glycogenosis.

Oral giant cell granuloma in a patient with glycogen storage disease

The glycogen storage disease (GSD) is a group of inherited disorders that involve deficiencies in the enzymes that metabolize glycogen. The purpose of the present paper is to report a rare case of GSD type 1b that presented both peripheral and central giant cell granuloma, and to discuss the possible explanation for this unusual finding. The use of corticosteroids in the management of central giant cell granuloma is also demonstrated.

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

Introduction

Glycogen storage disease type Ib is an autosomal recessive transmitted disorder of glycogen metabolism caused by mutations in the glucose-6-phosphate translocase gene on chromosome 11q23 and leads to disturbed glycogenolysis as well as gluconeogenesis. Besides hepatomegaly, growth retardation, hypoglycemia, hyperlactatemia, hyperuricemia and hyperlipidemia, patients suffer from neutropenia associated with functional defects predisposing for severe infections. In order to attenuate these complications, long-term treatment with granulocyte colony-stimulating factor is common but this is associated with an increased risk for acute myeloid leukemia or myelodysplastic syndromes in patients with inherited bone marrow failures such as severe congenital neutropenia. Onset of these myeloid malignancies is linked to cytogenetic aberrations involving chromosome 7. In addition, granulocyte colony-stimulating factor is known to stimulate proliferation of monosomy 7 cells in vitro. To our knowledge, we report for the first time a case report of a patient with glycogen storage disease type Ib, who developed acute myeloid leukemia with a classical monosomy 7 and acute myeloid leukemia-associated translocation t(3;8)(q26;q24) after 14 years of continuous treatment with granulocyte colony-stimulating factor.

Case presentation

A 28-year-old Turkish man with glycogen storage disease type Ib was admitted to our department because of dyspnea and increasing fatigue. He also presented with gum bleeding, bone pain in his legs, night sweats, recurrent episodes of fever with temperatures up to 39°C and hepatosplenomegaly.

A blood count taken on the day of admission showed pancytopenia and a differential count displayed 30% blasts. A bone marrow biopsy was taken which showed a hypercellular marrow with dysplastic features of all three cell lines, while blast count was 20%. Classical cytogenetic analyses as well as fluorescence in situ hybridization showed a monosomy 7 with a translocation t(3;8)(q26;q24). Based on these findings, the diagnosis of acute myeloid leukemia was made.

Conclusion

Our observations suggest that bone marrow examinations including cytogenetic analysis should be carried out on a regular basis in patients with glycogen storage disease type Ib who are on long-term treatment with granulocyte colony-stimulating factor for severe neutropenia, since this treatment might also contribute to an increased risk for acute myeloid leukemia or myelodysplastic syndromes.

Nutritional therapy for glycogen storage diseases

Glycogen storage diseases (GSDs) are a group of inherited disorders characterized by enzyme defects that affect the glycogen synthesis and degradation cycle, classified according to the enzyme deficiency and the affected tissue. The understanding of GSD has increased in recent decades, and nutritional management of some GSDs has allowed better control of hypoglycemia and metabolic complications. However, growth failure and liver, renal, and other complications are frequent problems in the long-term outcome. Hypoglycemia is the main biochemical consequence of GSD type I and some of the other GSDs. The basis of dietary therapy is nutritional manipulation to prevent hypoglycemia and improve metabolic dysfunction, with the use of continuous nocturnal intragastric feeding or cornstarch therapy at night and foods rich in starches with low concentrations of galactose and fructose during the day and to prevent hypoglycemia during the night.