Metabolic Profiling in Human Fibroblasts Enables Subtype Clustering in Glycogen Storage Disease

Glycogen storage disease subtypes I and III (GSD I and GSD III) are monogenic inherited disorders of metabolism that disrupt glycogen metabolism. Unavailability of glucose in GSD I and induction of gluconeogenesis in GSD III modify energy sources and possibly, mitochondrial function. Abnormal mitochondrial structure and function were described in mice with GSD Ia, yet significantly less research is available in human cells and ketotic forms of the disease. We hypothesized that impaired glycogen storage results in distinct metabolic phenotypes in the extra- and intracellular compartments that may contribute to pathogenesis. Herein, we examined mitochondrial organization in live cells by spinning-disk confocal microscopy and profiled extra- and intracellular metabolites by targeted LC-MS/MS in cultured fibroblasts from healthy controls and from patients with GSD Ia, GSD Ib, and GSD III. Results from live imaging revealed that mitochondrial content and network morphology of GSD cells are comparable to that of healthy controls. Likewise, healthy controls and GSD cells exhibited comparable basal oxygen consumption rates. Targeted metabolomics followed by principal component analysis (PCA) and hierarchical clustering (HC) uncovered metabolically distinct poises of healthy controls and GSD subtypes. Assessment of individual metabolites recapitulated dysfunctional energy production (glycolysis, Krebs cycle, succinate), reduced creatinine export in GSD Ia and GSD III, and reduced antioxidant defense of the cysteine and glutathione systems. Our study serves as proof-of-concept that extra- and intracellular metabolite profiles distinguish glycogen storage disease subtypes from healthy controls. We posit that metabolite profiles provide hints to disease mechanisms as well as to nutritional and pharmacological elements that may optimize current treatment strategies.

Large animal models and new therapies for glycogen storage disease

Glycogen storage diseases (GSD), a unique category of inherited metabolic disorders, were first described early in the twentieth century. Since then, the biochemical and genetic bases of these disorders have been determined, and an increasing number of animal models for GSD have become available. At least seven large mammalian models have been developed for laboratory research on GSDs. These models have facilitated the development of new therapies, including gene therapy, which are undergoing clinical translation. For example, gene therapy prolonged survival and prevented hypoglycemia during fasting for greater than one year in dogs with GSD type Ia, and the need for periodic re-administration to maintain efficacy was demonstrated in that dog model. The further development of gene therapy could provide curative therapy for patients with GSD and other inherited metabolic disorders.

Exercise in muscle glycogen storage diseases

Glycogen storage diseases (GSD) are inborn errors of glycogen or glucose metabolism. In the GSDs that affect muscle, the consequence of a block in skeletal muscle glycogen breakdown or glucose use, is an impairment of muscular performance and exercise intolerance, owing to 1) an increase in glycogen storage that disrupts contractile function and/or 2) a reduced substrate turnover below the block, which inhibits skeletal muscle ATP production. Immobility is associated with metabolic alterations in muscle leading to an increased dependence on glycogen use and a reduced capacity for fatty acid oxidation. Such changes may be detrimental for persons with GSD from a metabolic perspective. However, exercise may alter skeletal muscle substrate metabolism in ways that are beneficial for patients with GSD, such as improving exercise tolerance and increasing fatty acid oxidation. In addition, a regular exercise program has the potential to improve general health and fitness and improve quality of life, if executed properly. In this review, we describe skeletal muscle substrate use during exercise in GSDs, and how blocks in metabolic pathways affect exercise tolerance in GSDs. We review the studies that have examined the effect of regular exercise training in different types of GSD. Finally, we consider how oral substrate supplementation can improve exercise tolerance and we discuss the precautions that apply to persons with GSD that engage in exercise.

Serum lipid and lipoprotein profile of patients with glycogen storage disease types I, III and IX

With current dietary therapy, life expectancy in glycogen storage disease (GSD) has improved considerably and more children reach adulthood. Notwithstanding intensive dietary therapy, moderate to severe hyperlipidaemia is still observed frequently. There is limited information about the type and extent of hyperlipidaemia. We studied the lipid profile in 20 patients, aged 8-54 years, of the three (types I, III and IX) most common forms of adult GSD. Hyperlipidaemia was shown to be type-specific, affecting predominantly patients with GSD type Ia, who showed marked combined hypercholesterolaemia and hypertriglyceridaemia. By contrast, a heterogeneous distribution of HDL was found in patients with GSD I and III. There was no significant difference in Apo Al and Apo B concentrations between groups. In addition, mass measurements of the fractions of VLDL1, VLDL2 and IDL were raised in all patients with GSD Ia by comparison with all other patients with GSD. Patients with GSD type Ia have lipid concentrations and individual mass measurements that are consistent with ranges found in patients who have a significant risk of atherosclerosis. Accumulated evidence, however, suggest GSD type Ia patients do not have an increased risk of atherosclerotic cardiovascular disease (CVD) but the reason remains unknown. Intervention to reduce their lipid levels could therefore be on the basis of seeking to prevent the risk of pancreatitis rather than that of CVD.

Combined liver-kidney transplantation in glycogen storage disease Ia: a case beyond the guidelines

Glycogen storage disease type Ia (GSD Ia) is a rare metabolic disorder due to hepatic glucose-6-phosphatase deficiency. Although great progress has been made in managing affected patients, severe hypoglycemia, lactic acidosis, hyperlipidemia, hepatic cytolysis, and impaired kidney function are frequent. Liver transplantation is the only radical treatment, for which the main indications are hepatic adenomatosis, hepatocellular carcinoma, or severe hepatic dysfunction. We present the case of a patient with end-stage renal disease without focal hepatic lesions and with moderate hepatic metabolic control, and we explain how combined liver-kidney transplantation (LKT) made it possible to correct the metabolic defects responsible for the impaired glucose homeostasis, liberalize the diet, and give birth to a healthy child after an uneventful pregnancy. Patients with end-stage renal disease that resulted from GSD Ia should be considered for LKT even in the absence of hepatic lesions with the aim of improving their quality of life.

The natural course of non–classic Pompe’s disease; a review of 225 published cases

Pompe's disease is a neuromuscular disorder caused by deficiency of lysosomal acid alpha-glucosidase. Recombinant human alpha- glucosidase is under evaluation as therapeutic drug. In light of this development we studied the natural course of cases not fitting the definition of classic infantile Pompe's disease. Our review of 109 reports including 225 cases shows a continuous spectrum of phenotypes. The onset of symptoms ranged from 0 to 71 years. Based on the available literature, no criteria to delineate clinical sub-types could be established.A common denominator of these cases is that first symptoms were related to or caused by muscle weakness. In general, patients with a later onset of symptoms seemed to have a better prognosis. Respiratory failure was the most frequent cause of death. CK, LDH, ASAT, ALAT and muscle glycogen levels were frequently but not always elevated. In most cases a muscle biopsy revealed lysosomal pathology, but normal muscle morphology does not exclude Pompe's disease. In 10% of the cases in which the enzyme assay on leukocytes was used, a normal alpha-glucosidase activity was reported. Data on skeletal muscle strength and function, pulmonary function, disability, handicap and quality of life were insufficiently reported in the literature. Studies of non-classic Pompe's disease should focus on these aspects, before enzyme replacement therapy becomes generally available.

Liver glycogenoses: are they a possible cause of polyneuropathy? A cross-sectional study

We encountered two children suffering from liver glycogenoses (GSD) over a period of 5 years (1992-1997) who presented with a demyelinating peripheral neuropathy diagnosed by electromyography (EMG) and nerve conduction studies (NCV). The aim of the study was to evaluate the involvement of muscle and motor nerve in children suffering from liver glycogenoses. In a cross-sectional study, 22 children suffering from liver GSD (with no current neurological symptoms) and 20 age- and sex- matched clinically free children (control group) underwent creatine phospho-kinase (CPK), EMG, and NCV studies. Abnormal EMG and/or NCV studies were found in 11 children. Six (27.27 per cent) were found to have axonopathy, three (13.63 per cent) demyelinating polyneuropathy, and two (9.1 per cent) had mixed axonal and demyelinating neuropathy. Two children with axonopathy had GSD type VI, another had GSD type IV, and three had GSD of undiagnosed type. Three of those having a demyelinating polyneuropathy had GSD type III, another had GSD type IV, and the last had GSD of undiagnosed type. None were found to have a cardiomyopathy or a myopathy on EMG. This is the first report of neuropathy associated with GSD types III, IV, and VI in children. It might be discovered by EMG and/or NCV studies in a clinically, neurologically normal child suffering from GSD, or present as an acute polyneuropathy.

[Therapeutic trials for the patients with muscle glycogen storage diseases]

Muscle glycogen storage diseases (GSDs) are disorders of inborn error of metabolism, in which gene therapy restoring the deficient enzymes may ultimately cure the diseases. However, considering the pathophysiological basis of GSDs other treatments such as substrate supplementation, activation of the residual enzyme and enzyme replacement, are also important. Therapeutic trials in progress include the combined use of vitamin B6 and cornstarch for GSD type V, enzyme replacement therapy using rh-alpha-glucosidase for GSD type II, and ketogenic diet for GSD type IX.

[Mitochondrial and metabolic myopathies]

Mitochondrial and metabolic myopathies constitute a group of disorders characterised by abnormal muscular metabolism of energy. Most of these disorders are genetically transmitted. Recent progress in the field has led to spectacular advances in their classification and the understanding of the mechanisms involved, particularly in mitochondrail myopathies. Diagnosis can be made et any age; the patient can present manifestations that can be misleading for the clinician. Lipid myopathies and glycogenoses usually present as a myopathic syndrome associated with cramps, spasm and myalgia, with fatigue on effort. Acute episodes of rhabdomyolysis on effort can occur, with an attendant risk of renal failure. Mitochondrial myopathies have multi-organ manifestations and muscular involvement is not always at the forefront. Although diagnosis may be suggested by clinical factors, it should be confirmed by teams and laboratories that specialize in muscular disorders.

Mutations in the liver glycogen synthase gene in children with hypoglycemia due to glycogen storage disease type 0

Glycogen storage disease type 0 (GSD-0) is a rare form of fasting hypoglycemia presenting in infancy or early childhood and accompanied by high blood ketones and low alanine and lactate concentrations. Although feeding relieves symptoms, it often results in postprandial hyperglycemia and hyperlactatemia. The glycogen synthase (GS) activity has been low or immeasurable in liver biopsies, whereas the liver glycogen content has been only moderately decreased. To investigate whether mutations in the liver GS gene (GYS2) on chromosome 12p12.2 were involved in GSD-0, we determined the exon-intron structure of the GYS2 gene and examined nine affected children from five families for linkage of GSD-0 to the GYS2 gene. Mutation screening of the 16 GYS2 exons was done by single-strand conformational polymorphism (SSCP) and direct sequencing. Liver GS deficiency was diagnosed from liver biopsies (GS activity and glycogen content). GS activity in the liver of the affected children was extremely low or nil, resulting in subnormal glycogen content. After suggestive linkage to the GYS2 gene had been established (LOD score = 2.9; P < 0.01), mutation screening revealed several different mutations in these families, including a premature stop codon in exon 5 (Arg246X), a 5'-donor splice site mutation in intron 6 (G+1T--> CT), and missense mutations Asn39Ser, Ala339Pro, His446Asp, Pro479Gln, Ser483Pro, and Met491Arg. Seven of the affected children carried mutations on both alleles. The mutations could not be found in 200 healthy persons. Expression of the mutated enzymes in COS7 cells indicated severely impaired GS activity. In conclusion, the results demonstrate that GSD-0 is caused by different mutations in the GYS2 gene.

Morphologic findings in biopsied skeletal muscle and cultured fibroblasts from a female patient with Danon's disease (lysosomal glycogen storage disease without acid maltase deficiency)

A family is reported in which three members were affected by cardiomyopathy. Two members died unexpectedly in their second decade. Only a 23-year-old male suffered from the triad of clinical manifestations (cardiomyopathy, mental retardation and vacuolar myopathy). Morphologic findings and biochemical studies of his biopsied skeletal muscle and cultured fibroblasts confirmed lysosomal glycogen storage disease with normal acid maltase that was first described by Danon et al. In this study we demonstrated early morphologic changes, storage of glycogen and abnormal membranous structures in disorganized myofibers in biopsied skeletal muscle from the elder sister, who only showed cardiomyopathy clinically. The aggregation of autophagosomes was prominent in cultured fibroblasts, with an increased glycogen content. The activity of acid alpha-glucosidase was higher than normal. This is a systemic storage disease with different expression in males and females.

Reliability of histological criteria in glycogen storage disease of the liver

The histological criteria for the diagnosis of the hepatic glycogen storage diseases (GSDs) are well recognized. However, some biopsies do not have the characteristic features peculiar to their type and not all biopsies with GSD changes are confirmed by enzyme analysis. We reviewed the liver biopsies of 59 patients with clinically suspected GSD. The enzyme defects in 31 of 40 patients with GSD morphology were demonstrated by enzyme analysis. We describe the history and histology of the 9 patients with GSD morphology not confirmed by enzyme analysis, present the diagnoses of the 19 patients shown not to have a GSD, and evaluate the reliability of the morphological criteria used to distinguish the types of hepatic GSD. In this study the predictive value of a biopsy with GSD changes was 90%. Mosaicism, the most sensitive criterion in the diagnosis of GSD, is not type-specific. Fibrosis does not reliably distinguish between the GSD types and although nuclear hyperglycogenation and lipid are characteristic of type I GSD, these features are not diagnostic of any particular enzyme deficiency. The lack of morphological specificity implies that a complete enzyme analysis be performed on each biopsy. A normal enzyme analysis does not exclude a GSD and careful long-term follow-up may be necessary.

[Molecular pathology of hepatic glycogen storage disease]

Recent advances of molecular analyses of hepatic glycogen storage diseases have made some progress in understanding of glycogen metabolism. Glucose-6-phosphatase has been shown to comprise at least five different polypeptides, the catalytic subunit, a regulatory Ca2+ binding protein, three transport proteins (glucose-6-phosphate, phosphate/pyrophosphate, glucose). A defect of these protein could cause type I glycogenosis. Only cDNAs of the regulatory Ca2+ binding protein and glucose transport protein were cloned. In type III glycogenosis, using monospecific antibody, correlation of biochemical defects with myopathy and cardiomyopathy was investigated. In type VI glycogenosis, the cDNA of liver phosphorylase was cloned, which will be useful for delineating the molecular defect involved in the disease and family analysis. In type VIII glycogenosis, phosphorylase kinase deficiency, only subunits of muscle type (alpha, beta, gamma, delta) were cloned and clonings of hepatic type subunits were waited. In the near feature, hepatic glycogen storage disease and glycogen metabolism were reevaluated from the points of molecular defects.

[Hepatic glycogenoses. Introduction]

Liver glycogenosis (GSD) are hereditary in diseases caused by deficiencies of the three major enzymatic systems involved degradation of glycogen: glucose-6-phosphatase (GSD VI). The aims of this paper are, in a first part, to summarize the biological and physiological aspects of these disorders in order to propose an update diagnostic process, and, in a second part, to point out the clinical features and the possible evolution of such patients becoming adults, according to the French experience.

A new variant of type IV glycogenosis: deficiency of branching enzyme activity without apparent progressive liver disease

Type IV glycogenosis is due to branching enzyme deficiency and is usually manifested clinically by progressive liver disease with cirrhosis and hepatic failure between the second and fourth years of life. We describe a 5-year-old boy who, following an acute febrile illness at 2 years of age, was first noted to have hepatomegaly with mildly elevated serum transaminase levels. Liver biopsy revealed hepatic fibrosis with periodic-acid Schiff-positive, diastase-resistant inclusions in hepatocytes and fibrillar inclusions characteristic of amylopectin by electron microscopy. Enzymatic assay revealed deficient hepatic branching enzyme activity with normal activity of glucose-6-phosphatase, debranching enzyme and phosphorylase activities. During the succeeding 3 years, he grew and developed normally with apparent resolution of any clinical evidence of liver disease and only intermittent elevation in serum transaminase levels associated with fever and prolonged fasting. Repeat liver biopsy at 4 years of age showed persistence of scattered hepatocellular periodic-acid Schiff-positive, diastase-resistant inclusions, but no progression of hepatic fibrosis in spite of persistent deficiency of hepatic branching enzyme activity. Skeletal muscle and skin fibroblasts from the patient also showed deficient enzyme activity. Skin fibroblasts from both parents exhibited half the normal control activity, suggesting a heterozygote state. This is the first documented patient with deficiency of branching enzyme but without evidence of progressive hepatic disease. This patient, coupled with reports of other patients with late onset hepatic or muscle disease with branching enzyme deficiency, suggests that the defect resulting in Type IV glycogen storage disease is more heterogenous and possibly more common than previously suspected.

Hepatic glycogen storage disease

The management of patients with glycogen storage disease is based on an understanding of the biochemistry. The outlook for many patients has improved so that they can now grow up normally.

Clinical diversity in glycogenosis type II. Biosynthesis and in situ localization of acid alpha-glucosidase in mutant fibroblasts

The molecular basis of clinical diversity in glycogenosis type II (Pompe's disease) was investigated by comparing the nature of acid alpha-glucosidase deficiency in cultured fibroblasts from 30 patients. Biosynthetic forms of acid alpha-glucosidase with different molecular mass were separated electrophoretically and identified by immunoblotting. Immuno-electron microscopy was employed to determine the intracellular localization of mutant enzyme. Our studies illustrate that maturation of acid alpha-glucosidase is associated with transport to the lysosomes. Deficiency of catalytically active mature enzyme in lysosomes is common to all clinical phenotypes but, in the majority of cases, is more profound in early onset than in late onset forms of the disease. Thus, the results suggest that the clinical course of glycogenosis type II is primarily determined by the amount of functional acid alpha-glucosidase. The role of secondary factors can, however, not be excluded because three adult patients were identified with very low activity and little enzyme in the lysosomes.

Glycogen storage disease. Studies related to the mechanism of glycogenosome formation

Glycogen storage diseases of type I, II, III, IV, V and the other muscle types, were examined electron microscopically, biochemically and physicochemically. Glycogenosomes (glycogen containing vacuoles) were found in the affected tissues of type II, type III variant of muscle glycogen storage disease, type IV and muscle type phosphorylase b kinase deficiency (disorder of the phosphorylase b kinase activation mechanism). The acid alpha-glucosidase activity was decreased only in the case of type II glycogen storage disease (Pompe's disease). The other types of glycogen storage disease showed no decrease in acid alpha-glucosidase activity. Moreover, one patient with type II disease also revealed a decrease in neutral alpha-glucosidase activity. In all cases where glycogenosomes were found, the extracted glycogen macromolecules showed some molecular abnormality or deviation when compared with normal native glycogen macromolecules.

A new variant of glycogen storage disease. Type IXc

Three siblings, a body and two girls, had clinical, laboratory, and morphologic findings that were suggestive of glycogen storage disease (GSD) type IXa. Patients of both sexes with phosphorylase kinase (PK) deficiency usually have an excessive glycogen content only in the liver and normal glycogen content and PK activity in muscle. The siblings in this study had an increased glycogen content in the liver but also in muscle and reduced PK activity in liver, muscle, erythrocytes, and leukocytes. This condition should be labeled as GSD type IXc.

[Muscular diseases: epidemiology of progressive muscular dystrophies]

Epidemiology of muscular dystrophies has been important in the prevention of these diseases. In fact the genetic counselling, after a preliminary epidemiological investigation, reduced the incidence rate of Duchenne muscular dystrophy in the Veneto Region. Furthermore the new biochemical data on dismetabolic muscular diseases revealed a future strategy in the early identification of muscular dystrophies for their epidemiology and genetic prevention as well as for the new systems of research used in the field of muscular dystrophies.