Skeletal and cardiac muscle involvement in children with glycogen storage disease type III

Glycogen storage disease type III: a mixed-methods study to assess the burden of disease

Background

Glycogen storage disease type III (GSD III) is a rare inherited disorder that results from a glycogen debranching enzyme deficiency.

Objectives

The purpose of this research was to collect data on the signs, symptoms, and impacts of GSD III from the perspective of adult patients and caregivers of individuals with GSD III.

Design

Online survey and qualitative interviews.

Methods

Following institutional review board approval, adult patients and caregivers of children with GSD III were recruited through advocacy networks and clinical sites. If eligible, participants were consented, screened, and sent a survey and/or participated in a 60-min interview. The survey and interview included questions about family history, diagnosis, signs and symptoms, impacts, and management of GSD III. Conceptual models were developed following the analysis of results.

Results

In all, 29 adults and 46 caregivers completed the online survey and/or the interviews with 73 survey and 19 interview respondents. Adults and caregivers reported digestive, musculoskeletal, growth and physical appearance, and cardiac signs and symptoms. Liver conditions were reported by most respondents (83%). Adults and caregivers frequently reported impacts such as difficulty keeping up with peers (77%) and difficulty exercising/difficulty with physical activity (53%). Hypoglycemia was frequently reported in both adults and children, with more than half reporting hospitalizations due to hypoglycemia. Caregivers focused on hypoglycemia when reporting signs/symptoms that most interfere with their child's life and prevention of hypoglycemia as a desired outcome for an effective therapy. Adults most often reported muscle weakness as a top interfering symptom and the most important goal of a potential therapy. Impacts were also reported in activities of daily living, cognitive, emotional, work/school, and sleep domains.

Conclusion

Individuals with GSD III experience a broad spectrum of symptoms and disease impacts. There is an unmet need for therapies that improve metabolic control, reduce the burden of dietary management, reduce fatigue and liver problems, and improve muscle strength and function.

Mutational analysis and clinical investigations of medically diagnosed GSD 1a patients from Pakistan

Glycogen storage disease type I (GSD I) is a rare autosomal recessive inborn error of carbohydrate metabolism caused by the defects of glucose-6-phosphatase complex (G6PC). Disease causing variants in the G6PC gene, located on chromosome 17q21 result in glycogen storage disease type Ia (GSD Ia). Age of onset of GSD Ia ranges from 0.5 to 25 years with presenting features including hemorrhage, hepatic, physical and blood related abnormalities. The overall goal of proposed study was clinical and genetic characterization of GSD Ia cases from Pakistani population. This study included forty GSD Ia cases presenting with heterogeneous clinical profile including hypoglycemia, hepatomegaly, lactic acidosis i.e., pH less than 7.2, hyperuricemia, seizures, epistaxis, hypertriglyceridemia (more than180 mg/dl) and sometimes short stature. All coding exons and intron-exon boundaries of G6PC gene were screened to identify pathogenic variant in 20 patients based on availability of DNA samples and willingness to participate in molecular analysis. Pathogenic variant analysis was done using PCR-Sanger sequencing method and pathogenic effect predictions for identified variants were carried out using PROVEAN, MutationTaster, Polyphen 2, HOPE, Varsome, CADD, DANN, SIFT and HSF software. Overall, 21 variants were detected including 8 novel disease causing variants i.e., G6PC (NM_000151.4):c.71A>C (p.Gln24Pro), c.109G>C(p.Ala37Pro), c.133G>C(p.Val45Leu), c.49_50insT c.205G>A(p.Asp69Asn), c.244C>A(p.Gln82Lys) c.322A>C(p.Thr108Pro) and c.322A>C(p.Cys284Tyr) in the screened regions of G6PC gene. Out of 13 identified polymorphisms, 3 were identified in heterozygous condition while 10 were found in homozygous condition. This study revealed clinical presentation of GSD Ia cases from Pakistan and identification of novel disease-causing sequence variants in coding region and intron-exon boundaries of G6PC gene.

French recommendations for the management of glycogen storage disease type III

The aim of the Protocole National De Diagnostic et de Soins/French National Protocol for Diagnosis and Healthcare (PNDS) is to provide advice for health professionals on the optimum care provision and pathway for patients with glycogen storage disease type III (GSD III).The protocol aims at providing tools that make the diagnosis, defining the severity and different damages of the disease by detailing tests and explorations required for monitoring and diagnosis, better understanding the different aspects of the treatment, defining the modalities and organisation of the monitoring. This is a practical tool, to which health care professionals can refer. PNDS cannot, however, predict all specific cases, comorbidities, therapeutic particularities or hospital care protocols, and does not seek to serve as a substitute for the individual responsibility of the physician in front of his/her patient.

Glycogen storage diseases: An update

Glycogen storage diseases (GSDs), also referred to as glycogenoses, are inherited metabolic disorders of glycogen metabolism caused by deficiency of enzymes or transporters involved in the synthesis or degradation of glycogen leading to aberrant storage and/or utilization. The overall estimated GSD incidence is 1 case per 20000-43000 live births. There are over 20 types of GSD including the subtypes. This heterogeneous group of rare diseases represents inborn errors of carbohydrate metabolism and are classified based on the deficient enzyme and affected tissues. GSDs primarily affect liver or muscle or both as glycogen is particularly abundant in these tissues. However, besides liver and skeletal muscle, depending on the affected enzyme and its expression in various tissues, multiorgan involvement including heart, kidney and/or brain may be seen. Although GSDs share similar clinical features to some extent, there is a wide spectrum of clinical phenotypes. Currently, the goal of treatment is to maintain glucose homeostasis by dietary management and the use of uncooked cornstarch. In addition to nutritional interventions, pharmacological treatment, physical and supportive therapies, enzyme replacement therapy (ERT) and organ transplantation are other treatment approaches for both disease manifestations and long-term complications. The lack of a specific therapy for GSDs has prompted efforts to develop new treatment strategies like gene therapy. Since early diagnosis and aggressive treatment are related to better prognosis, physicians should be aware of these conditions and include GSDs in the differential diagnosis of patients with relevant manifestations including fasting hypoglycemia, hepatomegaly, hypertransaminasemia, hyperlipidemia, exercise intolerance, muscle cramps/pain, rhabdomyolysis, and muscle weakness. Here, we aim to provide a comprehensive review of GSDs. This review provides general characteristics of all types of GSDs with a focus on those with liver involvement.

Clinical and Functional Characterization of Novel AGL Variants in Two Families with Glycogen Storage Disease Type III

Purpose

Glycogen storage disease type III (GSDIII) is a uncommon autosomal recessive inherited metabolic disorder, which is caused by variants in the AGL gene. The purpose of this study was to elucidate the clinical and functional features of two novel variants in two families with GSDIIIa.

Methods

We collected the clinical and laboratory data of the two patients. Genetic testing was performed using GSDs gene panel sequencing, and the identified variants were classified according to the American College of Medical Genetics (ACMG) criteria. The pathogenicity of the novel variants was furthermore assessed through bioinformatics analysis and cellular functional validation experiments.

Results

The two patients were hospitalized with abnormal liver function or hepatomegaly, which was characterized by remarkably elevated liver enzyme and muscle enzyme levels, as well as hepatomegaly, and were eventually diagnosed with GSDIIIa. Genetic analysis detected two novel variants of AGL gene in the two patients: c.1484A > G (p.Y495C), c.1981G > T (p.D661Y). Bioinformatics analysis indicated that the two novel missense mutations most likely altered the protein's conformation and therefore made the enzyme it encodes less active. Based on the ACMG criteria, both variants were considered likely pathogenic, in accordance with the functional analysis results, which demonstrated that the mutated protein was still localized in the cytoplasm and that the glycogen content of cells transfected with the mutated AGL was increased compared to cells transfected with the wild-type one.

Conclusion

These findings indicated that the two newly identified variants in the AGL gene (c.1484A > G; c.1981G > T) were undoubtedly pathogenic mutations, inducing a slight reduction in glycogen debranching enzyme activity and a mild increase in intracellular glycogen content. Two patients who visited us with abnormal liver function, or hepatomegaly, improved dramatically after treatment with oral uncooked cornstarch, but the effects on skeletal muscle and myocardium required further observation.

Metabolic Cardiomyopathies and Cardiac Defects in Inherited Disorders of Carbohydrate Metabolism: A Systematic Review

Heart failure (HF) is a progressive chronic disease that remains a primary cause of death worldwide, affecting over 64 million patients. HF can be caused by cardiomyopathies and congenital cardiac defects with monogenic etiology. The number of genes and monogenic disorders linked to development of cardiac defects is constantly growing and includes inherited metabolic disorders (IMDs). Several IMDs affecting various metabolic pathways have been reported presenting cardiomyopathies and cardiac defects. Considering the pivotal role of sugar metabolism in cardiac tissue, including energy production, nucleic acid synthesis and glycosylation, it is not surprising that an increasing number of IMDs linked to carbohydrate metabolism are described with cardiac manifestations. In this systematic review, we offer a comprehensive overview of IMDs linked to carbohydrate metabolism presenting that present with cardiomyopathies, arrhythmogenic disorders and/or structural cardiac defects. We identified 58 IMDs presenting with cardiac complications: 3 defects of sugar/sugar-linked transporters (GLUT3, GLUT10, THTR1); 2 disorders of the pentose phosphate pathway (G6PDH, TALDO); 9 diseases of glycogen metabolism (GAA, GBE1, GDE, GYG1, GYS1, LAMP2, RBCK1, PRKAG2, G6PT1); 29 congenital disorders of glycosylation (ALG3, ALG6, ALG9, ALG12, ATP6V1A, ATP6V1E1, B3GALTL, B3GAT3, COG1, COG7, DOLK, DPM3, FKRP, FKTN, GMPPB, MPDU1, NPL, PGM1, PIGA, PIGL, PIGN, PIGO, PIGT, PIGV, PMM2, POMT1, POMT2, SRD5A3, XYLT2); 15 carbohydrate-linked lysosomal storage diseases (CTSA, GBA1, GLA, GLB1, HEXB, IDUA, IDS, SGSH, NAGLU, HGSNAT, GNS, GALNS, ARSB, GUSB, ARSK). With this systematic review we aim to raise awareness about the cardiac presentations in carbohydrate-linked IMDs and draw attention to carbohydrate-linked pathogenic mechanisms that may underlie cardiac complications.

Suppression of pullulanase-induced cytotoxic T cell response with a dual promoter in GSD IIIa mice

Glycogen debranching enzyme deficiency in glycogen storage disease type III (GSD III) results in excessive glycogen accumulation in multiple tissues, primarily the liver, heart, and skeletal muscle. We recently reported that an adeno-associated virus vector expressing a bacterial debranching enzyme (pullulanase) driven by the ubiquitous CMV enhancer/chicken β-actin (CB) promoter cleared glycogen in major affected tissues of infant GSD IIIa mice. In this study, we developed a potentially novel dual promoter consisting of a liver-specific promoter (LSP) and the CB promoter for gene therapy in adult GSD IIIa mice. Ten-week treatment with an adeno-associated virus vector containing the LSP-CB dual promoter in adult GSD IIIa mice significantly increased pullulanase expression and reduced glycogen contents in the liver, heart, and skeletal muscle, accompanied by the reversal of liver fibrosis, improved muscle function, and a significant decrease in plasma biomarkers alanine aminotransferase, aspartate aminotransferase, and creatine kinase. Compared with the CB promoter, the dual promoter effectively decreased pullulanase-induced cytotoxic T lymphocyte responses and enabled persistent therapeutic gene expression in adult GSD IIIa mice. Future studies are needed to determine the long-term durability of dual promoter-mediated expression of pullulanase in adult GSD IIIa mice and in large animal models.

A New Perspective on the Quality of Life of Children with Glycogen Storage Diseases

PURPOSE

This study aimed to assess the quality of life (QoL) of children with glycogen storage disease (GSD) and their parents and to determine the impact of myopathies.

METHODS

A prospective case-control study was conducted at the Cairo University Children's Hospital and National Liver Institute, Menoufia University. A promising new style of questionnaire called the Stark Quality of Life Questionnaire was used to assess the quality of life.

RESULTS

Fifty-two children diagnosed with GSD (cases) and 55 age- and sex-matched healthy children (controls) were included. A statistically significant difference was found between cases and controls regarding food intake; mental behavior parameters such as mood, energy, and social contact; and physical behavior parameters such as running and tying shoelaces. Children with myopathies had significantly lower QoL scores in most of the parameters.

CONCLUSION

GSDs alter children and their parents' mental and physical abilities. Lower QoL scores were detected in children with both skeletal myopathy and cardiomyopathy, but the difference was not statistically significant when compared with the children without myopathies.

A retrospective longitudinal study and comprehensive review of adult patients with glycogen storage disease type III

INTRODUCTION

A deficiency of glycogen debrancher enzyme in patients with glycogen storage disease type III (GSD III) manifests with hepatic, cardiac, and muscle involvement in the most common subtype (type a), or with only hepatic involvement in patients with GSD IIIb.

OBJECTIVE AND METHODS

To describe longitudinal biochemical, radiological, muscle strength and ambulation, liver histopathological findings, and clinical outcomes in adults (≥18 years) with glycogen storage disease type III, by a retrospective review of medical records.

RESULTS

Twenty-one adults with GSD IIIa (14 F & 7 M) and four with GSD IIIb (1 F & 3 M) were included in this natural history study. At the most recent visit, the median (range) age and follow-up time were 36 (19-68) and 16 years (0-41), respectively. For the entire cohort: 40% had documented hypoglycemic episodes in adulthood; hepatomegaly and cirrhosis were the most common radiological findings; and 28% developed decompensated liver disease and portal hypertension, the latter being more prevalent in older patients. In the GSD IIIa group, muscle weakness was a major feature, noted in 89% of the GSD IIIa cohort, a third of whom depended on a wheelchair or an assistive walking device. Older individuals tended to show more severe muscle weakness and mobility limitations, compared with younger adults. Asymptomatic left ventricular hypertrophy (LVH) was the most common cardiac manifestation, present in 43%. Symptomatic cardiomyopathy and reduced ejection fraction was evident in 10%. Finally, a urinary biomarker of glycogen storage (Glc4) was significantly associated with AST, ALT and CK.

CONCLUSION

GSD III is a multisystem disorder in which a multidisciplinary approach with regular clinical, biochemical, radiological and functional (physical therapy assessment) follow-up is required. Despite dietary modification, hepatic and myopathic disease progression is evident in adults, with muscle weakness as the major cause of morbidity. Consequently, definitive therapies that address the underlying cause of the disease to correct both liver and muscle are needed.

Physical therapy assessment and whole-body magnetic resonance imaging findings in children with glycogen storage disease type IIIa: A clinical study and review of the literature

INTRODUCTION

Early recognized manifestations of GSD III include hypoglycemia, hepatomegaly, and elevated liver enzymes. Motor symptoms such as fatigue, muscle weakness, functional impairments, and muscle wasting are typically reported in the 3rd to 4th decade of life.

OBJECTIVE

In this study, we investigated the early musculoskeletal findings in children with GSD IIIa, compared to a cohort of adults with GSD IIIa.

METHODS

We utilized a comprehensive number of physical therapy outcome measures to cross-sectionally assess strength and gross motor function including the modified Medical Research Council (mMRC) scale, grip and lateral/key pinch, Gross Motor Function Measure (GMFM), Gait, Stairs, Gowers, Chair (GSGC) test, 6 Minute Walk Test (6MWT), and Bruininks-Oseretsky Test of Motor Proficiency Ed. 2 (BOT-2). We also assessed laboratory biomarkers (AST, ALT, CK and urine Glc4) and conducted whole-body magnetic resonance imaging (WBMRI) to evaluate for proton density fat fraction (PDFF) in children with GSD IIIa. Nerve Conduction Studies and Electromyography results were analyzed where available and a thorough literature review was conducted.

RESULTS

There were a total of 22 individuals with GSD IIIa evaluated in our study, 17 pediatric patients and 5 adult patients. These pediatric patients demonstrated weakness on manual muscle testing, decreased grip and lateral/key pinch strength, and decreased functional ability compared to non-disease peers on the GMFM, 6MWT, BOT-2, and GSGC. Additionally, all laboratory biomarkers analyzed and PDFF obtained from WBMRI were increased in comparison to non-diseased peers. In comparison to the pediatric cohort, adults demonstrated worse overall performance on functional assessments demonstrating the expected progression of disease phenotype with age.

CONCLUSION

These results demonstrate the presence of early musculoskeletal involvement in children with GSD IIIa, most evident on physical therapy assessments, in addition to the more commonly reported hepatic symptoms. Muscular weakness in both children and adults was most significant in proximal and trunk musculature, and intrinsic musculature of the hands. These findings indicate the importance of early assessment of patients with GSD IIIa for detection of muscular weakness and development of treatment approaches that target both the liver and muscle.

Narrative review of glycogen storage disorder type III with a focus on neuromuscular, cardiac and therapeutic aspects

Glycogen storage disorder type III (GSDIII) is a rare inborn error of metabolism due to loss of glycogen debranching enzyme activity, causing inability to fully mobilize glycogen stores and its consequent accumulation in various tissues, notably liver, cardiac and skeletal muscle. In the pediatric population, it classically presents as hepatomegaly with or without ketotic hypoglycemia and failure to thrive. In the adult population, it should also be considered in the differential diagnosis of left ventricular hypertrophy or hypertrophic cardiomyopathy, myopathy, exercise intolerance, as well as liver cirrhosis or fibrosis with subsequent liver failure. In this review article, we first present an overview of the biochemical and clinical aspects of GSDIII. We then focus on the recent findings regarding cardiac and neuromuscular impairment associated with the disease. We review new insights into the pathophysiology and clinical picture of this disorder, including symptomatology, imaging and electrophysiology. Finally, we discuss current and upcoming treatment strategies such as gene therapy aimed at the replacement of the malfunctioning enzyme to provide a stable and long-term therapeutic option for this debilitating disease.

Beneficial Effects of Modified Atkins Diet in Glycogen Storage Disease Type IIIa

<b><i>Introduction:</i></b> Glycogen storage disease Type III (GSD III) is an autosomal recessive disease caused by the deficiency of glycogen debranching enzyme, encoded by the AGL gene. Two clinical types of the disease are most prevalent: GSD IIIa involves the liver and muscle, whereas IIIb affects only the liver. The classical dietetic management of GSD IIIa involves prevention of fasting, frequent feeds with high complex carbohydrates in small children, and a low-carb-high-protein diet in older children and adults. Recently, diets containing high amount of fat, including ketogenic and modified Atkins diet (MAD), have been suggested to have favorable outcome in GSD IIIa. <b><i>Methods:</i></b> Six patients, aged 3–31 years, with GSD IIIa received MAD for a duration of 3–7 months. Serum glucose, transaminases, creatine kinase (CK) levels, capillary ketone levels, and cardiac parameters were followed-up. <b><i>Results:</i></b> In all patients, transaminase levels dropped in response to MAD. Decrease in CK levels were detected in 5 out of 6 patients. Hypoglycemia was evident in 2 patients but was resolved by adding uncooked cornstarch to diet. <b><i>Conclusion:</i></b> Our study demonstrates that GSD IIIa may benefit from MAD both clinically and biochemically.

Molecular Diagnosis of Panel-Based Next-Generation Sequencing Approach and Clinical Symptoms in Patients With Glycogen Storage Disease: A Single Center Retrospective Study

Aim: The aim of this study was to investigate the clinical utility of panel-based next-generation sequencing (NGS) in the diagnostic approach of glycogen storage disease (GSD). Methods: We performed a retrospective review of the 32 cases with suspected GSDs between April 2013 and November 2019 through panel-based NGS, clinical and biochemical data and long-term complications. Results: Of the 32 clinical cases, we identified 41 different variants, including 24 missense (58.5%), one synonymous (2.4%), three nonsense (8%), one splice (2.4%), four frameshift (9.8%), one deletion (2.4%), four insertions (9.8%), two deletion-insertion (4.9%) and one duplication(2.4%), of which 13(31.7%) were previously unreported in the literature. In addition, patients with different types of GSDs showed important differences in biochemical parameters (i.e., CK, rGGT, TG, and UA). Conclusions: The panel-based NGS played an important diagnostic role in the suspicious GSDs patients, especially in the mild phenotype and ruled out detectable pathologic conditions. Besides, differences between our GSDs patients reflect biochemical heterogeneity.

Gene therapy for glycogen storage diseases

The focus of this review is the development of gene therapy for glycogen storage diseases (GSDs). GSD results from the deficiency of specific enzymes involved in the storage and retrieval of glucose in the body. Broadly, GSDs can be divided into types that affect liver or muscle or both tissues. For example, glucose-6-phosphatase (G6Pase) deficiency in GSD type Ia (GSD Ia) affects primarily the liver and kidney, while acid α-glucosidase (GAA) deficiency in GSD II causes primarily muscle disease. The lack of specific therapy for the GSDs has driven efforts to develop new therapies for these conditions. Gene therapy needs to replace deficient enzymes in target tissues, which has guided the planning of gene therapy experiments. Gene therapy with adeno-associated virus (AAV) vectors has demonstrated appropriate tropism for target tissues, including the liver, heart and skeletal muscle in animal models for GSD. AAV vectors transduced liver and kidney in GSD Ia and striated muscle in GSD II mice to replace the deficient enzyme in each disease. Gene therapy has been advanced to early phase clinical trials for the replacement of G6Pase in GSD Ia and GAA in GSD II (Pompe disease). Other GSDs have been treated in proof-of-concept studies, including GSD III, IV and V. The future of gene therapy appears promising for the GSDs, promising to provide more efficacious therapy for these disorders in the foreseeable future.

A lower energetic, protein and uncooked cornstarch intake is associated with a more severe outcome in glycogen storage disease type III: an observational study of 50 patients

Background Glycogen storage disease type III (GSDIII), due to a deficiency of glycogen debrancher enzyme (GDE), is particularly frequent in Tunisia. Phenotypic particularities of Tunisian patients remain unknown. Our aim was to study complications of GSDIII in a Tunisian population and to explore factors interfering with its course. Methods A retrospective longitudinal study was conducted over 30 years (1986-2016) in the referral metabolic center in Tunisia. Results Fifty GSDIII patients (26 boys), followed for an average 6.75 years, were enrolled. At the last evaluation, the median age was 9.87 years and 24% of patients reached adulthood. Short stature persisted in eight patients and obesity in 19 patients. Lower frequency of hypertriglyceridemia (HTG) was associated with older patients (p<0.0001), higher protein diet (p=0.068) and lower caloric intake (p=0.025). Hepatic complications were rare. Cardiac involvement (CI) was frequent (91%) and occurred early at a median age of 2.6 years. Severe cardiomyopathy (50%) was related to lower doses of uncooked cornstarch (p=0.02). Neuromuscular involvement (NMI) was constant, leading to a functional discomfort in 64% of cases and was disabling in 34% of cases. Severe forms were related to lower caloric (p=0.005) and protein intake (p<0.015). Conclusions A low caloric, protein and uncooked cornstarch intake is associated with a more severe outcome in GSDIII Tunisian patients. Neuromuscular and CIs were particularly precocious and severe, even in childhood. Genetic and epigenetic factors deserve to be explored.

Inhibition of Glycogen Synthase II with RNAi Prevents Liver Injury in Mouse Models of Glycogen Storage Diseases

Glycogen storage diseases (GSDs) of the liver are devastating disorders presenting with fasting hypoglycemia as well as hepatic glycogen and lipid accumulation, which could lead to long-term liver damage. Diet control is frequently utilized to manage the potentially dangerous hypoglycemia, but there is currently no effective pharmacological treatment for preventing hepatomegaly and concurrent liver metabolic abnormalities, which could lead to fibrosis, cirrhosis, and hepatocellular adenoma or carcinoma. In this study, we demonstrate that inhibition of glycogen synthesis using an RNAi approach to silence hepatic Gys2 expression effectively prevents glycogen synthesis, glycogen accumulation, hepatomegaly, fibrosis, and nodule development in a mouse model of GSD III. Mechanistically, reduction of accumulated abnormally structured glycogen prevents proliferation of hepatocytes and activation of myofibroblasts as well as infiltration of mononuclear cells. Additionally, we show that silencing Gys2 expression reduces hepatic steatosis in a mouse model of GSD type Ia, where we hypothesize that the reduction of glycogen also reduces the production of excess glucose-6-phosphate and its subsequent diversion to lipid synthesis. Our results support therapeutic silencing of GYS2 expression to prevent glycogen and lipid accumulation, which mediate initial signals that subsequently trigger cascades of long-term liver injury in GSDs.

Long term longitudinal study of muscle function in patients with glycogen storage disease type IIIa

Glycogen storage disease type III (GSDIII) is an autosomal recessive disorder caused by mutations in the AGL gene coding for the glycogen debranching enzyme. Current therapy is based on dietary adaptations but new preclinical therapies are emerging. The identification of outcome measures which are sensitive to disease progression becomes critical to assess the efficacy of new treatments in upcoming clinical trials. In order to prepare future longitudinal studies or therapeutic trials with large cohorts, information about disease progression is required. In this study we present preliminary longitudinal data of Motor Function Measure (MFM), timed tests, Purdue pegboard test, and handgrip strength collected over 5 to 9years of follow-up in 13 patients with GSDIII aged between 13 and 56years old. Follow-up for nine of the 13 patients was up to 9years. Similarly to our previous cross-sectional retrospective study, handgrip strength significantly decreased with age in patients older than 37years. MFM scores started to decline after the age of 35. The Purdue pegboard score also significantly reduced with increasing age (from 13years of age) but with large inter-visit variations. The time to stand up from a chair or to climb 4 stairs increased dramatically in some but not all patients older than 30years old. In conclusion, this preliminary longitudinal study suggests that MFM and handgrip strength are the most sensitive muscle function outcome measures in GSDIII patients from the end of their third decade. Sensitive muscle outcome measures remain to be identified in younger GSDIII patients but is challenging as muscle symptoms remain discrete and often present as accumulated fatigue.

Molecular analysis of glycogen storage disease type Ia in Iranian Azeri Turks: identification of a novel mutation

Glycogen storage diseases (GSDs) are caused by abnormalities in enzymes that are involved in the regulation of gluconeogenesis and glycogenolysis. GSD I, an autosomal recessive metabolic disorder, is the most common GSD and has four subtypes. Here, we examined GSD Ia caused by the defective glucose-6-phosphatase catalytic (G6PC) gene. We investigated the frequency of GSD Ia and clarified its molecular aspect in patients with the main clinical and biochemical characteristics of GSD, including 37 unrelated patients with a mean age of three years at the time of diagnosis. All patients belonged to the Azeri Turkish population. Hypoglycaemia and hypertriglyceridaemia were the most frequent laboratory findings. Mutations were detected by performing direct sequencing. Mutation analysis of the G6PC gene revealed that GSD Ia accounted for 11% in GSD patients with involvement of liver. Three patients were homozygous for R83C mutation. In addition, a novel stop mutation, Y85X, was identified in a patient with the typical features of GSD Ia.

Cross-sectional retrospective study of muscle function in patients with glycogen storage disease type III

Glycogen storage disease type III is an inherited metabolic disorder characterized by liver and muscle impairment. This study aimed to identify promising muscle function measures for future studies on natural disease progression and therapeutic trials. The age-effect on the manual muscle testing (MMT), the hand-held dynamometry (HHD), the motor function measure (MFM) and the Purdue pegboard test was evaluated by regression analysis in a cross-sectional retrospective single site study. In patients aged between 13 and 56 years old, the Purdue pegboard test and dynamometry of key pinch and knee extension strength were age-sensitive with annual losses of 1.49, 1.10 and 0.70% of the predicted values (%pred), respectively. The MFM score and handgrip strength were also age-sensitive but only in patients older than 29 and 37 years old with annual losses of 1.42 and 1.84%pred, respectively. Muscle strength assessed by MMT and elbow extension measured by HHD demonstrated an annual loss of less than 0.50%pred and are thus unlikely to be promising outcome measures for future clinical trials. In conclusion, our results identified age-sensitive outcomes from retrospective data and may serve for future longitudinal studies in which an estimation of the minimal number of subjects is provided.

Glycogen metabolism in humans

In the human body, glycogen is a branched polymer of glucose stored mainly in the liver and the skeletal muscle that supplies glucose to the blood stream during fasting periods and to the muscle cells during muscle contraction. Glycogen has been identified in other tissues such as brain, heart, kidney, adipose tissue, and erythrocytes, but glycogen function in these tissues is mostly unknown. Glycogen synthesis requires a series of reactions that include glucose entrance into the cell through transporters, phosphorylation of glucose to glucose 6-phosphate, isomerization to glucose 1-phosphate, and formation of uridine 5'-diphosphate-glucose, which is the direct glucose donor for glycogen synthesis. Glycogenin catalyzes the formation of a short glucose polymer that is extended by the action of glycogen synthase. Glycogen branching enzyme introduces branch points in the glycogen particle at even intervals. Laforin and malin are proteins involved in glycogen assembly but their specific function remains elusive in humans. Glycogen is accumulated in the liver primarily during the postprandial period and in the skeletal muscle predominantly after exercise. In the cytosol, glycogen breakdown or glycogenolysis is carried out by two enzymes, glycogen phosphorylase which releases glucose 1-phosphate from the linear chains of glycogen, and glycogen debranching enzyme which untangles the branch points. In the lysosomes, glycogen degradation is catalyzed by α-glucosidase. The glucose 6-phosphatase system catalyzes the dephosphorylation of glucose 6-phosphate to glucose, a necessary step for free glucose to leave the cell. Mutations in the genes encoding the enzymes involved in glycogen metabolism cause glycogen storage diseases.

Heart Disease in Disorders of Muscle, Neuromuscular Transmission, and the Nerves

Little is known regarding cardiac involvement (CI) by neuromuscular disorders (NMDs). The purpose of this review is to summarise and discuss the major findings concerning the types, frequency, and severity of cardiac disorders in NMDs as well as their diagnosis, treatment, and overall outcome. CI in NMDs is characterized by pathologic involvement of the myocardium or cardiac conduction system. Less commonly, additional critical anatomic structures, such as the valves, coronary arteries, endocardium, pericardium, and even the aortic root may be involved. Involvement of the myocardium manifests most frequently as hypertrophic or dilated cardiomyopathy and less frequently as restrictive cardiomyopathy, non-compaction, arrhythmogenic right-ventricular dysplasia, or Takotsubo-syndrome. Cardiac conduction defects and supraventricular and ventricular arrhythmias are common cardiac manifestations of NMDs. Arrhythmias may evolve into life-threatening ventricular tachycardias, asystole, or even sudden cardiac death. CI is common and carries great prognostic significance on the outcome of dystrophinopathies, laminopathies, desminopathies, nemaline myopathy, myotonias, metabolic myopathies, Danon disease, and Barth-syndrome. The diagnosis and treatment of CI in NMDs follows established guidelines for the management of cardiac disease, but cardiotoxic medications should be avoided. CI in NMDs is relatively common and requires complete work-up following the establishment of a neurological diagnosis. Appropriate cardiac treatment significantly improves the overall long-term outcome of NMDs.

Muscle Ultrasound in Patients with Glycogen Storage Disease Types I and III

In glycogen storage diseases (GSDs), improved longevity has resulted in the need for neuromuscular surveillance. In 12 children and 14 adults with the "hepatic" (GSD-I) and "myopathic" (GSD-III) phenotypes, we cross-sectionally assessed muscle ultrasound density (MUD) and muscle force. Children with both "hepatic" and "myopathic" GSD phenotypes had elevated MUD values (MUD Z-scores: GSD-I > 2.5 SD vs. GSD-III > 1 SD, p < 0.05) and muscle weakness (GSD-I muscle force; p < 0.05) of myopathic distribution. In "hepatic" GSD-I adults, MUD stabilized (GSD-I adults vs. GSD-I children, not significant), concurring with moderate muscle weakness (GSD-I adults vs. healthy matched pairs, p < 0.05). In "myopathic" GSD-III adults, MUD increased with age (MUD-GSD III vs. age: r = 0.71-0.83, GSD-III adults > GSD-III children, p < 0.05), concurring with pronounced muscle weakness (GSD-III adults vs. GSD-I adults, p < 0.05) of myopathic distribution. Children with "hepatic" and "myopathic" GSD phenotypes were both found to have myopathy. Myopathy stabilizes in "hepatic" GSD-I adults, whereas it progresses in "myopathic" GSD-III adults. Muscle ultrasonography provides an excellent, non-invasive tool for neuromuscular surveillance per GSD phenotype.