Glycogen Storage Disease Type III Research Articles

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

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

Generation of three induced pluripotent stem cell lines from patients with glycogen storage disease type III

Glycogen storage disease type III (GSDIII) is an autosomal recessive disorder characterized by a deficiency of glycogen debranching enzyme (GDE) leading to cytosolic glycogen accumulation and inducing liver and muscle pathology. Skin fibroblasts from three GSDIII patients were reprogrammed into induced pluripotent stem cells (iPSCs) using non-integrated Sendai virus. All of the three lines exhibited normal morphology, expression of pluripotent markers, stable karyotype, potential of trilineage differentiation and absence of GDE expression, making them valuable tools for modeling GSDIII disease in vitro, studying pathological mechanisms and investigating potential treatments.

The multifaceted roles of the brain glycogen.

Glycogen is a biologically essential macromolecule that is directly involved in multiple human diseases. While its primary role in carbohydrate storage and energy metabolism in the liver and muscle is well characterized, recent research has highlighted critical metabolic and non-metabolic roles for glycogen in the brain. In this review, the emerging roles of glycogen homeostasis in the healthy and diseased brain are discussed with a focus on advancing our understanding of the role of glycogen in the brain. Innovative technologies that have led to novel insights into glycogen functions are detailed. Key insights into how cellular localization impacts neuronal and glial function are discussed. Perturbed glycogen functions are observed in multiple disorders of the brain, including where it serves as a disease driver in the emerging category of neurological glycogen storage diseases (n-GSDs). n-GSDs include Lafora disease (LD), adult polyglucosan body disease (APBD), Cori disease, Glucose transporter type 1 deficiency syndrome (G1D), GSD0b, and late-onset Pompe disease (PD). They are neurogenetic disorders characterized by aberrant glycogen which results in devastating neurological and systemic symptoms. In the most severe cases, rapid neurodegeneration coupled with dementia results in death soon after diagnosis. Finally, we discuss current treatment strategies that are currently being developed and have the potential to be of great benefit to patients with n-GSD. Taken together, novel technologies and biological insights have resulted in a renaissance in brain glycogen that dramatically advanced our understanding of both biology and disease. Future studies are needed to expand our understanding and the multifaceted roles of glycogen and effectively apply these insights to human disease.

Hypertrophic cardiomyopathy in the structure of infiltrative diseases in children

Introduction. In 2006, the American Heart Association identified two main groups of cardiomyopathies (CM) as primary and secondary, referring to the primary CM heart diseases of genetic, acquired or mixed etiology, and to the secondary — pathological involvement of the myocardium as a part of a systemic pathology.
 Aim: to determine the most common phenocopies of hypertrophic CM (HCM) in children, due to the accumulation of pathological substances in the myocardium and present their differences.
 Materials and methods. Instrumental diagnostic methods (echocardiography, electrocardiography, 24-hour Holter ECG monitoring), laboratory tests (N-terminal propeptide of natriuretic hormone, creatine phosphokinase, creatine phosphokinase-MB, lactate dehydrogenase, aspartate aminotransferase, alanine aminotransferase, lactate, ammonia), and molecular genetic tests were used. 
 Results. Nucleotide variants in non-sarcomeric genes causing myocardial hypertrophy were identified in one hundred four (39%) patients: infiltrative diseases with heart damage were diagnosed in 46 cases, syndromes from the RAS-pathy group were diagnosed in 58 cases. Patients with storage diseases included 12 children with Pompe disease, 2 cases with PRKAG2 syndrome, 11 cases had Danon disease, 15 — Corey–Forbes disease, and 6 — Friedreich ataxia. Adverse events were reported in group of patients with Pompe disease (9 deaths), and with Danon’s disease (2 deaths). 
 Conclusion. The phenocopy varieties of HCM in children are represented by a wide variety of genetic variants and often by diseases from the group of glycogen metabolism disorders, fatty acid oxidation disorders, and mitochondrial diseases. Identification of the genetic causes of ventricular myocardial hypertrophy in children is the key to early diagnosis of rare diseases, timely and adequate treatment, as well as predicting the course and outcome of the disease.

CO169 A Mixed Methods Approach to Characterize the Global Prevalence of Glycogen Storage Disease Type III and Associated Disease Complications

Glycogen storage disease type III (GSDIII) is a rare inherited disorder. Historically, GSDIII prevalence estimates have varied with limited generalizability. Complications associated with GSDIII are burdensome and not well characterized. We sought to provide updated prevalence ranges for GSDIII and investigate complications among diagnosed patients.

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

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. 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. 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. 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.

Pathological modeling of glycogen storage disease type III with CRISPR/Cas9 edited human pluripotent stem cells.

Introduction: Glycogen storage disease type III (GSDIII) is a rare genetic disease caused by mutations in the AGL gene encoding the glycogen debranching enzyme (GDE). The deficiency of this enzyme, involved in cytosolic glycogen degradation, leads to pathological glycogen accumulation in liver, skeletal muscles and heart. Although the disease manifests with hypoglycemia and liver metabolism impairment, the progressive myopathy is the major disease burden in adult GSDIII patients, without any curative treatment currently available. Methods: Here, we combined the self-renewal and differentiation capabilities of human induced pluripotent stem cells (hiPSCs) with cutting edge CRISPR/Cas9 gene editing technology to establish a stable AGL knockout cell line and to explore glycogen metabolism in GSDIII. Results: Following skeletal muscle cells differentiation of the edited and control hiPSC lines, our study reports that the insertion of a frameshift mutation in AGL gene results in the loss of GDE expression and persistent glycogen accumulation under glucose starvation conditions. Phenotypically, we demonstrated that the edited skeletal muscle cells faithfully recapitulate the phenotype of differentiated skeletal muscle cells of hiPSCs derived from a GSDIII patient. We also demonstrated that treatment with recombinant AAV vectors expressing the human GDE cleared the accumulated glycogen. Discussion: This study describes the first skeletal muscle cell model of GSDIII derived from hiPSCs and establishes a platform to study the mechanisms that contribute to muscle impairments in GSDIII and to assess the therapeutic potential of pharmacological inducers of glycogen degradation or gene therapy approaches.

Muscle Pathology in a Case of Glycogen Storage Disease III (P6-8.014)

<h3>Objective:</h3> To describe histopathological features on muscle biopsy in glycogen storage disease III (GSDIII). <h3>Background:</h3> GSDIII is a rare disease caused by autosomal recessive mutations in <i>AGL</i> which encodes the glycogen debranching enzyme. Enzyme deficiency leads to glycogen accumulation primarily in liver, heart and skeletal muscle. Clinical presentation varies, and given the rarity, there is a paucity of literature on the skeletal muscle histopathology. <h3>Design/Methods:</h3> We describe a patient suspected to have GSD based on muscle biopsy and subsequently confirmed on exome sequencing. <h3>Results:</h3> A 53-year-old man with history of congenital hepatomegaly and hypertrophic cardiomyopathy presented with 3 years of proximal muscle weakness and atrophy. Family history was notable for elevated liver enzymes in his mother. Examination showed symmetric proximal weakness with reduced reflexes. Electrodiagnostic testing revealed a myopathic pattern with muscle membrane irritability. CK was elevated at 7207 U/L, but testing was otherwise unremarkable including GAA enzyme activity and myositis and LGMD panels. Muscle biopsy showed a severe vacuolar myopathy with large vacuoles filled with lightly basophilic PAS-positive and diastase sensitive material, indicative of normal glycogen and arguing against polyglucosan bodies. Additional myopathic features included significant myofiber size variation, ring fibers, and necrotic and regenerating myofibers. Atrophic nonspecific esterase-positive myofibers were also present. Acid phosphatase was negative and electron microscopy demonstrated abundant non-membrane bound sarcoplasmic glycogen, consistent with a non-lysosomal glycogen storage myopathy. Subsequent exome sequencing revealed two clinically significant variants in the <i>AGL</i> gene, c.3965delT (p.V1322AfsX27) and c.256 C&gt;T (p.Q86X). <h3>Conclusions:</h3> In GSDIII, muscle biopsy shows prominent vacuolar pathology with abundant non-membrane bound sarcoplasmic glycogen deposits. In contrast to Pompe disease, acid phosphatase is negative, demonstrating the absence of lysosomal activation in GSDIII. <b>Disclosure:</b> Dr. Alrasheed has nothing to disclose. Dr. Mozaffar has received personal compensation in the range of $10,000-$49,999 for serving as a Consultant for Alexion Pharmaceuticals. Dr. Mozaffar has received personal compensation in the range of $10,000-$49,999 for serving as a Consultant for Argenx. Dr. Mozaffar has received personal compensation in the range of $10,000-$49,999 for serving as a Consultant for Sanofi-Genzyme. Dr. Mozaffar has received personal compensation in the range of $500-$4,999 for serving as a Consultant for Amicus. Dr. Mozaffar has received personal compensation in the range of $500-$4,999 for serving as a Consultant for Modis Therapeutics. Dr. Mozaffar has received personal compensation in the range of $5,000-$9,999 for serving as a Consultant for UCB/ Ra Pharmaceuticals. Dr. Mozaffar has received personal compensation in the range of $500-$4,999 for serving as a Consultant for Maze Therapeutics. Dr. Mozaffar has received personal compensation in the range of $500-$4,999 for serving as a Consultant for Spark Therapeutics. Dr. Mozaffar has received personal compensation in the range of $5,000-$9,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Sarepta. Dr. Mozaffar has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for National Institutes of Health. Dr. Mozaffar has received personal compensation in the range of $5,000-$9,999 for serving on a Speakers Bureau for Argenx. Dr. Mozaffar has received personal compensation in the range of $500-$4,999 for serving as an officer or member of the Board of Directors for Neuromuscular Disease Foundation. The institution of Dr. Mozaffar has received research support from NIH. The institution of Dr. Mozaffar has received research support from Muscular Dystrophy Association. The institution of Dr. Mozaffar has received research support from Sanofi-Genzyme. The institution of Dr. Mozaffar has received research support from Argenx. The institution of Dr. Mozaffar has received research support from Amicus Therapeutics. The institution of Dr. Mozaffar has received research support from Spark Therapeutics. The institution of Dr. Mozaffar has received research support from Audentes Therapeutics. The institution of Dr. Mozaffar has received research support from Cartesian. Dr. Mozaffar has received personal compensation in the range of $500-$4,999 for serving as a Study Section Member with NIH. Mari Perez-Rosendahl has nothing to disclose.

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.

RWD48 Introduction to Odyssey: Real-World Rare Disease Data Collection Program From Digitized Health Records of Patients With Glycogen Storage Disease Type III (GSDIII) in the United States

RWD48 Introduction to Odyssey: Real-World Rare Disease Data Collection Program From Digitized Health Records of Patients With Glycogen Storage Disease Type III (GSDIII) in the United States

EPH47 Common and Serious Complications Among Patients with Glycogen Storage Disease Type III (GSDIII)

Glycogen Storage Disease Type III (GSDIII) is a rare inherited deficiency of glycogen-debranching enzyme characterized by organ dysfunction due to glycogen accumulation in tissues, as well as hypoglycemia. Current management practices to avoid hypoglycemia and preserve skeletal and cardiac muscles include a high-protein diet and uncooked cornstarch supplementation. This retrospective cohort study investigated common and serious complications among US patients with GSDIII.

Aerobic capacity and skeletal muscle characteristics in glycogen storage disease IIIa: an observational study

BackgroundIndividuals with glycogen storage disease IIIa (GSD IIIa) (OMIM #232400) experience muscle weakness and exercise limitation that worsen through adulthood. However, normative data for markers of physical capacity, such as strength and cardiovascular fitness, are limited. Furthermore, the impact of the disease on muscle size and quality is unstudied in weight bearing skeletal muscle, a key predictor of physical function. We aim to produce normative reference values of aerobic capacity and strength in individuals with GSD IIIa, and to investigate the role of muscle size and quality on exercise impairment.ResultsPeak oxygen uptake (V̇O2peak) was lower in the individuals with GSD IIIa than predicted based on demographic data (17.0 (9.0) ml/kg/min, 53 (24)% of predicted, p = 0.001). Knee extension maximum voluntary contraction (MVC) was also substantially lower than age matched predicted values (MVC: 146 (116) Nm, 57% predicted, p = 0.045), though no difference was found in MVC relative to body mass (1.88 (2.74) Nm/kg, 61% of predicted, p = 0.263). There was a strong association between aerobic capacity and maximal leg strength (r = 0.920; p = 0.003). Substantial inter-individual variation was present, with a high physical capacity group that had normal leg strength (MVC), and relatively high V̇O2peak, and a low physical capacity that display impaired strength and substantially lower V̇O2peak. The higher physical capacity sub-group were younger, had larger Vastus Lateralis (VL) muscles, greater muscle quality, undertook more physical activity (PA), and reported higher health-related quality of life.ConclusionsV̇O2peak and knee extension strength are lower in individuals with GSD IIIa than predicted based on their demographic data. Patients with higher physical capacity have superior muscle size and structure characteristics and higher health-related quality of life, than those with lower physical capacity. This study provides normative values of these important markers of physical capacity.

Glikojen depo hastalığı Tip 3’ün dil tutulumu ile likenoid infiltrasyon birlikteliği

Glycogen storage disease (GSD) type III is an autosomal recessive metabolic disorder and inborn error of metabolism characterized by a deficiency of glycogen debranching enzymes which is affecting 1/100000 every live birth. Clinical presentation is classified into four groups according to the muscular and liver involvement. GSD IIIa, the most common form of GSD III, primarily affects the liver, cardiac muscle, and skeletal muscle. Treatment mainly involves a high-protein diet, to facilitate gluconeogenesis. A 28-year-old male presented to our outpatient clinic with a 2-month history of white asymptomatic lesions on his tongue. He was diagnosed with GSD type 3 when he was six months old, and he has no other systemic disease, drug use or smoking history. A punch biopsy was performed, in superficial dermis band type lymphohistiocytic lichenoid infiltration was detected, also vacuolization of muscle cells and positive PAS staining were seen histologically. Topical high potent corticosteroids and dietary recommendations were offered to him. We want to present this case because of the rarity of lingual muscle involvement in glycogen storage disorders.

Effects of acute nutritional ketosis during exercise in adults with glycogen storage disease type IIIa are phenotype-specific: An investigator-initiated, randomized, crossover study.

Glycogen storage disease type IIIa (GSDIIIa) is an inborn error of carbohydrate metabolism caused by a debranching enzyme deficiency. A subgroup of GSDIIIa patients develops severe myopathy. The purpose of this study was to investigate whether acute nutritional ketosis (ANK) in response to ketone‐ester (KE) ingestion is effective to deliver oxidative substrate to exercising muscle in GSDIIIa patients. This was an investigator‐initiated, researcher‐blinded, randomized, crossover study in six adult GSDIIIa patients. Prior to exercise subjects ingested a carbohydrate drink (~66 g, CHO) or a ketone‐ester (395 mg/kg, KE) + carbohydrate drink (30 g, KE + CHO). Subjects performed 15‐minute cycling exercise on an upright ergometer followed by 10‐minute supine cycling in a magnetic resonance (MR) scanner at two submaximal workloads (30% and 60% of individual maximum, respectively). Blood metabolites, indirect calorimetry data, and in vivo 31P‐MR spectra from quadriceps muscle were collected during exercise. KE + CHO induced ANK in all six subjects with median peak βHB concentration of 2.6 mmol/L (range: 1.6‐3.1). Subjects remained normoglycemic in both study arms, but delta glucose concentration was 2‐fold lower in the KE + CHO arm. The respiratory exchange ratio did not increase in the KE + CHO arm when workload was doubled in subjects with overt myopathy. In vivo 31P MR spectra showed a favorable change in quadriceps energetic state during exercise in the KE + CHO arm compared to CHO in subjects with overt myopathy. Effects of ANK during exercise are phenotype‐specific in adult GSDIIIa patients. ANK presents a promising therapy in GSDIIIa patients with a severe myopathic phenotype.Trial registration numberClinicalTrials.gov identifier: NCT03011203.

Genotypic and clinical analysis of 49 Chinese children with hepatic glycogen storage diseases.

BackgroundGlycogen storage disease (GSD) is a relatively rare inborn metabolic disorder, our study aims to investigate the genotypic and clinical feature of hepatic GSDs in China.MethodsThe clinical and genotypic data of 49 patients with hepatic GSDs were collected retrospectively and analyzed.ResultsAfter gene sequencing, 49 patients were diagnosed as GSDs, including GSD Ia (24 cases), GSD IIIa (11 cases), GSD IXa (8 cases), GSD VI (3 cases) and GSD Ib (3 cases). About 45 gene variants of G6PC, AGL, PHKA2, PYGL, and SLC37A4 were detected; among which, 22 variants were unreported previously. c.648G>T (p. Leu216Leu) of G6PC exon 5 is the most common variant for GSD Ia patients (20/24,83.33%）, splice variant c.1735+1G>T of AGL exon 13 is relatively common among GSD IIIa, while novel variant accounts for the majority of GSD IXa and GSD VI patients. As for clinical features, there was no significant difference in the onset age among group GSD Ia, GSD IIIa, and GSD IXa, but the age at diagnosis and average disease duration from diagnosis of GSD Ia were significantly higher than GSD IIIa and GSD IXa. Body weight of GSD patients was basically normal, but growth retardation was relatively common among them, especially for GSD Ia patients; and renomegaly was only found in GSD Ia. Besides, serum cholesterol, triglyceride, lactic acid, and uric acid in GSD Ia were significantly higher than those with GSD IIIa and IXa (p < 0.05); but ALT, AST, CK, and LDH of GSD III and GSD IXa were significantly higher when compared to GSD Ia (p < 0.05).ConclusionsAll hepatic GSDs patients share similarity in clinical and biochemical spectrum, but delayed diagnosis and biochemical metabolic abnormalities were common in GSD Ia. For family with GSD proband, pedigree analysis and genetic testing is strongly recommended.

Deep morphological analysis of muscle biopsies from type III glycogenesis (GSDIII), debranching enzyme deficiency, revealed stereotyped vacuolar myopathy and autophagy impairment

Glycogen storage disorder type III (GSDIII), or debranching enzyme (GDE) deficiency, is a rare metabolic disorder characterized by variable liver, cardiac, and skeletal muscle involvement. GSDIII manifests with liver symptoms in infancy and muscle involvement during early adulthood. Muscle biopsy is mainly performed in patients diagnosed in adulthood, as routine diagnosis relies on blood or liver GDE analysis, followed by AGL gene sequencing. The GSDIII mouse model recapitulate the clinical phenotype in humans, and a nearly full rescue of muscle function was observed in mice treated with the dual AAV vector expressing the GDE transgene.In order to characterize GSDIII muscle morphological spectrum and identify novel disease markers and pathways, we performed a large international multicentric morphological study on 30 muscle biopsies from GSDIII patients. Autophagy flux studies were performed in human muscle biopsies and muscles from GSDIII mice. The human muscle biopsies revealed a typical and constant vacuolar myopathy, characterized by multiple and variably sized vacuoles filled with PAS-positive material. Using electron microscopy, we confirmed the presence of large non-membrane bound sarcoplasmic deposits of normally structured glycogen as well as smaller rounded sac structures lined by a continuous double membrane containing only glycogen, corresponding to autophagosomes. A consistent SQSTM1/p62 decrease and beclin-1 increase in human muscle biopsies suggested an enhanced autophagy. Consistent with this, an increase in the lipidated form of LC3, LC3II was found in patients compared to controls. A decrease in SQSTM1/p62 was also found in the GSDIII mouse model.In conclusion, we characterized the morphological phenotype in GSDIII muscle and demonstrated dysfunctional autophagy in GSDIII human samples.These findings suggest that autophagic modulation combined with gene therapy might be considered as a novel treatment for GSDIII.

METABOLIC DISTURBANCES IN NEUROMUSCULAR DISEASES: I.1A journey through the growing world of muscle glycogenosis

Muscle glycogenosis constitute a growing number of inborn errors of glycogen metabolism. Deficiencies of virtually all enzymes which intervene in the synthesis or degradation of glycogen, may cause glycogen storage disease (GSD) because of aberrant storage or utilization of glycogen. The different GSDs are each denoted by a roman numeral that reflects the historical sequence of their discovery and often also by the name of the author of the first description. Muscle glycogenosis may be subclassified into the following categories: disorders of glycogen synthesis; disorders of glycogen breakdown; disorders of glycolysis; and lysosomal glycogenosis. Clinical features are closely related to the enzyme deficiency, with either exercise intolerance associated with rhabdomyolysis episodes, or permanent muscle weakness. Other organs may also be involved such as heart or liver, depending on the involved enzyme and severity of enzyme deficiency. In-vivo metabolic studies with exercise tests and muscle biopsy are important tools allowing precise diagnosis, but the place of dedicated gene panels is rapidly increasing. The most frequent muscle glycogenosis is McArdle disease (GSDV), Pompe disease (GSDII) and debranching enzyme deficiency (GSDIII), but the field of glycogenosis has been greatly expanded over the past few years with the discovery of new metabolic diseases that have allowed new metabolic pathways to be deciphered. We will emphasize on the clinical and pathological features of recently described muscle glycogenosis caused by GYG1, RBCK1 and PGM1 gene mutations. The initial steps of glycogen synthesis are involved in deficiencies of glycogenin-1 (GYG1). Phosphoglucomutase deficiency disrupts two metabolic pathways: the connection between galactose and glycogen on the one hand, and glucose metabolism on the other. On the other hand, the metabolic consequences of mutations in the ubiquitin ligase gene RBCK1 are still poorly understood.

Whole-Body Muscle Magnetic Resonance Imaging in Glycogen-Storage Disease Type III.

The main objective of this study was to describe muscle involvement on whole-body magnetic resonance imaging scans in adults at different stages of glycogen-storage disease type III (GSDIII). Fifteen patients, 16-59 years of age, were examined on a 3-T system. The examinations consisted of coronal and axial T1-weighted images or fat images with a Dixon technique, and were scored for 47 muscles using Mercuri's classification. Muscle changes consisted of internal bright signals of fatty replacement. Distribution across muscles showed predominant signal alteration in the lower limbs and postural muscles. This finding is consistent with the overall clinical presentation of GSDIII and the results of heatmap scores. Review of the MRI scans provided new information regarding recurrent muscle changes, particularly in the soleus, gastrocnemius medial head, and thoracic extensor muscles. Whole-body muscle imaging provides clinically relevant information regarding muscle involvement in GSDIII. A severity score may contribute to improved patient management. Muscle Nerve, 2019.

Elucidating the role of Agl in bladder carcinogenesis by generation and characterization of genetically engineered mice.

Amylo-α-1,6-glucosidase,4-α-glucanotransferase (AGL) is an enzyme primarily responsible for glycogen debranching. Germline mutations lead to glycogen storage disease type III (GSDIII). We recently found AGL to be a tumor suppressor in xenograft models of human bladder cancer (BC) and low levels of AGL expression in BC are associated with poor patient prognosis. However, the impact of low AGL expression on the susceptibility of normal bladder to carcinogenesis is unknown. We address this gap by developing a germline Agl knockout (Agl-/-) mouse that recapitulates biochemical and histological features of GSDIII. Agl-/- mice exposed to N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN) had a higher BC incidence compared with wild-type mice (Agl+/+). To determine if the increased BC incidence observed was due to decreased Agl expression in the urothelium specifically, we developed a urothelium-specific conditional Agl knockout (Aglcko) mouse using a Uroplakin II-Cre allele. BBN-induced carcinogenesis experiments repeated in Aglcko mice revealed that Aglcko mice had a higher BC incidence than control (Aglfl/fl) mice. RNA sequencing revealed that tumors from Agl-/- mice had 19 differentially expressed genes compared with control mice. An 'Agl Loss' gene signature was developed and found to successfully stratify normal and tumor samples in two BC patient datasets. These results support the role of AGL loss in promoting carcinogenesis and provide a rationale for evaluating Agl expression levels, or Agl Loss gene signature scores, in normal urothelium of populations at risk of BC development such as older male smokers.

Neuromuscular Involvement in Glycogen Storage Disease Type III in Fifty Tunisian Patients: Phenotype and Natural History in Young Patients.

Our aim was to describe the natural history of neuromuscular involvement (NMI) in glycogen storage disease type III (GSDIII). We conducted a longitudinal study of 50 Tunisian patients, 9.87 years old in average. NMI was diagnosed at an average age of 2.66 years and was clinically overt in 85% of patients. Patients with clinical features were older (p = 0.001). Complaints were dominated by exercise intolerance (80%), noticed at 5.33 years in average. Physical signs, observed at 6.75 years in average, were dominated by muscle weakness (62%). Functional impairment was observed in 64% of patients, without any link with age (p = 0.255). Among 33 patients, 7 improved. Creatine kinase (CK) and aspartate aminotransferase (AST) levels were higher with age.Electrophysiological abnormalities, diagnosed in average at 6.5 years, were more frequent after the first decade (p = 0.0005). Myogenic pattern was predominant (42%). Nerve conduction velocities were slow in two patients. Lower caloric intake was associated with more frequent clinical and electrophysiological features. Higher protein intake was related to fewer complaints and physical anomalies. Neuromuscular investigation is warranted even in asymptomatic patients, as early as the diagnosis of GSDIII is suspected. Muscle involvement can be disabling even in children. Favorable evolution is possible in case of optimal diet.