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

A functional mini-GDE transgene corrects impairment in models of glycogen storage disease type III

Glycogen storage disease type III (GSDIII) is a rare inborn error of metabolism affecting liver, skeletal muscle, and heart due to mutations of the AGL gene encoding for the glycogen debranching enzyme (GDE). No curative treatment exists for GSDIII. The 4.6 kb GDE cDNA represents the major technical challenge toward the development of a single recombinant adeno-associated virus-derived (rAAV-derived) vector gene therapy strategy. Using information on GDE structure and molecular modeling, we generated multiple truncated GDEs. Among them, an N-terminal-truncated mutant, ΔNter2-GDE, had a similar efficacy in vivo compared with the full-size enzyme. A rAAV vector expressing ΔNter2-GDE allowed significant glycogen reduction in heart and muscle of Agl-/- mice 3 months after i.v. injection, as well as normalization of histology features and restoration of muscle strength. Similarly, glycogen accumulation and histological features were corrected in a recently generated Agl-/- rat model. Finally, transduction with rAAV vectors encoding ΔNter2-GDE corrected glycogen accumulation in an in vitro human skeletal muscle cellular model of GSDIII. In conclusion, our results demonstrated the ability of a single rAAV vector expressing a functional mini-GDE transgene to correct the muscle and heart phenotype in multiple models of GSDIII, supporting its clinical translation to patients with GSDIII.

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.

Metabolic Myopathies in the Era of Next-Generation Sequencing

Metabolic myopathies are rare inherited disorders that deserve more attention from neurologists and pediatricians. Pompe disease and McArdle disease represent some of the most common diseases in clinical practice; however, other less common diseases are now better-known. In general the pathophysiology of metabolic myopathies needs to be better understood. Thanks to the advent of next-generation sequencing (NGS), genetic testing has replaced more invasive investigations and sophisticated enzymatic assays to reach a final diagnosis in many cases. The current diagnostic algorithms for metabolic myopathies have integrated this paradigm shift and restrict invasive investigations for complicated cases. Moreover, NGS contributes to the discovery of novel genes and proteins, providing new insights into muscle metabolism and pathophysiology. More importantly, a growing number of these conditions are amenable to therapeutic approaches such as diets of different kinds, exercise training protocols, and enzyme replacement therapy or gene therapy. Prevention and management-notably of rhabdomyolysis-are key to avoiding serious and potentially life-threatening complications and improving patients' quality of life. Although not devoid of limitations, the newborn screening programs that are currently mushrooming across the globe show that early intervention in metabolic myopathies is a key factor for better therapeutic efficacy and long-term prognosis. As a whole NGS has largely increased the diagnostic yield of metabolic myopathies, but more invasive but classical investigations are still critical when the genetic diagnosis is unclear or when it comes to optimizing the follow-up and care of these muscular disorders.

Glycogen storage disease type IIIa in pregnant women: A guide to management

Glycogen storage disease type IIIa (GSD‐IIIa) is an autosomal recessive disorder that impairs glycogenolysis, producing ketotic hypoglycaemia, hepatomegaly, cardiac and skeletal myopathy. During pregnancy, increased metabolic demand requires careful management. There are few case reports about pregnancy in GSD‐IIIa, however none detail management during caesarean section. This case describes a 25‐year‐old women with GSD‐IIIa diagnosed at 5 months of age. She had modest metabolic control with complications including hepatomegaly, mild skeletal myopathy and poor enteral function requiring multiple operative interventions. She had a planned pregnancy managed by a multidisciplinary team, which included a metabolic geneticist, maternal–fetal medicine specialist and metabolic dietitian. Nocturnal cornstarch was provided to meet basal carbohydrate requirements and a high protein diet with regular carbohydrates was consumed throughout the day. The woman remained well during the antenatal period and had an induction of labour at 38 weeks gestation. She had an emergency caesarean section in early labour due to an abnormal cardiotocography (CTG). The intraoperative and postoperative period were uncomplicated. A live baby boy was born in good condition, weighing 2440 g with APGARs of 9 and 9 at 1 and 5 min. She was managed in labour with glucose 10% IV at 3.5 mg/kg/min, hourly blood sugar level (BSL) monitoring and early epidural anaesthetic. The aim of the first 24‐h post‐partum was prevention of hypoglycaemia, which required strict management with dextrose 10% IV at 3.5 mg/kg/min, oral carbohydrate supplementation and BSL monitoring. This case highlights the complexity of GSD‐IIIa as well as provides a proposed plan for management during pregnancy.

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.

Genetic analysis and long-term treatment monitoring of 11 children with glycogen storage disease type IIIa

Objectives To investigate the clinical and genetic characteristics of children with glycogen storage disease type IIIa (GSD IIIa) and to explore the muscle involvement and manifestations of GSD IIIa patients. Methods The clinical data of 11 patients with GSD IIIa diagnosed by genetic testing from 2003 to 2019 were retrospectively analyzed. Results Twenty variants of AGL gene were detected in 11 patients, eight of which were novel variants. Before treatment, the height was significantly backward. All patients had hepatomegaly. Abnormal biochemical indicators were mainly manifested as significantly increased serum liver and muscle enzymes, accompanied by hypertriglyceridemia, hypoglycemia, hyperlactacidemia, slightly elevated pyruvic acid, and metabolic acidosis. After treatment, the height and liver size of the patients were significantly improved. At the same time, alanine aminotransferase (ALT), aspartate aminotransferase (AST), triglyceride (TG), lactic acid and pyruvic acid in children were significantly decreased, while creatine kinase (CK) was significantly increased. During follow-up monitoring, six patients developed ventricular hypertrophy. Lactate dehydrogenase (LDH) (691.67 ± 545.27 vs. 362.20 ± 98.66), lactic acid (3.18 ± 3.05 vs. 1.10 ± 0.40), and pyruvic acid (64.30 ± 39.69 vs. 32.06 ± 4.61) were significantly increased in patients with ventricular hypertrophy compared with those without ventricular hypertrophy. Conclusions In clinical cases of upper respiratory tract infection or gastrointestinal symptoms accompanied by hypoglycemia, dyslipidemia, metabolites disorders, elevated serum liver, and muscle enzymes, the possibility of GSD IIIa should be vigilant. During treatment monitoring, if lactic acid, pyruvic acid, LDH, and CK rise, it indicates that the disease is not well controlled and there is the possibility of cardiac hypertrophy.

A Novel Gene Therapy Approach for GSD III Using an AAV Vector Encoding a Bacterial Glycogen Debranching Enzyme

Glycogen storage disease type III (GSD III) is an inherited disorder caused by a deficiency of glycogen debranching enzyme (GDE), which results in the accumulation of abnormal glycogen (limit dextrin) in the cytoplasm of liver, heart, and skeletal muscle cells. Currently, there is no curative treatment for this disease. Gene therapy with adeno-associated virus (AAV) provides an optimal treatment approach for monogenic diseases like GSD III. However, the 4.6 kb human GDE cDNA is too large to be packaged into a single AAV vector due to its small carrying capacity. To overcome this limitation, we tested a new gene therapy approach in GSD IIIa mice using an AAV vector ubiquitously expressing a smaller bacterial GDE, Pullulanase, whose cDNA is 2.2 kb. Intravenous injection of the AAV vector (AAV9-CB-Pull) into 2-week-old GSD IIIa mice blocked glycogen accumulation in both cardiac and skeletal muscles, but not in the liver, accompanied by the improvement of muscle functions. Subsequent treatment with a liver-restricted AAV vector (AAV8-LSP-Pull) reduced liver glycogen content by 75% and reversed hepatic fibrosis while maintaining the effect of AAV9-CB-Pull treatment on heart and skeletal muscle. Our results suggest that AAV-mediated gene therapy with Pullulanase is a possible treatment for GSD III.

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.

Challenges of Gene Therapy for the Treatment of Glycogen Storage Diseases Type I and Type III

Glycogen storage diseases (GSDs) type I (GSDI) and type III (GSDIII), the most frequent hepatic GSDs, are due to defects in glycogen metabolism, mainly in the liver. In addition to hypoglycemia and liver pathology, renal, myeloid, or muscle complications affect GSDI and GSDIII patients. Currently, patient management is based on dietary treatment preventing severe hypoglycemia and increasing the lifespan of patients. However, most of the patients develop long-term pathologies. In the past years, gene therapy for GSDI has generated proof of concept for hepatic GSDs. This resulted in a recent clinical trial of adeno-associated virus (AAV)-based gene replacement for GSDIa. However, the current limitations of AAV-mediated gene transfer still represent a challenge for successful gene therapy in GSDI and GSDIII. Indeed, transgene loss over time was observed in GSDI liver, possibly due to the degeneration of hepatocytes underlying the physiopathology of both GSDI and GSDIII and leading to hepatic tumor development. Moreover, multitissue targeting requires high vector doses to target nonpermissive tissues such as muscle and kidney. Interestingly, recent pharmacological interventions or dietary regimen aiming at the amelioration of the hepatocyte abnormalities before the administration of gene therapy demonstrated improved efficacy in GSDs. In this review, we describe the advances in gene therapy and the limitations to be overcome to achieve efficient and safe gene transfer in GSDs.