Cardiac Pathology in Glycogen Storage Disease Type III

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.

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.

Sudden cardiac death in the young: A consensus statement on recommended practices for cardiac examination by pathologists from the Society for Cardiovascular Pathology

Sudden cardiac death is, by definition, an unexpected, untimely death caused by a cardiac condition in a person with known or unknown heart disease. This major international public health problem accounts for approximately 15-20% of all deaths. Typically more common in older adults with acquired heart disease, SCD also can occur in the young where the cause is more likely to be a genetically transmitted process. As these inherited disease processes can affect multiple family members, it is critical that these deaths are appropriately and thoroughly investigated. Across the United States, SCD cases in those less than 40 years of age will often fall under medical examiner/coroner jurisdiction resulting in scene investigation, review of available medical records and a complete autopsy including toxicological and histological studies. To date, there have not been consistent or uniform guidelines for cardiac examination in these cases. In addition, many medical examiner/coroner offices are understaffed and/or underfunded, both of which may hamper specialized examinations or studies (e.g., molecular testing). Use of such guidelines by pathologists in cases of SCD in decedents aged 1-39 years of age could result in life-saving medical intervention for other family members. These recommendations also may provide support for underfunded offices to argue for the significance of this specialized testing. As cardiac examinations in the setting of SCD in the young fall under ME/C jurisdiction, this consensus paper has been developed with members of the Society of Cardiovascular Pathology working with cardiovascular pathology-trained, practicing forensic pathologists.

Echocardiographic Assessment of Patients with Glycogen Storage Disease in a Single Center

Glycogen storage disease (GSD) is a hereditary metabolic disorder caused by enzyme deficiency resulting in glycogen accumulation in the liver, muscle, heart, or kidney. GSD types II, III, IV, and IX are associated with cardiac involvement. However, cardiac manifestation in other GSD types is unclear. This study aimed to describe whether energy deprivation and the toxic effects of accumulated glycogen affect the heart of patients with GSD. We evaluated the left ventricle (LV) wall mass, LV systolic and diastolic function and myocardial strain with conventional echocardiography and two-dimensional speckle-tracking echocardiography (2D STE) in 62 patients with GSD type I, III, VI and IX who visited the Wonju Severance Hospital in 2021. Among the GSD patients, the echocardiographic parameters of 55 pediatrics were converted into z-scores and analyzed. Of the patients, 43 (62.3%), 7 (11.3%) and 12 (19.4%) patients were diagnosed with GSD type I, type III, and type IX, respectively. The median age was 9 years (range, 1-36 years), with 55 children under 18 years old and seven adults over 18 years. For the 55 pediatric patients, the echocardiographic parameters were converted into a z-score and analyzed. Multiple linear regression analysis showed that the BMI z-score (p = 0.022) and CK (p = 0.020) predicted increased LV mass z-score, regardless of GSD type. There was no difference in the diastolic and systolic functions according to myocardial thickness; however, 2D STE showed a negative correlation with the LV mass (r = -0.28, p = 0.041). Given that patients with GSD tend to be overweight, serial evaluation with echocardiography might be required for all types of GSD.

Improvement in hypertrophic cardiomyopathy after using a high-fat, high-protein and low-carbohydrate diet in a non-adherent child with glycogen storage disease type IIIa

Background

Glycogen storage diseases type IIIa and b (GSDIII) are rare inherited metabolic disorders that are caused by deficiencies of the glycogen debranching enzyme, resulting in the accumulation of abnormal glycogen (‘limit dextrin’) in the muscles. The cardiac storage of limit dextrin causes a form of cardiomyopathy similar to primary hypertrophic cardiomyopathy. Treatment with a high fat diet is controversial but we report a positive outcome in a child with cardiomyopathy.

Case presentation

A 9-year-old boy with GSDIIIa developed left ventricular hypertrophy at 4.3 years of age. A high-fat (50%), high protein (20%), low-carbohydrates (30%) diet was introduced. After 18 months, echocardiogram, biochemical and clinical parameters improved (Creatine Kinase (CK), 1628➔1125 U/L; left ventricular outflow tract (LVOT), 35➔20 mmHg; interventricular septum (IVS), 21➔10 mm). The diet was abandoned for 2 years resulting in reversal of symptoms, but recommencement showed improvement after 6 months.

Conclusion

A high fat, high protein and low carbohydrate diet was successful in reversing cardiomyopathy. This form of treatment should be considered in children with GSD IIIa with cardiomyopathy.

The biallelic novel pathogenic variants in AGL gene in a chinese patient with glycogen storage disease type III

BACKGROUND

Glycogen storage disease type III (GSD III) is a rare autosomal recessive glycogenolysis disorder due to AGL gene variants, characterized by hepatomegaly, fasting hypoglycemia, hyperlipidemia, elevated hepatic transaminases, growth retardation, progressive myopathy, and cardiomyopathy. However, it is not easy to make a definite diagnosis in early stage of disease only based on the clinical phenotype and imageology due to its clinical heterogeneity.

CASE PRESENTATION

We report a two-year-old girl with GSD III from a nonconsanguineous Chinese family, who presented with hepatomegaly, fasting hypoglycemia, hyperlipidemia, elevated levels of transaminases. Accordingly, Sanger sequencing, whole‑exome sequencing of family trios, and qRT-PCR was performed, which revealed that the patient carried the compound heterogeneous variants, a novel frameshift mutation c.597delG (p. Q199Hfs*2) and a novel large gene fragment deletion of the entire exon 13 in AGL gene. The deletion of AGL was inherited from the proband's father and the c.597delG variant was from the mother.

CONCLUSIONS

In this study, we identified two novel variants c.597delG (p. Q199Hfs*2) and deletion of the entire exon 13 in AGL in a Chinese GSD III patient. We extend the mutation spectrum of AGL. We suggest that high-throughput sequencing technology can detect and screen pathogenic variant, which is a scientific basis about genetic counseling and clinical diagnosis.

Multi-Omics Approach Profiling Metabolic Remodeling in Early Systolic Dysfunction and in Overt Systolic Heart Failure

Metabolic remodeling plays an important role in the pathophysiology of heart failure (HF). We sought to characterize metabolic remodeling and implicated signaling pathways in two rat models of early systolic dysfunction (MOD), and overt systolic HF (SHF). Tandem mass tag-labeled shotgun proteomics, phospho-(p)-proteomics, and non-targeted metabolomics analyses were performed in left ventricular myocardium tissue from Sham, MOD, and SHF using liquid chromatography–mass spectrometry, n = 3 biological samples per group. Mitochondrial proteins were predominantly down-regulated in MOD (125) and SHF (328) vs. Sham. Of these, 82% (103/125) and 66% (218/328) were involved in metabolism and respiration. Oxidative phosphorylation, mitochondrial fatty acid β-oxidation, Krebs cycle, branched-chain amino acids, and amino acid (glutamine and tryptophan) degradation were highly enriched metabolic pathways that decreased in SHF > MOD. Glycogen and glucose degradation increased predominantly in MOD, whereas glycolysis and pyruvate metabolism decreased predominantly in SHF. PKA signaling at the endoplasmic reticulum–mt interface was attenuated in MOD, whereas overall PKA and AMPK cellular signaling were attenuated in SHF vs. Sham. In conclusion, metabolic remodeling plays an important role in myocardial remodeling. PKA and AMPK signaling crosstalk governs metabolic remodeling in progression to SHF.

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.

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.

Biomarkers in Glycogen Storage Diseases: An Update

Glycogen storage diseases (GSDs) are a group of 19 hereditary diseases caused by a lack of one or more enzymes involved in the synthesis or degradation of glycogen and are characterized by deposits or abnormal types of glycogen in tissues. Their frequency is very low and they are considered rare diseases. Except for X-linked type IX, the different types are inherited in an autosomal recessive pattern. In this study we reviewed the literature from 1977 to 2020 concerning GSDs, biomarkers, and metabolic imbalances in the symptoms of some GSDs. Most of the reported studies were performed with very few patients. Classification of emerging biomarkers between different types of diseases (hepatics GSDs, McArdle and PDs and other possible biomarkers) was done for better understanding. Calprotectin for hepatics GSDs and urinary glucose tetrasaccharide for Pompe disease have been approved for clinical use, and most of the markers mentioned in this review only need clinical validation, as a final step for their routine use. Most of the possible biomarkers are implied in hepatocellular adenomas, cardiomyopathies, in malfunction of skeletal muscle, in growth retardation, neutropenia, osteopenia and bowel inflammation. However, a few markers have lost interest due to a great variability of results, which is the case of biotinidase, actin alpha 2, smooth muscle, aorta and fibroblast growth factor receptor 4. This is the first review published on emerging biomarkers with a potential application to GSDs.

Histopathological substrate of the atrial myocardium in the progression of obstructive sleep apnoea-related atrial fibrillation

BACKGROUND

Obstructive sleep apnoea (OSA) is closely related to atrial fibrillation (AF), and OSA-induced atrial structural remodelling is the basis of AF maintenance. However, the process of atrial structural remodelling during the progression of acute OSA to chronic OSA is still unclear.

OBJECTIVE

To investigate changes in the atrial myocardium in acute sleep apnoea (6 h) and chronic sleep apnoea (12 weeks) by echocardiography, atrial myocardium morphology analysis, PAS staining, TUNEL staining, Masson's trichrome staining and analyses of ultrastructural changes.

METHODS

Eighteen adult beagle dogs under general anaesthesia were used to establish an OSA model. The animals were divided into the control group, acute OSA group and chronic OSA group, and there were six animals in each group. Cardiac ultrasounds of dogs from the three groups were examined. Left and right atrial muscle tissues were taken for HE staining, PAS staining, TUNEL staining, Masson's trichrome staining and transmission electron microscopy.

RESULTS

In the acute OSA model, the left atrial diameter of the dogs began to increase 3 h after ventilation, and this difference was more obvious at 6 h. The morphology of the myocardial cells did not change significantly, but mitochondrial swelling was observed in some atrial myocytes at 3 h. In the chronic OSA model, the left atrial diameter gradually increased, the volume of the right and left atria increased, the glycogen and collagen volume fractions and apoptosis ratio were significantly increased in atrial myocytes, mitochondria swelling and lengthening occurred in some atrial myocytes, the matrix became lighter, the mitochondrial ridge density decreased and the myofilament arrangement was disordered. The disc was distorted and not continuous, and there was some cardiomyocyte necrosis.

CONCLUSION

With the prolongation of apnoea, the atrium gradually enlarges, myocardial cells become disordered, glycogen aggregates, the number of necrotic cells increases, fibrosis worsens, mitochondrial abnormalities occur and the arrangement of the discs are disordered, providing a basis for the maintenance of AF.

Liver fibrosis during clinical ascertainment of glycogen storage disease type III: a need for improved and systematic monitoring

PURPOSE

In glycogen storage disease type III (GSD III), liver aminotransferases tend to normalize with age giving an impression that hepatic manifestations improve with age. However, despite dietary treatment, long-term liver complications emerge. We present a GSD III liver natural history study in children to better understand changes in hepatic parameters with age.

METHODS

We reviewed clinical, biochemical, histological, and radiological data in pediatric patients with GSD III, and performed a literature review of GSD III hepatic findings.

RESULTS

Twenty-six patients (median age 12.5 years, range 2-22) with GSD IIIa (n = 23) and IIIb (n = 3) were enrolled in the study. Six of seven pediatric patients showed severe fibrosis on liver biopsy (median [range] age: 1.25 [0.75-7] years). Markers of liver injury (aminotransferases), dysfunction (cholesterol, triglycerides), and glycogen storage (glucose tetrasaccharide, Glc₄) were elevated at an early age, and decreased significantly thereafter (p < 0.001). Creatine phosphokinase was also elevated with no significant correlation with age (p = 0.4).

CONCLUSION

Liver fibrosis can occur at an early age, and may explain the decrease in aminotransferases and Glc₄ with age. Our data outlines the need for systematic follow-up and specific biochemical and radiological tools to monitor the silent course of the liver disease process.

Distinct Clinical and Genetic Findings in Iranian Patients With Glycogen Storage Disease Type 3

OBJECTIVES

Glycogen storage disease type 3 (GSD-III) is a rare inherited metabolic disorder caused by glycogen debranching enzyme deficiency. Various pathogenic mutations of the AGL gene lead to abnormal accumulation of glycogen in liver, skeletal, and cardiac muscles. Here, we report distinct clinical and genetic data of Iranian patients with GSD-III.

METHODS

Clinical and laboratory data of 5 patients with GSD-III were recorded. Genetic investigation was performed to identify the causative mutations.

RESULTS

Three patients had typical liver involvement in childhood and one was diagnosed 2 years after liver transplantation for cirrhosis of unknown etiology. Four patients had vacuolar myopathy with glycogen excess in muscle biopsy. All patients had novel homozygous mutations of the AGL gene namely c.378T>A, c.3295T>C, c.3777G>A, c.2002-2A>G, and c.1183C>T.

CONCLUSIONS

This is the first comprehensive report of patients with GSD-III in Iran with 2 uncommon clinical presentations and 5 novel mutations in the AGL gene.

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.

Rescue of GSDIII Phenotype with Gene Transfer Requires Liver- and Muscle-Targeted GDE Expression

Glycogen storage disease type III (GSDIII) is an autosomal recessive disorder caused by a deficiency of glycogen-debranching enzyme (GDE), which results in profound liver metabolism impairment and muscle weakness. To date, no cure is available for GSDIII and current treatments are mostly based on diet. Here we describe the development of a mouse model of GSDIII, which faithfully recapitulates the main features of the human condition. We used this model to develop and test novel therapies based on adeno-associated virus (AAV) vector-mediated gene transfer. First, we showed that overexpression of the lysosomal enzyme alpha-acid glucosidase (GAA) with an AAV vector led to a decrease in liver glycogen content but failed to reverse the disease phenotype. Using dual overlapping AAV vectors expressing the GDE transgene in muscle, we showed functional rescue with no impact on glucose metabolism. Liver expression of GDE, conversely, had a direct impact on blood glucose levels. These results provide proof of concept of correction of GSDIII with AAV vectors, and they indicate that restoration of the enzyme deficiency in muscle and liver is necessary to address both the metabolic and neuromuscular manifestations of the disease.

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.

[Characteristics of lipid metabolism and the cardiovascular system in glycogenosis types I and III]

Glycogen storage disease (GSD) is an inherited metabolic disorder characterized by early childhood lipid metabolic disturbances with potentially proatherogenic effects. The review outlines the characteristics of impaired lipid composition and other changes in the cardiovascular system in GSD types I and III. It analyzes the factors enabling and inhibiting the development of atherosclerosis in patients with GSD. The review describes the paradox of vascular resistance to the development of early atherosclerosis despite the proatherogenic composition of lipids in the patients of this group.

High prevalence of arrhythmic and myocardial complications in patients with cardiac glycogenosis due to PRKAG2 mutations

AIMS

Mutations in PRKAG2, the gene encoding for the γ2 subunit of 5'-AMP-activated protein kinase (AMPK), are responsible for an autosomal dominant glycogenosis with a cardiac presentation, associating hypertrophic cardiomyopathy (HCM), ventricular pre-excitation (VPE), and progressive heart block. The aim of this study was to perform a retrospective time-to-event study of the clinical manifestations associated with PRKAG2 mutations.

METHODS AND RESULTS

A cohort of 34 patients from 9 families was recruited between 2001 and 2010. DNA were sequenced on all exons and flanking sequences of the PRKAG2 gene using Sanger sequencing. Overall, four families carried the recurrent p.Arg302Gln mutation, and the five others carried private mutations among which three had never been reported. In the total cohort, at 40 years of age, the risk of developing HCM was 61%, VPE 70%, conduction block 22%, and sudden cardiac death (SCD) 20%. The global survival at 60 years of age was 66%. Thirty-two per cent of patients (N = 10) required a device implantation (5 pacemakers and 5 defibrillators) at a median age of 66 years, and two patients required heart transplant. Only one patient presented with significant skeletal muscle symptoms. No significant differences regarding the occurrence of VPE, ablation complications, or death incidence were observed between different mutations.

CONCLUSION

This study of patients with PRKAG2 mutations provides a more comprehensive view of the natural history of this disease and demonstrates a high risk of cardiac complications. Early recognition of this disease appears important to allow an appropriate management.

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.

Rapamycin transiently induces mitochondrial remodeling to reprogram energy metabolism in old hearts

Rapamycin, an inhibitor of mTOR signaling, has been shown to reverse diastolic dysfunction in old mice in 10 weeks, highlighting its therapeutic potential for a poorly treatable condition. However, the mechanisms and temporal regulation of its cardiac benefits remain unclear. We show that improved diastolic function in old mice begins at 2-4 weeks, progressing over the course of 10-week treatment. While TORC1-mediated S6 phosphorylation and TORC2 mediated AKT and PKCα phosphorylation are inhibited throughout the course of treatment, rapamycin inhibits ULK phosphorylation and induces autophagy during just the first week of treatment, returning to baseline at two weeks and after. Concordantly, markers of mitochondrial biogenesis increase over the first two weeks of treatment and return to control levels thereafter. This transient induction of autophagy and mitochondrial biogenesis suggests that damaged mitochondria are replaced by newly synthesized ones to rejuvenate mitochondrial homeostasis. This remodeling is shown to rapidly reverse the age-related reduction in fatty acid oxidation to restore a more youthful substrate utilization and energetic profile in old isolated perfused hearts, and modulates the myocardial metabolomein vivo. This study demonstrates the differential and dynamic mechanisms following rapamycin treatment and highlights the importance of understanding the temporal regulation of rapamycin effects.

Natural Progression of Canine Glycogen Storage Disease Type IIIa

Glycogen storage disease type IIIa (GSD IIIa) is caused by a deficiency of glycogen debranching enzyme activity. Hepatomegaly, muscle degeneration, and hypoglycemia occur in human patients at an early age. Long-term complications include liver cirrhosis, hepatic adenomas, and generalized myopathy. A naturally occurring canine model of GSD IIIa that mimics the human disease has been described, with progressive liver disease and skeletal muscle damage likely due to excess glycogen deposition. In the current study, long-term follow-up of previously described GSD IIIa dogs until 32 mo of age (n = 4) and of family-owned GSD IIIa dogs until 11 to 12 y of age (n = 2) revealed that elevated concentrations of liver and muscle enzyme (AST, ALT, ALP, and creatine phosphokinase) decreased over time, consistent with hepatic cirrhosis and muscle fibrosis. Glycogen deposition in many skeletal muscles; the tongue, diaphragm, and heart; and the phrenic and sciatic nerves occurred also. Furthermore, the urinary biomarker Glc4, which has been described in many types of GSD, was first elevated and then decreased later in life. This urinary biomarker demonstrated a similar trend as AST and ALT in GSD IIIa dogs, indicating that Glc4 might be a less invasive biomarker of hepatocellular disease. Finally, the current study further demonstrates that the canine GSD IIIa model adheres to the clinical course in human patients with this disorder and is an appropriate model for developing novel therapies.

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

Glycogen storage disease type III (GSD III) may present with hepatic disease or may involve both skeletal and cardiac muscles as well. To assess the prevalence of neuromuscular and cardiac involvement in a group of children with GSD III, 28 children with GSD III, diagnosed by enzymatic assay, were enrolled in the study after an informed consent was obtained from their parents/guardians and after the study protocol was approved by our institutional ethical committee. Their mean age was 6.6 + 3.1 years. All cases were assessed neurologically by clinical examination, electromyography (EMG), and nerve conduction velocity. The heart was examined clinically by electrocardiogram and echocardiography. Seventeen patients (61 %) had myopathic changes by EMG, three of them had associated neuropathic changes. Creatine phosphokinase (CPK) was elevated in all myopathic cases except one. Children with myopathic changes were significantly older (p = 0.02), and CPK was significantly higher (p < 0.0001). Nine cases had left ventricular (LV) hypertrophy, seven of them had myopathic changes by EMG.

CONCLUSION

Myopathic changes are not uncommon in children with GSD III. Myopathic changes tend to occur in older age and are associated with higher CPK level. Cardiac muscle involvement is less common in this age group and may, on occasion, occur alone without skeletal muscle involvement. Despite mild degrees of affection in this age group, it is recommended to perform prospective annual screening using EMG and echocardiography in order to augment dietary therapy regimen to prevent progression to life threatening complications.

Hepatic glycogen storage disorders: what have we learned in recent years?

PURPOSE OF REVIEW

Glycogen storage disorders (GSDs) are inborn errors of metabolism with abnormal storage or utilization of glycogen. The present review focuses on recent advances in hepatic GSD types I, III and VI/IX, with emphasis on clinical aspects and treatment.

RECENT FINDINGS

Evidence accumulates that poor metabolic control is a risk factor for the development of long-term complications, such as liver adenomas, low bone density/osteoporosis, and kidney disease in GSD I. However, mechanisms leading to these complications remain poorly understood and are being investigated. Molecular causes underlying neutropenia and neutrophil dysfunction in GSD I have been elucidated. Case series provide new insights into the natural course and outcome of GSD types VI and IX. For GSD III, a high protein/fat diet has been reported to improve (cardio)myopathy, but the beneficial effect of this dietary concept on muscle and liver disease manifestations needs to be further established in prospective studies.

SUMMARY

Although further knowledge has been gained regarding pathophysiology, disease course, treatment, and complications of hepatic GSDs, more controlled prospective studies are needed to assess effects of different dietary and medical treatment options on long-term outcome and quality of life.

Postmortem Findings and Clinical Correlates in Individuals with Infantile-Onset Pompe Disease

Pompe disease (OMIM 232300), a glycogen storage disorder caused by deficiency in the lysosomal enzyme acid alpha-glucosidase (EC 3.2.1.20), results in weakness and cardiomyopathy in infants affected with the classic form. Although the primary disease manifestations are due to glycogen accumulation in skeletal and cardiac muscle, glycogen also accumulates in a variety of additional tissues. To improve our understanding of disease pathogenesis in long-term survivors, we reviewed postmortem results for three infants with the classic form of Pompe disease. We have observed a number of new complications in long-term survivors of infantile-onset Pompe disease, and we focused this postmortem study on pathological correlates. Findings in survivors include cardiac arrhythmias, which may be related to glycogen accumulation in cardiac conduction tissue; urinary incontinence, likely due to glycogen accumulation in smooth muscle; and refractory errors, possibly related to accumulation in ocular structures. These observations provide potential pathophysiologic correlates for complications in long-term survivors of infantile Pompe disease.

Glycogen storage disease type III: modified Atkins diet improves myopathy

BACKGROUND

Frequent feeds with carbohydrate-rich meals or continuous enteral feeding has been the therapy of choice in glycogen storage disease (Glycogenosis) type III. Recent guidelines on diagnosis and management recommend frequent feedings with high complex carbohydrates or cornstarch avoiding fasting in children, while in adults a low-carb-high-protein-diet is recommended. While this regimen can prevent hypoglycaemia in children it does not improve skeletal and heart muscle function, which are compromised in patients with glycogenosis IIIa. Administration of carbohydrates may elicit reactive hyperinsulinism, resulting in suppression of lipolysis, ketogenesis, gluconeogenesis, and activation of glycogen synthesis. Thus, heart and skeletal muscle are depleted of energy substrates. Modified Atkins diet leads to increased blood levels of ketone bodies and fatty acids. We hypothesize that this health care intervention improves the energetic balance of muscles.

METHODS

We treated 2 boys with glycogenosis IIIa aged 9 and 11 years with a modified Atkins diet (10 g carbohydrate per day, protein and fatty acids ad libitum) over a period of 32 and 26 months, respectively.

RESULTS

In both patients, creatine kinase levels in blood dropped in response to Atkins diet. When diet was withdrawn in one of the patients he complained of chest pain, reduced physical strength and creatine kinase levels rapidly increased. This was reversed when Atkins diet was reintroduced. One patient suffered from severe cardiomyopathy which significantly improved under diet. Patients with glycogenosis IIIa benefit from an improved energetic state of heart and skeletal muscle by introduction of Atkins diet both on a biochemical and clinical level. Apart from transient hypoglycaemia no serious adverse effects were observed.

Improvement of Cardiomyopathy After High-Fat Diet in Two Siblings with Glycogen Storage Disease Type III

Glycogenosis type III (GSD III) is an autosomal recessive disorder due to amylo-1,6-glucosidase deficiency. This disease causes limit dextrin storage in affected tissues: liver, skeletal muscles, and heart in GSD IIIa and only liver in GSD IIIb. Cardiomyopathy is quite frequent in GSD IIIa with variable severity and progression of manifestations. It is not clear if diet manipulation may interfere with cardiomyopathy's progression. Recent case reports showed improvement of cardiomyopathy following a ketogenic diet.Two siblings (girl and boy), 7- and 5-year-old, both affected with GSD IIIa, developed severe and rapidly worsening left ventricular hypertrophy in the first years of life, while treated with frequent diurnal and nocturnal hyperproteic meals followed by orally administered uncooked cornstarch. Subsequently they were treated with high-fat (60%) and high-protein (25%), low-carbohydrate (15%) diet. After 12 months exertion dyspnea disappeared in the girl and biochemical blood tests, cardiac enzymes, and congestive heart failure markers improved in both (CK 3439→324, 1304→581 U/L; NT-proBNP 2084→206, 782→135 pg/mL, respectively); ultrasound assessment in both patients showed a relevant reduction of the thickness of interventricular septum (30→16, 16→11 mm, respectively) and left ventricle posterior wall (18→7, 13→8 mm, respectively) and an improvement of the outflow obstruction. A diet rich in fats as well as proteins and poor in carbohydrates could be a beneficial therapeutic choice for GSD III with cardiomyopathy. Future research is needed to confirm the beneficial effect of this treatment and to design treatment strategies with the aim to provide alternative source of energy and prevent glycogen accumulation.

Glycogen storage disease type III in Egyptian children: a single centre clinico-laboratory study

BACKGROUND AND STUDY AIMS

Glycogen storage disease type III (GSD III) is an autosomal recessive disorder caused by deficiency of glycogen debrancher enzyme and is characterised by clinical variability.

PATIENTS AND METHODS

We herein describe the clinical and laboratory findings in 31 Egyptian patients with GSD III presenting to the Paediatric Hepatology Unit, Cairo University, Egypt.

RESULTS

Eighteen patients (58%) were males. Their ages ranged between 6 months to 12 years. The main presenting complaint was progressive abdominal distention in 55%. Twelve patients (38.7%) had a history of recurrent attacks of convulsions; four had an erroneous diagnosis of hypocalcaemia and epilepsy. Doll-like facies was noted in 90%. Abdominal examination of all cases revealed abdominal distention and soft hepatomegaly which had bright echogenicity by ultrasound. Hypertriglyceridaemia was present in 93.6%, hyperlactacidaemia in 51.6% and hyperuricaemia in 19.4%. Liver biopsy showed markedly distended hepatocytes with well distinct cytoplasmic boundaries and 32% had macrovesicular fatty changes. Serum creatine kinase was elevated in 64.6% of patients and correlated positively and significantly with age (r=0.7 and P=<0.001), while serum triglycerides correlated negatively with age (r=-0.4 and P=0.05).

CONCLUSION

Blood glucose assessment and search for hepatomegaly in an infant with recurrent seizures may prevent delay in the diagnosis. A huge soft liver reaching the left midclavicular line that appears echogenic on ultrasonography is characteristic of GSD III. A distended hepatocyte with rarified cytoplasm is pathognomonic but not diagnostic. Hypertriglyceridaemia correlates negatively with age, in contrary to CK level.