Glycogen storage disease: clinical, biochemical, and molecular heterogeneity

Role of glucose metabolism in amelogenesis

BACKGROUND

Cell energy metabolism plays a pivotal role in organ development and function by regulating cell behavior in pathophysiological conditions. Glucose metabolism is the central cascade for obtaining energy in mammalian cells, and cells alter the glucose metabolic pathway depending on intra- and extracellular environments. Therefore, glucose metabolism is closely associated with cell differentiation stages, and cell energy metabolism plays a vital role not only in energy production but also in cell fate regulation in organogenesis.

HIGHLIGHT

During enamel formation, the timing of the expression of passive and active glucose transporters, glycogen synthesis, and glycogen degradation is strictly regulated according to the energy demand of ameloblast-lineage cells. These glucose metabolic reactions are particularly active in the maturation stage of ameloblasts. Furthermore, autophagy, a key regulator of cellular energy homeostasis that modulates glucose metabolism, occurs during both the secretory and maturation stages of ameloblasts. Disruption of glucose metabolism cascade and autophagy induces enamel hypoplasia, as demonstrated in both in vitro and in vivo models.

CONCLUSION

Adequate energy supply via glucose metabolism is essential for enamel matrix secretion and maturation. A thorough understanding of the precise regulation of energy metabolism in amelogenesis facilitates comprehension of the normal enamel formation process and pathological conditions affecting it. This review summarizes glucose metabolic processes during amelogenesis, focusing on glucose uptake, glycogenesis, and glycogenolysis.

A deep learning approach for blood glucose monitoring and hypoglycemia prediction in glycogen storage disease

Glycogen storage disease (GSD) is a group of rare inherited metabolic disorders characterized by abnormal glycogen storage and breakdown. These disorders are caused by mutations in G6PC1, which is essential for proper glucose storage and metabolism. With the advent of continuous glucose monitoring systems, development of algorithms to analyze and predict glucose levels has gained considerable attention, with the aim of preemptively managing fluctuations before they become problematic. However, there is a lack of research focusing specifically on patients with GSD. Therefore, this study aimed to forecast glucose levels in patients with GSD using state-of-the-art deep-learning (DL) algorithms. This retrospective study utilized blood glucose data from patients with GSD who were either hospitalized or managed at Yonsei University Wonju Severance Christian Hospital, Korea, between August 2020 and February 2024. In this study, three state-of-the-art DL models for time-series forecasting were employed: PatchTST, LTSF N-Linear, and TS Mixer. First, the models were used to predict the patients' Glucose levels for the next hour. Second, a binary classification task was performed to assess whether hypoglycemia could be predicted alongside direct glucose levels. Consequently, this is the first study to demonstrate the capability of forecasting glucose levels in patients with GSD using continuous glucose-monitoring data and DL models. Our model provides patients with GSD with a more accessible tool for managing glucose levels. This study has a broader effect, potentially serving as a foundation for improving the care of patients with rare diseases using DL-based solutions.

Broadening the Phenotype and Genotype Spectrum of Glycogen Storage Disease by Unraveling Novel Variants in an Iranian Patient Cohort

Glycogen storage diseases (GSDs) are a group of rare inherited metabolic disorders characterized by clinical, locus, and allele heterogeneity. This study aims to investigate the phenotype and genotype spectrum of GSDs in a cohort of 14 families from Iran using whole-exome sequencing (WES) and variant analysis. WES was performed on 14 patients clinically suspected of GSDs. Variant analysis was performed to identify genetic variants associated with GSDs. A total of 13 variants were identified, including six novel variants, and seven previously reported pathogenic variants in genes such as AGL, G6PC, GAA, PYGL, PYGM, GBE1, SLC37A4, and PHKA2. Most types of GSDs observed in the cohort were associated with hepatomegaly, which was the most common clinical presentation. This study provides valuable insights into the phenotype and genotype spectrum of GSDs in a cohort of Iranian patients. The identification of novel variants adds to the growing body of knowledge regarding the genetic landscape of GSDs and has implications for genetic counseling and future therapeutic interventions. The diverse nature of GSDs underscores the need for comprehensive genetic testing methods to improve diagnostic accuracy. Continued research in this field will enhance our understanding of GSDs, ultimately leading to improved management and outcomes for individuals affected by these rare metabolic disorders.

Metabolic aspects of glycogenolysis with special attention to McArdle disease

The physiological function of muscle glycogen is to meet the energy demands of muscle contraction. The breakdown of glycogen occurs through two distinct pathways, primarily cytosolic and partially lysosomal. To obtain the necessary energy for their function, skeletal muscles utilise also fatty acids in the β-oxidation. Ketogenesis is an alternative metabolic pathway for fatty acids, which provides an energy source during fasting and starvation. Diseases arising from impaired glycogenolysis lead to muscle weakness and dysfunction. Here, we focused on the lack of muscle glycogen phosphorylase (PYGM), a rate-limiting enzyme for glycogenolysis in skeletal muscles, which leads to McArdle disease. Metabolic myopathies represent a group of genetic disorders characterised by the limited ability of skeletal muscles to generate energy. Here, we discuss the metabolic aspects of glycogenosis with a focus on McArdle disease, offering insights into its pathophysiology. Glycogen accumulation may influence the muscle metabolic dynamics in different ways. We emphasize that a proper treatment approach for such diseases requires addressing three important and interrelated aspects, which include: symptom relief therapy, elimination of the cause of the disease (lack of a functional enzyme) and effective and early diagnosis.

Lysosomal Dysfunction: Connecting the Dots in the Landscape of Human Diseases

Lysosomes are the main organelles responsible for the degradation of macromolecules in eukaryotic cells. Beyond their fundamental role in degradation, lysosomes are involved in different physiological processes such as autophagy, nutrient sensing, and intracellular signaling. In some circumstances, lysosomal abnormalities underlie several human pathologies with different etiologies known as known as lysosomal storage disorders (LSDs). These disorders can result from deficiencies in primary lysosomal enzymes, dysfunction of lysosomal enzyme activators, alterations in modifiers that impact lysosomal function, or changes in membrane-associated proteins, among other factors. The clinical phenotype observed in affected patients hinges on the type and location of the accumulating substrate, influenced by genetic mutations and residual enzyme activity. In this context, the scientific community is dedicated to exploring potential therapeutic approaches, striving not only to extend lifespan but also to enhance the overall quality of life for individuals afflicted with LSDs. This review provides insights into lysosomal dysfunction from a molecular perspective, particularly in the context of human diseases, and highlights recent advancements and breakthroughs in this field.

Severe perioperative lactic acidosis in a pediatric patient with glycogen storage disease type Ia: a case report

BACKGROUND

Glycogen storage disease (GSD) is a group of rare inherited metabolic disorders caused by enzyme deficiencies in glycogen catabolism. GSD type Ia is a congenital deficiency of the enzyme responsible for the final step in glucose production by glycolysis, resulting in impaired carbohydrate metabolism.

CASE PRESENTATION

A 14-year-old boy with GSD type Ia was scheduled for a maxillary cystectomy under general anesthesia. He was taking oral sugars such as uncooked cornstarch regularly to prevent hypoglycemia. Perioperatively, glucose was administered via the peripheral vein for fasting; however, severe lactic acidosis occurred. He also developed hypercapnia because of intraoperative poor ventilation caused by hepatomegaly.

CONCLUSIONS

We experienced a child with GSD type Ia who developed severe lactic acidosis despite continuous glucose infusion. Further studies are required to determine appropriate perioperative management for patients with GSD, including fasting glucose administration.

Aberrant glucose metabolism underlies impaired macrophage differentiation in glycogen storage disease type Ib

Glycogen storage disease type Ib (GSD-Ib) is an autosomal recessive disorder caused by a deficiency in the glucose-6-phosphate (G6P) transporter (G6PT) that is responsible for transporting G6P into the endoplasmic reticulum. GSD-Ib is characterized by disturbances in glucose homeostasis, neutropenia, and neutrophil dysfunction. Although some studies have explored neutrophils abnormalities in GSD-Ib, investigations regarding monocytes/macrophages remain limited so far. In this study, we examined the impact of G6PT deficiency on monocyte-to-macrophage differentiation using bone marrow-derived monocytes from G6pt-/- mice as well as G6PT-deficient human THP-1 monocytes. Our findings revealed that G6PT-deficient monocytes exhibited immature differentiation into macrophages. Notably, the impaired differentiation observed in G6PT-deficient monocytes seemed to be associated with abnormal glucose metabolism, characterized by enhanced glucose consumption through glycolysis, even under quiescent conditions with oxidative phosphorylation. Furthermore, we observed a reduced secretion of inflammatory cytokines in G6PT-deficient THP-1 monocytes during the inflammatory response, despite their elevated glucose consumption. In conclusion, this study sheds light on the significance of G6PT in monocyte-to-macrophage differentiation and underscores its importance in maintaining glucose homeostasis and supporting immune response in GSD-Ib. These findings may contribute to a better understanding of the pathogenesis of GSD-Ib and potentially pave the way for the development of targeted therapeutic interventions.

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.

The structural mechanism of human glycogen synthesis by the GYS1-GYG1 complex

Glycogen is the primary energy reserve in mammals, and dysregulation of glycogen metabolism can result in glycogen storage diseases (GSDs). In muscle, glycogen synthesis is initiated by the enzymes glycogenin-1 (GYG1), which seeds the molecule by autoglucosylation, and glycogen synthase-1 (GYS1), which extends the glycogen chain. Although both enzymes are required for proper glycogen production, the nature of their interaction has been enigmatic. Here, we present the human GYS1:GYG1 complex in multiple conformations representing different functional states. We observe an asymmetric conformation of GYS1 that exposes an interface for close GYG1 association, and propose this state facilitates handoff of the GYG1-associated glycogen chain to a GYS1 subunit for elongation. Full activation of GYS1 widens the GYG1-binding groove, enabling GYG1 release concomitant with glycogen chain growth. This structural mechanism connecting chain nucleation and extension explains the apparent stepwise nature of glycogen synthesis and suggests distinct states to target for GSD-modifying therapeutics.

Hepatic manifestations of systemic disease: an imaging-based review

The liver is responsible for many processes that maintain human metabolic homeostasis and can be affected by several pediatric systemic diseases. In this manuscript, we explore key pathological findings and imaging features across multiple modalities of a spectrum of congenital, metabolic and autoimmune disorders. Strengthening the radiologists' knowledge regarding potential hepatic manifestations of these systemic diseases will ultimately lead to improved care for pediatric patients.

Diagnosis and follow-up of Glycogen Storage Disease (GSD) Type VI from the largest GSD center in China

Glycogen storage disease (GSD) type VI is a glycogenolysis disorder caused by variants of PYGL. Knowledge about this disease is limited because only approximately 50 cases have been reported. we investigated the clinical profiles, molecular diagnosis, and treatment outcomes in patients with gsd VI from 2000 to 2021. The main initial clinical features of this cohort include hepatomegaly, short stature, elevated liver transaminases, hypertriglyceridemia, fasting hypoglycemia, and hyperuricemia. After uncooked cornstarch treatment, the stature and biochemical parameters improved significantly (P < 0.05). However, hyperuricemia recurred in most patients during adolescence. Among the 56 GSD VI patients, 54 biallelic variants and two single allelic variants of PYGL were identified, of which 43 were novel. There were two hotspot variants, c.1621-258_2178-23del and c.2467C>T p.(Gln823*), mainly in patients from Southwest and South China. c.1621-258_2178-23del is a 3.6 kb deletion that results in an out-of-frame deletion r.1621_2177del and an in-frame deletion r.1621_2265del. Our data show for the first time that long-term monitoring of uric acid is recommended for older GSD VI patients. This study also broadens the variant spectrum of PYGL and indicates that there are two hot-spot variants in China. This article is protected by copyright. All rights reserved.

Organ defects of the Usp7 mutant mouse strain indicate the essential role of K63-polyubiquitinated Usp7 in organ formation

BACKGROUND

K63-linked polyubiquitination of proteins have nonproteolytic functions and regulate the activity of many signal transduction pathways. USP7, a HIF1α deubiquitinase, undergoes K63-linked polyubiquitination under hypoxia. K63-polyubiquitinated USP7 serves as a scaffold to anchor HIF1α, CREBBP, the mediator complex, and the super elongation complex to enhance HIF1α-induced gene transcription. However, the physiological role of K63-polyubiquitinated USP7 remains unknown.

METHODS

Using a Usp7^K444R point mutation knock-in mouse strain, we performed immunohistochemistry and standard molecular biological methods to examine the organ defects of liver and kidney in this knock-in mouse strain. Mechanistic studies were performed by using deubiquitination, immunoprecipitation, and quantitative immunoprecipitations (qChIP) assays.

RESULTS

We observed multiple organ defects, including decreased liver and muscle weight, decreased tibia/fibula length, liver glycogen storage defect, and polycystic kidneys. The underlying mechanisms include the regulation of protein stability and/or modulation of transcriptional activation of several key factors, leading to decreased protein levels of Prr5l, Hnf4α, Cebpα, and Hnf1β. Repression of these crucial factors leads to the organ defects described above.

CONCLUSIONS

K63-polyubiquitinated Usp7 plays an essential role in the development of multiple organs and illustrates the importance of the process of K63-linked polyubiquitination in regulating critical protein functions.

mRNA therapy restores euglycemia and prevents liver tumors in murine model of glycogen storage disease

Glycogen Storage Disease 1a (GSD1a) is a rare, inherited metabolic disorder caused by deficiency of glucose 6-phosphatase (G6Pase-α). G6Pase-α is critical for maintaining interprandial euglycemia. GSD1a patients exhibit life-threatening hypoglycemia and long-term liver complications including hepatocellular adenomas (HCAs) and carcinomas (HCCs). There is no treatment for GSD1a and the current standard-of-care for managing hypoglycemia (Glycosade®/modified cornstarch) fails to prevent HCA/HCC risk. Therapeutic modalities such as enzyme replacement therapy and gene therapy are not ideal options for patients due to challenges in drug-delivery, efficacy, and safety. To develop a new treatment for GSD1a capable of addressing both the life-threatening hypoglycemia and HCA/HCC risk, we encapsulated engineered mRNAs encoding human G6Pase-α in lipid nanoparticles. We demonstrate the efficacy and safety of our approach in a preclinical murine model that phenotypically resembles the human condition, thus presenting a potential therapy that could have a significant therapeutic impact on the treatment of GSD1a.

Liver Transplantation for Glycogen Storage Disease Type IV

Glycogen storage disease type IV (GSD IV) is a rare autosomal recessive disorder caused by glycogen-branching enzyme (GBE) deficiency, leading to accumulation of amylopectin-like glycogen that may damage affected tissues. The clinical manifestations of GSD IV are heterogeneous; one of which is the classic manifestation of progressive hepatic fibrosis. There is no specific treatment available for GSD IV. Currently, liver transplantation is an option. It is crucial to evaluate long-term outcomes of liver transplantation. We reviewed the published literature for GSD IV patients undergoing liver transplantation. To date, some successful liver transplantations have increased the quantity and quality of life in patients. Although the extrahepatic manifestations of GSD IV may still progress after transplantation, especially cardiomyopathy. Patients with cardiac involvement are candidates for cardiac transplantation. Liver transplantation remains the only effective therapeutic option for treatment of GSD IV. However, liver transplantation may not alter the extrahepatic progression of GSD IV. Patients should be carefully assessed before liver transplantation.

Role of Metabolism in Bone Development and Homeostasis

Carbohydrates, fats, and proteins are the underlying energy sources for animals and are catabolized through specific biochemical cascades involving numerous enzymes. The catabolites and metabolites in these metabolic pathways are crucial for many cellular functions; therefore, an imbalance and/or dysregulation of these pathways causes cellular dysfunction, resulting in various metabolic diseases. Bone, a highly mineralized organ that serves as a skeleton of the body, undergoes continuous active turnover, which is required for the maintenance of healthy bony components through the deposition and resorption of bone matrix and minerals. This highly coordinated event is regulated throughout life by bone cells such as osteoblasts, osteoclasts, and osteocytes, and requires synchronized activities from different metabolic pathways. Here, we aim to provide a comprehensive review of the cellular metabolism involved in bone development and homeostasis, as revealed by mouse genetic studies.

Other types of diffuse liver disease: is there a way to do it?

There are a variety of less common diffuse liver diseases that can be asymptomatic or cause severe liver dysfunction. For the majority of them, the association of clinical, laboratory, and imaging findings are needed to narrow the differential diagnosis. In this article, we will review and describe the rarer diffuse liver diseases including drug-related liver disease, inflammatory and infectious diseases, and deposition disorders such as amyloidosis, glycogen storage disease, Wilson's disease, and alpha-1 antitrypsin deficiency. Abdominal radiologists should be familiar with the imaging features of different types of diffuse liver diseases to help the multidisciplinary team involved in the treatment of these patients. The data related to some of these conditions are scarce and sometimes experimental, but we want to demonstrate to the reader the value of imaging techniques in their analysis and introduce the potential of new imaging methods.

Diagnosis of hepatic glycogen storage disease patients with overlapping clinical symptoms by massively parallel sequencing: a systematic review of literature

BACKGROUND

Glycogen storage diseases (GSDs) with liver involvement are complex disorders with similar manifestations. Currently, the main diagnostic methods such as tissue diagnosis, either histopathology or enzyme assay, are invasive. Meanwhile, GSDs are diseases with significant genetic heterogeneity, and gene-sequencing methods can be more useful. This systematic review aims to review the literature to assess the value of massively parallel sequencing in the diagnosis of GSDs on patients with previously undiagnosed hepatic involvement.

METHODS

Relevant studies identified in the MEDLINE/PubMed, EMBASE, Cochrane Library, Scopus, and Web of Science Core Collection databases up to July 2019 with no time and language restrictions. Publications were included in the review if they analyzed GSDs with hepatic involvement (GSD I, GSD III, GSD IV, GSD VI, GSD IX), using targeted gene sequencing (TGS) or exome sequencing (ES).

RESULTS

Eleven studies were included in this systematic review. ES demonstrated a 93% diagnostic yield. These methods correctly distinguished all types of pathogenic variants. The diagnostic yield of the TGS method was around 79.7%.

CONCLUSIONS

According to our results, TGS analysis can be considered as the first-line diagnostic method with valuable results and ES can be used to diagnose complex cases of GSD with liver involvement. Overall, these molecular methods are considered as accurate diagnostic tools, which expedite correct diagnosis and treatment with significant cost-effectiveness by reducing unnecessary and inaccurate tests.

PROSPERO REGISTRATION

CRD42020139931. Registered 8 January 2020.

An infant presenting with extreme hypertriglyceridemia diagnosed as glycogen storage disease type Ia

Background Marked hypertriglyceridemia in infancy is extremely rare. Patients with severe hypertriglyceridemia in early life may be unmasked by a primary or secondary cause. Case presentation A female infant was born in a good condition with normal Apgar scores. No special clinical symptoms and signs had been found within the first two months of life. Poor oral intake and failure to thrive were two main clinical manifestations when she was referred to our hospital at the age of 3.5 months. The milky serum was the only one characteristic presentation. Laboratory testing showed extremely high level of triglycerides, cholesterol and lactate. Many other laboratory indexes cannot be detected because of severe hyperlipemic samples. Multi-gene panel testing for 249 genes about genetic and metabolic liver disease were performed. Gene analysis revealed a G6PC gene deficiency. The patient was a homozygote for c.248G > A, p.R83H and her parents were both the heterozygotes. The infant had been diagnosed as glycogen storage disease type Ia. Conclusions We report an infant presenting with extreme hypertriglyceridemia diagnosed as glycogen storage disease type Ia by genetic testing. The gene panel can be used to confirm the diagnosis and delineate the exact type of glycogen storage disease, which could ultimately really help to reduce unnecessary tests and invasive examinations. Serum lipid should be close monitoring in order to prevent the complications and improve the prognosis.

Nutrition and medical support during pregnancy and lactation in women with inborn errors of intermediary metabolism disorders (IEMDs)

The establishment of expanded newborn screening (NBS) not only results in the early diagnosis and treatment of neonates with inborn errors of intermediary metabolism disorders (IEMDs) but also helps the affected females to reach the reproductive age under medical and dietetic support, as well as to give birth to normal infants. In this review, we aimed to focus on laboratory investigation tests, dietetic management and medical support for most known IEMD pregnant and lactating women, such as those suffering from aminoacidopathies, carbohydrate metabolic diseases and fatty acid (FAO) oxidation disorders.

PRE AND POST-OPERATIVE OTORHINOLARYNGOLOGY SURGERY CARE IN PATIENTS WITH GLYCOGEN STORAGE DISEASE TYPE 1

OBJECTIVE

To discuss aspects of pre and post-operative otorhinolaryngology surgery in patients with glycogen storage disease type 1b.

CASE DESCRIPTION

Description of three clinical cases with probable glycogen storage disease type 1b who underwent otorhinolaryngology surgery, showing the importance of multidisciplinary interaction to avoid episodes of hypoglycemia.

COMMENTS

Patients with glycogen storage disease type 1b present recurrent infections, including the otorhinolaryngology affections. When there is an indication for surgical treatment, the caloric intake should be carefully followed in order to prevent hypoglycemia. The way to ensure this is to perform the pre and postoperative period in the hospital ward. In the postoperative period, it is important to make a slow transition between the intravenous and oral routes and not suspend the infusion of glucose during the surgical procedure. The cases illustrate the need for the interaction of the otorhinolaryngologic surgeon with the anesthesiologist, the pediatrician and the gastro-pediatrician in the management of these patients, avoiding hypoglycemic episodes.

Hepatic glycogen storage diseases: pathogenesis, clinical symptoms and therapeutic management

Glycogen storage diseases (GSDs) are genetically determined metabolic diseases that cause disorders of glycogen metabolism in the body. Due to the enzymatic defect at some stage of glycogenolysis/glycogenesis, excess glycogen or its pathologic forms are stored in the body tissues. The first symptoms of the disease usually appear during the first months of life and are thus the domain of pediatricians. Due to the fairly wide access of the authors to unpublished materials and research, as well as direct contact with the GSD patients, the article addresses the problem of actual diagnostic procedures for patients with the suspected diseases. Knowledge and awareness of the problem among physicians seem insufficient, and research on the diagnosis and treatment of GSD is still ongoing, resulting in a heterogeneous GSD typology and a changing way of its diagnosis and treatment.

A Case of Glycogen Storage Disease IV with Rare Homozygous Mutations in the Glycogen Branching Enzyme Gene

Glycogen storage disease (GSD) IV is a rare autosomal recessive inherited disorder caused by mutations in the gene coding for glycogen branching enzyme leading to progressive liver disease. GSD IV is associated with mutations in GBE1, which encodes the glycogen branching enzyme. We report a case of GSD IV with rare homozygous mutations in the GBE1 gene (c.791G>A (p.Gly264Glu), which was successfully treated by liver transplantation.

Biochemical and clinical aspects of glycogen storage diseases

The synthesis of glycogen represents a key pathway for the disposal of excess glucose while its degradation is crucial for providing energy during exercise and times of need. The importance of glycogen metabolism is also highlighted by human genetic disorders that are caused by mutations in the enzymes involved. In this review, we provide a basic summary on glycogen metabolism and some of the clinical aspects of the classical glycogen storage diseases. Disruptions in glycogen metabolism usually result in some level of dysfunction in the liver, muscle, heart, kidney and/or brain. Furthermore, the spectrum of symptoms observed is very broad, depending on the affected enzyme. Finally, we briefly discuss an aspect of glycogen metabolism related to the maintenance of its structure that seems to be gaining more recent attention. For example, in Lafora progressive myoclonus epilepsy, patients exhibit an accumulation of inclusion bodies in several tissues, containing glycogen with increased phosphorylation, longer chain lengths and irregular branch points. This abnormal structure is thought to make glycogen insoluble and resistant to degradation. Consequently, its accumulation becomes toxic to neurons, leading to cell death. Although the genes responsible have been identified, studies in the past two decades are only beginning to shed light into their molecular functions.

Vitamin B₆ and Its Role in Cell Metabolism and Physiology

Vitamin B₆ is one of the most central molecules in cells of living organisms. It is a critical co-factor for a diverse range of biochemical reactions that regulate basic cellular metabolism, which impact overall physiology. In the last several years, major progress has been accomplished on various aspects of vitamin B₆ biology. Consequently, this review goes beyond the classical role of vitamin B₆ as a cofactor to highlight new structural and regulatory information that further defines how the vitamin is synthesized and controlled in the cell. We also discuss broader applications of the vitamin related to human health, pathogen resistance, and abiotic stress tolerance. Overall, the information assembled shall provide helpful insight on top of what is currently known about the vitamin, along with addressing currently open questions in the field to highlight possible approaches vitamin B₆ research may take in the future.

Are We There Yet? How and When Specific Biotechnologies Will Improve Human Health

Patient X: A 67-year-old Caucasian man slips on a patch of ice. He has abrasions to his hands and has sustained significant damage to his hip. At the emergency room, he informs clinicians he takes atorvastatin, metformin, and glimepiride to treat hypertension and Type 2 Diabetes Mellitus (T2DM). X-rays reveal a fractured hip, which will require total hip replacement surgery.

[Molecular and clinical characterization of Colombian patients suffering from type III glycogen storage disease]

INTRODUCTION

Type III glycogen storage disease (GSD III) is an autosomal recessive disorder in which a mutation in the AGL gene causes deficiency of the glycogen debranching enzyme. The disease is characterized by fasting hypoglycemia, hepatomegaly and progressive myopathy. Molecular analyses of AGL have indicated heterogeneity depending on ethnic groups. The full spectrum of AGL mutations in Colombia remains unclear.

OBJECTIVE

To describe the clinical and molecular characteristics of ten Colombian patients diagnosed with GSD III.

MATERIALS AND METHODS

We recruited ten Colombian children with a clinical and biochemical diagnosis of GSD III to undergo genetic testing. The full coding exons and the relevant exon-intron boundaries of the AGL underwent Sanger sequencing to identify mutation.

RESULTS

All patients had the classic phenotype of the GSD III. Genetic analysis revealed a mutation p.Arg910X in two patients. One patient had the mutation p.Glu1072AspfsX36, and one case showed a compound heterozygosity with p.Arg910X and p.Glu1072AspfsX36 mutations. We also detected the deletion of AGL gene 3, 4, 5, and 6 exons in three patients. The in silico studies predicted that these defects are pathogenic. No mutations were detected in the amplified regions in three patients.

CONCLUSION

We found mutations and deletions that explain the clinical phenotype of GSD III patients. This is the first report with a description of the clinical phenotype and the spectrum of AGL mutations in Colombian patients. This is important to provide appropriate prognosis and genetic counseling to the patient and their relatives.

Genetic analysis and clinical assessment of four patients with Glycogen Storage Disease Type IIIa in China

Background

Glycogen Storage Disease Type III (GSD III) is a rare autosomal recessive metabolic disorder caused by AGL gene mutation. There is significant heterogeneity between the clinical manifestations and the gene mutation of AGL among different ethnic groups. However, GSD III is rarely reported in Chinese population.

Case presentation

In this study, we aimed to study the genetic and clinical characteristics of four patients with GSD IIIa from China, especially the neurological manifestations. Meanwhile, we conducted a literature review of GSD IIIa cases reported in Chinese population to investigate the relationship between genotype and phenotype.

Conclusions

Three different AGL gene mutations were identified in our patients: c.206dupA, c.1735 + 1G > T and c.2590 C>T. Moreover, progressive myopathy accompanied by elevated creatine kinase level was the main manifestation of our patients in adolescents. Our results showed that AGL c.206dupA was a novel mutation and caused severe clinical manifestations. AGL c.1735 + 1G > T might be a recurrent mutation in the Chinese population. Genetic analysis of AGL gene mutation combined with muscle magnetic resonance imaging (MRI) might provide greater benefit to the patient in diagnosing GSD IIIa, rather than an invasive diagnostic procedure of biopsy.

Electronic supplementary material

The online version of this article (10.1186/s12881-018-0560-6) contains supplementary material, which is available to authorized users.

[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.

Partial correction of neutrophil dysfunction by oral galactose therapy in glycogen storage disease type Ib

Glycogen storage disease type Ib (GSD-Ib) is characterized by impaired glucose homeostasis, neutropenia and neutrophil dysfunction. Mass spectrometric glycomic profiling of GSD-Ib neutrophils showed severely truncated N-glycans, lacking galactose. Experiments indicated the hypoglycosylation of the electron transporting subunit of NADPH oxidase, which is crucial for the defense against bacterial infections. In phosphoglucomutase 1 (PGM1) deficiency, an inherited disorder with an enzymatic defect just one metabolic step ahead, hypogalactosylation can be successfully treated by dietary galactose. We hypothesized the same pathomechanism in GSD-Ib and started a therapeutic trial with oral galactose and uridine. The aim was to improve neutrophil dysfunction through the correction of hypoglycosylation in neutrophils. The GSD-Ib patient was treated for 29weeks. Monitoring included glycomics analysis of the patient's neutrophils and neutrophil function tests including respiratory burst activity, phagocytosis and migration. Although no substantial restoration of neutrophil glycosylation was found, there was partial improvement of respiratory burst activity.

Rapid height growth after liver transplantation in adulthood

Glycogen storage disease Ib is a rare, inherited metabolic disorder caused by glucose-6-phosphatase translocase deficiency. Its main symptoms are hypoglycemia, hyperlipidemia, neutropenia, hepatomegaly, liver adenomas and short stature. The exact mechanism of short stature in this disease is unclear, the most feasible possibility is that it is caused by impairment of growth-hormone and insulin-like growth factor I axis. Here we report the case of a patient who showed typical symptoms of glycogen storage disease Ib since his infancy, his height being under 1 percentile since then. Later-developed hypothyroidism and hypogonadism have also contributed to his short stature. Hypothyroidism was treated but sexual steroid substitution was not started because of an increased risk of hepatic adenomas. Because he developed hepatic adenoma at the age of 23, he had to undergo orthotopic liver transplantation. At the time of the transplantation his height was 128cm. The transplantation was followed by rapid height growth; our patient's height reached 160.3cm 62months after transplantation. We observed that while his IGF-I level increased, his GH level remained unchanged. During the post-transplantation period we ensured adequate calcium and vitamin D supplementation, leaving hormonal substitution unchanged. According to our knowledge, this is the first report of a rapid height growth as big as 32cm, of an individual over the age of 20, not related to endocrine treatment but liver transplantation.

Unique Exercise Lactate Profile in Muscle Phosphofructokinase Deficiency (Tarui Disease); Difference Compared with McArdle Disease

INTRODUCTION

Glycogen storage disease V (GSDV, McArdle disease) and GSDVII (Tarui disease) are the most common of the rare disorders of glycogen metabolism. Both are associated with low lactate levels on exercise. Our aim was to find out whether lactate response associated with exercise testing could distinguish between these disorders.

METHODS

Two siblings with Tarui disease, two patients with McArdle disease and eight healthy controls were tested on spiroergometric exercise tests with follow-up of venous lactate and ammonia.

RESULTS

A late increase of lactate about three times the basal level was seen 10-30 min after exercise in patients with Tarui disease being higher than in McArdle disease and lower than in the controls. Ammonia was increased in Tarui disease.

DISCUSSION

Our results suggest that follow-up of lactate associated with exercise testing can be utilized in diagnostics to distinguish between different GSD diseases.

The diagnostic value of biexponential apparent diffusion coefficients in myopathy

To investigate the performance of a biexponential signal decay model using DWI in myopathies and to differentiate Polymyositis (PM)/Dermatomyositis (DM), Glycogen Storage Diseases (GSDs) and Muscular Dystrophies (MDs) utilizing diffusion-weighted imaging. 11 healthy volunteers (control group) and 46 patients with myopathy were enrolled in the retrospective study. 27 of 46 patients had PM/DM, 7 patients GSDs and 12 patients MDs. After conventional MR sequences, diffusion weighted imaging with a b-factor ranging from 0 to 1200 s/mm(2) was performed on both thighs. The intra-muscular signal-to-noise ratios (SNRs) on multiple-b DWI images were measured for 7 different muscles and compared among the different groups. The median T2 signal intensity and biexponential apparent diffusion coefficients (ADC), including standard ADC, fast ADC, and slow ADC values, were compared among the different groups. The intra-muscular SNRs were statistically significantly different depending on the b value, and also found among the 4 groups (p < 0.05). The median T2 signal intensity of the normal muscles in control group was statistically significantly lower than that of edematous muscles in the PM/DM, GSDs and MDs groups (p = 0.000), while there were no statistically significant differences among the PM/DM, GSDs, and MDs groups (p > 0.05). The median standard ADC value of the edematous muscles in GSDs was statistically significantly lower than that of normal muscles in the control group (p = 0.000) and the median ADC value of the edematous muscles in PM/DM patients was statistically significantly greater than that of the GSDs (p = 0.000) and MDs groups (p = 0.005). The median slow ADC value of the edematous muscles in MDs patients and PM/DM patients was statistically significantly greater than that of GSDs patients (p < 0.05). Intra-muscular SNR decay curves and biexponential ADC parameters are useful in distinguishing among PM/DM, GSDs, and MDs.

The glycogen metabolism via Akt signaling is important for the secretion of enamel matrix in tooth development

Cells alter their energy metabolism depending on the stage of differentiation or various environments. In the ameloblast differentiation of continuous growing mouse incisors, we found temporary glycogen storage in preameloblasts before the start of enamel matrix secretion and investigated the relationship between enamel matrix secretion and glycogen metabolism. Immunohistochemistry showed that in the transitional stage from preameloblasts to secretory ameloblasts, the glycogen synthase changed from the inactive form to the active form, the expression of glycogen phosphorylase increased, and further, the levels of IGF-1, IGF-1 receptor and activated Akt increased. These results suggested that the activation of Akt signaling via IGF is linked to the onset of both glycogen metabolism and enamel matrix deposition. In the experiments using organ culture and ameloblast cell line, the activation of Akt signaling by IGF-1 stimulated glycogen metabolism through the up-regulation of Glut-1,-4 and Gsk-3β and the dephosphorylation of glycogen synthase. Subsequently, they resulted in increased enamel matrix secretion. In contrast, some inhibitors of Akt signals and glycogen synthesis/degradation down-regulated enamel matrix secretion. Taking these findings together, glycogen metabolism via Akt signaling is an essential system for the secretion of enamel matrix in ameloblast differentiation.

Molecular and clinical delineation of 12 patients with glycogen storage disease type III in Western Turkey

BACKGROUND

Glycogen storage disease type III (GSD III; MIM #232400) is an autosomal recessive inherited disorder characterized by fasting hypoglycemia, growth retardation, hepatomegaly, progressive myopathy, and cardiomyopathy. GSD III is caused by deficiency in the glycogen debranching enzyme (gene symbol: AGL). Molecular analyses of AGL have indicated heterogeneity depending on ethnic groups. In Turkey we reported 13 different AGL mutations from GSD III patients in the Eastern region; however, the full spectrum of AGL mutations in Turkish population remains unclear. Here we investigated 12 GSD III patients mostly from Western Turkey.

METHODS

The full coding exons, their relevant exon-intron boundaries, and the 5'- and 3'-flanking regions of the patients' AGL were sequenced. AGL haplotypes were determined. Splicing mutations were characterized by RNA transcript analysis.

RESULTS

Twelve different mutations were identified: 7 novel AGL mutations [69-base pair deletion (c.1056_1082+42del69), 21-base par deletion (c.3940_3949+11del21), two small duplications (c.364_365dupCT and c.1497_1500dupAGAG), and 3 splicing mutations (c.1736-11A>G, c.3259+1G>A and c.3588+2T>G)], along with 5 known mutations (c.1019delA, c.958+1G>A, c.4161+5G>A, p.R864X and p.R1218X). Transcripts of splicing mutations (c.1736-11A>G, c.3588+2T>G and c.4161+5G>A) were shown to cause aberrant splicing. AGL haplotype analyses suggested that c.1019delA and c.958+1G>A are founder mutations in Turkish patients, while p.R864X is a recurrent mutation.

CONCLUSIONS

Our study broadens the spectrum of AGL mutations and demonstrates that mutations in Western Turkey are different from those in the Eastern region.

Inherent lipid metabolic dysfunction in glycogen storage disease IIIa

We studied two patients from a nonconsanguineous family with life-long abnormal liver function, hepatomegaly and abnormal fatty acid profiles. Abnormal liver function, hypoglycemia and muscle weakness are observed in various genetic diseases, including medium-chain acyl-CoA dehydrogenase (MCAD) deficiency and glycogen storage diseases. The proband showed increased free fatty acids, mainly C8 and C10, resembling fatty acid oxidation disorder. However, no mutation was found in ACADM and ACADL gene. Sequencing of theamylo-alpha-1, 6-glucosidase, 4-alpha-glucanotransferase (AGL) gene showed that both patients were compound heterozygotes for c.118C > T (p.Gln40X) and c.753_756 del CAGA (p.Asp251Glufsx29), whereas their parents were each heterozygous for one of these mutations. The AGL protein was undetectable in EBV-B cells from the two patients. Transcriptome analysis demonstrated a significant different pattern of gene expression in both of patients’ cells, including genes involving in the PPAR signaling pathway, fatty acid biosynthesis, lipid synthesis and visceral fat deposition and metabolic syndrome. This unique gene expression pattern is probably due to the absence of AGL, which potentially accounts for the observed clinical phenotypes of hyperlipidemia and hepatocyte steatosis in glycogen storage disease type IIIa.

Protein degradation and quality control in cells from laforin and malin knockout mice

Lafora disease is a progressive myoclonus epilepsy caused by mutations in the EPM2A or EPM2B genes that encode a glycogen phosphatase, laforin, and an E3 ubiquitin ligase, malin, respectively. Lafora disease is characterized by accumulation of insoluble, poorly branched, hyperphosphorylated glycogen in brain, muscle, heart, and liver. The laforinmalin complex has been proposed to play a role in the regulation of glycogen metabolism and protein quality control. We evaluated three arms of the protein degradation/ quality control process (the autophago-lysosomal pathway, the ubiquitin-proteasomal pathway, and the endoplasmic reticulum (ER) stress response) in mouse embryonic fibroblasts from Epm2a(-/-), Epm2b(-/-), and Epm2a(-/-) Epm2b(-/-) mice. The levels of LC3-II, a marker of autophagy, were decreased in all knock-out cells as compared with wild type even though they still showed a slight response to starvation and rapamycin. Furthermore, ribosomal protein S6 kinase and S6 phosphorylation were increased. Under basal conditions there was no effect on the levels of ubiquitinated proteins in the knock-out cells, but ubiquitinated protein degradation was decreased during starvation or stress. Lack of malin (Epm2b(-/-) and Epm2a(-/-) Epm2b(-/-) cells) but not laforin (Epm2a(-/-) cells) decreased LAMP1, a lysosomal marker. CHOP expression was similar in wild type and knock-out cells under basal conditions or with ER stress-inducing agents. In conclusion, both laforin and malin knock-out cells display mTOR-dependent autophagy defects and reduced proteasomal activity but no defects in the ER stress response. We speculate that these defects may be secondary to glycogen overaccumulation. This study also suggests a malin function independent of laforin, possibly in lysosomal biogenesis and/or lysosomal glycogen disposal.

Ketogenic diet in neuromuscular and neurodegenerative diseases

An increasing number of data demonstrate the utility of ketogenic diets in a variety of metabolic diseases as obesity, metabolic syndrome, and diabetes. In regard to neurological disorders, ketogenic diet is recognized as an effective treatment for pharmacoresistant epilepsy but emerging data suggests that ketogenic diet could be also useful in amyotrophic lateral sclerosis, Alzheimer, Parkinson's disease, and some mitochondriopathies. Although these diseases have different pathogenesis and features, there are some common mechanisms that could explain the effects of ketogenic diets. These mechanisms are to provide an efficient source of energy for the treatment of certain types of neurodegenerative diseases characterized by focal brain hypometabolism; to decrease the oxidative damage associated with various kinds of metabolic stress; to increase the mitochondrial biogenesis pathways; and to take advantage of the capacity of ketones to bypass the defect in complex I activity implicated in some neurological diseases. These mechanisms will be discussed in this review.

X-linked glycogen storage disease IXa manifested in a female carrier due to skewed X chromosome inactivation

BACKGROUND

Glycogen storage disease (GSD) is a group of inherited metabolic disorders due to enzymatic deficiency involved in glycogen breakdown. In various subtypes of GSD, GSD IXa is an X-linked recessive disorder, which only manifested in males. Here, we report a case of X-linked GSD IXa manifested in a female Chinese patient accompanying a skewed X-chromosome inactivation (XCI).

METHODS

A 29-y-old Chinese female was admitted to evaluate mild hepatomegaly, which was repeatedly observed in serial abdominal ultrasonographic examinations. GSDIXa was suspected. To identify the mutation and the disease mechanism, we performed sequencing analysis of the PHKA2 gene, XCI assay and cDNA expression analysis.

RESULTS

Sequencing analysis revealed a heterozygous mutation in the PHKA2 gene (c.3614C>T; p.P1205L) of the patient. In XCI assay, the proband showed a skewed XCI pattern cDNA expression analysis showed a preferential expression of the mutant allele in leukocytes of the patient.

CONCLUSIONS

This is a rare report of X-linked GSD IXa manifested in a female carrier with skewed XCI. Skewed XCI can play a key role in the manifestation of X-linked recessive disorders in female carriers.

[Exercise-induced muscle pain due to phosphofrutokinase deficiency: Diagnostic contribution of metabolic explorations (exercise tests, 31P-nuclear magnetic resonance spectroscopy)]

INTRODUCTION

Muscle phosphofructokinase deficiency, the seventh member of the glycogen storage diseases family, is also called Tarui's disease (GSD VII).

METHODS

We studied two patients in two unrelated families with Tarui's disease, analyzing clinical features, CK level, EMG, muscle biopsy findings and molecular genetics features. Metabolic muscle explorations (forearm ischemic exercise test [FIET]; bicycle ergometer exercise test [EE]; 31P-nuclear magnetic resonance spectroscopy of calf muscle [31P-NMR-S]) are performed as appropriate.

RESULTS

Two patients, a 47-year-old man and a 38-year-old woman, complained of exercise-induced fatigue since childhood. The neurological examination was normal or showed light weakness. Laboratory studies showed increased CPK, serum uric acid and reticulocyte count without anemia. There was no increase in the blood lactate level during the FIET or the EE although there was a light increase in the respiratory exchange ratio during the EE. 31P-NMR-S revealed no intracellular acidification or accumulated intermediates such as phosphorylated monoesters (PME) known to be pathognomic for GSD VII. Two new mutations were identified.

DISCUSSION

FIET and EE were non-contributive to diagnosis, but 31P-NMR provided a characteristic spectra of Tarui's disease, in agreement with phosphofructokinase activity level in erythrocytes. Muscle biopsy does not always provide useful information for diagnosis. In these two cases, genetic studies failed to establish a genotype-phenotype correlation.

CONCLUSION

The search for phosphofructokinase deficiency should be continued throughout life in adults experiencing fatigability or weakness because of the severe disability for daily life activities caused by the late onset form.

Nuclear receptors and epigenetic signaling: novel regulators of glycogen metabolism in skeletal muscle

Glycogen is an energy storage depot for the mammalian species. This review focuses on recent developments that have identified the role of nuclear hormone receptor (NR) signaling and epigenomic control in the regulation of important genes that modulate glycogen metabolism. Specifically, new studies have revealed that the NR4A subgroup (of the NR superfamily) are strikingly sensitive to beta-adrenergic stimulation in skeletal muscle, and transgenic studies in mice have revealed the expression of these NRs affects endurance and glycogen levels in muscle. Furthermore, other studies have demonstrated that one of the NR coregulator class of enzymes that mediate chromatin remodeling, the histone methyltransferases (for example, protein arginine methyltransferase 4) regulates the expression of several genes involved in glycogen metabolism and glycogen storage diseases in skeletal muscle. Importantly, NRs and histone methyltransferases, have the potential to be pharmacologically exploited and may provide novel targets in the quest to treat disorders of glycogen storage.

Whole exome sequencing in foetal akinesia expands the genotype-phenotype spectrum of GBE1 glycogen storage disease mutations

The clinically and genetically heterogenous foetal akinesias have low rates of genetic diagnosis. Exome sequencing of two siblings with phenotypic lethal multiple pterygium syndrome identified compound heterozygozity for a known splice site mutation (c.691+2T>C) and a novel missense mutation (c.956A>G; p.His319Arg) in glycogen branching enzyme 1 (GBE1). GBE1 mutations cause glycogen storage disease IV (GSD IV), including a severe foetal akinesia sub-phenotype. Re-investigating the muscle pathology identified storage material, consistent with GSD IV, which was confirmed biochemically. This study highlights the power of exome sequencing in genetically heterogeneous diseases and adds multiple pterygium syndrome to the phenotypic spectrum of GBE1 mutation.

Drug repositioning for personalized medicine

Human diseases can be caused by complex mechanisms involving aberrations in numerous proteins and pathways. With recent advances in genomics, elucidating the molecular basis of disease on a personalized level has become an attainable goal. In many cases, relevant molecular targets will be identified for which approved drugs already exist, and the potential repositioning of these drugs to a new indication can be investigated. Repositioning is an accelerated route for drug discovery because existing drugs have established clinical and pharmacokinetic data. Personalized medicine and repositioning both aim to improve the productivity of current drug discovery pipelines, which expend enormous time and cost to develop new drugs, only to have them fail in clinical trials because of lack of efficacy or toxicity. Here, we discuss the current state of research in these two fields, focusing on recent large-scale efforts to systematically find repositioning candidates and elucidate individual disease mechanisms in cancer. We also discuss scenarios in which personalized drug repositioning could be particularly rewarding, such as for diseases that are rare or have specific mutations, as well as current challenges in this field. With an increasing number of drugs being approved for rare cancer subtypes, personalized medicine and repositioning approaches are poised to significantly alter the way we diagnose diseases, infer treatments and develop new drugs.

Association of the congenital neuromuscular form of glycogen storage disease type IV with a large deletion and recurrent frameshift mutation

Anderson disease, also known as glycogen storage disease type IV (MIM 232500), is a rare autosomal recessive disorder caused by a deficiency of glycogen branching enzyme. Glycogen storage disease type IV has a broad clinical spectrum ranging from a perinatal lethal form to a nonprogressive later-onset disease in adults. Here, we report 2 unrelated infants who were born small for their gestational age and who had profound hypotonia at birth and thus needed mechanical ventilation. Both of these patients shared the same frameshift mutation (c.288delA, pGly97GlufsX46) in the GBE1 gene. In addition, both of these patients were found to have 2 different large deletions in the GBE1 gene; exon 7 and exons 2 to 7, respectively, on the other alleles. This case report also highlights the need for a more comprehensive search for large deletion mutations associated with glycogen storage disease type IV, especially if routine GBE1 gene sequencing results are equivocal.