Myofiber-type-dependent 'boulder' or 'multitudinous pebble' formations across distinct amylopectinoses

At least five enzymes including three E3 ubiquitin ligases are dedicated to glycogen's spherical structure. Absence of any reverts glycogen to a structure resembling amylopectin of the plant kingdom. This amylopectinosis (polyglucosan body formation) causes fatal neurological diseases including adult polyglucosan body disease (APBD) due to glycogen branching enzyme deficiency, Lafora disease (LD) due to deficiencies of the laforin glycogen phosphatase or the malin E3 ubiquitin ligase and type 1 polyglucosan body myopathy (PGBM1) due to RBCK1 E3 ubiquitin ligase deficiency. Little is known about these enzymes' functions in glycogen structuring. Toward understanding these functions, we undertake a comparative murine study of the amylopectinoses of APBD, LD and PGBM1. We discover that in skeletal muscle, polyglucosan bodies form as two main types, small and multitudinous ('pebbles') or giant and single ('boulders'), and that this is primarily determined by the myofiber types in which they form, 'pebbles' in glycolytic and 'boulders' in oxidative fibers. This pattern recapitulates what is known in the brain in LD, innumerable dust-like in astrocytes and single giant sized in neurons. We also show that oxidative myofibers are relatively protected against amylopectinosis, in part through highly increased glycogen branching enzyme expression. We present evidence of polyglucosan body size-dependent cell necrosis. We show that sex influences amylopectinosis in genotype, brain region and myofiber-type-specific fashion. RBCK1 is a component of the linear ubiquitin chain assembly complex (LUBAC), the only known cellular machinery for head-to-tail linear ubiquitination critical to numerous cellular pathways. We show that the amylopectinosis of RBCK1 deficiency is not due to loss of linear ubiquitination, and that another function of RBCK1 or LUBAC must exist and operate in the shaping of glycogen. This work opens multiple new avenues toward understanding the structural determinants of the mammalian carbohydrate reservoir critical to neurologic and neuromuscular function and disease.

Case 318: Adult Polyglucosan Body Disease

HISTORY

A 72-year-old man sought care for a cognitive deterioration over the past 5 years. There was a documented decline in his performance on the Mini-Mental State Examination (30 of 30 in 2016, 23 of 30 in 2021), with mainly episodic memory impairment. A more detailed history revealed a gait problem, paresthesia in both feet, and nocturnal urinary frequency. Clinical examination findings were suggestive of a length-dependent polyneuropathy. In addition, a right-sided Babinski sign was noted. Electromyography and a nerve conduction study corroborated a peripheral axonal sensorimotor neuropathy. MRI of the brain was performed.

Rapid ultra-performance liquid chromatography-tandem mass spectrometry method for the simultaneous determination of three characteristic urinary saccharide metabolites in patients with glycogen storage diseases (type Ⅰb and Ⅱ)

Urinary 1,5-anhydroglucitol (1, 5-AG), 6-α-D-glucopyranosyl-maltotriose (Glc4) and maltotetraose (M4) are important biomarkers for glycogen storage disease (types Ib and Ⅱ). This study aimed to develop and validate an ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) to detect these three urinary saccharide metabolites. Urine samples were diluted and then analyzed. Chromatographic separation was performed on an Acquity™ UPLC Amide column (2.1 × 100 mm, 1.7 μm) with gradient elution. The quantitation of analytes was achieved on a 5500 Qtrap mass spectrometer using negative multiple reaction monitoring (MRM) mode. The calibration curves for all analytes were linear over the range of 0.500 to 100 μg/mL with a correlation coefficient, R2 ≥ 0.999. The percent relative standard deviations (RSD%) were ≤12.8%, and the percent relative errors (RE%) were in the range of -11.7%-11.0%. The relative matrix effects of all analytes were between 87.2% and 104% with RSD% < 3.10% across three concentrations. The developed analytical method was simple, accurate, and reliable for rapid and simultaneous analysis of these three urinary saccharide metabolites. It was applied to healthy volunteers and patients. To our knowledge, it was the first validated assay for urinary maltotetraose quantification. This work provides support for exploring the potential of maltotetraose as a biomarker for Pompe disease.

AAV-based gene therapy prevents and halts the progression of dilated cardiomyopathy in a mouse model of phosphoglucomutase 1 deficiency (PGM1-CDG)

Phosphoglucomutase 1 (PGM1) deficiency is recognized as the third most common N-linked congenital disorders of glycosylation (CDG) in humans. Affected individuals present with liver, musculoskeletal, endocrine, and coagulation symptoms; however, the most life-threatening complication is the early onset of dilated cardiomyopathy (DCM). Recently, we discovered that oral D-galactose supplementation improved liver disease, endocrine, and coagulation abnormalities, but does not alleviate the fatal cardiomyopathy and the associated myopathy. Here we report on left ventricular ejection fraction (LVEF) in 6 individuals with PGM1-CDG. LVEF was pathologically low in most of these individuals and varied between 10% and 65%. To study the pathobiology of the cardiac disease observed in PGM1-CDG, we constructed a novel cardiomyocyte-specific conditional Pgm2 gene (mouse ortholog of human PGM1) knockout (Pgm2 cKO) mouse model. Echocardiography studies corroborated a DCM phenotype with significantly reduced ejection fraction and left ventricular dilation similar to those seen in individuals with PGM1-CDG. Histological studies demonstrated excess glycogen accumulation and fibrosis, while ultrastructural analysis revealed Z-disk disarray and swollen/fragmented mitochondria, which was similar to the ultrastructural pathology in the cardiac explant of an individual with PGM1-CDG. In addition, we found decreased mitochondrial function in the heart of KO mice. Transcriptomic analysis of hearts from mutant mice demonstrated a gene signature of DCM. Although proteomics revealed only mild changes in global protein expression in left ventricular tissue of mutant mice, a glycoproteomic analysis unveiled broad glycosylation changes with significant alterations in sarcolemmal proteins including different subunits of laminin-211, which was confirmed by immunoblot analyses. Finally, augmentation of PGM1 in KO mice via AAV9-PGM1 gene replacement therapy prevented and halted the progression of the DCM phenotype.

Urine-Derived Epithelial Cells as a New Model to Study Renal Metabolic Phenotypes of Patients with Glycogen Storage Disease 1a

Glycogen storage diseases (GSDs) represent a model of pathological accumulation of glycogen disease in the kidney that, in animal models, results in nephropathy due to abnormal autophagy and mitochondrial function. Patients with Glycogen Storage Disease 1a (GSD1a) accumulate glycogen in the kidneys and suffer a disease resembling diabetic nephropathy that can progress to renal failure. In this study, we addressed whether urine-derived epithelial cells (URECs) from patients with GSD1a maintain their biological features, and whether they can be used as a model to study the renal and metabolic phenotypes of this genetic condition. Studies were performed on cells extracted from urine samples of GSD1a and healthy subjects. URECs were characterized after the fourth passage by transmission electron microscopy and immunofluorescence. Reactive oxygen species (ROS), at different glucose concentrations, were measured by fluorescent staining. We cultured URECs from three patients with GSD1a and three healthy controls. At the fourth passage, URECs from GSD1a patients maintained their massive glycogen content. GSD1a and control cells showed the ciliary structures of renal tubular epithelium and the expression of epithelial (E-cadherin) and renal tubular cells (aquaporin 1 and 2) markers. Moreover, URECs from both groups responded to changes in glucose concentrations by modulating ROS levels. GSD1a cells were featured by a specific response to the low glucose stimulus, which is the condition that more resembles the metabolic derangement of patients with GSD1a. Through this study, we demonstrated that URECs might represent a promising experimental model to study the molecular mechanisms leading to renal damage in GSD1a, due to pathological glycogen storage.

Metabolic Myopathies

PURPOSE OF REVIEW

Metabolic myopathies are disorders that affect skeletal muscle substrate oxidation. Although some drugs and hormones can affect metabolism in skeletal muscle, this review will focus on the genetic metabolic myopathies.

RECENT FINDINGS

Impairments in glycogenolysis/glycolysis (glycogen storage disease), fatty acid transport/oxidation (fatty acid oxidation defects), and mitochondrial metabolism (mitochondrial myopathies) represent most metabolic myopathies; however, they often overlap clinically with structural genetic myopathies, referred to as pseudometabolic myopathies. Although metabolic myopathies can present in the neonatal period with hypotonia, hypoglycemia, and encephalopathy, most cases present clinically in children or young adults with exercise intolerance, rhabdomyolysis, and weakness. In general, the glycogen storage diseases manifest during brief bouts of high-intensity exercise; in contrast, fatty acid oxidation defects and mitochondrial myopathies usually manifest during longer-duration endurance-type activities, often with fasting or other metabolic stressors (eg, surgery, fever). The neurologic examination is often normal between events (except in the pseudometabolic myopathies) and evaluation requires one or more of the following tests: exercise stress testing, blood (eg, creatine kinase, acylcarnitine profile, lactate, amino acids), urine (eg, organic acids, myoglobin), muscle biopsy (eg, histology, ultrastructure, enzyme testing), and targeted (specific gene) or untargeted (myopathy panels) genetic tests.

SUMMARY

Definitive identification of a specific metabolic myopathy often leads to specific interventions, including lifestyle, exercise, and nutritional modifications; cofactor treatments; accurate genetic counseling; avoidance of specific triggers; and rapid treatment of rhabdomyolysis.

Clinical, Biochemical, and Molecular Characterization of Two Families with Novel Mutations in the LDHA Gene (GSD XI)

Lactate dehydrogenase (LDH) catalyzes the reversible conversion of L-lactate to pyruvate. LDH-A deficiency is an autosomal recessive disorder (glycogenosis type XI, OMIM#612933) caused by mutations in the LDHA gene. We present two young adult female patients presenting with intolerance to anaerobic exercise, episodes of rhabdomyolysis, and, in one of the patients, psoriasis-like dermatitis. We identified in the LDHA gene a homozygous c.410C>A substitution that predicts a p.Ser137Ter nonsense mutation in Patient One and a compound heterozygous c.410C>A (p.Ser137Ter) and c.750G>A (p.Trp250Ter) nonsense mutation in Patient Two. The pathogenicity of the variants was demonstrated by electrophoretic separation of LDH isoenzymes. Moreover, a flat lactate curve on the forearm exercise test, along with the clinical combination of myopathy and psoriatic-like dermatitis, can also lead to the diagnosis.

Glycogen synthase downregulation rescues the amylopectinosis of murine RBCK1 deficiency

Longer glucan chains tend to precipitate. Glycogen, by far the largest mammalian glucan and the largest molecule in the cytosol with up to 55 000 glucoses, does not, due to a highly regularly branched spherical structure that allows it to be perfused with cytosol. Aberrant construction of glycogen leads it to precipitate, accumulate into polyglucosan bodies that resemble plant starch amylopectin and cause disease. This pathology, amylopectinosis, is caused by mutations in a series of single genes whose functions are under active study toward understanding the mechanisms of proper glycogen construction. Concurrently, we are characterizing the physicochemical particularities of glycogen and polyglucosans associated with each gene. These genes include GBE1, EPM2A and EPM2B, which respectively encode the glycogen branching enzyme, the glycogen phosphatase laforin and the laforin-interacting E3 ubiquitin ligase malin, for which an unequivocal function is not yet known. Mutations in GBE1 cause a motor neuron disease (adult polyglucosan body disease), and mutations in EPM2A or EPM2B a fatal progressive myoclonus epilepsy (Lafora disease). RBCK1 deficiency causes an amylopectinosis with fatal skeletal and cardiac myopathy (polyglucosan body myopathy 1, OMIM# 615895). RBCK1 is a component of the linear ubiquitin chain assembly complex, with unique functions including generating linear ubiquitin chains and ubiquitinating hydroxyl (versus canonical amine) residues, including of glycogen. In a mouse model we now show (i) that the amylopectinosis of RBCK1 deficiency, like in adult polyglucosan body disease and Lafora disease, affects the brain; (ii) that RBCK1 deficiency glycogen, like in adult polyglucosan body disease and Lafora disease, has overlong branches; (iii) that unlike adult polyglucosan body disease but like Lafora disease, RBCK1 deficiency glycogen is hyperphosphorylated; and finally (iv) that unlike laforin-deficient Lafora disease but like malin-deficient Lafora disease, RBCK1 deficiency's glycogen hyperphosphorylation is limited to precipitated polyglucosans. In summary, the fundamental glycogen pathology of RBCK1 deficiency recapitulates that of malin-deficient Lafora disease. Additionally, we uncover sex and genetic background effects in RBCK1 deficiency on organ- and brain-region specific amylopectinoses, and in the brain on consequent neuroinflammation and behavioural deficits. Finally, we exploit the portion of the basic glycogen pathology that is common to adult polyglucosan body disease, both forms of Lafora disease and RBCK1 deficiency, namely overlong branches, to show that a unified approach based on downregulating glycogen synthase, the enzyme that elongates glycogen branches, can rescue all four diseases.

Molecular and clinical profiling in a large cohort of Asian Indians with glycogen storage disorders

Glycogen storage disorders occur due to enzyme deficiencies in the glycogenolysis and gluconeogenesis pathway, encoded by 26 genes. GSD’s present with overlapping phenotypes with variable severity. In this series, 57 individuals were molecularly confirmed for 7 GSD subtypes and their demographic data, clinical profiles and genotype-phenotype co-relations are studied. Genomic DNA from venous blood samples was isolated from clinically affected individuals. Targeted gene panel sequencing covering 23 genes and Sanger sequencing were employed. Various bioinformatic tools were used to predict pathogenicity for new variations. Close parental consanguinity was seen in 76%. Forty-nine pathogenic variations were detected of which 27 were novel. Variations were spread across GSDIa, Ib, III, VI, IXa, b and c. The largest subgroup was GSDIII in 28 individuals with 24 variations (12 novel) in AGL. The 1620+1G>C intronic variation was observed in 5 with GSDVI (PYGL). A total of eleven GSDIX are described with the first Indian report of type IXb. This is the largest study of GSDs from India. High levels of consanguinity in the local population and employment of targeted sequencing panels accounted for the range of GSDs reported here.

Clinical and biochemical footprints of inherited metabolic diseases. VIII. Neoplasias

Cancer, caused by multiple cumulative pathogenic variants in tumor suppressor genes and proto-oncogenes, is a leading cause of mortality worldwide. The uncontrolled and rapid cell growth of the tumors requires a reprogramming of the complex cellular metabolic network to favor anabolism. Adequate management and treatment of certain inherited metabolic diseases might prevent the development of certain neoplasias, such as hepatocellular carcinoma in tyrosinemia type 1 or hepatocellular adenomas in glycogen storage disorder type 1a. We reviewed and updated the list of known metabolic etiologies associated with various types of benign and malignant neoplasias, finding 64 relevant inborn errors of metabolism. This is the eighth article of the series attempting to create a comprehensive list of clinical and metabolic differential diagnosis by system involvement.

Maximal Multistage Shuttle Run Test-induced Myalgia in a Patient with Muscle Phosphorylase B Kinase Deficiency

Muscle phosphorylase b kinase (PHK) deficiency is a rare mild metabolic disorder caused by mutations of the PHKA1 gene encoding the αM subunit of PHK. A 16-year-old boy experienced myalgia during the maximal multistage 20-m shuttle run test targeting the maximal oxygen consumption. Although an ischemic forearm exercise test was normal, a muscle biopsy revealed subsarcolemmal glycogen accumulation. He harbored a novel insertion mutation in the PHKA1 gene that resulted in premature termination of the αM subunit close to the C-terminus. Compared with previously reported cases, his reduction in PHK activity was relatively mild.

AAV-Mediated Artificial miRNA Reduces Pathogenic Polyglucosan Bodies and Neuroinflammation in Adult Polyglucosan Body and Lafora Disease Mouse Models

Adult polyglucosan body disease (APBD) and Lafora disease (LD) are autosomal recessive glycogen storage neurological disorders. APBD is caused by mutations in the glycogen branching enzyme (GBE1) gene and is characterized by progressive upper and lower motor neuron dysfunction and premature death. LD is a fatal progressive myoclonus epilepsy caused by loss of function mutations in the EPM2A or EPM2B gene. These clinically distinct neurogenetic diseases share a common pathology. This consists of time-dependent formation, precipitation, and accumulation of an abnormal form of glycogen (polyglucosan) into gradually enlarging inclusions, polyglucosan bodies (PBs) in ever-increasing numbers of neurons and astrocytes. The growth and spread of PBs are followed by astrogliosis, microgliosis, and neurodegeneration. The key defect in polyglucosans is that their glucan branches are longer than those of normal glycogen, which prevents them from remaining in solution. Since the lengths of glycogen branches are determined by the enzyme glycogen synthase, we hypothesized that downregulating this enzyme could prevent or hinder the generation of the pathogenic PBs. Here, we pursued an adeno-associated virus vector (AAV) mediated RNA-interference (RNAi) strategy. This approach resulted in approximately 15% reduction of glycogen synthase mRNA and an approximately 40% reduction of PBs across the brain in the APBD and both LD mouse models. This was accompanied by improvements in early neuroinflammatory markers of disease. This work represents proof of principle toward developing a single lifetime dose therapy for two fatal neurological diseases: APBD and LD. The approach is likely applicable to other severe and common diseases of glycogen storage.

Modifiable factors affecting renal preservation in type I glycogen storage disease after liver transplantation: a single-center propensity-match cohort study

BACKGROUND AND AIMS

Glycogen storage disease type I (GSD-I) is an autosomal recessive disorder of carbohydrate metabolism, resulting in limited production of glucose and excessive glycogen storage in the liver and kidneys. These patients are characterized by life-threatening hypoglycemia, metabolic derangements, hepatomegaly, chronic kidney disease, and failure to thrive. Liver transplantation (LT) has been performed for poor metabolic control and delayed growth. However, renal outcome was diverse in pediatric GSD patients after LT. The aim of this study was to investigate the long-term outcome of renal function in pediatric GSD-I patients after living donor LT (LDLT), and to identify modifiable variables that potentially permits LT to confer native renal preservation.

METHODS

The study included eight GSD-Ia and one GSD-Ib children with a median age of 9.0 (range 4.2-15.7) years at the time of LT. Using propensity score matching, 20 children with biliary atresia (BA) receiving LT were selected as the control group by matching for age, sex, pre-operative serum creatinine (SCr) and pediatric end-stage liver disease (PELD) score. Renal function was evaluated based on the SCr, estimated glomerular filtration rate (eGFR), microalbuminuria, and morphological changes in the kidneys. Comparability in long-term renal outcome in terms of anatomic and functional parameters will help to identify pre-LT factors of GSD-I that affect renal prognosis.

RESULTS

The clinical and biochemical characteristics of the GSD and BA groups were similar, including immunosuppressive regimens and duration of follow-up (median 15 years) after LT. Overall, renal function, including eGFR and microalbuminuria was comparable in the GSD-I and BA groups (median eGFR: 111 vs. 123 ml/min/1.73m2, P = 0.268; median urine microalbuminuria to creatinine ratio: 16.0 vs. 7.2 mg/g, P = 0.099, respectively) after LT. However, in the subgroups of the GSD cohort, patients starting cornstarch therapy at an older age (≥ 6-year-old) before transplantation demonstrated a worse renal outcome in terms of eGFR change over years (P < 0.001). In addition, the enlarged kidney in GSD-I returned to within normal range after LT.

CONCLUSIONS

Post-LT renal function was well-preserved in most GSD-I patients. Early initiation of cornstarch therapy before preschool age, followed by LT, achieved a good renal prognosis.

Alleviation of a polyglucosan storage disorder by enhancement of autophagic glycogen catabolism

This work employs adult polyglucosan body disease (APBD) models to explore the efficacy and mechanism of action of the polyglucosan-reducing compound 144DG11. APBD is a glycogen storage disorder (GSD) caused by glycogen branching enzyme (GBE) deficiency causing accumulation of poorly branched glycogen inclusions called polyglucosans. 144DG11 improved survival and motor parameters in a GBE knockin (Gbeys/ys ) APBD mouse model. 144DG11 reduced polyglucosan and glycogen in brain, liver, heart, and peripheral nerve. Indirect calorimetry experiments revealed that 144DG11 increases carbohydrate burn at the expense of fat burn, suggesting metabolic mobilization of pathogenic polyglucosan. At the cellular level, 144DG11 increased glycolytic, mitochondrial, and total ATP production. The molecular target of 144DG11 is the lysosomal membrane protein LAMP1, whose interaction with the compound, similar to LAMP1 knockdown, enhanced autolysosomal degradation of glycogen and lysosomal acidification. 144DG11 also enhanced mitochondrial activity and modulated lysosomal features as revealed by bioenergetic, image-based phenotyping and proteomics analyses. As an effective lysosomal targeting therapy in a GSD model, 144DG11 could be developed into a safe and efficacious glycogen and lysosomal storage disease therapy.

A retrospective in-depth analysis of continuous glucose monitoring datasets for patients with hepatic glycogen storage disease: Recommended outcome parameters for glucose management

Continuous glucose monitoring (CGM) systems have great potential for real-time assessment of glycemic variation in patients with hepatic glycogen storage disease (GSD). However, detailed descriptions and in-depth analysis of CGM data from hepatic GSD patients during interventions are scarce. This is a retrospective in-depth analysis of CGM parameters, acquired in a continuous, real-time fashion describing glucose management in 15 individual GSD patients. CGM subsets are obtained both in-hospital and at home, upon nocturnal dietary intervention (n = 1), starch loads (n = 11) and treatment of GSD Ib patients with empagliflozin (n = 3). Descriptive CGM parameters, and parameters reflecting glycemic variation and glycemic control are considered useful CGM outcome parameters. Furthermore, the combination of first and second order derivatives, cumulative sum and Fourier analysis identified both subtle and sudden changes in glucose management; hence, aiding assessment of dietary and medical interventions. CGM data interpolation for nocturnal intervals reduced confounding by physical activity and diet. Based on these analyses, we conclude that in-depth CGM analysis can be a powerful tool to assess glucose management and optimize treatment in individual hepatic GSD patients.

[The application of continuous glucose monitoring in the management of hepatic glycogen storage disease]

Objective: Continuous glucose monitoring (CGM) were performed in children with hepatic glycogen storage disease (GSD) to accurately understand the situation of glucose levels during their treatment, and to provide support for optimizing their nutritional management. Methods: In this retrospective research, 42 patients with hepatic GSD who under went 72 h CGM were collected from Department of Pediatrics, Tongji Hospital of Tongji Medical College, Huazhong University of Science and Technology from October 2019 to January 2020. According to the genetic test results, they were divided into 5 groups: type Ⅰa, type Ⅰb, type Ⅲa, type Ⅵ and type Ⅸa. After long-term follow up and regular treatment, the clinical data (induding course, age, height, weight and biochemical parameters, etc.) on the day of CGM were summarized, and 72 h CGM were performed to assess the occurrence of hypoglycemia and hyperglycemia.χ² test, Fisher exact probability method, t test, analysis of variance or nonparametric test were used for comparison between groups. Results: Forty-two cases of hepatic GSD patients included 25 males and 17 females (20 cases of type Ⅰa, 3 cases of type Ⅰb, 10 cases of type Ⅲa, 3 cases of type Ⅵ and 6 cases of type Ⅸa).The age was 9.5 (6.7, 12.9) years, and the course of disease was 6.8 (5.1, 11.3) years. The average levels of glucose of the patients were all normal. However, the levels of standard deviation of blood glucose (SDBG) and mean amplitude of glycemic excursion (MAGE) were significantly different (F=2.747, 3.029,both P<0.05). Among them, the SDBG of type Ⅰa and Ⅲa were significantly higher than those of type Ⅸa ((1.10±0.36), (0.98±0.30) vs. (0.62±0.26) mmol/L, t=3.010, 2.440, both P<0.05), while the MAGE of type Ⅰ was higher than that of Ⅸa and Ⅲa ((2.3±0.9) mmol/L vs. (1.2±0.6) and (1.7±0.6) mmol/L, t=2.734, 2.302, both P<0.05, respectively). Conclusions: CGMS can accurately assess the fluctuations of blood glucose and effectively detect hidden hypoglycemia and hyperglycemia in hepatic GSD patients. For different types of hepatic GSD, individualized corn starch treatment doses should be given according to the different situation of blood glucose, so as to optimize the patient's treatment and improve their prognosis.

Adult polyglucosan body disease-an atypical compound heterozygous with a novel GBE1 mutation

INTRODUCTION

Adult polyglucosan body disease (APBD) is an autosomal recessive leukodystrophy characterized by neurogenic bladder starting after 40 years old, spastic paraparesis and peripheral neuropathy. It is mainly resultant from the GBE1 homozygous p.Tyr329Ser (c.986A>C) mutation, especially in Ashkenazi-Jewish patients, although some cases of compound heterozygous have been reported. A genotype-phenotype correlation is not established, but atypical phenotypes have been described mainly in non-p.Tyr329Ser pathogenic variants.

CASE REPORT

We describe an atypical case in a 62-year-old Portuguese woman, presenting the typical clinical triad of APBD plus prominent autonomic dysfunction, suggested by orthostatic hypotension and thermoregulatory dysfunction; she has compound heterozygous GBE1 mutations, namely, p.Asn541Asp (c.1621A>G) and p.Arg515Gly (c.1543C>G), the last one not yet reported in literature and whose pathogenicity was suggested by bioinformatics analysis and confirmed by sural nerve biopsy that showed intra-axonal polyglucosan bodies.

DISCUSSION

Besides the report of a novel GBE1 mutation, this case also expands the phenotypic spectrum of this disorder, reinforcing autonomic dysfunction as a possible and prominent manifestation of APBD, mimicking autosomal dominant leukodystrophy with autonomic disease in some way. Therefore, we questioned a possible relationship between this genotype and the phenotype marked by dysautonomia. Additionally, we review previously reported cases of APBD in non-homozygous p.Tyr329Ser patients with atypical phenotypes.

Secondary diabetes as a rare complication of glycogen storage disease 1a: case report and review of literature

Glycogen storage diseases (GSDs) are disorders of carbohydrate metabolism and hypoglycemia is their hallmark. Secondary diabetes with glycogen storage disease, which seems rather paradoxical, has been rarely reported. A 13-year-old girl previously diagnosed to have GSD 1a presented to the emergency with multiple episodes of vomiting and loss of consciousness. She had hyperglycemia, ketonuria, hyperlactatemia and metabolic acidosis, suggestive of diabetic ketosis with acidosis possibly contributed by both high serum lactate and serum ketones. Her glycated hemoglobin was high, with detectable serum insulin levels, which suggested secondary diabetes in the background of GSD Ia. Her management posed a therapeutic challenge. She was managed with insulin and achieved good glycemic control. We wish to conclude that GSD may rarely lead to secondary diabetes as a complication and the management is complex owing to the nature of the disease. Insulin remains the mainstay of the treatment.

Creation and implementation of a European registry for patients with McArdle disease and other muscle glycogenoses (EUROMAC registry)

BACKGROUND

International patient registries are of particular importance for rare disorders, as they may contribute to overcome the lack of knowledge derived from low number of patients and limited awareness of these diseases, and help to learn more about their geographical or population-based specificities, which is relevant for research purposes and for promoting better standards of care and diagnosis. Our objective was to create and implement a European registry for patients with McArdle disease and other muscle glycogenoses (EUROMAC) and to disseminate the knowledge of these disorders.

RESULTS

Teams from nine different countries (United Kingdom, Spain, Italy, France, Germany, Denmark, Greece, Turkey and USA) created a consortium that developed the first European registry dedicated to rare muscle glycogenoses. A work plan was implemented to design the database and platform that constitute the registry, by choosing clinical, genetics and molecular variables of interest, based on experience gained from previous national registries for similar metabolic disorders. Among dissemination activities, several teaching events were organized in different countries, especially those where the consortium considered the awareness of these diseases needs to be promoted among health professionals and patients.

CONCLUSION

EUROMAC represents a step forward in the knowledge of those disorders to which it is dedicated, and will have relevant clinical outcomes at the diagnostic, epidemiological, clinical and research level.