Juvenile-onset permanent weakness in muscle phosphofructokinase deficiency

Comparative transcriptome analysis of skeletal muscle in ADSSL1 myopathy

ADSSL1 myopathy was recently identified as the cause of muscular disorders in Korean patients with distal myopathy. We generated transcriptome profiles of muscles from control subjects and patients with ADSSL1 myopathy. In the present study, RNA sequencing was conducted with seven vastus lateralis muscle samples from four patients with ADSSL1 myopathy and three control subjects. The hierarchical clustering result revealed a separation between myopathy and control groups. A total of 1,260 transcripts were significantly differentially expressed (|fold change| ≥ 2, p < 0.05), with 740 upregulated transcripts and 520 downregulated transcripts in myopathy group. Eighteen transcripts that mapped to purine metabolism pathway were significantly differentially expressed between the two groups, with ten downregulated transcripts and eight upregulated transcripts in myopathy group. In particular, three genes involved in purine nucleotide cycle (ADSSL1, ADSL, and AMPD1) were significantly downregulated in myopathy group. Ten transcripts in glycolysis/gluconeogenesis pathway were also significantly differentially expressed. This is the first study on the altered expression of transcripts in muscle tissues from patients with ADSSL1 myopathy. Our results provide new insights into the pathogenesis of ADSSL1 myopathy.

Cardiomyopathy as presenting sign of glycogenin-1 deficiency-report of three cases and review of the literature

We describe a new type of cardiomyopathy caused by a mutation in the glycogenin-1 gene (GYG1). Three unrelated male patients aged 34 to 52 years with cardiomyopathy and abnormal glycogen storage on endomyocardial biopsy were homozygous for the missense mutation p.Asp102His in GYG1. The mutated glycogenin-1 protein was expressed in cardiac tissue but had lost its ability to autoglucosylate as demonstrated by an in vitro assay and western blot analysis. It was therefore unable to form the primer for normal glycogen synthesis. Two of the patients showed similar patterns of heart dilatation, reduced ejection fraction and extensive late gadolinium enhancement on cardiac magnetic resonance imaging. These two patients were severely affected, necessitating cardiac transplantation. The cardiomyocyte storage material was characterized by large inclusions of periodic acid and Schiff positive material that was partly resistant to alpha-amylase treatment consistent with polyglucosan. The storage material had, unlike normal glycogen, a partly fibrillar structure by electron microscopy. None of the patients showed signs or symptoms of muscle weakness but a skeletal muscle biopsy in one case revealed muscle fibres with abnormal glycogen storage. Glycogenin-1 deficiency is known as a rare cause of skeletal muscle glycogen storage disease, usually without cardiomyopathy. We demonstrate that it may also be the cause of severe cardiomyopathy and cardiac failure without skeletal muscle weakness. GYG1 should be included in cardiomyopathy gene panels.

Diseases of the skeletal muscle

After the advances created by the use of cryostat sections and histochemistry 60 years ago, muscle histopathology is now living a real renaissance. In the field of genetic neuromuscular disorders, muscle biopsy analysis is fundamental to address questions about pathogenicity and protein expression when new genes are discovered through next-generation sequencing approaches. Moreover, the identification of the same gene mutated in previously considered distinct histopathologic entities imposes a constant reassessment of morphologic boundaries in several groups of disorders. In other fields like the acquired inflammatory myopathies, histologic analysis nowadays helps to affirm a diagnosis, set up therapeutic strategies, and verify the success of immunosuppressive treatment. In this exciting scenario morphologists are definitely key figures in the neuromuscular field. The objective of this chapter is to give an overview on morphology of the most frequent and recently identified muscle conditions, stressing the importance that only a combined analysis of clinical findings, muscle histology, and specific ancillary investigations is effective in reaching a precise diagnosis and orienting therapy.

A novel neuromuscular form of glycogen storage disease type IV with arthrogryposis, spinal stiffness and rare polyglucosan bodies in muscle

Glycogen storage disease type IV (GSD IV) is an autosomal recessive disorder causing polyglucosan storage in various tissues. Neuromuscular forms present with fetal akinesia deformation sequence, lethal myopathy, or mild hypotonia and weakness. A 3-year-old boy presented with arthrogryposis, motor developmental delay, weakness, and rigid spine. Whole body MRI revealed fibroadipose muscle replacement but sparing of the sartorius, gracilis, adductor longus and vastus intermedialis muscles. Polyglucosan bodies were identified in muscle, and GBE1 gene analysis revealed two pathogenic variants. We describe a novel neuromuscular GSD IV phenotype and confirm the importance of muscle morphological studies in early onset neuromuscular disorders.

Glycogen metabolism in humans

In the human body, glycogen is a branched polymer of glucose stored mainly in the liver and the skeletal muscle that supplies glucose to the blood stream during fasting periods and to the muscle cells during muscle contraction. Glycogen has been identified in other tissues such as brain, heart, kidney, adipose tissue, and erythrocytes, but glycogen function in these tissues is mostly unknown. Glycogen synthesis requires a series of reactions that include glucose entrance into the cell through transporters, phosphorylation of glucose to glucose 6-phosphate, isomerization to glucose 1-phosphate, and formation of uridine 5'-diphosphate-glucose, which is the direct glucose donor for glycogen synthesis. Glycogenin catalyzes the formation of a short glucose polymer that is extended by the action of glycogen synthase. Glycogen branching enzyme introduces branch points in the glycogen particle at even intervals. Laforin and malin are proteins involved in glycogen assembly but their specific function remains elusive in humans. Glycogen is accumulated in the liver primarily during the postprandial period and in the skeletal muscle predominantly after exercise. In the cytosol, glycogen breakdown or glycogenolysis is carried out by two enzymes, glycogen phosphorylase which releases glucose 1-phosphate from the linear chains of glycogen, and glycogen debranching enzyme which untangles the branch points. In the lysosomes, glycogen degradation is catalyzed by α-glucosidase. The glucose 6-phosphatase system catalyzes the dephosphorylation of glucose 6-phosphate to glucose, a necessary step for free glucose to leave the cell. Mutations in the genes encoding the enzymes involved in glycogen metabolism cause glycogen storage diseases.

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.

Late-onset polyglucosan body myopathy in five patients with a homozygous mutation in GYG1

Five Sardinian patients presented in their 5th or 6th decade with progressive limb girdle muscle weakness but their muscle biopsies showed vacuolar myopathy. The more or less abundant subsarcolemmal and intermyofibrillar vacuoles showed intense, partially α-amylase resistant, PAS-positive deposits consistent with polyglucosan. The recent description of late-onset polyglucosan myopathy has prompted us to find new genetic defects in the gene (GYG1) encoding glycogenin-1, the crucial primer enzyme of glycogen synthesis in muscle. We found a single homozygous intronic mutation harbored by five patients, who, except for two siblings, appear to be unrelated but all five live in central or south Sardinian villages.

Rhabdomyolysis: a genetic perspective

Rhabdomyolysis (RM) is a clinical emergency characterized by fulminant skeletal muscle damage and release of intracellular muscle components into the blood stream leading to myoglobinuria and, in severe cases, acute renal failure. Apart from trauma, a wide range of causes have been reported including drug abuse and infections. Underlying genetic disorders are also a cause of RM and can often pose a diagnostic challenge, considering their marked heterogeneity and comparative rarity.

In this paper we review the range of rare genetic defects known to be associated with RM. Each gene has been reviewed for the following: clinical phenotype, typical triggers for RM and recommended diagnostic approach. The purpose of this review is to highlight the most important features associated with specific genetic defects in order to aid the diagnosis of patients presenting with hereditary causes of recurrent RM.

A new muscle glycogen storage disease associated with glycogenin-1 deficiency

We describe a slowly progressive myopathy in 7 unrelated adult patients with storage of polyglucosan in muscle fibers. Genetic investigation revealed homozygous or compound heterozygous deleterious variants in the glycogenin-1 gene (GYG1). Most patients showed depletion of glycogenin-1 in skeletal muscle, whereas 1 showed presence of glycogenin-1 lacking the C-terminal that normally binds glycogen synthase. Our results indicate that either depletion of glycogenin-1 or impaired interaction with glycogen synthase underlies this new form of glycogen storage disease that differs from a previously reported patient with GYG1 mutations who showed profound glycogen depletion in skeletal muscle and accumulation of glycogenin-1.