Polysaccharide storage myopathy in canine phosphofructokinase deficiency (type VII glycogen storage disease)

Muscle Pathology in Free-Ranging Stranded Cetaceans

Despite the profound impact that skeletal muscle disorders may pose for the daily activities of wild terrestrial and marine mammals, such conditions have been rarely described in cetaceans. In this study, the authors aimed to determine the nature and prevalence of skeletal muscle lesions in small and large odontocetes and mysticetes ( n = 153) from 19 different species. A macroscopic evaluation of the epaxial muscle mass and a histologic examination of the longissimus dorsi muscle were performed in all cases. The only macroscopically evident change was variable degrees of atrophy of the epaxial muscles ( longissimus dorsi, multifidus, spinalis) in emaciated specimens. The histopathological study revealed single or combined morphological changes in 91.5% of the cases. These changes included the following: degenerative lesions (75.2%), muscle atrophy (37.9%), chronic myopathic changes (25.5%), parasitic infestation (9.2%), and myositis (1.9%). The skeletal muscle is easily sampled during a necropsy and provides essential microscopic information that reflects both local and systemic conditions. Thus, skeletal muscle should be systematically sampled, processed, and examined in all stranded cetaceans.

Spontaneous complex polysaccharide inclusions in the skeletal muscle of purpose-bred beagle dogs

Amylase-resistant, periodic acid-Schiff (PAS)-positive inclusions were identified in the skeletal muscle of four of twenty-four purpose-bred beagle dogs from a routine toxicology study. Affected myofibers contained amorphous material filling up to 20% of the sarcoplasm that stained lightly basophilic with hematoxylin and eosin and was strongly PAS-positive with amylase resistance. Transmission electron micrographic examination of the inclusions revealed granular, non-membrane-bound, electron-dense material, consistent with polysaccharide. Although skeletal muscle inclusions with similar features have been reported in dogs in conjunction with systemic metabolic disorders and less often in muscle adjacent to nonmyogenic sarcomas, all four of these dogs lacked clinical or pathological findings diagnostic of a concurrent systemic metabolic or localized skeletal muscle disorder. Furthermore, these skeletal muscle inclusions were present in both vehicle- and test article-treated dogs and were considered an incidental finding that may occur spontaneously in clinically normal beagle dogs; as such, their presence in drug-treated animals should be interpreted with caution.

Hemolysis, myopathy, and cardiac disease associated with hereditary phosphofructokinase deficiency in two Whippets

Two male castrated Whippet littermates were presented at 1 year of age for pallor, tachycardia, systolic heart murmur, dark yellow to orange feces, intermittent lethargy, pigmenturia, and muscle shivering or cramping after exercise. Persistent macrocytic hypochromic anemia with marked reticulocytosis and metarubricytosis was found when CBC results were compared with reference values for Whippets. Increased serum creatine kinase activity and hyperkalemia also were sometimes present over the 4-year period of evaluation. Progressively increasing serum concentrations of N-terminal prohormone brain natriuretic peptide suggested cardiac disease. Erythrocytes from the whippets were less osmotically fragile but more alkaline fragile than those from control dogs. Erythrocyte phosphofructokinase (PFK) activities and 2,3-diphosphoglycerate concentrations were decreased. Restriction enzyme-based DNA test screening and DNA sequencing revealed the same mutation in the muscle-PFK gene of the Whippets as seen in English Springer Spaniel dogs with PFK deficiency. This is the first report of PFK deficiency in Whippet dogs. In addition to causing hemolysis and exertional myopathy, heart disease may be a prominent clinical component of PFK deficiency in this breed and has not been previously recognized in PFK-deficient English Springer Spaniels.

A GYS1 gene mutation is highly associated with polysaccharide storage myopathy in Cob Normand draught horses

Glycogen storage diseases or glycogenoses are inherited diseases caused by abnormalities of enzymes that regulate the synthesis or degradation of glycogen. Deleterious mutations in many genes of the glyco(geno)lytic or the glycogenesis pathways can potentially cause a glycogenosis, and currently mutations in fourteen different genes are known to cause animal or human glycogenoses, resulting in myopathies and/or hepatic disorders. The genetic bases of two forms of glycogenosis are currently known in horses. A fatal neonatal polysystemic type IV glycogenosis, inherited recessively in affected Quarter Horse foals, is due to a mutation in the glycogen branching enzyme gene (GBE1). A second type of glycogenosis, termed polysaccharide storage myopathy (PSSM), is observed in adult Quarter Horses and other breeds. A severe form of PSSM also occurs in draught horses. A mutation in the skeletal muscle glycogen synthase gene (GYS1) was recently reported to be highly associated with PSSM in Quarter Horses and Belgian draught horses. This GYS1 point mutation appears to cause a gain-of-function of the enzyme and to result in the accumulation of a glycogen-like, less-branched polysaccharide in skeletal muscle. It is inherited as a dominant trait. The aim of this work was to test for possible associations between genetic polymorphisms in four candidate genes of the glycogen pathway or the GYS1 mutation in Cob Normand draught horses diagnosed with PSSM by muscle biopsy.

Insulin sensitivity in Belgian horses with polysaccharide storage myopathy

OBJECTIVE

To determine insulin sensitivity, proportions of muscle fiber types, and activities of glycogenolytic and glycolytic enzymes in Belgians with and without polysaccharide storage myopathy (PSSM).

ANIMALS

10 Quarter Horses (QHs) and 103 Belgians in which PSSM status had been determined.

PROCEDURES

To determine insulin sensitivity, a hyperinsulinemic euglycemic clamp (HEC) technique was used in 5 Belgians with PSSM and 5 Belgians without PSSM. Insulin was infused i.v. at 3 mU/min/kg for 3 hours, and concentrations of blood glucose and plasma insulin were determined throughout. An i.v. infusion of glucose was administered to maintain blood glucose concentration at 100 mg/dL. Activities of glycogenolytic and glycolytic enzymes were assessed in snap-frozen biopsy specimens of gluteus medius muscle obtained from 4 Belgians with PSSM and 5 Belgians without PSSM. Percentages of type 1, 2a, and 2b muscle fibers were determined via evaluation of >or= 250 muscle fibers in biopsy specimens obtained from each Belgian used in the aforementioned studies and from 10 QHs (5 with PSSM and 5 without PSSM).

RESULTS

Belgians with and without PSSM were not significantly different with respect to whole-body insulin sensitivity, muscle activities of glycogenolytic and glycolytic enzymes, or proportions of muscle fiber types. However, Belgians had an increased proportion of type 2a and decreased proportion of type 2b muscle fibers, compared with proportions in QHs, regardless of PSSM status.

CONCLUSIONS AND CLINICAL RELEVANCE

PSSM in Belgians may be attributable to excessive glycogen synthesis rather than decreased glycogen utilization or enhanced glucose uptake into muscle cells.

Idiopathic complex polysaccharide storage disease in an abyssinian cat

A glycogen storage disease affecting primarily the skeletal muscle and, to a lesser degree, the cardiac muscle, spinal cord, and brain was diagnosed in a 10-year-old neutered Abyssinian cat with a 4-year history of paresis progressing to acute paralysis. Microscopically, these tissues contained inclusions that were pale basophilic in hematoxylin and eosin-stained slides, diastase resistant, periodic acid-Schiff positive, and blue-to-almost black with iodine stain. By transmission electron microscopy, the inclusions consisted of cytosolic, usually sharply demarcated, nonmembrane-bound deposits of finely granular and filamentous material. On the basis of the structural and histochemical staining characteristics, the inclusions were believed to be aggregates of abnormally stored, unbranched glycogen. A defect in glucose metabolism is suspected to be the underlying pathologic process, but an exact cause remains elusive.

Molecular cloning of equine muscle-type phosphofructokinase cDNA

The complete coding region sequence of equine muscle-type phosphofructokinase (ePFKM) was obtained from skeletal muscle of a thoroughbred horse. The deduced amino acid sequence of ePFKM showed 97%, 96%, 96%, 96% and 95% identity to canine, human, mouse, rabbit and rat PFKM, respectively. The amino and carboxyl terminal halves of ePFKM presented a structure of tandem repeat, as other mammalian PFKMs. As the amino acid residues constituting various ligand-binding sites were also conserved, it is thought that ePFKM has enzymatic activity similar to PFKM in other mammals.

Complex polysaccharide inclusions in skeletal muscle adjacent to sarcomas in two dogs

Inclusions of periodic acid-Schiff-positive, amylase resistant material were found within skeletal muscle fibers adjacent to an osteosarcoma in the proximal femur of an 8-year-old intact female Cocker Spaniel dog (dog No. 1) and adjacent to a synovial cell sarcoma of the stifle joint in a 7-year-old spayed female Bouvier des Flandres dog (dog No. 2). Inclusions were pale blue-gray with hematoxylin and eosin stain and formed irregular inclusions, replacing up to approximately 80% of the fiber diameter. Inclusions from dog No. 2 were of non-membrane-bound granular to filamentous material that occasionally formed discrete, elongate electron-dense masses. The features of these inclusions were similar to those of materials previously described as complex polysaccharide, polyglucosan bodies, amylopectin, and Lafora bodies. Evidence for a generalized metabolic disorder was not found in these two dogs, suggesting that storage of complex polysaccharide can occur as a relatively nonspecific response to metabolic alterations in skeletal muscle in a variety of conditions.

Muscle and nerve biopsy

Biopsy of muscle and nerve is an essential component of the diagnostic plan for animals with suspected neuromuscular disease. This article includes descriptions of the biopsy procedures and information regarding appropriate biopsy site selection and correct handling and processing of the tissues. The normal and pathological appearance of muscle and nerve using routine histochemical and histological techniques are described and illustrated emphasizing the basic myopathic and neuropathic responses of the neuromuscular system.

Neuromuscular complications in endocrine and metabolic disorders

Many of the endocrine and metabolic myopathies have no unique features, and for most clinicians, it is not possible to remember the clinical nuances of all the specific abnormalities and deficiencies responsible for these myopathies. This can make this group of diseases difficult to suspect. It is more important to recognize the general features of myopathic disease and to consider muscle biopsies as a preliminary diagnostic technique, with the potential for further investigation if a myopathy is confirmed.

Skeletal muscle metabolic response to exercise in horses with 'tying-up' due to polysaccharide storage myopathy

Polysaccharide storage myopathy (PSSM) is a distinct cause of exertional rhabdomyolysis in Quarter Horses that results in glycogen and abnormal polysaccharide accumulation. The purpose of this study was to determine if excessive glycogen storage in PSSM is due to a glycolytic defect that impairs utilisation of this substrate during exercise. Muscle biopsies, blood lactates and serum CK were obtained 1) at rest from 5 PSSM Quarter Horses, 4 normal Quarter Horses (QH controls) and 6 Thoroughbreds with recurrent exertional rhabdomyolysis (TB RER) and 2) after a maximal treadmill exercise test in PSSM and QH controls. In addition, 3 PSSM horses performed a submaximal exercise test. At rest, muscle glycogen concentrations were 2.4x and 1.9x higher in PSSM vs. QH controls or TB RER, respectively. Muscle lactates at rest were similar between PSSM and QH controls but significantly higher in PSSM vs. TB RER. Muscle glucose-6-phosphate concentrations were also higher in PSSM horses than controls combined. During maximal exercise, mean muscle glycogen concentrations declined 2.7x more and mean lactate increased 2x more in PSSM vs. QH controls; however, differences were not statistically significant. Blood lactate concentrations after maximal exercise did not reflect generally higher muscle lactate in PSSM vs. QH controls. No change in blood lactate concentrations occurred in PSSM horses with submaximal exercise. Serum CK activity increased significantly 4 h after maximal and submaximal exercise and was significantly higher in PSSM vs. QH controls. These results show that during maximal exercise, PSSM horses utilised muscle glycogen and produce lactic acid via a functional glycolytic pathway and that during submaximal exercise oxidative metabolism was unimpaired. The excessive glycogen storage and formation of abnormal polysaccharide in PSSM horses therefore appear to reflect increased glycogen synthesis rather than decreased utilisation. The specific subset of horses with exertional rhabdomyolysis due to PSSM would likely benefit clinically from a diet low in soluble carbohydrates like grain with fat added as well as gradually increasing daily exercise to reduce excessive glycogen accumulation and enhance utilisation.

Congenital erythrocyte enzyme deficiencies

Congenital hemolytic anemias resulting from PK, PFK, and G6PD enzyme deficiencies have been reported in domestic animals. Dogs with PFK deficiency may have episodes of intravascular hemolysis with hemoglobinuria in addition to a persistent compensated hemolytic anemia. Patients with mild G6PD deficiency are not anemic but may show increased susceptibility to oxidant-induced erythrocyte injury. Persistent methemoglobinemia has been reported in dogs and cats with methemoglobin reductase enzyme deficiency. Affected animals have cyanotic-appearing mucous membranes but show no or only mild clinical signs attributable to hypoxemia. Enzyme assays are usually done after acquired causes of hemolytic anemia and methemoglobinemia have been ruled out.

Rhabdomyolysis in childhood. A primer on normal muscle function and selected metabolic myopathies characterized by disordered energy production

Patients with rhabdomyolysis present an important clinical problem. In acute episodes immediate treatment may be necessary to prevent significant morbidity and mortality. Evaluation of affected patients necessitates an understanding of basic muscle pathophysiology and of the variety of disturbances that can interfere with muscle energy metabolism. The physician must then pursue a systematic stepwise evaluation (Table 6) that includes obtaining relevant history and laboratory studies, as well as arranging for appropriate provocative testing and muscle biopsy. Once the diagnosis is established, patient and family counseling is necessary, particularly in genetic disorders. Unfortunately, specific therapies have not proven entirely successful, and treatment generally has been directed at reducing the severity of rhabdomyolytic episodes.

Characterization of phosphofructokinase-deficient canine erythrocytes

Dogs homozygously affected with muscle-type phosphofructokinase (PFK) deficiency had about 20% of normal erythrocyte PFK activity and exhibited a compensated haemolytic anaemia. Erythrocyte glucose-6-phosphate and fructose-6-phosphate concentrations were increased and dihydroxyacetone phosphate and 2,3-bisphosphoglycerate values were below normal in affected dogs. Other intermediates distal to the PFK step were not significantly below normal and fructose-1,6-bisphosphate was even above normal. Erythrocyte ATP was higher than normal in affected dogs owing to the reticulocytes present. Abnormal adenylate metabolism was demonstrated by low ATP/AMP and ADP/AMP ratios and the inability to maintain ATP content when affected erythrocytes were incubated with cyanide. Glucose-1,6-bisphosphate content was normal, and fructose-2,6-bisphosphate content in affected canine erythrocytes was higher than normal. Studies of erythrocyte PFK isozymes revealed altered enzyme kinetic properties in affected dogs which appeared to be due to the loss of the M-type subunit.