Late-onset muscle phosphofructokinase deficiency

Hereditary myopathies associated with hematological abnormalities

The diagnostic evaluation of a patient with suspected hereditary muscle disease can be challenging. Clinicians rely largely on clinical history and examination features, with additional serological, electrodiagnostic, radiologic, histopathologic, and genetic investigations assisting in definitive diagnosis. Hematological testing is inexpensive and widely available, but frequently overlooked in the hereditary myopathy evaluation. Hematological abnormalities are infrequently encountered in this setting; however, their presence provides a valuable clue, helps refine the differential diagnosis, tailors further investigation, and assists interpretation of variants of uncertain significance. A diverse spectrum of hematological abnormalities is associated with hereditary myopathies, including anemias, leukocyte abnormalities, and thrombocytopenia. Recurrent rhabdomyolysis in certain glycolytic enzymopathies co-occurs with hemolytic anemia, often chronic and mild in phosphofructokinase and phosphoglycerate kinase deficiencies, or acute and fever-associated in aldolase-A and triosephosphate isomerase deficiency. Sideroblastic anemia, commonly severe, accompanies congenital-to-childhood onset mitochondrial myopathies including Pearson marrow-pancreas syndrome and mitochondrial myopathy, lactic acidosis, and sideroblastic anemia phenotypes. Congenital megaloblastic macrocytic anemia and mitochondrial dysfunction characterize SFXN4-related myopathy. Neutropenia, chronic or cyclical, with recurrent infections, infantile-to-childhood onset skeletal myopathy and cardiomyopathy are typical of Barth syndrome, while chronic neutropenia without infection occurs rarely in DNM2-centronuclear myopathy. Peripheral eosinophilia may accompany eosinophilic inflammation in recessive calpainopathy. Lipid accumulation in leukocytes on peripheral blood smear (Jordans' anomaly) is pathognomonic for neutral lipid storage diseases. Mild thrombocytopenia occurs in autosomal dominant, childhood-onset STIM1 tubular aggregate myopathy, STIM1 and ORAI1 deficiency syndromes, and GNE myopathy. Herein, we review these hereditary myopathies in which hematological features play a prominent role.

A novel image-based high-throughput screening assay discovers therapeutic candidates for adult polyglucosan body disease

Glycogen storage disorders (GSDs) are caused by excessive accumulation of glycogen. Some GSDs [adult polyglucosan (PG) body disease (APBD), and Tarui and Lafora diseases] are caused by intracellular accumulation of insoluble inclusions, called PG bodies (PBs), which are chiefly composed of malconstructed glycogen. We developed an APBD patient skin fibroblast cell-based assay for PB identification, where the bodies are identified as amylase-resistant periodic acid-Schiff's-stained structures, and quantified. We screened the DIVERSet CL 10 084 compound library using this assay in high-throughput format and discovered 11 dose-dependent and 8 non-dose-dependent PB-reducing hits. Approximately 70% of the hits appear to act through reducing glycogen synthase (GS) activity, which can elongate glycogen chains and presumably promote PB generation. Some of these GS inhibiting hits were also computationally predicted to be similar to drugs interacting with the GS activator protein phosphatase 1. Our work paves the way to discovering medications for the treatment of PB-involving GSD, which are extremely severe or fatal disorders.

Diagnostic evaluation of rhabdomyolysis

Rhabdomyolysis is characterized by severe acute muscle injury resulting in muscle pain, weakness, and/or swelling with release of myofiber contents into the bloodstream. Symptoms develop over hours to days after an inciting factor and may be associated with dark pigmentation of the urine. Serum creatine kinase and urine myoglobin levels are markedly elevated. Clinical examination, history, laboratory studies, muscle biopsy, and genetic testing are useful tools for diagnosis of rhabdomyolysis, and they can help differentiate acquired from inherited causes of rhabdomyolysis. Acquired causes include substance abuse, medication or toxic exposures, electrolyte abnormalities, endocrine disturbances, and autoimmune myopathies. Inherited predisposition to rhabdomyolysis can occur with disorders of glycogen metabolism, fatty acid β-oxidation, and mitochondrial oxidative phosphorylation. Less common inherited causes of rhabdomyolysis include structural myopathies, channelopathies, and sickle-cell disease. This review focuses on the differentiation of acquired and inherited causes of rhabdomyolysis and proposes a practical diagnostic algorithm. Muscle Nerve 51: 793-810, 2015.

[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.

Juvenile-onset permanent weakness in muscle phosphofructokinase deficiency

We describe a 41-year-old Moroccan woman with phosphofructokinase (PFK) deficiency who presented slowly progressive muscular weakness since childhood, without rhabdomyolysis episode or hemolytic anemia. Deltoid biopsy revealed massive glycogen storage in the majority of muscle fibers and polysaccharide deposits. PFK activity in muscle was totally absent. A novel homozygous non-sense mutation was detected in PFKM gene. Our observation suggests that juvenile-onset fixed muscle weakness may be a predominant clinical feature of PFK deficiency. Vacuolar myopathy with polyglucosan deposits remains an important morphological hallmark of this rare muscle glycogenosis.

Comparative Skeletal Muscle Histopathologic and Ultrastructural Features in Two Forms of Polysaccharide Storage Myopathy in Horses

Polysaccharide storage myopathy (PSSM) has been found in more than 35 different horse breeds through identification of abnormal storage of polysaccharide in muscle biopsies. A dominant mutation in the glycogen synthase 1 gene ( GYS1) accounts for a substantial proportion of PSSM cases in at least 17 breeds, including Quarter Horses, but some horses diagnosed with PSSM by muscle histopathologic analysis are negative for the mutation. We hypothesized that a second distinct form of glycogen storage disease exists in GYS1 -negative horses with PSSM. The objectives of this study were to compare the histopathologic features, ultrastructure of polysaccharide, signalment, history, and presenting complaints of GYS1 -negative Quarter Horses and related breeds with PSSM to those of GYS1 -positive horses with PSSM. The total histopathologic score in frozen sections of skeletal muscle stained with hematoxylin and eosin, periodic acid Schiff (PAS) and amylase-PAS stains from 53 GYS1-negative horses did not differ from that of 52 GYS1 -positive horses. Abnormal polysaccharide was fine granular or homogenous in appearance (49/53; 92%), often amylase-sensitive (28/53; 53%), more commonly located under the sarcolemma, and consisting of β glycogen particles in GYS1 -negative horses. However, in GYS1 -positive horses, abnormal polysaccharide was usually coarse granular (50/52; 96%), amylase-resistant (51/52; 98%), more commonly cytoplasmic, and consisting of β glycogen particles or, in some myofibers, filamentous material surrounded by β glycogen particles. Retrospective analysis found that GYS1 -negative horses ( n = 43) were younger at presentation (4.9 ± 0.6 years vs. 6.7 ± 0.3 years for GYS1 -positive horses) and were more likely to be intact males than GYS1 -positive horses ( n = 160). We concluded that 2 forms of PSSM exist and often have distinctive abnormal polysaccharide. However, because evaluation of the histologic appearance of polysaccharide can be subjective and affected by age, the gold standard for diagnosis of PSSM at present would appear to be testing for the GYS1 mutation followed by evaluating muscle biopsy for characteristic abnormal polysaccharide in those horses that are negative for the mutation.

Differential diagnosis of idiopathic inflammatory myopathies

Symmetric proximal muscle weakness has many potential etiologies. An onset over weeks to months and elevated serum levels of muscle enzymes point to the diagnosis of an idiopathic inflammatory myopathy, including dermatomyositis, polymyositis, and inclusion body myositis. However, there is a broad differential diagnosis, including certain muscular dystrophies, metabolic myopathies, drug- or toxin-induced myotoxicity, neuropathies, and infectious myositides. The differentiation is critical for defining appropriate treatment. In addition, an alternative diagnosis may explain the lack of response to immunosuppressive treatment for some patients with polymyositis. Careful clinical evaluation and choice of available diagnostic tests are required to establish the correct diagnosis.

Differentiating idiopathic inflammatory myopathies from metabolic myopathies

The metabolic myopathies are a heterogeneous group of diseases, including glycogenoses, disorders of lipid metabolism, and mitochondrial myopathies, that result primarily from inborn errors of metabolism. Most of these metabolic defects cause medical conditions that manifest early in life. Nevertheless, clinical presentations during the teenage years and adulthood are increasingly being recognized. Many of the clinical manifestations of these diseases are difficult to differentiate from those observed in the idiopathic inflammatory myopathies, especially polymyositis. A directed evaluation using the clinical, laboratory, and genetic approaches summarized in this article, however, should allow for the differentiation of most metabolic myopathies from polymyositis and other forms of idiopathic inflammatory myopathy. The diagnosis of a metabolic myopathy should be considered in patients who appear to have polymyositis but lack the characteristic changes of inflammation found on EMG, MRI, or muscle histology, or in such patients who are refractory to immunosuppressive therapy. The forearm ischemic exercise test is especially useful to screen for some inborn errors of glycogen metabolism or glycolysis and for myoadenylate deaminase deficiency. Thorough analysis of muscle tissue, including histology, histochemistry, biochemistry, and occasionally electron microscopy, is often necessary to make the diagnosis of a metabolic myopathy. Advances in molecular biology methods and knowledge of the precise genetic defects associated with these metabolic defects are dramatically increasing our capacity to diagnose patients with a widening range of myopathies. It is expected that, with further understanding of the mechanisms of the metabolic and idiopathic inflammatory myopathies, the differentiation of these disorders into their pathogenetic components, and the capacity to diagnose them will continue to improve. These are essential factors in improving genetic counseling and eventually the therapy of these serious, and currently incurable, disorders.

Chronic fatigue syndrome: a matter of enzyme deficiencies?

The etiology of chronic fatigue syndrome (CFS) remains an enigma. But literature concerning chronic fatigue which does not focus on CFS points to all sorts of enzyme deficiencies as possible causes. The deficiencies are probably dismissed as causes of CFS because other characteristic symptoms are lacking in CFS patients. But these symptoms are often also lacking in patients with a deficiency. Symptom patterns in enzyme deficiencies are extremely variable. Therefore, patients with CFS should be screened systematically for enzyme deficiencies.

Glycogen storage myopathies

The glycogen storage myopathies are caused by enzyme defects in the glycogenolytic or in the glycolytic pathway affecting skeletal muscle alone or in conjunction with other tissues. The authors review recent findings in this area, including a new entity, aldolase deficiency, and the wealth of molecular genetic data that are rapidly accumulating. Despite this progress, genotype-phenotyp3 correlations are still murky in most glycogen storage myopathies.

Use of fructose-2,6-diphosphate to assay for phosphofructokinase activity in human muscle

OBJECTIVE

Use fructose-2,6-diphosphate (fru-2,6-P2) for measuring phosphofructokinase (PFK) activity in muscles.

DESIGN AND METHODS

PFK activity was measured at 2 mmol/L MgCl2 and 5 mmol/L adenosine triphosphate (ATP) (mol/L MgCl2:mol/L ATP 0.4) without and with fru-2,6-P2.

RESULTS

Human muscle extracts had little PFK activity when assayed at mol/L MgCl2:mol/L ATP of 0.4 to 0.78 without fru-2,6-P2; 1.83 +/- 0.91 units/g muscle. Addition of fru-2,6-P2 produced an immediate 20- to 57-fold increase in activity; 52.8 +/- 12.5 units/g muscle. Raising the mol/L ratio of MgCl2 to ATP to 0.87 and higher without fru-2,6-P2 produced 34%-76% of the PFK activity seen with fru-2,6-P2. A PFK deficiency patient had a trace of activity, which was independent of mol/L MgCl2:mol/L ATP and not activated by fru-2,6-P2.

CONCLUSION

The almost complete absence of activity without fru-2,6-P2 at 0.40 mol/L MgCl2:mol/L ATP, and the restoration of maximum activity by fru-2,6-P2 provides an assay for verified PFK activity that could lead to a more accurate diagnosis in patients with PFK deficiency.

Phosphofructokinase deficiency: recent advances in molecular biology

Phosphofructokinase (PFK) plays a major role in glycolysis. Deficiency of PFK-M is characterized by muscle weakness due to fuel crisis in exercising muscles. To elucidate the gene defect of PFK-deficient patients, we have cloned and determined the complete structure and transcription mechanism of human PFK-M mRNA and gene. Molecular defects were investigated in three unrelated Japanese family cases. The first case was characterized by a point mutation at the donor site of intron 15 of the PFK-M gene. Cryptic splicing resulted in a 25 amino acid truncation in the patient's PFK-M. The second case possessed a point mutation at the donor site of intron 19, resulting in the skipping of exon 19 and the truncation of 55 amino acids. In the third case, a missense mutation was identified in the coding region. The review of an updated mutation repertoire indicates the heterogeneity of the molecular mechanism of the disease.

A new variant case of muscle phosphofructokinase deficiency, coexisting with gastric ulcer, gouty arthritis, and increased hemolysis

Muscle phosphofructokinase (PFK) deficiency includes both clinically and genetically heterogeneous conditions. A 22-year-old man with muscle PFK deficiency due to previously unrecognized mutation was admitted because of gastric ulcer. He had noticed mild fatigability on vigorous exercise, but had never experienced painful cramps and myoglobinuria. His history included five time relapses of gastric ulcer and gouty arthritis at ages 19 and 21 years. His laboratory data showing impaired muscle glycolysis, increased hemolysis, and myogenic hyperuricemia had aspects in common with those reported for the classic form of this disease, except that lactate concentrations in his blood increased considerably after exercise. The mutant PFK enzyme of this patient, who was demonstrated to have a missense mutation, could exert some catalytic activity that permitted glycolytic flux in vivo, thus leading to the absence of typical myopathic symptoms. The association of relapsing gastric ulcer with muscle PFK deficiency was detected for the first time. There is a possibility that oxygen radical-induced tissue damage resulting from increased hypoxanthine on exertion plays a role in the pathogenesis of ulceration, since the patient is more tolerant to exercise than reported cases with the classic form of muscle PFK deficiency.

Mutations in muscle phosphofructokinase gene

Mutations in the muscle phosphofructokinase gene (PFK-M) result in a metabolic myopathy characterized by exercise intolerance and compensated hemolysis. PFK deficiency, glycogenosis type VII (Tarui disease) is a rare, autosomal, recessively inherited disorder. Multiple mutations, including splicing defects, frameshifts, and missense mutations, have recently been identified in patients from six different ethnic backgrounds establishing genetic heterogeneity of the disease. There is no obvious correlation between the genotype and phenotypic expression of the disease. PFK-M deficiency appears to be prevalent among people of Ashkenazi Jewish descent. Molecular diagnosis is now feasible for Ashkenazi patients who share two common mutations in the gene; the more frequent is an exon 5 splicing defect, which accounts for approximately 68% of mutant alleles in this population.

Polyglucosan body myopathy: a new case

We report a 51-yr-old woman with late-onset progressive weakness affecting proximal limb muscles. Muscle biopsy revealed a vacuolar myopathy with accumulation of amylopectin-like polysaccharide resembling the polyglucosan found in type IV glycogenosis and adult-onset polyglucosan body disease. A biochemical study ruled out specific enzymatic defects known to cause storage of this abnormal material. Our case confirms the existence of a 'polyglucosan body myopathy' as a distinct clinicopathological entity in which the biochemical defect is unknown.

[Muscular glycogenoses]

Muscular glycogenosis is a disease resulting from genetic abnormalities altering an enzyme which is involved in glycogen metabolism. In addition to disorders of glycogenolysis and glycolysis, there are other pathological processes such as acid maltase (alpha-glucosidase) deficiency and diseases associated with abnormal glycogen structure. Glycolysis is the only metabolic pathway that can produce ATP in the absence of oxygen. It is then easy to understand that any disturbance in this energy pathway can result in dysfunction of the muscle machine and in a number of symptoms which are common to these abnormalities. An overall review of the various diseases know to exist on the glycogenolytic and glycolytic pathway will enable the reader to acquire a better knowledge of their particular features.

Metabolic causes of myoglobinuria

To evaluate the proportion of cases of myoglobinuria that can be ascribed to specific metabolic defects, we have studied eight enzymes--phosphorylase, phosphorylase kinase, phosphofructokinase (PFK), phosphoglycerate kinase (PGK), phosphoglycerate mutase (PGAM), lactate dehydrogenase (LDH), carnitine palmitoyltransferase (CPT), and myoadenylate deaminase (MAD)--in muscle biopsy specimens from 77 consecutive patients with myoglobinuria (documented in 44, suspected in 33). Enzyme defects were found in 36 patients: CPT deficiency in 17, phosphorylase deficiency in 10, phosphorylase kinase deficiency in 4, MAD deficiency in 3, PGK deficiency in 1, and a combined defect of CPT and MAD in 1. Exercise was the main precipitating factor, both in patients with and in those without detectable enzymopathies. Thirty patients had specific enzymopathies without myoglobinuria: 14 had phosphorylase deficiency, 9 had MAD deficiency, 3 had phosphorylase kinase deficiency, 3 had PFK deficiency, and 1 had PGAM deficiency. Systematic biochemical evaluation of muscle biopsy specimens revealed specific enzymopathies in about half of the patients with idiopathic myoglobinuria. The rest may have blocks of metabolic pathways not yet studied routinely, such as beta oxidation, or genetic defects of the sarcolemma, such as Becker's muscular dystrophy.

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

A severe, progressive myopathy developed in an 11-year-old, phosphofructokinase (PFK)-deficient, male, English Springer Spaniel dog. Results from a routine neurological examination were normal. Examination of histologic sections of skeletal muscle revealed large accumulations of material in some myofibers. These deposits were pale, basophilic, somewhat flocculent, and slightly granular with hematoxylin and eosin stain. Most fascicles examined in sections of limb and trunk muscles were affected to some degree, with up to 10% of muscle fibers being involved. Deposits stained strongly with periodic acid-Schiff and were resistant to digestion by alpha amylase but were removed by incubation with gamma amylase. Deposits were faintly positive with Gomori's methenamine silver technique and alcian blue (pH 2.5) and were brown-gray with Lugol's iodine solution but were negative with other stains. Based on staining characteristics, the deposits seemed to consist primarily of an amylopectin-like polysaccharide(s). Alcian blue staining (pH 2.5) was removed by treatment with neuraminidase but not with hyaluronidase, indicating that some sialic acid residues were also present. Electron microscopically, the deposits were composed of short granular filaments, small granules and amorphous material. They were not membrane bound. The morphologic appearance and staining characteristics of the deposits were remarkably similar to deposits previously described in human PFK-deficient myopathy. As expected, total PFK activities were markedly reduced when assayed in skeletal muscles of this dog. In contrast with other PFK-deficient dogs, muscle glycogen in this animal was not increased above that of normal dogs.