Congenital and metabolic myopathies of childhood or adult onset

OBJECTIVES

To investigate the clinical presentation, histological findings, and outcome of patients with congenital and metabolic myopathies (CM and MM) in whom the disease was diagnosed in childhood or adulthood.

PATIENTS AND METHODS

We reviewed the diagnosis of all skeletal muscle biopsies performed by our group between 1984 and 1996 (13 years). All patients with CM and MM of childhood or adult onset were included in the study. Patients with mitochondrial myopathies were excluded because they are multisystemic disorders with a more distinct picture than that observed in other MM. We retrospectively reviewed the clinical history, with special emphasis on the clinical patterns of presentation, histological findings, and outcome.

RESULTS

Among 1,865 biopsies, 28 (1.5%) fulfilled the diagnostic criteria for CM (seven nemaline myopathies, four multicore myopathies, three centronuclear myopathies) or MM (five adult-onset acid maltase deficiency, three myophosphorylase deficiency, three phosphofructokinase deficiency, two carnitine palmitoyl transferase deficiency, and one carnitine deficiency). In nearly half of the patients, mild stable weakness was the major complaint, whereas in one third muscular symptoms were intermittent and related to exercise. In a small number of cases, a persistently raised serum creatine kinase in an asymptomatic patient was the reason for muscle biopsy. Histological examination of skeletal muscle was highly indicative of a specific muscle disease in 26 of the 28 cases. After a mean follow-up of 7 years, the outcome has generally been good, and in most patients the myopathy did not worsen, most remaining ambulatory.

CONCLUSION

CM and MM presenting in childhood or adulthood are infrequent; the symptoms are usually mild or moderate, and the prognosis generally is good.

Impaired aerobic glycolysis in muscle phosphofructokinase deficiency results in biphasic post-exercise phosphocreatine recovery in 31P magnetic resonance spectroscopy

Using 31P magnetic resonance spectroscopy, energy metabolism in calf muscles of two patients with biochemically and genetically proven muscular phosphofructokinase deficiency, and an asymptomatic heterozygote was monitored during isometric foot plantarflexion performed under aerobic and anaerobic conditions and in the aerobic recovery phases. In the heterozygote only a moderate alteration from normal was found in terms of an elevated ATP demand during exercise. In the homozygote, hexose phosphates, indicated as phosphomonoesters, increased dramatically during contraction. Phosphomonoester accumulation resulted in consumption of free inorganic phosphate (P(i)). During ischemic exercise the absence of glycolytic ATP formation resulted in a linear time course of phosphocreatine breakdown and a moderate alkalinization. During the recovery, phosphocreatine resynthesis showed a biphasic time course, indicating that mitochondrial function itself was not directly affected. At first glance, the early depletion of P(i) below initial resting levels and the rate of phosphate splitting from sugar phosphates seemed to become the limiting factor for the rate of the oxidative phosphorylation and creatine kinase reaction. However, the actual concentrations of P(i) and ADP estimated at the onset of delay were too high to exclusively explain the dramatic delay in PCr resynthesis. For this reason, a reduced turnover of the citric acid cycle was assumed, which was caused by the complete absence of glycolysis in PFK deficiency patients. Furthermore, results from PFK deficiency patients were compared with previous findings from myophosphorylase deficiency patients in the literature.

Late-onset muscle weakness in partial phosphofructokinase deficiency: a unique myopathy with vacuoles, abnormal mitochondria, and absence of the common exon 5/intron 5 junction point mutation

Three patients (ages 51, 59, and 79) from two generations of an Ashkenazi Jewish family had partial (33% activity) phosphofructokinase (PFK) deficiency that presented with fixed muscle weakness after the age of 50 years. MR spectroscopy revealed accumulation of phosphomonoesters during exercise. Muscle biopsy showed a vacuolar myopathy with increased autophagic activity and several ragged-red and cytochrome c oxidase-negative fibers. The older patient, age 79 at biopsy, had several necrotic fibers. Electron microscopy revealed subsarcolemmal and intermyofibrillar glycogen accumulation and proliferation of mitochondria with paracrystalline inclusions, probably related to reduced availability of energy due to impaired glycolysis. The common point mutation of exon 5/intron 5 junction seen in Jewish Ashkenazi patients with PFK deficiency was excluded. We conclude that late-onset fixed muscle weakness occurs in partial PFK deficiency and it may represent the end result of continuing episodes of muscle fiber destruction. Partial enzyme deficiency in two successive generations suggests a unique molecular mechanism.

Partial block of glycolysis in late-onset phosphofructokinase deficiency myopathy

A late-onset, myopathic variant of phosphofructokinase (PFK) deficiency has been previously described in two patients of Ashkenazic descent. We report here on a non-Ashkenazic woman with the onset, at the age of 48 years, of a progressive limb girdle myopathy that was not preceded by a history of exercise intolerance. Muscle biopsy findings at the age of 58 years showed deposition of amylopectin-like material in muscle fibers and the absence of histochemical PFK activity. Enzymatic PFK activity in vitro was only 4% of normal. Since the forearm ischemic exercise test induced a sub-normal production of serum lactate, the patient underwent phosphorus magnetic resonance spectroscopy (31P-MRS), a non-invasive method that allows in vivo assessment of the functional status of the glycolytic pathway and mitochondrial oxidative metabolism by measuring the high-energy phosphates and cytosolic pH. In vivo, 31P-MRS disclosed a residual glycolytic flux and a normal rate of ATP production both at rest and during exercise. These results suggest that, in some patients, muscle PFK deficiency may be partial in vivo, and more severe in vitro, possibly due to protein or mRNA instability rather than absence. The presence of these findings in a patient with the late-onset myopathic form is compatible with a distinct pathogenetic mechanism, relying on progressive polysaccharide accumulation, rather than on acute energetic shortage in muscle fibers.

[Silent exercise-induced enzymatic myopathies at rest in adults. A cause of confusion with fibromyalgia]

Exercise-induced enzymatic myopathies include carnitine palmityl transferase deficiency and, among muscular glycogenoses, Mac Ardle's and Tarui diseases. These diseases are usually recognized when exercise-induced myalgias, myoglobinuria and raised creatinine kinase (CK) levels are present. However, myoglobinuria may be absent in 10 to 50 percent of the cases, and CK levels are often normal at rest; thus, the diagnosis is often delayed for several years, with a risk of acute renal failure in 10 to 30 percent of the patients. We report 6 cases of exercise-induced enzymatic myopathies with normal CK levels and with electromyographic studies at rest. The main clinical features of these cases and those of similar conditions reported in the literature are male sex, onset of the disease before the age of 15 years, episodes of severe exercise-induced myalgias, cramps and muscle weakness and myogenic hyperuricaemia at rest in muscular glycogenosis.

Fatal familial infantile glycogen storage disease: multisystem phosphofructokinase deficiency

An infant girl of consanguinous Bedouin parents suffered from fatal early onset of progressive generalized muscle weakness. Her older brother suffered from similar weakness and cardiomyopathy, which led to his death at the age of 21 months. A muscle biopsy performed on the propositus at the age of 9 months was PAS-negative, and showed nonspecific myopathic changes. A second muscle biopsy, performed at 21 months of age, a few days before her death, and postmortem study of heart and liver, disclosed excessive extralysosomal glycogen storage and reduced phosphofructokinase-1 (PFK-1) activity. Because the genes encoded for PFK-1 in liver and muscle are located on separate chromosomes, the reduced enzyme activity in both tissues could not be related to a single mutation for this enzyme. Activity of 6-phosphofructose-2-kinase (PFK-2), a recently discovered physiological activator to all PFK-1 isozymes, was normal in the liver. The possibility that this multisystem PFK-1 deficiency may be related to the absence of a yet unknown activator, common to all PFK-1 isozymes, is discussed.

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.

Fatal infantile form of muscle phosphofructokinase deficiency

We studied a girl with an infantile syndrome of limb weakness, seizures, cortical blindness, and corneal opacifications; she died at age 7 months of respiratory failure. There was no consanguinity or family history of neuromuscular diseases. Histochemical and biochemical studies of muscle showed mildly increased glycogen content and markedly decreased PFK activity (1.4% of the normal mean). Anaerobic glycolysis in vitro confirmed the metabolic block. Immunofluorescence and immunotitration by ELISA using monoclonal antibodies against subunit M of PFK showed a normal amount of cross-reacting material. The brain showed typical features of neuroaxonal dystrophy. This variant of PFK deficiency may be due to a distinct genetic defect.

Muscle phosphofructokinase deficiency: abnormal polysaccharide in a case of late-onset myopathy

A 61-year-old woman with muscle phosphofructokinase (PFK) deficiency had mild limb weakness all her life but no cramps or myoglobinuria. For 5 years the limb weakness progressed. In muscle, PFK activity was 1% of normal and glycogen concentration was elevated (2.13%). By light microscopy, a minor component of the accumulated glycogen appeared as PAS-positive, diastase-resistant inclusions in 10% of muscle fibers. The inclusions had a filamentous fine structure that resembled the abnormal long-chain glycogen of brancher enzyme deficiency. Iodine absorption spectra of both the inclusions and a diastase-resistant fraction of isolated glycogen resembled amylopectin. The abnormal polysaccharide in PFK deficiency may be related to greatly elevated concentration of muscle glucose-6-phosphate, an activator of the chain-elongating enzyme glycogen synthase.

Glycogen storage disease in skeletal muscle. Morphological, ultrastructural and biochemical aspects in 10 cases

We analyzed clinical, histological and biochemical findings in 10 patients with glycogen storage disease in skeletal muscle. Four patients were deficient in acid-alpha-glucosidase (Glycogenosis type II), three of them with late infantile onset and one patient adult form. Five patients, two of them siblings, were deficient in myophosphorylase (glycogenosis type V, McArdle's disease). One patient was a newborn with phosphofructokinase deficiency (glycogenosis type VII, Tarui's disease). Of the study of our cases we would like to outline the following features: in the glycogenosis type II the deposit is fundamentally intralysosomal in the late infantile form, storage of mucopolysaccharides and deposit in interstitial fibroblasts were found, while in the adult form glycogen storage is minimal. In the glycogenosis type V the storage of glycogen is free and of a small amount. In two patients we have observed enzymatic activity in regenerating fibres. In glycogenosis type VII the storage is free, of considerable quantity and the interstitial cells are also affected; no storage is observed in the satellite cells.

Myopathies related to diabetes mellitus and other metabolic diseases

Although it has long been known that both large and small blood vessels are abnormal in the tissues of diabetic patients, recent work has emphasized the widening of capillary basement membranes in diabetic tissues. Current views of the nature of this lesion and its relationship to diabetes are discussed and diabetic muscle and nerve lesions are emphasized. Other metabolic diseases with significant muscle pathology are types II, III and VII glycogen storage diseases. Myopathy with abnormal mitochondria is reviewed.

Liver glycogenosis and cataracts in a mentally deficient child

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