Congenital inflammatory myopathy

We present 3 patients with congenital inflammatory myopathy and summarize the literature. CNS involvement (microcephaly/intellectual delay) may or may not be present. Serum creatine kinase activity is elevated, the EMG is myopathic, and the muscle biopsy reveals inflammatory infiltrates, muscle fiber damage, and class I major histocompatibility complex products in muscle sarcolemma. Possible etiologies include intrauterine viral infection or an autoimmune process. Treatment with steroids may result in some motor improvement but has no effect on the CNS involvement. Despite a common time of presentation, these patients have a heterogeneous clinical profile, often suggesting a congenital muscular dystrophy syndrome.

Dystrophin is localized to the plasma membrane of human skeletal muscle fibers by electron-microscopic cytochemical study

Electron-microscopic immunoperoxidase technique revealed plasmalemmal localization of dystrophin in microscopically normal human skeletal muscle fibers obtained from nine routine diagnostic muscle biopsies. There was no evidence of periodicity of the immunoreactive product nor was there any evidence of immunostaining in any organelle besides the plasma membrane. Dystrophin appears to be a cytoskeletal protein associated with the plasmalemma. Its function is presumed to be the maintenance of the mechanical stability of the surface membrane so that it can withstand the normal contraction-induced stresses without disruption.

Myoclonus epilepsy and ragged-red fibres (MERRF). 1. A clinical, pathological, biochemical, magnetic resonance spectrographic and positron emission tomographic study

Thirteen patients, including 6 from one family, with the syndrome of myoclonus epilepsy and ragged-red fibres (MERRF) were studied. There was considerable heterogeneity in the age of onset, severity and associated clinical features. Postmortem studies in 3 patients from the one family showed a particular system degeneration. In addition, the youngest and most severely affected family member showed the pathological changes of Leigh's syndrome. Cortical dysfunction is a prominent clinical feature in MERRF, but postmortem examination failed to reveal cortical abnormalities. Positron emission tomographic studies, however, showed decreased cortical metabolic rates for glucose and oxygen utilization, with normal cortical blood flow and cerebral pH. Analyses of kinetic rate constants for uptake and phosphorylation of the glucose analogue, fluorodeoxyglucose showed decreased hexokinase-mediated phosphorylation: normal K1 and k2 values but reduced k3. Phosphorus magnetic resonance spectroscopy studies suggested a normal cerebral intracellular pH. Biochemical studies on muscle homogenates in 6 patients showed partial deficiencies of the activities of certain mitochondrial enzymes in 4 cases, whereas in 2 patients no abnormality was found. Our data, combined with previous reports, show that MERRF is biochemically and genetically heterogeneous. Our experience, and analysis of the literature, suggests that many cases previously described as the Ramsay Hunt syndrome, as well as other hitherto unclassified system degenerations associated with myoclonus epilepsy, are examples of MERRF. These data permit the formulation of a hypothesis to explain the clinical, biochemical and genetic heterogeneity of MERRF, and its overlap with Leigh's syndrome. We suggest that different biochemical defects of the mitochondrial respiratory chain may cause similar cerebral metabolic effects, as measured by positron emission tomography, resulting in similar phenotypes. Reduced activity of one enzyme, however, may result in different phenotypes, depending on the severity of the defect and its tissue distribution. Moreover, the phenotypic expression of certain biochemical defects may be influenced by randomly occurring factors such as fever, which may increase metabolic demand and result in more deleterious cellular metabolic effects.

cDNA clone and expression analysis of rodent fast and slow skeletal muscle troponin I mRNAs

We have characterized the structure and expression of rodent mRNAs encoding the fast and slow skeletal muscle isoforms of the contractile regulatory protein, troponin I (TnIfast and TnIslow). TnIfast and TnIslow cDNA clones were isolated from mouse and rat muscle cDNA clone libraries and were used as isoform-specific probes in Northern blot and in situ hybridization studies. These studies showed that the TnIfast and TnIslow mRNAs are expressed in skeletal muscle, but not cardiac muscle or other tissues, and that they are differentially expressed in individual muscle fibers. Fiber typing on the basis of in situ hybridization analysis of TnI isoform mRNA content showed an excellent correlation with fiber type as assessed by myosin ATPase histochemistry. These results directly demonstrate that the differential expression of skeletal muscle TnI isoforms in the various classes of vertebrate striated muscle cells is based on gene regulatory mechanisms which control the abundances of specific TnI mRNAs in individual muscle cells. Both TnIfast and TnIslow mRNAs are expressed, at comparable levels, in differentiated cultures of rat L6 and mouse C2 muscle cell lines. Thus, although neuronal input has been shown to be an important factor in determining fast versus slow isoform-specific expression in skeletal muscle, both TnIfast and TnIslow genes can be expressed in muscle cells in the absence of nerve. Comparison of the deduced rodent TnI amino acid sequences with previously determined rabbit protein sequences showed that residues with potential fast/slow isoform-specific function are present in several discrete clusters, two of which are located near previously identified actin and troponin C binding sites.

Dystrophin is expressed in mdx skeletal muscle fibers after normal myoblast implantation

In mdx mice, the dystrophin gene of the X chromosome is defective and, as a result, immunoreactive dystrophin is undetectable in all muscle fibers of all animals of this highly inbred strain. This study showed that implantation of suspensions of clonal cultures of normal human myoblasts into different regions of quadriceps muscles of 6-to-10-day-old mdx mice or 60-day-old mdx mice (whose muscles have been crushed 4 days before implantation) results in the appearance of scattered fiber segments containing microscopically demonstrable immunoreactive dystrophin. In the animals that received the normal myoblast implantation in the prenecrotic stage of the disease (6 to 10 days of age), the dystrophin-positive fiber segments (demonstrated at ages 35, 45, and 60 days) escaped necrosis. This was determined by the absence of the characteristic chains of central nuclei, a reliable marker of prior necrosis in mdx muscle fibers. By heavy labeling of the nuclear DNA of the transplantable human myoblasts with H3-thymidine during culturing, and by sequential performance of an immunocytochemical staining for dystrophin and autoradiography on the same sections, some dystrophin-positive fiber segments were shown to contain radiolabeled myonuclei. It was concluded that nondystrophic myoblasts fused with host muscle fibers to form mosaic muscle fibers in which the normal dystrophin gene of the implanted myoblasts was expressed. This approach may be employed for the mitigation of the deleterious consequences of a gene defect in recessively inherited human muscle diseases such as Duchenne dystrophy.

Segmental necrosis and its demarcation in experimental micropuncture injury of skeletal muscle fibers

Muscle fibers of rat gastrocnemii were punctured in vivo with a tungsten wire whose tip was 10 microns wide. After two hours, most punctured fibers had clearly necrotic segments. The length of necrotic segments appeared to increase between three and four hours. Demarcation of surviving stumps from necrotic segments by a membrane was complete in most muscles by seven hours. At the boundary between necrotic segments and nondemarcated stumps there was a cap of densely aggregated or hypercontracted myofilaments which stained strongly for precipitated calcium. The membrane which demarcated the stumps was found partially formed in the necrotic pulp close to this cap, attached to the plasma membrane. While forming it had a free edge and probably resulted from spontaneous aggregation of phospholipids in the pulp. Other portions of newly formed membrane were found encircling organelles inside necrotic segments. Prompt formation of a demarcating membrane probably limits the extent of necrosis in injured fibers.

Developmental regulation of cell-surface glycoproteins in clonal cultures of human skeletal muscle satellite cells

Pure populations of myogenic cells were obtained by cloning satellite cells from human skeletal muscle biopsies. Cell-surface glycoproteins at various stages of myogenesis were analysed by one- and two-dimensional gel electrophoresis. A total of 14 distinct proteins were detectable at the cell surface, on the basis of their susceptibility to desialation by exogenous neuraminidase or their iodination by exogenous lactoperoxidase. Reproducible changes in lectin binding or iodination of eight of these proteins occurred during myogenesis. Only two of the developmentally regulated proteins were components of the detergent-insoluble extracellular matrix fraction. Developmental regulation of these two proteins was unaffected by growth of cultures in 5-bromo-2'-deoxyuridine to inhibit myogenesis. In contrast, developmental regulation of the other cell-surface proteins was inhibited by growth in 5-bromo-2'-deoxyuridine, suggesting that changes in these proteins are tightly coupled to satellite cell differentiation. These studies represent the first systematic analysis of the surface proteins of pure, clonally derived, primary cultures of normal myogenic cells.

Vacuolation of muscle fibers near sarcolemmal breaks represents T-tubule dilatation secondary to enhanced sodium pump activity

Transsected rat soleus muscles incubated in oxygenated Krebs solution in vitro at 37 degrees C develop prominent vacuolation in the vicinity of the cut ends of muscle fibers which extends further along the fiber with increasing time of incubation. Electron microscopy shows that the vacuoles represent dilated segments of T-tubules. Their formation is prevented if the muscle is not cut, or in the following situations: omission of Na+ from the medium, incubation at 10 degrees C, or in media containing either 2,4-dinitrophenol or ouabain. Vacuole formation is considerably reduced by substituting Cl- with organic anions or by adding 9-anthracene carboxylic acid to the medium. These results suggest that a massive influx of sodium into the muscle fibers through their cut ends results in maximal stimulation of the Na+-K+-ATPase of the T-tubular membrane leading to increasing Na+ concentration in the lumen of T-tubules followed by influx of Cl- to maintain the electrical gradient. The accumulation of these ions leads to the entry of water from either the extracellular space or the sarcoplasm and consequent dilatation of T-tubules. Rapid incorporation of lipids into T-tubular membrane to increase its surface is presumably necessary for this to occur. Similar T-tubular dilatation appears to occur in vivo in surviving portions of muscle fibers adjacent to segmental necrosis.

Familial myopathy with changes resembling inclusion body myositis and periventricular leucoencephalopathy. A new syndrome

Five of 6 male siblings were affected by a progressive myopathy beginning in early childhood. Muscle biopsies in all patients showed the characteristic changes of inclusion body myositis. Computerized tomography and magnetic resonance imaging revealed a markedly abnormal appearance of cerebral white matter in the 4 affected patients tested, but clinical and other laboratory examinations failed to demonstrate evidence of central white matter dysfunction. Muscle biopsies and brain imaging were normal in all clinically unaffected family members. On the basis of the genetics, muscle biopsy findings and cerebral white matter changes, we conclude that this constellation represents a hitherto undescribed syndrome.

Small-caliber skeletal muscle fibers do not suffer necrosis in mdx mouse dystrophy

The prevalence of internal nuclei in muscle fibers (centronucleation), which is a reliable cumulative index of all prior muscle fiber necrosis, was measured at different ages in different muscles of mdx mice and was correlated with muscle fiber diameter. The prevalence of centronucleated fibers (as percentage of total number of fibers) rose gradually after age 20 days until it reached a peak level of 80% at age 60 days. No significant centronucleation (or necrosis) was observed in the following circumstances: in 4 different limb muscles before age 15 days, in leg muscles that were denervated by peripheral nerve section or rendered immobile by high thoracic cordotomy at 15 days, or in rotator extraocular muscles throughout the animals' life span. In these situations, muscle fiber diameter remained below approximately 20 micron. The mechanism by which small-diameter fibers are resistant to necrosis in mdx dystrophy is unknown, but a similar situation exists in hamster and Duchenne muscular dystrophy.

The Duchenne muscular dystrophy gene product is localized in sarcolemma of human skeletal muscle

Duchenne muscular dystrophy (DMD) and its milder form, Becker muscular dystrophy (BMD), are allelic X-linked muscle disorders in man. The gene responsible for the disease has been cloned from knowledge of its map location at band Xp21 on the short arm of the X chromosome. The product of the DMD gene, a protein of relative molecular mass 400,000 (Mr 400K) recently named dystrophin, has been reported to co-purify with triads of mouse and rabbit skeletal muscle when assayed using polyclonal antibodies raised against fusion proteins encoded by regions of mouse DMD complementary DNA. Here we show that antibodies directed against synthetic peptides and fusion proteins derived from the N-terminal region of human DMD cDNA strongly react with an antigen present in skeletal muscle sarcolemma on cryostat sections of normal human muscle biopsies. This immunoreactivity is reduced or absent in muscle fibres from DMD patients but appears normal in muscle fibres from patients with other myopathic diseases. The same antibodies specifically react with a 400K protein in sodium dodecyl sulphate (SDS) extracts of normal human muscle subjected to Western blot analysis. We conclude that the product of the DMD gene is associated with the sarcolemma rather than with the triads and speculate that it strengthens the sarcolemma by anchoring elements of the internal cytoskeleton to the surface membrane.

Sarcoplasmic reticulum adenosine triphosphatase deficiency with probable autosomal dominant inheritance

We report a family in which four members in two generations (mother, her son, and two daughters) suffered from impaired muscle relaxation aggravated by exercise. Muscle biopsies from two sisters showed moderate degree of histochemical type 2 fiber atrophy and excess of internal nuclei. Microscopic immunocytochemistry, using a monoclonal antibody raised against purified chicken SR-ATPase, revealed severe reduction of the immunoreactive ATPase of SR was markedly decreased on Western blots of muscle proteins. This family appears to have a clinically, electromyographically, and biochemically distinct metabolic myopathy associated with deficiency of SR-ATPase, with a probable autosomal dominant inheritance pattern that is phenotypically similar to recently described recessive cases.

Expression of immunoreactive major histocompatibility complex products in human skeletal muscles

Immunoreactive class 1 and class 2 major histocompatibility complex gene products (MHCP) and beta 2 microglobulin (beta 2 MG) were demonstrated by microscopic immunocytochemistry in cryostat sections of skeletal muscle biopsies of 67 patients with various neuromuscular diseases. Diagnoses included normal muscle, chronic partial denervation, Duchenne dystrophy, polymyositis, dermatomyositis, inclusion body myositis, and miscellaneous neuromuscular diseases. Normal mature muscle fibers did not express MHCP, but blood vessels showed both class 1 and 2 MHCP and beta 2 MG. Regenerating muscle fibers showed consistent sarcolemmal class 1 MHCP expression irrespective of the disease. In polymyositis, the majority of extrafusal muscle fibers of most patients showed strong sarcolemmal class 1 MHCP expression. In dermatomyositis, muscle fibers situated either in perifascicular or in randomly clustered distribution revealed strong class 1 MHCP reactivity. In inclusion body myositis, scattered small clusters of muscle fibers were positive for class 1 MHCP. In polymyositis and inclusion body myositis, particularly strong class 1 MHCP expression was invariably seen in nonnecrotic muscle fibers partially invaded by lymphocytes whose cytotoxic effects are believed to be class 1 MHCP restricted. Factors or agents that trigger class 1 MHCP expression are presumed also to sensitize lymphocytes to muscle fibers in these diseases, but their identity remains obscure at this time. In dermatomyositis, the expression of MHCP in perifascicular muscle fibers and in areas of capillary loss may represent the triggering of MHCP expression by a nonspecific cellular stress reaction, in this case probably low-grade ischemia.

Progressive dystonia with bilateral putaminal hypodensities

Three unrelated patients, aged 4, 18, and 47 years, had generalized dystonia associated with bilateral striatal hypodensities on computed tomography. Mitochondrial encephalopathy was considered to be the most likely diagnosis, but this could not be proved. These patients confirm previous reports linking acquired generalized dystonia with bilateral putaminal lesions and they highlight the problem in differential diagnosis of this clinicoradiologic syndrome.

Combined central and peripheral myelinopathy

We studied clinical, electrophysiologic, and nerve biopsy findings in two men with evidence of severe central and peripheral demyelinating disease. These patients may be rare examples of MS with associated severe, chronic, clinically evident peripheral demyelinating neuropathy. Alternatively, they may be cases of some other form of combined central-peripheral myelinopathy or fortuitous coincidence of MS with idiopathic inflammatory-demyelinating neuropathy. There have been only five other reports of clinically evident combined central-peripheral myelinopathy, but there have also been reports of only electrophysiologic or nerve biopsy evidence (without clinical manifestation) of peripheral neuropathy in MS patients.

The clinical consequences of X-chromosome inactivation: Duchenne muscular dystrophy in one of monozygotic twins

We have ascertained retrospectively a female patient, one of identical twins, who was diagnosed at age 23 years as having Duchenne muscular dystrophy (DMD). A muscle biopsy at that time showed a pattern in which large areas of destroyed muscle fibers replaced with adipose tissue were interspersed with normal-appearing muscle fascicles. The visualization of Barr bodies in the muscle biopsy, plus the patient's normal menstrual history served to rule out Turner's syndrome. The clinical expression of DMD in only one of monozygotic twins is strongly suggestive of uneven lyonization, with an excess of paternally derived X-chromosomes being inactivated in the patient. This view is supported by the appearance of the muscle biopsy. Twinning may conceivably predispose to uneven lyonization by reducing the size of the muscle cell anlage at the time of X-chromosome inactivation. Alternatively, lyonization may occur before the splitting of the embryonic mass, and by chance, the two embryonic centers could end up with a significantly different proportion of active maternal and paternal X-chromosomes.

Glucocorticoid excess induces preferential depletion of myosin in denervated skeletal muscle fibers

The combined effects of dexamethasone treatment (1 mg/Kg/day) plus denervation (DEX-DEN), were studied at 7, 13, and 28 days by microscopic, biochemical, and physiological techniques in plantaris and soleus muscles of adult rats. The results were compared with corresponding dexamethasone-treated (DEX) and denervated (DEN) muscles and appropriate controls. There was a significantly more marked atrophy of all fiber types in the DEX-DEN plantares at 7 and 13 days than in either DEX or DEN muscles. The degree of atrophy was greatest in type 2B fibers in DEX-DEN plantares. Electron microscopy revealed a severe preferential depletion of thick myofilaments in DEX-DEN plantares and solei but not in DEX or DEN muscles. The thick myofilament depletion in DEX-DEN muscles occurred in addition to a severe overall reduction of myofibrillar caliber. Gel electrophoresis showed a marked preferential decrease of myosin heavy chain in DEX-DEN plantares and solei, but not in either DEX or DEN muscles. Myosin light chains were also markedly reduced in DEX-DEN plantares and solei. In vitro physiological studies showed a marked reduction of the denervation-induced twitch potentiation in DEX-DEN solei. Maximal tetanic tension (20 Hz stimulation) per gram weight of muscle as well as the twitch-tetanus ratio was significantly reduced only in DEX-DEN solei in relation to controls. Myosin depletion in DEX-DEN muscles may be due to a severe preferential inhibition of its synthesis coupled with an accelerated catabolism.