Spectrum Of Muscle Diseases Research Articles

Dystrophinopathies and Limb-Girdle Muscular Dystrophies.

Muscular dystrophies are a heterogeneous group of inherited diseases. The natural history of these disorders along with their management have changed mainly due to a better understanding of their pathophysiology, the evolution of standards of care, and new treatment options. Dystrophinopathies include both Duchenne's and Becker's muscular dystrophies, but in reality they are a spectrum of muscle diseases caused by mutations in the gene that encodes the protein dystrophin. Duchenne's muscular dystrophy is the most common form of inherited muscle disease of childhood. The current standards of care considerably prolong independent ambulation and survival. Several therapeutic options either aiming at substituting/correcting the primary protein defect or limiting the progression of the dystrophic process are currently being explored in clinical trials.Limb-girdle muscular dystrophies (LGMDs) are rare and heterogeneous conditions, characterized by weakness and wasting of the pelvic and shoulder girdle muscles. Originally classified into dominant and recessive, > 30 genetic forms of LGMDs are currently recognized. Further understanding of the pathogenic mechanisms of LGMD will help identifying novel therapeutic approaches that can be tested in clinical trials.

A case of hypertrophic cardiomyopathy secondary to dystrophinopathy

Dystrophinopathies include a spectrum of muscle diseases caused by mutations in the Duchenne Muscular Dystrophy (DMD) gene which encodes the protein “dystrophin”. Commonly, it presents as DMD or Becker Muscular Dystrophy. Cases of DMD usually have dilated cardiomyopathy and a few have hypertrophic cardiomyopathy. Contiguous gene deletion syndromes are disorders with coincident expression of otherwise unrelated inborn errors of metabolism. Xp21 deletion syndrome is a deletion syndrome most frequently affecting the X-linked congenital adrenal hypoplasia, glycerol kinase and dystrophin loci. We present a floppy infant with hypertrophic cardiomyopathy who was subsequently diagnosed as DMD with a strong possibility of contiguous gene deletion syndrome in the family.

Common Data Elements for Muscle Biopsy Reporting.

There is no current standard among myopathologists for reporting muscle biopsy findings. The National Institute of Neurological Disorders and Stroke has recently launched a common data element (CDE) project to standardize neuromuscular data collected in clinical reports and to facilitate their use in research. To develop a more-uniform, prospective reporting tool for muscle biopsies, incorporating the elements identified by the CDE project, in an effort to improve reporting and educational resources. The variation in current biopsy reporting practice was evaluated through a study of 51 muscle biopsy reports from self-reported diagnoses of genetically confirmed or undiagnosed muscle disease from the Congenital Muscle Disease International Registry. Two reviewers independently extracted data from deidentified reports and entered them into the revised CDE format to identify what was missing and whether or not information provided on the revised CDE report (complete/incomplete) could be successfully interpreted by a neuropathologist. Analysis of the data highlighted showed (1) inconsistent reporting of key clinical features from referring physicians, and (2) considerable variability in the reporting of pertinent positive and negative histologic findings by pathologists. We propose a format for muscle-biopsy reporting that includes the elements in the CDE checklist and a brief narrative comment that interprets the data in support of a final interpretation. Such a format standardizes cataloging of pathologic findings across the spectrum of muscle diseases and serves emerging clinical care and research needs with the expansion of genetic-testing therapeutic trials.

The spectrum of statin myopathy

This review discusses the spectrum of myopathies associated with statin use, with special attention given to a recently identified statin-associated autoimmune-necrotizing myopathy. The clinical characteristics of these patients, pathologic findings, associated autoantibody and immunogenetic risk factors are discussed. In the past several years, a novel form of autoimmunemyopathy associated with statin use has been described. Patients with this form of myositis have unique clinical, pathologic and pathophysiologic features when compared with those with self-limited statin toxic myopathy. An autoantibody directed against HMG-CoA reductase (HMGCR), the pharmacologic target of statins, characterizes the disease and can be used in clinical practice to identify these patients and direct therapy. Still, many questions remain to be answered regarding the pathogenic mechanisms at play, risk factors for developing the disease, long-term prognosis and effects of rechallenge with statins or other cholesterol-lowering drugs. Statins can cause a spectrum of muscle diseases, most of which are self-limited and improve with discontinuation of the offending agent. In a subgroup, an autoimmune necrotizing myopathy develops that persists after discontinuation of statins. Specific autoantibody testing can help identify these patients in clinical practice and determine the need for immunosuppressive therapy.

Skeletal muscle-specific T-tubule protein STAC3 mediates voltage-induced Ca 2+ release and contractility

Excitation-contraction (EC) coupling comprises events in muscle that convert electrical signals to Ca(2+) transients, which then trigger contraction of the sarcomere. Defects in these processes cause a spectrum of muscle diseases. We report that STAC3, a skeletal muscle-specific protein that localizes to T tubules, is essential for coupling membrane depolarization to Ca(2+) release from the sarcoplasmic reticulum (SR). Consequently, homozygous deletion of src homology 3 and cysteine rich domain 3 (Stac3) in mice results in complete paralysis and perinatal lethality with a range of musculoskeletal defects that reflect a blockade of EC coupling. Muscle contractility and Ca(2+) release from the SR of cultured myotubes from Stac3 mutant mice could be restored by application of 4-chloro-m-cresol, a ryanodine receptor agonist, indicating that the sarcomeres, SR Ca(2+) store, and ryanodine receptors are functional in Stac3 mutant skeletal muscle. These findings reveal a previously uncharacterized, but required, component of the EC coupling machinery of skeletal muscle and introduce a candidate for consideration in myopathic disorders.

Insufficient Membrane Fusion in Dysferlin-Deficient Muscle Fibers after Heavy-Ion Irradiation

Recently, SJL/J mice have been used as an animal model in studies of dysferlinopathy, a spectrum of muscle diseases caused by defects in dysferlin protein. In this study we irradiated muscle fibers isolated from skeletal muscle of SJL/J mice with heavy-ion microbeam, and the ultrastructural changes were observed by electron microscopy. The plasma membrane of heavy-ion beam irradiated areas showed irregular protrusions and invaginations. Disruption of sarcomeric structures and the enhancement of autophagy were also observed. In addition, many vesicles of varying size and shape were seen to be accumulated just beneath the plasma membrane. This finding further supports the recent hypothesis that dysferlin functions as a membrane fusion protein in the wound healing system of plasma membrane, and that the defect in dysferlin causes insufficient membrane fusion resulting in accumulation of vesicles.