The history of human muscular dystrophy with reference to clinical, histological and biochemical studies is reviewed. The value of the recent discovery of an experimental mouse with hereditary muscular dystrophy with clinical, histological, and biochemical similarities to human muscular dystrophy is discussed. The histology of normal muscle, with special reference to ultrastructure, is also reviewed. For this investigation mouse muscle samples for the electron microscope were fixed in Palades osmic acid solution, embedded in methacrylate or epon and stained with either lead hydroxide or phosphotungstic acid. A method for obtaining one day old muscle samples, while keeping the animals alive until the dystrophic symptoms are noted clinically, is outlined. Light microscope sections were obtained from electron microscope blocks and examined after staining with toluidine blue. Experimental results by light and electron microscope observations showed there to be no histological differences between one day old dystrophic and normal muscle. However one day old muscle showed histological differences compared to older muscle. The chief differences were the smaller size of fibers, random distribution of mitochondria and enlarged nuclei, and the presence of abundant interfibrillar sarcoplasm with a conspicuous granular components. The regular repeating pattern of the endoplasmic reticulum of adult muscle fibers was hot seen. Some "atypical" fibers showed similarities to altered fibers seen in older dystrophic mice. The mitochondria were swollen and vacuolated with few cristae and pale matrix. Endoplasmic reticular components were vacuolated and adjacent myofibrils were disorganized. Atrophy of fibers was first noted at 14 days of age and were conspicuous at 63 days. By 63 days alterations were also noted in mitochondria and endoplasmic reticulum and these changes became more prominent with the progress of the disease. Atrophy of the myofibrils was evident and the Z-bands were often irregular and out of register. Connective tissue also increased greatly. Several miscellaneous structures are also discussed. The histological findings are compared to those found by other workers. Several suggestions put forward by others as to the possible cause of the disease are summarized. On the basis of morphological findings it is suggested that ribonucleo-protein synthesis in the nuclei of dystrophic muscle fibers is increased but that there may be some intermediate stage at fault which prevents the conversion of amino acids to myofilaments. / Medicine, Faculty of / Graduate

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Robea Balle, Department of Human Genetics, MRC Unit for Skeletal Disorders, UCT Medical School, Observatory, Cape Town, South Africa. Duchenne muscular dystrophy (DMD) is a lethal X-linked neuromuscular disorder, characterised by progressive muscle wasting and weakness. DMD has its onset in early childhood, leading to physical handicap by the mid-teens and usually death by the age of twenty years. Becker muscular dystrophy (BMD) is the allelic form of DMD and is differentiated by its age of onset and milder phenotype. DMD and BMD are incurable and the most effective way of managing affected families is by preventing the recurrence of the di9order. The use of intragenic and closely linked flanking markers facilitates the identification of the defective X chromosome in female carriers and their affected male foetuses. DMD is thought to be the most common of the heritable muscle disorders, having an incidence of l in 3 300. When extrapolated to the large South African population, it presents a significant socioeconomic problem. For this reason, it was decided to develop a molecular genetic service for carrier identification and diagnostic predictions. The first step in the South African study involved the collection of biological material from affected individuals. In so doing, minimum prevalence's in the four major ethnic groups of Black, Caucasian, Indian and Mixed ancestry, were established. Although ascertainment was incomplete for a number of reasons, a markedly increased DMD frequency in the Indian population and a low frequency in the Black population was apparent. In the Caucasian group, an unexpectedly high BMD frequency, compared to DMD, was observed. 110 males affected with DMD and 18 with BMD were screened for deletions using genomic and cDNA probes and multiplex polymerase chain reaction (PCR) technology. Deletions were detected in the dystrophin gene of 47 DMD and 6 BMD patients, occurring predominantly in the 3' region of the gene (65%) and to a lesser extent in the 5' region of the gene (287.). The deletion frequency within individual ethnic groups,

Duchenne muscular dystrophy (DMD) is the most common type of muscular dystrophy caused by the loss of functional dystrophin. DMD is characterized by scoliosis, muscle wasting, loss of ambulation and a reduced life span. The first line of treatment for DMD is glucocorticoids (GCs). GCs are prescribed primarily for their anti-inflammatory and immunosuppressive effects; however, GC treatment is known to cause significant muscle atrophy. In DMD, GC treatment has been shown to improve muscle strength for the first 6 months and stabilization of the disease for up to 3 years. However, long term treatment reduces muscle function and accelerates disease progression. It is paradoxical that we use a medication that causes muscle wasting to treat a muscle wasting disease. The regeneration and function of muscle is dependent on the proper regulation and functioning of muscle satellite cells (MuSCs) to restore and repair muscle tissue. The impact GCs have on MuSCs from activation to proliferation and differentiation into muscle fibers is not well understood. GCs have many mechanisms of action by acting as a ligand to the glucocorticoid receptor (GR) to cause downstream effects by direct DNA binding or indirectly by regulating proteins. To study the role of GCs, we examined the effects of GC treatment on myoblast morphology, the cytoskeletal network, post-translational modifications (PTMs) of tubulin subunits, and the organization of microtubule organizing centers (MTOCs) in proliferating and differentiating myoblasts. This study shows that the GR is an essential regulator of myotube morphology and proper myonuclei placement. Furthermore, dexamethasone (DEX) treatment causes branching of the MT network, as well as an increase in the expression of the stabilizing MT markers, acetylated and detyrosinated tubulin during early differentiation. DEX treatment was also found to misposition the Golgi complex, a primary MTOC for the cytoskeletal network, from the periphery of the nucleus to the center of the nucleus during early differentiation. Finally, we found very few differentially expressed genes between WT and GRMuSC-/- myoblasts between early and late differentiation, indicating that these morphological defects we see are not due to GCs regulating gene expression. Thus, GCs act through the GR to modify the MT network during early differentiation, causing morphological changes in myoblasts that persist throughout differentiation.

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No description available.

Duchenne and Becker muscular dystrophies (DMD, BMD) are allelic X-linked diseases which affect approximately one in 3500 male newborns. They are caused by mutations in a gene positioned on the short arm of the X chromosome at Xp21. The first indication of the location of this gene was the description of rare females expressing DMD and who were found to have constitutional X;autosome translocations with an X chromosome breakpoint at this site. There are now 24 such females known worldwide. They express DMD as a consequence of preferential inactivation of the normal X chromosome. In order to contribute to the understanding of the aetiology of mutations causing DMD and the aetiology of constitutional translocations, two types of study have been performed here. Firstly, the detailed mapping of the X chromosome breakpoints of DMD-associated X;autosome translocations has been investigated. The results of this study have been compared with data on the physical distribution of mutations causing DMD in male patients. Secondly, one translocation, an X;l translocation with an autosomal breakpoint at Ip34, has been selected for more detailed investigation and the DNA sequence has been determined at the site of the rearrangement. Translocation breakpoint mapping studies were performed by somatic cell hybrid analysis. Hybrids were karyotyped and this information was used to construct a hybrid panel for the purpose of determining the autosomal localisations of anonymous DNA probes. The mapping of seven probes using this panel is described. The work described in this thesis revealed that the distribution of translocation breakpoints within the DMD gene appears to be random and may differ from the distribution of mutations in male patients. The X;l translocation whose breakpoints are cloned and sequenced was found to involve two expressed loci, one coding for dystrophin on the X chromosome and one for the leukocyte antigen related protein on chromosome 1. Sequence data revealed that a deletion of four to seven nucleotides from the X chromosome and a duplication of two to five nucleotides are associated with the translocation. The possible involvement of trinucleotides adjacent to the breakpoints, and of a LINE, a SINE and a stretch of potential Z-DNA within 1 kb of the X chromosome or the chromosome 1 breakpoint, is discussed.

Thesis (Ph. D.)--University of Missouri--Columbia, 2002. / Typescript. Vita. Includes bibliographical references (leaves 141-160). Also issued on the Internet.

Duchenne muscular dystrophy is an inherited, X-linked recessive skeletal muscle disorder that is characterized by mutations in the dystrophin gene [1]. Therefore, the disease affects primarily males and women are typically carriers. 1 in 3500 males in the United States are affected [1]. Dystrophin is a critical, large scaffolding protein in the dystrophin-glycoprotein complex found at the sarcolemma of skeletal muscle [1]. The complex helps maintain sarcolemma integrity and stability during muscle contractions by coupling the extracellular matrix proteins to the intracellular cytoskeleton in skeletal muscle [1]. Loss-of-function mutations in the dystrophin protein affect all skeletal muscle found throughout the human body. The 427 kD protein is also present in cardiac muscle, the brain, and peripheral nerves, thus affecting these tissues over time, as well [1]. One theory suggests the weakened stability of the dystrophin-glycoprotein complex when dystrophin is not expressed results in transient membrane tears during contraction, which permit pathological calcium influx [1]. Damaged skeletal muscle results in repair and regeneration of the tissue however, continual damage over time (referred to as muscle wasting) results in extensive fibrosis and loss of muscle fibers. The purpose of this thesis is to provide a comprehensive review on several molecular mechanisms that underlie Duchenne muscular dystrophy and to investigate current treatments and propose potential therapeutic targets for future research.

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