Becker muscular dystrophy (BMD) and Klinefelter''s syndrome: a possible cause of variable expression of BMD within a pedigree.

We describe a man with Becker muscular dystrophy whose weakness was minimal in contrast to that of his more severely affected nephews. This man had a Klinefelter karyotype (47,XXY) and his mild symptoms may be attributed to him being heterozygous for the muscular dystrophy gene. This is the first report of a person with both Klinefelter's syndrome and Becker muscular dystrophy. This combination may be one explanation for the variable expression of X linked muscular dystrophy noted in some pedigrees.     

A population study of adult onset limb-girdle muscular dystrophy.

Complete ascertainment of adult onset limb-girdle muscular dystrophy in the Lothian Region of Scotland was attempted. Ten index cases were identified giving a prevalence of 1.3 per 100 000 (0.9 per 100 000 for cases where the diagnosis of muscular dystrophy was supported by both electromyographic and muscle biopsy findings). In these 10 sibships there had been 11 affected subjects, significantly less than the 16.5 cases expected for autosomal recessive inheritance. Excluding cases suspected of being Becker muscular dystrophy, the prevalence was 0.7 per 100 000 (0.3 per 100 000 for proven cases of muscular dystrophy) and there remained a significant difference between the number of cases observed (5) and the number expected (9.1) for autosomal recessive inheritance. The prevalence of limb-girdle muscular dystrophy with onset in adult life has apparently declined over the past 30 years, as would be expected with the recognition of other conditions which cause the same pattern of weakness, making this a relatively rare disorder which should only be considered when other diagnoses have been excluded. The possibility that some cases diagnosed as limb-girdle muscular dystrophy may have had Becker muscular dystrophy emphasises the urgent need for a greater understanding of the biochemical basis of these conditions so that such diagnostic and genetic counselling dilemmas can be resolved.     

Dystrobrevin deficiency at the sarcolemma of patients with muscular dystrophy

Mutations in the genes encoding dystrophin or dystrophin-associated proteins are responsible for Duchenne muscular dystrophy or various forms of limb-girdle muscular dystrophies respectively. We have recently cloned the gene for the murine 87 kDa postsynaptic protein dystrobrevin, a dystrophin-associated protein. Anti-dystrobrevin antibodies stain the sarcolemma in normal skeletal muscle indicating that dystrobrevin co-localises with dystrophin and the dystrophin- associated protein complex. By contrast, dystrobrevin membrane staining is severely reduced in muscles of Duchenne muscular dystrophy patients, consistent with dystrobrevin being a dystrophin-associated protein. Interestingly, dystrobrevin staining at the sarcolemma is dramatically reduced in patients with limb-girdle muscular dystrophy arising from the loss of one or all of the sarcoglycan components. Normal dystrobrevin staining is observed in patients with other forms of limb- girdle muscular dystrophy where dystrophin and the rest of the dystrophin-associated protein complex are normally expressed and in other neuromuscular disorders. Our results show that dystrobrevin- deficiency is a generic feature of dystrophies linked to dystrophin and the dystrophin-associated proteins. This is the first indication that a cytoplasmic component of the dystrophin-associated protein complex may be involved in the pathogenesis of limb-girdle muscular dystrophy.      

Fascioscapulohumeral muscular dystrophy: a progressive degenerative disease that responds to diltiazem

The authors believe that with fascioscapulohumeral muscular dystrophy (FSHD), like Duchenne muscular dystrophy, there is Ca2+ dysregulation in the muscle cells. The dysregulated Ca2+ can cause cell death in various ways. One mechanism may be Ca2+ triggering abnormal levels of tumor necrosis factor (TNF-alpha). Another mechanism may involve excessive Ca2+ levels within the mitochondria which would cause this organelle's membrane to collapse ultimately inducing apoptosis and/or necrosis. With this in mind, it has been reported that in FSHD there is over expression of adenine nucleotide translocator-1 (ANT-1). This Ca2+ dependent protein, which is a component of the mitochondrial permeability transition pore, could be an important culprit in mitochondrial membrane collapse. Therefore, dysregulated Ca2+ as well as TNF-alpha, in addition to over-expression of ANT-1, may result in cell disruption ultimately causing the characteristic dystrophic muscle wasting. The present investigators have noted that some individuals with FSHD benefit from a regimen of diltiazem, a Ca2+ channel blocker. Initial results using diltiazem may represent the first beneficial treatment for a form of muscular dystrophy. Even if there is only a slowing of progression, this would be a positive first step. A combination of several different Ca2+ regulating agents and TNF-alpha inhibitors may be necessary to truly alter and/or reverse the deleterious effects of this form of muscular dystrophy.     

Genetic linkage between Becker muscular dystrophy and a polymorphic DNA sequence on the short arm of the X chromosome.

A study of DNA restriction fragment polymorphisms and Becker muscular dystrophy has shown eight families informative for the cloned sequence L1.28, which is located on the short arm of the X chromosome between Xp110 and Xp113. Analysis of these families reveals linkage between the two loci, with the maximum likelihood estimate of the genetic distance being 16 centiMorgans (95% confidence limits between 7 and 32 centiMorgans). Since a study of DNA polymorphisms in Duchenne muscular dystrophy has shown a comparable linkage distance with L1.28, our results suggest that the locus for Becker muscular dystrophy, like that for Duchenne dystrophy, is on the short arm of the X chromosome, and further that these two loci may be closely linked or possibly allelic.     

Systemic membrane defect in the proximal muscular dystrophies.

We studied lymphocyte capping in 61 patients with Duchenne, Becker, limb-girdle, facioscapulohumeral and congenital muscular dystrophies. All showed a markedly diminished percentage of capped cells when compared with 86 normal controls, providing support for previous evidence that an alteration in membrane fluidity may be a common pathogenic feature in several genetically distinct forms of proximal muscular dystrophy. Heterozygous carriers of Duchenne muscular dystrophy showed diminished capping that was indistinguishable from that of afflicted males and was often present even when serum enzyme levels were normal. Studies in 25 families with 16 suspected sporadic cases indicated that no more than four out of 30 afflicted males may represent new mutations. These findings imply that most cases of Duchenne dystrophy might be prevented by a population screening program for carrier females combined with prenatal detection of afflicted males.     

Expression of transforming growth factor-beta 1 and its relation to endomysial fibrosis in progressive muscular dystrophy.

Progressive muscular dystrophy is characterized by muscle fiber necrosis, regeneration, and endomysial fibrosis. Although absence of dystrophin has been known as the cause of muscle fiber degeneration, pathogenesis of interstitial fibrosis is still unknown. Transforming growth factor-beta 1 (TGF-beta 1) induces accumulation of extracellular matrix in various diseases, such as liver cirrhosis and interstitial pneumonitis. To investigate its function on the pathogenesis of progressive muscular dystrophy, it was necessary to determine the degree of TGF-beta 1 expression and the site of TGF-beta 1 immunoreactivity. In Duchenne muscular dystrophy and most of Becker muscular dystrophy, high TGF-beta 1 immunoreactivity expressed on muscle fibers and extracellular space. In other myopathies with endomysial fibrosis, however, TGF-beta 1 was seldom observed. We also examined the immunoreactivity of the latent TGF-beta binding protein, which is bound to the TGF-beta precursors. In all Duchenne muscular dystrophy and half of Becker muscular dystrophy cases, high latent TGF-beta 1 binding protein immunoreactivity was seen, but in other myopathies its immunoreactivity was seldom seen on muscle fibers or extracellular space. Therefore TGF-beta 1 may play an important role in synthesis and accumulation of extracellular matrix in progressive muscular dystrophy.     

Analysis of motor control and kinesthetic perception in patients with progressive muscular dystrophy

The purpose of this study was to examine motor control and kinesthetic perception of upper extremity in patients with Duchenne progressive muscular dystrophy. Nine normal subjects and nine subjects with muscular dystrophy performed a pursuit tracking task with step wave target by means of isometric contraction, and simultaneously estimated magnitude of muscular tension during tracking behavior. The results were as follows: (1) the muscular electrical activity measured from the EMGs was directly proportional to the muscular tension for both the normal and the muscular dystrophy groups, (2) the speed of step response for the muscular dystrophy group was slower than that for the normal group, and (3) the exponent of power function for the muscular dystrophy group tended to be smaller than that for the normal group. These results were discussed in terms of the stage of disability in progressive muscular dystrophy.     

Age-dependent effect of myostatin blockade on disease severity in a murine model of limb-girdle muscular dystrophy

Myostatin (MSTN) is a muscle-specific secreted peptide that functions to limit muscle growth through an autocrine regulatory feedback loop. Loss of MSTN activity in cattle, mice, and humans leads to a profound phenotype of muscle overgrowth, associated with more and larger fibers and enhanced regenerative capacity. Deletion of MSTN in the mdx mouse model of Duchenne muscular dystrophy enhances muscle mass and reduces disease severity. In contrast, loss of MSTN activity in the dyW/dyW mouse model of laminin-deficient congenital muscular dystrophy, a much more severe and lethal disease model, does not improve all aspects of muscle pathology. Here we examined disease severity associated with myostatin (mstn-/-) deletion in mice nullizygous for delta-sarcoglycan (scgd-/-), a model of limb-girdle muscular dystrophy. Early loss of MSTN activity achieved either by monoclonal antibody administration or by gene deletion each improved muscle mass, regeneration, and reduced fibrosis in scgd-/- mice. However, antibody-mediated inhibition of MSTN in late-stage dystrophic scgd-/- mice did not improve disease. These findings suggest that MSTN inhibition may benefit muscular dystrophy when instituted early or if disease is relatively mild but that MSTN inhibition in severely affected or late-stage disease may be ineffective.     

Gastric hypomotility in Duchenne's muscular dystrophy

In Duchenne's muscular dystrophy, functional impairment of smooth muscle in the gastrointestinal tract can cause acute gastric dilatation and intestinal pseudo-obstruction that may be fatal. We describe a patient with this syndrome who at autopsy had smooth-muscle degeneration of the stomach. To provide objective evidence of functional smooth-muscle impairment in Duchenne's dystrophy, we performed gastric-emptying studies in 11 patients and 11 normal controls, using technetium-99m radionuclide scintigraphy in a test meal of oatmeal. The patients with Duchenne's dystrophy had delayed gastric-emptying times (118.18 +/- 32.21 minutes [mean +/- SEM]) as compared with controls (42.5 +/- 3.4 minutes, P less than 0.01). The cause of the pathological and functional abnormalities we describe in smooth muscle is unknown but may be a deficiency of dystrophin, the recently identified gene product of the Duchenne's muscular dystrophy locus.     

Genetic analysis of the Duchenne muscular dystrophy gene

Molecular biology techniques have changed the way in which we now consider a patient with Duchenne muscular dystrophy or Becker muscular dystrophy. Using cDNA probes, it has been shown that approximately 65% of the patients with Duchenne muscular dystrophy or Becker muscular dystrophy have gene deletions. The identification of a deletion allows the disease to be confirmed by noninvasive DNA testing. Furthermore, the identification of the gene defect can help distinguish Becker muscular dystrophy from other clinically similar neuromuscular disorders. Most importantly, the elucidation of the gene defects has resulted in the application of direct carrier and prenatal diagnostics.     

Transplantation of genetically corrected human iPSC-derived progenitors in mice with limb-girdle muscular dystrophy

Mesoangioblasts are stem/progenitor cells derived from a subset of pericytes found in muscle that express alkaline phosphatase. They have been shown to ameliorate the disease phenotypes of different animal models of muscular dystrophy and are now undergoing clinical testing in children affected by Duchenne's muscular dystrophy. Here, we show that patients with a related disease, limb-girdle muscular dystrophy 2D (LGMD2D), which is caused by mutations in the gene encoding α-sarcoglycan, have reduced numbers of this pericyte subset and thus produce too few mesoangioblasts for use in autologous cell therapy. Hence, we reprogrammed fibroblasts and myoblasts from LGMD2D patients to generate human induced pluripotent stem cells (iPSCs) and developed a protocol for the derivation of mesoangioblast-like cells from these iPSCs. The iPSC-derived mesoangioblasts were expanded and genetically corrected in vitro with a lentiviral vector carrying the gene encoding human α-sarcoglycan and a promoter that would ensure expression only in striated muscle. When these genetically corrected human iPSC-derived mesoangioblasts were transplanted into α-sarcoglycan-null immunodeficient mice, they generated muscle fibers that expressed α-sarcoglycan. Finally, transplantation of mouse iPSC-derived mesoangioblasts into α-sarcoglycan-null immunodeficient mice resulted in functional amelioration of the dystrophic phenotype and restoration of the depleted progenitors. These findings suggest that transplantation of genetically corrected mesoangioblast-like cells generated from iPSCs from LGMD2D patients may be useful for treating this type of muscular dystrophy and perhaps other forms of muscular dystrophy as well.     

Canine X-linked muscular dystrophy as an animal model of Duchenne muscular dystrophy: a review.

Canine X-linked muscular dystrophy is a spontaneously occurring, progressive, degenerative myopathy of dogs that is clinically and pathologically similar to Duchenne muscular dystrophy in man. The molecular basis for the disease has been shown to be a lack of dystrophin, the protein product of the Duchenne muscular dystrophy gene. Breeding colonies of dystrophic dogs have been established. This report reviews the findings of genetic, clinical, pathologic, molecular biologic, and immunocytochemical studies of the canine model, and compares the features of the canine disease to those of Duchenne dystrophy in man.     

Canine X-linked muscular dystrophy as an animal model of Duchenne muscular dystrophy: A review

Canine X-linked muscular dystrophy is a spontaneously occurring, progressive, degenerative myopathy of dogs that is clinically and pathologically similar to Duchenne muscular dystrophy in man. The molecular basis for the disease has been shown to be a lack of dystrophin, the protein product of the Duchenne muscular dystrophy gene. Breeding colonies of dystrophic dogs have been established. This report reviews the findings of genetic, clinical, pathologic, molecular biologic, and immunocytochemical studies of the canine model, and compares the features of the canine disease to those of Duchenne dystrophy in man.     

A Neurogenic Component in Muscular Dystrophy

Evidence for a neurogenic component in mouse and human muscular dystrophy is briefly reviewed. Such evidence comes from certain clinical observations, electrophysiological studies, muscle pathology, nervous system pathology, transplantation experiments in animals, and tissue culture studies. The evidence is at present rather conflicting though the results of recent tissue culture experiments are more convincing. If there is a neurogenic component in dystrophy then the basic defect may have to be sought in the central nervous system rather than in the muscle itself. It is argued, however, that a neurogenic component in dystrophy cannot be simply a defect in the anterior horn cells of the spinal cord since the clinical features and the laboratory and pathological findings are quite different from those in spinal muscular atrophy.     

Utility of dystrophin and utrophin staining in childhood muscular dystrophy

To determine the utility of dystrophin and utrophin staining in the differential diagnosis of childhood muscular dystrophy. Fifty muscle biopsies of histologically confirmed cases of childhood muscular dystrophy, below 16 years of age, were stained immunohistochemically for dystrophin and utrophin. All the 30 muscle biopsies of patients with Duchenne muscular dystrophy (DMD) showed all or majority of muscle fibers deficient for dystrophin and positive for utrophin. In the 4 female DMD carriers there was mosaic pattern of staining for dystrophin and reciprocal positivity for utrophin. All the muscle biopsies of patients with other childhood onset muscular dystrophies were positive for dystrophin and negative for utrophin. This study shows that dystrophin staining differentiates DMD and DMD carriers from other childhood muscular dystrophies and utrophin staining is of no added value. Utrophin up-regulation may compensate for structural deficiency in dystrophic muscle.     

The roles of prostaglandins and calcium accumulation in muscular dystrophy

There is good evidence that abnormal calcium accumulation may be a final common pathway of muscle degeneration in the muscular dystrophies. Prostaglandins are able to promote calcium entry into cells and excess prostaglandin activity coupled with a defect in intracellular calcium release could cause toxic accumulations of calcium in intracellular organelles such as mitochondria. Serotonin stimulates prostaglandin synthesis while tricyclic antidepressants inhibit calcium release from intracellular organelles thus possibly accounting for the models of muscular dystrophy reported using this combination. The prostaglandin/calcium hypothesis can account for the effects of vitamin E, steroids and local anaesthetic-like drugs in muscular dystrophy. Since many drugs already in clinical use for other purposes can be used to control prostaglandin synthesis or action this hypothesis has immediate potential clinical applications.     

Congenital muscular dystrophy with neurological abnormalities: Association with Hirschsprung disease

We report on a baby girl with congenital muscular dystrophy (CMD) with neurological abnormalities (“CMD Plus” condition), who also had Hirschsprung disease. This association may indicate a category of congenital muscular dystrophy with involvement of the visceral nervous system. We propose that Hirschsprung disease be added to the list of anomalies pertaining to the “CMD Plus” array, and that CMD should be considered when Hirschsprung disease occurs with central nervous system anomalies. © 1993 Wiley-Liss, Inc.     

Genetic counseling in Becker type X-linked muscular dystrophy. II: Practical considerations

A frequent problem of genetic counseling in Becker muscular dystrophy (BMD) is the differential diagnosis between BMD and the autosomal recessive benign limb-girdle muscular dystrophy (LGMD) if the pedigree pattern is not typical of X-linkage. In this situation, the a priori probability that a woman and her husband may be heterozygotes for LGMD can be shown to be 80 mu/a (mu = mutation rate in BMD; a = incidence ratio between BMD and LGMD). In addition, the age-corrected serum creatine kinase (CK) values of all female relatives are also important for the risk calculation of a woman being carrier of BMD.