Objective To understand belief in a specific scientific claim by studying the pattern of citations among papers stating it. Design A complete citation network was constructed from all PubMed indexed English literature papers addressing the belief that β amyloid, a protein accumulated in the brain in Alzheimer’s disease, is produced by and injures skeletal muscle of patients with inclusion body myositis. Social network theory and graph theory were used to analyse this network. Main outcome measures Citation bias, amplification, and invention, and their effects on determining authority. Results The network contained 242 papers and 675 citations addressing the belief, with 220 553 citation paths supporting it. Unfounded authority was established by citation bias against papers that refuted or weakened the belief; amplification, the marked expansion of the belief system by papers presenting no data addressing it; and forms of invention such as the conversion of hypothesis into fact through citation alone. Extension of this network into text within grants funded by the National Institutes of Health and obtained through the Freedom of Information Act showed the same phenomena present and sometimes used to justify requests for funding. Conclusion Citation is both an impartial scholarly method and a powerful form of social communication. Through distortions in its social use that include bias, amplification, and invention, citation can be used to generate information cascades resulting in unfounded authority of claims. Construction and analysis of a claim specific citation network may clarify the nature of a published belief system and expose distorted methods of social citation.

https://www.bmj.com/content/bmj/339/bmj.b2680.full.pdf

How citation distortions create unfounded authority: analysis of a citation network.

The three major forms of immune-mediated inflammatory myopathy are dermatomyositis (DM), polymyositis (PM), and inclusion-body myositis (IBM). They each have distinctive clinical and histopathologic features that allow the clinician to reach a specific diagnosis in most cases. Magnetic resonance imaging is sometimes helpful, particularly if the diagnosis of IBM is suspected but has not been formally evaluated. Myositis-specific antibodies are not helpful diagnostically but may be of prognostic value; most antibodies have low sensitivity. Muscle biopsy is mandatory to confirm the diagnosis of an inflammatory myopathy and to allow unusual varieties such as eosinophilic, granulomatous, and parasitic myositis, and macrophagic myofasciitis, to be recognized. The treatment of the inflammatory myopathies remains largely empirical and relies upon the use of corticosteroids, immunosuppressive agents, and intravenous immunoglobulin, all of which have nonselective effects on the immune system. Further controlled clinical trials are required to evaluate the relative efficacy of the available therapeutic modalities particularly in combinations, and of newer immunosuppressive agents (mycophenolate mofetil and tacrolimus) and cytokine-based therapies for the treatment of resistant cases of DM, PM, and IBM. Improved understanding of the molecular mechanisms of muscle injury in the inflammatory myopathies should lead to the development of more specific forms of immunotherapy for these conditions.

Inflammatory myopathies: Clinical, diagnostic and therapeutic aspects

The myosin heavy chain (MyHC) is the molecular motor of muscle and forms the backbone of the sarcomere thick filaments. Different MyHC isoforms are of importance for the physiological properties of different muscle fiber types. Hereditary myosin myopathies have emerged as an important group of diseases with variable clinical and morphological expression depending on the mutated isoform and type and location of the mutation. Dominant mutations in developmental MyHC isoform genes (MYH3 and MYH8) are associated with distal arthrogryposis syndromes. Dominant or recessive mutations affecting the type IIa MyHC (MYH2) are associated with early-onset myopathies with variable muscle weakness and ophthalmoplegia as a consistent finding. Myopathies with scapuloperoneal, distal or limb-girdle muscle weakness including entities, such as myosin storage myopathy and Laing distal myopathy are the result of usually dominant mutations in the gene for slow/β cardiac MyHC (MYH7). Protein aggregation is part of the features in some of these myopathies. In myosin storage myopathy protein aggregates are formed by accumulation of myosin beneath the sarcolemma and between myofibrils. In vitro studies on the effects of different mutations associated with myosin storage myopathy and Laing distal myopathy indicate altered biochemical and biophysical properties of the light meromyosin, which is essential for thick filament assembly. Protein aggregates in the form of tubulofilamentous inclusions in association with vacuolated muscle fibers are present at late stage of dominant myosin IIa myopathy and sometimes in Laing distal myopathy. These protein aggregates exhibit features indicating defective degradation of misfolded proteins. In addition to protein aggregation and muscle fiber degeneration some of the myosin mutations cause functional impairment of the molecular motor adding to the pathogenesis of myosinopathies.

/pdf/myosinopathies-pathology-and-mechanisms-42vrnidwqe.pdf

Myosinopathies: pathology and mechanisms.

Distal myopathy refers to a heterogeneous group of disorders in which the initial manifestations are weakness and atrophy of the hands and feet. We report a family segregating an autosomal dominant distal myopathy, with multiple affected individuals in whom vocal cord and pharyngeal weakness may accompany the distal myopathy, without involvement of the ocular muscles. To our knowledge, this pedigree displays a distinct distal myopathy with the added features of pharyngeal and vocal cord dysfunction (VCPDM) that has not been previously reported. We mapped the MPD2 gene for VCPDM to chromosome 5q within a 12-cM linkage interval between markers D5S458 and D5S1972 in a large pedigree (a maximum LOD score of 12.94 at a recombination fraction of 0 for D5S393) and combined genome screening and DNA pooling successfully adapted to fluorescent markers. This technique provides for the possibility of fully automated genome scans.

Vocal Cord and Pharyngeal Weakness with Autosomal Dominant Distal Myopathy: Clinical Description and Gene Localization to 5q31

In 1954 based on their own detailed clinical studies and an extensive review of the earlier literature, Walton and Nattrass1 proposed a new and valuable classification of the muscular dystrophies. Ten years later Walton reviewed advances in the subject in the BMJ . 2 3 Many developments have taken place since then during a period in which there have been important advances in the application of molecular biology to medicine. Using protein studies and gene studies it is possible in the majority of cases to establish the precise diagnosis of a particular type of dystrophy, and thus provide a prognosis as well as genetic counselling and a reliable prenatal diagnosis. These developments could hardly have been imagined 30 years ago.

#### Summary points

The muscular dystrophies are a heterogeneous group of inherited disorders characterised by progressive muscle wasting and weakness

The genes and the protein products that are responsible for the dystrophies have been identified for most types of dystrophy

Using muscle protein studies and molecular genetic studies in the majority of cases it is possible to establish a precise diagnosis, provide a prognosis, detect preclinical cases, identify carriers, and offer prenatal diagnostic testing

The quality of life of individuals with dystrophy can be much improved by a positive attitude to management which includes respiratory care, physiotherapy, and the surgical correction of contractures

A molecular genetic approach seems to offer the best prospect for developing effective treatment in the future

This brief review is partly based on a survey of the most recent literature and partly based on nearly 40 years of personal clinical and research experience of these disorders. During the past 10 years the European Neuromuscular Centre, now based in the Netherlands, has encouraged and coordinated both clinical and laboratory studies of dystrophy, many of which have led directly or indirectly to the advances …

https://www.bmj.com/content/bmj/317/7164/991.full.pdf

The muscular dystrophies.

We have studied a family segregating a form of autosomal dominant distal myopathy (MIM 160500) and containing nine living affected individuals. The myopathy in this family is closest in clinical phenotype to that first described by Gowers in 1902. A search for linkage was conducted using microsatellite, VNTR, and RFLP markers. In total, 92 markers on all 22 autosomes were run. Positive linkage was obtained with 14 of 15 markers tested on chromosome 14, with little indication of linkage elsewhere in the genome. Maximum two-point LOD scores of 2.60 at recombination fraction .00 were obtained for the markers MYH7 and D14S64--the family structure precludes a two-point LOD score > or = 3. Recombinations with D14S72 and D14S49 indicate that this distal myopathy locus, MPD1, should lie between these markers. A multipoint analysis assuming 100% penetrance and using the markers D14S72, D14S50, MYH7, D14S64, D14S54, and D14S49 gave a LOD score of exactly 3 at MYH7. Analysis at a penetrance of 80% gave a LOD score of 2.8 at this marker. This probable localization of a gene for distal myopathy, MPD1, on chromosome 14 should allow other investigators studying distal myopathy families to test this region for linkage in other types of the disease, to confirm linkage or to demonstrate the likely genetic heterogeneity.

Autosomal dominant distal myopathy: linkage to chromosome 14.

Although there have been considerable advances in our understanding of the immunopathogenesis of the different forms of autoimmune inflammatory myopathy, the treatment of these conditions remains largely empirical, being based upon the use of immunosuppressive and immunomodulatory therapies which, for the most part, are non-selective in their actions. Corticosteroids are usually effective in adult and childhood cases of polymyositis and dermatomyositis, but are only rarely helpful in inclusion body myositis, which is usually also unresponsive to other forms of immunosuppressive therapy. Alternate-day corticosteroid therapy has a role in patients with mild disease and as a means of minimizing the side-effects of steroids. This may also be achieved by the early introduction of a second-line agent such as methotrexate or azathioprine, which will allow more rapid steroid withdrawal and may also improve the chances of inducing a remission in more severe cases. In patients who fail to respond adequately to oral corticosteroids, or who relapse after an initial response, intravenous immunoglobulin therapy or pulse therapy with intravenous methylprednisolone are promising approaches which appeal as safer alternatives to cytotoxic drugs. However these forms of treatment will require further evaluation in prospective clinical trials. The same applies to cyclosporin, which has a more selective action on T cells, and which has been reported to be effective in resistant cases of adult and juvenile polymyositis and dermatomyositis. In the longer term, the development of more specific forms of immunotherapy for these myopathies, aimed at blocking autoantigen presentation or its interaction with T cells, awaits the identification of the target antigens and T cells which initiate the autoimmune process

Treatment of inflammatory myopathies

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Autosomal dominant distal myopathy: linkage to chromosome 14.

Treatment of inflammatory myopathies