Inclusion body myositis

Chaperones and the Proteasome System: Regulating the Construction and Demolition of Striated Muscle

Protein folding factors (chaperones) are required for many diverse cellular functions. In striated muscle, chaperones are required for contractile protein function, as well as the larger scale assembly of the basic unit of muscle, the sarcomere. The sarcomere is complex and composed of hundreds of proteins and the number of proteins and processes recognized to be regulated by chaperones has increased dramatically over the past decade. Research in the past ten years has begun to discover and characterize the chaperones involved in the assembly of the sarcomere at a rapid rate. Because of the dynamic nature of muscle, wear and tear damage is inevitable. Several systems, including chaperones and the ubiquitin proteasome system (UPS), have evolved to regulate protein turnover. Much of our knowledge of muscle development focuses on the formation of the sarcomere but recent work has begun to elucidate the requirement and role of chaperones and the UPS in sarcomere maintenance and disease. This review will cover the roles of chaperones in sarcomere assembly, the importance of chaperone homeostasis and the cooperation of chaperones and the UPS in sarcomere integrity and disease.

Functional impairment in patients with sporadic Inclusion Body Myositis

INTRODUCTION

We conducted a retrospective chart review of 53 patients diagnosed with sporadic Inclusion Body Myositis (sIBM) who have been followed at the McMaster Neuromuscular Clinic since 1996.

OBJECTIVES

We reviewed patient medical histories in order to compare our findings with similar cohorts, and analyzed quantitative strength data to determine functionality in guiding decisions related to gait assistive devices.

METHODS

Patient information was acquired through retrospective clinic chart review.

RESULTS

Our study found knee extension strength decreased significantly as patients transitioned to using more supportive gait assistive devices (P < 0.05). A decline to below 30 Nm was particularly indicative of the need for a preliminary device (i.e. cane)(P < 0.05). Falls and fear of falling poses a significant threat to patient physical well-being. The prevalence of dysphagia increased as patients required more supportive gait devices, and finally a significant negative correlation was found between time after onset and creatine kinase (CK) levels (P < 0.01).

CONCLUSION

This study supports that knee extension strength may be a useful tool in advising patients concerning ambulatory assistance. Further investigations concerning gait assistive device use and patient history of falling would be beneficial in preventing future falls and improving long-term patient outcomes.

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

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 beta 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.

Patterns of muscle involvement in inclusion body myositis: clinical and magnetic resonance imaging study

The differential patterns of muscle involvement in the upper and lower limbs in sporadic inclusion body myositis (sIBM) were examined in 18 patients using both quantitative and manual muscle testing as well as magnetic resonance imaging (MRI) in 9 patients. Weakness of the quadriceps femoris and the forearm flexors was present in most patients, but there was considerable variability in the patterns and severity of muscle involvement. MRI disclosed preferential patterns of muscle involvement within functional groups such as the quadriceps femoris, in which there was severe involvement of the vasti with relative sparing of the rectus femoris, and the triceps surae, in which selective involvement of the medial gastrocnemius was common. Involvement of flexor digitorum profundus on MRI was found in only one third of patients. The results emphasize the variability in the clinical phenotype and differential susceptibility of muscles to the disease process in sIBM.

Mitochondrial DNA variants in inclusion body myositis

Mitochondrial DNA variants have been shown to be associated with many diseases. Mutations at mitochondrial DNA nucleotide positions 3192, 3196, 3397 and 4336 have been described in association with late-onset Alzheimer's disease. The pathological similarities between inclusion body myositis and Alzheimer's disease prompted an analysis of the relationship between the reported mutations and sporadic inclusion body myositis. The 4336G variant was not significantly increased in patients with inclusion body myositis or Alzheimer's disease when compared to controls. None of the patients with inclusion body myositis carried mutations at nucleotide positions 3192, 3196 and 3397. A transition at nucleotide position 4580 was detected in some patients with inclusion body myositis and Alzheimer's disease but was not significantly higher in frequency when compared to controls. Phylogenetic analysis showed that the 4336G and 4580A variants clustered together in their respective group. A group of patients with inclusion body myositis also clustered together on a separate branch of the phylogenetic tree. Closer investigation of this group revealed a common polymorphism at nucleotide position 16311. The frequency of the 16311C variant was higher in inclusion body myositis than in Alzheimer's disease and controls, although when only caucasian patients were considered the increased frequency was not statistically significant. Further studies will be required to determine whether this variant plays a role in the pathogenesis of inclusion body myositis.

Dermatomyositis with the features of inclusion body myositis associated with carcinoma of the bladder

Inclusion body myositis (IBM) is a unique category of inflammatory myopathy. It is characterized histologically by the presence of muscle fibres with rimmed vacuoles and abnormal intracellular accumulations of proteins. We report here a 62-year-old patient with bladder carcinoma, where the signs of IBM overlapped with clinical features of dermatomyositis (DM). A combination of cutaneous changes typical for DM with histological and other features of IBM is exceedingly rare, and has not been previously addressed in dermatological literature. To the best of our knowledge this is also the first description of the association of DM/IBM with internal malignancy.

Inflammatory Myopathy

Patients with polymyositis or dermatomyositis should be treated with prednisone (approximately 1 mg/kg/d) for an initial period of 4 to 6 weeks. Once improvement occurs, the dose should be tapered and converted to an alternate-day regimen, which should be continued for at least 12 months. Methotrexate or azathioprine should be administered concomitantly to patients in whom there is inadequate control. The early introduction of one of these drugs allows more rapid reduction in the dose of prednisone and helps to avert serious side effects. Intravenous immunoglobulin therapy is indicated for patients who have immunodeficiency, who are unable to tolerate immu-nosuppressive drugs, whose conditions are deteriorating, or who have severe relapses. Cyclosporine or cyclophosphamide may be effective for resistant disease. Patients with inclusion body myositis should undergo a 3- to 6-month trial of prednisone, alone or in combination with methotrexate or azathioprine. Maintenance doses of these drugs should be continued if the patient's condition improves or stabilizes.

The genetic basis for the association of the 8.1 ancestral haplotype (A1, B8, DR3) with multiple immunopathological diseases

An individual's major histocompatibility complex (MHC) ancestral haplotype (AH) is the clearest single determinant of susceptibility to MHC associated immunopathological disease, as it defines the alleles carried at all loci in the MHC. However, the direct effects of any of the 150-200 genes that constitute the MHC are difficult to determine since recombination only occurs at defined hotspots. This review concerns the 8.1 AH (HLA-A1, C7, B8, C4AQ0, C4B1, DR3, DQ2), which is carried by most Caucasians with HLA-B8. It is associated with accelerated human immunodeficiency virus (HIV) disease, and susceptibility to insulin-dependent diabetes mellitus (IDDM), systemic lupus erythematosus, dermatitis herpetiformis, common variable immunodeficiency and IgA deficiency, myasthenia gravis and several other conditions. We have mapped susceptibility genes for HIV, IDDM and myasthenia gravis to the central MHC between HLA-B and the tumour necrosis factor or complement genes. Here we consider which of the remaining 8.1-associated diseases are more closely associated with HLA-DR3 and/or DQ2. Several candidate genes in the central MHC have the potential to modulate immune or inflammatory responses in an antigen-independent manner, as is seen in studies of cultured cells from healthy carriers of the 8.1 AH. Hence these genes may act as a common co-factor in the diverse immunopathological conditions associated with the 8.1 AH.

Sporadic inclusion-body myositis and its similarities to Alzheimer disease brain. Recent approaches to diagnosis and pathogenesis, and relation to aging

Sporadic inclusion-body myositis (s-IBM) is the most common, debilitating and progressive muscle disease beginning at the age 50 or later. The most characteristic pathologic feature is vacuolar degeneration of muscle fibers accompanied by intrafiber congophilia and clusters ("tangles") of paired-helical filaments, containing phosphorylated tau. An unusual feature of sporadic inclusion-body myositis is accumulation within its abnormal muscle fibers of several proteins that are characteristic of Alzheimer disease brain, including epitopes of beta-amyloid precursor protein (betaAPP), phosphorylated tau, alpha-1-antichymotrypsin, apolipoprotein E, and presenilin-1. Indicators of oxidative stress are also present within abnormal s-IBM muscle fibers. In this review, we describe new advances seeking the pathogenic mechanism of sporadic inclusion-body myositis. We hypothesize on the possible pathogenic role of abnormally accumulated proteins, and we propose that important contributory factors leading to inclusion-body myositis are the milieu of muscle-fiber aging and oxidative stress. In addition, we present evidence that overexpression of adenovirus-transferred betaAPP gene in cultured human muscle fibers induces aspects of the inclusion-body myositis phenotype, and suggest that betaAPP-overexpression is an early event in the pathogenic cascade causing inclusion-body myositis.

Diagnosis of amyotrophic lateral sclerosis

This review of the differential diagnosis of amyotrophic lateral sclerosis focuses on two themes. The first is practical, how to establish the diagnosis based primarily on clinical findings buttressed by electrodiagnosis. The main considerations are multifocal motor neuropathy and cervical spondylotic myelopathy. The second theme is the relationship of motor neuron disease to other conditions, including benign fasciculation (Denny-Brown, Foley syndrome), paraneoplastic syndromes, lymphoproliferative disease, radiation damage, monomelic amyotrophy (Hirayama syndrome), as well as an association with parkinsonism, dementia and multisystem disorders of the central nervous system.

Treatment of inflammatory myopathies

The treatment of the immune-mediated inflammatory myopathies remains largely empirical. Corticosteroids are usually effective in polymyositis and dermatomyositis but may need to be combined with methotrexate or azathioprine in some patients. Intravenous immunoglobulin (IVIg) is effective as add-on therapy in some patients not adequately controlled with steroids or immunosuppressive agents, but further controlled trials of IVIg are necessary to define the indications and optimal dose regimens. Cyclophosphamide, cyclosporin, or chlorambucil may be effective in patients with refractory polymyositis or dermatomyositis. Low-dose whole body or lymphoid irradiation is a last option in severely disabled patients resistant to all other treatments. As a small proportion of patients with inclusion body myositis respond to corticosteroid or immunosuppressive therapy, a 3-6-month trial of such therapy is justified in this condition. More specific immunotherapy for these disorders awaits identification of the target antigens and further clarification of the immunopathogenetic mechanisms.

Theiler's murine encephalomyelitis virus-induced cardiac and skeletal muscle disease

The DA strain of Theiler's murine encephalomyelitis virus, a member of the cardiovirus genus of picornaviruses, induces a restricted and persistent infection associated with a demyelinating process following intracerebral inoculation of mice; both virus infection and the immune response are believed to contribute to the late white matter disease. We now report that intraperitoneal inoculation with DA produces an acute myositis that progresses to a chronic inflammatory muscle disease in CD-1 mice as well as several inbred mouse strains. Some mouse strains also develop central nervous system white matter disease and a focal myocarditis. Infectious virus in skeletal muscle falls to undetectable levels 3 weeks postinoculation (p.i.), although viral genome persists for at least 12 weeks p.i., the longest period of observation. Severe combined immunodeficient animals have evidence of muscle pathology as long as 5 weeks p.i., suggesting that DA virus is capable of inducing chronic muscle disease in the absence of an immune response. The presence in immunocompetent mice, however, of prominent muscle inflammation in the absence of infectious virus suggests that the immune system also contributes to the pathology. T lymphocytes are the predominant cell type infiltrating the skeletal muscle during the chronic disease. This murine model may further our understanding of virus-induced chronic myositis and help to clarify the pathogenesis of human inflammatory myopathies.

Investigation of muscle disease

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