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Inclusion Body Myositis Research - what's new? 2005

A sample of MAJOR, selected articles from the medical literature.

October 2005
Inclusion body myopathy and Paget disease is linked to a novel mutation in the VCP gene
Haubenberger, D MD; Bittner, R E. MD; Rauch-Shorny, S MD; Zimprich, F MD, PhD; Mannhalter, C PhD; Wagner, L MD; Mineva, I PhD; Vass, K MD; Auff, E MD; Zimprich, A MD
Abstract: Mutations in the valosin-containing protein (VCP) on chromosome 9p13-p12 were recently found to be associated with hereditary inclusion body myopathy, Paget disease of the bone, and frontotemporal dementia (IBMPFD). We identified a novel missense mutation in the VCP gene (R159H; 688G>A) segregating with this disease in an Austrian family of four affected siblings, who exhibited progressive proximal myopathy and Paget disease of the bone but without clinical signs of dementia.
Discussion: A mutational hotspot in exon 5 was described at position 155 in IBMPFD in the original report on VCP mutations. Six presumably independent mutational events were observed at this codon, with four of them being R>H changes. The mutation described in our study is only four amino acids away from this mutational hotspot, and of the same type (R>H). Cross-species protein alignment shows strong conservation of this codon (see figure). These observations can be regarded as two further pieces of evidence that the R159H substitution is pathogenic.
The clinical features of our kindred differ in two respects from other published cases. Firstly, the course of disease at the time of examination seems somewhat milder than in the previously published families. For example, none of our described patients needed professional caregivers. Secondly, whereas all four affected siblings showed typical features of myopathy and Paget disease of the bone, none of them displayed signs of frontotemporal dementia. This may seem surprising because the typical age at onset of frontotemporal dementia in mutation carriers is reported to be at 53 years, yet all of our patients are over 60 years of age. Conversely, frontotemporal dementia has been shown to have a low penetrance in this trial. Only 30% of mutation carriers seem to develop dementia at all. Thus, families and individuals carrying mutations in the VCP gene show an astonishingly variable degree in the occurrence of the three cardinal phenotypes: myopathy, Paget disease, and dementia. This is further substantiated by the recent finding of a novel R155C mutation carrier who exhibited inclusion body myopathy and a novel type of frontotemporal demantia but no signs of Paget disease of the bone.
Whether the absence of dementia and the milder phenotype in our kindred is due to the specific nature of the present mutation remains to be determined by future phenotype-genotype correlations. More data on VCP mutations, its clinical and neuropathological phenotypes, and penetrance in IBMPFD families are needed to gain further insight into possible common pathomechanisms in this multisystem disorder.

August 2005
Hum Pathol. 2005 Aug;36(8):917-21.
Positive troponin T without cardiac involvement in inclusion body myositis.
Schwarzmeier JD, Hamwi A, Preisel M, Resl C, Preusser M, Sluga E, Horcher E, Shehata MM.
Hematology Department, Internal Medicine I, Medical University of Vienna, A-1097 Vienna, Austria. josef.schwarzmeier@meduniwien.ac.at
Cardiac troponin T (cTnT) is considered as a specific marker for acute myocardial infarction. Here, we present a case with elevated cTnT, determined by a third-generation assay, without signs of a myocardial lesion. Routine investigation of a 66-year-old female patient with indolent B-cell lymphoma revealed increased serum levels of creatine kinase (CK), MB fraction of CK (CK-MB), and cTnT, although she did not complain of cardiac symptoms. Electrocardiographic monitoring, echocardiography, magnetic resonance computed angiography, and percutaneous coronary angiography excluded myocardial damage. However, the close follow-up showed a steady increase of CK-MB and cTnT levels and gradual development of weakness in both thighs. A biopsy of the right quadriceps muscle led to the diagnosis of inclusion body myositis. In contrast to cTnT, cardiac troponin I could not be detected retrospectively in any of her serum samples. These results demonstrate for the first time that cTnT is elevated in patients with inclusion body myositis.

The 26S proteasome system is involved in eliminating various proteins, including ubiquitinated misfolded/unfolded proteins, and its inhibition results in cellular accumulation of protein aggregates. Intramuscle-fiber ubiquitinated multiprotein-aggregates are char-acteristic of sporadic inclusion-body myositis (s-IBM) muscle fibers. Two major types of aggregates exist, containing either amyloid-b (Ab) or phosphorylated tau (p-tau). We have now asked whether abnormalities of the 26S proteasome contribute to s-IBM pathogenesis and whether the multiprotein aggregates have features of aggresomes. Using cultured human muscle fibers we also studied the effect of amyloid-b precursor protein (AbPP) overexpression on proteasome function and the influence of proteasome inhibition on aggresome formation. We report that in s-IBM muscle biopsies 26S proteasome subunits were immunodetected in the g-tubulin-associated aggresomes, which also contained Ab, p-tau, ubiquitin, and HSP70. In addition, a) expression of proteasome subunits was greatly increased, b) the 20Sa proteasome subunit co-immunoprecipitated with AbPP/Ab, and c) the three major proteasomal proteolytic activities were reduced. In cultured muscle fibers, AbPP-overexpressing fibers displayed diminished proteasomal proteolytic activities, and addition of proteasome inhibitor strikingly increased aggresome formation. Accordingly, proteasome dysfunction in s-IBM muscle fibers may play a role in accumulation of misfolded, potentially cytotoxic proteins and may be induced by increased intracellular AbPP/Ab.

Hereditary Inclusion Body Myopathy (HIBM) is an autosomal recessive neuromuscular disorder associated with mutations in UDP-N-acetylglucosamine 2-epimerase (GNE)/N-acetylmannosamine kinase (MNK), the bi-functional and rate-limiting enzyme of sialic acid biosynthesis. We developed individual GNE and MNK enzymatic assays and determined reduced activities in cultured fibroblasts of patients with HIBM harboring missense mutations in either or both the GNE and MNK enzymatic domains. To assess the effects of individual mutations on enzyme activity, normal and mutated GNE/MNK enzymatic domains were synthesized in a cell-free in vitro transcription-translation system and subjected to the GNE and MNK enzymatic assays. This cell-free system was validated for both GNE and MNK activities, and revealed that mutations in one enzymatic domain (in GNE, G135V, V216A, and R246W; in MNK, A631V, M712T) affected not only that domain's enzyme activity, but also the activity of the other domain. Moreover, studies of the residual enzyme activity associated with specific mutations revealed a discrepancy between the fibroblasts and the cell-free systems. Fibroblasts exhibited higher residual activities of both GNE and MNK than the cell-free system. These findings add complexity to the tightly regulated system of sialic acid biosynthesis. This cell-free approach can be applied to other glycosylation pathway enzymes that are difficult to evaluate in whole cells because their substrate specificities overlap with those of ancillary enzymes.

Inclusion body myositis (IBM) is the most common age-related degenerative skeletal muscle disorder. The aberrant intracellular accumulation of the b-amyloid (Ab) peptide within skeletal muscle is a pathological hallmark of IBM. Skeletal muscle is comprised of both slow and fast twitch fibers, which are present in different proportions in various muscles. It remains unclear if fast and/or slow twitch fibers are differentially involved in IBM pathogenesis. To better understand the molecular pathogenesis of IBM, we analyzed human IBM muscle biopsies and muscle from a transgenic mouse model of IBM (MCK-bAPP). Here we report that the majority of histopathologically-affected fibers in human IBM biopsies were type II fast fibers. Skeletal muscle from MCK-bAPP mice exhibited higher transgene expression and steady-state levels of human bAPP in fast type IIB fibers compared to slow type I fibers. These findings indicate that fast twitch fibers may selectively accumulate and be more vulnerable to bAPP- and Ab-mediated damage in IBM. These findings also highlight parallels between the MCK-bAPP mice and the human IBM condition.

The idiopathic inflammatory myopathies (IIM) are a heterogeneous group of neuromuscular disorders subdivided into polymyositis (PM), sporadic inclusion body myositis (sIBM) and dermatomyositis (DM). Chemokines play an essential role in sustained inflammation associated with IIM. We studied the distribution of the a-chemokine receptors CXCR1, 2, 3 and their ligands interferon-g (IFN-g)-inducible T cell a chemoattractant (I-TAC), IFN-g-inducible protein of 10 kDa (IP-10), monokine induced by IFN-g (MIG) and growth-related oncogene (GRO) in IIM using immunohistochemistry, immunofluorescence and Western blotting. Abundant expression of IP-10 was observed on macrophages and T cells surrounding and invading non-necrotic muscle fibers in PM and sIBM and in T cells in perimysial infiltrates of DM. IP-10 was also localized to blood vessel endothelial cells in all inflammatory and normal muscle tissues. The distribution of other a-chemokines was variable: Only low levels of MIG and I-TAC were detected; GRO was localized to the endomysial infiltrates of some PM and sIBM samples, but not in DM. Muscle tissues were invariably CXCR1 negative, while a subset of inflammatory cells in all IIM were CXCR2 positive. Strong CXCR3 expression was observed on the majority of T cells in each IIM. We describe the differential repertoire of a-chemokines in IIM, and offer additional proof of the predominance of Th1-driven reactions in the immunopathogenesis of all three diagnostic subgroups. We suggest the Th1-mediated immunity in general, and the CXCR3/IP-10 interaction in particular, as potential targets for novel therapeutic intervention in IIM.

The clinical features of inclusion body myositis (IBM) were of minor importance in the design of consensus diagnostic criteria, mainly because of controversial views on the specificity of signs and symptoms, although some authors reported "typical"signs. To re-assess the clinical spectrum of IBM, a single investigator using a standard protocol studied a cohort of 64 patients cross-sectionally. Symptom onset was before the age of 50 years in 20% of cases. Only a few patients (14 %) started with weakness other than that of quadriceps, finger flexor or pharyngeal muscles. The sequence of power loss was erratic, but onset of symptoms with quadriceps weakness predicted an earlier onset of dysphagia in older patients (>/= 56 years) compared with younger ones (< 56 years) (p = 0.02). Despite widespread weakness patients had favourable scores on three commonly used function scales and they kept their employment. Complete wheel-chair dependency was rare (3 %). A dominant characteristic was the anatomical distribution of afflicted muscles: ventral extremity muscle groups were more affected than dorsal muscle groups and girdle muscles were least affected, the latter preserving postural stability. Ankylosis, especially in extension of the fingers,was frequently present. Together with the sparing of intrinsic hand muscles it was helpful in the preservation of many skilful movements.IBM has a unique distribution of muscle weakness. Ankylotic contractures are common. We feel that their joint impact on daily functioning is characteristic for the disease.

Myostatin is a negative regulator of muscle mass and strength. Sporadic inclusion-body myositis (s-IBM) is the most common degenerative muscle disease of older persons and is characterized by pronounced muscle wasting. s-IBM is of unknown etiology and pathogenesis, and it lacks definitive treatment. We have now demonstrated in samples from 12 s-IBM biopsies that: (1) by light and electron microscopic immunocytochemistry, myostatin/myostatin precursor is accumulated within muscle fibers and co-localized with amyloid-b (Ab); (2) by immunoblots, both myostatin and myostatin precursor are increased; and (3) by immunoprecipitation, myostatin precursor complexes with Ab. Our study suggests that myostatin/myostatin precursor, either alone, or bound to Ab, may play a novel role in the pathogenesis of s-IBM.

Intravenous immunoglobulin (IVIg) is an effective tool for the treatment of diseases with immune pathogenesis. This article reviews the current knowledge of the benefits of treating with IVIg patients with myasthenia gravis (MG), Lambert Eaton myasthenic syndrome (LEMS), dermatomyositis (DM), polymyositis (PM) and inclusion body myositis (IBM). MYASTHENIA GRAVIS : Treatment of MG with IVIg was reported to be beneficial in a number of case series and two randomised controlled trials, in which efficacy was measured by clinical improvement using myasthenic muscle score and decrease in anti-acetylcholine receptor antibodies (AchRAb). According to the results, IVIg could be recommended for crisis and severe exacerbation. In many other clinical conditions, such as response to treatment of mild or moderate exacerbation, changes in steroid dosage and before thymectomy, IVIg has also been reported to be helpful, but no controlled trials to confirm its efficacy have been performed. LAMBERT-EATON MYASTHENIC SYNDROME : A placebo-controlled crossover study reported a significant clinical improvement in the amplitude of the resting CMAP following IVIg treatment. Further experience from case reports also indicates that IVIg is useful in patients with LEMS, both as a short- and long-term treatment, especially when immunosuppressive drugs are not fully effective. INFLAMMATORY MYOPATHIES/DERMATOMYOSITIS: : In a double-blind placebo-controlled crossover trial in patients with DM resistant to other treatments, IVIg was shown to produce a significant increase of muscle strength as well as a marked improvement in immunopathological parameters in repeated muscle biopsies (before and after IVIg). Thus, IVIg is an important therapy in patients with DM resistant to other conventional therapies. POLYMYOSITIS: : No randomised trials have been undertaken. One study showed clinical improvement and a reduction in the need of prednisone in patients with chronic refractory PM. INCLUSION BODY MYOSITIS: Three controlled trials showed some muscle strength improvement, although the changes did not reach statistical significance. However improvement in swallowing was repeatedly observed, suggesting that some patients with severe dysphagia may derive a modest benefit from IVIg therapy. CONCLUSION : Controlled trials indicate that in MG, LEMS, and DM, IVIg at a total dose of 2 g/kg is a highly useful therapy. Uncontrolled trials and case reports indicate benefit in many different clinical situations, but further clinical investigation is required.

Researchers find etanercept helpful in small IBM study
TMA Medical Advisory Board Member Richard J. Barohn, MD, and others studied nine IBM patients who were treated with etanercept (Enbrel) to assess whether the drug - sometimes used with good effect in other forms of myositis - could slow the progression of weakness in inclusion body myositis (IBM). They treated the group of IBM patients with etanercept, a tumor necrosis factor inhibitor, and monitored disease progression in the patients.

In a retrospective pilot study the patients, meeting accepted diagnostic criteria, received 25 mgs of etanercept two times over a time period of 11 to 23 months for an average duration of 17 months [this is likely a misprint as Enbrel is usually given as 25mg 2x week or 50mg 1x week during a course of treatment]. The strength of the elbow flexors and handgrip was assessed at the beginning of the trial and again at six and 12 months. The data from the patients in the etanercept group were compared to a control group of six IBM patients who had undergone similar testing but who had not received the drug. The etanercept was well tolerated by the group of IBM patients who received it.

Researchers noted that grip strength improved in IBM patients treated with etanercept. In untreated patients, grip strength worsened. This difference was significant at 12 months. This preliminary data suggest that etancercept may affect disease progression in IBM. The researchers concluded that longer, prospective, controlled studies are warranted.

From: The Myositis Association, Outlook, Spring 2005, page 7. Reprinted with permission. Also see: Enbrel and sIBM.

International Scientific Conference on Sporadic Inclusion-Body Myositis

TMA Medical Advisory Board members Valerie Askanas, MD, PhD, Professor of Neurology and Pathology at the University of Southern California Keck School of Medicine in Los Angeles, and Marinos C. Dalakas, MD, Chief, Neuromuscular Diseases Section at the National Institute of Neurological Disorders and Stroke, NIH, in Bethesda MD, organized the first international scientific conference on sporadic inclusion-body myositis January 26-28, 2005, in Los Angeles. W. King Engel, MD, Professor of Neurology and Pathology at the University of Southern California Keck School of Medicine in Los Angeles, assisted in leading and developing the program agenda.

TMA sponsored this very successful first international scientific Conference on sporadic inclusion body myositis. The full title of the Conference was Frontiers of Research Potentially Relevant to Treatment of Inclusion-Body Myositis. Sporadic IBM is so named because, although it may have genetic components, it is not an inherited illness like hereditary IBM.

The purpose of this highly focused Conference was for the prominent scientists - all of whom were specifically invited - to identify priorities for further research and treatment. Those invited were leaders in research fields related to the disease process of sIBM. Conference organizers invited the world's leading experts on s-IBM, and also experts in the fields they identified as related: cellular disturbances in Alzheimer's Disease, protein degradation, oxidative stress, and immunology. Among the presenters was 2004 Nobel Laureate in Chemistry, Dr. Aaron Ciechanover from Israel. One of the major goals, said Dr. Askanas, was to involve Conference participants who are world-class basic scientists but who have not yet worked on s-IBM. She reported that the Conference was successful in this regard, as the attendees expressed their interest in participating in s-IBM research and developing various collaborations.

Conference Summary
Dr. Askanas provided the following report. The proceedings will be published in Neurology, the journal of the American Academy of Neurologists.

Sporadic inclusion-body myositis is the most common progressive muscle disease in people older than 50. It causes progressively severe weakness of all four limbs but no impairment of mental function. No successful treatment is currently available. Neither the cause of s-IBM nor the exact disease process is known. Two theories predominate: an amyloid-b-related degenerative process, and an autoimmune dysregulation. An intriguing feature is the accumulation within sIBM muscle fibers of amyloid-b (Ab), phosphorylated tau and several other Alzheimer-characteristic proteins. There is also prominent evidence of misfolding of proteins. The pronounced T-cell inflammation is also striking, characterized by activated, antigen-driven, cytotoxic CD8+ T cells.

The Conference opened with a lecture by Caleb E. Finch, PhD, a world expert on aging from the University of Southern California in Los Angeles. The scientific program opened with a lecture by Dr. W. King Engel. Dr. Engel devoted his presentation to clinical features, pathologic diagnostic criteria and the clinical course of s-IBM. In order to demonstrate to the basic scientists the clinical issues and the degree of disability caused by s-IBM, Dr. Engel presented two volunteer patients as part of his lecture. Two intense days of lectures followed.

Dr. Ciechanover gave a very stimulating, one-hour, after-dinner lecture, presenting the work that led to identifying the important role of ubiquitin in the degradation of proteins, the research that led to his Nobel Prize.

During the meeting and during the breaks, there were lively and intense discussions among the participants. Presentations and discussions at the Conference identified the following areas as worthy of further pursuit in the treatment for s-IBM:
= identify better compounds to treat an inflammatory component;
= develop new approaches to combat intra-cellular amyloidosis;
= seek new compounds to prevent oligomerization of amyloid-b4;
= seek new compounds to increase the function of the 26S proteasome system selectively in muscle.

Publication and distribution of the supplement (to Neurology) is being funded by the Muscular Dystrophy Association. Additional financial supportfor the Conference was provided by Crescent Healthcare, Inc.

From: The Myositis Association, Outlook, Spring, 2005, page 3. Reprinted with permission.

May 2005
Neurobiol Aging. 2005 May;26(5):645-54.
Age- and region-dependent alterations in Abeta-degrading enzymes: implications for Abeta-induced disorders.
Caccamo A, Oddo S, Sugarman MC, Akbari Y, Laferla FM.
Department of Neurobiology and Behavior, University of California, Irvine, 1109 Gillespie Neuroscience Bldg., Irvine, CA 92697-4545, USA.
Accumulation of amyloid beta-protein (Abeta) is a fundamental feature of certain human brain disorders such as Alzheimer's disease (AD) and Down syndrome and also of the skeletal muscle disorder inclusion body myositis (IBM). Emerging evidence suggests that the steady-state levels of Abeta are determined by the balance between production and degradation. Although the proteolytic processes leading to Ab formation have been extensively studied, less is known about the proteases that degrade Ab, which include insulin-degrading enzyme (IDE) and neprilysin (NEP). Here we measured the steady-state levels of these proteases as a function of age and brain/muscle region in mice and humans. In the hippocampus, which is vulnerable to AD pathology, IDE and NEP steady-state levels diminish as function of age. By contrast, in the cerebellum, a brain region not marked by significant Abeta accumulation, NEP and IDE levels either increase or remain unaltered during aging. Moreover, the steady-state levels of IDE and NEP are significantly higher in the cerebellum compared to the cortex and hippocampus. We further show that IDE is more oxidized in the hippocampus compared to the cerebellum of AD patients. In muscle, we find differential levels of IDE and NEP in fast versus slow twitch muscle fibers that varies with aging. These findings suggest that age- and region-specific changes in the proteolytic clearance of Abeta represent a critical pathogenic mechanism that may account for the susceptibility of particular brain or muscle regions in AD and IBM.