Inclusion body myositis (IBM)

Clinical, histological, immunohistochemical and ultrastructural features of 5 cases of inclusion body myositis -4 sporadic (s-IBM) and one hereditary (h-IBM) form are described. These patients (3 men, 2 women) had chronic progressive weakness of varying severity in all 4 extremities with sparing of cranial muscles. Elevation of CPK was noted in 2 patients. Electromyography revealed features of myopathy in 4 and additional neurogenic changes in 2 subjects. Clinical diagnosis was often other than inclusion body myositis. Presence of characteristic eosinophilic inclusions within the vacuoles established the diagnosis. The inclusions were congophilic and showed positivity to ubiquitin, beta-amyloid and SMI-31 in the sporadic cases while congophila was absent in the hereditary form. Immunostaining to hyperphosphorylated-tau was negative in both s-IBM and h-IBM. Membraneous whorls were observed at ultrastructural level. None of the patients improved with steroids and trial with other immunosuppressants was unsuccessful.

Inclusion body myositis

Sporadic inclusion body myositis is a severely disabling muscle disease that mainly affects elderly individuals. The typical distribution of muscle weakness, poor response to immunosuppressive treatment, pathological accumulation of various proteins in vacuolated muscle fibres, inflammatory reaction and mitochondrial changes have all been subjects of recent research that has led to better understanding of the pathogenic events that leads to muscle degeneration and weakness.

Mapping of a candidate region for susceptibility to inclusion body myositis in the human major histocompatibility complex

Inclusion body myositis (IBM) is a form of idiopathic inflammatory myopathy of unknown aetiology. A strong association with HLA class II (HLA-DR3) suggested a role for genes in the human major histocompatibility complex (MHC) in the predisposition to this disease. In this study, we have taken advantage of the ancestral haplotype (AH) concept and historical recombinations to map for a possible susceptibility gene(s) in the MHC. We performed detailed typing of three MHC-related HSP70 genes and defined allelic combinations in the context of MHC AH. We also modified existing methods to give a simple and accurate method for typing two TNF microsatellites. Using the HSP70 and TNF markers and HLA-DR, -B, and C4 typing of our patients with IBM, we defined a potential site for the MHC-associated susceptibility gene(s) in the region between HLA-DR and C4.

Familial inclusion body myopathy with desmin storage

We report two adult familial cases of inclusion body myopathy (IBM) with desmin storage in skeletal muscle. Clinically, both patients presented late-onset, progressive, symmetrical, both proximal and distal muscle weakness. Muscle biopsy findings were identical in both cases and consisted of marked variability in fiber size, increased number of central nuclei and vacuolation involving 10% of fibers. Single or multiple vacuoles were located subsarcolemmally or in the center, and were rimmed by basophilic material. At the ultrastructural level, tubulofilamentous nuclear and cytoplasmic inclusions of 16-21 nm in diameter were frequently observed. In addition, large subsarcolemmal and central deposits composed of electron-dense granular material were present in many fibers. Immunocytochemistry revealed staining for desmin, vimentin and ubiquitin within both inclusions and vacuolated fibers. Possible structural and functional associations between these two types of muscle changes remain unclear. They may either represent two coexistent disease processes or merely reflect an abnormal form of muscle fiber degradation, with unidentifiable specificity.

Fine-structure mapping of the hereditary inclusion body myopathy locus

The gene responsible for a recessive form of hereditary inclusion body myopathy (HIBM) has previously been mapped to a 10-cM interval on chromosome 9p1-q1. We report the results of further mapping studies using two-point linkage analyses and linkage disequilibrium analyses with 20 HIBM families. We demonstrate that the HIBM gene (HGMW-approved symbol IBM2) lies between loci D9S1791 and D9S50, which are about 1 Mb apart. Genetic analyses in 56 affected individuals of Persian, Afghani, and Iraqi Jewish descent demonstrated a common haplotype at these loci, indicating that a founding mutation accounts for disease in these related ethnic groups. beta-Tropomyosin, an abundant skeletal muscle protein that maps within 1 cM of D9S1791, was excluded as the disease gene because an intragenic polymorphism did not exhibit linkage disequilibrium in HIBM probands. We conclude that the disease gene resides in a 1-Mb interval on chromosome 9 and speculate that a novel muscle protein encoded there is mutated in HIBM.

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.

Normal in vivo skeletal muscle oxidative metabolism in sporadic inclusion body myositis assessed by 31P-magnetic resonance spectroscopy

Sporadic inclusion body myositis (s-IBM) is a chronic inflammatory myopathy of unknown pathogenesis. The common findings of ragged red fibres, cytochrome c oxidase-negative fibres and multiple mitochondrial DNA deletions in the muscle of patients with s-IBM have suggested that a deficit of energy metabolism may be of pathogenic relevance. To test this hypothesis we used 31P magnetic resonance spectroscopy to assess in vivo skeletal muscle mitochondrial function in the calf muscles of 12 patients with definite s-IBM. Eleven patients showed multiple mitochondrial DNA deletions in skeletal muscle and 67% showed ragged red fibres and/or cytochrome c oxidase-negative fibres. T1-weighted MR images showed increased signal intensity in the calf muscle of all patients except one. The involvement of calf muscle was confirmed by 31P magnetic resonance spectroscopy of resting muscle, which disclosed abnormalities in metabolite ratios in all patients. However, muscle oxidative metabolism assessed during recovery from exercise was normal in patients with s-IBM, as maximum rates of mitochondrial ATP production and post-exercise ADP recovery rates were within the normal range in all cases. We conclude that muscle mitochondrial abnormalities are a secondary process and unlikely to play a significant role in the pathogenesis of s-IBM.

Sporadic inclusion-body myositis and hereditary inclusion-body myopathies: current concepts of diagnosis and pathogenesis

We discuss the pathologic diagnostic criteria and review the major new advances related to seeking the pathogenic mechanism of sporadic inclusion-body myositis (s-IBM) and hereditary inclusion-body myopathy (h-IBM). A classification of the various h-IBM syndromes is also presented. The several forms of the h-IBMs have different genetic transmissions and probably different genetic defects. In neither s-IBM nor the h-IBMs are the sequential steps of the pathogenic cascade understood. Because s-IBM and the h-IBMs have a number of characteristic pathologic features in common, we postulate that their different causes trigger the same upstream aberration leading to a similar downstream cascade of pathologic events, which are ultimately responsible for the characteristic muscle-fiber degeneration. Muscle-biopsy and experimental evidence is given supporting our hypothesis that overexpression of beta-amyloid precursor protein within abnormal muscle fibers is an early upstream event causing the pathogenic cascade. We also present evidence supporting our concept that muscle aging and oxidative stress are important factors contributing to the s-IBM-specific muscle fiber destruction. Additionally, the intriguing parallels between the pathologic phenotype of IBM muscle fibers and Alzheimer's disease brain are summarized.

Genetics of inclusion body myopathies

We review the current knowledge about the genetic susceptibility to develop inflammatory inclusion body myositis, especially in relation to the increased presence of the HLA DR3 allele in patients with familial and sporadic forms, indicating an autoimmune predisposition. The main focus of the review is the clinical and genetic presentations of the various hereditary inclusion body myopathies. Criteria for diagnosis and classification of these myopathies are presented. The spectrum of the recessive forms of hereditary inclusion body myopathies currently linked to chromosome 9p1-q1 is described, with emphasis on the up-to-date status of the gene search for these forms.

Hereditary inclusion body myopathies

Hereditary inclusion body myopathies comprise autosomal recessive and autosomal dominant muscle disorders that have a variable clinical phenotype but share similar morphological features. These include rimmed vacuoles within muscle fibres and collections of intrasarcoplasmic and intranuclear tubulofilamentous inclusions, 16-18 nm in external diameter. The resemblances and the differences between the sporadic and the hereditary inclusion body myopathies are discussed. Recent advances in the identification of various proteins involved in these diseases are mentioned because they have provided better insight into their underlying pathophysiological mechanisms. Linkage studies have allowed the localization of the genetic defect of some hereditary inclusion body myopathies and related disorders, contributing to their individualization.

Autosomal dominant myopathy with congenital joint contractures, ophthalmoplegia, and rimmed vacuoles

We describe a new myopathy in a large family with 19 affected cases. Inheritance was autosomal dominant. Characteristic clinical features were congenital joint contractures, which normalized during early childhood, external ophthalmoplegia, and proximal muscle weakness. Muscle atrophy was most prominent in the pectoralis and quadriceps muscles. The clinical course was nonprogressive in childhood, but most adult cases experienced deterioration of muscle function, starting from 30 to 50 years of age. The major histopathological change of skeletal muscle in childhood was focal disorganization of myofilaments. In adults with progressive muscle weakness, the muscle biopsies showed dystrophic changes and rimmed vacuoles with cytoplasmic and intranuclear inclusions of 15- to 21-nm filaments. These findings suggests that this new disease should be classified as a variant of hereditary inclusion body myopathy.

Inclusion body myositis in twins

Sporadic inclusion body myositis (s-IBM) is characterized by late onset of slowly progressive weakness that involves the quadriceps and volar forearm muscles early in the course of the disease. There are hereditary forms of inclusion body myopathy (h-IBM) that histologically resemble s-IBM. The lack of inflammation on biopsy and the different ages at onset and patterns of muscle weakness distinguish s-IBM from h-IBM. We report twin brothers with the typical clinical and histologic features of s-IBM. The occurrence of s-IBM in these twins suggests the possibility of a genetic susceptibility to developing s-IBM.

Nitric oxide-induced oxidative stress in autosomal recessive and dominant inclusion-body myopathies

Autosomal-recessive and autosomal-dominant hereditary inclusion-body myopathies are severe, progressive muscle diseases, characterized pathologically by vacuolated muscle fibres containing paired helical filaments. We immunostained muscle biopsy specimens from quadriceps-sparing autosomal-recessive and autosomal-dominant inclusion-body myopathy subjects, disease-control subjects and normal patients, utilizing isoform-specific antibodies against the neuronal and inducible forms of nitric oxide synthase, and antibodies against nitrotyrosine. Approximately 75% of the vacuolated muscle fibres in all recessive and dominant inclusion-body myopathy patients contained inclusions strongly immunoreactive with antibodies against neuronal and inducible nitric oxide synthase which, by immunoelectron microscopy, were colocalized to clusters of tubulofilaments (previously shown, by us, to be paired helical filaments). Strong nitrotyrosine immunoreactivity was in the form of multiple dots and large granular patches, which ultrastructurally did not immunolocalize to tubulofilaments. Excess intracellular nitric oxide can combine with superoxide to produce highly toxic peroxynitrite, which can nitrate tyrosines of proteins. The presence of nitrotyrosine is indicative of nitric oxide-induced oxidative stress. Our data suggest that oxidative stress plays a role in the pathogenic cascade of hereditary inclusion-body myopathies.

HLA allele distribution distinguishes sporadic inclusion body myositis from hereditary inclusion body myopathies

We studied the HLA class II associations in patients with sporadic inclusion body myositis (s-IBM) and hereditary inclusion body myopathies (h-IBM) and attempted to distinguish these myopathies on the basis of HLA allele assignments. Forty-five patients, 30 with s-IBM and 15 with h-IBM, underwent HLA class II allele-specific typing using polymerase chain reaction sequence-specific primers for 71 alleles contained in the DRbeta1, DRbeta3-5, and DQbeta1 loci. In s-IBM, we found a high (up to 77%) frequency of DRbeta1*0301, DRbeta3*0101 (or DRbeta3*0202) and DQbeta1*0201 alleles. No significant association with alleles in the DR and DQ haplotypes was found among the 15 h-IBM patients. The strong association of prominent alleles with s-IBM, but not h-IBM, suggests that s-IBM is a distinct disorder with an immunogenetic background that differs from h-IBM.

Clinical, serologic, and immunogenetic features of familial idiopathic inflammatory myopathy

OBJECTIVE

To describe the clinical, serologic, and immunogenetic features of familial idiopathic inflammatory myopathy (IIM) and to compare these with the features of sporadic IIM.

METHODS

Clinical signs and symptoms, autoantibodies, HLA-DRB1 and DQA1 alleles, and GM/KM phenotypes were compared among 36 affected and 28 unaffected members of 16 unrelated families in which 2 or more blood relatives developed an IIM. In addition, findings in patients with familial IIM were compared with those in 181 patients with sporadic IIM. The families included 3 pairs of monozygotic twins with juvenile dermatomyositis, 11 families with other siblings or relatives with polymyositis or dermatomyositis, and 2 families with inclusion body myositis.

RESULTS

The clinical features of familial IIM were similar to those of sporadic IIM, although the frequency of myositis-specific autoantibodies was lower in familial than in sporadic IIM. DRB1*0301 was a common genetic risk factor for familial and sporadic IIM, but contributed less to the genetic risk of familial IIM (etiologic fraction 0.35 versus 0.51 in sporadic IIM). Homozygosity at the HLA-DQA1 locus was found to be a genetic risk factor unique to familial IIM (57% versus 24% of controls; odds ratio 4.2, corrected P = 0.002).

CONCLUSION

These findings emphasize that 1) familial muscle weakness is not always due to inherited metabolic defects or dystrophies, but may be the result of the development of IIM in several members of the same family, and 2) multiple genetic factors are likely important in the etiology and disease expression of familial IIM, as is also the case for sporadic myositis, but DQA1 homozygosity is a distinct risk factor for familial IIM.

Oligoclonal expansion of muscle infiltrating T cells in inclusion body myositis

Inclusion body myositis (IBM) is the most common muscle disease affecting individuals over 50 years of age. An important feature of IBM is invasion of muscle fibers by T cells. The muscle infiltrating T cells show a restricted usage of variable (V) alpha/beta gene families. In this study we have investigated the clonality of T cells using two of the predominant V beta families i.e. V beta 3 and V beta 8 in three patients with IBM. The study was performed by reverse transcription and polymerase chain reaction (RT-PCR) analysis, followed by cloning and sequencing of the T cell receptor complementarity determining region 3. We found oligoclonal expansion of V beta 3 bearing muscle infiltrating T cells in two patients and of V beta 8 in one patient, supporting the concept that antigen stimulated T cells are important in the pathogenesis of IBM. Results of HLA typing indicated a genetic predisposition for the disease by the presence of DR3, DR52 and DQB1*0201/0202 in all three patients.

Inclusion body myositis and myopathies

Sporadic inclusion body myositis is a frequent, acquired, adult-onset vacuolar myopathy affecting proximal and distal muscles with a distinct, easily identifiable clinical pattern. Although its primary cause is still unknown, autoimmune, viral, and degenerative processes, alone or in combination, are being considered. A uniform and sustained therapeutic response using the currently available immunomodulatory agents has not yet been achieved. Hereditary, inherited noninflammatory rimmed vacuolar myopathies with similar histologic features, collectively called hereditary inclusion body myopathies, are being redefined with the use of molecular genetics. The implications of the recent advances in clinical and basic sciences are discussed in the present review.

Mitochondrial abnormalities and peripheral neuropathy in inflammatory myopathy, especially inclusion body myositis

Computer retrieval in a database, comprising 7,225 muscle cases, revealed that mitochondrial myopathies do not occur more frequently in inflammatory myopathies (3.74%) than in the whole series (3.69%). A more detailed study of inclusion body myositis (IBM), however, showed that severe mitochondrial alterations were apparent in about twice as many IBM cases as expected. This confirms recent studies of others although a causal relationship has thus far not been established. Identification of mitochondrial deletions by Southern blotting corresponded to the presence of severe structural abnormalities of mitochondria. Peripheral neuropathy of variable severity was noted in all cases of IBM and mitochondrial myopathy. By contrast, the association of severe mitochondrial abnormalities with polymyositis, systemic scleroderma, and vasculitis observed in some cases of the present series may be incidental or age dependent.

An inflammatory, familial, inclusion body myositis with autoimmune features and a phenotype identical to sporadic inclusion body myositis. Studies in three families

We describe the occurrence of an inflammatory inclusion body myositis in siblings of a single generation in three separate families. The disease in this total of seven patients was characterized by selective and early involvement of forearm and finger flexors, confirmed by MRI, and weakness of the quadriceps, triceps and foot extensors. Muscle biopsies in at least two members from each family showed endomysial inflammation, red-rimmed vacuoles, intracellular amyloid deposition and 15-18-nm tubulo-filaments within the vacuolated muscle fibres. Immunocytochemistry on serial muscle biopsy sections demonstrated an abundance of CD8+ cells invading non-necrotic, MHC-1-expressing muscle fibres. Immunogenetic studies showed the presence of the DR3 allele (DRB1*0301/0302) in all seven patients. The combination of the clinical, histological, immunopathological and immunogenetic features indicate that these patients have a disease identical to sporadic inclusion body myositis (s-IBM). We conclude that the classic, inflammatory, s-IBM can also occur in families (familial inclusion body myositis), in a pattern analogous to the familial occurrence of other autoimmune neurological diseases such as myasthenia gravis and multiple sclerosis. These observations strengthen the view that s-IBM behaves like other autoimmune diseases and has disease susceptibility linked to the DR3 allele.

Various types of hereditary inclusion body myopathies map to chromosome 9p1-q1

Hereditary inclusion body myopathies are a clinically heterogeneous group of disorders characterized by adult-onset, slowly progressive muscle weakness and typical histopathology: rimmed vacuoles and filamentous inclusions. The disorders are usually inherited as an autosomal recessive trait. The gene responsible for the disease found in Iranian Jews, who present with quadriceps-sparing myopathy, maps to chromosome 9p1-q1. We address the question of whether hereditary inclusion myopathies are genetically as well as clinically heterogeneous disorders. We mapped the disease gene segregating in two families of Afghani-Jewish and one family of Iraqi-Jewish descent to the chromosome 9 locus. Similarly, the disease gene segregating in a non-Jewish family from India mapped to the same locus. By contrast, the disease gene segregating in a French-Canadian family in which affected individuals had central nervous system involvement as well as hereditary inclusion body myopathy, did not map to this locus. We conclude that many but not all forms of autosomal recessive hereditary inclusion body myopathy are caused by a gene defect that maps to chromosome 9p1-q1.

Apolipoprotein E and apolipoprotein E messenger RNA in muscle of inclusion body myositis and myopathies

Sporadic inclusion body myositis and the hereditary inclusion body myopathies are severe, progressive muscle diseases, characterized pathologically by vacuolated muscle fibers containing paired helical filaments. We immunostained muscle biopsy specimens from sporadic inclusion body myositis, hereditary inclusion body myopathy, disease control, and normal patients with several antibodies against apolipoprotein E (ApoE). Approximately 80 to 90% of the vacuolated muscle fibers of sporadic inclusion body myositis contained well-defined, strongly immunoreactive ApoE inclusions. In hereditary inclusion body myopathy, only rare vacuolated fibers had immunoreactive inclusions, whereas most had diffuse cytoplasmic ApoE immunoreactivity. Ultrastructurally, ApoE immunoreactivity in sporadic myositis was localized mainly to the paired helical filaments. By contrast, in the hereditary form, ApoE immunoreactivity occurred on material in close proximity to the paired helical filaments, but never was on the paired helical filaments. In both muscle diseases, ApoE was also on the 6- to 10-nm filaments and amorphous material. In the sporadic form, ApoE-immunoreactive deposits colocalized with Congo red-positive deposits; however, in muscle fibers from patients with hereditary disease there was no congophilia. ApoE messenger RNA was not detectable in muscle fibers from patients with hereditary or sporadic disease but was expressed abundantly in muscle macrophages. In all control and inclusion body myositis or myopathy biopsy specimens, ApoE immunoreactivity was strong at the postsynaptic domain of neuromuscular junctions; nonjunctional regions of normal fibers were negative for ApoE. ApoE immunoreactivity occurred diffusely in regenerating muscle fibers, a subset of which had detectable ApoE messenger RNA.

The spectrum of familial inclusion body myopathies in 13 families and a description of a quadriceps-sparing phenotype in non-Iranian Jews

The frequency, patterns of inheritance and clinical phenotypes of inherited myopathies with histologic features of rimmed vacuoles, tubulofilamentous inclusions and absence of inflammation (familial and hereditary inclusion body myopathy [f-IBM]) are poorly defined. Quadriceps sparing is a characteristic of f-IBM seen in the Iranian Jewish population. Among 101 patients with the feature of a red-rimmed vacuolar myopathy, characterized as inclusion body myopathy, seen during the last 4 years, we identified 13 families with f-IBM (12.8% frequency when one member per family was considered). Five families had an autosomal dominant and eight had an autosomal recessive form of inheritance. Among the latter group, five patients with early-onset disease (two Caucasian Americans, an Asian Indian, and two unrelated Iranian Jews) had the distinct feature of quadriceps sparing, which was confirmed by MRI of the thighs. Their disease began with weakness and strophy of the foot extensors, forearm flexors, and first dorsal interossei muscles and progressed to the forearm flexors, girdle, and axial muscles, but spared the quadriceps. Serum CK was normal. Muscle biopsies showed rimmed vacuoles, small fibers in groups, amyloid deposition (in one patient), tubulofilaments, and no inflammation. Immunocytochemistry did not reveal abnormalities of various membrane or cytoskeletal proteins. Major histocompatibility complex (MHC) class I antigen was expressed only in a few degenerating fibers invaded by macrophages. T-cell infiltrates were not present. We conclude that in a large referral population, dominant and recessive hereditary and familial forms of IBM are not rare. Quadriceps-sparing myopathy appears to be a clinically distinct, autosomal recessive, nonimmune, distal vacuolar myopathy that is not limited to Iranian-Jewish ethnic groups.

[Inclusion body myositis]

Inclusion body myositis has been recently recognized as a clinical entity although its exact definition remains uncertain. Initially considered to be an inflammatory dermatomyositis, inclusion body myositis can actually take on three specific forms: disseminated muscle atrophy and weakness, pseudopolymyositis, or pseudo-degenerative disease. Inclusion body myositis is different from non-inflammatory neuromuscular diseases with vacuoles. Abnormal deposits are seen within the muscle fiber may contain amyloid substance, beta-amyloid precursor, ubiquitin, antichymotrypsin, protein tau, apolipoprotein E and even prions. The signification of these deposits is unknown. Deletions in mitochondrial DNA have been demonstrated but do not appear to play a causal role. More and more hereditary forms are being recognized and certain may be related to an abnormality in chromosome 9.

Multiple mitochondrial DNA deletions in sporadic inclusion body myositis: a study of 56 patients

Inclusion body myositis, a chronic inflammatory disorder, is the most common cause of myopathy in adults over the age of 50. Diagnosis is based on clinical features and distinctive morphological findings by both light and electron microscopy. The causes of inclusion body myositis are still unknown. Ultrastructural mitochondrial changes and ragged-red fibers are common in patients with sporadic inclusion body myositis, and multiple [correction of mutiple] mitochondrial DNA (mtDNA) deletions have been reported in 3 such patients, suggesting that mtDNA mutations may have a pathogenetic role. We studied 56 patients with sporadic inclusion body myositis, using a combination of clinical, morphological, biochemical, and molecular genetic analyses to determine the frequency and the distribution of mtDNA deletions. Using the polymerase chain reaction, we found multiple mtDNA deletions in 73% of patients, compared to 40% of normal age-matched control subjects and 47% of disease control subjects. The presence of deletions correlated with morphological evidence of ragged-red, cytochrome c oxidase-negative fibers, and with defects of complexes I and IV of the electron transport chain. Although aging may account for a proportion of mtDNA deletions in patients with sporadic inclusion body myositis and control subjects, mtDNA alterations may be accelerated in sporadic inclusion body myositis.

Inclusion body myositis

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Apolipoprotein E epsilon 4 in inclusion body myositis

The genetic predisposition to inclusion body myositis (IBM) is probably multifactorial. The deposition of the beta-amyloid protein is a characteristic histological feature of both IBM and Alzheimer's disease (AD). The epsilon 4 allele of apolipoprotein E (APO E) has been strongly associated with familial and late-onset AD. We therefore compared the APO E allele frequencies in a group of 14 patients with IBM with those in a group of patients with other inflammatory muscle diseases and in the general population. The frequency of the epsilon 4 allele in IBM was increased (0.29) compared with that in patients with other inflammatory muscle diseases (0.15) and the general population (0.13) (p < 0.05). These data suggest that APO E genotype may be one of the factors involved in determining the predisposition to the development of IBM.

New advances in the understanding of sporadic inclusion-body myositis and hereditary inclusion-body myopathies

This review emphasizes new advances in seeking the pathogenic mechanisms of sporadic inclusion-body myositis and hereditary inclusion-body myopathy syndromes. Clinical and pathologic similarities and differences between sporadic and hereditary forms are described. Hypotheses are presented regarding the possible causes and consequences of abnormally accumulated intramyofiber beta-amyloid precursor protein (beta APP) (including beta-amyloid protein and C- and N-terminal epitopes), hyperphosphorylated tau, alpha 1-antichymotrypsin, apolipoprotein E, prion protein, ubiquitin, nicotinic acetylcholine receptor and its 43-kD associated protein, fibroblast growth factor, and transforming growth factor-beta. Also increased are beta APP mRNA and prion protein mRNA. Striking similarities between the pathology of muscle specimens from sporadic inclusion-body myositis and samples from the brains of patients with Alzheimer's disease in regard to Congo red positivity and accumulations of several proteins are discussed. Because most of the proteins that pathologically accumulate throughout the abnormal muscle fibers also accumulate focally at normal human neuromuscular junctions, the possible "junctionalization" of nonjunctional nuclei as a pathogenic mechanism in the muscle fiber is discussed.