Familial inclusion body myositis among Kurdish-Iranian Jews

Hereditary inclusion body myopathy: A myopathy with unique topography of weakness, yet frequently misdiagnosed: Case series and review of literature

Background:

Hereditary inclusion body myopathy (HIBM) continues to be underrecognized clinically despite a characteristic topography of weakness with total sparing of quadriceps muscles and patient being wheelchair bound. We report seven patients of HIBM from four families in North India.

Methods and Results:

Seven patients from four different families were diagnosed to have HIBM. There was no consanguinity in any of the families. While one patient had two affected siblings, another had one affected siblings and the family history was noncontributory in two patients. Two of the siblings were available for examination and confirmed clinically to be suffering from HIBM. Among the seven patients, only one was still ambulatory at the time of diagnosis.

Discussion:

This is the first case report of occurrence of HIBM in North Indian population. Despite its unique clinical presentation, HIBM is frequently misdiagnosed resulting in unnecessary diagnostic and therapeutic interventions. A high index of suspicion of this rare myopathy along with proper clinical examination may go a long way in accurate prognostication and management of these patients.

Novel GNE mutations in autosomal recessive hereditary inclusion body myopathy patients

Hereditary Inclusion Body Myopathy (HIBM, IBM2, MIM:600737) is an autosomal recessive adult onset progressive muscle wasting disorder. It is associated with the degeneration of distal and proximal muscles, while often sparing the quadriceps. The bifunctional enzyme UDP-GlcNAc 2-epimerase/ManNAc kinase (GNE/MNK), encoded by the GNE gene, catalyzes the first two committed, rate-limiting steps in the biosynthesis of N-acetylneunaminic acid (sialic acid). Affected individuals have been identified with mutations in the GNE gene. In the present study, the GNE coding region of 136 symptomatic patients were sequenced. A total of 41 patients were found to have GNE mutations. Eight novel mutations were discovered among seven patients. Of the eight novel mutations, seven were missense (p.I150V, p.Y186C, p.M265T, p.V315T, p.N317D, p.G669R, and p.S699L) and one was nonsense (p.W495X), all of which span the epimerase, kinase, and allosteric domains of GNE. In one patient, one novel mutation was found in the allosteric region and kinase domain of the GNE gene. Mutations in the allosteric region lead to a different disease, sialuria; however, this particular mutation has not been described in patients with sialuria. The pathological significance of this variation with GNE function remains unknown and further studies are needed to identify its connection with HIBM. These findings further expand the clinical and genetic spectrum of HIBM.

A case of hereditary inclusion body myopathy: 1 patient, 2 novel mutations

Hereditary inclusion body myopathy is an autosomal recessive disorder that presents in early adulthood with slowly progressive weakness sparing the quadriceps. Muscle histopathology reveals rimmed vacuoles without inflammation. The disorder is caused by a mutation in the gene for UDP-N-acetylglucosamine 2-epimerase-N-acetylmannosamine kinase (GNE), a bifunctional enzyme involved in protein glycosylation. Over 40 mutations have been described to date. We present a case of a young woman with progressive lower extremity weakness. Clinical presentation, laboratory evaluation, electrodiagnostic testing, muscle pathology, and genetic sequencing are described. The patient was found to have heterozygous mutations in the GNE gene, confirming the diagnosis of hereditary inclusion body myopathy. The mutations she carried have not been described previously. We briefly review the clinical, histopathologic, and molecular genetic findings of this disorder.

Hereditary Inclusion Body Myopathy (HIBM2)

Hereditary inclusion body myopathy type 2 (HIBM2) is a myopathy characterized by progressive muscle weakness with early adult onset. The disease is the result of a recessive mutation in the Glucosamine (UDP-N-acetyl)-2-epimerase/N-acetylmannosamine kinase gene (GNE), which results in reduced enzyme function and sialic acid levels. A majority of individuals with HIBM2 are from Iranian-Jewish or Japanese decent, but isolated cases have been identified world wide. This article reviews the diagnostic criteria for HIBM2. Current research with a highlight on the biology of the disease and the role of GNE in the sialic acid pathway are assessed. Finally, therapeutic investigations and animal models are discussed with a focus on future studies to better understand the pathology of Hereditary Inclusion Body Myopathy and move therapeutic agents towards clinical trials.

Hereditary inclusion body myopathy: a decade of progress

Hereditary Inclusion Body Myopathy (HIBM) is an autosomal recessive, quadriceps sparing type commonly referred to as HIBM but also termed h-IBM or Inclusion Body Myopathy 2 (IBM2). The clinical manifestations begin with muscle weakness progressing over the next 10-20 years uniquely sparing the quadriceps until the most advanced stage of the disease. Histopathology of an HIBM muscle biopsy shows rimmed vacuoles on Gomori's trichrome stain, small fibers in groups and tubulofilaments without evidence of inflammation. In affected individuals distinct mutations have been identified in the GNE gene, which encodes the bifunctional enzyme uridine diphospho-N-acetylglucosamine (UDP-GlcNAc) 2-epimerase/N-acetyl-mannosamine (ManNAc) kinase (GNE/MNK). GNE/MNK catalyzes the first two committed steps in the biosynthesis of acetylneuraminic acid (Neu5Ac), an abundant and functionally important sugar. The generation of HIBM animal models has led to novel insights into both the disease and the role of GNE/MNK in pathophysiology. Recent advances in therapeutic approaches for HIBM, including administration of N-acetyl-mannosamine (ManNAc), a precursor of Neu5Ac will be discussed.

Genetic and environmental risk factors for idiopathic inflammatory myopathies

Although the studies discussed are beginning to reveal a number of genetic and possible environmental risk factors for myositis, further investigations are needed to fully understand and classify these syndromes. The difficulties in this process include small numbers of subjects with varying disease phenotypes available for study, polygenic risk factors for which it remains unclear which are primary and which are secondary or linked genes, and the lack of validated environmental exposure assessment tools. New technologies and international collaborative approaches, however, may overcome some of these difficulties and allow us to identify genetic and environmental risk factors, as well as the critical gene-environment interactions in the IIM and its subgroups. Nonetheless, our understanding of these diseases is still in the early stages. Although we have learned a great deal about these disorders through detailed investigations over the last several decades, we have even further to go to understand the environmental triggers and genetic susceptibilities for the myositis syndromes.

Sporadic inclusion body myositis and hereditary inclusion body myopathy

Sporadic inclusion body myositis (s-IBM) is a common but under-recognized myopathy in individuals over 50 years of age. An awareness of the clinical phenotype and of the electrodiagnostic and histopathologic features should lead to improved recognition, and should minimize confusion with polymyositis, motor neuron disease, and other neuromuscular disorders. Treatment efficacy has been difficult to judge because of the insidious progression of the disease over many years, but immunomodulating therapy is generally less effective than in polymyositis and dermatomyositis, and may not be effective at all in many patients. The hereditary inclusion body myopathies (h-IBM) are a heterogeneous group of recessively and dominantly inherited vacuolar myopathies that share some histologic features with s-IBM. Oxidative stress may play a role in the pathogenesis of both s-IBM and h-IBM.

Hereditary neuromuscular diseases

This article presents the actual classification of neuromuscular diseases based on present expansion of our knowledge and understanding due to genetic developments. It summarizes the genetic and clinical presentations of each disorder together with CT findings, which we studied in a large group of patients with neuromuscular diseases. The muscular dystrophies as the largest and most common group of hereditary muscle diseases will be highlighted by giving detailed information about the role of CT and MRI in the differential diagnosis. The radiological features of neuromuscular diseases are atrophy, hypertrophy, pseudohypertrophy and fatty infiltration of muscles on a selective basis. Although the patterns and distribution of involvement are characteristic in some of the diseases, the definition of the type of disease based on CT scan only is not always possible.

Clinical delineation and localization to chromosome 9p13.3-p12 of a unique dominant disorder in four families: hereditary inclusion body myopathy, Paget disease of bone, and frontotemporal dementia

Autosomal dominant myopathy, Paget disease of bone, and dementia constitute a unique disorder (MIM 605382). Here we describe the clinical, biochemical, radiological, and pathological characteristics of 49 affected (23 male, 26 female) individuals from four unrelated United States families. Among these affected individuals 90% have myopathy, 43% have Paget disease of bone, and 37% have premature frontotemporal dementia. EMG shows myopathic changes and muscle biopsy reveals nonspecific myopathic changes or blue-rimmed vacuoles. After candidate loci were excluded, a genome-wide screen in the large Illinois family showed linkage to chromosome 9 (maximum LOD score 3.64 with marker D9S301). Linkage analysis with a high density of chromosome 9 markers generated a maximum two-point LOD score of 9.29 for D9S1791, with a maximum multipoint LOD score of 12.24 between D9S304 and D9S1788. Subsequent evaluation of three additional families demonstrating similar clinical characteristics confirmed this locus, refined the critical region, and further delineated clinical features of this unique disorder. Hence, autosomal dominant inclusion body myopathy (HIBM), Paget disease of bone (PDB), and frontotemporal dementia (FTD) localizes to a 1.08-6.46 cM critical interval on 9p13.3-12 in the region of autosomal recessive IBM2.

X-linked myopathy with excessive autophagy: a clinicopathological study of five new families

In 1988, Kalimo et al. (Ann Neurol 23 (1988) 258)described a new type of X-linked myopathy in a Finnish family. The clinical course was characterized by slow progression of muscle weakness without loss of ambulation in childhood and no evidence of cardiac, respiratory, or central nervous system involvement. Muscle fibers were not necrotic and showed excessive autophagic activity and exocytosis of the phagocytosed material. These authors proposed the name X-linked myopathy with excessive autophagy. Subsequently, only one French family has been reported with similar clinical and histopathological data. We report here five new families with a total of eight affected boys with the same clinical and histopathological features as reported in the original families. Histopathological findings of an asymptomatic mother are also reported. Vacuolar changes in muscle fibers result both from invaginations of the sarcolemma along with a variable component of basal lamina and from an autophagic process. The complement C5b-9 membrane attack complex associated with MHC class 1 antigen and calcium deposits is involved in muscle fiber damage. Among the X-linked myopathies, the identification of this new type is of great interest because of its favorable prognosis and unique morphological findings.

Update on the genetics of the idiopathic inflammatory myopathies

A number of lines of investigation suggest that, as is likely the case for other autoimmune diseases, the idiopathic inflammatory myopathies (IIM) develop as a result of specific environmental exposures in genetically susceptible individuals. Current data imply that multiple genes are involved in the etiology of these complex disorders. Targeted gene studies and whole genome approaches have begun to identify several genetic risk factors for autoimmune diseases, but the rarity and heterogeneity of the IIM have limited our knowledge of their associated genes. Current findings suggest that human leukocyte antigen (HLA) genes on chromosome 6, particularly HLA DRB1*0301 and the linked allele DQA1*0501, have the strongest associations with all clinical forms of IIM in white patients. Different HLA alleles, however, may confer risk or protection for myositis in distinct ethnic, serologic, and environmental exposure groups. Non-HLA genetic risk factors, which have been documented for other autoimmune diseases, are now being identified for the IIM. These include polymorphic genes encoding immunoglobulin heavy chains (defined by serologic markers known as Gm allotypes), cytokines and their receptors, and certain proteins that accumulate in the myocyte vacuoles of inclusion body myositis patients. Selected allelic polymorphisms of interleukin-1 receptor antagonist variable number tandem repeats and genes for tumor necrosis factor alpha and interleukin-1 alpha also have recently been associated with IIM. The pathogenic bases for the differences among the many clinically, pathologically and immunologically defined syndromes known as the IIM will be elucidated through a better understanding of the multiple genes that define risks for their development, as well as through investigations of gene-gene and gene-environment interactions.

Familial autoimmunity and the idiopathic inflammatory myopathies

Many lines of evidence suggest that autoimmune diseases result from chronic immune activation following environmental exposures in genetically susceptible individuals. A genetic basis for autoimmunity is supported by twin and family studies, candidate gene investigations, animal models, and whole genome microsatellite scans. These findings predict, and clinical observations support, familial clustering of a number of individual autoimmune diseases, notably lupus, multiple sclerosis, type-1 diabetes mellitus, rheumatoid arthritis, and recently the idiopathic inflammatory myopathies. Yet, not only is the same autoimmune disease increased in prevalence in pedigrees of persons affected with a given disorder, but other autoimmune diseases are as well. We review these data and propose a hypothesis consistent with these findings. This model posits that a rheumatic disease, as currently classified, is actually composed of a number of elemental disorders. Each of these is defined by the minimal necessary and sufficient environmental exposures and genes that result in a pathology leading to a given sign-symptom complex.

Autosomal dominant late adult onset distal leg myopathy

A distal myopathy characterised by an autosomal dominant inheritance, with clinical onset around the age of 60, early involvement of posterior leg and thigh muscles, and normal or slightly-elevated creatine kinase levels was identified in three members of a French kindred. Tibialis anterior muscles were involved only in the most severely-affected sibling. Histological features included large multiple nonrimmed vacuolation and focal intrasarcoplasmic masses which immunoreacted with the anti-desmin antibody. Cytoplasmic and intranuclear tubulofilamentous inclusions were observed by electron microscopy. The condition of this familial syndrome is discussed in relation to previously-identified autosomal dominant distal myopathies and inclusion body myopathies.

Overview of distal myopathies: from the clinical to the molecular

Five distinct predominantly distal myopathies have been identified with discrete clinical and genetic patterns as follows: (1) Welander myopathy (late adult onset, type 1), with autosomal dominant inheritance and unknown molecular localization; (2) Markesbery-Griggs/Udd myopathies (late adult onset, type 2), with autosomal dominant inheritance and linkage to chromosome 2q; (3) Nonaka myopathy (early adult onset, type 1), with autosomal recessive inheritance and molecular localization to 9p1-q1. Nonaka myopathy is identical to quadriceps-sparing familial inclusion body myopathy; (4) Miyoshi myopathy (early adult onset, type 2), with autosomal recessive inheritance and localization to 2p; (5) Laing myopathy (early onset, type 3), with autosomal dominant inheritance and linkage to chromosome 14. The gene and abnormal gene product have not yet been defined for any of the distal myopathies. However, it is already clear that disorders allelic to the distal myopathies can begin with proximal weakness. Given such major phenotypic variation, it is possible that some of the diseases we regard as distal myopathies may become obsolete. Instead, these conditions may become known by their genetic mutation or abnormal gene product, much like Duchenne and Becker dystrophy.

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.

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.

Gene locus for autosomal recessive distal myopathy with rimmed vacuoles maps to chromosome 9

Distal myopathy with rimmed vacuoles is an autosomal recessive muscular disorder, characterized clinically by weakness of the distal muscles in the lower limbs in early adulthood. Recently, the gene locus for familial vacuolar myopathy with autosomal recessive inheritance (hereditary inclusion body myopathy) was mapped to chromosome 9 by genome-wide linkage analysis of nine Persian-Jewish families. Since both disease conditions share similar clinical, genetic, and histopathological features, we analyzed seven families with distal myopathy with rimmed vacuoles using ten microsatellite markers within the region of the hereditary inclusion body myopathy locus. Significantly high cumulative pairwise lod scores were obtained with three markers: D9S248 (Z(max) = 5.90 at theta = 0), D9S43 (Z(max) = 5.25 at theta = 0), and D9S50 (Z(max) = 4.23 at theta = 0). Detection of obligate recombination events as well as multipoint linkage analysis revealed that the most likely location of the distal myopathy with rimmed vacuoles gene is in a 23.3-cM interval defined by D9S319 and D9S276 on chromosome 9. The results raise the possibility that distal myopathy with rimmed vacuoles and hereditary inclusion body myopathy in Persian Jews are allelic diseases.

A rapidly progressive adolescent-onset oculopharyngeal somatic syndrome with rimmed vacuoles in two siblings

We describe 2 Greek siblings who developed a rapidly progressive oculopharyngeal somatic syndrome, at the ages of 11 and 14 years, with muscle biopsies showing rimmed vacuoles and, in 1 case, cytoplasmic and intranuclear tubulofilamentous inclusions 25 nm in diameter. Although a similar pattern of muscle involvement with rimmed vacuoles is described in autosomal dominant oculopharyngeal muscular dystrophy, the age of onset, the rapid progression of the symptoms, and the nature of the tubulofilaments distinguish this as a separate entity.

[Cytoplasmic inclusion bodies: a study in several diseases and a review of the literature]

Among 1400 muscle biopsies, we studied 16 cases with rimmed vacuoles, whose histology suggests cytoplasm inclusion bodies. We tried to correlate the clinical, laboratory and histopatological data in order to verify the specificity of cytoplasm inclusion bodies to certain diseases. The creatinekinase was increased in 10 cases. In all cases electromyography was abnormal. Muscle histochemistry revealed myopathy in 5 cases, mixed pattern in 7, denervation in 2 and in 2 cases, inflammatory myopathy. Electron microscopy showed the presence of filaments in 8 cases (nuclear, disseminated in cytoplasm or in the subsarcolemmal region). The patients were classified according to history, heredity, laboratory, electrophysiologic, histochemistry data and electron microscopy: in myositis with inclusion cytoplasmic bodies (4 cases), juvenile spinal muscular atrophy (6 cases), distal myopathies (3 cases), limb-girdle dystrophy (2 cases) and peripheral neuropathy (1 case). We present a revision on the pathogenesis and possible etiology of rimmed vacuoles and their relationship with several diseases.

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.

Autosomal dominant limb girdle myopathy with ragged-red fibers and cardiomyopathy. A pedigree study by in vivo 31P-MR spectroscopy indicating a multisystem mitochondrial defect

We describe a late-onset autosomal dominant limb girdle myopathy, associated with dilated cardiomyopathy and mental deterioration. In two affected members of the pedigree with histochemical (ragged-red and cytocrome c oxidase - negative fibers) and ultrastructural abnormalities of muscle mitochondria, in vivo muscle phosphorus MR spectroscopy disclosed a slow rate of phosphocreatine resynthesis after exercise. Brain phosphorus MR spectroscopy revealed a defect of the energy metabolism in the two patients and in a third asymptomatic member, as shown by a significantly low phosphocreatine, increased ADP and decreased phosphorylation potential. Molecular analysis of muscle mitochondrial DNA failed to reveal any known mutation, including multiple deletions of the mtDNA which have been associated with some autosomal dominant mitochondrial diseases. The multisystem clinical involvement, the presence of ragged-red fibers and the alterations revealed by in vivo brain and muscle 31P-MRS suggest that this limb-girdle syndrome represents an unusual phenotype of mitochondrial cytopathy.

Diagnosis in neuromuscular diseases

The diagnosis of neuromuscular diseases can be challenging and successful in the majority of patients, due to advancements in electrophysiology, muscle and nerve biopsy immunohistochemistry, and cytogenetics. This article reviews diverse topics, highlighting these recent achievements, with an emphasis on how they affect the clinical and laboratory diagnosis of specific neuromuscular disorders.

Glucocorticoid-sensitive hereditary inclusion body myositis

We report a hereditary muscle disorder with features of inclusion body myositis (IBM) in two adult sisters with slowly progressive asymmetrical muscle weakness. The findings of light microscopic and ultrastructural investigations of muscle biopsy specimens were consistent with a diagnosis of IBM. Both patients improved and stabilized on immunosuppressive treatment with corticosteroids and azathioprine. This differentiates our patients from other sporadic and familial cases of IBM. Clinical and histological features are described and compared with those of other previously reported families with IBM.

Hereditary inclusion body myopathy maps to chromosome 9p1-q1

Hereditary inclusion body myopathy (HIBM) is a unique disorder of unknown etiology that typically occurs in individuals of Persian Jewish descent. Distinguishing features of the disorder from other limb girdle myopathies include elderly age of onset, ethnic predisposition, and sparing of the quadriceps despite severe involvement of all other proximal leg muscles. Involved muscles demonstrate fibers with rimmed vacuoles and filamentous cytoplasmic and nuclear inclusions. Additional histological features are accumulations of beta-amyloid protein and the absence of inflammatory cells. To identify the chromosomal location of the gene responsible for HIBM, nine Persian Jewish families with HIBM were evaluated. Genomewide linkage analyses identified the recessive IBM locus on chromosome 9 band p1-q1 (maximum lod score at D9S166 = 5.32, theta = 0.0). This region contains the Friedreich's Ataxia gene, raising the possibility that HIBM may be a related neurogenic disorder.

Exons 16 and 17 of the amyloid precursor protein gene in familial inclusion body myopathy

Accumulation of beta-amyloid protein (A beta) occurs in some muscle fibers of patients with inclusion body myopathy and resembles the type of amyloid deposits seen in the affected tissues of patients with Alzheimer's disease and cerebrovascular amyloidosis. Because mutations in exons 16 and 17 of the beta-amyloid precursor protein (beta APP) gene on chromosome 21 have been identified in patients with early-onset familial Alzheimer's disease and Dutch-type cerebrovascular amyloidosis, we searched for mutations of the same region in patients with familial inclusion body myopathy. Sequencing of both alleles in 8 patients from four unrelated families did not reveal any mutations in these exons. The amyloid deposition in familial forms of inclusion body myopathy may be either due to errors in other gene loci, or it is secondary reflecting altered beta APP metabolism or myocyte degeneration and cell membrane degradation.

Rimmed basophilic vacuoles and filamentous inclusions in neuromuscular disorders

To study the incidence of rimmed basophilic vacuoles (RBV) and 15-21 nm filamentous inclusions in neuromuscular disorders, other than inclusion body myositis (IBM) and to determine the diagnostic value of RBV quantitation in the differential diagnosis of IBM, we reviewed 1600 muscle biopsies for RBV and 750 biopsies for filamentous inclusions. The number of RBV-positive fibers per 10 mm2--the RBV-fiber density--was determined. The incidence of RBV in non-IBM biopsies was 8.8 per 1000. Major diagnostic categories were neurogenic disorders (n = 7) and limb girdle muscular dystrophies (LGMD) (n = 3). In IBM (n = 7) the RBV-fiber density ranged from 10.4 to 63.1 and was significantly higher than in neurogenic disorders (0.9-4.4) and LGMD (1.1-2.7). The highest value was found in rigid spine syndrome (205.8). Filamentous inclusions were seen in 2.7 per 1000 non-IBM biopsies, including familial oculopharyngeal muscular dystrophy with distal myopathy (OPMD-DM), rigid spine syndrome, acid maltase deficiency and amyloid neuropathy. RBV and filamentous inclusions coexisted in rigid spine syndrome and in familial OPMD-DM. RBV, as well as filamentous inclusions, has a very low incidence in non-IBM neuromuscular disorders; the RBV-fiber density may help to discriminate neurogenic disorders and LGMD from IBM.

Muscle fiber degeneration in distal myopathy with rimmed vacuole formation

In 11 patients with distal myopathy with rimmed vacuole formation (DMRV), a well-known autosomal recessively inherited disorder, the rimmed vacuole formation appears to be the main pathological change accounting for the progressive muscle fiber degeneration. To gain a better understanding of the pathophysiology of the vacuole formation, we applied Congo red and immunohistochemical stains to muscle biopsies from these patients and the results were compared with those of patients with inclusion body myositis (IBM). The vacuoles in DMRV contained Congophilic amyloid material and deposits immunoreactive for beta-amyloid protein, both the NH2 and COOH termini of beta-amyloid protein precursor, ubiquitin, and tau protein. These results were similar to those seen in our present cases of IBM as well as in previously reported cases. Therefore, there may be no pathogenetic differences in the formation of rimmed vacuoles in DMRV and IBM. Nevertheless, the degenerative process involved in rimmed vacuole formation in various diseases may share a common pathogenetic mechanism with that in amyloid-plaque formation in Alzheimer's disease brain as has been proposed previously.

beta-Amyloid precursor epitopes in muscle fibers of inclusion body myositis

Sporadic inclusion body myositis (IBM) and hereditary inclusion body myopathy (hIBM) are severe and progressive muscle diseases, characterized pathologically by vacuolated muscle fibers that contain 15- to 21-nm cytoplasmic tubulofilaments (CTFs). Those vacuolated muscle fibers also contain abnormally accumulated ubiquitin and beta-amyloid protein (A beta), and they contain amyloid in beta-pleated sheets as indicated by Congo red and crystal violet positivity. Using several well-characterized antibodies, we have now demonstrated that, in addition to A beta, two other epitopes, N-terminal and C-terminal, of the beta-amyloid precursor protein (beta PP) are abnormally accumulated in IBM vacuolated muscle fibers and similarly in hIBM. At the light microscopy level, immunoreactivities of N- and C-epitopes of beta PP closely colocalized with A beta and ubiquitin immunoreactivities. However, by immunogold electronmicroscopy, even though N-, C-, and A beta epitopes of beta PP and ubiquitin colocalized at the amorphous and dense floccular structures, only A beta was localized to the 6- to 10-nm amyloid-like fibrils and only ubiquitin was localized to CTFs. beta PP immunoreactive structures were often in proximity to CTFs, but CTFs themselves never contained beta PP immunoreactivities. The fact that A beta but not C- or N-terminal epitopes of beta PP localized to the 6- to 10-nm amyloid-like fibrils suggests that free A beta might be generated during beta PP processing and, after aggregation, may be responsible for the amyloid present within IBM muscle fibers. Our study demonstrates that three epitopes of beta PP accumulate abnormally in diseased human muscle, and therefore this phenomenon is not unique to Alzheimer's disease, Down's syndrome brain, and Dutch-type cerebrovascular amyloidosis.

Inclusion body myositis: clinical and histopathological features of 36 patients

Thirty-six patients (15 females, 21 males) with inclusion body myositis (IBM) were studied. The diagnosis was established according to clinical and histopathological criteria. Clinical features were insidious onset of slowly progressive muscle weakness and wasting with depressed or absent tendon reflexes especially in the lower limbs. The pattern of muscle weakness was variable. The majority of patients (58%) showed proximal and symmetrical weakness usually most prominent in the legs. Isolated distal (6%) and asymmetrical weakness (19%) was less frequently observed. Myalgia occurred in 42% of the patients. The age at onset of symptoms ranged from 20 to 73 years (mean 47 years). Serum creatine kinase levels were normal (11%) or mildly elevated (89%). Needle electromyography revealed myopathic features in about 80% of the patients, and results of nerve conduction studies were normal in most of the cases. The predominant histopathological findings were numerous muscle fibers with rimmed vacuoles (100% of the patients), groups of atrophic fibers (92%), and inflammatory infiltrates (89%). The inflammatory infiltrates were located predominantly at endomysial sites and were composed mainly of T8 cells. Electron microscopy showed characteristic intracytoplasmic filamentous inclusions in all 36 cases. Immunosuppressive treatment in 16 patients failed to prevent disease progression in all but one patient with an associated Sjögren's syndrome. It is concluded that the consistent combination of typical histopathological findings and characteristic clinical features offers a firm basis for the diagnosis of IBM. IBM should be suspected in any adult patient presenting with clinical signs of a chronic polymyositis unresponsive to immunosuppressive therapy. The etiology and pathogenesis of IBM remain to be established.

Strong immunoreactivity of alpha 1-antichymotrypsin co-localizes with beta-amyloid protein and ubiquitin in vacuolated muscle fibers of inclusion-body myositis

In 10 of 10 inclusion-body myositis (IBM) patients, including 1 hereditary case, vacuolated muscle fibers contained large or small cytoplasmic inclusions immunoreactive for alpha 1-antichymotrypsin (alpha 1-ACT). All IBM muscle biopsies had characteristic cytoplasmic tubulo-filaments by electron microscopy. None of 17 control muscle biopsies contained the alpha 1-ACT immunoreactive inclusions characteristic of IBM. In vacuolated muscle fibers, alpha 1-ACT immunoreactive inclusions colocalized with beta-amyloid protein and ubiquitin immunoreactivities. Our study provides the first demonstration of alpha 1-ACT accumulations in abnormal human muscle, and it suggest that, as in Alzheimer's disease and Down's syndrome, alpha 1-ACT may be involved in the pathogenesis of IBM.

Inclusion body myositis with abundant ring fibers

A 37-year-old male presenting with a 7-year history of leg weakness was found to have moderate weakness confined to the quadriceps and myopathic changes on electromyography. Serum creatine phosphokinase was 2130 units/liter. Biopsy of the quadriceps muscle revealed an inflammatory myopathy with cytoplasmic and nuclear filamentous inclusions characteristic of inclusion body myositis. An unusual finding was the large proportion of ring fibers along with severe atrophy and fibrosis. The pathogenesis of the ring fibers in this setting is discussed.

Inclusion body myositis: its relative frequency in elderly people

Inclusion body myositis (IBM) is a distinct, steroid resistant, form of inflammatory myopathy. Its recognition is the more important because of the preponderant occurrence in the elderly, in whom steroid treatment is hazardous. Since the relative frequency of IBM among inflammatory myopathies in the elderly is undetermined, we retrospectively studied its frequency among all our patients over 50 years, diagnosed between 1980 and 1991 with inflammatory myopathy. Nine of 15 patients with inflammatory myopathy appeared to suffer from IBM. In a further 2 patients this diagnosis was strongly suspected. We conclude that IBM is the most frequent inflammatory myopathy in the elderly. This observation warrants restraint with steroids in the management of inflammatory myopathy in the elderly.

Immunolocalization of ubiquitin in muscle biopsies of patients with inclusion body myositis and oculopharyngeal muscular dystrophy

In 10/10 inclusion body myositis (IBM) patients and 2/2 oculopharyngeal muscular dystrophy (OPMD) patients, vacuolated muscle fibers contained darkly stained ubiquitin (Ub)-immunoreactive cytoplasmic inclusions. By electronmicroscopy, Ub-immunoreactive material was strictly localized to the 15-21 nm pathologic cytoplasmic tubulofilaments (CTFs). None of 18 control muscle biopsies contained the Ub-immunoreactive inclusions that are typical for IBM and OPMD. Thus, (a) finding that CTFs are ubiquitinated places their protein in the Ub-mediated turnover pathway and provides their first molecular marker; (b) easy accessibility, as compared to the central nervous system, of muscle tissue containing ubiquitinated inclusions should be advantageous for biochemical and molecular studies and may provide information important to both systems.