Myositis with sarcoplasmic inclusions in Nakajo-Nishimura syndrome: a genetic inflammatory myopathy.

AIMS: Nakajo-Nishimura syndrome (NNS) is an autosomal recessive disease caused by biallelic mutations in the PSMB8 gene that encodes the immunoproteasome subunit ß5i. There have been only a limited number of reports on the clinicopathological features of the disease in genetically confirmed cases. METHODS: We studied clinical and pathological features of three NNS patients who all carry the homozygous p.G201V mutations in PSMB8. Patients' muscle specimens were analysed with histology and immunohistochemistry. RESULTS: All patients had episodes of typical periodic fever and skin rash, and later developed progressive muscle weakness and atrophy, similar to previous reports. Oral corticosteroid was used for treatment but showed no obvious efficacy. On muscle pathology, lymphocytes were present in the endomysium surrounding non-necrotic fibres, as well as in the perimysium perivascular area. Nearly all fibres strongly expressed MHC-I in the sarcolemma. In the eldest patient, there were abnormal protein aggregates in the sarcoplasm, immunoreactive to p62, TDP-43 and ubiquitin antibodies. CONCLUSIONS: These results suggest that inflammation, inclusion pathology and aggregation of abnormal proteins underlie the progressive clinical course of the NNS pathomechanism.

Diagnostic potential of sarcoplasmic myxovirus resistance protein A expression in subsets of dermatomyositis.

AIMS: To elucidate the diagnostic value of sarcoplasmic expression of myxovirus resistance protein A (MxA) for dermatomyositis (DM) specifically analysing different DM subforms, and to test the superiority of MxA to other markers. METHODS: Immunohistochemistry for MxA and retinoic acid-inducible gene I (RIG-I) was performed on skeletal muscle samples and compared with the item presence of perifascicular atrophy (PFA) in 57 DM patients with anti-Mi-2 (n = 6), -transcription intermediary factor 1 gamma (n = 10), -nuclear matrix protein 2 (n = 13), -melanoma differentiation-associated gene 5 (MDA5) (n = 10) or -small ubiquitin-like modifier activating enzyme (n = 1) autoantibodies and with no detectable autoantibody (n = 17). Among the patients, nine suffered from cancer and 22 were juvenile-onset type. Disease controls included antisynthetase syndrome (ASS)-associated myositis (n = 30), immune-mediated necrotizing myopathy (n = 9) and inclusion body myositis (n = 5). RESULTS: Sarcoplasmic MxA expression featured 77% sensitivity and 100% specificity for overall DM patients, while RIG-I staining and PFA reached respectively 14% and 59% sensitivity and 100% and 86% specificity. In any subset of DM, sarcoplasmic MxA expression showed higher sensitivity than RIG-I and PFA. Some anti-MDA5 antibody-positive DM samples distinctively showed a scattered staining pattern of MxA. No ASS samples had sarcoplasmic MxA expression even though six patients had DM skin rash. CONCLUSIONS: Sarcoplasmic MxA expression is more sensitive than PFA and RIG-I expression for a pathological diagnosis of DM, regardless of the autoantibody-related subgroup. In light of its high sensitivity and specificity, it may be considered a pathological hallmark of DM per se. Also, lack of MxA expression in ASS supports the idea that ASS is a distinct entity from DM.

NDUFAF3 variants that disrupt mitochondrial complex I assembly may associate with cavitating leukoencephalopathy.

Genetic abnormalities in mitochondrial complex assembling factors are associated with leukoencephalopathy. We present a 1-year-old girl with consciousness disturbance after a respiratory infection. Brain MRI revealed leukoencephalopathy with bilaterally symmetrical hyperintensity in the substantia nigra, medial thalamic nuclei, and basal nuclei, as well as cavities in the cerebral white matter and corpus callosum. Lactate levels in the spinal fluid were high, while magnetic resonance spectroscopy of the cerebral white matter and basal nuclei showed high peak lactate levels, suggesting mitochondrial dysfunction. The respiratory enzyme activity of complex I was reduced to 17% to 21% in skeletal muscle. Whole exome sequencing identified compound heterozygous variations in NDUFAF3, involved in the assembly of mitochondrial complex I (c.342_343insGTG:p.117Valdup, c.505C > A:p.Pro169Thr). Two-dimensional, blue-native polyacrylamide gel electrophoresis (PAGE) and sodium dodecyl sulfate-PAGE revealed reductions in Q-module (NDUFS2, NDUFS3, and NDUFA9) and P-module (NDUFB10 and NDUFB11) subunits, indicating disruption of mitochondrial complex I assembly. Our report expands the spectrum of clinical phenotypes associated with pathogenic variants of NDUFAF3.

Altered TDP-43-dependent splicing in HSPB8-related distal hereditary motor neuropathy and myofibrillar myopathy.

BACKGROUND AND PURPOSE: Mutations in the small heat-shock protein 22 gene (HSPB8) have been associated with Charcot-Marie-Tooth disease type 2L, distal hereditary motor neuropathy (dHMN) type IIa and, more recently, distal myopathy/myofibrillar myopathy (MFM) with protein aggregates and TDP-43 inclusions. The aim was to report a novel family with HSPB8K141E -related dHMN/MFM and to investigate, in a patient muscle biopsy, whether the presence of protein aggregates was paralleled by altered TDP-43 function. METHODS: We reviewed clinical and genetic data. We assessed TDP-43 expression by qPCR and alternative splicing of four previously validated direct TDP-43 target exons in four genes by reverse transcriptase-polymerase chain reaction. RESULTS: The triplets and their mother presented in the second to third decade of life with progressive weakness affecting distal and proximal lower limb and truncal muscles. Nerve conduction study showed a motor axonal neuropathy. The clinical features, moderately raised creatin kinase levels, selective pattern of muscle involvement on magnetic resonance imaging and pathological changes on muscle biopsy, including the presence of protein aggregates, supported the diagnosis of a contemporary primary muscle involvement. In affected muscle tissue we observed a consistent alteration of TDP-43-dependent splicing in three out of four TDP-43-target transcripts (POLDIP3, FNIP1 and BRD8), as well as a significant decrease of TDP-43 mRNA levels. CONCLUSIONS: Our study confirmed the role of mutated HSPB8 as a cause of a combined neuromuscular disorder encompassing dHMN and MFM with protein aggregates. We identified impaired RNA metabolism, secondary to TDP-43 loss of function, as a possible pathological mechanism of HSPB8K141E toxicity, leading to muscle and nerve degeneration.

Fatal infantile cardioencephalomyopathy with COX deficiency and mutations in SCO2, a COX assembly gene.

Mammalian cytochrome c oxidase (COX) catalyses the transfer of reducing equivalents from cytochrome c to molecular oxygen and pumps protons across the inner mitochondrial membrane. Mitochondrial DNA (mtDNA) encodes three COX subunits (I-III) and nuclear DNA (nDNA) encodes ten. In addition, ancillary proteins are required for the correct assembly and function of COX (refs 2, 3, 4, 5, 6). Although pathogenic mutations in mtDNA-encoded COX subunits have been described, no mutations in the nDNA-encoded subunits have been uncovered in any mendelian-inherited COX deficiency disorder. In yeast, two related COX assembly genes, SCO1 and SCO2 (for synthesis of cytochrome c oxidase), enable subunits I and II to be incorporated into the holoprotein. Here we have identified mutations in the human homologue, SCO2, in three unrelated infants with a newly recognized fatal cardioencephalomyopathy and COX deficiency. Immunohistochemical studies implied that the enzymatic deficiency, which was most severe in cardiac and skeletal muscle, was due to the loss of mtDNA-encoded COX subunits. The clinical phenotype caused by mutations in human SCO2 differs from that caused by mutations in SURF1, the only other known COX assembly gene associated with a human disease, Leigh syndrome.

Characterization of the Asian myopathy patients with VCP mutations.

BACKGROUND AND PURPOSE: Mutations in the valosin-containing protein (VCP) gene are known to cause inclusion body myopathy with Paget's disease of bone and frontotemporal dementia (IBMPFD) and familial amyotrophic lateral sclerosis (ALS). Despite an increasing number of clinical reports, only one Asian family with IBMPFD has been described. METHODS: To characterize patients with VCP mutations, we screened a total of 152 unrelated Asian families who were suspected to have rimmed vacuolar myopathy. RESULTS: We identified VCP mutations in seven patients from six unrelated Asian families. Five different missense mutations were found, including a novel p.Ala439Pro substitution. All patients had adult-onset progressive muscle wasting with variable involvement of axial, proximal, and distal muscles. Two of seven patients were suggested to have mild brain involvement including cerebellar ataxia, and only one showed radiological findings indicating a change in bone. Findings from skeletal muscle indicated mixed neurogenic and myogenic changes, fibers with rimmed vacuoles, and the presence of cytoplasmic and nuclear inclusions. These inclusions were immunopositive for VCP, ubiquitin, transactivation response DNA-binding protein 43, and also histone deacetylase 6 (HDAC6), of which function is regulated by VCP. Evidence of early nuclear and mitochondrial damage was also characteristic. CONCLUSIONS: Valosin-containing protein mutations are not rare in Asian patients, and gene analysis should be considered for patients with adult-onset rimmed vacuolar myopathy with neurogenic changes. A wide variety of central and peripheral nervous system symptoms coupled with rare bone abnormalities may complicate diagnosis.

State of the art in muscle lipid diseases.

Fatty acid oxidation in mitochondrial matrix is a major source of energy in muscle, especially when physiological energy demand is increased and exceeds what can be provided through glycolysis. Not surprisingly, a group of muscle disorders due to defects in this system usually leads to the development of acute rhabdomyolysis in conditions such as infection, fasting and prolonged exercise. This group includes beta-oxidation cycle defects and deficiencies of carnitine palmitoyltransferase II (CPTH) and very-long-chain acyl-CoA dehydrogenase (VLCAD). Muscle pathology is usually not very helpful for the diagnosis but immunohistochemistry may be useful for screening VLCAD deficiency. Another group of lipid dysmetablolism is lipid storage myopathy (LSM) that is pathologically characterized by increased lipid droplets both in number and size in muscle fibers. So far, causative genes have been identified in four different LSMs, comprising primary carnitine deficiency, multiple acyl-CoA dehydrogenase deficiency or glutaric aciduria type II, neutral lipid storage disease with ichthyosis, and neutral lipid storage disease with myopathy. Clinically, the LSM patients show slowly progressive muscle weakness unlike the former group. Final diagnosis is usually made by specific biochemical assays with mutation analyses. As some effective drugs have been widely used and some promising therapies are under certified, comprehensive understanding of these diseases from clinical, pathological and molecular aspects would be of much help for the patients.

Thymidine phosphorylase gene mutations in MNGIE, a human mitochondrial disorder.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive human disease associated with multiple deletions of skeletal muscle mitochondrial DNA (mtDNA), which have been ascribed to a defect in communication between the nuclear and mitochondrial genomes. Examination of 12 MNGIE probands revealed homozygous or compound-heterozygous mutations in the gene specifying thymidine phosphorylase (TP), located on chromosome 22q13.32-qter. TP activity in leukocytes from MNGIE patients was less than 5 percent of controls, indicating that loss-of-function mutations in TP cause the disease. The pathogenic mechanism may be related to aberrant thymidine metabolism, leading to impaired replication or maintenance of mtDNA, or both.

Danon disease: a novel Lamp-2 gene mutation in a family with four affected members.

This is a report of a family with four members affected with Danon disease and variable clinical presentations, including cardiomyopathy, skeletal muscle pathology, and hepatopathy. Analysis by electron microscopy of the quadriceps muscle from the proband and his brother showed abnormal mitochondria, and immunohistochemistry revealed no expression of LAMP-2 protein. This defect is due to a yet undescribed mutation located at the second nucleotide in the intron 8 of the Lamp-2 gene (c.1093+2 T>A) that generated exon 8 skipping confirmed at RNA level in the proband.

A unique case of limb-girdle muscular dystrophy type 2A carrying novel compound heterozygous mutations in the human CAPN3 gene.

A unique sib pair afflicted by limb girdle muscular dystrophy type 2A (LGMD2A) is described showing a slowly progressive autosomal recessive type of muscular dystrophy with onset in the third and fourth decades. The patients had early asymmetric muscle involvement characterized by prominent biceps brachii atrophy with sparing of the knee extensors. Additional findings included elevation of serum creatine kinase level, myopathic EMG changes and dystrophic type of pathology on muscle biopsy. Asymmetrical wasting of muscles in the extremities exhibited uniform and highly selective CT imaging patterns. RNA and DNA analyses confirmed novel compound heterozygous mutations (R147X/L212F) in the human CAPN3 gene.

Perspectives on distal myopathy with rimmed vacuoles or hereditary inclusion body myopathy: contributions from an animal model. Lack of sialic acid, a central determinant in sugar chains, causes myopathy?

Distal myopathy with rimmed vacuoles (DMRV) or hereditary inclusion body myopathy (hIBM) is an adult onset slowly progressive myopathy secondary to mutations in the UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE) gene that encodes a bifunctional enzyme which catalyzes the rate-limiting step in sialic acid biosynthesis. Many hypotheses have been proposed to explain why patients develop weakness and atrophy, but are most views are obscure and thus are still considered controversial, partly because of the lack of an appropriate model with which these theories could be clarified. In this review, we briefly summarize the progress in DMRV research, and highlight efforts of researchers in generating the animal model for this myopathy.

Emerinopathy and laminopathy clinical, pathological and molecular features of muscular dystrophy with nuclear envelopathy in Japan.

Mutations in the genes for nuclear envelope proteins of emerin (EMD) and lamin A/C (LMNA) are known to cause Emery-Dreifuss muscular dystrophy (EDMD) and limb girdle muscular dystrophy (LGMD). We compared clinical features of the muscular dystrophy patients associated with mutations in EMD (emerinopathy) and LMNA (laminopathy) in our series. The incidence of laminopathy was slightly higher than that of emerinopathy. The age at onset of the disease in emerinopathy was variable and significantly older than in laminopathy. The initial symptom of emerinopathy was also variable, whereas nearly all laminopathy patients presented initially with muscle weakness. Calf hypertrophy was often seen in laminopathy, underscoring the importance of mutation screening for LMNA in childhood muscular dystrophy with calf hypertrophy. The clinical spectrum of emerinopathy is actually wider than previously known including EDMD, LGMD, conduction defects with minimal muscle/joint involvement, and their intermittent forms. Pathologically, no marked difference was observed between emerinopathy and laminopathy. Increased number and variation in size of myonuclei were detected. More precise observations using electron microscopy is warranted to characterize the detailed nuclear changes in nuclear envelopathy.

Allelic heterogeneity of GNE gene mutation in two Tunisian families with autosomal recessive inclusion body myopathy.

Autosomal recessive hereditary inclusion body myopathy (AR-HIBM), with sparing of the quadriceps, is characterized by adult-onset, with weakness and atrophy of distal lower limb muscles, and typical histopathological findings in muscle biopsy. AR hIBM is associated with mutations in the UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE) gene on chromosome 9p12-13 . We report two unrelated Tunisian families with clinical and pathological features of AR HIBM. One distinct homozygous GNE missense mutation, M712T, previously reported in Middle Eastern Jewish patients, and a newly identified one, L379H, were found in one patient from each family. We conclude that AR HIBM in Tunisia shows an allelic genetic heterogeneity.

Non-collagenic etiologies of muscle weakness with joint deformities: about two paradigmatic case reports.

Muscle weakness associated to marked joint deformities is not an uncommon clinical situation in daily neuromuscular clinics. These abnormalities encompass a large variety of conditions including non-primary muscle disorders. Besides well-defined and rather readily recognisable hereditary syndromes such as Bethlem myopathy or Ullrich congenital muscular dystrophy, some unusual etiologies should also be considered. We report here two paradigmatic cases in which we found mutations in two novel genes corresponding to two newly described entities (progressive pseudorheumatoid dysplasia, PPD, and infantile systemic hyalinosis, ISH) both conditions in which the clinical picture can mimick primary muscle disease.