Myoglobinopathy is an adult-onset autosomal dominant myopathy with characteristic sarcoplasmic inclusions.

Myoglobin, encoded by MB, is a small cytoplasmic globular hemoprotein highly expressed in cardiac myocytes and oxidative skeletal myofibers. Myoglobin binds O2, facilitates its intracellular transport and serves as a controller of nitric oxide and reactive oxygen species. Here, we identify a recurrent c.292C>T (p.His98Tyr) substitution in MB in fourteen members of six European families suffering from an autosomal dominant progressive myopathy with highly characteristic sarcoplasmic inclusions in skeletal and cardiac muscle. Myoglobinopathy manifests in adulthood with proximal and axial weakness that progresses to involve distal muscles and causes respiratory and cardiac failure. Biochemical characterization reveals that the mutant myoglobin has altered O2 binding, exhibits a faster heme dissociation rate and has a lower reduction potential compared to wild-type myoglobin. Preliminary studies show that mutant myoglobin may result in elevated superoxide levels at the cellular level. These data define a recognizable muscle disease associated with MB mutation.

Hereditary myopathy with early respiratory failure: occurrence in various populations.

OBJECTIVE: Several families with characteristic features of hereditary myopathy with early respiratory failure (HMERF) have remained without genetic cause. This international study was initiated to clarify epidemiology and the genetic underlying cause in these families, and to characterise the phenotype in our large cohort. METHODS: DNA samples of all currently known families with HMERF without molecular genetic cause were obtained from 12 families in seven different countries. Clinical, histopathological and muscle imaging data were collected and five biopsy samples made available for further immunohistochemical studies. Genotyping, exome sequencing and Sanger sequencing were used to identify and confirm sequence variations. RESULTS: All patients with clinical diagnosis of HMERF were genetically solved by five different titin mutations identified. One mutation has been reported while four are novel, all located exclusively in the FN3 119 domain (A150) of A-band titin. One of the new mutations showed semirecessive inheritance pattern with subclinical myopathy in the heterozygous parents. Typical clinical features were respiratory failure at mid-adulthood in an ambulant patient with very variable degree of muscle weakness. Cytoplasmic bodies were retrospectively observed in all muscle biopsy samples and these were reactive for myofibrillar proteins but not for titin. CONCLUSIONS: We report an extensive collection of families with HMERF with five different mutations in exon 343 of TTN, which establishes this exon as the primary target for molecular diagnosis of HMERF. Our relatively large number of new families and mutations directly implies that HMERF is not extremely rare, not restricted to Northern Europe and should be considered in undetermined myogenic respiratory failure.

Welander distal myopathy is caused by a mutation in the RNA-binding protein TIA1.

OBJECTIVE: A study was undertaken to identify the molecular cause of Welander distal myopathy (WDM), a classic autosomal dominant distal myopathy. METHODS: The genetic linkage was confirmed and defined by microsatellite and single nucleotide polymorphism haplotyping. The whole linked genomic region was sequenced with targeted high-throughput and Sanger sequencing, and coding transcripts were sequenced on the cDNA level. WDM muscle biopsies were studied by Western blotting and immunofluorescence microscopy. Splicing of TIA1 and its target genes in muscle and myoblast cultures was analyzed by reverse transcriptase polymerase chain reaction. Mutant TIA1 was characterized by cell biological studies on HeLa cells, including quantification of stress granules by high content analysis and fluorescence recovery after photobleaching (FRAP) experiments. RESULTS: The linked haplotype at 2p13 was narrowed down to <806 kb. Sequencing by multiple methods revealed only 1 segregating coding mutation, c.1362 G>A (p.E384K) in the RNA-binding protein TIA1, a key component of stress granules. Immunofluorescence microscopy of WDM biopsies showed a focal increase of TIA1 in atrophic and vacuolated fibers. In HeLa cells, mutant TIA1 constructs caused a mild increase in stress granule abundance compared to wild type, and showed slower average fluorescence recovery in FRAP. INTERPRETATION: WDM is caused by mutated TIA1 through a dominant pathomechanism probably involving altered stress granule dynamics.

Diagnostic challenge in desmin cardiomyopathy with transformation of clinical phenotypes.

Desmin cardiomyopathy is a rare cause of congestive heart failure. Its clinical manifestation in adulthood often is associated with conduction disorders and a neuromuscular phenotype. Only a few cases have been reported, with early manifestation in childhood mostly due to severe cardiomyopathy dilation and conduction abnormalities. However, the disease can result in the variety of clinical phenotypes, including hypertrophic, restrictive, and arrhythmogenic cardiomyopathy. This report describes the first case of desmin cardiomyopathy with early manifestation in adolescence and transformation of several clinical phenotypes over time, representing sufficient difficulties for the correct clinical diagnosis and treatment of the disease at an early stage.

Altered autophagy gene expression and persistent atrophy suggest impaired remodeling in chronic hemiplegic human skeletal muscle.

INTRODUCTION: Upper motor neuron lesions after stroke are a major cause of disability. We aimed to determine whether skeletal muscles from these patients display typical molecular signatures of inflammation, growth arrest, and atrophy. METHODS: Muscle biopsies were analyzed for morphological, histochemical, ultrastructural, and molecular features indicative of changes in gene expression involved in muscle atrophy. RESULTS: Chronic hemiplegia resulted in ~9.5% atrophy, fiber type shifts, and histochemical and ultrastructural signs of impaired remodeling. TNF and TWEAK expressions were unaltered, but MSTN mRNA was lower (-73%, P < 0.05) in paretic tibialis anterior vs. age-matched controls. The expression of autophagy-related genes (BCN-1, LC3, and GABARAPL1) was lower in paretic tibialis anterior (-81%, -48%, and -60%, respectively, P < 0.01) and soleus (-85%, -54%, and -60% respectively, P < 0.01) compared with old controls. CONCLUSIONS: Persistent atrophy in chronic spastic hemiplegia may be associated with impaired remodeling partly due to altered autophagy gene expression.

Feasibility and effects of a physical exercise programme in adults with myotonic dystrophy type 1: a randomized controlled pilot study.

OBJECTIVE: To investigate the feasibility and effects of a physical exercise programme on functioning and health-related quality of life in adults with myotonic dystrophy type 1. DESIGN: A randomized controlled trial. SUBJECTS: Thirty-five adults with myotonic dystrophy type 1. METHODS: After stratification for level of functioning, study participants were assigned by lot to either a training group or a control group. Training-group participants attended a 60-minute comprehensive group-training programme, Friskis&Svettis® Open Doors, twice a week for 14 weeks. The six-minute walk test was the primary outcome measure and the timed-stands test, the timed up-and-go test, the Epworth sleepiness scale and the Short Form-36 health survey were secondary outcome measures. RESULTS: Intention-to-treat analyses revealed no significant differences in any outcome measures, except for an increased between-group difference after intervention in the Short Form-36 mental health subscale and a decrease in the vitality subscale for the control group. The programme was well tolerated and many training-group participants perceived subjective changes for the better. No negative effects were reported. CONCLUSION: The Friskis&Svettis® Open Doors programme was feasible for adults with myotonic dystrophy type 1 who had been screened for cardiac involvement, had distal or mild-to-moderate proximal muscle impairment, and no severe cognitive impairments. No beneficial or detrimental effects were evident.

Differences in aberrant expression and splicing of sarcomeric proteins in the myotonic dystrophies DM1 and DM2.

Aberrant transcription and mRNA processing of multiple genes due to RNA-mediated toxic gain-of-function has been suggested to cause the complex phenotype in myotonic dystrophies type 1 and 2 (DM1 and DM2). However, the molecular basis of muscle weakness and wasting and the different pattern of muscle involvement in DM1 and DM2 are not well understood. We have analyzed the mRNA expression of genes encoding muscle-specific proteins and transcription factors by microarray profiling and studied selected genes for abnormal splicing. A subset of the abnormally regulated genes was further analyzed at the protein level. TNNT3 and LDB3 showed abnormal splicing with significant differences in proportions between DM2 and DM1. The differential abnormal splicing patterns for TNNT3 and LDB3 appeared more pronounced in DM2 relative to DM1 and are among the first molecular differences reported between the two diseases. In addition to these specific differences, the majority of the analyzed genes showed an overall increased expression at the mRNA level. In particular, there was a more global abnormality of all different myosin isoforms in both DM1 and DM2 with increased transcript levels and a differential pattern of protein expression. Atrophic fibers in DM2 patients expressed only the fast myosin isoform, while in DM1 patients they co-expressed fast and slow isoforms. However, there was no increase of total myosin protein levels, suggesting that aberrant protein translation and/or turnover may also be involved.

Mice expressing L345P mutant desmin exhibit morphological and functional changes of skeletal and cardiac mitochondria.

Desmin mutations underlie inherited myopathies/cardiomyopathies with varying severity and involvement of the skeletal and cardiac muscles. We developed a transgenic mouse model expressing low level of the L345P desmin mutation (DESMUT mice) in order to uncover changes in skeletal and cardiac muscles caused by this mutation. The most striking ultrastructural changes in muscle from DESMUT mice were mitochondrial swelling and vacuolization. The mitochondrial Ca(2+) level was significantly increased in skeletal and cardiac myocytes from DESMUT mice compared to wild type cells during and after contractions. In isolated DESMUT soleus muscles, contractile function and recovery from fatigue were impaired. A SHIRPA screening test for neuromuscular performance demonstrated decreased motor function in DESMUT compared to WT mice. Echocardiographic changes in DESMUT mice included left ventricular wall hypertrophy and a decreased left ventricular chamber dimension. The results imply that low levels of L345P desmin acts, at least partially, by a dominant negative effect on mitochondria.

The kinase domain of titin controls muscle gene expression and protein turnover.

The giant sarcomeric protein titin contains a protein kinase domain (TK) ideally positioned to sense mechanical load. We identified a signaling complex where TK interacts with the zinc-finger protein nbr1 through a mechanically inducible conformation. Nbr1 targets the ubiquitin-associated p62/SQSTM1 to sarcomeres, and p62 in turn interacts with MuRF2, a muscle-specific RING-B-box E3 ligase and ligand of the transactivation domain of the serum response transcription factor (SRF). Nuclear translocation of MuRF2 was induced by mechanical inactivity and caused reduction of nuclear SRF and repression of transcription. A human mutation in the titin protein kinase domain causes hereditary muscle disease by disrupting this pathway.

Influence of isoflurane concentration and hypoxia on functional magnetic resonance imaging for the detection of bicuculline-induced neuronal activation.

Our present study shows that transient changes in relative cerebral blood volume (rCBV) induced by stimulation with bicuculline under six different conditions of anesthesia can be detected with high spatial resolution functional magnetic resonance imaging (fMRI). Bicuculline was administered at a low dose to induce neural activation, and no seizure activity was noted. Of the six conditions, the maximal reaction to bicuculline was observed under 1.5% isoflurane in 60% nitrogen and 40% oxygen. Our results imply that the rCBV changes under this level of isoflurane anesthesia with body temperature maintained at 37.5 degrees C are probably suitable for further fMRI studies.

Electrophoretic determination of the myosin/actin ratio in the diagnosis of critical illness myopathy.

OBJECTIVE: To develop a rapid method to quantify myosin in muscle biopsy specimens from patients with critical illness myopathy (CIM). DESIGN: Percutaneous muscle biopsy specimens at different stages of CIM were examined by light microscopy and transmission electron microscopy (TEM) and by horizontal pore gradient SDS electrophoresis (SDS-PAGE). The myosin/actin ratio was calculated densitometrically. Neurophysiological examinations were performed at various times during the course of CIM. SETTING: All patients were treated in intensive care units at Karolinska Hospital. PATIENTS AND PARTICIPANTS: We studied 11 patients with CIM, 5 patients with axonal neuropathies, and 42 control individuals. MEASUREMENTS AND RESULTS: The histopathological changes included in all cases muscle fiber atrophy, degeneration, regeneration, nuclear changes, and reduction in myofibrillar ATPase activity in both type I and II fibers. In severely affected muscles fiber type differentiation was lost. On TEM preferential loss of thick filaments was the dominant finding. In some patients changes were present only in parts of the specimen. The neurophysiological examinations indicated myopathy in five patients and combined myopathy and neuropathy in five and suggested neuropathy in one. The SDS-pore PAGE used showed a technical variation of 4-5%. Quantitative results were obtained within 1 day and night. The mean value of the myosin/actin ratio in controls was 1.37+/-0.21 and in CIM patients 0.37+/-0.17, without overlapping with the control values. CONCLUSIONS: Considering the diagnostic difficulty using morphological and neurophysiological methods, especially in early stages of CIM, we suggest including SDS-pore PAGE to determine the myosin/actin ratio for rapid diagnosis of CIM.

Welander distal myopathy outside the Swedish population: phenotype and genotype.

Welander distal myopathy is a late onset disorder that is mainly seen in Sweden. It is linked to chromosome 2p13 and all Swedish patients show a common shared haplotype, indicating a founder mutation. Here we report the clinical manifestations, magnetic resonance imaging, pathophysiology and haplotype analysis of Welander patients in the Finnish population. The clinical examination of patients from 12 different families showed a distal myopathy with onset in the long extensor muscles of the hands and fingers, also seen in Swedish Welander patients. Muscle biopsies showed characteristic myopathic changes. Haplotype analysis with the five polymorphic markers that make up the common core haplotype, seen in the Swedish patients, revealed that this haplotype is also co-segregating in the Finnish patients and a common ancestry is therefore further supported for patients with Welander distal myopathy.