Mitochondrial Ca(2+) uptake has key roles in cell life and death. Physiological Ca(2+) signaling regulates aerobic metabolism, whereas pathological Ca(2+) overload triggers cell death. Mitochondrial Ca(2+) uptake is mediated by the Ca(2+) uniporter complex in the inner mitochondrial membrane, which comprises MCU, a Ca(2+)-selective ion channel, and its regulator, MICU1. Here we report mutations of MICU1 in individuals with a disease phenotype characterized by proximal myopathy, learning difficulties and a progressive extrapyramidal movement disorder. In fibroblasts from subjects with MICU1 mutations, agonist-induced mitochondrial Ca(2+) uptake at low cytosolic Ca(2+) concentrations was increased, and cytosolic Ca(2+) signals were reduced. Although resting mitochondrial membrane potential was unchanged in MICU1-deficient cells, the mitochondrial network was severely fragmented. Whereas the pathophysiology of muscular dystrophy and the core myopathies involves abnormal mitochondrial Ca(2+) handling, the phenotype associated with MICU1 deficiency is caused by a primary defect in mitochondrial Ca(2+) signaling, demonstrating the crucial role of mitochondrial Ca(2+) uptake in humans.

The LMNA mutations identified appear to correlate with a relatively severe phenotype. Our results further broaden the spectrum of laminopathies and define a new disease entity that we suggest is best classified as a congenital muscular dystrophy (LMNA-related congenital muscular dystrophy, or L-CMD).

Dominant mutations in the skeletal muscle ryanodine receptor (RYR1) gene are well-recognized causes of both malignant hyperthermia susceptibility (MHS) and central core disease (CCD). More recently, recessive RYR1 mutations have been described in few congenital myopathy patients with variable pathology, including multi-minicores. Although a clinical overlap between patients with dominant and recessive RYR1 mutations exists, in most cases with recessive mutations the pattern of muscle weakness is remarkably different from that observed in dominant CCD. In order to characterize the spectrum of congenital myopathies associated with RYR1 mutations, we have investigated a cohort of 44 patients from 28 families with clinical and/or histopathological features suggestive of RYR1 involvement. We have identified 25 RYR1 mutations, 9 of them novel, including 12 dominant and 13 recessive mutations. With only one exception, dominant mutations were associated with a CCD phenotype, prominent cores and predominantly occurred in the RYR1 C-terminal exons 101 and 102. In contrast, the 13 recessive RYR1 mutations were distributed evenly along the entire RYR1 gene and were associated with a wide range of clinico-pathological phenotypes. Protein expression studies in nine cases suggested a correlation between specific mutations, RyR1 protein levels and resulting phenotype: in particular, whilst patients with dominant or recessive mutations associated with typical CCD phenotypes appeared to have normal RyR1 expression, individuals with more generalized weakness, multi-minicores and external ophthalmoplegia had a pronounced depletion of the RyR1 protein. The phenomenon of protein depletion was observed in some patients compound heterozygous for recessive mutations at the genomic level and silenced another allele in skeletal muscle, providing additional information on the mechanism of disease in these patients. Our data represent the most extensive study of RYR1-related myopathies and indicate complex genotype-phenotype correlations associated with mutations differentially affecting assembly and function of the RyR1 calcium release channel.

Our study provides a framework for providing information to patients with Duchenne muscular dystrophy and their families when introducing GC therapy. The study also highlights the importance of collecting longitudinal natural history data on patients treated according to standardised protocols, and clearly identifies the benefits and the side-effect profile of two treatment regimens, which will help with informed choices and implementation of targeted surveillance.

Objective: There are currently no effective treatments to halt the muscle breakdown in Duchenne muscular dystrophy (DMD), although genetic-based clinical trials are being piloted. Most of these trials have as an endpoint the restoration of dystrophin in muscle fibers, hence requiring sufficiently well-preserved muscle of recruited patients. The choice of the muscles to be studied and the role of noninvasive methods to assess muscle preservation therefore require further evaluation. Methods:We studied the degree of muscle involvement in the lower leg muscles of 34 patients with DMD Ͼ8 years, using muscle MRI. In a subgroup of 15 patients we correlated the muscle MRI findings with the histology of open extensor digitorum brevis (EDB) muscle biopsies. Muscle MRI involvement was assigned using a scale 0-4 (normal-severe). Results:In all patients we documented a gradient of involvement of the lower leg muscles: the posterior compartment (gastrocnemius Ͼ soleus) was most severely affected; the anterior compartment (tibialis anterior/posterior, popliteus, extensor digitorum longus) least affected. Muscle MRI showed EDB involvement that correlated with the patient's age (p ϭ 0.055). We show a correlation between the MRI and EDB histopathologic changes, with MRI 3-4 grades associated with a more severe fibro-adipose tissue replacement. The EDB was sufficiently preserved for bulk and signal intensity in 18/22 wheelchair users aged 10-16.6 years. Conclusion:This study provides a detailed correlation between muscle histology and MRI changes in DMD and demonstrates the value of this imaging technique as a reliable tool for the selection of muscles in patients recruited into clinical trials. Neurology ® 2011;76:346-353 GLOSSARY AO ϭ antisense oligonucleotide; DMD ϭ Duchenne muscular dystrophy; EDB ϭ extensor digitorum brevis; KAFO ϭ knee-ankle-foot orthosis; NSA ϭ number of signal averages; TE ϭ echo time; TR ϭ repetition time.The progressive loss of muscle fibers and their replacement by fat and connective tissue is part of the disease course of DMD.1 Despite several exhaustive natural history studies on the clinical course of DMD, the progression of pathology in individual muscle groups is poorly defined. 2Information on muscle pathology in DMD is limited to the muscles that are biopsied at the time of diagnosis (often quadriceps femoris), 2 the mean age at diagnosis being ϳ4.5 years. 3,4 There are now early clinical trials using novel genetic-based techniques in boys with DMD with the aim to restore dystrophin expression. These include the drug PTC124, 5 which allows

Ryanodine receptor 1 (RYR1) mutations are a common cause of congenital myopathies associated with both dominant and recessive inheritance. Histopathological findings frequently feature central cores or multi-minicores, more rarely, type 1 predominance/uniformity, fiber-type disproportion, increased internal nucleation, and fatty and connective tissue. We describe 71 families, 35 associated with dominant RYR1 mutations and 36 with recessive inheritance. Five of the dominant mutations and 35 of the 55 recessive mutations have not been previously reported. Dominant mutations, typically missense, were frequently located in recognized mutational hotspot regions, while recessive mutations were distributed throughout the entire coding sequence. Recessive mutations included nonsense and splice mutations expected to result in reduced RyR1 protein. There was wide clinical variability. As a group, dominant mutations were associated with milder phenotypes; patients with recessive inheritance had earlier onset, more weakness, and functional limitations. Extraocular and bulbar muscle involvement was almost exclusively observed in the recessive group. In conclusion, our study reports a large number of novel RYR1 mutations and indicates that recessive variants are at least as frequent as the dominant ones. Assigning pathogenicity to novel mutations is often difficult, and interpretation of genetic results in the context of clinical, histological, and muscle magnetic resonance imaging findings is essential.

The purpose of this study was to investigate the effects of high-force eccentric muscle contractions on collagen remodeling and on circulating levels of matrix metalloproteinases (MMP) and tissue inhibitors of metalloproteinases (TIMP) in humans. Nine volunteers [5 men and 4 women, mean age 23 (SD 4) yr] each performed a bout of 100 maximum voluntary eccentric contractions of the knee extensors. Muscle biopsies were taken before exercise and on days 4 and 22 afterward. Image analysis of stained tissue sections was used to quantify endomysial collagen staining intensity. Maximum voluntary contractile isometric force was recorded preexercise and on days 1, 2, 3, 4, 8, 11, and 14 postexercise. Venipuncture blood samples were also drawn on these days for measurement of serum creatine kinase activity and concentrations of MMP-9, TIMP-1, TIMP-2, and the MMP-2/TIMP-2 complex. Maximum voluntary contractile force declined by 39 +/- 23% (mean +/- SD) on day 2 postexercise and recovered thereafter. Serum creatine kinase activity peaked on day 4 postexercise (P < 0.01). Collagen type IV staining intensity increased significantly on day 22 postexercise to 126 +/- 29% (mean +/- SD) of preexercise values (P < 0.05). Serum MMP-9 levels increased on day 8 postexercise (P < 0.01), and serum TIMP-1 was also significantly elevated on days 1, 2, 3, 4, and 14 postexercise (P < 0.05). These results suggest that a single bout of eccentric muscle contractions results in remodeling of endomysial type IV collagen, possibly via the MMP pathway.

Phosphoinositides are small phospholipids that control diverse cellular downstream signaling events. Their spatial and temporal availability is tightly regulated by a set of specific lipid kinases and phosphatases. Congenital muscular dystrophies are hereditary disorders characterized by hypotonia and weakness from birth with variable eye and central nervous system involvement. In individuals exhibiting congenital muscular dystrophy, early-onset cataracts, and mild intellectual disability but normal cranial magnetic resonance imaging, we identified bi-allelic mutations in INPP5K, encoding inositol polyphosphate-5-phosphatase K. Mutations impaired phosphatase activity toward the phosphoinositide phosphatidylinositol (4,5)-bisphosphate or altered the subcellular localization of INPP5K. Downregulation of INPP5K orthologs in zebrafish embryos disrupted muscle fiber morphology and resulted in abnormal eye development. These data link congenital muscular dystrophies to defective phosphoinositide 5-phosphatase activity that is becoming increasingly recognized for its role in mediating pivotal cellular mechanisms contributing to disease.