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Myology research highlights

Discover our weekly selection of scientific and medical publications in the field of myology and of neuromuscular diseases :  summary of each publication aimed at the general reader, highlighting the main points of the article and the authors’ conclusions
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For your information, there are at present more than 1250 news items on myology online.
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31/10/2014 - Characterisation of patients with tubular aggregate myopathy caused by mutations in STIM1

Tubular aggregate myopathies (TAMs) are muscle disorders characterised by abnormal accumulations of densely packed single-walled or double-walled membrane tubules in muscle fibres. Recently, STIM1, encoding a major calcium sensor of the endoplasmic reticulum, was identified as a TAM gene. The present study aimed to define the clinical, histological and ultrastructural phenotype of tubular aggregate myopathy and to assess the STIM1 mutation spectrum. The authors describe six new TAM families harbouring one known and four novel STIM1 mutations. All identified mutations were heterozygous missense mutations affecting highly conserved amino acids in the calcium-binding EF-hand domains, demonstrating the presence of a mutation hot spot for TAM. They show that the mutations induce constitutive STIM1 clustering, strongly suggesting that calcium sensing and consequently calcium homoeostasis is impaired. Histological and ultrastructural analyses define a common picture with tubular aggregates labelled with Gomori trichrome and Nicotinamide adenine dinucleotide (NADH) tetrazolium reductase, substantiating their endoplasmic reticulum origin. The aggregates were observed in both fibre types and were often accompanied by nuclear internalisation and fibre size variability. The phenotypical spectrum ranged from childhood onset progressive muscle weakness and elevated creatine kinase levels to adult-onset myalgia without muscle weakness and normal CK levels. The present study expands the phenotypical spectrum of STIM1-related tubular aggregate myopathy. STIM1 should therefore be considered for patients with tubular aggregate myopathies involving either muscle weakness or myalgia as the first and predominant clinical sign.


31/10/2014 - Safety of follistatin gene therapy in patients with Becker muscular dystrophy

Becker muscular dystrophy (BMD) is a variant of dystrophin deficiency resulting from DMD gene mutations. Phenotype is variable with loss of ambulation in late teenage or late mid-life years. There is currently no treatment for this condition. In this BMD proof-of-principle clinical trial, a potent myostatin antagonist, follistatin (FS), was used to inhibit the myostatin pathway. Extensive pre-clinical studies, using adeno-associated virus (AAV) to deliver follistatin, demonstrated an increase in strength. For this trial, we used the alternatively spliced FS344 to avoid potential binding to off target sites. AAV1.CMV.FS344 was delivered to 6 BMD patients by direct bilateral intramuscular quadriceps injections. Cohort 1 included 3 subjects receiving 3X1011 vg/kg/leg. The distance walked on the 6MWT was the primary outcome measure. Patients 01 and 02 improved 58 meters (m) and 125 meters, respectively. Patient 03 showed no change. In Cohort 2, Patients 05 and 06 received 6X1011 vg/kg/leg with improved 6MWT by 108 m and 29 m, whereas, Patient 04 showed no improvement. No adverse effects were encountered. Histological changes corroborated benefit showing reduced endomysial fibrosis, reduced central nucleation, more normal fiber size distribution with muscle hypertrophy, especially at high dose. The results are encouraging for treatment of dystrophin-deficient muscle diseases.


31/10/2014 - AAN releases guideline for LGMD diagnosis and treatment

The American Academy of Neurology (AAN) has reviewed the current evidence and made practice recommendations regarding the diagnosis and treatment of all forms of limb-girdle muscular dystrophy (LGMD) and some forms of distal muscular dystrophy (DD). Most LGMDs are rare, with estimated prevalences ranging from 0.07 per 100,000 to 0.43 per 100,000. The frequency of some muscular dystrophies varies based on the ethnic background of the population studied. Some LGMD subtypes have distinguishing features, including pattern of muscle involvement, cardiac abnormalities, extramuscular involvement, and muscle biopsy findings. The few published therapeutic trials were not designed to establish clinical efficacy of any treatment. For patients with suspected muscular dystrophy, clinicians should use a clinical approach to guide genetic diagnosis based on clinical phenotype, inheritance pattern, and associated manifestations (Level B). Clinicians should refer newly diagnosed patients with an LGMD subtype and high risk of cardiac complications for cardiology evaluation even if they are asymptomatic from a cardiac standpoint (Level B). In patients with LGMD with a known high risk of respiratory failure, clinicians should obtain periodic pulmonary function testing (Level B). Clinicians should refer patients with muscular dystrophy to a clinic that has access to multiple specialties designed specifically to care for patients with neuromuscular disorders (Level B). Clinicians should not offer patients with LGMD gene therapy, myoblast transplantation, neutralizing antibody to myostatin, or growth hormone outside of a research study designed to determine efficacy and safety of the treatment (Level R).


31/10/2014 - Clinical aspects of patients with sarcoglycanopathies under steroids therapy

Sarcoglycanopathies include four subtypes of autosomal recessive limb-girdle muscular dystrophies. Patients usually present with progressive weakness leading to early loss of ambulation and premature death. No effective treatment is currently available. Here, the authors present clinical aspects and outcomes of six children with sarcoglycanopathies treated with steroids for at least one year. Patient files were retrospectively analyzed for steroid use. Stabilization of muscle strength was noted in one patient, a slight improvement in two, and a slight worsening in three. In addition, variable responses of forced vital capacity and cardiac function were observed. No overt clinical improvement was observed in patients with sarcoglycanopathies under steroid therapy. Prospective controlled studies including a larger number of patients are necessary to determine the effects of steroids for sarcoglycanopathies.


31/10/2014 - Preimplantation diagnosis using next generation sequencing identifies a rare genetic disease

The use of Next Generation Sequencing (NGS) in the diagnosis of rare genetic pathologies is becoming ever more widespread in clinical practice. The following study reports the first case of preimplantation diagnosis through NGS of a form of LAMA2-related muscular dystrophy. A couple went to the Reproductive Medicine Centre for a preconceptional genetic consultation and for advice regarding secondary infertility. The couple already had a 3-year-old child who was suffering from a form of muscular dystrophy that has yet to be genetically defined. The disease had been diagnosed at the age of 6 months. A blood sample was taken from both parents and the child in order to analyze the DNA through the Illumina NextSeq 500 platform and an enrichment protocol, Trusight One Sequencing Panel, created by Illumina for the simultaneous sequencing of the exon regions of 4,813 clinically relevant genes. This led to the identification of 2 point mutations in the LAMA2 gene, each inherited by a parent. The couple then underwent a cycle of IVF (in vitro fertilization). A preimplantation genetic diagnosis was carried out on the embryos obtained after setting up a protocol for the analysis of a point mutation in the LAMA2 gene, (this mutation has yet to be described in literature) and the normal embryos together with the recessive LAMA2-related muscular dystrophy related carriers were transferred. There were no complications during pregnancy, which terminated with a cesarean section at 39 weeks and the birth of a healthy 3430-gram baby. Given its robustness, reliability and reproducibility, NGS could also be useful in prenatal diagnosis. This technique could guarantee an ample and quick analysis of the genes involved in development, making it possible to organize medical interventions during pregnancy and after birth.


31/10/2014 - Reliability of the motor function measure in Charcot-Marie-Tooth disease

In this descriptive study, the applicability and responsiveness of the motor function measure (total score and sub-scores D1, D2 and D3) in 233 patients aged 4-86 years, with Charcot-Marie-Tooth disease was investigated. Scores and sub-scores were analyzed by age and by disease subtypes. Sensitivity to change (responsiveness) was estimated in patients having had at least two evaluations with at least six months between the first and the second. Motor function measure scores decreased with age, especially sub-scores D1 and D3. There were no significant differences between the scores according to type of Charcot-Marie-Tooth disease. The scores were significantly higher for ambulatory than for non-ambulatory patients. Significant responsiveness was demonstrated only in type 2 Charcot-Marie-Tooth disease. These results suggest that, especially for D1 and D3 sub-scores, the motor function measure is a reliable and valid outcome measure that can be usefully applied in longitudinal follow-up. Studies of longer duration could demonstrate its responsiveness in other Charcot-Marie-Tooth disease subtypes.


17/10/2014 - Asynchronous regeneration drives muscle fibrosis in DMD patients

This study aimed to determine the mechanisms underlying failure of muscle regeneration that is observed in dystrophic muscle through hypothesis generation using muscle profiling data (human dystrophy and murine regeneration). The authors  found that transforming growth factor β-centered networks strongly associated with pathological fibrosis and failed regeneration were also induced during normal regeneration but at distinct time points. They hypothesized that asynchronously regenerating microenvironments are an underlying driver of fibrosis and failed regeneration. This hypothesis was validated using an experimental model of focal asynchronous bouts of muscle regeneration in wild-type (WT) mice. A chronic inflammatory state and reduced mitochondrial oxidative capacity are observed in bouts separated by 4 d, whereas a chronic profibrotic state was seen in bouts separated by 10 d. Treatment of asynchronously remodeling WT muscle with either prednisone or VBP15 mitigated the molecular phenotype. This asynchronous regeneration model for pathological fibrosis and muscle wasting in the muscular dystrophies is likely generalizable to tissue failure in chronic inflammatory states in other regenerative tissues.


17/10/2014 - New Guideline provides direction for the diagnosis and treatment of limb-girdle muscular dystrophies

This report reviews the current evidence and makes practice recommendations regarding the diagnosis and treatment of limb-girdle muscular dystrophies (LGMDs). The authors establish that most LGMDs are rare, with estimated prevalences ranging from 0.07 per 100,000 to 0.43 per 100,000. The frequency of some muscular dystrophies varies based on the ethnic background of the population studied. Some LGMD subtypes have distinguishing features, including pattern of muscle involvement, cardiac abnormalities, extramuscular involvement, and muscle biopsy findings. The few published therapeutic trials were not designed to establish clinical efficacy of any treatment. For patients with suspected muscular dystrophy, it is recommended that clinicians use a clinical approach to guide genetic diagnosis based on clinical phenotype, inheritance pattern, and associated manifestations (Level B). Clinicians should refer newly diagnosed patients with an LGMD subtype and high risk of cardiac complications for cardiology evaluation even if they are asymptomatic from a cardiac standpoint (Level B). In patients with LGMD with a known high risk of respiratory failure, clinicians should obtain periodic pulmonary function testing (Level B). Clinicians should refer patients with muscular dystrophy to a clinic that has access to multiple specialties designed specifically to care for patients with neuromuscular disorders (Level B). Clinicians should not offer patients with LGMD gene therapy, myoblast transplantation, neutralizing antibody to myostatin, or growth hormone outside of a research study designed to determine efficacy and safety of the treatment (Level R). Detailed results and recommendations are available on the Neurology® Web site at Neurology.org.
 


15/10/2014 - A new muscle glycogen storage disease associated with Glycogenin-1 deficiency

This study describes a slowly progressive myopathy in seven unrelated adult patients with storage of polyglucosan in muscle fibers. Genetic investigation revealed homozygous or compound heterozygous deleterious variants in the glycogenin-1 gene (GYG1). Most patients showed depletion of glycogenin-1 in skeletal muscle whereas one showed presence of glycogenin-1 lacking the C-terminal that normally binds glycogen synthase. These results indicate that either depletion of glycogenin-1 or impaired interaction with glycogen synthase underlies this new form of glycogen storage disease that differs from a previously reported patient with GYG1 mutations who showed profound glycogen depletion in skeletal muscle and accumulation of glycogenin-1.


15/10/2014 - BIN1 mutations cause centronuclear myopathy

Centronuclear myopathies are congenital muscle disorders characterized by type I myofibre predominance and an increased number of muscle fibres with nuclear centralization. The severe neonatal X-linked form is due to mutations in MTM1, autosomal recessive centronuclear myopathy with neonatal or childhood onset results from mutations in BIN1 (amphiphysin 2), and dominant cases were previously associated to mutations in DNM2 (dynamin 2). Here, the authors aimed to determine the genetic basis and physiopathology of patients with mild dominant centronuclear myopathy without mutations in DNM2. Therefore, they established and characterized a homogeneous cohort of nine patients from five families with a progressive adult-onset centronuclear myopathy without facial weakness, including three sporadic cases and two families with dominant disease inheritance. All patients had similar histological and ultrastructural features involving type I fibre predominance and hypotrophy, as well as prominent nuclear centralization and clustering. Heterozygous BIN1 mutations were identified in all patients and the molecular diagnosis was complemented by functional analyses. Two mutations in the N-terminal amphipathic helix strongly decreased the membrane-deforming properties of amphiphysin 2 and three stop-loss mutations resulted in a stable protein containing 52 supernumerary amino acids. Immunolabelling experiments revealed abnormal central accumulation of dynamin 2, caveolin-3, and the autophagic marker p62, and general membrane alterations of the triad, the sarcolemma, and the basal lamina as potential pathological mechanisms. In conclusion, the authors identified BIN1 as the second gene for dominant centronuclear myopathy. These data provide the evidence that specific BIN1 mutations can cause either recessive or dominant centronuclear myopathy and that both disorders involve different pathomechanisms.



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