Jean-Claude Kaplan

Genotype-phenotype analysis in 2,405 patients with a dystrophinopathy using the UMD-DMD database: a model of nationwide knowledgebase.

UMD–DMD France is a knowledgebase developed through a multicenter academic effort to provide an up‐to‐date resource of curated information covering all identified mutations in patients with a dystrophinopathy. The current release includes 2,411 entries consisting in 2,084 independent mutational events identified in 2,046 male patients and 38 expressing females, which corresponds to an estimated number of 39 people per million with a genetic diagnosis of dystrophinopathy in France. Mutations consist in 1,404 large deletions, 215 large duplications, and 465 small rearrangements, of which 39.8% are nonsense mutations. The reading frame rule holds true for 96% of the DMD patients and 93% of the BMD patients. Quality control relies on the curation by four experts for the DMD gene and related diseases. Data on dystrophin and RNA analysis, phenotypic groups, and transmission are also available. About 24% of the mutations are de novo events. This national centralized resource will contribute to a greater understanding of prevalence of dystrophinopathies in France, and in particular, of the true frequency of BMD, which was found to be almost half (43%) that of DMD. UMD–DMD is a searchable anonymous database that includes numerous newly developed tools, which can benefit to all the scientific community interested in dystrophinopathies. Dedicated functions for genotype‐based therapies allowed the prediction of a new multiexon skipping (del 45–53) potentially applicable to 53% of the deleted DMD patients. Finally, such a national database will prove to be useful to implement the international global DMD patients registries under development. Hum Mutat 30:1–12, 2009.

The 2014 version of the gene table of monogenic neuromuscular disorders (nuclear genome)

This table is published annually in theDecember issue. Its purpose is to provide the reader ofNeuromuscular Disorders with an updated list of monogenic muscle diseases due to a primary defect residing in the nuclear genome. It comprises diseases in which the causative gene is known or at least localized on a chromosome, if not yet identified. Diseases for which the locus has not been mapped or which are due to defects involving mitochondrial genes are not included.

Variable phenotype of del45-55 Becker patients correlated with nNOSµ mislocalization and RYR1 hypernitrosylation

Duchenne and Becker muscular dystrophies (DMD and BMD) are muscle-wasting diseases caused by mutations in the DMD gene-encoding dystrophin. Usually, out-of-frame deletions give rise to DMD, whereas in-frame deletions result in BMD. BMD patients exhibit a less severe disease because an abnormal but functional dystrophin is produced. This is the rationale for attempts to correct the reading frame by using an exon-skipping strategy. In order to apply this approach to a larger number of patients, a multi-exon skipping strategy of exons 45-55 has been proposed, because it should correct the mRNA reading frame in almost 75% of DMD patients with a deletion. The resulting dystrophin lacks part of the binding site for the neuronal nitric oxide synthase (nNOSμ), which normally binds to spectrin-like repeats 16 and 17 of the dystrophin. Since these domains are encoded by exons 42-45, we investigated the nNOSμ status in muscle biopsies from 12 BMD patients carrying spontaneous deletions spaning exons 45-55. We found a wide spectrum of nNOSμ expression and localization. The strictly cytosolic mislocalization of nNOSμ was associated with the more severe phenotypes. Cytosolic NO production correlated with both hypernitrosylation of the sarcoplasmic reticulum calcium-release-channel ryanodine receptor type-1 (RyR1) and release of calstabin-1, a central hub of Ca(2+) signaling and contraction in muscle. Finally, this study shows that the terminal truncation of the nNOS-binding domain in the therapeutic del45-55 dystrophin is not innocuous, since it can perturb the nNOS-dependent stability of the RyR1/calstabin-1 complex.

Assessment of the structural and functional impact of in-frame mutations of the DMD gene, using the tools included in the eDystrophin online database.

BackgroundDystrophin is a large essential protein of skeletal and heart muscle. It is a filamentous scaffolding protein with numerous binding domains. Mutations in the DMD gene, which encodes dystrophin, mostly result in the deletion of one or several exons and cause Duchenne (DMD) and Becker (BMD) muscular dystrophies. The most common DMD mutations are frameshift mutations resulting in an absence of dystrophin from tissues. In-frame DMD mutations are less frequent and result in a protein with partial wild-type dystrophin function. The aim of this study was to highlight structural and functional modifications of dystrophin caused by in-frame mutations.Methods and resultsWe developed a dedicated database for dystrophin, the eDystrophin database. It contains 209 different non frame-shifting mutations found in 945 patients from a French cohort and previous studies. Bioinformatics tools provide models of the three-dimensional structure of the protein at deletion sites, making it possible to determine whether the mutated protein retains the typical filamentous structure of dystrophin. An analysis of the structure of mutated dystrophin molecules showed that hybrid repeats were reconstituted at the deletion site in some cases. These hybrid repeats harbored the typical triple coiled-coil structure of native repeats, which may be correlated with better function in muscle cells.ConclusionThis new database focuses on the dystrophin protein and its modification due to in-frame deletions in BMD patients. The observation of hybrid repeat reconstitution in some cases provides insight into phenotype-genotype correlations in dystrophin diseases and possible strategies for gene therapy. The eDystrophin database is freely available: http://edystrophin.genouest.org/.

The 2011 version of the gene table of neuromuscular disorders.

1. Muscular dystrophies; 2. Congenital muscular dystrophies; 3. Congenital myopathies; 4. Distal myopathies; 5. Other myopathies; 6. Myotonic syndromes; 7. Ion channel muscle diseases; 8. Malignant hyperthermias; 9. Metabolic myopathies; 10. Hereditary cardiomyopathies; 11. Congenital myasthenic syndromes; 12. Spinal muscular atrophies; 13. Hereditary ataxias; 14. Hereditary motor and sensory neuropathies; 15. Hereditary paraplegias; 16. Other neuromuscular disorders

Innovating therapies for muscle diseases.

The neuromuscular disorders (NMDs) involve many different genetic and acquired diseases. Corticosteroids (e.g., prednisone and deflazacort) are prescribed for some NMDs as a palliative treatment to slow down disease progression to some extent. For the vast majority of NMDs, no specific therapy is currently available that stops progression or reverses the clinical deficits of the diseases. However, recent progress with different therapeutic approaches is now resulting in numerous clinical trials. In this chapter, we give an overview of the current state of the art, opportunities and challenges for gene therapy, cell therapy, antisense-mediated modulation of splicing, and numerous drug therapies for NMDs in general, and Duchenne muscular dystrophy as a paradigm in particular. Although none of the proposed strategies has yet proven to be of therapeutic value in patients, it is reasonable to expect that clinical efficacy will soon be demonstrated for some of the more advanced approaches.

Does the severity of the LGMD2A phenotype in compound heterozygotes depend on the combination of mutations

Introduction: Limb‐girdle muscular dystrophy type 2A (LGMD2A) is caused by a deficiency of calpain‐3/p94. Although the symptoms in most LGMD2A patients are generally homogeneous, some variation in the severity and progression of the disease has been reported. Methods: We describe 2 patients who carry the same combination of compound heterozygous mutations (pG222R/pR748Q) and whose symptoms are exceptionally benign compared to homozygotes with each missense mutation. Results: The benign phenotype observed in association with the combined pG222R and pR748Q mutations suggested that it may result from a compensatory effect of compound heterozygosity rather than the individual mutations themselves. Our analyses revealed that these two mutations exert different effects on the protease activity of calpain‐3, suggesting “molecular complementation” in these patients. Conclusion: We propose several hypotheses to explain how this specific combination of mutations may rescue the normal proteolytic activity of calpain‐3, resulting in an exceptionally benign phenotype. Muscle Nerve, 2011

Lost after translation

M/S n° 11, vol. 24, novembre 2008 concentration d’As la plus elevee, que devrait eviter le puit. Y a-t-il possibilite d’une strategie exploitant ces donnees [7] ? Elle serait surement d’un cout eleve dans des zones aussi denses et irriguees que les deltas du Gange ou de l’Irrawady, mais valent d’etre envisagees en considerant la gravite dramatique des intoxications a l’As. ‡ Rice poisoning by arsenic REFERENCES

G.P.75 Variable phenotype of del45–55 Becker patients correlated to nNOSμ mislocalization and RYR1 hypernitrosylation

Abstract Duchenne (DMD) and Becker (BMD) muscular dystrophies are muscle-wasting diseases caused by mutations in the DMD gene encoding dystrophin. Usually, out-of-frame deletions give rise to DMD whereas in-frame deletions result in BMD. BMD patients exhibit a less severe disease because an abnormal but functional dystrophin is produced. This is the rationale for attempts to correct the reading frame by using an exon-skipping strategy. In order to apply this approach to a larger number of patients, a strategy of exons 45–55 multi-skipping has been proposed, because it would correct the mRNA reading frame in almost 75% of DMD patients with a deletion. The resulting dystrophin lacks part of the binding site for the neuronal nitric oxide synthase (nNOSμ), which normally binds to spectrin-like repeats 16 and 17 of dystrophin. Knowing that these domains are encoded by exons 42–45, we investigated the nNOSμ status in muscle biopsies from twelve BMD patients with deletions of exons 45–55. We found a wide spectrum of nNOSμ expression and localization. The strictly cytosolic mislocalization of nNOSμμ was associated with the more severe phenotypes. The cytosolic NO production correlated with both hypernitrosylation of the sarcoplasmic reticulum calcium-release-channel RyR1 and release of calstabin-1, a central hub to Ca2+ signaling and contraction in muscle. This study shows that the terminal truncation of the nNOS binding domain in the “therapeutic” del45–55 dystrophin is not innocuous since, in some cases, it may perturb the nNOS dependent stability of the RyR1/calstabin-1 complex.

In mito veritas

M/S n° 5, vol. 24, mai 2008 Dès 1976, Klaus Wrogemann (Université du Manitoba, Canada) avait écrit ces lignes prophétiques sur le rôle des mitochondries dans les maladies musculaires : « It is suggested that the mechanism of muscle-cell necrosis in various muscle diseases is explained by an increased net influx of calcium into cells which triggers a « vicious cycle » of mitochondrial calcium overloading and energy depletion. If correct, this hypothesis may offer the basis for a more rational treatment of some muscle diseases even before their primary aetiology is known » [1]