Rabah Ben Yaou

De novo LMNA mutations cause a new form of congenital muscular dystrophy

To describe a new entity of congenital muscular dystrophies caused by de novo LMNA mutations.

Mutations of the FHL1 Gene Cause Emery-Dreifuss Muscular Dystrophy

Emery-Dreifuss muscular dystrophy (EDMD) is a rare disorder characterized by early joint contractures, muscular dystrophy, and cardiac involvement with conduction defects and arrhythmias. So far, only 35% of EDMD cases are genetically elucidated and associated with EMD or LMNA gene mutations, suggesting the existence of additional major genes. By whole-genome scan, we identified linkage to the Xq26.3 locus containing the FHL1 gene in three informative families belonging to our EMD- and LMNA-negative cohort. Analysis of the FHL1 gene identified seven mutations, in the distal exons of FHL1 in these families, three additional families, and one isolated case, which differently affect the three FHL1 protein isoforms: two missense mutations affecting highly conserved cysteines, one abolishing the termination codon, and four out-of-frame insertions or deletions. The predominant phenotype was characterized by myopathy with scapulo-peroneal and/or axial distribution, as well as joint contractures, and associated with a peculiar cardiac disease characterized by conduction defects, arrhythmias, and hypertrophic cardiomyopathy in all index cases of the seven families. Heterozygous female carriers were either asymptomatic or had cardiac disease and/or mild myopathy. Interestingly, four of the FHL1-mutated male relatives had isolated cardiac disease, and an overt hypertrophic cardiomyopathy was present in two. Expression and functional studies demonstrated that the FHL1 proteins were severely reduced in all tested patients and that this was associated with a severe delay in myotube formation in the two patients for whom myoblasts were available. In conclusion, FHL1 should be considered as a gene associated with the X-linked EDMD phenotype, as well as with hypertrophic cardiomyopathy.

The TREAT‐NMD Duchenne Muscular Dystrophy Registries: Conception, Design, and Utilization by Industry and Academia

Duchenne muscular dystrophy (DMD) is an X‐linked genetic disease, caused by the absence of the dystrophin protein. Although many novel therapies are under development for DMD, there is currently no cure and affected individuals are often confined to a wheelchair by their teens and die in their twenties/thirties. DMD is a rare disease (prevalence <5/10,000). Even the largest countries do not have enough affected patients to rigorously assess novel therapies, unravel genetic complexities, and determine patient outcomes. TREAT‐NMD is a worldwide network for neuromuscular diseases that provides an infrastructure to support the delivery of promising new therapies for patients. The harmonized implementation of national and ultimately global patient registries has been central to the success of TREAT‐NMD. For the DMD registries within TREAT‐NMD, individual countries have chosen to collect patient information in the form of standardized patient registries to increase the overall patient population on which clinical outcomes and new technologies can be assessed. The registries comprise more than 13,500 patients from 31 different countries. Here, we describe how the TREAT‐NMD national patient registries for DMD were established. We look at their continued growth and assess how successful they have been at fostering collaboration between academia, patient organizations, and industry.

108th ENMC International Workshop, 3rd Workshop of the MYO-CLUSTER project: EUROMEN, 7th International Emery-Dreifuss Muscular Dystrophy (EDMD) Workshop, 13-15 September 2002, Naarden, The Netherlands.

Inserm UR582 (ex 523), Institut de Myologie, Bâtiment Babinski, G.H. Pitie-Salpetriere, 47, boulevard de l’Hopital, 75 651 Paris Cedex 13, France Laboratoire de Genetique Moleculaire et Chromosomique, IURC, Montpellier, France Institute of Cardiology, University of Bologna, Bologna, Italy Department of Paediatrics and Neonatal Medicine, Imperial College School of Medicine, Hammersmith Campus, London, UK Department of Neurology, Academic Medical Centre, Amsterdam, The Netherlands Service de Cardiologie, GH Cochin, Paris, France Randall Center, Kings College, London, UK Neuromuscular Unit, M.R.C. Polish Academy of Sciences, Warsaw, Poland ITOI, Unit of Bologna, c/o IOR, Bologna, Italy Istituto Ortopedico Rizzoli, Neuromuscular Unit, Bologna, Italy MRIC, North East Wales Institute, Wrexham, UK Department of Internal Medicine and Cardiology Medical University of Warsaw, Warsaw, Poland Department of Cardiology, University Hospital Maastricht, Maastricht, The Netherlands Dipartimento di Biopatologia e Diagnostica per Immagini, Rome, Italy Istituto di Genetica Biochimica ed Evoluzionistica, CNR (IGBE-CNR), Pavia, Italy Division of Medical Genetics, University of Leicester, Leicester, UK Institute of Human Genetics, Greifswald, Germany

Clinical and genetic heterogeneity in laminopathies.

Mutations in the LMNA gene encoding lamins A/C are responsible for more than ten different disorders called laminopathies which affect various tissues in an isolated (striated muscle, adipose tissue or peripheral nerve) or systemic (premature aging syndromes) fashion. Overlapping phenotypes are also observed. Associated with this wide clinical variability, there is also a large genetic heterogeneity, with 408 different mutations being reported to date. Whereas a few hotspot mutations emerge for some types of laminopathies, relationships between genotypes and phenotypes remain poor for laminopathies affecting the striated muscles. In addition, there is important intrafamilial variability, explained only in a few cases by digenism, thus suggesting an additional contribution from modifier genes. In this regard, a chromosomal region linked to the variability in the age at onset of myopathic symptoms in striated muscle laminopathies has recently been identified. This locus is currently under investigation to identify modifier variants responsible for this variability.

Cellular microenvironments reveal defective mechanosensing responses and elevated YAP signaling in LMNA-mutated muscle precursors.

ABSTRACT The mechanisms underlying the cell response to mechanical forces are crucial for muscle development and functionality. We aim to determine whether mutations of the LMNA gene (which encodes lamin A/C) causing congenital muscular dystrophy impair the ability of muscle precursors to sense tissue stiffness and to respond to mechanical challenge. We found that LMNA-mutated myoblasts embedded in soft matrix did not align along the gel axis, whereas control myoblasts did. LMNA-mutated myoblasts were unable to tune their cytoskeletal tension to the tissue stiffness as attested by inappropriate cell-matrix adhesion sites and cytoskeletal tension in soft versus rigid substrates or after mechanical challenge. Importantly, in soft two-dimensional (2D) and/or static three-dimensional (3D) conditions, LMNA-mutated myoblasts showed enhanced activation of the yes-associated protein (YAP) signaling pathway that was paradoxically reduced after cyclic stretch. siRNA-mediated downregulation of YAP reduced adhesion and actin stress fibers in LMNA myoblasts. This is the first demonstration that human myoblasts with LMNA mutations have mechanosensing defects through a YAP-dependent pathway. In addition, our data emphasize the crucial role of biophysical attributes of cellular microenvironment to the response of mechanosensing pathways in LMNA-mutated myoblasts.

Contractures and hypertrophic cardiomyopathy in a novel FHL1 mutation

We investigated a large German family (n = 37) with male members who had contractures, rigid spine syndrome, and hypertrophic cardiomyopathy. Muscle weakness or atrophy was not prominent in affected individuals. Muscle biopsy disclosed a myopathic pattern with cytoplasmic bodies. We used microsatellite markers and found linkage to a locus at Xq26‐28, a region harboring the FHL1 gene. We sequenced FHL1 and identified a new missense mutation within the third LIM domain that replaces a highly conserved cysteine by an arginine (c.625T>C; p.C209R). Our finding expands the phenotypic spectrum of the recently identified FHL1‐associated myopathies and widens the differential diagnosis of Emery–Dreifuss–like syndromes. ANN NEUROL 2010;67:136–140

Heart-hand syndrome of Slovenian type: a new kind of laminopathy

Background: Heart–hand syndromes are a heterogeneous group of genetic disorders characterised by the association of congenital cardiac disease and limb deformities. Laminopathies are a group of diseases caused by mutations in the LMNA gene encoding A-type lamins. Results: We report a new LMNA mutation (c.1609-12T>G, IVS9-12 T>G) that creates a new cryptic splicing site with the retention of 11 intronic nucleotides in the mRNA. This LMNA mutation segregates with a new type of heart–hand syndrome in a previously reported family suffering from adult onset progressive conduction system disease, atrial and ventricular tachyarrhythmias, sudden death, dilated cardiomyopathy, and brachydactyly with predominant foot involvement. Analysis of the fibroblasts of two affected family members identified for the first time a truncated lamin A/C protein resulting from the frame shift created by the new splicing site, together with nuclear envelope abnormalities confirming that this LMNA mutation is pathogenic. Conclusions: This new heart–hand syndrome should therefore be considered as a new kind of laminopathy. As part of laminopathies with heart involvement, patients presenting with this phenotype and their relatives are at risk for developing sudden cardiac death and should beneficiate from appropriate LMNA genetic diagnosis.

Becker muscular dystrophy severity is linked to the structure of dystrophin

In-frame exon deletions of the Duchenne muscular dystrophy (DMD) gene produce internally truncated proteins that typically lead to Becker muscular dystrophy (BMD), a milder allelic disorder of DMD. We hypothesized that differences in the structure of mutant dystrophin may be responsible for the clinical heterogeneity observed in Becker patients and we studied four prevalent in-frame exon deletions, i.e. Δ45-47, Δ45-48, Δ45-49 and Δ45-51. Molecular homology modelling revealed that the proteins corresponding to deletions Δ45-48 and Δ45-51 displayed a similar structure (hybrid repeat) than the wild-type dystrophin, whereas deletions Δ45-47 and Δ45-49 lead to proteins with an unrelated structure (fractional repeat). All four proteins in vitro expressed in a fragment encoding repeats 16-21 were folded in α-helices and remained highly stable. Refolding dynamics were slowed and molecular surface hydrophobicity were higher in fractional repeat containing Δ45-47 and Δ45-49 deletions compared with hybrid repeat containing Δ45-48 and Δ45-51 deletions. By retrospectively collecting data for a series of French BMD patients, we showed that the age of dilated cardiomyopathy (DCM) onset was delayed by 11 and 14 years in Δ45-48 and Δ45-49 compared with Δ45-47 patients, respectively. A clear trend toward earlier wheelchair dependency (minimum of 11 years) was also observed in Δ45-47 and Δ45-49 patients compared with Δ45-48 patients. Muscle dystrophin levels were moderately reduced in most patients without clear correlation with the deletion type. Disease progression in BMD patients appears to be dependent on the deletion itself and associated with a specific structure of dystrophin at the deletion site.

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/.