Véronique Labelle

Analysis of the DYSF mutational spectrum in a large cohort of patients

Dysferlinopathies belong to the heterogeneous group of autosomal recessive muscular dystrophies. Mutations in the gene encoding dysferlin (DYSF) lead to distinct phenotypes, mainly Limb Girdle Muscular Dystrophy type 2B (LGMD2B) and Miyoshi myopathy (MM). Here, we analysed the mutational data from the largest cohort described to date, a cohort of 134 patients, included based on clinical suspicion of primary dysferlinopathy and/or dysferlin protein deficiency identified on muscle biopsy samples. Data were compiled from 38 patients previously screened for mutations in our laboratory (Nguyen, et al., 2005; Nguyen, et al., 2007), and 96 supplementary patients screened for DYSF mutations using genomic DHPLC analysis, and subsequent sequencing of detected variants, in a routine diagnostic setting. In 89 (66%) out of 134 patients, molecular analysis identified two disease causing mutations, confirming the diagnosis of primary Dysferlinopathy on a genetic basis. Furthermore, one mutation was identified in 30 patients, without identification of a second deleterious allele. We are currently developing complementary analysis for patients in whom only one or no disease‐causing allele could be identified using the genomic screening procedure. Altogether, 64 novel mutations have been identified in this cohort, which corresponds to approximately 25% of all DYSF mutations reported to date. The mutational spectrum of this cohort significantly shows a higher proportion of nonsense mutations, but a lower proportion of deleterious missense changes as compared to previous series.

A Naturally Occurring Human Minidysferlin Protein Repairs Sarcolemmal Lesions in a Mouse Model of Dysferlinopathy

A naturally occurring miniversion of the dysferlin protein found in a patient shows that gene therapy by minigene transfer may be possible in dysferlinopathies. The Best Things Come in Small Packages Muscular dystrophies are a group of more than 30 individually rare genetic disorders characterized by progressive muscle wasting, which cause chronic disabilities in both children and adults. Although there is no definitive cure, the genetic cause of many muscular dystrophies is known, and several treatment strategies are currently being investigated. In particular, there are promising possibilities for the development of gene therapy–based treatments to replace the defective proteins that cause these diseases. However, several significant practical hurdles remain, including the packaging size limitation of the most widely used adeno-associated virus (AAV)–derived vector. Dysferlinopathies are a subgroup of muscular dystrophies that usually manifest in the second decade of life. They are caused by mutations in a gene encoding for the large 237-kD plasma membrane protein dysferlin, which plays a role in muscle membrane repair. Unfortunately, the large size of the gene precludes it from being packaged in its entirety into the AAV vector for use in gene therapy. However, partially functional miniature versions of the 427-kD dystrophin protein, which cause a mild form of dystrophy known as Becker muscular dystrophy, have previously been discovered. This helped to overcome the size limitations of the AAV vector and could be used in a gene therapy approach to lessen the severe phenotype associated with the more common Duchenne muscular dystrophy, which is also caused by mutant dystrophin. Now, Krahn et al. have discovered a substantially truncated form of dysferlin in a patient with a moderate form of dysferlinopathy, which may also help pave the way toward the development of a gene therapy–based strategy for treating dysferlinopathies. The authors found that this naturally occurring minidysferlin protein was more than three times smaller than the wild-type protein. This meant it could be successfully packaged into the AAV vector, which was then injected into dysferlin-deficient mice, resulting in stable expression of the truncated protein. Muscle fibers isolated from these mice were efficiently repaired after wound healing, indicating that this miniprotein still retained at least part of its critical function. This work provides an important basis for both minidysferlin and exon-skipping gene therapy strategies, making dysferlinopathies the second group of muscular dystrophies that could be targeted by these approaches. Dysferlinopathies are autosomal recessive, progressive muscle dystrophies caused by mutations in DYSF, leading to a loss or a severe reduction of dysferlin, a key protein in sarcolemmal repair. Currently, no etiological treatment is available for patients affected with dysferlinopathy. As for other muscular dystrophies, gene therapy approaches based on recombinant adeno-associated virus (rAAV) vectors are promising options. However, because dysferlin messenger RNA is far above the natural packaging size of rAAV, full-length dysferlin gene transfer would be problematic. In a patient presenting with a late-onset moderate dysferlinopathy, we identified a large homozygous deletion, leading to the production of a natural “minidysferlin” protein. Using rAAV-mediated gene transfer into muscle, we demonstrated targeting of the minidysferlin to the muscle membrane and efficient repair of sarcolemmal lesions in a mouse model of dysferlinopathy. Thus, as previously demonstrated in the case of dystrophin, a deletion mutant of the dysferlin gene is also functional, suggesting that dysferlin’s structure is modular. This minidysferlin protein could be used as part of a therapeutic strategy for patients affected with dysferlinopathies.

Segregation of a totally skewed pattern of X chromosome inactivation in four familial cases of Rett syndrome without MECP2 mutation: implications for the disease

BACKGROUND Rett syndrome is a neurodevelopmental disorder affecting only girls; 99.5% of Rett syndrome cases are sporadic, although several familial cases have been reported. Mutations in the MECP2 gene were identified in approximately 70-80% of sporadic Rett syndrome cases. METHODS We have screened theMECP2 gene coding region for mutations in five familial cases of Rett syndrome and studied the patterns of X chromosome inactivation (XCI) in each girl. RESULTS We found a mutation inMECP2 in only one family. In the four families without mutation in MECP2, we found that (1) all mothers exhibit a totally skewed pattern of XCI; (2) six out of eight affected girls also have a totally skewed pattern of XCI; and (3) it is the paternally inherited X chromosome which is active in the patients with a skewed pattern of XCI. Given that the skewing of XCI is inherited in our families, we genotyped the whole X chromosome using 32 polymorphic markers and we show that a locus potentially responsible for the skewed XCI in these families could be located on the short arm of the X chromosome. CONCLUSION These data led us to propose a model for familial Rett syndrome transmission in which two traits are inherited, an X linked locus abnormally escaping X chromosome inactivation and the presence of a skewed XCI in carrier women.

UMD‐DYSF, a novel locus specific database for the compilation and interactive analysis of mutations in the dysferlin gene

Mutations in the dysferlin gene (DYSF) lead to a complete or partial absence of the dysferlin protein in skeletal muscles and are at the origin of dysferlinopathies, a heterogeneous group of rare autosomal recessive inherited neuromuscular disorders. As a step towards a better understanding of the DYSF mutational spectrum, and towards possible inclusion of patients in future therapeutic clinical trials, we set up the Universal Mutation Database for Dysferlin (UMD‐DYSF), a Locus‐Specific Database developed with the UMD® software. The main objective of UMD‐DYSF is to provide an updated compilation of mutational data and relevant interactive tools for the analysis of DYSF sequence variants, for diagnostic and research purposes. In particular, specific algorithms can facilitate the interpretation of newly identified intronic, missense‐ or isosemantic‐exonic sequence variants, a problem encountered recurrently during genetic diagnosis in dysferlinopathies. UMD‐DYSF v1.0 is freely accessible at www.umd.be/DYSF/. It contains a total of 742 mutational entries corresponding to 266 different disease‐causing mutations identified in 558 patients worldwide diagnosed with dysferlinopathy. This article presents for the first time a comprehensive analysis of the dysferlin mutational spectrum based on all compiled DYSF disease‐causing mutations reported in the literature to date, and using the main bioinformatics tools offered in UMD‐DYSF. ©2011 Wiley‐Liss, Inc. Hum Mutat 33:E2317–E2331, 2012.

Exclusion of Mutations in the Dysferlin Alternative Exons 1 of DYSF-v1, 5a, and 40a in a Cohort of 26 Patients

Mutations in the gene encoding dysferlin (DYSF; MIM# 603009, 2p13, GenBank NM_003494.2) cause primary dysferlinopathies, which are autosomal recessive muscular dystrophies. DYSF has a large mutational spectrum, and genetic diagnosis is complicated by incomplete mutation detection rates. Recently, novel dysferlin transcripts were characterized by identifying alternative exons 1 of DYSF-v1 (GenBank DQ267935), exon 5a (GenBank DQ976379), and exon 40a (GenBank EF015906). To evaluate the frequency of possible mutations in the newly identified DYSF alternative exons, we screened the corresponding genomic regions for mutations in a cohort of 26 patients, carrying only one mutation undoubtedly considered as disease causing in the 55 canonical DYSF exons. No disease-causing mutation was identified in alternative exons 1 of DYSF-v1, exon 5a, and exon 40a, demonstrating a low frequency of disease-causing mutations in these exons.

Novel ancestral Dysferlin splicing mutation which migrated from the Iberian peninsula to South America

Primary dysferlinopathies are a group of recessive heterogeneous muscular dystrophies. The most common clinical presentations are Miyoshi myopathy and LGMD2B. Additional presentations range from isolated hyperCKemia to severe functional disability. Symptomatology begins in the posterior muscle compartment of the calf and its clinical course progresses slowly in Miyoshi myopathy whereas LGMD2B involves predominantly the proximal muscles of the lower limbs. The age of onset ranges from 13 to 60years in Caucasians. We present five patients that carry a novel mutation in the exon12/intron12 boundary: c.1180_1180+7delAGTGCGTG (r.1054_1284del). We provide evidence of a founder effect due to a common ancestral origin of this mutation, detected in heterozygosity in four patients and in homozygosity in one patient.

Clinical heterogeneity and a high proportion of novel mutations in a Chinese cohort of patients with dysferlinopathy.

BACKGROUND AND AIMS Dysferlinopathies are a group of autosomal recessive muscular dystrophies caused by mutations in the dysferlin gene. This study presents clinical features and the mutational spectrum in the largest cohort of Chinese patients analyzed to date. PATIENTS AND METHODS A total of 36 unrelated Chinese patients with diagnostic suspicion of dysferlinopathy were clinically and genetically characterized. RESULTS Patients were divided into five phenotypes: 19 patients with limb girdle muscular dystrophy (LGMD) type 2B, 10 with Miyoshi myopathy (MM), 1 with distal anterior compartment myopathy (DACM), 3 with exercise intolerance, and 3 with asymptomatic hypercreatine phosphokinasemia (hyperCPKemia). Thirty-one patients showed an absence or drastic reduction of dysferlin expression by Westernblot. Forty-three mutations were identified in DYSF, including 31 novel. CONCLUSION Our study underlines clinical heterogeneity and a high proportion of novel mutations in Chinese patients affected with dysferlinopathy.