Copy number variation analysis increases the diagnostic yield in muscle diseases

Objective: Copy number variants (CNVs) were analyzed from next-generation sequencing data, with the aim of improving diagnostic yield in skeletal muscle disorder cases.& para;& para;Methods: Four publicly available bioinformatic analytic tools were used to analyze CNVs from sequencing data from patients with muscle diseases. The patients were previously analyzed with a targeted gene panel for single nucleotide variants and small insertions and deletions, without achieving final diagnosis. Variants detected by multiple CNV analysis tools were verified with either array comparative genomic hybridization or PCR. The clinical significance of the verified CNVs was interpreted, considering previously identified variants, segregation studies, and clinical information of the patient cases.& para;& para;Results: Combining analysis of all different mutation types enabled integration of results and identified the final cause of the disease in 9 myopathy cases. Complex effects like compound heterozygosity of different mutation types and compound disease arising from variants of different genes were unraveled. We identified the first large intragenic deletion of the titin (TTN) gene implicated in the pathogenesis of a severe form of myopathy. Our work also revealed a "double-trouble" effect in a patient carrying a single heterozygous insertion/deletion mutation in the TTN gene and a Becker muscular dystrophy causing deletion in the dystrophin gene.& para;& para;Conclusions: Causative CNVs were identified proving that analysis of CNVs is essential for increasing the diagnostic yield in muscle diseases. Complex severe muscular dystrophy phenotypes can be the result of different mutation types but also of the compound effect of 2 different genetic diseases.Peer reviewe

Frizzled related protein deficiency impairs muscle strength, gait and calpain 3 levels

BACKGROUND: Limb-girdle muscular dystrophy recessive 1 calpain3-related (LGMDR1), previously known as LGMD2A, is a disease caused by mutations in the CAPN3 gene. It is characterized by progressive weakness and muscle degeneration. Frizzled related protein (FRZB), upregulated in LGMDR1, was identified as a key regulator of the crosstalk between Wnt and integrin signalling pathways. FRZB gene silencing showed a recovery in the expression of some of the costamere protein levels in myotubes. RESULTS: Here, we performed a comprehensive characterization of Frzb-/- mice muscles to study the absence of Frzb in skeletal muscle and eventual links with the molecular characteristics of LGMDR1 patient muscles. Frzb-/- mice showed reduced muscle size and strength. Gait analysis showed that Frzb-/- mice moved more slowly but no impaired regeneration capacity was observed after muscle injury. Additionally, Frzb-/- mice muscle showed an increased number of mesoangioblasts. Lack of Frzb gene in Frzb-/- mice and its increased expression in LGMDR1 patients, showed contrary regulation of Rora, Slc16a1, Tfrc and Capn3 genes. The reciprocal regulation of Frzb and Capn3 genes further supports this axis as a potential target for LGMDR1 patients. CONCLUSIONS: Our data confirm a role for Frzb in the regulation of Rora, Slc16a1, Tfrc, and Capn3 genes in muscle cells. In vivo, reduced muscle strength and gait in the Frzb-/- mice are intriguing features. The reciprocal relationship between FRZB and CAPN3 further supports a key role for this axis in patients with LGMDR1.status: publishe

ENTIRE CAPN3 GENE DELETION IN A PATIENT WITH LIMB-GIRDLE MUSCULAR DYSTROPHY TYPE 2A

International audienceLimb-girdle muscular dystrophy type 2A (LGMD2A) due to mutations in the CAPN3 gene is one of the most common of autosomal recessive limb-girdle muscular dystrophies. We describe a patient who had a typical LGMD2A phenotype and posterior compartment involvement on MRI. Different genetic analyses were performed, including microarray analysis. There was an apparently homozygous mutation in exon 24, c.2465G>T, p.(*822Leuext62*), and a lack of correlation in the disease segregation analyses. This suggested the presence of a genomic rearrangement. In fact, a heterozygous deletion of the entire CAPN3 gene was found. This novel deletion comprised the terminal region of the GANC gene and the entire CAPN3 gene. This finding points out the need to reconsider and adapt our current strategy of molecular diagnosis in order to detect these types of genomic rearrangements that escape standard mutation screening procedures

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Genotype-phenotype correlations in recessive titinopathies

International audiencePurpose High throughput sequencing analysis has facilitated the rapid analysis of the entire titin (TTN) coding sequence. This has resulted in the identification of a growing number of recessive titinopathy patients. The aim of this study was to (1) characterize the causative genetic variants and clinical features of the largest cohort of recessive titinopathy patients reported to date and (2) to evaluate genotype-phenotype correlations in this cohort. Methods We analyzed clinical and genetic data in a cohort of patients with biallelic pathogenic or likely pathogenicTTNvariants. The cohort included both previously reported cases (100 patients from 81 unrelated families) and unreported cases (23 patients from 20 unrelated families). Results Overall, 132 causative variants were identified in cohort members. More than half of the cases had hypotonia at birth or muscle weakness and a delayed motor development within the first 12 months of life (congenital myopathy) with causative variants located along the entire gene. The remaining patients had a distal or proximal phenotype and a childhood or later (noncongenital) onset. All noncongenital cases had at least one pathogenic variant in one of the final threeTTNexons (362-364). Conclusion Our findings suggest a novel association between the location of nonsense variants and the clinical severity of the disease