Amyloidose bei Muskeldystrophie

Mutations in the gene encoding dysferlin (DYSF) cause limb-girdle muscular dystrophy 2B (LGMD2B) and Miyoshi myopathy (MM). We were able to examine eight patients suspected of LGMD2B clinically, histochemically. The genotype was determined in every case. We found sarcolemmal and interstitial amyloid deposits in four muscle sections. All of the mutations associated with amyloid were located in the N-terminal region of dysferlin, and dysferlin clearly proved to be a component of the amyloid deposits. Dysferlin-deficient muscular dystrophy is the first muscular dystrophy in which amyloidosis is involved. This fact must be considered in the process of developing therapeutic strategies. The influence of the amyloid deposits on the pathogenesis of the disease and the possible involvement of other organs in the progressive course are as yet unclear.     

Muscular dystrophy with marked Dysferlin deficiency is consistently caused by primary dysferlin gene mutations

Dysferlin is a 237-kDa transmembrane protein involved in calcium-mediated sarcolemma resealing. Dysferlin gene mutations cause limb-girdle muscular dystrophy (LGMD) 2B, Miyoshi myopathy (MM) and distal myopathy of the anterior tibialis. Considering that a secondary Dysferlin reduction has also been described in other myopathies, our original goal was to identify cases with a Dysferlin deficiency without dysferlin gene mutations. The dysferlin gene is huge, composed of 55 exons that span 233 140 bp of genomic DNA. We performed a thorough mutation analysis in 65 LGMD/MM patients with ≤20% Dysferlin. The screening was exhaustive, as we sequenced both genomic DNA and cDNA. When required, we used other methods, including real-time PCR, long PCR and array CGH. In all patients, we were able to recognize the primary involvement of the dysferlin gene. We identified 38 novel mutation types. Some of these, such as a dysferlin gene duplication, could have been missed by conventional screening strategies. Nonsense-mediated mRNA decay was evident in six cases, in three of which both alleles were only detectable in the genomic DNA but not in the mRNA. Among a wide spectrum of novel gene defects, we found the first example of a ‘nonstop'' mutation causing a dysferlinopathy. This study presents the first direct and conclusive evidence that an amount of Dysferlin ≤20% is pathogenic and always caused by primary dysferlin gene mutations. This demonstrates the high specificity of a marked reduction of Dysferlin on western blot and the value of a comprehensive molecular approach for LGMD2B/MM diagnosis.     

Dysferlin is a plasma membrane protein and is expressed early in human development

Recently, a single gene, DYSF, has been identified which is mutated in patients with limb-girdle muscular dystrophy type 2B (LGMD2B) and with Miyoshi myopathy (MM). This is of interest because these diseases have been considered as two distinct clinical conditions since different muscle groups are the initial targets. Dysferlin, the protein product of the gene, is a novel molecule without homology to any known mammalian protein. We have now raised a monoclonal antibody to dysferlin and report on the expression of this new protein: immunolabelling with the antibody (designated NCL-hamlet) demonstrated a polypeptide of approximately 230 kDa on western blots of skeletal muscle, with localization to the muscle fibre membrane by microscopy at both the light and electron microscopic level. A specific loss of dysferlin labelling was observed in patients with mutations in the LGMD2B/MM gene. Furthermore, patients with two different frameshifting mutations demonstrated very low levels of immunoreactive protein in a manner reminiscent of the dystrophin expressed in many Duchenne patients. Analysis of human fetal tissue showed that dysferlin was expressed at the earliest stages of development examined, at Carnegie stage 15 or 16 (embryonic age 5-6 weeks). Dysferlin is present, therefore, at a time when the limbs start to show regional differentiation. Lack of dysferlin at this critical time may contribute to the pattern of muscle involvement that develops later, with the onset of a muscular dystrophy primarily affecting proximal or distal muscles.     

CD4+ cells,macrophages, MHC-I and C5b-9 involve the pathogenesis of dysferlinopathy

Objective: Dysferlin is a sarcolemmal protein that plays an important role in membrane repair by regulating vesicle fusion with the sarcolemma. Mutations in the dysferlin gene (DYSF) lead to multiple clinical phenotypes, including Miyoshi myopathy (MM), limb girdle muscular dystrophy type 2B (LGMD 2B), and distal myopathy with anterior tibial onset (DMAT). Patients with dysferlinopathy also show muscle inflammation, which often leads to a misdiagnosis as inflammatory myopathy. In this study, we examined and analyzed the dyferlinopathy-associated immunological features. Methods: Comparative immunohistochemical analysis of inflammatory cell infiltration, and muscle expression of MHC-I and C5b-9 was performed using muscle biopsy samples from 14 patients with dysferlinopathy, 7 patients with polymyositis, and 8 patients with either Duchenne muscular dystrophy or Becker muscular dystrophy (DMD/BMD). Results: Immunohistochemical analysis revealed positive staining for immune response-related CD4⁺ cells, macrophages, MHC-I and C5b-9 in dysferlinopathy, which is in a different mode of polymyositis and DMD/BMD. Conclusion: These results demonstrated the involvement of immune factors in the pathogenesis of dysferlinopathy.     

Asymptomatic carriers for homozygous novel mutations in the FKRP gene: the other end of the spectrum

Autosomal recessive limb-girdle muscular dystrophy linked to 19q13.3 (LGMD2I) was recently related to mutations in the fukutin-related protein gene (FKRP) gene. Pathogenic changes in the same gene were detected in congenital muscular dystrophy patients (MDC1C), a severe disorder. We have screened 86 LGMD genealogies to assess the frequency and distribution of mutations in the FKRP gene in Brazilian LGMD patients. We found 13 Brazilian genealogies, including 20 individuals with mutations in the FKRP gene, and identified nine novel pathogenic changes. The commonest C826A European mutation was found in 30% (9/26) of the mutated LGMD2I alleles. One affected patient homozygous for the FKRP (C826A) mutation also carries a missense R125H change in one allele of the caveolin-3 gene (responsible for LGMD1C muscular dystrophy). Two of her normal sibs were found to be double heterozygotes. In two unrelated LGMD2I families, homozygous for novel missense mutations, we identified four asymptomatic carriers, all older than 20 years. Genotype-phenotype correlation studies in the present study as well as in patients from different populations suggests that the spectrum of variability associated with mutations in the FKRP gene seems to be wider than in other forms of LGMD. It also reinforces the observations that pathogenic mutations are not always determinant of an abnormal phenotype, suggesting the possibility of other mechanisms modulating the severity of the phenotype that opens new avenues for therapeutic approaches.     

Seven autosomal recessive limb-girdle muscular dystrophies in the Brazilian population: from LGMD2A to LGMD2G

The autosomal recessive limb-girdle muscular dystrophies (AR-LGMDs) are a heterogeneous group of disorders of progressive weakness of the pelvic and shoulder girdle musculature. The clinical course is characterized by great variability, ranging from severe forms with onset in the first decade and rapid progression resembling clinically Xp21 Duchenne muscular dystrophy (DMD) to milder forms with later onset and slower course. Eight genes are mapped for the AR-LGMDs; they are: LGMD2A (CAPN3) at 15q, LGMD2B (dysferlin) at 2p, LGMD2C (gamma-SG) at 13q, LGMD2D (alpha-SG) at 17q, LGMD2E (beta-SG) at 4q, LGMD2F (6-SG) at 5q, LGMD2G at 17q, and more recently LGMD2H at 9q. The LGMD2F (delta-SG) and LGMD2G genes were mapped in Brazilian AR-LGMD families. Linkage analysis in two unlinked families excluded the eight AR-LGMD genes, indicating that there is at least one more gene responsible for AR-LGMD. We have analyzed 140 patients (from 40 families) affected with one of seven autosomal recessive LGMD loci, that is, from LGMD2A to LGMD2G. The main observations were: 1) all LGMD2E and LGMD2F patients had a severe condition, but considerable inter- and intra-familial clinical variability was observed among patients from all other groups; 2) serum CK activities showed the highest values in LGMD2D (alpha-SG) patients among sarcoglycanopathies and LGMD2B (dysferlin) patients among nonsarcoglycanopathies; 3) comparison between LGMD2A (CAPN3) and LGMD2B (dysferlin) showed that the first have on average a more severe course and have calf hypertrophy more frequently (86% versus 13%); and 4) inability to walk on toes was observed in approximately 70% of LGMD2B patients.     

Myoferlin, a candidate gene and potential modifier of muscular dystrophy

Dysferlin, the gene product of the limb girdle muscular dystrophy (LGMD) 2B locus, encodes a membrane-associated protein with homology to Caenorhabditis elegans fer-1. Humans with mutations in dysferlin ( DYSF ) develop muscle weakness that affects both proximal and distal muscles. Strikingly, the phenotype in LGMD 2B patients is highly variable, but the type of mutation in DYSF cannot explain this phenotypic variability. Through electronic database searching, we identified a protein highly homologous to dysferlin that we have named myoferlin. Myoferlin mRNA was highly expressed in cardiac muscle and to a lesser degree in skeletal muscle. However, antibodies raised to myoferlin showed abundant expression of myoferlin in both cardiac and skeletal muscle. Within the cell, myoferlin was associated with the plasma membrane but, unlike dysferlin, myoferlin was also associated with the nuclear membrane. Ferlin family members contain C2 domains, and these domains play a role in calcium-mediated membrane fusion events. To investigate this, we studied the expression of myoferlin in the mdx mouse, which lacks dystrophin and whose muscles undergo repeated rounds of degeneration and regeneration. We found upregulation of myoferlin at the membrane in mdx skeletal muscle. Thus, myoferlin ( MYOF ) is a candidate gene for muscular dystrophy and cardiomyopathy, or possibly a modifier of the muscular dystrophy phenotype.     

Genomic screening for beta-sarcoglycan gene mutations: missense mutations may cause severe limb-girdle muscular dystrophy type 2E (LGMD 2E)

Autosomal recessive limb-girdle muscular dystrophies (LGMDs) are genetically heterogeneous. A subgroup of these disorders is caused by mutations in the dystrophin-associated sarcoglycan complex. Truncating mutations in the 43 kDa beta-sarcoglycan gene (LGMD 2E) were originally identified in a sporadic case of Duchenne-like muscular dystrophy, and a common missense mutation (T151R) was identified independently in Indiana Amish pedigrees with a milder form of LGMD. To facilitate mutational analysis of larger numbers of patients directly from genomic DNA, as opposed to reverse transcribed RNA from muscle biopsies, we have determined the genomic structure of the beta-sarcoglycan gene. The open reading frame of the beta-sarcoglycan coding region extends over six exons. Primers were designed for PCR amplification of single exons from genomic DNA and subsequent single strand conformation polymorphism (SSCP) analysis. We screened 15 patients from the Brazilian LGMD patient population, 13 of whom followed a severe course. Most of the patients had been assessed previously for deficiency of alpha- sarcoglycan immunofluorescence on muscle biopsy sections as a marker for disease of the sarcoglycan complex. Novel mutations in two familial and two sporadic cases of severe childhood-onset LGMD were identified. Only one of these patients carried a truncating mutation (homozygous 2 bp deletion, FS164TER), while the other three carried missense mutations (homozygous R91P, homozygous M100K, heterozygous recessive L108R; only one allele could be identified in this family). All three missense mutations occurred in exon 3, coding for the immediate extracellular domain. Complete absence for all three of the known sarcoglycans was noted by immunohistochemistry on muscle biopsy sections of the patients.      

Dysferlin deficiency shows compensatory induction of Rab27A/Slp2a that may contribute to inflammatory onset

Mutations in the dysferlin gene cause limb girdle muscular dystrophy 2B (LGMD2B) and Miyoshi myopathy. Dysferlin-deficient cells show abnormalities in vesicular traffic and membrane repair although onset of symptoms is not commonly seen until the late teenage years and is often associated with subacute onset and marked muscle inflammation. To identify molecular networks specific to dysferlin-deficient muscle that might explain disease pathogenesis, muscle mRNA profiles from 10 mutation-positive LGMD2B/MM patients were compared with a disease control [LGMD2I; (n = 9)], and normal muscle samples (n = 11). Query of inflammatory pathways suggested LGMD2B-specific increases in co-stimulatory signaling between dendritic cells and T cells (CD86, CD28, and CTLA4), associated with localized expression of both versican and tenascin. LGMD2B muscle also showed an increase in vesicular trafficking pathway proteins not normally observed in muscle (synaptotagmin-like protein Slp2a/SYTL2 and the small GTPase Rab27A). We propose that Rab27A/Slp2a expression in LGMD2B muscle provides a compensatory vesicular trafficking pathway that is able to repair membrane damage in the absence of dysferlin. However, this same pathway may release endocytotic vesicle contents, resulting in an inflammatory microenvironment. As dysferlin deficiency has been shown to enhance phagocytosis by macrophages, together with our findings of abnormal myofiber endocytosis pathways and dendritic-T cell activation markers, these results suggest a model of immune and inflammatory network over-stimulation that may explain the subacute inflammatory presentation.     

Clinical and pathological characteristics of four Korean patients with limb-girdle muscular dystrophy type 2B

Limb-girdle muscular dystrophy type 2B (LGMD2B), a subtype of autosomal recessive limb-girdle muscular dystrophy (ARLGMD), is characterized by a relatively late onset and slow progressive course. LGMD2B is known to be caused by the loss of the dysferlin protein at sarcolemma in muscle fibers. In this study, the clinical and pathological characteristics of Korean LGMD2B patients were investigated. Seventeen patients with ARLGMD underwent muscle biopsy and the histochemical examination was performed. For the immunocytochemistry, a set of antibodies against dystrophin, alpha, beta, gamma, delta-sarcoglycans, dysferlin, caveolin-3, and beta-dystroglycan was used. Four patients (24%) showed selective loss of immunoreactivity against dysferlin at the sarcolemma on the muscle specimens. Therefore, they were classified into the LGMD2B category. The age at the onset of disease ranged from 9 yr to 33 yr, and none of the patients was wheelchair bound at the neurological examination. The serum creatine kinase (CK) was high in all the patients (4010-5310 IU/L). The pathologic examination showed mild to moderate dystrophic features. These are the first Korean LGMD2B cases with a dysferlin deficiency confirmed by immunocytochemistry. The clinical, pathological, and immunocytochemical findings of the patients with LGMD2B in this study were in accordance with those of other previous reports.     

Identification of mutations in the gene encoding lamins A/C in autosomal dominant limb girdle muscular dystrophy with atrioventricular conduction disturbances (LGMD1B)

LGMD1B is an autosomal dominantly inherited, slowly progressive limb girdle muscular dystrophy, with age-related atrioventricular cardiac conduction disturbances and the absence of early contractures. The disease has been linked to chromosome 1q11-q21. Within this locus another muscular dystrophy, the autosomal dominant form of Emery-Dreifuss muscular dystrophy (AD-EDMD) has recently been mapped and the corresponding gene identified. AD-ADMD is characterized by early contractures of elbows and Achilles tendons and a humero-peroneal distribution of weakness combined with a cardiomyopathy with conduction defects. The disease gene of AD-EDMD is LMNA which encodes lamins A/C, two proteins of the nuclear envelope. In order to identify whether or not LGMD1B and AD-EDMD are allelic disorders, we carried out a search for mutations in the LMNA gene in patients with LGMD1B. For this, PCR/SSCP/sequencing screening was carried out for the 12 exons of LMNA on DNA samples of individuals from three LGMD1B families that were linked to chromo-some 1q11-q21. Mutations were identified in all three LGMD1B families: a missense mutation, a deletion of a codon and a splice donor site mutation, respectively. The three mutations were identified in all affected members of the corresponding families and were absent in 100 unrelated control subjects. The present identification of mutations in the LMNA gene in LGMD1B demonstrates that LGMD1B and AD-EDMD are allelic disorders. Further analysis of phenotype-genotype relationship will help to clarify the variability of the phenotype observed in these two muscular dystrophies.     

Dysferlin deficiency enhances monocyte phagocytosis: a model for the inflammatory onset of limb-girdle muscular dystrophy 2B

Dysferlin deficiency causes limb-girdle muscular dystrophy type 2B (LGMD2B; proximal weakness) and Miyoshi myopathy (distal weakness). Muscle inflammation is often present in dysferlin deficiency, and patients are frequently misdiagnosed as having polymyositis. Because monocytes normally express dysferlin, we hypothesized that monocyte/macrophage dysfunction in dysferlin-deficient patients might contribute to disease onset and progression. We therefore examined phagocytic activity, in the presence and absence of cytokines, in freshly isolated peripheral blood monocytes from LGMD2B patients and in the SJL dysferlin-deficient mouse model. Dysferlin-deficient monocytes showed increased phagocytic activity compared with control cells. siRNA-mediated inhibition of dysferlin expression in the J774 macrophage cell line resulted in significantly enhanced phagocytosis, both at baseline and in response to tumor necrosis factor-alpha. Immunohistochemical analysis revealed positive staining for several mononuclear cell activation markers in LGMD2B human muscle and SJL mouse muscle. SJL muscle showed strong up-regulation of endocytic proteins CIMPR, clathrin, and adaptin-alpha, and LGMD2B muscle exhibited decreased expression of decay accelerating factor, which was not dysferlin-specific. We further showed that expression levels of small Rho family GTPases RhoA, Rac1, and Cdc 42 were increased in dysferlin-deficient murine immune cells compared with control cells. Therefore, we hypothesize that mild myofiber damage in dysferlin-deficient muscle stimulates an inflammatory cascade that may initiate, exacerbate, and possibly perpetuate the underlying myofiber-specific dystrophic process.     

High incidence of 550delA mutation of CAPN3 in LGMD2 patients from Russia

Autosomal recessive limb gird muscular dystrophy (LGMD2) is a clinically and genetically heterogeneous group of diseases that are characterized by progressive atrophy and weakness of the proximal limb muscles. At least eight genetic loci leading to LGMD2 are recognized. The proportion of particular gene involved in producing different forms of LGMD2 shows a marked geographical variation. We studied 19 LGMD2 patients from Russia (15 families) and found calpain 3 (CAPN3) gene mutations in most of the patients studied. Sequence analysis of the fourth exons revealed two sibs - heterozygous compound for a 15-bp deletion (nt598-612) and 550 adenine deletion, and two sibs homozygous for a 550delA. We developed assay based on allele specific amplification (ASA) for rapid screening of the 550delA. The ASA assay of the LGMD2 patients under study showed that 7 patients from 6 families were homozygous for 550delA and 7 patients from 4 families were heterozygous for 550delA. A linkage analysis employing four microsatellites flanking the LGMD2A locus was performed. We found complete haplotype identity in most cases what favors the possibility of a common founder. Heterozygous carriers of 550delA were found in general population. The crude estimate of the mutation frequency is 1/150. Hum Mutat 15:295, 2000.     

Two endoplasmic reticulum-associated degradation (ERAD) systems for the novel variant of the mutant dysferlin: ubiquitin/proteasome ERAD(I) and autophagy/lysosome ERAD(II)

Dysferlin is a type-II transmembrane protein and the causative gene of limb girdle muscular dystrophy type 2B and Miyoshi myopathy (LGMD2B/MM), in which specific loss of dysferlin labeling has been frequently observed. Recently, a novel mutant (L1341P) dysferlin has been shown to aggregate in the muscle of the patient. Little is known about the relationship between degradation of dysferlin and pathogenesis of LGMD2B/MM. Here, we examined the degradation of normal and mutant (L1341P) dysferlin. Wild-type (wt) dysferlin mainly localized to the ER/Golgi, associated with retrotranslocon, Sec61alpha, and VCP(p97), and was degraded by endoplasmic reticulum (ER)-associated degradation system (ERAD) composed of ubiquitin/proteasome. In contrast, mutant dysferlin spontaneously aggregated in the ER and induced eukaryotic translation initiation factor 2alpha (eIF2alpha) phosphorylation and LC3 conversion, a key step for autophagosome formation, and finally, ER stress cell death. Unlike proteasome inhibitor, E64d/pepstatin A, inhibitors of lysosomal proteases did not stimulate the accumulation of the wt-dysferlin, but stimulated aggregation of mutant dysferlin in the ER. Furthermore, deficiency of Atg5 and dephosphorylation of eIF2alpha, key molecules for LC3 conversion, also stimulated the mutant dysferlin aggregation in the ER. Rapamycin, which induces eIF2alpha phosphorylation-mediated LC3 conversion, inhibited mutant dysferlin aggregation in the ER. Thus, mutant dysferlin aggregates in the ER-stimulated autophagosome formation to engulf them via activation of ER stress-eIF2alpha phosphorylation pathway. We propose two ERAD models for dysferlin degradation, ubiquitin/proteasome ERAD(I) and autophagy/lysosome ERAD(II). Mutant dysferlin aggregates on the ER are degraded by the autophagy/lysosome ERAD(II), as an alternative to ERAD(I), when retrotranslocon/ERAD(I) system is impaired by these mutant aggregates.     

Molecular and muscle pathology in a series of caveolinopathy patients

Mutations in the caveolin-3 gene (CAV3) cause limb girdle muscular dystrophy (LGMD) type 1C (LGMD1C) and other muscle phenotypes. We screened 663 patients with various phenotypes of unknown etiology, for caveolin-3 protein deficiency, and we identified eight unreported caveolin-deficient patients (from seven families) in whom four CAV3 mutations had been detected (two are unreported). Following our wide screening, we estimated that caveolinopathies are 1% of both unclassified LGMD and other phenotypes, and demonstrated that caveolin-3 protein deficiency is a highly sensitive and specific marker of primary caveolinopathy. This is the largest series of caveolinopathy families in whom the effect of gene mutations has been analyzed for protein level and phenotype. We showed that the same mutation could lead to heterogeneous clinical phenotypes and muscle histopathological changes. To study the role of the Golgi complex in the pathological pathway of misfolded caveolin-3 oligomers, we performed a histopathological study on muscle biopsies from caveolinopathy patients. We documented normal caveolin-3 immunolabeling at the plasmalemma in some regenerating fibers showing a proliferation of the Golgi complex. It is likely that caveolin-3 overexpression occurring in regenerating fibers (compared with caveolin-deficient adult fibers) may lead to an accumulation of misfolded oligomers in the Golgi and to its consequent proliferation.     

Identification of lamin A/C ( LMNA) gene mutations in Korean patients with autosomal dominant Emery-Dreifuss muscular dystrophy and limb-girdle muscular dystrophy 1B

Mutations in the LMNA gene encoding lamins A and C by alternative splicing have been found to cause at least four different kinds of genetic disorders: autosomal dominant Emery-Dreifuss muscular dystrophy (EDMD2; MIM 181350); limb-girdle muscular dystrophy type 1B (LGMD1B; MIM 159001); dilated cardiomyopathy type 1A (CMD1A; MIM 115200); and familial partial lipodystrophy (FPLD; MIM 151660). Recently, we have studied two Korean patients with atrioventricular conduction defects. They had variable extents of muscular dystrophy; one patient was diagnosed with EDMD2 and the other with LGMD1B. We performed a mutation analysis of the LMNA gene by direct sequencing and found two different missense mutations: R249Q and R377L, in the EDMD2 and LGMD1B patient, respectively. The R249Q mutation is located within the central rod domain of the LMNA gene, and has been described in at least five unrelated sporadic EDMD2 patients. On the other hand, the R377L mutation, also located within the rod domain, is a novel mutation, although a histidine substitution instead of leucine (R377H) has been reported previously in an LGMD1B patient. To our knowledge, this is the first report of LMNA gene mutations in Korean patients with EDMD2 and LGMD1B. Received: November 19, 2001 / Accepted: February 8, 2002     

Disruption of muscle membrane and phenotype divergence in two novel mouse models of dysferlin deficiency

Limb girdle muscular dystrophy type 2B and Miyoshi myopathy are clinically distinct forms of muscular dystrophy that arise from defects in the dysferlin gene. Here, we report two novel lines of dysferlin-deficient mice obtained by (a) gene targeting and (b) identification of an inbred strain, A/J, bearing a retrotransposon insertion in the dysferlin gene. The mutations in these mice were located at the 3' and 5' ends of the dysferlin gene. Both lines of mice lacked dysferlin and developed a progressive muscular dystrophy with histopathological and ultrastructural features that closely resemble the human disease. Vital staining with Evans blue dye revealed loss of sarcolemmal integrity in both lines of mice, similar to that seen in mdx and caveolin-3 deficient mice. However, in contrast to the latter group of animals, the dysferlin-deficient mice have an intact dystrophin glycoprotein complex and normal levels of caveolin-3. Our findings indicate that muscle membrane disruption and myofiber degeneration in dysferlinopathy were directly mediated by the loss of dysferlin via a new pathogenic mechanism in muscular dystrophies. We also show that the mutation in the A/J mice arose between the late 1970s and the early 1980s, and had become fixed in the production breeding stocks. Therefore, all studies involving the A/J mice or mice derived from A/J, including recombinant inbred, recombinant congenic and chromosome substitution strains, should take into account the dysferlin defect in these strains. These new dysferlin-deficient mice should be useful for elucidating the pathogenic pathway in dysferlinopathy and for developing therapeutic strategies.