miR-379 links glucocorticoid treatment with mitochondrial response in Duchenne muscular dystrophy.

Duchenne Muscular Dystrophy (DMD) is a lethal muscle disorder, caused by mutations in the DMD gene and affects approximately 1:5000-6000 male births. In this report, we identified dysregulation of members of the Dlk1-Dio3 miRNA cluster in muscle biopsies of the GRMD dog model. Of these, we selected miR-379 for a detailed investigation because its expression is high in the muscle, and is known to be responsive to glucocorticoid, a class of anti-inflammatory drugs commonly used in DMD patients. Bioinformatics analysis predicts that miR-379 targets EIF4G2, a translational factor, which is involved in the control of mitochondrial metabolic maturation. We confirmed in myoblasts that EIF4G2 is a direct target of miR-379, and identified the DAPIT mitochondrial protein as a translational target of EIF4G2. Knocking down DAPIT in skeletal myotubes resulted in reduced ATP synthesis and myogenic differentiation. We also demonstrated that this pathway is GC-responsive since treating mice with dexamethasone resulted in reduced muscle expression of miR-379 and increased expression of EIF4G2 and DAPIT. Furthermore, miR-379 seric level, which is also elevated in the plasma of DMD patients in comparison with age-matched controls, is reduced by GC treatment. Thus, this newly identified pathway may link GC treatment to a mitochondrial response in DMD.

Genomic organization of the dysferlin gene and novel mutations in Miyoshi myopathy.

OBJECTIVE: Mutations in the skeletal muscle gene dysferlin cause two autosomal recessive forms of muscular dystrophy: Miyoshi myopathy (MM) and limb girdle muscular dystrophy type 2B (LGMD2B). The purpose of this study was to define the genomic organization of the dysferlin gene and conduct mutational screening and a survey of clinical features in 21 patients with defined molecular defects in the dysferlin gene. METHODS: Genomic organization of the gene was determined by comparing the dysferlin cDNA and genomic sequence in P1-derived artificial chromosomes (PACs) containing the gene. Mutational screening entailed conformational analysis and sequencing of genomic DNA and cDNA. Clinical records of patients with defined dysferlin gene defects were reviewed retrospectively. RESULTS: The dysferlin gene encompasses 55 exons spanning over 150 kb of genomic DNA. Mutational screening revealed nine novel mutations associated with MM. The range of onset in this patient group was narrow with a mean of 19.0 +/- 3.9 years. CONCLUSION: This study confirms that the dysferlin gene is mutated in MM and LGMD2B and extends understanding of the timing of onset of the disease. Knowledge of the genomic organization of the gene will facilitate mutation detection and investigations of the molecular biologic properties of the dysferlin gene.

Loss of calpain 3 proteolytic activity leads to muscular dystrophy and to apoptosis-associated IkappaBalpha/nuclear factor kappaB pathway perturbation in mice.

Calpain 3 is known as the skeletal muscle-specific member of the calpains, a family of intracellular nonlysosomal cysteine proteases. It was previously shown that defects in the human calpain 3 gene are responsible for limb girdle muscular dystrophy type 2A (LGMD2A), an inherited disease affecting predominantly the proximal limb muscles. To better understand the function of calpain 3 and the pathophysiological mechanisms of LGMD2A and also to develop an adequate model for therapy research, we generated capn3-deficient mice by gene targeting. capn3-deficient mice are fully fertile and viable. Allele transmission in intercross progeny demonstrated a statistically significant departure from Mendel's law. capn3-deficient mice show a mild progressive muscular dystrophy that affects a specific group of muscles. The age of appearance of myopathic features varies with the genetic background, suggesting the involvement of modifier genes. Affected muscles manifest a similar apoptosis-associated perturbation of the IkappaBalpha/nuclear factor kappaB pathway as seen in LGMD2A patients. In addition, Evans blue staining of muscle fibers reveals that the pathological process due to calpain 3 deficiency is associated with membrane alterations.

A diagnostic fluorescent marker kit for six limb girdle muscular dystrophies.

The autosomal progressive muscular dystrophies which are grouped together under the term limb girdle muscular dystrophies (LGMD) are diseases characterized by a progressive impairment of the proximal limb muscles and myopathic changes on electromyogram and muscle biopsy. Eight independent purely recessive genetic entities have been recognized in this group of diseases by genetic localization or causative gene identification. We have developed fluorescent genetic markers bracketing six of these loci (LGMD2A-LGMD2F). The marker loci were genotyped in 96 LGMD2 families leading to genetic definition of 25 of them either with a high likelihood or with a suggested localization (7 LGMD2A, 5 LGMD2B, 4 LGMD2C, 4 LGMD2D, 2 LGMD2E and 3 LGMD2F). In addition, 18 families were excluded for all six tested loci; for 45 of the 53 remaining families at least one exclusion could be demonstrated. This kit, which makes the rapid genetic testing of LGMD2 families possible, may be useful in a diagnostic process.

A gene related to Caenorhabditis elegans spermatogenesis factor fer-1 is mutated in limb-girdle muscular dystrophy type 2B.

The limb-girdle muscular dystrophies are a genetically heterogeneous group of inherited progressive muscle disorders that affect mainly the proximal musculature, with evidence for at least three autosomal dominant and eight autosomal recessive loci. The latter mostly involve mutations in genes encoding components of the dystrophin-associated complex; another form is caused by mutations in the gene for the muscle-specific protease calpain 3. Using a positional cloning approach, we have identified the gene for a form of limb-girdle muscular dystrophy that we previously mapped to chromosome 2p13 (LGMD2B). This gene shows no homology to any known mammalian gene, but its predicted product is related to the C. elegans spermatogenesis factor fer-1. We have identified two homozygous frameshift mutations in this gene, resulting in muscular dystrophy of either proximal or distal onset in nine families. The proposed name 'dysferlin' combines the role of the gene in producing muscular dystrophy with its C. elegans homology.

Beta-sarcoglycan: genomic analysis and identification of a novel missense mutation in the LGMD2E Amish isolate.

The sarcoglycan complex is involved in the etiology of four autosomal recessive limb-girdle muscular dystrophies (LGMD2C-F). A missense mutation (T151R) in the beta-sarcoglycan gene on chromosome 4q12 has been shown to cause a mild form of LGMD2E in 11 families from a Southern Indiana Amish community sharing a common haplotype. We now report that two sibs from another Amish family with mild LGMD2E are compound heterozygotes for chromosome 4q12 markers. In order to characterize the genetic defect in this new family, we determined the genomic organization of the beta-sarcoglycan gene. A second missense mutation (R91C) has now been identified in this LGMD2E Amish family. This mutation is also present in the homozygous state in another family of probable Amish ancestry. Finally, analysis of all the components of the dystrophin-glycoprotein complex was performed for the first time on a biopsy from a patient homozygous for the beta-sarcoglycan mutation (T151R). Interestingly, in addition to the loss of the entire sarcoglycan complex, we detected a reduction of alpha-dystroglycan which suggests a role for the sarcoglycan complex in stabilizing alpha-dystroglycan at the sarcolemma.

Identification of muscle-specific calpain and beta-sarcoglycan genes in progressive autosomal recessive muscular dystrophies.

The autosomal recessive forms of limb-girdle muscular dystrophies are encoded by at least five distinct genes. The work performed towards the identification of two of these is summarized in this report. This success illustrates the growing importance of genetics in modern nosology.

Beta-sarcoglycan: characterization and role in limb-girdle muscular dystrophy linked to 4q12.

beta-Sarcoglycan, a 43 kDa dystrophin-associated glycoprotein, is an integral component of the dystrophin-glycoprotein complex. We have cloned human beta-sarcoglycan cDNA and mapped the beta-sarcoglycan gene to chromosome 4q12. Pericentromeric markers and an intragenic polymorphic CA repeat cosegregated perfectly with autosomal recessive limb-girdle muscular dystrophy in several Amish families. A Thr-to-Arg missense mutation was identified within the beta-sarcoglycan gene that leads to a dramatically reduced expression of beta-sarcoglycan in the sarcolemma and a concomitant loss of adhalin and 35 DAG, which may represent a disruption of a functional subcomplex within the dystrophin-glycoprotein complex. Thus, the beta-sarcoglycan gene is the fifth locus identified (LGMD2E) that is involved in autosomal recessive limb-girdle muscular dystrophy.

Preferential localization of the limb-girdle muscular dystrophy type 2A gene in the proximal part of a 1-cM 15q15.1-q15.3 interval.

A gene for a recessive form of limb-girdle muscular dystrophy (LGMD2A) has been localized to chromosome 15. A physical map of the 7-cM candidate 15q15.1-q21.1 region has been constructed by means of a 10-12-Mb continuum of overlapping YAC clones. New microsatellite markers developed from these YACs were genotyped on large, consanguineous LGMD2A pedigrees from different origins. The identification of recombination events in these families allowed the restriction of the LGMD2A region to an estimated 1-cM interval, equivalent to approximately 3-4 Mb. Linkage disequilibrium data on genetic isolates from the island of Réunion and from the Amish community suggest a preferential location of the LGMD2A gene in the proximal part of this region. Analysis of the interrelated pedigrees from Réunion revealed the existence of at least six different carrier haplotypes. This allelic heterogeneity is incompatible with the presumed existence of a founder effect and suggests that multiple LGMD2A mutations may segregate in this population.

Mutations in the proteolytic enzyme calpain 3 cause limb-girdle muscular dystrophy type 2A.

Limb-girdle muscular dystrophies (LGMDs) are a group of inherited diseases whose genetic etiology has yet to be elucidated. The autosomal recessive forms (LGMD2) constitute a genetically heterogeneous group with LGMD2A mapping to chromosome 15q15.1-q21.1. The gene encoding the muscle-specific calcium-activated neutral protease 3 (CANP3) large subunit is located in this region. This cysteine protease belongs to the family of intracellular calpains. Fifteen nonsense, splice site, frameshift, or missense calpain mutations cosegregate with the disease in LGMD2A families, six of which were found within La Réunion island patients. A digenic inheritance model is proposed to account for the unexpected presence of multiple independent mutations in this small inbred population. Finally, these results demonstrate an enzymatic rather than a structural protein defect causing a muscular dystrophy, a defect that may have regulatory consequences, perhaps in signal transduction.

Genetic heterogeneity of autosomal recessive limb-girdle muscular dystrophy in a genetic isolate (Amish) and evidence for a new locus.

Limb-girdle muscular dystrophy (LGMD) is a hereditary myopathy presenting clinical and genetic heterogeneity. In 1991, a recessive form (LGMD2A) was linked to chromosome 15q in a genetic isolate from the Isle of La Réunion. Confirmation of this localization was subsequently reported in Brazilian and northern Indiana Amish pedigrees. Here we report the exclusion of the LGMD2A locus in six Amish kindreds from southern Indiana that are related by multiple consanguineous links to the same northern Indiana families in which the involvement of the chromosome 15 locus was previously demonstrated. These findings indicate unexpected genetic heterogeneity of LGMD in an Indiana Amish isolate. Furthermore, genetic analyses also ruled out the possible involvement of the chromosome 2 locus recently described (LGMD2B), thus demonstrating that a mutation within at least one additional locus leads to this condition. Several candidate genes putatively involved in neuromuscular disorders were also excluded.

Regional localization of human chromosome 15 loci.

One hundred forty-nine chromosome 15 loci were mapped by PCR with respect to chromosome breakpoints in three somatic cell hybrids retaining total or part of chromosome 15 and to a 10-Mb YAC contig. This chromosome was subdivided into 5 regions, yielding an average resolution of more than 1 sequence tagged site per megabase. The mapped loci included 18 genes, 60 cDNA-derived sequence tagged sites, and 69 microsatellites. In addition, the amount of chromosome 15 retained in line A15.1 has been defined. This work represents the first attempt at an integration of the human physical, expression, and genetic maps of chromosome 15.

Mapping of a chromosome 15 region involved in limb girdle muscular dystrophy.

A gene responsible for an autosomal recessive form of limb girdle muscular dystrophy (LGMD2, MIM number 253600) has been localized on chromosome 15. After genotyping additional markers of this chromosome, two were found to flank the disease locus within an interval that was assessed as 7 centiMorgans. The screening of the CEPH YAC libraries with the corresponding probes allowed the isolation of YACs which were used in fluorescence in situ hybridization to define the LGMD2 cytogenetic interval as 15q15.1-15q21.1. Four different approaches were pursued for the establishment of the physical map of this area which allowed the assembly of an uninterrupted YAC contig spanning an estimated 10-12 megabases, with an average STS resolution of 140 kb or for the 25 polymorphic microsatellites on this map, of 400 kb. Twelve genes and 25 genetic markers were positioned in this contig, which is constituted of a minimum of 10 clones.

Flow characteristics in single and sequential aorto-coronary by-pass grafts.

Thirty five patients, operated upon with an aorto-coronary by-pass graft to left anterior descending artery and to a major diagonal branch, were prospectively analysed. The patients were divided into two comparable groups, in whom a single graft technique and a sequential graft technique was used respectively. Flows through the by-passes were measured electromagnetically during the operation. Flow to left anterior descending artery was significantly higher through an isolated by-pass than through a sequential by-pass. Flow to diagonal branch showed no significant difference in the two groups. The resistance of the intramyocardial coronary bed of the left anterior descending artery was lower with single than with sequential by-pass technique, while no difference existed between the resistance of intramyocardial coronary bed of the diagonal branch with both techniques. Blood velocity was higher in single by-pass to the left anterior descending artery than in the peripheral segment of sequential vein graft directed to the anterior descending artery.