Search

Aims: To increase our understanding of profibrotic mechanisms in dystrophic muscle., Methods and Results: Extracellular matrix, fibrosis-related molecules and histopathology were assessed in skeletal muscle of patients with Duchenne muscular dystrophy (DMD), Becker muscular dystrophy (BMD), and congenital muscular dystrophy type 1A (MDC1A).Osteopontin expression was much higher in DMD and MDC1A than in BMD and control muscle. Osteopontin was expressed in mononuclear cell infiltrates, on some muscle fibre surfaces, in regenerating fibres, and in calcified fibres. In all pathological muscles, matrix metalloproteinase (MMP)-1 was increased around groups of fibres that were also characterized by absence of collagen 1. The amounts of MMP-2, MMP-9 and tissue inhibitor of MMP -1 transcripts were also increased, whereas their proteins were variably expressed in muscle fibres (surface or cytoplasm) and at foci of necrosis and regeneration. Inflammatory cells, fibroblasts and myofibroblasts were more numerous in DMD and MDC1A than in BMD muscle., Conclusions: Several fibrosis-related factors are greatly altered in severely dystrophic skeletal muscle. Osteopontin was the most conspicuously upregulated, both as transcript and as protein, in muscle fibres and infiltrating cells, indicating an intimate involvement in fibrosis, and also in inflammation and muscle regeneration, although its precise roles in these processes remain to be elucidated., (© 2011 Blackwell Publishing Limited.)

Merosin-deficient congenital muscular dystrophy (MD) type 1A (MDC1A) is one of the most frequent forms of CMD in Western countries. The classical form, characterized by a total lack of laminin alpha2 chain expression, usually shows severe clinical features; cases with complete laminin alpha2 deficiency and mild phenotype have also been reported, although the mechanisms underlying the lack of genotype-phenotype correlation have not been elucidated. Epilepsy and focal cortical dysplasia-in addition to the classical diffuse white matter abnormalities-have been described in some of these patients associated with cognitive deterioration. We report on a patient with total laminin alpha2 deficiency due to a homozygous stop-codon mutation in the LAMA2 gene, with mild evolution. When 6.9 years old, she developed focal occipital seizures and absence-like status when awake, with probable relation to an extensive bilateral occipital micropolygyria. Soon afterwards she lost ambulation and developed cognitive deterioration. Our case confirms that the clinical spectrum of MDC1A is more heterogeneous than previously thought.

Clinical features and molecular data are described for a patient with undetectable expression of laminin alpha2 chain (merosin) and severe congenital muscular dystrophy. Molecular analysis of the LAMA2 gene revealed two previously un-described mutations. The patient achieved independent sitting at age 2, but lost head balance at age 7; he was never able to stand unsupported. Cerebral magnetic resonance imaging revealed diffuse hypomyelination in both cerebral hemispheres; electrophysiological assessment revealed progressive sensorimotor axonal polyneuropathy. Investigation of the primary molecular defect in congenital muscular dystrophy patients is important for genetic counseling, because the clinical features of the various forms overlap, and because significant laminin alpha2 chain reduction may occur in patients with primary defects in other genes.

Biglycan and decorin are small extracellular proteoglycans that interact with cytokines, whose activity they may modulate, and with matrix proteins, particularly collagens. To better understand their role in muscle fibrosis, we investigated expression of decorin and biglycan transcripts and protein in muscle of several forms of muscular dystrophy, and also expression of perlecan, an extracellular proteoglycan unrelated to collagen deposition. In Duchenne muscular dystrophy (DMD) and LAMA2-mutated congenital muscular dystrophy (MDC1A) we also quantitated transcript levels of the profibrotic cytokine TGF-beta1. We examined muscle biopsies from nine DMD patients, aged 2-8 years; 14 BMD (Becker muscular dystrophy) patients (nine aged 1-5 years; five aged 30-37 years); four MDC1A patients (aged 2-7 years); six dysferlin-deficient patients (aged 19-53 years) with mutation ascertained in two, and normal expression of proteins related to limb girdle muscular dystrophies in the others; 10 sarcoglycan-deficient patients: seven with alpha-sarcoglycan mutation, two with beta-sarcoglycan mutation and one with gamma-sarcoglycan mutation (five aged 8-15 years; five aged 26-43 years); and nine children (aged 1-6 years) and 12 adults (aged 16-61 years) suspected of neuromuscular disease, but who had normal muscle on biopsy. Biglycan mRNA levels varied in DMD and MDC1A depending on the quantitation method, but were upregulated in BMD, sarcoglycanopathies and dysferlinopathy. Decorin mRNA was significantly downregulated in DMD and MDC1A, whereas TGF-beta1 was significantly upregulated. Decorin mRNA was normal in paediatric BMD, but upregulated in adult BMD, sarcoglycanopathies and dysferlinopathy. Perlecan transcript levels were similar to those of age-matched controls in all disease groups. By immunohistochemistry, decorin and biglycan were mainly localized in muscle connective tissue; their presence increased in relation to increased fibrosis in all dystrophic muscle. By visual inspection, decorin bands on immunoblot did not differ from those of age-matched controls in all patient groups. However, when the intensity of the bands was quantitated against vimentin and normalized against sarcomeric actin, in DMD and MDC1A the ratio of band intensities was significantly lower than in age-matched controls. Variations in the transcript and protein levels of these proteoglycans in different muscular dystrophies probably reflect the variable disruption of extracellular matrix organization that occurs in these diseases. The significantly lowered decorin levels in DMD and MDC1A may be related to the increased TGF-beta1 levels, suggesting a therapeutic role of decorin in these severe dystrophies.

Objective: To determine if laminin-alpha2 deficiency is due to mutations in the LAMA2 gene or secondary to mutations in other congenital muscular dystrophy genes., Methods: We performed molecular analysis of LAMA2, by single-strand conformation polymorphism and sequencing, in 15 patients with undetectable or greatly reduced laminin-alpha2 expression. We also performed 4 prenatal diagnoses and investigated a founder effect., Results: We found 1 known and 9 previously undescribed LAMA2 mutations spanning all protein domains. These were nonsense or frameshifts causing laminin-alpha2 absence or, in 1 case, a homozygous missense mutation producing partial protein expression and milder phenotype. LAMA2 mutations were undetected in 5 patients, in 2 of whom FKRP mutations explained the phenotype. In 3 prenatal cases, the fetus was heterozygous for the mutation of interest and pregnancy continued; in 1 case, the fetus was affected and aborted. In 2 patients, the Cys967Stop mutation and identical haplotypes flanking the LAMA2 gene indicated a founder effect., Conclusions: The clinical phenotype was severe in most patients with LAMA2 mutations and associated with undetectable protein expression. One case with no protein and another with partial expression had milder phenotypes. Typical white matter alterations on magnetic resonance imaging were found in all patients with LAMA2 mutations, supporting the utility of magnetic resonance imaging in differential diagnosis. The founder mutation (Cys967Stop) probably originated in Albania. Genetic characterization of affected families is mainly of use for prenatal diagnosis.

We describe a second large Italian kindred with autosomal dominant vacuolar myopathy characterized by variable severity, adult-onset weakness of distal limb muscles, and no cardiac involvement. At least 19 individuals over four generations are affected. Histopathological and immunochemical features of the vacuoles, present in many fibers, indicate protein degradation abnormalities with dysregulation of the lysosomal pathway and activation of the ubiquitin-proteasomal pathway. Linkage analysis localized the defect to the 19p13.3 locus in a region with no known genes. We speculate that the primary defect may be an abnormality in the lysosomal degradation pathway or related components.

Nonsense mutations outside the splicing consensus sequence have been reported to cause skipping of the nonsense-containing exon in several human diseases. We describe, for the first time, nonsense-mediated exon skipping in the laminin alpha2 (LAMA2) gene. Two siblings from a consanguineous family had altered expression of the laminin alpha2 chain and moderate clinical manifestations. In both we identified the new nonsense mutation Arg744Stop, which we expected to result in a totally non-functional polypeptide. However, analysis of the transcript revealed skipping of exon 15, containing the mutation, even though the consensus sequences for splicing at both ends of the exon and the beginning of intron 15 were unaltered. Exon skipping restored the open reading frame of the mutant transcript and resulted in a truncated protein. In cases where the genetic findings do not elucidate the phenotype, mRNA analysis is necessary to clarify the primary effect of mutations. Our findings also point to the necessity of immunochemical screening for expression of laminin alpha2 chain in atypical dystrophic adults as well as children.

Two young males with limb-girdle muscular dystrophy (LGMD) resulting from sarcoglycan deficiency died at 27 (patient 1) and 18 years (patient 2) of severe cardiomyopathy. Genetic analysis showed that they were compound heterozygotes for mutations in the beta sarcoglycan gene. One of these mutations, an 8 bp duplication in exon 3, was common to both patients. The second mutation in patient 2 was a 4 bp deletion at the splice donor site of intron 2, not reported previously. Patient 2 had more severe heart and skeletal muscle defects with faster deterioration; no sarcoglycans were detected in his skeletal muscle. The second mutation in patient 1, inferred because the unaffected father carries the 8 bp duplication, was not found. In patient 1, both heart and skeletal muscle were analysed and showed reduction of all sarcoglycans in both tissues and incorrect localisation of alpha and gamma sarcoglycans in heart. Therefore mutations in one sarcoglycan gene can disrupt the entire sarcoglycan complex in both skeletal and cardiac muscle. Differing expression patterns of sarcoglycan components in heart and skeletal muscle could be the result of alternatively spliced transcripts in these tissues. By sequencing an alternative transcript, highly expressed in the heart and skeletal muscle of patient 1, we found an 87 bp cryptic exon not previously reported. Although cardiomyopathy can result from mutations in alpha and gamma sarcoglycans, we show for the first time that the condition can also be caused by mutations in the beta sarcoglycan gene. This report therefore expands the phenotype of sarcoglycanopathies and suggests that cardiac function in LGMD patients with defective sarcoglycan expression should be monitored.

We evaluated transforming growth factor-beta1 (TGF-beta1) expression in the muscle of four laminin alpha2-negative, four laminin alpha2-positive and seven partial laminin alpha2-deficient congenital muscular dystrophy (CMD) patients, and compared it to Duchenne muscular dystrophy (DMD) patients and controls. TGF-beta1 mRNA levels in skeletal muscle from laminin alpha2-negative and laminin alpha2-positive CMD patients were significantly greater than in controls (P < 0.05 and P < 0.005, respectively), while in partial laminin alpha2-deficient muscular dystrophy patients the amount was not significantly higher than in controls (P > 0.1). The TGF-beta1 values were lower than those found in DMD, although the extent of fibrosis was greater in CMD than in DMD and controls. Our findings suggest that TGF-beta1 is involved in CMD muscle fibrosis, but differently from what we observed in DMD muscles as it seems not to be the major player in connective tissue proliferation.

Emery-Dreifuss muscular dystrophy (EDMD) is an X-linked inherited disease characterized by early contracture of the elbows, Achilles tendons and post-cervical muscles, slow progressive muscle wasting and weakness and cardiomyopathy presenting with arrhythmia and atrial paralysis: heart block can eventually lead to sudden death. The EDMD geneencodes a novel ubiquitous protein, emerin, which decorates the nuclear rim of many cell types. Amino acid sequence homology and cellular localization suggested that emerin is a member of the nuclear lamina-associated protein family. These findings did not explain the role of emerin nor account for the skeletal muscle- and heart-specific clinical manifestations associated with the disorder. Now we report that emerin localizes to the inner nuclear membrane, via its hydrophobic C-terminal domain, but that in heart and cultured cardiomyocytes it is also associated with the intercalated discs. We propose a general role for emerin in membrane anchorage to the cytoskeleton. In the nuclear envelope emerin plays a ubiquitous and dispensable role in association of the nuclear membrane with the lamina. In heart its specific localization to desmosomes and fasciae adherentes could account for the characteristic conduction defects described in patients.

We have raised an anti-emerin polyclonal antibody against a fusion protein encompassing most of the hydrophilic portion of emerin. Using this antibody, we have analyzed emerin expression in Emery-Dreifuss muscular dystrophy (EDMD) patients and controls, by immunocytochemistry, in skeletal muscle and skin, and by immunoblot, in peripheral blood mononuclear cells and lymphoblasts. Emerin was localized on the surfaces of nuclei in control skeletal muscle and skin but was absent or reduced in patient skeletal muscle, was absent from the skin of patients, and was expressed only in a few nuclei in a patient's mother. Immunoblot of peripheral blood cells from EDMD patients showed absence of the emerin band, altered-size emerin, or a protein of normal molecular mass but slightly reduced quantity. The diagnosis of X-linked EDMD is normally confirmed by genetic analysis of the STA gene coding for emerin. We propose immunocytochemical evaluation of emerin expression in skin biopsies as a sensitive and more convenient tool for diagnosing X-linked EDMD and, in particular, for distinguishing it from the autosomal dominant form. This technique may be applied to suspected EDMD patients, especially sporadic cases or those with incomplete clinical phenotype, and also suspected carriers. Immunoblot of peripheral blood cells is also useful, but it may not unequivocally identify carriers and some patients.

The absence of dystrophin in muscle fibers is associated with a major reduction in dystrophin-associated proteins (DAPs) and disruption of the linkage between the subsarcolemmal cytoskeleton and the extracellular matrix. We investigated the expression of the DAPs beta-dystroglycan, alpha-sarcoglycan, gamma-sarcoglycan and syntrophin as well as utrophin in the muscles of 13 Duchenne muscular dystrophy (DMD) carriers (with variable percentages of dystrophin-deficient fibers and with a range of clinical symptoms), 2 Becker muscular dystrophy (BMD) carriers (expressing a highly truncated protein in some fibers), 2 girls with a DMD-like phenotype, and 11 BMD carriers with almost normal dystrophin expression (reduced or patchy distribution in a few fibers only and rare dystrophin-deficient fibers). DAPs were highly reduced in all fibers lacking dystrophin in the DMD carriers, but were almost normal in the dystrophin-deficient fibers of the 2 BMD carriers with highly truncated dystrophin. In the 11 BMD carriers with nearly normal dystrophin, the few fibers with reduced or patchy dystrophin immunostaining also showed reduced DAP expression in correlation with dystrophin expression. Immunoblot for beta-dystroglycan and alpha-sarcoglycan confirmed the immunohistochemical findings. Utrophin expression was slightly increased in a proportion of fibers in the DMD and BMD carriers with dystrophin mosaicism. We found no correlation between utrophin expression and DAP expression. We conclude that absence or reduction of dystrophin in muscle fibers of DMD and BMD carriers causes a reduction of DAPs in the same fibers, as observed in DMD and BMD patients, while utrophin does not seem to play a role in DAP expression in adult muscle.

We report adhalin deficiency in 8 patients with clinically diagnosed muscular dystrophy, dystrophic histopathological features, high plasma creatine kinase levels, normal expression of dystrophin, and marked variability of symptoms. Although the distribution of hyposthenia was similar in all 8 patients and predominantly involved muscles in the pelvic girdle, age at onset and rate of disease progression were highly variable: In 2 patients onset, at ages 24 and 25, was later than has been previously observed. We found no apparent relation between disease severity and the quantity of adhalin expressed. Two kinds of myopathy with adhalin deficiency have been reported: one caused by a mutation in the adhalin gene on chromosome 17 (primary adhalinopathy) and the other linked to chromosome 13. The product of the gene on chromosome 13 is probably associated with adhalin and its deficiency results in secondary adhalinopathy. The severity of clinical phenotypes in these adhalinopathies seems to relate more to the kind and site of the mutations than to the residual amount of the protein. We also detected a variable reduction in the laminin beta 1 subunit by immunohistochemistry in most patients, confirming that this is commonly associated with adhalin deficiency.

We report on a family with a boy affected by Duchenne muscular dystrophy (DMD) and an asymptomatic cousin with a Becker-type dystrophin abnormality, diagnosed by chance. Dystrophin gene analysis showed that these conditions were caused by two distinct deletions with breakpoints in different exons. In Xp21 families, DNA analysis and dystrophin testing of asymptomatic males with high CK plasma levels might detect different dystrophin mutations in separate haplotypes as in our family, although we stress there should be clear clinical or familial indications for such testing.

We have investigated protein expression and genotype in 59 Becker muscular dystrophy (BMD) patients. The aim was to identify possible causes of the marked variability in phenotype in patients with similar deletions/mutations. The patients were examined neurologically and functionally and underwent Manual Muscle Testing. Dystrophin expression was analysed by immunohistochemistry and western blot using antibodies against six different segments of the protein. DNA mutations were investigated by PCR amplification of 30 exons. Based on dystrophin expression at the sarcolemma, two groups of patients were identified: group A (29 patients) with the classic patchy distribution of dystrophin and group B (30 patients) with absence or reduction of one or more dystrophin portions and variable, although mostly normal, expression of the other portions of the protein. Dystrophin molecular weight was normal or slightly reduced in group A and was variably reduced, generally conspicuously so, in group B. The quantity of dystrophin expressed varied markedly in both groups. The pattern of immunohistochemical staining in group B patients correlated with milder clinical phenotype, suggesting that small dystrophin molecules lacking a portion in the N-terminus or in the rod domain, are more functional than proteins with normal or slightly reduced molecular weight that display the BMD-typical patchy distribution at the sarcolemma.