Dysferlin, a novel skeletal muscle gene, is mutated in Miyoshi myopathy and limb girdle muscular dystrophy

Mutation impact on dysferlin inferred from database analysis and computer-based structural predictions

Dysferlin is a large sarcolemmal protein implicated in the repair of surface membrane tears in muscle cells. Mutations in dysferlin result in limb girdle muscular dystrophy type 2B and Miyoshi myopathy. Using a cDNA based approach we identified eight new pathogenic dysferlin alleles. To better understand how missense mutations could lead to reduced or absent dysferlin expression levels, we mapped missense mutations from our own and from published databases (n=55) to the secondary protein structure of dysferlin, deduced by computerized structural prediction tools. We found the protein to be very sensitive to the alteration of residues that were predicted to be buried inside the protein structure. We identified seven putative C2 domains, one more than commonly reported, of both type I and type II topology in dysferlin. Missense mutations often affected those structures as well as residues that were highly conserved between members of the ferlin family. Thus, alteration of structurally important residues in dysferlin could lead to improper folding and degradation of the mutant protein.

Painful enlargement of the calf muscles in limb girdle muscular dystrophy type 2B (LGMD2B) with a novel compound heterozygous mutation in DYSF

Limb girdle muscular dystrophy type 2B (LGMD2B) and Miyoshi Myopathy are caused by mutations in the dysferlin gene. The phenotype of these allelic disease variants can vary considerably. We report on an adolescent female with a severe and rapidly progressing clinical course of LGMD2B which has been suggested by the muscle histopathology and Western blot and proven by mutation analysis in the Dysferlin gene. We detected a novel compound heterozygous mutation of which one affects the extracellular part of the protein. This is the first report on a mutation in this region of dysferlin and might explain the unusual phenotype of the patient.

Patients with a non-dysferlin Miyoshi myopathy have a novel membrane repair defect

Two autosomal recessive muscle diseases, limb girdle muscular dystrophy type 2B (LGMD2B) and Miyoshi myopathy (MM), are caused by mutations in the dysferlin gene. These mutations result in poor ability to repair cell membrane damage, which is suggested to be the cause for this disease. However, many patients who share clinical features with MM-type muscular dystrophy do not carry mutations in dysferlin gene. To understand the basis of MM that is not due to mutations in dysferlin gene, we analyzed cells from patients in one such family. In these patients, we found no defects in several potential candidates - annexin A2, caveolin-3, myoferlin and the MMD2 locus on chromosome 10p. Similar to dysferlinopathy, these cells also exhibit membrane repair defects and the severity of the defect correlated with severity of their disease. However, unlike dysferlinopathy, none of the conventional membrane repair pathways are defective in these patient cells. These results add to the existing evidence that cell membrane repair defect may be responsible for MM-type muscular dystrophy and indicate that a previously unsuspected genetic lesion that affects cell membrane repair pathway is responsible for the disease in the non-dysferlin MM patients.

Limb-girdle muscular dystrophy in the United States

Limb-girdle muscular dystrophy (LGMD) has been linked to 15 chromosomal loci, 7 autosomal-dominant (LGMD1A to E) and 10 autosomal-recessive (LGMD2A to J). To determine the distribution of subtypes among patients in the United States, 6 medical centers evaluated patients with a referral diagnosis of LGMD. Muscle biopsies provided histopathology and immunodiagnostic testing, and their protein abnormalities along with clinical parameters directed mutation screening. The diagnosis in 23 patients was a disorder other than LGMD. Of the remaining 289 unrelated patients, 266 had muscle biopsies sufficient for complete microscopic evaluation; 121 also underwent Western blotting. From this combined evaluation, the distribution of immunophenotypes is 12% calpainopathy, 18% dysferlinopathy, 15% sarcoglycanopathy, 15% dystroglycanopathy, and 1.5% caveolinopathy. Genotypes distributed among 2 dominant and 7 recessive subtypes have been determined for 83 patients. This study of a large racially and ethnically diverse population of patients with LGMD indicates that establishing a putative subtype is possible more than half the time using available diagnostic testing. An efficient approach to genotypic diagnosis is muscle biopsy immunophenotyping followed by directed mutational analysis. The most common LGMDs in the United States are calpainopathies, dysferlinopathies, sarcoglycanopathies, and dystroglycanopathies.

Histological and Immunohistological Changes of the Skeletal Muscles in Older SJL/J Mice

SJL/J mice have been studied as the model animals for autoimmunological diseases. Recently it was clarified that SJL/J mice have a defect of dysferlin. Human limb girdle muscular dystrophy 2B and Miyoshi myopathy also have a defect of dysferlin. In this study we present the histological and immunohistological changes in the natural course. Histological study revealed that SJL/J mice had inflammatory, degenerative changes, and neurogenic changes in later ages. As for interstitial inflammatory cells, the macrophages were dominant in any age, and in the T cell subset, the CD4+ T cells were more abundant than the CD8+ T cells, and few B cells were seen. The laboratory data showed a high level of creatine kinase in all ages. It is suspected that the inflammatory changes were induced by the primary immunological abnormality or by the defect of dysferlin in SJL/J mice.

Muscle protein analysis in the detection of heterozygotes for recessive limb girdle muscular dystrophy type 2B and 2E

The diagnosis of isolated heterozygotes for recessive LGMD is quite difficult because no specific biochemical or protein assays are available, and the molecular analysis is not feasible due to the wide genetic heterogeneity. We investigated a series of definite heterozygotes for different forms of LGMD to determine whether the carrier status will result in a detectable protein defect in muscle biopsy. Definite heterozygotes from 4 families (3 LGMD2B and 1 LGMD2E) underwent quantitative immunoblot analysis of mutant protein in their muscle. While the quantity of beta-sarcoglycan was nearly normal in the LGMD2E carrier, the levels of dysferlin protein were reduced to 50% of controls in the carriers of LGMD2B. We have demonstrated the value of protein analysis in the identification of both familial and isolated LGMD2B heterozygotes, and suggested the use of dysferlin protein testing to select muscle biopsies from suspected carriers for a subsequent mutation analysis. Muscle protein analysis would be used to screen asymptomatic patients who underwent muscle biopsy because of unexplained hyperCKemia.

Dysferlin is a new marker for leaky brain blood vessels in multiple sclerosis

Dysferlin is a muscle protein involved in cell membrane repair and its deficiency is associated with muscular dystrophy. We describe that dysferlin is also expressed in leaky endothelial cells. In the normal central nervous system (CNS), dysferlin is only present in endothelial cells of circumventricular organs. In the inflamed CNS of patients with multiple sclerosis (MS) or in animals with experimental autoimmune encephalomyelitis, dysferlin reactivity is induced in endothelial cells and the expression is associated with vascular leakage of serum proteins. In MS, dysferlin expression in endothelial cells is not restricted to vessels with inflammatory cuffs but is also present in noninflamed vessels. In addition, many blood vessels with perivascular inflammatory infiltrates lack dysferlin expression in inactive lesions or in the normal-appearing white matter. In vitro, dysferlin can be induced in endothelial cells by stimulation with tumor necrosis factor-alpha. Hence, dysferlin is not only a marker for leaky brain vessels, but also reveals dissociation of perivascular inflammatory infiltrates and blood-brain barrier disturbance in multiple sclerosis.

Macrophages promote muscle membrane repair and muscle fibre growth and regeneration during modified muscle loading in mice in vivo

Muscle injury or modified muscle use can stimulate muscle invasion by leucocytes that have the potential to increase tissue damage or promote tissue growth and repair. In the present investigation, we examined the role of macrophages in muscle injury, repair and regeneration during modified muscle loading. Weight-bearing was removed from the hindlimbs of mice for 10 days followed by reloading through normal ambulation. During the unloading period, soleus muscle fibre cross-section decreased by 38%. Prior to the onset of reloading, mice received a series of intraperitoneal injections of anti-F4/80, which binds a mouse macrophage surface antigen. Although anti-F4/80 injections did not affect macrophage numbers in soleus muscles at 2 days of reloading, macrophages were reduced by 86% at 4 days of reloading. Muscle membrane lysis during the reloading period did not differ at 2 days of reloading between anti-F4/80-treated mice and mice that received isotype control antibody. However, control animals showed large decreases in the number of fibres with membrane lesions at 4 days of reloading, but this membrane repair did not occur in macrophage-depleted mice. Macrophage-depletion also reduced muscle regeneration (indicated by central nucleation) and satellite cell differentiation (indicated by reductions in MyoD-expressing satellite cells) and prevented growth of muscle fibres that normally occurred in control animals between days 2 and 4 of reloading. These findings collectively show that macrophages play a significant role in muscle fibre membrane repair, regeneration and growth during increased muscle use after a period of atrophy.

The limb-girdle muscular dystrophies--diagnostic strategies

The limb-girdle muscular dystrophies are a group of disorders where our understanding of their underlying molecular basis has made huge strides over the past years, revealing great heterogeneity at the clinical and molecular level. The availability of direct protein and/ or gene based approaches to diagnosis means that these disorders can now be precisely defined, and such definition of a precise diagnosis is increasingly allowing directed management for these diseases by the ability to predict specific complications such as those of the cardiac or respiratory systems. An algorithm combining clinical, biochemical and molecular testing is described which will aid precision of diagnosis and direct specific testing towards the cases most likely to benefit. This brings advantages for the patients of today in recognising the specific risks of their disorders, and in the future will be the starting point for specific gene and protein based therapies.

The inflammatory reaction pattern distinguishes primary dysferlinopathies from idiopathic inflammatory myopathies: an important role for the membrane attack complex

Degenerative muscle changes in dysferlinopathies are often accompanied by inflammatory infiltrates and may even mimic primary idiopathic inflammatory myopathies. In the present study, the inflammatory reaction pattern with respect to the cellular composition of the infiltrates and the expression of potent cytokines was characterized in dysferlinopathies and in idiopathic inflammatory myopathies. Cellular infiltrates in dysferlinopathies mainly consisted of CD4+CD25- T cells and macrophages. We noted a prominent expression of interferon-gamma which may contribute to the marked upregulation of MHC class I antigen observed on the vast majority of muscle fibres. Furthermore, membrane attack complex positive deposits were found on intact as well as necrotic muscle fibres. Collectively, our study indicates that the inflammatory reaction pattern in dysferlinopathies is distinct from the one in idiopathic inflammatory myopathies. In particular, membrane attack complex deposits and a pro-inflammatory milieu in the absence of interleukin-10 expression may contribute to progressive muscle damage in dysferlinopathies.

Molecular biology of distal muscular dystrophies--sarcomeric proteins on top

During the last 10 years several muscular dystrophies within the group of distal myopathies have been clarified as to the molecular genetic cause of the disease. Currently, the next steps are carried out to identify the molecular pathogenesis downstream of the gene defects. Some early ideas on what is going on in the muscle cells based on the defect proteins are emerging. However, in no single distal muscular dystrophy these efforts have yet reached the point where direct trials for therapy would have been launched, and in many distal dystrophies the causative gene is still lacking. When comparing the gene defects in the distal dystrophies with the more common proximal muscular dystrophies such as dystrophinopathies or limb-girdle muscular dystrophies, there is a striking difference: the genes for distal dystrophies encode sarcomere proteins whereas the genes for proximal dystrophies more often encode sarcolemmal proteins.

Identification and characterization of a novel human dysferlin transcript: dysferlin_v1

Mutations in the dysferlin (DYSF) gene are associated with limb girdle muscular dystrophy type 2B and Miyoshi myopathy. In this study, we report the identification and characterization of a novel dysferlin transcript that we named DYSF_v1 (GenBank accession: DQ267935). This transcript differs from the currently known dysferlin transcript (GenBank accession: AF075575) in the sequence of the entire first exon which spans 232 bases. This unique first exon is derived from intron 1 of DYSF, and has an immediate upstream 5' untranslated region containing CpG islands and sequences consistent with transcription factor binding sites. Exon 1 of DYSF_v1 shares 85% sequence homology and has similar genomic organization with the first exon of mouse dysferlin. Northern blot analysis showed that the DYSF_v1 transcript spans 7.5 kb and is expressed in human skeletal muscle, heart, placenta, brain, spleen, kidney, intestine, and lung tissues. DYSF_v1 retains phylogenic conservancy and shows similar expression pattern as the currently known human dysferlin.

Clinical and genetic analysis of Korean patients with Miyoshi myopathy: identification of three novel mutations in the DYSF gene

Miyoshi myopathy (MM) is an autosomal recessive distal muscular dystrophy caused by mutations in the dysferlin gene (DYSF) on chromosome 2p13. Although MM patients and their mutations in the DYSF gene have been found from all over the world, there is only one report of genetically confirmed case of MM in Korea. Recently, we encountered three unrelated Korean patients with MM and two of them have previously been considered as having a type of inflammatory myopathy. The clinical and laboratory evaluation showed typical features of muscle involvement in MM in all patients but one patient initially had moderate proximal muscle involvement and another showed incomplete quadriparesis with rapid progression. Direct sequencing analysis of the DYSF gene revealed that each patient had compound heterozygous mutations (Gln832X and Trp992Arg, Gln832X and Trp999Cys, and Lys1103X and Ile1401HisfsX8, respectively) among which three were novel. Although MM has been thought to be quite rare in Korea, it should be considered in a differential diagnosis of patients exhibiting distal myopathy.

Molecular and cellular basis of calpainopathy (limb girdle muscular dystrophy type 2A)

Limb girdle muscular dystrophy type 2A results from mutations in the gene encoding the calpain 3 protease. Mutations in this disease are inherited in an autosomal recessive fashion and result in progressive proximal skeletal muscle wasting but no cardiac abnormalities. Calpain 3 has been shown to proteolytically cleave a wide variety of cytoskeletal and myofibrillar proteins and to act upstream of the ubiquitin-proteasome pathway. In this review, we summarize the known biochemical and physiological features of calpain 3 and hypothesize why mutations result in disease.

Loss of Podocyte Dysferlin Expression Is Associated With Minimal Change Nephropathy

We report a case of limb-girdle muscular dystrophy type 2B (LGMD2B) associated with minimal change disease. Immunohistochemical examination of quadriceps muscle showed a deficiency in dysferlin in sarcolemma, and dysferlin gene analysis showed 3370 G missense mutation, leading us to the diagnosis of LGMD2B. The patient also developed glomerular proteinuria. We also explored urinary protein levels in 3 other patients with dysferlinopathy and found microalbuminuria with albumin excretion of 0.14 to 0.18 g/d in 2 patients. Renal abnormalities during LGMD2B and kidney dysferlin expression have never been reported. Renal biopsy showed a lack of glomerular dysferlin expression compared with a positive immunohistochemical marking in patients with idiopathic minimal change nephropathy and healthy controls. We therefore suggest that dysferlin is present in glomeruli and may be associated with glomerular permeability.

Non-syndromic, autosomal-recessive deafness

Non-syndromic deafness is a paradigm of genetic heterogeneity with 85 loci and 39 nuclear disease genes reported so far. Autosomal-recessive genes are responsible for about 80% of the cases of hereditary non-syndromic deafness of pre-lingual onset with 23 different genes identified to date. In the present article, we review these 23 genes, their function, and their contribution to genetic deafness in different populations. The wide range of functions of these DFNB genes reflects the heterogeneity of the genes involved in hearing and hearing loss. Several of these genes are involved in both recessive and dominant deafness, or in both non-syndromic and syndromic deafness. Mutations in the GJB2 gene encoding connexin 26 are responsible for as much as 50% of pre-lingual, recessive deafness. By contrast, mutations in most of the other DFNB genes have so far been detected in only a small number of families, and their contribution to deafness on a population scale might therefore be limited. Identification of all genes involved in hereditary hearing loss will help in our understanding of the basic mechanisms underlying normal hearing, in early diagnosis and therapy.

Expression of myoferlin in skeletal muscles of patients with dysferlinopathy

Myoferlin is a novel protein of unknown function with high homology to dysferlin, the gene mutations of which cause limb girdle muscular dystrophy type 2B and Miyoshi myopathy. The myoferlin gene seems to be a candidate for the modifier, and because of the high homology to dysferlin myoferlin may work as a compensator for the absence of dysferlin in dysferlinopathy. This hypothesis is based on the observation that utrophin, which has 80% homology with dystrophin, is overexpressing in the dystrophin deficient myofibers. To test this hypothesis, we investigated the myoferlin expression by immunoblot and immunohistochemical analysis in muscles of five patients with dysferlinopathy. For this aim, we generated a myoferlin specific antibody that does not cross react with dysferlin, and performed the immunoblot, immunohistochemical and immunoelectron microscopic studies. Immunohistochemical analysis showed that the antibodies against myoferlin and dysferlin clearly stained the normal human myofiber surface membranes. The electron microscopy of single immunogold labeled samples for myoferlin showed the presence of the molecular signal along the normal muscle cell membrane. Immunoblot analysis showed that the intensity of 230-kDa myoferlin band of dysferlinopathy muscle extracts was similar to that of normal muscle extracts. The immunostaining of dysferlinopathy muscles with anti-myoferlin antibody revealed a weak immunoreactivity along the muscle cell surface. Thus, the compensatory overexpression of myoferlin was not detected in muscles with dysferlinopathy.

FER-1 regulates Ca2+ -mediated membrane fusion during C. elegans spermatogenesis

FER-1 is required for fusion of specialized vesicles, called membranous organelles, with the sperm plasma membrane during Caenorhabditis elegans spermiogenesis. To investigate its role in membranous organelle fusion, we examined ten fer-1 mutations and found that they all cause the same defect in membrane fusion. FER-1 and the ferlin protein family are membrane proteins with four to seven C2 domains. These domains commonly mediate Ca2+ -dependent lipid-processing events. Most of the fer-1 mutations fall within these C2 domains, showing that they have distinct, non-redundant functions. We found that membranous organelle fusion requires intracellular Ca2+ and that C2 domain mutations alter Ca2+ sensitivity. This suggests that the C2 domains are involved in Ca2+ sensing and further supports their independent function. Using two immunological approaches we found three FER-1 isoforms, two of which might arise from FER-1 by proteolysis. By both light and electron microscopy, these FER-1 proteins were found to be localized to membranous organelle membranes. Dysferlin, a human homologue of FER-1 involved in muscular dystrophy, is required for vesicle fusion during Ca2+ -induced muscle membrane repair. Our results suggest that the ferlin family members share a conserved mechanism to regulate cell-type-specific membrane fusion.

Lariat branch point mutation in the dysferlin gene with mild limb-girdle muscular dystrophy

The authors report a genotype-phenotype correlation in a limb-girdle muscular dystrophy 2B family. Two severely affected sisters were homozygous for a dysferlin null mutation. Their mildly affected compound heterozygous mother harbored, in addition to one null allele, an in-frame exon-skipping allele caused by a novel lariat branch point mutation. The dysferlin molecule arising from the latter allele appeared to partially complement the null mutation, likely accounting for the mother's mild phenotype.

Mendelian disorders deserve more attention

The study of inherited monogenic diseases has contributed greatly to our mechanistic understanding of pathogenic mutations and gene regulation, and to the development of effective diagnostic tools. But interest has gradually shifted away from monogenic diseases, which collectively affect only a small fraction of the world's population, towards multifactorial, common diseases. The quest for the genetic variability associated with common traits should not be done at the expense of Mendelian disorders, because the latter could still contribute greatly to understanding the aetiology of complex traits.

Pex19p Binds Pex30p and Pex32p at Regions Required for Their Peroxisomal Localization but Separate from Their Peroxisomal Targeting Signals

The assembly of proteins in the peroxisomal membrane is a multistep process requiring their recognition in the cytosol, targeting to and insertion into the peroxisomal membrane, and stabilization within the lipid bilayer. The peroxin Pex19p has been proposed to be either the receptor that recognizes and targets newly synthesized peroxisomal membrane proteins (PMP) to the peroxisome or a chaperone required for stabilization of PMPs at the peroxisomal membrane. Differentiating between these two roles for Pex19p could be achieved by determining whether the peroxisomal targeting signal (PTS) and the region of Pex19p binding of a PMP are the same or different. We addressed the role for Pex19p in the assembly of two PMPs, Pex30p and Pex32p, of the yeast Saccharomyces cerevisiae. Pex30p and Pex32p control peroxisome size and number but are dispensable for peroxisome formation. Systematic truncations from the carboxyl terminus, together with in-frame deletions of specific regions, have identified PTSs essential for targeting Pex30p and Pex32p to peroxisomes. Both Pex30p and Pex32p interact with Pex19p in regions that do not overlap with their PTSs. However, Pex19p is required for localizing Pex30p and Pex32p to peroxisomes, because mutations that disrupt the interaction of Pex19p with Pex30p and Pex32p lead to their mislocalization to a compartment other than peroxisomes. Mutants of Pex30p and Pex32p that localize to peroxisomes but produce cells exhibiting the peroxisomal phenotypes of cells lacking these proteins demonstrate that the regions in these proteins that control peroxisomal targeting and cell biological activity are separable. Together, our data show that the interaction of Pex19p with Pex30p and Pex32p is required for their roles in peroxisome biogenesis and are consistent with a chaperone role for Pex19p in stabilizing or maintaining membrane proteins in peroxisomes.

Calpain-3 mutations in Turkey

Autosomal recessive limb-girdle muscular dystrophies (LGMD2s) are a clinically and genetically heterogeneous group of disorders, characterized by progressive involvement of the proximal limb girdle muscles; the group includes at least 10 different genetic entities. The calpainopathies (LGMD2A), a subgroup of LGMD2s, are estimated to be the most common forms of LGMD2 in all populations so far investigated. LGMD2A is usually characterized by symmetrical and selective atrophy of pelvic, scapular and trunk muscles and a moderate to gross elevation of serum CK. However, the course is highly variable. It is caused by mutations in the CAPN3 gene, which encodes for the calpain-3 protein. Until now, 161 pathogenic mutations have been found in the CAPN3 gene. In the present study, through screening of 93 unrelated LGMD2 families, we identified 29 families with LGMD2A, 21 (22.6%) of which were identified as having CAPN3 gene mutations. We detected six novel (p.K211N, p.D230G, p.Y322H, p.R698S, p.Q738X, c.2257delGinsAA) and nine previously reported mutations (c.550delA, c.19_23del, c.1746-20C>G, p.R49H, p.R490Q, p.Y336N, p.A702V, p.Y537X, p.R541Q) in the CAPN3 gene. There may be a wide variety of mutations, but clustering of specific mutations (c.550delA: 40%, p.R490Q: 10%) could be used in the diagnostic scheme in Turkey.

Absence of dysferlin alters myogenin expression and delays human muscle differentiation "in vitro"

Mutations in dysferlin cause a type of muscular dystrophy known as dysferlinopathy. Dysferlin may be involved in muscle repair and differentiation. We compared normal human skeletal muscle cultures expressing dysferlin with muscle cultures from dysferlinopathy patients. We quantified the fusion index of myoblasts as a measure of muscle development and conducted optic and electronic microscopy, immunofluorescence, Western blot, flow cytometry, and real-time PCR at different developmental stages. Short interference RNA was used to corroborate the results obtained in dysferlin-deficient cultures. A luciferase reporter assay was performed to study myogenin activity in dysferlin-deficient cultures. Myoblasts fusion was consistently delayed as compared with controls whereas the proliferation rate did not change. Electron microscopy showed that control cultured cells at 10 days were fusiform, whereas dysferlin-deficient cells were star-shaped and large. After 15 days the normal multinucleated appearance and structured myofibrils were not present in dysferlin-deficient cells. Strikingly, myogenin was not detected in myotubes from dysferlin-deficient cultures using Western blot, and mRNA analysis showed low levels (p < 0.05) compared with controls. Flow cytometry and immunofluorescence also showed reduced levels of myogenin in dysferlin-deficient cultures. When the dysferlin gene was knocked down ( approximately 80%), myogenin mRNA leveled down to approximately 70%. MyoD and desmin mRNA levels in controls and dysferlin-deficient cultures were similar. The reporter luciferase assay demonstrated a low myogenin activity in dysferlin-deficient cultures. These results point to a functional link between dysferlin and myogenin, and both proteins may share a new signaling pathway involved in differentiation of skeletal muscle in vitro.

Distal myopathies

PURPOSE OF REVIEW

The distal myopathies are a heterogeneous group of disorders that pose a challenge to both the clinician and geneticist. This article summarizes the findings of recent clinical, genetic and molecular studies and the current diagnostic approach to this group of patients.

RECENT FINDINGS

Publications over the past 5 years describe a number of new clinical phenotypes and genetic loci and further emphasize the overlap in clinical phenotype between a number of these disorders and between the distal and limb girdle myopathies and hereditary inclusion body myopathies. Recent studies have led to the identification of the genes and mutations responsible for early onset (Laing) myopathy and tibial (Udd) myopathy, and for distal myopathy with rimmed vacuoles (Nonaka), which has been shown to be allelic with quadriceps sparing hereditary inclusion body myopathy (IBM2), and have elucidated the underlying pathogenetic mechanisms in these conditions. New diagnostic approaches using magnetic resonance imaging, and a blood-based assay for dysferlin deficiency, have also been reported.

SUMMARY

These findings have important implications for future genetic linkage and gene expression studies and for the diagnostic approach to patients with a distal myopathy phenotype. They also hold promise for the eventual development of therapies for this group of disorders.

A Rostrocaudal Muscular Dystrophy Caused by a Defect in Choline Kinase Beta, the First Enzyme in Phosphatidylcholine Biosynthesis

Muscular dystrophies include a diverse group of genetically heterogeneous disorders that together affect 1 in 2000 births worldwide. The diseases are characterized by progressive muscle weakness and wasting that lead to severe disability and often premature death. Rostrocaudal muscular dystrophy (rmd) is a new recessive mouse mutation that causes a rapidly progressive muscular dystrophy and a neonatal forelimb bone deformity. The rmd mutation is a 1.6-kb intragenic deletion within the choline kinase beta (Chkb) gene, resulting in a complete loss of CHKB protein and enzymatic activity. CHKB is one of two mammalian choline kinase (CHK) enzymes (alpha and beta) that catalyze the phosphorylation of choline to phosphocholine in the biosynthesis of the major membrane phospholipid phosphatidylcholine. While mutant rmd mice show a dramatic decrease of CHK activity in all tissues, the dystrophy is only evident in skeletal muscle tissues in an unusual rostral-to-caudal gradient. Minor membrane disruption similar to dysferlinopathies suggest that membrane fusion defects may underlie this dystrophy, because severe membrane disruptions are not evident as determined by creatine kinase levels, Evans Blue infiltration, and unaltered levels of proteins in the dystrophin-glycoprotein complex. The rmd mutant mouse offers the first demonstration of a defect in a phospholipid biosynthetic enzyme causing muscular dystrophy, representing a unique model for understanding mechanisms of muscle degeneration.

Therapy insight: cardiovascular complications associated with muscular dystrophies

The muscular dystrophies are commonly associated with cardiovascular complications, including cardiomyopathy and cardiac arrhythmias. These complications are caused by intrinsic defects in cardiomyocyte and cardiac conduction system function, and by the presence of severe skeletal muscle disease, which also contributes to cardiac dysfunction. Unlike the skeletal muscle degenerative process, for which treatment options are currently limited, therapy is available for the cardiovascular complications that accompany muscular dystrophy. New therapies for skeletal muscle degeneration are moving into clinical trials and, ultimately, into clinical practice. These therapies are expected to also improve the cardiac function, longevity and wellbeing of muscular dystrophy patients.

Proteomic investigation of the molecular pathophysiology of dysferlinopathy

Mutations in dysferlin gene cause several types of muscular dystrophy in humans, including the limb-girdle muscular dystrophy type 2B and the distal muscular dystrophy of Miyoshi. The dysferlin gene product is a membrane-associated protein belonging to the ferlins family of proteins. The function of the dysferlin protein and the cause of deterioration and regression of muscle fibres in its absence, are incompletely known. A functional clue may be the presence of six hydrophilic domains, C2, that bind calcium and mediate the interaction of proteins with cellular membranes. Dysferlin seems to be involved in the membrane fusion or repair. Molecular diagnosis of dysferlinopathies is now possible and the types of gene alterations that have been characterized so far include missense mutations, deletions and insertions.

Early onset distal muscular dystrophy with normal dysferlin expression

A 7-year-old boy, who was noted to be a slow runner at the age of 2 years, had progressive muscle weakness and atrophy, preferentially affecting distal muscles. At 3 years of age, he had scoliosis and difficulty in standing on tip-toe. Serum creatine kinase was 1074IU/l. Muscle CT scan showed low-density areas in the lower legs and upper arms, but predominantly in the gastrocnemius and soleus muscles. Biopsy of the biceps brachii muscle showed moderate dystrophic changes with normal dysferlin expression on immunohistochemical and western blot analyses. Although muscle involvement mimicked that seen in Miyoshi myopathy (MM), the very early onset of the disease and scoliosis were quite unusual for MM. We, therefore, made the diagnosis of early onset dysferlin-positive distal muscular dystrophy, probably a new type of distal muscular dystrophy.

Normal myoblast fusion requires myoferlin

Muscle growth occurs during embryonic development and continues in adult life as regeneration. During embryonic muscle growth and regeneration in mature muscle, singly nucleated myoblasts fuse to each other to form myotubes. In muscle growth, singly nucleated myoblasts can also fuse to existing large, syncytial myofibers as a mechanism of increasing muscle mass without increasing myofiber number. Myoblast fusion requires the alignment and fusion of two apposed lipid bilayers. The repair of muscle plasma membrane disruptions also relies on the fusion of two apposed lipid bilayers. The protein dysferlin, the product of the Limb Girdle Muscular Dystrophy type 2 locus, has been shown to be necessary for efficient, calcium-sensitive, membrane resealing. We now show that the related protein myoferlin is highly expressed in myoblasts undergoing fusion, and is expressed at the site of myoblasts fusing to myotubes. Like dysferlin, we found that myoferlin binds phospholipids in a calcium-sensitive manner that requires the first C2A domain. We generated mice with a null allele of myoferlin. Myoferlin null myoblasts undergo initial fusion events, but they form large myotubes less efficiently in vitro, consistent with a defect in a later stage of myogenesis. In vivo, myoferlin null mice have smaller muscles than controls do, and myoferlin null muscle lacks large diameter myofibers. Additionally, myoferlin null muscle does not regenerate as well as wild-type muscle does, and instead displays a dystrophic phenotype. These data support a role for myoferlin in the maturation of myotubes and the formation of large myotubes that arise from the fusion of myoblasts to multinucleate myotubes.

Aberrant dysferlin trafficking in cells lacking caveolin or expressing dystrophy mutants of caveolin-3

Mutations in the dysferlin (DYSF) and caveolin-3 (CAV3) genes are associated with muscle disease. Dysferlin is mislocalized, by an unknown mechanism, in muscle from patients with mutations in caveolin-3 (Cav-3). To examine the link between Cav-3 mutations and dysferlin mistargeting, we studied their localization at high resolution in muscle fibers, in a model muscle cell line, and upon heterologous expression of dysferlin in muscle cell lines and in wild-type or caveolin-null fibroblasts. Dysferlin shows only partial overlap with Cav-3 on the surface of isolated muscle fibers but co-localizes with Cav-3 in developing transverse (T)-tubules in muscle cell lines. Heterologously expressed dystrophy-associated mutant Cav3R26Q accumulates in the Golgi complex of muscle cell lines or fibroblasts. Cav3R26Q and other Golgi-associated mutants of both Cav-3 (Cav3P104L) and Cav-1 (Cav1P132L) caused a dramatic redistribution of dysferlin to the Golgi complex. Heterologously expressed epitope-tagged dysferlin associates with the plasma membrane in primary fibroblasts and muscle cells. Transport to the cell surface is impaired in the absence of Cav-1 or Cav-3 showing that caveolins are essential for dysferlin association with the PM. These results suggest a functional role for caveolins in a novel post-Golgi trafficking pathway followed by dysferlin.

The differential gene expression profiles of proximal and distal muscle groups are altered in pre-pathological dysferlin-deficient mice

The selective pattern of muscle involvement is a key feature of muscular dystrophies. Dysferlinopathy is a good model for studying this process since it shows variable muscle involvement that can be highly selective even in individual patients. The transcriptomes of proximal and distal muscles from wildtype C57BL/10 and dysferlin deficient C57BL/10.SJL-Dysf mice at a prepathological stage were assessed using the Affymetrix oligonucleotide-microarray system. We detected significant variation in gene expression between proximal and distal muscle in wildtype mice. Dysferlin defiency, even in the absence of pathological changes, altered this proximal distal difference but with little specific overlap with previous microarray analyses of dysferlinopathy. In conclusion, proximal and distal muscle groups show distinct patterns of gene expression and respond differently to dysferlin deficiency. This has implications for the selection of muscles for future microarray analyses, and also offers new routes for investigating the selectivity of muscle involvement in muscular dystrophies.

Variations in gene expression among different types of human skeletal muscle

There is a consistent variation in the response of different skeletal muscle groups to mutations in genes known to cause muscular dystrophy, yet these muscles appear histologically similar. To better understand these phenotypic differences, we analyzed gene expression patterns in control muscle specimens obtained from four sites at autopsy: deltoid, quadriceps, gastrocnemius, and tibialis anterior (TA). A total of 35 muscle samples from nine individuals (four pediatric and five geriatric) were studied. Factors potentially influencing gene expression in the different samples included individuality, age, muscle type, gender, cause of death, postmortem interval, and ethnicity. The first three factors, in decreasing order, were found to have a significant impact on the stratification of muscle specimens. A novel analytic method, using a second round of normalization, was used to elicit differences between muscle types. This approach may be extended to a broader survey, potentially elucidating a molecular classification of the skeletal muscles.

Increased Susceptibility to Complement Attack due to Down-Regulation of Decay-Accelerating Factor/CD55 in Dysferlin-Deficient Muscular Dystrophy

Dysferlin is expressed in skeletal and cardiac muscles. However, dysferlin deficiency results in skeletal muscle weakness, but spares the heart. We compared intraindividual mRNA expression profiles of cardiac and skeletal muscle in dysferlin-deficient SJL/J mice and found down-regulation of the complement inhibitor, decay-accelerating factor/CD55, in skeletal muscle only. This finding was confirmed on mRNA and protein levels in two additional dysferlin-deficient mouse strains, A/J mice and Dysf-/- mice, as well as in patients with dysferlin-deficient muscular dystrophy. In vitro, the absence of CD55 led to an increased susceptibility of human myotubes to complement attack. Evidence is provided that decay-accelerating factor/CD55 is regulated via the myostatin-SMAD pathway. In conclusion, a novel mechanism of muscle fiber injury in dysferlin-deficient muscular dystrophy is demonstrated, possibly opening therapeutic avenues in this to date untreatable disorder.

Extensive scanning of the calpain-3 gene broadens the spectrum of LGMD2A phenotypes

BACKGROUND

The limb girdle muscular dystrophies (LGMD) are a heterogeneous group of Mendelian disorders highlighted by weakness of the pelvic and shoulder girdle muscles. Seventeen autosomal loci have been so far identified and genetic tests are mandatory to distinguish among the forms. Mutations at the calpain 3 locus (CAPN3) cause LGMD type 2A.

OBJECTIVE

To obtain unbiased information on the consequences of CAPN3 mutations.

PATIENTS

530 subjects with different grades of symptoms and 300 controls.

METHODS

High throughput denaturing HPLC analysis of DNA pools.

RESULTS

141 LGMD2A cases were identified, carrying 82 different CAPN3 mutations (45 novel), along with 18 novel polymorphisms/variants. Females had a more favourable course than males. In 94% of the more severely affected patient group, the defect was also discovered in the second allele. This proves the sensitivity of the approach. CAPN3 mutations were found in 35.1% of classical LGMD phenotypes. Mutations were also found in 18.4% of atypical patients and in 12.6% of subjects with high serum creatine kinase levels.

CONCLUSIONS

A non-invasive and cost-effective strategy, based on the high throughput denaturing HPLC analysis of DNA pools, was used to obtain unbiased information on the consequences of CAPN3 mutations in the largest genetic study ever undertaken. This broadens the spectrum of LGMD2A phenotypes and sets the carrier frequency at 1:103.

Protein studies in dysferlinopathy patients using llama-derived antibody fragments selected by phage display

Mutations in dysferlin, a member of the fer1-like protein family that plays a role in membrane integrity and repair, can give rise to a spectrum of neuromuscular disorders with phenotypic variability including limb-girdle muscular dystrophy 2B, Myoshi myopathy and distal anterior compartment myopathy. To improve the tools available for understanding the pathogenesis of the dysferlinopathies, we have established a large source of highly specific antibody reagents against dysferlin by selection of heavy-chain antibody fragments originating from a nonimmune llama-derived phage-display library. By utilizing different truncated forms of recombinant dysferlin for selection and diverse selection methodologies, antibody fragments with specificity for two different dysferlin domains could be identified. The selected llama antibody fragments are functional in Western blotting, immunofluorescence microscopy and immunoprecipitation applications. Using these antibody fragments, we found that calpain 3, which shows a secondary reduction in the dysferlinopathies, interacts with dysferlin.

Changes in dysferlin, proteins from dystrophin glycoprotein complex, costameres, and cytoskeleton in human soleus and vastus lateralis muscles after a long-term bedrest with or without exercise

This study was designed to evaluate the effects of hypokinesia and hypodynamia on cytoskeletal and related protein contents in human skeletal muscles. Twelve proteins: dystrophin and its associated proteins (DGC), dysferlin, talin, vinculin and meta-vinculin, alpha-actinin, desmin, actin, and myosin, were quantitatively analyzed during an 84-day long-term bedrest (LTBR). The preventive or compensatory effects of maximal resistance exercise (MRE) as a countermeasure were evaluated. Most of these proteins are involved in several myopathies, and they play an important role in muscle structure, fiber cohesion, cell integrity maintenance, and force transmission. This is the first comparison of the cytoskeletal protein contents between slow postural soleus (SOL) and mixed poly-functional vastus lateralis (VL) human muscles. Protein contents were higher in VL than in SOL (from 12 to 94%). These differences could be mainly explained by the differential mechanical constraints imposed on the muscles, i.e., cytoskeletal protein contents increase with mechanical constraints. After LTBR, proteins belonging to the DGC, dysferlin, and proteins of the costamere exhibited large increases, higher in SOL (from 67 to 216%) than in VL (from 32 to 142%). Plasma membrane remodeling during muscle atrophy is probably one of the key points for interpreting these modifications, and mechanisms other than those involved in the resistance of the cytoskeleton to mechanical constraints may be implicated (membrane repair). MRE compensates the cytoskeletal changes induced by LTBR in SOL, except for gamma-sarcoglycan (+70%) and dysferlin (+108%). The exercise only partly compensated the DGC changes induced in VL, and, as for SOL, dysferlin remained largely increased (+132%). Moreover, vinculin and metavinculin, which exhibited no significant change in VL after LTBR, were increased with MRE during LTBR, reinforcing the pre-LTBR differences between SOL and VL. This knowledge will contribute to the development of efficient space flight countermeasures and rehabilitation methods in clinical situations where musculoskeletal unloading is a component.

An emergency response team for membrane repair

On demand, rapid Ca(2+)-triggered homotypic and exocytic membrane-fusion events are required to repair a torn plasma membrane, and we propose that this emergency-based fusion differs fundamentally from other rapid, triggered fusion reactions. Emergency fusion might use a specialized protein and organelle emergency response team that can simultaneously promote impromptu homotypic fusion events between organelles and exocytic fusion events along the vertices between these fusion products and the plasma membrane.

Limb-girdle muscular dystrophy in childhood

LGMD refers to a class of muscular dystrophies with onset in the proximal muscles. They are genetically heterogeneous, with both autosomal recessive and dominant forms. The autosomal recessive forms are more common and in general follow a more severe course compared to the dominant forms. It is important to reach a specific genetic diagnosis beyond making a group diagnosis of LGMD to provide adequate genetic counseling, to predict risks for the patient such as the development of cardiomyopathy, and to be able to take advantage of specific treatments when they become available. Establishing a specific diagnosis requires knowledge about the individual clinical features, expert analysis of the muscule biopsy, and the guided initiation of appropriate genetic testing.

Morphogenetic pathway of spore wall assembly in Saccharomyces cerevisiae

The Saccharomyces cerevisiae spore is protected from environmental damage by a multilaminar extracellular matrix, the spore wall, which is assembled de novo during spore formation. A set of mutants defective in spore wall assembly were identified in a screen for mutations causing sensitivity of spores to ether vapor. The spore wall defects in 10 of these mutants have been characterized in a variety of cytological and biochemical assays. Many of the individual mutants are defective in the assembly of specific layers within the spore wall, leading to arrests at discrete stages of assembly. The localization of several of these gene products has been determined and distinguishes between proteins that likely are involved directly in spore wall assembly and probable regulatory proteins. The results demonstrate that spore wall construction involves a series of dependent steps and provide the outline of a morphogenetic pathway for assembly of a complex extracellular structure.

Gene expression in the spermatogenically inactive "dark" and maturing "light" testicular tissues of the prepubertal colt

In the testis of the 1.5-year-old horse, spermatogenesis initiates locally in grossly light, central areas that contrast with grossly dark, peripheral areas that are as yet inactive in spermatogenesis. Gene expression was compared between "light" and "dark" tissues of 1.5-year-old horse testes to identify mechanisms important to the initiation of spermatogenesis. Microarrays containing human cDNAs were used to assess expression levels of 9132 genes simultaneously in matched pairs of dark and light testis tissues from 3 prepubertal colts. In all 3 analyses, dysferlin (DYS), down-regulated in ovarian cancer 1 (DOC1), and Golgi apparatus protein 1 (GLG1) genes were preferentially expressed in dark tissues, while outer dense fiber of sperm tails (ODF2) and phosphodiesterase 3B (PDE3B) genes were more highly expressed in light testis tissue (>1.7 balanced difference value, Incyte GEM tools software). Expression levels of 88 additional genes appeared to be different between dark and light tissues in 2 of the 3 microarray analyses. The preferential expression of DYS, DOC1, ODF2, and PDE3B genes in dark or light testis tissues was confirmed on Northern blots and localized to cell types by in situ hybridization. Future studies to determine the role of genes regulated during the initiation of spermatogenesis may aid in elucidating molecular mechanisms during this critical time as well as in identifying new therapies for enhancing male fertility.

Expression profiling with progression of dystrophic change in dysferlin-deficient mice (SJL)

The SJL mouse is a model for human dysferlinopathy (limb-girdle muscular dystrophy type 2B and Miyoshi myopathy). We used cDNA microarrays to compare the expression profiles of 10,012 genes in control and SJL quadriceps femoris muscles in order to find genes involved in the degeneration and regeneration process and in dysferlin's functional network. Many genes involved in the process of muscle regeneration are observed to be up-regulated in SJL mice, including cardiac ankyrin repeated protein (CARP), Neuraminidase 2, interleukin-6, insulin-like growth factor-2 and osteopontin. We found the upregulation of S100 calcium binding proteins, neural precursor cell expressed, developmentally down-regulated gene 4-like (NEDD4L) with C2 domain, and intracellular protein traffic associated proteins (Rab6 and Rab2). These proteins have the potential to interact with dysferlin. We must reveal some other molecules which may work with dysferlin in order to clarify the pathological network of dysferlinopathy. This process may lead to future improvements in the therapy for human dysferlinopathy.

Diagnostic immunohistochemistry in neuromuscular disorders

Most neuromuscular disorders display only non-specific myopathological features in routine histological preparations. However, a number of proteins, including sarcolemmal, sarcomeric, and nuclear proteins as well as enzymes with defects responsible for neuromuscular disorders, have been identified during the past two decades, allowing a more specific and firm diagnosis of muscle diseases. Identification of protein defects relies predominantly on immunohistochemical preparations and on Western blot analysis. While immunohistochemistry is very useful in identifying abnormal expression of primary protein abnormalities in recessive conditions, it is less helpful in detecting primary defects in dominantly inherited disorders. Abnormal immunohistochemical expression patterns can be confirmed by Western blot analysis which may also be informative in dominant disorders, although its role has yet to be established. Besides identification of specific protein defects, immunohistochemistry is also helpful in the differentiation of inflammatory myopathies by subtyping cellular infiltrates and demonstrating up-regulation of subtle immunological parameters such as cell adhesion molecules. The role of immunohistochemistry in denervating disorders, however, remains controversial in the absence of a reliable marker of muscle fibre denervation. Nevertheless, as well as the diagnostic value of immunocytochemical analysis it may also widen understanding of muscle fibre pathology as well as help in the development of therapeutic strategies.

Dysferlin Interacts with Affixin (β-Parvin) at the Sarcolemma

The dysferlin gene is defective in Miyoshi myopathy (MM) and limb girdle muscular dystrophy type 2B (LGMD2B). Dysferlin is a sarcolemmal protein that is implicated in calcium-dependent membrane repair. Affixin (beta-parvin) is a novel, integrin-linked kinase-binding protein that is involved in the linkage between integrin and the cytoskeleton. Here we show that affixin is a dysferlin binding protein that colocalizes with dysferlin at the sarcolemma of normal human skeletal muscle. The immunoreactivity of affixin was reduced in sarcolemma of MM and LGMD2B muscles, although the total amount of the affixin protein was normal. Altered immunoreactivity of affixin was also observed in other muscle diseases including LGMD1C, where both affixin and dysferlin showed quite similar changes with a reduction of sarcolemmal staining with or without cytoplasmic accumulations. Colocalization of dysferlin and affixin was confirmed by immunofluorescence analysis using dysferlin-expressing C2 myoblasts. Wild-type and mutant dysferlin colocalized with endogenous affixin. The interaction of dysferlin and affixin was confirmed by immunoprecipitation study using normal human and mouse skeletal muscles. Using immunoprecipitation with deletion mutants of dysferlin, we have identified that C-terminal region of dysferlin is an apparent binding site for affixin. We also found N-terminal calponin homology domain of affixin as a binding site for dysferlin. Our results suggest that affixin may participate in membrane repair with dysferlin.

Human umbilical cord blood cells differentiate into muscle in sjl muscular dystrophy mice

Limb girdle muscular dystrophy type 2B form (LGMD-2B) and Miyoshi myopathy (MM) are both caused by mutations in the dysferlin (dysf) gene. In this study, we used dysferlin-deficient sjl mice as a mouse model to study cell therapy for LGMD-2B and MM. A single-blind study evaluated the therapeutic potential of human umbilical cord blood (HUCB) as a source of myogenic progenitor stem cells. Three groups of donor cells were used: unfractionated mononuclear HUCB cells, HUCB subfractionated to enrich for cells that were negative for lineage surface markers (LIN(-)) and substantially enriched for the CD34 surface marker (CD34(+)), and irradiated control spleen cells. We administrated 1 x 10(6) donor cells to each animal intravenously and euthanized them at different time points (1-12 weeks) after transplantation. All animals were immunosuppressed (FK506 and leflunomide) from the day before the injection until the time of euthanasia. Immunohistochemical analyses documented that a small number of human cells from the whole HUCB and LIN(-)CD34(+/-)-enriched HUCB subgroups engraft in the recipient muscle to express both dysferlin and human-specific dystrophin at 12 weeks after transplantation. We conclude that myogenic progenitor cells are present in the HUCB, that they can disseminate into muscle after intravenous administration, and that they are capable of myogenic differentiation in host muscle.

Myostatin propeptide‐mediated amelioration of dystrophic pathophysiology

Mutations in myostatin (GDF8) cause marked increases in muscle mass, suggesting that this transforming growth factor-beta (TGF-beta) superfamily member negatively regulates muscle growth. Myostatin blockade therefore offers a strategy for reversing muscle wasting in Duchenne's muscular dystrophy (DMD) without resorting to genetic manipulation. Here, we demonstrate that pharmacological blockade using a myostatin propeptide stabilized by fusion to IgG-Fc improved pathophysiology of the mdx mouse model of DMD. Functional benefits evidenced by specific force improvement, exceeded those reported previously using myostatin antibody-mediated blockade. More importantly, use of a propeptide blockade strategy obviates possibilities of anti-idiotypic responses that could potentially limit the effectiveness of antibody-mediated myostatin blockade strategies over time. This study provides a novel pharmacological strategy for treatment of diseases associated with muscle wasting such as DMD and since it uses an endogenous inhibitor of myostatin should help circumvent technical hurdles and toxicity associated with conventional gene or cell based therapies.

The Clinical Features of Facioscapulohumeral Muscular Dystrophy Associated With Borderline (>/=35 kb) 4q35 EcoRI Fragments

OBJECTIVES

: The objectives of this study were to characterize the clinical features of facioscapulohumeral muscular dystrophy (FSHD) in patients with borderline (>/=35 kb) EcoRI fragments and to compare patients with borderline EcoRI fragments with FSHD patients harboring fragments of <35 kb.

BACKGROUND

: Most patients with FSHD harbor 4q35 EcoRI fragments of less than 35 kb. The clinical findings in patients with borderline fragments are not well known.

METHODS

: The authors conducted a retrospective review of patients with FSHD followed at a regional neuromuscular center over a 12-year period.

RESULTS

: Eleven patients with DNA-positive FSHD, found to harbor borderline (>/=35 kb) EcoRI fragments (group 1), were compared with 30 patients with fragments of <35 kb (group 2). Group 1 patients were less likely (18%) to present with the classic FSHD phenotype as compared with group 2 patients (63%). Statistically significant differences in clinical disease severity and manual muscle testing scores were noted between the 2 groups, with group 1 patients showing less severe weakness and disability at presentation.

CONCLUSIONS

: Patients with borderline fragments are more likely to have a partial or less severe form of FSHD, probably resulting from a less disruptive DNA alteration at the 4q35 locus.

Diagnostic Immunohistology of Muscle Diseases

The diagnostic muscle biopsy has seen the use of virtually every histologic technique in existence over the past 50 years. Since the 1960s, enzyme histochemistry has become the chief technique in evaluating muscle biopsies. However, the increasing knowledge of cellular constituents and associated connective tissue of the myofiber coupled with the increasing availability of a broad diversity of antibodies to these proteins promises to bring the diagnosis of muscle disease to the same state of dependency upon immunohistochemistry as in the contemporary pathologic diagnosis of neoplasia. Immunohistochemistry may be used for both the identification of normal antigenic constituents in skeletal muscle and their loss, accumulation, or maldistribution in corresponding myopathies, sometimes with small biopsies or lacking frozen tissue, in paraffin sections. Three broad categories of muscle diseases will be characterized in terms of diagnostic antibodies in current use: dystrophic, congenital/structural, and inflammatory myopathies.

Recombinant adeno-associated virus vectors for gene therapy

Recombinant adeno-associated virus (rAAV) vectors are based on a non-pathogenic human parvovirus (AAV) that is unique in its ability to persist in human cells without causing any pathologic effects. Studies of the potential barriers to rAAV-mediated transduction of relatively resistant cells has led to an understanding of the mechanisms of cell attachment and entry, cytoplasmic translocation, nuclear entry, conversion to active double-stranded DNA, activation of transcription and establishment of persistent molecular forms. Each of these areas is individually discussed, as are recent applications in vivo in preclinical models and clinical trials.

Dysferlinopathy associated with rigid spine syndrome

Dysferlinopathy and rigid spine syndrome occurring in a 50-year-old man is reported. The patient noticed stiffness of knee and ankle joints, which gradually extended to neck, wrist and elbow joints leading to difficulty in anterior flexion. Muscular weakness and wasting of the lower extremities had developed since age 40, accompanied by a limitation of anterior bending of the spine. Elevated serum CK was noticed. Muscle CT revealed atrophy with moderate fatty replacement of muscles in the neck, shoulder and pelvic girdle, and marked replacement in the para-vertebral muscles, posterior compartment of hamstrings and calf muscles. Electromyography showed a typical myogenic pattern, and muscle biopsy disclosed dystrophic changes, compatible with limb-girdle muscular dystrophy 2B. Loss of dysferlin expression was verified by immunohistochemistry, which was confirmed by a mini-multiplex Western blotting system. Gene analyses of the dysferlin gene disclosed compound heterozygotes for frameshift (G3016 + 1A) and a missense mutation (G3370T). This study might propose some clues to resolve the combination of musular dystrophies and rigid spine syndrome.

Molecular diagnosis of inheritable neuromuscular disorders. Part II: Application of genetic testing in neuromuscular disease

Molecular genetic advances have led to refinements in the classification of inherited neuromuscular disease, and to methods of molecular testing useful for diagnosis and management of selected patients. Testing should be performed as targeted studies, sometimes sequentially, but not as wasteful panels of multiple genetic tests performed simultaneously. Accurate diagnosis through molecular testing is available for the vast majority of patients with inherited neuropathies, resulting from mutations in three genes (PMP22, MPZ, and GJB1); the most common types of muscular dystrophies (Duchenne and Becker, facioscapulohumeral, and myotonic dystrophies); the inherited motor neuron disorders (spinal muscular atrophy, Kennedy's disease, and SOD1 related amyotrophic lateral sclerosis); and many other neuromuscular disorders. The role of potential multiple genetic influences on the development of acquired neuromuscular diseases is an increasingly active area of research.