Abnormal localization of laminin subunits in muscular dystrophies

Identification of Candidate Protein Markers in Skeletal Muscle of Laminin-211-Deficient CMD Type 1A-Patients

Laminin-211 deficiency leads to the most common form of congenital muscular dystrophy in childhood, MDC1A. The clinical picture is characterized by severe muscle weakness, brain abnormalities and delayed motor milestones defining MDC1A as one of the most severe forms of congenital muscular diseases. Although the molecular genetic basis of this neurological disease is well-known and molecular studies of mouse muscle and human cultured muscle cells allowed first insights into the underlying pathophysiology, the definition of marker proteins in human vulnerable tissue such as skeletal muscle is still lacking. To systematically address this need, we analyzed the proteomic signature of laminin-211-deficient vastus muscle derived from four patients and identified 86 proteins (35 were increased and 51 decreased) as skeletal muscle markers and verified paradigmatic findings in a total of two further MDC1A muscle biopsies. Functions of proteins suggests fibrosis but also hints at altered synaptic transmission and accords with central nervous system alterations as part of the clinical spectrum of MDC1A. In addition, a profound mitochondrial vulnerability of the laminin-211-deficient muscle is indicated and also altered abundances of other proteins support the concept that metabolic alterations could be novel mechanisms that underline MDC1A and might constitute therapeutic targets. Intersection of our data with the proteomic signature of murine laminin-211-deficient gastrocnemius and diaphragm allowed the definition of nine common vulnerable proteins representing potential tissue markers.

Plasticity of the Muscle Stem Cell Microenvironment

Satellite cells (SCs) are adult muscle stem cells capable of repairing damaged and creating new muscle tissue throughout life. Their functionality is tightly controlled by a microenvironment composed of a wide variety of factors, such as numerous secreted molecules and different cell types, including blood vessels, oxygen, hormones, motor neurons, immune cells, cytokines, fibroblasts, growth factors, myofibers, myofiber metabolism, the extracellular matrix and tissue stiffness. This complex niche controls SC biology-quiescence, activation, proliferation, differentiation or renewal and return to quiescence. In this review, we attempt to give a brief overview of the most important players in the niche and their mutual interaction with SCs. We address the importance of the niche to SC behavior under physiological and pathological conditions, and finally survey the significance of an artificial niche both for basic and translational research purposes.

A Homozygous LAMA2 Mutation of c.818G>A Caused Partial Merosin Deficiency in a Japanese Patient

A complete loss of merosin, which is encoded by LAMA2, causes congenital muscular dystrophy with leukoencephalopathy. Partial merosin deficiency can be caused not only by primarily LAMA2 mutations, but also secondarily by dystroglycanopathy. Although it can be molecularly diagnosed based on a genetic analysis, this method is labor-intensive because of its huge genome size. A 26-year-old male patient presented with mild muscular weakness, joint contractures, and epilepsy. Double immunofluorescence staining of a muscle biopsy specimen showed mislocalization of merosin, and a genetic analysis revealed a homozygous c.818G>A (p.Arg273Lys) mutation in LAMA2. Double immunofluorescence staining and whole exome sequencing were useful for the diagnosis of partial merosin deficiency.

The role of laminins in the organization and function of neuromuscular junctions

The synapse between motor neurons and skeletal muscle is known as the neuromuscular junction (NMJ). Proper alignment of presynaptic and post-synaptic structures of motor neurons and muscle fibers, respectively, is essential for efficient motor control of skeletal muscles. The synaptic cleft between these two cells is filled with basal lamina. Laminins are heterotrimer extracellular matrix molecules that are key members of the basal lamina. Laminin α4, α5, and β2 chains specifically localize to NMJs, and these laminin isoforms play a critical role in maintenance of NMJs and organization of synaptic vesicle release sites known as active zones. These individual laminin chains exert their role in organizing NMJs by binding to their receptors including integrins, dystroglycan, and voltage-gated calcium channels (VGCCs). Disruption of these laminins or the laminin-receptor interaction occurs in neuromuscular diseases including Pierson syndrome and Lambert-Eaton myasthenic syndrome (LEMS). Interventions to maintain proper level of laminins and their receptor interactions may be insightful in treating neuromuscular diseases and aging related degeneration of NMJs.

Understanding the Role of ECM Protein Composition and Geometric Micropatterning for Engineering Human Skeletal Muscle

Skeletal muscle lost through trauma or disease has proven difficult to regenerate due to the challenge of differentiating human myoblasts into aligned, contractile tissue. To address this, we investigated microenvironmental cues that drive myoblast differentiation into aligned myotubes for potential applications in skeletal muscle repair, organ-on-chip disease models and actuators for soft robotics. We used a 2D in vitro system to systematically evaluate the role of extracellular matrix (ECM) protein composition and geometric patterning for controlling the formation of highly aligned myotubes. Specifically, we analyzed myotubes differentiated from murine C2C12 cells and human skeletal muscle derived cells (SkMDCs) on micropatterned lines of laminin compared to fibronectin, collagen type I, and collagen type IV. Results showed that laminin supported significantly greater myotube formation from both cells types, resulting in greater than twofold increase in myotube area on these surfaces compared to the other ECM proteins. Species specific differences revealed that human SkMDCs uniaxially aligned over a wide range of micropatterned line dimensions, while C2C12s required specific line widths and spacings to do the same. Future work will incorporate these results to engineer aligned human skeletal muscle tissue in 2D for in vitro applications in disease modeling, drug discovery and toxicity screening.

Extracellular matrix regulation in the muscle satellite cell niche

Increasing evidence points to extracellular matrix (ECM) components playing integral roles in regulating the muscle satellite cell (SC) niche. Even small alterations to the niche ECM can have profound effects on SC localization, activation, self-renewal, proliferation and differentiation. This review will focus on the ECM components that comprise the niche, how they are modulated in health and disease and how these changes are thought to affect SC function. Particular emphasis will be placed on the pathological niche and interventions that aim to restore healthy structure and function, as a better understanding of the interplay between the SC and its environment will drive more targeted and effective therapies.

Anoctamin 5 muscular dystrophy in Denmark: prevalence, genotypes, phenotypes, cardiac findings, and muscle protein expression

Since the initial description in 2010 of anoctamin 5 deficiency as a cause of muscular dystrophy, a handful of papers have described this disease in cases of mixed populations. We report the first large regional study and present data on new aspects of prevalence, muscular and cardiac phenotypic characteristics, and muscle protein expression. All patients in our neuromuscular unit with genetically unclassified, recessive limb girdle muscular dystrophy (LGMD2), Miyoshi-type distal myopathy (MMD) or persistent asymptomatic hyperCK-emia (PACK) were assessed for mutations in the ANO5 gene. Genetically confirmed patients were evaluated with muscular and cardiopulmonary examination. Among 40 unclassified patients (28 LGMD2, 5 MMD, 7 PACK), 20 were homozygous or compound heterozygous for ANO5 mutations, (13 LGMD2, 5 MMD, 2 PACK). Prevalence of ANO5 deficiency in Denmark was estimated at 1:100.000 and ANO5 mutations caused 11 % of our total cohort of LGMD2 cases making it the second most common LGMD2 etiology in Denmark. Eight patients complained of dysphagia and 3 dated symptoms of onset in childhood. Cardiac examinations revealed increased frequency of premature ventricular contractions. Four novel putative pathogenic mutations were discovered. Total prevalence and distribution of phenotypes of ANO5 disease in a representative regional cohort are described for the first time. A high prevalence of ANO5 deficiency was found among patients with unclassified LGMD2 (46 %) and MMD (100 %). The high incidence of reported dysphagia is a new phenotypic feature not previously reported, and cardiac investigations revealed that ANO5-patients may have an increased risk of ventricular arrhythmia.

Sarcolemma instability during mechanical activity in Largemyd cardiac myocytes with loss of dystroglycan extracellular matrix receptor function

The abnormal glycosylation and loss of extracellular matrix receptor function of the protein dystroglycan (DG) lead to the development of muscular dystrophy and cardiomyopathy. Dystroglycan is an important receptor for extracellular matrix proteins, such as laminin, in the basement membrane surrounding muscle. Large(myd) mice have a null mutation in a gene encoding the glycosyltransferase LARGE that results in abnormal glycosylation of α-DG and phenotypes similar to those in human α-DG glycosylation-deficient muscular dystrophy. Here, we show that Large(myd) hearts with the loss of DG extracellular matrix receptor function display a cardiomyopathy characterized by myocyte damage in patches of cells positive for membrane impermeant dyes. To examine the cellular mechanisms, we show that isolated adult cardiac myocytes from Large(myd) mice retain normal laminin-dependent cell adhesion, cell surface laminin deposition and basement membrane assembly. However, although isolated adult cardiac myocytes with the loss of α-DG glycosylation adhere normally to laminin substrates both passively and in the presence of mechanical activity, Large(myd) myocytes rapidly take up membrane impermeant dye following cyclical cell stretching. Therefore, while other cell surface laminin receptors are likely responsible for myocardial cell adhesion to the basement membrane, DG has a unique function of stabilizing the cardiac myocyte plasma membrane during repetitive mechanical activity by tightly binding the transmembrane dystrophin-glycoprotein complex to the extracellular matrix. This function of DG to stabilize the myocyte membrane during normal physiologic cell length changes is likely critical for the prevention of the myocardial damage and subsequent remodeling observed in α-DG glycosylation-deficient muscular dystrophies.

Skeletal muscle laminin and MDC1A: pathogenesis and treatment strategies

Laminin-211 is a cell-adhesion molecule that is strongly expressed in the basement membrane of skeletal muscle. By binding to the cell surface receptors dystroglycan and integrin α7β1, laminin-211 is believed to protect the muscle fiber from damage under the constant stress of contractions, and to influence signal transmission events. The importance of laminin-211 in skeletal muscle is evident from merosin-deficient congenital muscular dystrophy type 1A (MDC1A), in which absence of the α2 chain of laminin-211 leads to skeletal muscle dysfunction. MDC1A is the commonest form of congenital muscular dystrophy in the European population. Severe hypotonia, progressive muscle weakness and wasting, joint contractures and consequent impeded motion characterize this incurable disorder, which causes great difficulty in daily life and often leads to premature death. Mice with laminin α2 chain deficiency have analogous phenotypes, and are reliable models for studies of disease mechanisms and potential therapeutic approaches. In this review, we introduce laminin-211 and describe its structure, expression pattern in developing and adult muscle and its receptor interactions. We will also discuss the molecular pathogenesis of MDC1A and advances toward the development of treatment.

Zebrafish Fukutin family proteins link the unfolded protein response with dystroglycanopathies

Allelic mutations in putative glycosyltransferase genes, fukutin and fukutin-related protein (fkrp), lead to a wide range of muscular dystrophies associated with hypoglycosylation of α-dystroglycan, commonly referred to as dystroglycanopathies. Defective glycosylation affecting dystroglycan–ligand interactions is considered to underlie the disease pathogenesis. We have modelled dystroglycanopathies in zebrafish using a novel loss-of-function dystroglycan allele and by inhibition of Fukutin family protein activities. We show that muscle pathology in embryos lacking Fukutin or FKRP is different from loss of dystroglycan. In addition to hypoglycosylated α-dystroglycan, knockdown of Fukutin or FKRP leads to a notochord defect and a perturbation of laminin expression before muscle degeneration. These are a consequence of endoplasmic reticulum stress and activation of the unfolded protein response (UPR), preceding loss of dystroglycan–ligand interactions. Together, our results suggest that Fukutin family proteins may play important roles in protein secretion and that the UPR may contribute to the phenotypic spectrum of some dystroglycanopathies in humans.

Fukutin gene mutations cause dilated cardiomyopathy with minimal muscle weakness

OBJECTIVE

The fukutin gene (FKTN) is the causative gene for Fukuyama-type congenital muscular dystrophy, characterized by rather homogeneous clinical features of severe muscle wasting and hypotonia from early infancy with mental retardation. In contrast with the severe dystrophic involvement of skeletal muscle, cardiac insufficiency is quite rare. Fukuyama-type congenital muscular dystrophy is one of the disorders associated with glycosylation defects of alpha-dystroglycan, an indispensable molecule for intra-extra cell membrane linkage.

METHODS

Protein and functional analyses of alpha-dystroglycan and mutation screening of FKTN and other associated genes were performed.

RESULTS

Surprisingly, we identified six patients in four families showing dilated cardiomyopathy with no or minimal limb girdle muscle involvement and normal intelligence, associated with a compound heterozygous FKTN mutation. One patient died by rapid progressive dilated cardiomyopathy at 12 years old, and the other patient received cardiac implantation at 18 years old. Skeletal muscles from the patients showed minimal dystrophic features but have altered glycosylation of alpha-dystroglycan and reduced laminin binding ability. One cardiac muscle that underwent biopsy showed altered glycosylation of alpha-dystroglycan similar to that observed in a Fukuyama-type congenital muscular dystrophy patient.

INTERPRETATION

FKTN mutations could cause much wider spectrum of clinical features than previously perceived, including familial dilated cardiomyopathy and mildest limb girdle muscular dystrophy.

Bone marrow transplantation improves outcome in a mouse model of congenital muscular dystrophy

We examined whether pathogenesis in dystrophin-deficient (mdx) mice and laminin-alpha2-deficient (dy) mice is ameliorated by bone marrow transplantation (BMT). Green fluorescent protein (GFP) mice were used as donors. In mdx mice, BMT failed to produce any significant differences in muscle pathology, although some GFP-positive fibers with restored dystrophin expression were observed. In contrast, in the dy mice, BMT led to a significant increase in lifespan and an increase in growth rate, muscle strength, and respiratory function. We conclude that BMT improved outcome in dy mice but not mdx mice.

Laminin-induced autoimmune myositis in rats

The present study aimed to examine if immunization with laminin causes myositis in rats and whether the pathologic findings mirror human polymyositis and dermatomyositis. Rats were immunized with an emulsion of laminin and complete Freund's adjuvant. As a result, muscle fiber necrosis with infiltrating macrophages was frequently observed and mononuclear cells were observed in the endomysium. These mononuclear cells were composed of CD4+ cells, CD8+ T cells, and macrophages. CD4+ cells and CD8+ T cells were mainly located in the endomysium, whereas a large number of macrophages were located in the endomysium and infiltrating muscle fibers. A small number of B cells, detected by immunohistochemical staining, were mainly located in the perimysium. The nonnecrotic muscle fiber to which CD4+ T cells, CD8+ T cells, and perforin+ cells adhered was negative for antimerosin and antidystrophin antibodies. Muscle fiber necrosis in rats immunized with laminin may occur after denaturation of basement membrane proteins. In conclusion, the immunization with laminin induces moderate to severe myositis. We suggest that laminin may be an important antigen for connective tissue diseases such as polymyositis and dermatomyositis.

Dystrophin-glycoproteins associated in congenital muscular dystrophy: immunohistochemical analysis of 59 Brazilian cases

The congenital muscular dystrophies (CMD) are heterogeneous muscular diseases with early and dystrophic pattern on muscle biopsy. Many different subtypes have been genetically identified and most phenotypes not yet identified belong to the merosin-positive (MP) CMD subgroup. OBJECTIVE: To analyze the immunohistochemical expression of the main proteins of the dystrophin-glycoproteins associated complex in muscle biopsy of patients with different CMD phenotypes, for investigating a possible correlation with clinical and histopathological data. METHOD: Fifty-nine patients with CMD had clinical, histopathological and immunohistochemical data evaluated: 32 had MP-CMD, 23 CMD with merosin deficiency (MD-CMD), one Ullrich phenotype and three Walker-Warburg disease. RESULTS: Dystrophin and dysferlin were normal in all; among the patients with MD-CMD, merosin deficiency was partial in nine who showed the same clinical severity as those with total deficiency; the reduced expression of a-sarcoglycan (SG) and alpha-dystroglycan (DG) showed statistically significant correlation with severe MD-CMD phenotype. CONCLUSION: There is a greater relationship between merosin and the former proteins; among MP-CMD patients, no remarkable immunohistochemical/phenotypical correlations were found, although the reduced expression of beta-DG had showed statistically significant correlation with severe phenotype and marked fibrosis on muscular biopsy.

The muscle integrin binding protein (MIBP) interacts with alpha7beta1 integrin and regulates cell adhesion and laminin matrix deposition

Integrins are alphabeta transmembrane receptors that function in key cellular processes, including cell adhesion, differentiation, and extracellular matrix deposition through interactions with extracellular, membrane, and cytoplasmic proteins. We previously identified and cloned a muscle beta1 integrin cytoplasmic binding protein termed MIBP and found that the expression level of MIBP is critical in the decision-making process of terminal myogenic differentiation. We report here that MIBP interacts with the alpha7beta1 integrin but not the alpha5beta1 integrin in C2C12 myoblasts, suggesting an important role of integrin alpha chains in the regulation of the beta1-MIBP interaction. Furthermore, consistent with its selective binding activity toward the alpha7beta1 laminin receptor, we have found that overexpression of MIBP in C2C12 myoblasts resulted in a significant reduction of cell adhesion to laminin and inhibition of laminin matrix deposition. By contrast, neither cell adhesion to fibronectin nor fibronectin matrix deposition was significantly altered in cells overexpressing MIBP. Finally, we show that both the protein level and tyrosine phosphorylation of paxillin, a key signaling molecule involved in the cellular control of myogenic differentiation, are increased by MIBP. These results suggest that MIBP functions in the control of myogenic differentiation by regulating alpha7beta1 integrin-mediated cell interactions with laminin matrix and intracellular signaling through paxillin.

Clinical and molecular study in congenital muscular dystrophy with partial laminin alpha 2 (LAMA2) deficiency

Complete laminin alpha2 (LAMA2) deficiency causes approximately half of congenital muscular dystrophy (CMD) cases. Many loss-of-function mutations have been reported in these severe, neonatal-onset patients, but only single missense mutations have been found in milder CMD with partial laminin alpha2 deficiency. Here, we studied nine patients diagnosed with CMD who showed abnormal white-matter signal at brain MRI and partial deficiency of laminin alpha2 on immunofluorescence of muscle biopsy. We screened the entire 9.5 kb laminin alpha2 mRNA from patient muscle biopsy by direct capillary automated sequencing, single strand conformational polymorphism (SSCP), or denaturing high performance liquid chromatography (DHPLC) of overlapping RT-PCR products followed by direct sequencing of heteroduplexes. We identified laminin alpha2 sequence changes in six of nine CMD patients. Each of the gene changes identified, except one, was novel, including three missense changes and two splice-site mutations. The finding of partial laminin alpha2 deficiency by immunostaining is not specific for laminin alpha2 gene mutation carriers, with only two patients (22%) showing clear causative mutations, and an additional three patients (33%) showing possible mutations. The clinical presentation and disease progression was homogeneous in the laminin alpha2-mutation positive and negative CMD patients.

Profound skeletal muscle depletion of alpha-dystroglycan in Walker-Warburg syndrome

Walker-Warburg syndrome (WWS) is an autosomal recessive disorder characterized by the combined involvement of the central nervous and skeletal muscle systems. Although the molecular basis of WWS remains unknown, defects in the muscle fibre basal lamina are characteristic of other forms of congenital muscular dystrophy (CMD). In agreement with this, some forms of CMD, due to glycosyltransferase defects, display a reduction in the immunolabelling of alpha-dystroglycan, whilst beta-dystroglycan labelling appears normal. Here we describe an almost complete absence of alpha-dystroglycan using both immunohistochemistry and immunoblotting in two patients with WWS. In addition, there was a mild reduction of laminin-alpha 2. In contrast, immunohistochemical labelling of perlecan and collagen VI was normal. Linkage analysis excluded the recently identified POMT1 locus, responsible for a proportion of WWS cases. These results confirm that WWS is a genetically heterogeneous condition and suggest that disruption of the alpha-dystroglycan/laminin-alpha 2 axis in the basal lamina may play a role in the degeneration of muscle fibres in WWS-also in cases not due to POMT1 defects.

Deficiency of a 180-kDa extracellular matrix protein in Fukuyama type congenital muscular dystrophy skeletal muscle

Abnormalities of the proteins constituting the extracellular matrix have been shown to play important roles in the molecular pathogenesis of muscular dystrophies. In the present study, we have established a monoclonal antibody against a human skeletal muscle extracellular matrix protein. The antibody M1 recognized a single 180-kDa protein (p180) by immunoblot analysis of normal human skeletal muscle and gave a strong and continuous signal along the sarcolemma by immunohistochemical analysis. Furthermore, p180 could be solubilized either under a strong alkaline condition, or in the presence of EDTA or detergents such as Triton X-100, indicating that p180 was an extracellular matrix protein. Interestingly, p180 was deficient in the skeletal muscle of the patients with Fukuyama-type congenital muscular dystrophy (FCMD), but not other muscular diseases, by both immunohistochemical and immunoblot analyses. We presume that the deficiency of p180 in FCMD is caused specifically by the primary deficiency of fukutin, the causative protein of FCMD, and plays an important role in muscle cell degeneration in this disease.

A variant of congenital muscular dystrophy

We analyzed three Japanese patients (two boys and a girl) from two families with congenital muscular dystrophy (CMD) and brain involvement. One of the two families had two affected siblings of different sexes. Parental consanguinity was not documented in either family. All patients showed generalized hypotonia and weakness from infancy, delayed psychomotor development, facial muscle involvement, and joint contractures. Serum creatine kinase levels were markedly elevated. The histological change seen on muscle biopsy was characteristic of a dystrophic process, although dystrophin and merosin staining were normal. On MR imaging, cortical dysplasia and cerebral white matter abnormalities were observed. Although these clinical, myopathological and neuroradiological findings were typical of Fukuyama-type CMD (FCMD), full mutational analysis of the fukutin gene revealed neither a 3 kb insertion (Japanese founder mutation) nor point mutations. RT-PCR analysis of RNA isolated from lymphoblasts of a patient revealed normal expression of the FCMD transcript. As classification of CMD should be based on genetic background, our present cases with typical clinical, myopathological and neuroradiological findings of FCMD without mutation of the fukutin gene may represent a new variant (or variants) of CMD that is different from FCMD.

Mutations in the fukutin-related protein gene (FKRP) cause a form of congenital muscular dystrophy with secondary laminin alpha2 deficiency and abnormal glycosylation of alpha-dystroglycan

The congenital muscular dystrophies (CMD) are a heterogeneous group of autosomal recessive disorders presenting in infancy with muscle weakness, contractures, and dystrophic changes on skeletal-muscle biopsy. Structural brain defects, with or without mental retardation, are additional features of several CMD syndromes. Approximately 40% of patients with CMD have a primary deficiency (MDC1A) of the laminin alpha2 chain of merosin (laminin-2) due to mutations in the LAMA2 gene. In addition, a secondary deficiency of laminin alpha2 is apparent in some CMD syndromes, including MDC1B, which is mapped to chromosome 1q42, and both muscle-eye-brain disease (MEB) and Fukuyama CMD (FCMD), two forms with severe brain involvement. The FCMD gene encodes a protein of unknown function, fukutin, though sequence analysis predicts it to be a phosphoryl-ligand transferase. Here we identify the gene for a new member of the fukutin protein family (fukutin related protein [FKRP]), mapping to human chromosome 19q13.3. We report the genomic organization of the FKRP gene and its pattern of tissue expression. Mutations in the FKRP gene have been identified in seven families with CMD characterized by disease onset in the first weeks of life and a severe phenotype with inability to walk, muscle hypertrophy, marked elevation of serum creatine kinase, and normal brain structure and function. Affected individuals had a secondary deficiency of laminin alpha2 expression. In addition, they had both a marked decrease in immunostaining of muscle alpha-dystroglycan and a reduction in its molecular weight on western blot analysis. We suggest these abnormalities of alpha-dystroglycan are caused by its defective glycosylation and are integral to the pathology seen in MDC1C.

The expanding phenotype of laminin alpha2 chain (merosin) abnormalities: case series and review

Initial reports of patients with laminin alpha2 chain (merosin) deficiency had a relatively homogeneous phenotype, with classical congenital muscular dystrophy (CMD) characterised by severe muscle weakness, inability to achieve independent ambulation, markedly raised creatine kinase, and characteristic white matter hypodensity on cerebral magnetic resonance imaging. We report a series of five patients with laminin alpha2 deficiency, only one of whom has this severe classical CMD phenotype, and review published reports to characterise the expanded phenotype of laminin alpha2 deficiency, as illustrated by this case series. While classical congenital muscular dystrophy with white matter abnormality is the commonest phenotype associated with laminin alpha2 deficiency, 12% of reported cases have later onset, slowly progressive weakness more accurately designated limb-girdle muscular dystrophy. In addition, the following clinical features are reported with increased frequency: mental retardation (~6%), seizures (~8%), subclinical cardiac involvement (3-35%), and neuronal migration defects (4%). At least 25% of patients achieve independent ambulation. Notably, three patients with laminin alpha2 deficiency were asymptomatic, 10 patients had normal MRI (four with LAMA2 mutations reported), and between 10-20% of cases had maximum recorded creatine kinase of less than 1000 U/l. LAMA2 mutations have been identified in 25% of cases. Sixty eight percent of these have the classical congenital muscular dystrophy, but this figure is likely to be affected by ascertainment bias. We conclude that all dystrophic muscle biopsies, regardless of clinical phenotype, should be studied with antibodies to laminin alpha2. In addition, the use of multiple antibodies to different regions of laminin alpha2 may increase the diagnostic yield and provide some correlation with severity of clinical phenotype.

Merosin-positive congenital muscular dystrophy with mental retardation, microcephaly and central nervous system abnormalities unlinked to the Fukuyama muscular dystrophy and muscular-eye-brain loci: report of three siblings

Classical merosin (2 laminin)-positive congenital muscular dystrophy is a heterogeneous subgroup of disorders; a few cases characterized by severe mental retardation, brain involvement and no ocular abnormalities were called Fukuyama-like congenital muscular dystrophy. We report a family of healthy non-consanguineous parents, with four affected siblings, of which one died at the age of 7 months due to an intercurrent illness, who presented congenital hypotonia, severe mental retardation, microcephaly, delayed psychomotor development, generalized muscular wasting and weakness with mild facial involvement, calf pseudohypertrophy, joint contractures and areflexia. Muscle biopsy disclosed severe muscular dystrophy. Immunostaining for laminin 2 80 kDa and clone Mer3/22B2 monoclonal antibodies, 1 and 1 chain was preserved. Magnetic resonance imaging findings were consistent with pontocerebellar hypoplasia, bilateral opercular abnormalities and focal cortical dysplasia as well as minute periventricular white matter changes. Clusters of small T2-weighted focal hyperintensities in both cerebellar hemispheres consistent with cysts were observed in two of the three siblings studied with magnetic resonance imaging. Ophthalmologic and cardiologic examination was normal. Haplotype analysis using microsatellite markers excluded the Fukuyama congenital muscular dystrophy, LAMA2 and muscle-eye-brain disease loci. Thus, a wider spectrum of phenotypes, gene defects and protein deficiencies might be involved in congenital muscular dystrophy with brain abnormalities.

Massive muscle cell degeneration in the early stage of merosin-deficient congenital muscular dystrophy

Primary merosin-deficient congenital muscular dystrophy (CMD) is a severe form of congenital muscular disorder which is caused by mutations in the laminin alpha2 chain gene (LAMA2). The disease is characterized by marked dystrophic changes in skeletal muscles during early infancy, while little is known about the pathological process of the muscle fiber degeneration. Here, we report the immunohistochemical analysis of skeletal muscle in ten patients with primary merosin-deficient CMD using a panel of molecular markers for skeletal muscle proteins, cellular necrosis, and apoptosis. In the youngest patient (a 52 day old baby), prominent massive muscle cell degeneration occurred in association with the deposition of the C5-9 complement membrane attack complex (MAC). Most of the MAC-positive muscle fibers showed a severely deranged immunoreaction to dystrophin, dystroglycans, and other sarcolemmal proteins. In addition, we found scattered positive signals for apoptosis. Similar but milder changes were also observed in six other patients younger than 1 year. In the patients older than 3 years, muscle fibers positive for MAC and apoptotic signals were barely detectable. These findings imply that massive muscle fiber degeneration occurs in the very early stage of merosin-deficient CMD and may contribute to the severe dystrophic changes in muscle from early infancy.

Purification of mouse primary myoblasts based on alpha 7 integrin expression

Fundamental insights have come from the study of myogenesis. Primary myoblasts isolated directly from muscle tissue more closely approximate myogenesis than established cell lines. However, contamination of primary muscle cultures with nonmyogenic cells can complicate the results. To overcome this problem, we previously described a method for myoblast purification based on novel culture conditions (T. A. Rando and H. M. Blau, 1994, J. Cell Biol. 125, 1275--1287). Here we report a refinement of this method that leads directly to an enriched population of mouse primary myoblasts, within significantly fewer population doublings. The method described here avoids using adhesion as a criterion for selection. This advance capitalizes on the ability of the antibody CA5.5 to recognize alpha 7 integrin, a muscle-specific cell surface antigen. Enrichment of myoblasts to greater than 95% of the cell population can be achieved by a single round of flow cytometry or magnetic bead separation. This is the first description of a mouse myoblast purification method based on a cell-type-specific antigen. The ease of this procedure for isolating primary myoblasts should expand the opportunities for (1) using these cells in cell transplantation studies in animal models of human disease, (2) isolating and characterizing mutant myoblasts from transgenic animals, and (3) allowing in vitro studies of molecules that regulate muscle cell growth, differentiation, and neoplasia.

Fukuyama muscular dystrophy associated with lack of C-terminal domain of dystrophin

The first reported female patient with the Fukuyama type of congenital muscular dystrophy associated with a lack of C-terminal domain of dystrophin is presented. Clinically, the patient had characteristic features and magnetic resonance imaging findings of Fukuyama muscular dystrophy. Dystrophin analysis revealed a lack of the C-terminal domain but preserved N-terminal and rod domains of dystrophin in biopsied muscle. Moreover, she had reduced expression of merosin, syntrophin, and beta-dystroglycan in the skeletal muscle. Reverse transcriptase-polymerase chain reaction analysis of mRNA in the patient's muscle illustrated a complete lack of exons 71-74 of the dystrophin gene. These deletions, which remove the beta-dystroglycan and syntrophin binding site, may cause changes in the function of both beta-dystroglycan and syntrophin in human muscle.

Enhanced expression of the alpha 7 beta 1 integrin reduces muscular dystrophy and restores viability in dystrophic mice

Muscle fibers attach to laminin in the basal lamina using two distinct mechanisms: the dystrophin glycoprotein complex and the alpha 7 beta 1 integrin. Defects in these linkage systems result in Duchenne muscular dystrophy (DMD), alpha 2 laminin congenital muscular dystrophy, sarcoglycan-related muscular dystrophy, and alpha 7 integrin congenital muscular dystrophy. Therefore, the molecular continuity between the extracellular matrix and cell cytoskeleton is essential for the structural and functional integrity of skeletal muscle. To test whether the alpha 7 beta 1 integrin can compensate for the absence of dystrophin, we expressed the rat alpha 7 chain in mdx/utr(-/-) mice that lack both dystrophin and utrophin. These mice develop a severe muscular dystrophy highly akin to that in DMD, and they also die prematurely. Using the muscle creatine kinase promoter, expression of the alpha 7BX2 integrin chain was increased 2.0-2.3-fold in mdx/utr(-/-) mice. Concomitant with the increase in the alpha 7 chain, its heterodimeric partner, beta 1D, was also increased in the transgenic animals. Transgenic expression of the alpha 7BX2 chain in the mdx/utr(-/-) mice extended their longevity by threefold, reduced kyphosis and the development of muscle disease, and maintained mobility and the structure of the neuromuscular junction. Thus, bolstering alpha 7 beta 1 integrin-mediated association of muscle cells with the extracellular matrix alleviates many of the symptoms of disease observed in mdx/utr(-/-) mice and compensates for the absence of the dystrophin- and utrophin-mediated linkage systems. This suggests that enhanced expression of the alpha 7 beta 1 integrin may provide a novel approach to treat DMD and other muscle diseases that arise due to defects in the dystrophin glycoprotein complex. A video that contrasts kyphosis, gait, joint contractures, and mobility in mdx/utr(-/-) and alpha 7BX2-mdx/utr(-/-) mice can be accessed at http://www.jcb.org/cgi/content/full/152/6/1207.

Desmin-related myopathies in mice and man

Desmin, the main intermediate filament (IF) protein in skeletal and heart muscle cells, is of great importance as a part of the cytoskeleton. The IFs surround and interlink myofibrils, and connect the peripheral myofibrils with the sarcolemma. In myotendinous junctions and neuromuscular junctions of skeletal muscle fibres, desmin is enriched. In the heart, desmin is increased at intercalated discs, the attachment between cardiomyocytes, and it is the main component in Purkinje fibres of the conduction system. Desmin is the first muscle-specific protein to appear during myogenesis. Nevertheless, lack of desmin, as shown from experiments with desmin knockout (K/O) mice, does not influence myogenesis or myofibrillogenesis. However, the desmin knock-out mice postnatally develop a cardiomyopathy and a muscle dystrophy in highly used skeletal muscles. In other skeletal muscles the organization of myofibrils is remarkably unaffected. Thus, the main consequence of the lack of desmin is that the muscle fibres become more susceptible to damage. The loss of membrane integrity leads to a dystrophic process, with degeneration and fibrosis. In the heart cardiac failure develops, whereas in affected skeletal muscles regenerative attempts are seen. In humans, accumulations of desmin have been a hallmark for presumptive desmin myopathies. Recent investigations have shown that some families with such a myopathy have a defect in the gene coding for alphaB-crystallin, whereas others have mutations in the desmin gene. Typical features of these patients are cardiac affections and muscle weakness. Thus, mutations in the desmin gene is pathogenic for a distinct type of muscle disorder.

Merosin-deficient congenital muscular dystrophy with mental retardation and cerebellar cysts unlinked to the LAMA2, FCMD and MEB loci

We report a case of congenital muscular dystrophy with secondary merosin deficiency, structural involvement of the central nervous system and mental retardation in an 8-year-old girl from a consanguineous family. She had early-onset hypotonia, generalized muscle wasting, with weakness especially of the neck muscles, joint contractures, mental retardation and high creatine kinase. Muscle biopsy showed dystrophic changes with partial deficiency of the laminin alpha(2) chain. Cranial magnetic resonance imaging revealed multiple small cysts in the cerebellum, without cerebral cortical dysplasia or white matter changes. The laminin alpha(2) chain (6q2), Fukuyama type congenital muscular dystrophy (9q31-q33) and muscle-eye-brain disease (1p32-p34) loci were all excluded by linkage analysis. We suggest that this case represents a new entity in the nosology of congenital muscular dystrophy.

Laminins of the neuromuscular system

The mammalian neuromuscular system expresses seven laminin genes (alpha 1, alpha 2, alpha 4, alpha 5, beta 1, beta 2, and gamma 1), produces seven isoforms of the laminin trimer (laminins 1, 2, 4, 8, 9, 10, and 11), and distributes these trimers to at least seven distinct basal laminae (perineurial, endoneurial, terminal Schwann cell, myotendinous junction, synaptic cleft, synaptic fold, and extrajunctional muscle). The patterns of expression, assembly, and distribution are regulated during development, and primary and secondary changes in laminin expression occur in several neuromuscular genetic disorders. Functional studies using knockout and transgenic mice, and purified laminins and cell types, demonstrate that laminins are required components of basal laminae in the neuromuscular system. Collectively, laminins have both structural and signaling functions; individually, laminin isoforms have unique roles in regulating the behavior of nerve, muscle, and Schwann cell. Among them, laminin-2 (alpha 2 beta 1 gamma 1) plays an important structural role in supporting the muscle plasma membrane, laminin-4 regulates adhesion and differentiation of the myotendinous junction, and laminin-11 regulates nerve terminal differentiation and Schwann cell motility. Together, these observations reveal remarkable diversity in the formation and function of laminins and basal laminae, and suggest avenues for addressing some neuromuscular diseases.

Molecular basis of muscular dystrophies

Muscular dystrophies represent a heterogeneous group of disorders, which have been largely classified by clinical phenotype. In the last 10 years, identification of novel skeletal muscle genes including extracellular matrix, sarcolemmal, cytoskeletal, cytosolic, and nuclear membrane proteins has changed the phenotype-based classification and shed new light on the molecular pathogenesis of these disorders. A large number of genes involved in muscular dystrophy encode components of the dystrophin-glycoprotein complex (DGC) which normally links the intracellular cytoskeleton to the extracellular matrix. Mutations in components of this complex are thought to lead to loss of sarcolemmal integrity and render muscle fibers more susceptible to damage. Recent evidence suggests the involvement of vascular smooth muscle DGC in skeletal and cardiac muscle pathology in some forms of sarcoglycan-deficient limb-girdle muscular dystrophy. Intriguingly, two other forms of limb-girdle muscular dystrophy are possibly caused by perturbation of sarcolemma repair mechanisms. The complete clarification of these various pathways will lead to further insights into the pathogenesis of this heterogeneous group of muscle disorders.

Muscular dystrophy

Muscular dystrophy is a group of genetically determined muscular disorders marked by progressive wasting and weakness of the skeletal muscle, but which often affect cardiac and smooth muscles or other tissues. The patterns of inheritance are either dominant or recessive although the gene may be defective because of a new mutation. Growing evidence revealed the marked heterogeneity of the muscle disorders, and considerable numbers of Japanese scientists and physicians have contributed to the research progress in muscular dystrophy. Among these the discovery of an increased serum creatine kinase activity in muscular dystrophy opened the way for the most reliable laboratory test for muscular dystrophy in 1959, and subsequently accelerated progress in a broad range of research areas in medicine. Progress in modern genetics and molecular pathology provided another breakthrough in muscular dystrophy research and, in 1987, dystrophin was identified, a deficiency of which causes DMD. The present review article highlights contributions of Japanese scientists to muscular dystrophy research.

The Fukuyama congenital muscular dystrophy story

Fukuyama congenital muscular dystrophy is one of the most common autosomal recessive disorders in the Japanese population, characterized by congenital muscular dystrophy in combination with cortical dysgenesis (micropolygyria). Recently, we have identified the gene responsible for fukuyama congenital muscular dystrophy on 9q31, which encodes a novel 461-amino-acid protein termed fukutin. Most Fukuyama congenital muscular dystrophy-bearing chromosomes are derived from a single ancestral founder (87%), and a 3 kb-retrotransposal insertion into the 3' untranslated region of this gene was found to be a founder mutation. Two independent point mutations causing premature termination confirmed that that this gene is responsible for Fukuyama congenital muscular dystrophy. Fukuyama congenital muscular dystrophy is the first human disease to be caused by an ancient retrotransposal integration. Fukutin contains an amino-terminal signal sequence, which together with results from transfection experiments suggests that it is an extracellular protein. Discovery of the Fukuyama congenital muscular dystrophy gene represents an important step toward greater understanding of the pathogenesis of muscular dystrophies and also of normal brain development.

Heterogeneity of classic congenital muscular dystrophy with involvement of the central nervous system: report of five atypical cases

A heterogeneous group of patients with congenital muscular dystrophy associated with clinical or radiologic central nervous system involvement other than the severe classic form with merosin deficiency, muscle-eye-brain disease, and Walker-Warburg syndrome is described. A probable hereditary or familial occurrence could be suggested in all patients. One merosin-positive patient presented severe motor incapacity and cerebral atrophy without any clinical manifestation of central nervous system involvement. A second patient, also merosin-positive, had moderate motor and mental handicap, and epilepsy with no changes in neuroimaging. A third patient, found to have partial merosin deficiency by muscle biopsy, manifested severe psychomotor retardation and cerebral atrophy with foci of abnormal white-matter signal on magnetic resonance imaging. Finally, two merosin-positive siblings with microcephaly, mental retardation, and an incapacitating progressive neuromuscular course, exhibited cataracts without defects of neuronal migration or brain malformation. This report emphasizes the broad clinical spectrum and heterogeneity of merosin-positive congenital muscular dystrophy with associated central nervous system involvement, and illustrates the importance of further studies on clinical, immunohistochemical, and genetic grounds for identifying new subsets of congenital muscular dystrophy.

Assignment of a form of congenital muscular dystrophy with secondary merosin deficiency to chromosome 1q42

We have previously reported an autosomal recessive form of congenital muscular dystrophy, characterized by proximal girdle weakness, generalized muscle hypertrophy, rigidity of the spine, and contractures of the tendo Achilles, in a consanguineous family from the United Arab Emirates. Early respiratory failure resulting from severe diaphragmatic involvement was present. Intellect and the results of brain imaging were normal. Serum creatine kinase levels were grossly elevated, and muscle-biopsy samples showed dystrophic changes. The expression of the laminin-alpha2 chain of merosin was reduced on several fibers, but linkage analysis excluded the LAMA2 locus on chromosome 6q22-23. Here, we report the results of genomewide linkage analysis of this family, by use of homozygosity mapping. In all four affected children, an identical homozygous region was identified on chromosome 1q42, spanning 6-15 cM between flanking markers D1S2860 and D1S2800. We have identified a second German family with two affected children having similar clinical and histopathological features; they are consistent with linkage to the same locus. The cumulative LOD score was 3.57 (straight theta=.00) at marker D1S213. This represents a novel locus for congenital muscular dystrophy. We suggest calling this disorder "CMD1B." The expression of three functional candidate genes in the CMD1B critical region was investigated, and no detectable changes in their level of expression were observed. The secondary reduction in laminin-alpha2 chain in these families suggests that the primary genetic defect resides in a gene coding for a protein involved in basal lamina assembly.

Merosin and congenital muscular dystrophy

Merosin (also called as Laminin-2) is an isoform of laminin comprised of the alpha2, beta1 and gamma1 chains. In European populations, half of the patients with classical congenital muscular dystrophy have mutations of the LAMA2 gene (6q22-23) and present reduced or absence of laminin alpha2 chain. This form is generally referred to as merosin-deficient CMD. Merosin-deficient CMD is characterized by involvement of not only skeletal muscle but also central and peripheral nervous systems: Extensive brain white matter abnormalities are found by magnetic resonance imaging (MRI). However, most patients show no mental retardation. Recent case studies reported that some patients have several structural abnormalities such as abnormal cerebral cortical gyration, hypoplasia of cerebellum and pons, and dilation of ventricles. At present, functions of merosin related to muscle degeneration have not been fully elucidated. In addition, the mechanisms responsible for pathogenesis of diffuse brain white matter abnormalities remain to be determined. As mouse models for merosin-deficient CMD, three spontaneous mutants(dy, dy(2J), dy(PAS1)) and two mutants named dy(W) and dy(3K) by targeted gene disruption have been reported. These mice will help to elucidate the pathogenesis of merosin-deficient CMD and serve to develop therapy.

Muscle membrane-skeleton protein changes and histopathological characterization of muscle-eye-brain disease

Muscle-eye-brain disease belongs to congenital muscular dystrophies with central nervous system abnormalities. The etiology of MEB is still unknown, but abnormal immunoreactivity for laminin-2 has been reported. To evaluate disease progression in muscle tissue, 32 biopsy specimens from 17 muscle-eye-brain patients were analysed. The samples of four patients were studied by immunohistochemical techniques and by quantitative Western blotting. The samples showed a great variation in the muscle pathology. Regenerative fibers and mild fiber size variation were present in over 60%. At infancy, necrotic and regenerative fibers were common, while fat infiltration was the most prominent finding in the age group over five years. In quantitative studies, the amount of laminin alpha 2 chain was clearly reduced to 10-20% of normal. In contrast, laminin beta 2 chain was overexpressed in the Western blotting studies. These findings may reflect a yet unidentified primary disturbance in the basement membrane composition and function.

Novel mutations and genotype-phenotype relationships in 107 families with Fukuyama-type congenital muscular dystrophy (FCMD)

Fukuyama-type congenital muscular dystrophy (FCMD), one of the most common autosomal recessive disorders in the Japanese population, is characterized by congenital muscular dystrophy in combination with cortical dysgenesis (micropolygyria). Recently, we identified, on chromosome 9q31, the gene responsible for FCMD, which encodes a novel 461 amino acid protein which we have termed fukutin. Most FCMD-bearing chromosomes examined to date (87%) have been derived from a single ancestral founder, whose mutation consisted of a 3 kb retrotransposal insertion in the 3' non-coding region of the fukutin gene. FCMD is the first human disease known to be caused primarily by an ancient retrotransposal integration. We under-took a systematic analysis of the FCMD gene in 107 unrelated patients, and identified four novel non-founder mutations in five of them: one missense, one nonsense, one L1 insertion and a 1 bp insertion. The frequency of severe phenotypes, including Walker-Walberg syndrome-like manifestations such as hydrocephalus and microphthalmia, was significantly higher among probands who were compound heterozygotes carrying a point mutation on one allele and the founder mutation on the other, than it was among probands who were homozygous for the 3 kb retrotransposon. Remarkably, we detected no FCMD patients with non-founder (point) mutations on both alleles of the gene, and suggest that such cases might be embryonic-lethal. This could explain why few FCMD cases are reported in non-Japanese populations. Our results provided strong evidence that loss of function of fukutin is the major cause of FCMD, and appeared to shed some light on the mechanism responsible for the broad clinical spectrum seen in this disease.

Inherited disorders of the extracellular matrix

Primary and secondary defects in extracellular matrix proteins emphasize the role of these proteins in neuromuscular disorders; mutations have been found in the genes for the laminin-alpha 2 chain, for all three alpha chains of collagen VI and for integrin alpha 2. Secondary alterations in protein expression occur in association with these primary defects, and in other disorders they implicate the extracellular matrix. Animal models are helping to elucidate the function of some of these proteins, to develop therapeutic strategies and to suggest candidate proteins for other neuromuscular disorders.

Fukuyama-type congenital muscular dystrophy: close relation between changes in the muscle basal lamina and plasma membrane

Despite the recent advance in genetic study of Fukuyama-type congenital muscular dystrophy (FCMD), the mechanism of muscle degeneration in the disease remains unclear. To clarify it, muscle biopsies from six cases of FCMD were subjected to immunohistochemical and ultrastructural studies. On the muscle cell surface, decreased expression of laminin alpha2 subunit was seen along with aberrant expression of laminin alpha5 and neural cell adhesion molecule. Electron microscopy revealed breach of muscle basal lamina. The electron density of plasma membrane was significantly lower at the places without identifiable basal lamina. Thus in FCMD changes of laminin and other proteins on the cell surface involve a process common to developing muscles, and loss of normal structure of the basal lamina is closely associated with changes of the plasma membrane. This suggests that the primary cause of FCMD is related to formation and maintenance of the basal lamina.

Distribution of ten laminin chains in dystrophic and regenerating muscles

Using immunohistochemical methods, we assessed the distribution of all 10 known laminin chains (alpha1-5, beta1-3, gamma1 and gamma2) in skeletal muscles from patients with Duchenne, congenital, limb girdle, or Emery-Dreifuss muscular dystrophies. The alpha2, beta1 and gamma1 chains were abundant in the basal lamina surrounding muscle fibers in normal controls; alpha1, alpha3-alpha5, beta3, and gamma2 were undetectable; and beta2 was present at a low level. Compared to controls, levels of the alpha5 chain were increased in muscles from many dystrophic patients; levels of beta1 were reduced and/or levels of beta2 were increased in a minority. However, these changes were neither specific for, nor consistent within, diagnostic categories. In contrast, levels of alpha4 were increased in muscles from all patients with alpha2 laminin (merosin)-deficient congenital muscular dystrophy. Loss of alpha2 laminin in congenital dystrophy is disease-specific but some other changes in laminin isoform expression in dystrophic muscles could be secondary consequences of myopathy, denervation, regeneration or immaturity. To distinguish among these possibilities, we compared the laminins of embryonic, denervated, regenerating, and mutant mouse muscles with those in normal adult muscle. Embryonic muscle basal lamina contained alpha4 and alpha5 along with alpha2, and regenerating muscle re-expressed alpha5 but not alpha4. Levels of alpha5 but not alpha4 were increased in dystrophin (mdx) mutants and in dystrophin/utrophin double mutants (mdx:utrn -/-), models for Duchenne dystrophy. In contrast, laminin alpha4 was upregulated more than alpha5 in muscles of laminin alpha2 mutant mice (dy/dy; a model for alpha2-deficient congenital dystrophy). Based on these results, we hypothesize that the expression of alpha5 in many dystrophies reflects the regenerative process, whereas the selective expression of alpha4 in alpha2-deficient muscle is a specific compensatory response to loss of alpha2.

Decreased expression of laminin beta 1 in chromosome 21-linked Bethlem myopathy

Muscle biopsies of four patients affected by chromosome 21-linked Bethlem myopathy were investigated by means of immunohistochemistry, with monoclonal antibodies for laminin chains, dystrophin and dystrophin associated glycoproteins. The objective of this study was to determine whether an altered molecular structure of collagen type VI, characteristic of Bethlem myopathy, could influence the expression of the protein complex linking the extracellular matrix with the subsarcolemmal cytoskeleton. Normal expression of all proteins was found except for laminin beta 1, along with an age related progressive deficiency of this protein in the muscle fibre basal lamina. This study shows that Bethlem myopathy linked to chromosome 21 is associated with a secondary decrease in laminin beta 1 expression.

Merosin-positive congenital muscular dystrophy with transient brain dysmyelination, pontocerebellar hypoplasia and mental retardation

The congenital muscular dystrophies (CMDs) are a heterogeneous group of disorders. Among these, the laminin alpha 2 chain 'merosin' deficient CMD is caused by mutations of the LAMA2 gene on chr 6q2 and Fukuyama CMD is linked to chr 9q31. We report a 7-year-old boy who was born to consanguineous healthy parents. His motor and mental development were slow. Creatine kinase (CK) was elevated (2.100 U/l), and the muscle biopsy was dystrophic. He sat unsupported at 12 months and took his first steps at 3 years of age. At 6 years of age he could walk up to 500 m. He was mentally retarded and spoke single words only. At 1 year, MR imaging of the brain showed abnormal increased periventricular T2-signal, consistent with dysmyelination as well as pontocerebellar hypoplasia and several cerebellar cysts. The pattern of gyration was normal. Follow-up at 4 years showed normalization of the previously abnormal periventricular T2-signal. Immunohistochemical analysis of the skeletal muscle showed normal expression of laminin alpha 2 for a C-terminal antibody and antibodies to the 300 and 150 kDa fragments, as well as of laminins alpha 5, beta 1, beta 2 and gamma 1. The boy has two healthy younger brothers. Linkage analysis excluded the candidate loci on chromosomes 6q2 and 9q31. As such, the patient's data are suggestive of a new form of laminin alpha 2 positive CMD characterized by transient brain dysmyelination, pontocerebellar hypoplasia and mental retardation.

Expression of laminin alpha1, alpha2, alpha4, and alpha5 chains, fibronectin, and tenascin-C in skeletal muscle of dystrophic 129ReJ dy/dy mice

The dy/dy mouse is an animal model for human merosin-negative congenital muscular dystrophy (CMD), which has been reported to have reduced or no expression of the basement membrane protein laminin alpha2. We here investigate various myogenic and nonmyogenic tissues of mature dy/dy and control 129ReJ mice histologically and for laminin alpha2 expression. In addition, expression patterns of laminin alpha1, alpha2, alpha4, and alpha5 chains, the interstitial proteins fibronectin and tenascin-C, and the adhesion molecules VCAM-1, ICAM-1, and alpha4 integrin were characterized in skeletal muscle of 1- and 7-day and mature (>6 weeks old) dy/dy and control 129ReJ mice. The laminin alpha2 chain remained detectable in myogenic tissues of dy/dy mice by immunofluorescence using two different monoclonal antibodies and by Northern blot analysis. However, laminin alpha2 expression was significantly reduced or not detectable in nonmyogenic tissues of dy/dy mice, including skin, lung, kidney, brain, thymus, and eye. Focal lesions were observed in mature skeletal muscle only, characterized by necrotic tissue, isolated VCAM-1- and ICAM-1-positive cells indicative of inflammatory processes, and regenerating muscle fibers surrounded by intense tenascin-C and fibronectin expression. In contrast to studies on human CMD muscle, laminin alpha1 was not detectable in either dy/dy or control skeletal muscle using immunofluorescence or Northern blot analysis. Immunofluorescence localized laminin alpha4 to basement membranes of blood vessels, the endoneurium of the intramuscular nerves, and the neuromuscular junction in skeletal muscle of 1- and 7-day-old dy/dy and control mice. In mature muscle, laminin alpha4 expression shifted to the perineurium of intramuscular nerves in both dy/dy and control mice. Furthermore, strong upregulation of laminin alpha4 in the basement membranes of blood vessels, the perineurium of intramuscular nerves, and of isolated regenerating muscle fibers in the dy/dy mice was apparent. Investigation of 1-day-old animals revealed expression of laminin alpha5 in skeletal muscle fiber basement membranes of dy/dy but not control animals. This difference between dy/dy and control animals was no longer apparent at 7 days after birth, indicating a temporary shift in expression pattern of laminin alpha5 in dy/dy animals. Analysis of the extracellular matrix components of 1- and 7-day-old dy/dy and control skeletal muscle revealed an early onset of the dystrophy, even before histopathological features of the disease were evident. Our data confirm the absence of laminin alpha1 chain in myogenic tissues of both dy/dy and control mice and suggest compensation for reduced laminin alpha2 in dy/dy skeletal muscle by laminin alpha4 and, in early development, also laminin alpha5. These results have significant ramifications in the diagnosis of human merosin-negative CMD.

Immature astrocytes in Fukuyama congenital muscular dystrophy: an immunohistochemical study

Recent studies of Fukuyama congenital muscular dystrophy have focused on abnormalities of the basement membrane in muscle and brain. The cerebral cortex has a unique basement membrane at the glia limitans, which is intimately related to astrocytes in the developing brain, and the basement membrane may be partially produced by the astrocyte. In this study the cerebral astrocytes in six patients with Fukuyama congenital muscular dystrophy, including two fetal patients, were characterized by immunohistochemical study. In fetal Fukuyama congenital muscular dystrophy, astrocytes reacted less to antibodies of glial fibrillary acidic protein, S-100 protein, and alphaB-crystallin than control astrocytes, but in postnatal Fukuyama congenital muscular dystrophy, astrocytes reacted more to these antibodies and displayed beading of processes. Moreover, vimentin was positive in the astrocytes of two postnatal Fukuyama congenital muscular dystrophy patients. This astrocytic appearance may suggest immaturity of astrocytes in Fukuyama congenital muscular dystrophy. Astrocytes exhibiting beaded cytoplasmic processes were prominent at the subpia of the cortex and around vessels. The authors hypothesize that these immature astrocytes are unable to participate in the function of the cortical basement membrane, which is defective in Fukuyama congenital muscular dystrophy. Studies of neurons and meninges were similar to those of control subjects.

Assignment of the muscle-eye-brain disease gene to 1p32-p34 by linkage analysis and homozygosity mapping

Muscle-eye-brain disease (MEB) is an autosomal recessive disease of unknown etiology characterized by severe mental retardation, ocular abnormalities, congenital muscular dystrophy, and a polymicrogyria-pachygyria-type neuronal migration disorder of the brain. A similar combination of muscle and brain involvement is also seen in Walker-Warburg syndrome (WWS) and Fukuyama congenital muscular dystrophy (FCMD). Whereas the gene underlying FCMD has been mapped and cloned, the genetic location of the WWS gene is still unknown. Here we report the assignment of the MEB gene to chromosome 1p32-p34 by linkage analysis and homozygosity mapping in eight families with 12 affected individuals. After a genomewide search for linkage in four affected sib pairs had pinpointed the assignment to 1p, the MEB locus was more precisely assigned to a 9-cM interval flanked by markers D1S200 proximally and D1S211 distally. Multipoint linkage analysis gave a maximum LOD score of 6.17 at locus D1S2677. These findings provide a starting point for the positional cloning of the disease gene, which may play an important role in muscle function and brain development. It also provides an opportunity to test other congenital muscular dystrophy phenotypes, in particular WWS, for linkage to the same locus.

Merosin-deficient congenital muscular dystrophy. Partial genetic correction in two mouse models

Humans and mice with deficiency of the alpha2 subunit of the basement membrane protein laminin-2/merosin suffer from merosin-deficient congenital muscular dystrophy (MCMD). We have expressed a human laminin alpha2 chain transgene under the regulation of a muscle-specific creatine kinase promoter in mice with complete or partial deficiency of merosin. The transgene restores the synthesis and localization of merosin in skeletal muscle, and greatly improves muscle morphology and integrity and the health and longevity of the mice. However, the transgenic mice share with the nontransgenic dystrophic mice a progressive lameness of hind legs, suggestive of a nerve defect. These results indicate that the absence of merosin in tissues other than the muscle, such as nervous tissue, is a critical component of MCMD. Future gene therapies of human MCMD, and perhaps of other forms of muscular dystrophy, may require restoration of the defective gene product in multiple tissues.

An ancient retrotransposal insertion causes Fukuyama-type congenital muscular dystrophy

Fukuyama-type congenital muscular dystrophy (FCMD), one of the most common autosomal recessive disorders in Japan (incidence is 0.7-1.2 per 10,000 births), is characterized by congenital muscular dystrophy associated with brain malformation (micropolygria) due to a defect in the migration of neurons. We previously mapped the FCMD gene to a region of less than 100 kilobases which included the marker locus D9S2107 on chromosome 9q31. We have also described a haplotype that is shared by more than 80% of FCMD chromosomes, indicating that most chromosomes bearing the FCMD mutation could be derived from a single ancestor. Here we report that there is a retrotransposal insertion of tandemly repeated sequences within this candidate-gene interval in all FCMD chromosomes carrying the founder haplotype (87%). The inserted sequence is about 3 kilobases long and is located in the 3' untranslated region of a gene encoding a new 461-amino-acid protein. This gene is expressed in various tissues in normal individuals, but not in FCMD patients who carry the insertion. Two independent point mutations confirm that mutation of this gene is responsible for FCMD. The predicted protein, which we term fukutin, contains an amino-terminal signal sequence, which together with results from transfection experiments suggests that fukutin is a secreted protein. To our knowledge, FCMD is the first human disease to be caused by an ancient retrotransposal integration.