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

Genetic and Clinical Advances of Congenital Muscular Dystrophy

Objective:

The aim was to update the genetic and clinical advances of congenital muscular dystrophy (CMD), based on a systematic review of the literature from 1991 to 2017.

Data Sources:

Articles in English published in PubMed from 1991 to 2017 English were searched. The terms used in the literature searches were CMD.

Study Selection:

The task force initially identified citations for 98 published articles. Of the 98 articles, 52 studies were selected after further detailed review. Three articles, which were not written in English, were excluded from the study. This study referred to all the important and English literature in full.

Results:

CMD is a group of early-onset disorders encompassing great clinical and genetic heterogeneity. Patients present with muscle weakness typically from birth to early infancy, delay or arrest of gross motor development, and joint and/or spinal rigidity. The diagnosis of CMD relies on clinical findings, brain and muscle imaging, muscle biopsy histology, muscle and/or skin immunohistochemical staining, and molecular genetic testing.

Conclusions:

Advances in next-generation sequencing and histopathological techniques have enabled the recognition of distinct CMD subtypes supported by specific gene identification. Genetic counseling and multidisciplinary management of CMD play an important role in help patients and their family. Further elucidation of the significant clinical and genetic heterogeneity, therapeutic targets, and the clinical care for patients remains our challenge for the future.

Molecular signaling mechanisms of axon-glia communication in the peripheral nervous system

In this article we discuss the molecular signaling mechanisms that coordinate interactions between Schwann cells and the neurons of the peripheral nervous system. Such interactions take place perpetually during development and in adulthood, and are critical for the homeostasis of the peripheral nervous system (PNS). Neurons provide essential signals to control Schwann cell functions, whereas Schwann cells promote neuronal survival and allow efficient transduction of action potentials. Deregulation of neuron-Schwann cell interactions often results in developmental abnormalities and diseases. Recent investigations have shown that during development, neuronally provided signals, such as Neuregulin, Jagged, and Wnt interact to fine-tune the Schwann cell lineage progression. In adult, the signal exchange between neurons and Schwann cells ensures proper nerve function and regeneration. Identification of the mechanisms of neuron-Schwann cell interactions is therefore essential for our understanding of the development, function and pathology of the peripheral nervous system as a whole.

Genotype-phenotype correlation in a large population of muscular dystrophy patients with LAMA2 mutations

Merosin deficient congenital muscular dystrophy 1A (MDC1A) results from mutations in the LAMA2 gene. We report 51 patients with MDC1A and examine the relationship between degree of merosin expression, genotype and clinical features. Thirty-three patients had absence of merosin and 13 showed some residual merosin. Compared to the residual merosin group, patients with absent merosin had an earlier presentation (<7days) (P=0.0073), were more likely to lack independent ambulation (P=0.0215), or require enteral feeding (P=0.0099) and ventilatory support (P=0.0354). We identified 33 novel LAMA2 mutations; these were distributed throughout the gene in patients with absent merosin, with minor clusters in exon 27, 14, 25 and 26 (55% of mutations). Patients with residual merosin often carried at least one splice site mutation and less frequently frameshift mutations. This large study identified novel LAMA2 mutations and highlights the role of immunohistochemical studies for merosin status in predicting clinical severity of MDC1A.

Congenital muscular dystrophy. Part I: a review of phenotypical and diagnostic aspects

The congenital muscular dystrophies (CMDs) are a group of genetically and clinically heterogeneous hereditary myopathies with preferentially autosomal recessive inheritance, that are characterized by congenital hypotonia, delayed motor development and early onset of progressive muscle weakness associated with dystrophic pattern on muscle biopsy. The clinical course is broadly variable and can comprise the involvement of the brain and eyes. From 1994, a great development in the knowledge of the molecular basis has occurred and the classification of CMDs has to be continuously up dated. We initially present the main clinical and diagnostic data concerning the CMDs related to changes in the complex dystrophin-associated glycoproteins-extracellular matrix: CMD with merosin deficiency (CMD1A), collagen VI related CMDs (Ullrich CMD and Bethlem myopathy), CMDs with abnormal glycosylation of alpha-dystroglycan (Fukuyama CMD, Muscle-eye-brain disease, Walker-Warburg syndrome, CMD1C, CMD1D), and the much rarer CMD with integrin deficiency. Finally, we present other forms of CMDs not related with the dystrophin/glycoproteins/extracellular matrix complex (rigid spine syndrome, CMD1B, CMD with lamin A/C deficiency), and some apparently specific clinical forms not yet associated with a known molecular mechanism. The second part of this review concerning the pathogenesis and therapeutic perspectives of the different subtypes of CMD will be described in a next number.

Severe congenital muscular dystrophy in a LAMA2-mutated case

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

A congenital myopathy with diaphragmatic weakness not linked to the SMARD1 locus

Severe diaphragmatic weakness in infancy is rare. Common causes include structural myopathies, neuromuscular transmission defects, or anterior horn cell dysfunction (spinal muscular atrophy with respiratory distress, SMARD1). We describe a form of infantile diaphragmatic weakness without mutations in the SMARD1 gene, in which pathological and clinical features differ from known conditions, and investigations suggest a myopathy. We identified seven cases in four families. All presented soon after birth with feeding and breathing difficulties, marked head lag, facial weakness, and preserved antigravity movements in the limbs, with arms weaker than legs. All had paradoxical breathing and paralysis of at least one hemi-diaphragm. All required gastrostomy feeding, and all became ventilator-dependent. Investigations included myopathic EMG, muscle biopsy showing myopathic changes, normal electrophysiology and no mutations in SMN1 or IGHMBP2. These seven infants are affected by a myopathic condition clinically resembling SMARD1. However, its pathogenesis appears to be a myopathy affecting predominantly the diaphragm.

Obscurin: a multitasking muscle giant

Obscurin (approximately 800 kDa) is the third member of a family of giant proteins expressed in vertebrate striated muscle, along with titin (3-3.7 MDa) and nebulin (approximately 800 kDa). Like its predecessors, it is a multidomain protein composed of tandem adhesion modules and signaling domains. Unlike titin and nebulin, which are integral components of sarcomeres, obscurin is concentrated at the peripheries of Z-disks and M-lines, where it is appropriately positioned to communicate with the surrounding myoplasm. This unique distribution allows obscurin to bind small ankyrin 1, an integral component of the sarcoplasmic reticulum (SR) membrane. Obscurin also associates with the contractile apparatus through its binding to titin, sarcomeric myosin and perhaps other proteins of the contractile apparatus. Overexpression of the COOH-terminus of obscurin in primary myotubes has a dramatic and specific effect on the organization of sarcomeric myosin, indicating a role in the organization and regular assembly of A-bands. Given its ability to associate tightly, selectively and periodically with the periphery of the myofibril, its high affinity for an integral membrane protein of the SR and its close association with thick filaments, we speculate that obscurin is ideally suited to play key roles in modulating the organization and assembly of both the myofibril and the SR.

Congenital muscular dystrophies: new aspects of an expanding group of disorders

The congenital muscular dystrophies comprise a genetically and clinically heterogeneous group of disorders characterized by early onset of progressive muscle weakness and often involvement of other organ systems such as the brain and eyes. During the last decade, significant progress has been made to further characterize various forms of congenital muscular dystrophies based on their specific genetic and clinical appearance. This review represents an overview of the recent accomplishments as they relate to clinical, diagnostic, pathogenetic and therapeutic aspects of congenital muscular dystrophies.

Congenital muscular dystrophies and the extracellular matrix

During the past decade, considerable progress in the field of congenital muscular dystrophies (CMDs) had led to the identification of a growing number of causative genes. This genetic progress has uncovered crucial pathophysiological concepts and has been instrumental in redefining clinical phenotypes. Important new pathogenic mechanisms include the disorders of O-mannosyl-linked glycosylation of alpha-dystroglycan as well as the involvement of a collagen type VI in the pathogenesis of congenital disorders of muscle. Thus, an emerging theme among gene products involved in the pathogenesis of congenital muscular dystrophy is their intimate connection to the extracellular matrix. In this review, we focus on the clinical phenotypes that we are correlating with the novel genetic and biochemical findings encountered within CMD. This correlation will frequently lead to a considerably expanded clinical spectrum associated with a given CMD gene.

Congenital muscular dystrophy in Arab children

The congenital muscular dystrophies are autosomal recessive disorders with different clinical phenotypes, the spectrum of which varies between different ethnic communities. We report our findings in 21 Arab children with congenital muscular dystrophy. All 21 cases were of the pure type, with normal mental status, except 1 case with perinatal hypoxic-ischemic insult. Fourteen were laminin alpha2 (merosin) deficient, and six were laminin alpha2 positive; laminin alpha2 status was not determined in one patient. None of the laminin alpha2-deficient patients achieved independent ambulation, whereas three of the laminin alpha2-positive patients were able to walk. The elevated levels of serum creatine kinase did not differentiate the two groups and tended to decrease after the age of 5 years. Radiologic evaluation demonstrated an abnormal central white-matter signal in 11 of 13 laminin alpha2-deficient and in 1 of 5 laminin alpha2-positive patients; none had evidence of brain dysplasia. Nerve conduction velocities were normal in 5 of 5 laminin alpha2-positive patients, whereas in the laminin alpha2-deficient patients, it was slow in 9 of 11 for the motor nerves and normal in 8 of 9 for the sensory nerve. Two of the laminin alpha2-positive patients had pseudohypertrophy of the calves, and two of the laminin alpha2-deficient ones had seizures. The patient in whom the laminin alpha2 status was not determined had a severe course, an abnormal central white-matter signal, and epilepsy and resembled more the laminin alpha2-deficient group.

Syncoilin upregulation in muscle of patients with neuromuscular disease

Syncoilin may have a role in linking the desmin-associated intermediate filament network of the muscle fiber with the dystrophin-associated protein complex (DAPC). We have evaluated syncoilin in a range of neuromuscular disorders including Duchenne and Becker muscular dystrophy, central core disease, congenital muscular dystrophies, and neurogenic disorders. Our results show that syncoilin immunolabeling is not only altered in muscle fibers with alterations in the DAPC but also in response to a variety of genetic defects, including those associated with proteins of the extracellular matrix and the intracellular Ca2+-release channel (ryanodine receptor). The pattern of syncoilin immunolabeling in these diseases appeared to reflect a rearrangement of the intermediate filament-associated cytoskeleton that characterizes both muscle fiber development and conditions in which the cytoskeletal organization of the muscle fiber is significantly affected. These observations raise the possibility that mutations in the gene encoding for syncoilin may underlie some forms of muscle disease.

Obscurin is required for the lateral alignment of striated myofibrils in zebrafish

Obscurin/obscurin-MLCK is a giant sarcomere-associated protein with multiple isoforms whose interactions with titin and small ankyrin-1 suggest that it has an important role in myofibril assembly, structural support, and the sarcomeric alignment of the sarcoplasmic reticulum. In this study, we characterized the zebrafish orthologue of obscurin and examined its role in striated myofibril assembly. Zebrafish obscurin was expressed in the somites and central nervous system by 24 hours post-fertilization (hpf) and in the heart by 48 hpf. Depletion of obscurin using two independent morpholino antisense oligonucleotides resulted in diminished numbers and marked disarray of skeletal myofibrils, impaired lateral alignment of adjacent myofibrils, disorganization of the sarcoplasmic reticulum, somite segmentation defects, and abnormalities of cardiac structure and function. This is the first demonstration that obscurin is required for vertebrate cardiac and skeletal muscle development. The diminished capacity to generate and organize new myofibrils in response to obscurin depletion suggests that it may have a vital role in the causation of or adaptation to cardiac and skeletal myopathies.

Molecular etiopathogenesis of limb girdle muscular and congenital muscular dystrophies: Boundaries and contiguities

The muscular dystrophies are a heterogeneous group of inherited disorders characterized by progressive muscle wasting and weakness. These disorders present a large clinical variability regarding age of onset, patterns of skeletal muscle involvement, heart damage, rate of progression and mode of inheritance. Difficulties in classification are often caused by the relatively common sporadic occurrence of autosomal recessive forms as well as by intrafamilial clinical variability. Furthermore recent discoveries, particularly regarding the proteins linking the sarcolemma to components of the extracellular matrix, have restricted the gap existing between limb girdle (LGMD) and congenital muscular dystrophies (CMD). Therefore a renewed definition of boundaries between these two groups is required. Molecular genetic studies have demonstrated different causative mutations in the genes encoding a disparate collection of proteins involved in all aspects of muscle cell biology. These novel skeletal muscle genes encode highly diverse proteins with different localization within or at the surface of the skeletal muscle fibre, such as the sarcolemmal muscle membrane (dystrophin, sarcoglycans, dysferlin, caveolin-3), the extracellular matrix (alpha2 laminin, collagen VI), the sarcomere (telethonin, myotilin, titin, nebulin and ZASP), the muscle cytosol (calpain-3, TRIM32), the nucleus (emerin, lamin A/C) and the glycosilation pathway enzymes (fukutin and fukutin related proteins). The accumulating knowledge about the role of these different proteins in muscle pathology has led to a profound change in the original phenotype-based classification and shed new light on the molecular pathogenesis of these disorders.

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.

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.

Localisation of merosin-positive congenital muscular dystrophy to chromosome 4p16.3

The congenital muscular dystrophies (CMD) are a heterogeneous group of autosomal recessive disorders, which present within the first 6 months of life with hypotonia, muscle weakness and contractures, associated with dystrophic changes on skeletal muscle biopsy. We have previously reported a large consanguineous family segregating merosin-positive congenital muscular dystrophy, in which involvement of known CMD loci was excluded. A genome-wide linkage search of the family conducted using microsatellite markers spaced at 10-Mb intervals failed to identify a disease locus. A second scan using a high-density SNP array, however, permitted a novel CMD locus on 4p16.3 to be identified (multipoint LOD score 3.4). Four additional consanguineous CMD families with a similar phenotype were evaluated for linkage to a 4.14-Mb interval on 4p16.3; however, none showed any evidence of linkage to the region. Our findings further illustrate the utility of highly informative SNP arrays compared with standard panels of microsatellite markers for the mapping of recessive disease loci.

The role of defective glycosylation in congenital muscular dystrophy

The dystrophin glycoprotein complex (DGC) is an assembly of proteins spanning the sarcolemma of skeletal muscle cells. Defects in the DGC appear to play critical roles in several muscular dystrophies due to disruption of basement membrane organization. O -mannosyl oligosaccharides on alpha-dystroglycan, a major extracellular component of the DGC, are essential for normal binding of alpha-dystroglycan to ligands (such as laminin) in the extracellular matrix and subsequent signal transmission to actin in the cytoskeleton of the muscle cell. Muscle-Eye-Brain disease (MEB) and Walker-Warburg Syndrome (WWS) have mutations in genes encoding glycosyltransferases needed for O -mannosyl oligosaccharide synthesis. Myodystrophic myd mice and humans with Fukuyama Congenital Muscular Dystrophy (FCMD), congenital muscular dystrophy due to defective fukutin-related protein (FKRP) and MDC1D have mutations in putative glycosyltransferases. These human congenital muscular dystrophies and the myd mouse are associated with defective glycosylation of alpha-dystroglycan. It is expected other congenital muscular dystrophies will prove to have mutations in genes involved in glycosylation.

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.

Protein and DNA Analysis for the Prenatal Diagnosis of α2-Laminin–Deficient Congenital Muscular Dystrophy

Congenital muscular dystrophies (CMD) are characterized by neonatal hypotonia and/or artrogriposis associated with a dystrophic muscle biopsy. The CMD1A form is caused by a deficiency of the alpha2 chain of laminin 2 (LAMA2 gene at 6q2), a protein present in the basal lamina of muscle fibers, in Schwann cells, epidermis, and in fetal trophoblastic tissue. This allows its study for prenatal diagnosis in the chorionic villous (CV), which was performed in a family with one deceased affected CMD1A child. Immunohistochemical analysis of the CV using antibodies against the C- and N-terminal domains of the alpha2-laminin protein showed a normal positive labeling for both antibodies in the "at-risk" CV, which did not differ from the normal control CV. The integrity of the CV membrane was confirmed through the analysis with antibodies against alpha1, beta1, and gamma1 laminins. DNA study using markers flanking the 6q2 region showed that the affected patient and the "at-risk" fetus did not share the same haplotype. Therefore, the fetus was considered normal through both methodologies, which was confirmed after the birth of a clinically normal male baby. As the LAMA2 gene is very large and the spectrum of mutations causing disease is wide, the analysis of the protein in muscle biopsy has been largely used for the diagnosis. Besides, the possibility to detect it in the chorionic villous, mainly using positive markers, also offers a powerful tool for prenatal diagnosis.

Lco1 is a novel widely expressed lamin-binding protein in the nuclear interior

A-type lamins are localized at the nuclear envelope and in the nucleoplasm, and are implicated in human diseases called laminopathies. In a yeast two-hybrid screen with lamin C, we identified a novel widely expressed 171-kDa protein that we named Lamin companion 1 (Lco1). Three independent biochemical assays showed direct binding of Lco1 to the C-terminal tail of A-type lamins with an affinity of 700 nM. Lco1 also bound the lamin B1 tail with lower affinity (2 microM). Ectopic Lco1 was found primarily in the nucleoplasm and colocalized with endogenous intranuclear A-type lamins in HeLa cells. Overexpression of prelamin A caused redistribution of ectopic Lco1 to the nuclear rim together with ectopic lamin A, confirming association of Lco1 with lamin A in vivo. Whereas the major C-terminal lamin-binding fragment of Lco1 was cytoplasmic, the N-terminal Lco1 fragment localized in the nucleoplasm upon expression in cells. Furthermore, full-length Lco1 was nuclear in cells lacking A-type lamins, showing that A-type lamins are not required for nuclear targeting of Lco1. We conclude that Lco1 is a novel intranuclear lamin-binding protein. We hypothesize that Lco1 is involved in organizing the internal lamin network and potentially relevant as a laminopathy disease gene or modifier.

Abnormalities in alpha-dystroglycan expression in MDC1C and LGMD2I muscular dystrophies

We recently identified mutations in the fukutin related protein (FKRP) gene in patients with congenital muscular dystrophy type 1C (MDC1C) and limb girdle muscular dystrophy type 2I (LGMD2I). The sarcolemma of these patients typically displays an immunocytochemical reduction of alpha-dystroglycan. In this report we extend these observations and report a clear correlation between the residual expression of alpha-dystroglycan and the phenotype. Three broad categories were identified. Patients at the severe end of the clinical spectrum (MDC1C) were compound heterozygote between a null allele and a missense mutation or carried two missense mutations and displayed a profound depletion of alpha-dystroglycan. Patients with LGMD with a Duchenne-like severity typically had a moderate reduction in alpha-dystroglycan and were compound heterozygotes between a common C826A (Leu276Ileu) FKRP mutation and either a missense or a nonsense mutation. Individuals with the milder form of LGMD2I were almost invariably homozygous for the Leu276Ile FKRP mutation and showed a variable but subtle alteration in alpha-dystroglycan immunolabeling. Our data therefore suggest a correlation between a reduction in alpha-dystroglycan, the mutation and the clinical phenotype in MDC1C and LGMD2I which supports the hypothesis that dystroglycan plays a central role in the pathogenesis of these disorders.

Enzymatic diagnostic test for Muscle-Eye-Brain type congenital muscular dystrophy using commercially available reagents

OBJECTIVES

Mutations disrupting the interaction of extra-cellular ligands and alpha-dystroglycan are responsible for an etiologically heterogeneous group of autosomal recessive congenital muscular dystrophies (CMD) that can have associated brain and eye abnormalities. The objective is to develop a diagnostic test for one of these CMDs, Muscle-Eye-Brain disease (MEB), due to mutations in the gene encoding Protein O-Mannosyl beta-1,2-N-acetylglucosaminyltransferase 1 (POMGnT1).

DESIGN AND METHODS

POMGnT1 enzyme activity was determined in extracts of muscle biopsies from four MEB patients and various controls using commercially available reagents.

RESULTS

All four MEB muscle samples showed a highly significant decrease in POMGnT1 activity relative to controls.

CONCLUSIONS

The assay of POMGnT1 activity in MEB muscle provides a rapid and relatively simple diagnostic test for this disease. CMDs associated with brain malformations such as MEB, WWS and FCMD are heterogenous in clinical presentation and on radiologic examination, suggesting that POMGnT1 assays of muscle biopsies should be used as a screening procedure for MEB in all CMD patients associated with brain malformations.

Phenotypic spectrum associated with mutations in the fukutin-related protein gene

We describe 22 patients with mutations in the fukutin-related protein (FKPR) gene. Four patients had congenital muscular dystrophy (MDC1C), with presentation at birth, severe weakness and inability to stand unsupported. The other 18 had limb girdle muscular dystrophy (LGMD2I). Eleven showed a Duchenne-like course with loss of ambulation in the early teens while 7 had a milder phenotype. Muscle biopsy invariably showed abnormal expression of a-dystroglycan. MDC1C patients either carried 2 missense or 1 missense and 1 nonsense mutations. Patients with LGMD2I shared a common mutation (C826A,Leu276Ileu) and their phenotypic severity was correlated with the second allelic mutation.

Assessment of left ventricular systolic and diastolic functions in children with merosin-positive congenital muscular dystrophy

Cardiopathy is an expected finding in X-linked Duchenne and Becker muscular dystrophies. This holds true for some other forms such as autosomal recessive limb-girdle dystrophies. However, data on early-onset and usually severe congenital muscular dystrophies are limited. The purpose of this study was to investigate the presence of cardiac involvement in children with merosin-positive congenital muscular dystrophy. A total of 42 patients and 22 healthy subjects were evaluated by M-mode, 2D, and Doppler echocardiography. Cardiac anatomy, left ventricular dimensions, wall thickness and systolic and diastolic functions were investigated in patients and compared with those of healthy control subjects. Mean left ventricular ejection fraction and shortening fraction were significantly lower in the patient group (P<0.05 and P<0.001, respectively) and in three patients ejection fraction was below 55%. Although some impairments in left ventricular inflow indexes which were suggestive of left ventricular diastolic dysfunction were detected in patients with merosin-positive congenital muscular dystrophy they were not statistically significant. Our results suggest that left ventricular systolic abnormalities may occur in children with merosin-positive congenital muscular dystrophy.

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.

Merosin-deficient congenital muscular dystrophy with mental retardation and cerebellar cysts, unlinked to the LAMA2, FCMD, MEB and CMD1B loci, in three Tunisian patients

We report three Tunisian patients affected by congenital muscular dystrophy with mental retardation and cerebellar cysts on cranial magnetic resonance imaging. The clinical features were characterized by hypotonia at birth, joint contractures associated with severe psychomotor retardation, absence of speech, inability to walk in three patients, but calf hypertrophy was noted only in two patients. Brain magnetic resonance imaging showed several cerebellar cysts and vermis hypoplasia in all of the patients. Abnormality of the white matter was present in two patients. The pattern of gyration was normal in all cases. Serum creatine kinase was elevated in all three cases and their muscle biopsy showed dystrophic changes compatible with congenital muscular dystrophy. The immunohistochemical analysis of the skeletal muscle revealed partial merosin deficiency, more pronounced for the N-terminal antibody. Linkage analysis excluded congenital muscular dystrophy loci on chromosomes 6q22, 9q31, 1p32 and 1q42. These patients constituted a particular form of congenital muscular dystrophy with a combination of severe motor delay, mental retardation, partial merosin deficiency and cerebellar cysts. Two patients showed white matter abnormalities on magnetic resonance imaging and hypertrophy of the calves. These cases, in addition to those reported previously, confirmed the large phenotypic variability in the group of secondary merosin deficiency congenital muscular dystrophy.

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.

Congenital muscular dystrophy with adducted thumbs, ptosis, external ophthalmoplegia, mental retardation and cerebellar hypoplasia: a novel form of CMD

At least six different forms of congenital muscular dystrophy are associated with structural changes of the central nervous system, and three of these have been mapped: merosin-deficient congenital muscular dystrophy on chromosome 6q2, Fukuyama congenital muscular dystrophy on chromosome 9q31, and muscle eye brain disease on chromosome 1p32. Walker-Warburg syndrome, congenital muscular dystrophy with calf hypertrophy, pontocerebellar hypoplasia, and normal eyes, and congenital muscular dystrophy with severe mental retardation and cerebellar cysts are nosologically distinct and have been excluded from the known congenital muscular dystrophy loci with structural changes of the central nervous system. Here, we describe a novel congenital muscular dystrophy syndrome which is phenotypically distinct from the recognized forms of congenital muscular dystrophy with brain involvement. Two siblings, a boy and a girl, were born to consanguineous parents from Sicily. Both children were born with adducted thumbs and toe contractures. They were floppy from birth, walked late, showed profound generalized muscle weakness including facial muscles, elevated creatine kinase levels of 200-700U/l, and histological changes compatible with muscular dystrophy. In addition, both showed ptosis, external ophthalmoplegia, mild mental retardation, and mild cerebellar hypoplasia on MRI. Immunocytochemistry showed normal expression of muscle membrane proteins including laminin alpha 2, laminin beta 2, and alpha-dystroglycan. Linkage analysis excluded the candidate loci on chromosomes 6q2, 9q31, and 1q32. The gene locus for congenital muscular dystrophy 1B, MDC 1B, on chromosome 1q42 was also excluded. Adducted thumbs are a distinct clinical sign that has not been reported in congenital muscular dystrophy before and should facilitate recognition of further patients with this disorder.

Congenital muscular dystrophies

The number of new syndromes, loci, and genes responsible for CMD forms has dramatically increased in the last few years, and it has become increasingly evident that the classification of the different forms of CMD is a difficult task. A recent classification separated the forms of CMD that have been mapped (CMD diseases) from the ones with clearly defined clinical and pathologic features that have not been mapped yet (CMD syndromes). Eight CMD forms have been mapped up to now, and the genes responsible for three of them have been identified. This review describes an update of clinical, pathologic, and genetic findings in the different CMD forms.

Severe progressive form of congenital muscular dystrophy with calf pseudohypertrophy, macroglossia and respiratory insufficiency

A novel form of congenital muscular dystrophy in four unrelated patients is proposed. Congenital hypotonia, markedly increased CK, calf pseudohypertrophy and proximal weakness were common early findings. Two cases were severely affected since infancy and never walked. The phenotypical homogeneity was not very evident until advanced stages of the disease. All the patients showed catastrophic progression of the weakness, severe restrictive respiratory insufficiency, macroglossia, peculiar extreme amyotrophy of hands and feet, and a round and 'puffy' face. All patients became tetraplegic and required mechanical ventilation. Two cases had signs of mild cardiac involvement. The only non-tracheotomised patient died of respiratory complications. No mental retardation or specific brain abnormalities were observed. All patients showed secondary deficit of laminin 2 and up-regulation of laminin 5 in muscle. Expression of -dystroglycan was severely reduced in two available muscle samples. The known loci for congenital muscular dystrophies were excluded in the only consanguineous case by linkage analysis. Clinical, immunohistochemical and genetic findings strongly suggest a distinct entity.

Mutations in COL6A3 cause severe and mild phenotypes of Ullrich congenital muscular dystrophy

Ullrich congenital muscular dystrophy (UCMD) is an autosomal recessive disorder characterized by generalized muscular weakness, contractures of multiple joints, and distal hyperextensibility. Homozygous and compound heterozygous mutations of COL6A2 on chromosome 21q22 have recently been shown to cause UCMD. We performed a genomewide screening with microsatellite markers in a consanguineous family with three sibs affected with UCMD. Linkage of the disease to chromosome 2q37 was found in this family and in two others. We analyzed COL6A3, which encodes the alpha3 chain of collagen VI, and identified one homozygous mutation per family. In family I, the three sibs carried an A-->G transition in the splice-donor site of intron 29 (6930+5A-->G), leading to the skipping of exon 29, a partial reduction of collagen VI in muscle biopsy, and an intermediate phenotype. In family II, the patient had an unusual mild phenotype, despite a nonsense mutation, R465X, in exon 5. Analysis of the patient's COL6A3 transcripts showed the presence of various mRNA species-one of which lacked several exons, including the exon containing the nonsense mutation. The deleted splice variant encodes collagen molecules that have a shorter N-terminal domain but that may assemble with other chains and retain a functional role. This could explain the mild phenotype of the patient who was still ambulant at age 18 years and who showed an unusual combination of hyperlaxity and finger contractures. In family III, the patient had a nonsense mutation, R2342X, causing absence of collagen VI in muscle and fibroblasts, and a severe phenotype, as has been described in patients with UCMD. Mutations in COL6A3 are described in UCMD for the first time and illustrate the wide spectrum of phenotypes which can be caused by collagen VI deficiency.

Hypermyelinating neuropathy, mental retardation and epilepsy in a case of merosin deficiency

Children with a deficiency of laminin alpha 2 chain generally show an involvement of skeletal muscles, cerebral white matter and peripheral nerves. Among these patients, however, there is increasing evidence of molecular and phenotype heterogeneity. We report a 19-year-old girl with distal weakness, mental retardation and refractory epilepsy in whom elevated serum CK suggested a myopathy. Electrophysiological and neuroimaging examinations as well as studies of nerve and muscle biopsies were performed. Nerve conduction velocities were definitely reduced and brain MRI demonstrated a diffuse white matter involvement. The muscle biopsy showed both myopathic and neurogenic features. By immunohistochemistry laminin alpha 2 chain was mildly reduced in muscle and virtually absent in peripheral nerve. Teasing of sural nerve fibers showed a 'globular' hypermyelination characteristically located at the paranodal regions. A mild loss of myelinated fibers without any demyelination-remyelination changes was found. Haplotype analysis suggested linkage to the LAMA2 locus. Our case is peculiar as the putative mutation probably affects the expression of laminin alpha 2 chain is affected in a tissue specific manner: the protein is virtually absent in peripheral nerves but only mildly reduced in skeletal muscle. As to the disorder of nerve myelination, an absence or abnormal functioning of laminin alpha 2 chain can alter the feed-back control during myelinogenesis, leading to an over-ensheathment of axon. Alternatively, a compensatory up-regulation of other laminins can induce the hyperproduction of myelin sheaths. This case provides new evidence of the phenotypical heterogeneity of the LAMA2 gene and sheds light in understanding the role of laminin alpha 2 chain in myelination of peripheral nerve.

Hereditary neuromuscular diseases

This article presents the actual classification of neuromuscular diseases based on present expansion of our knowledge and understanding due to genetic developments. It summarizes the genetic and clinical presentations of each disorder together with CT findings, which we studied in a large group of patients with neuromuscular diseases. The muscular dystrophies as the largest and most common group of hereditary muscle diseases will be highlighted by giving detailed information about the role of CT and MRI in the differential diagnosis. The radiological features of neuromuscular diseases are atrophy, hypertrophy, pseudohypertrophy and fatty infiltration of muscles on a selective basis. Although the patterns and distribution of involvement are characteristic in some of the diseases, the definition of the type of disease based on CT scan only is not always possible.

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.

Congenital myopathies and congenital muscular dystrophies

Congenital myopathies and congenital myopathic dystrophies are distinct groups of inherited diseases of muscle, genetically heterogeneous, that manifest in early life or infancy. Congenital myopathic dystrophy is characterized by a dystrophic pattern, whereas no necrotic or degenerative changes are present in congenital myopathies. Much progress has been made in recent years in clarifying the classification of the congenital myopathies. This is a clinically and genetically heterogeneous group of conditions originally classified according to unique morphological changes seen in muscle. Not unlike the later-onset muscular dystrophies, the discovery of the genetic aetiology of many of the congenital myopathies has led to a revamping of how these conditions can now be diagnosed and this should enable physicians to give a more accurate prognosis to patients and their families. New mutations in the ryanodine receptor, slow tropomyosin, troponin T1, actin, and nebulin genes have been described in the last 2 years. Clinical and genetic guidelines for conditions like nemaline rod myopathy and central core disease have been suggested. The notion of minus and surplus protein myopathies has been developed. Several groups of congenital myopathic dystrophy have been identified. In the first category, without intellectual impairment or major structural brain abnormalities, half of the cases are merosin deficient due to mutations of the laminin alpha 2 chain gene. If generally the muscular phenotype is severe, mild allelic variants have been reported with early onset dystrophies and partial merosin deficiency. Among other pure congenital myopathic dystrophies unlinked to the laminin alpha 2 gene, one form has been assigned to chromosome 1q42. In the group of congenital myopathic dystrophies associated with mental retardation and structural brain abnormalities, two main entities are genetically characterized: (1) Fukuyama congenital myopathic dystrophy, affecting the Japanese population, is due to fukutin gene mutations, and (2) the muscle eye brain syndrome assigned to chromosome 1p32-34. In several cases, the gene localization remains unknown.

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.

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.