Identification of a new locus for a peculiar form of congenital muscular dystrophy with early rigidity of the spine, on chromosome 1p35-36

Pathogenic Variants in Selenoproteins and Selenocysteine Biosynthesis Machinery

Selenium is incorporated into selenoproteins as the 21st amino acid selenocysteine (Sec). There are 25 selenoproteins encoded in the human genome, and their synthesis requires a dedicated machinery. Most selenoproteins are oxidoreductases with important functions in human health. A number of disorders have been associated with deficiency of selenoproteins, caused by mutations in selenoprotein genes or Sec machinery genes. We discuss mutations that are known to cause disease in humans and report their allele frequencies in the general population. The occurrence of protein-truncating variants in the same genes is also presented. We provide an overview of pathogenic variants in selenoproteins genes from a population genomics perspective.

Selenoprotein N-related myopathy: a retrospective natural history study to guide clinical trials

Objective

To describe clinical features and disease progression of Selenoprotein N‐related myopathy in a large multicenter cohort of patients.

Methods

Cross‐sectional multicenter data analysis of 60 patients (53 families) with Selenoprotein N‐related myopathy and single‐center retrospective longitudinal analysis of 25 patients (21 families) over a median period of 5.3 years.

Results

The majority of patients (46/60, 77%) presented before age 2 years with hypotonia, poor head/neck control, and developmental delay. At last assessment (median age 14 years; range 2.5 to 36 years), 10/60 patients had minimal or no ambulation. Ventilatory support was initiated in 50/60 patients at a mean Forced Vital Capacity (FVC) of 38% and at a median age of 13 years. Forty‐five/60 patients developed scoliosis (at median age 12.1 years) and 18 had scoliosis surgery at a median age of 13.6 years. Five children needed nasogastric feeds and/or gastrostomy. Longitudinal data analysis on 25 patients showed progressive decline of Hammersmith functional motor scores (estimated annual change −0.55 point), time to walk 10 meter, time standing from sitting, and from lying. Sixteen patients had weights < 2nd centile. The estimated change in FVC % per year was −2.04, with a 95% CI (−2.94, −1.14).

Conclusions

This comprehensive analysis of patients with Selenoprotein N‐related myopathy further describes the clinical course of this rare condition. The observed functional motor and respiratory data provide evidence of the slow decline patients experience over time which is useful when considering therapeutic intervention.

The clinical, histologic, and genotypic spectrum of SEPN1-related myopathy: A case series

OBJECTIVE

To clarify the prevalence, long-term natural history, and severity determinants of SEPN1-related myopathy (SEPN1-RM), we analyzed a large international case series.

METHODS

Retrospective clinical, histologic, and genetic analysis of 132 pediatric and adult patients (2-58 years) followed up for several decades.

RESULTS

The clinical phenotype was marked by severe axial muscle weakness, spinal rigidity, and scoliosis (86.1%, from 8.9 ± 4 years), with relatively preserved limb strength and previously unreported ophthalmoparesis in severe cases. All patients developed respiratory failure (from 10.1±6 years), 81.7% requiring ventilation while ambulant. Histopathologically, 79 muscle biopsies showed large variability, partly determined by site of biopsy and age. Multi-minicores were the most common lesion (59.5%), often associated with mild dystrophic features and occasionally with eosinophilic inclusions. Identification of 65 SEPN1 mutations, including 32 novel ones and the first pathogenic copy number variation, unveiled exon 1 as the main mutational hotspot and revealed the first genotype-phenotype correlations, bi-allelic null mutations being significantly associated with disease severity (p = 0.017). SEPN1-RM was more severe and progressive than previously thought, leading to loss of ambulation in 10% of cases, systematic functional decline from the end of the third decade, and reduced lifespan even in mild cases. The main prognosis determinants were scoliosis/respiratory management, SEPN1 mutations, and body mass abnormalities, which correlated with disease severity. We propose a set of severity criteria, provide quantitative data for outcome identification, and establish a need for age stratification.

CONCLUSION

Our results inform clinical practice, improving diagnosis and management, and represent a major breakthrough for clinical trial readiness in this not so rare disease.

Muscle redox disturbances and oxidative stress as pathomechanisms and therapeutic targets in early-onset myopathies

Because of their contractile activity and their high oxygen consumption and metabolic rate, skeletal muscles continually produce moderate levels of reactive oxygen and nitrogen species (ROS/RNS), which increase during exercise and are buffered by multiple antioxidant systems to maintain redox homeostasis. Imbalance between ROS/RNS production and elimination results in oxidative stress (OxS), which has been implicated in ageing and in numerous human diseases, including cancer, diabetes or age-related muscle loss (sarcopenia). The study of redox homeostasis in muscle was hindered by its lability, by the many factors influencing technical OxS measures and by ROS/RNS important roles in signaling pathways and adaptative responses to muscle contraction and effort, which make it difficult to define a threshold between physiological signaling and pathological conditions. In the last years, new tools have been developed that facilitate the study of these key mechanisms, and deregulation of redox homeostasis has emerged as a key pathogenic mechanism and potential therapeutic target in muscle conditions. This is in particular the case for early-onset myopathies, genetic muscle diseases which present from birth or early childhood with muscle weakness interfering with ambulation and often with cardiac or respiratory failure leading to premature death. Inherited defects of the reductase selenoprotein N in SEPN1-related myopathy leads to chronic OxS of monogenic origin as a primary disease pathomechanism. In myopathies associated with mutations of the genes encoding the calcium channel RyR1, the extracellular matrix protein collagen VI or the sarcolemmal protein dystrophin (Duchenne Muscular Dystrophy), OxS has been identified as a relevant secondary pathophysiological mechanism. OxS being drug-targetable, it represents an interesting therapeutic target for these incurable conditions, and following preclinical correction of the cell or animal model phenotype, the first clinical trials with the antioxidants N-acetylcysteine (SEPN1- and RYR1-related myopathies) or epigallocatechin-gallate (DMD) have been launched recently. In this review, we provide an overview of the mechanisms involved in redox regulation in skeletal muscle, the technical tools available to measure redox homeostasis in muscle cells, the bases of OxS as a primary or secondary pathomechanism in early-onset myopathies and the innovative clinical trials with antioxidants which are currently in progress for these so-far untreatable infantile muscle diseases. Progress in our knowledge of redox homeostasis defects in these rare muscle conditions may be useful as a model paradigm to understand and treat other conditions in which OxS is involved, including prevalent conditions with major socioeconomic impact such as insulin resistance, cachexia, obesity, sarcopenia or ageing.

Rigid spinal muscular dystrophy and rigid spine syndrome: report of 7 children

Seven children (5 male, 2 female) were seen over the last 16 years with rigid spine syndrome. Six children had rigid spinal muscular dystrophy (selenoprotein N1-related myopathy [SEPN1RM]) and 1 had myopathy associated with rigid spine. The main presenting complaint in all was difficulty in bending the spine. The diagnosis was made on clinical features and imaging of the paraspinal muscles. Muscle histopathology revealed minimal myopathic changes to severe muscle degeneration. Genetic testing, which was only available for the last case, for selenoprotein was negative.

Intersection of selenoproteins and kinase signalling

The small, obscure group of selenoprotein oxidoreductases and the huge clan of kinases, the workhorses of cellular signalling, are rarely discussed together. Focusing on selenoproteins of unknown structures, we predict a thioredoxin-like fold for the Selenoprotein N (SelN) family and use the structure to rationalise effects of the muscular myopathy-linked mutations in the gene coding SelN. Discussing the recent prediction of a protein kinase-like domain in the Selenoprotein O (SelO), we reiterate evidence for an oxidoreductase function alongside the predicted kinase domain. Thus, we propose that SelO, the strongly conserved kinase-cum-tentative-oxidoreductase may reflect oxidoreductase regulation of kinase networks. Also, we use bibliometric and systems biology approach to explore the kinase-selenoprotein relationships that begin to emerge from the literature. This article is part of a Special Issue entitled: Inhibitors of Protein Kinases (2012).

Selenoprotein N in skeletal muscle: from diseases to function

Selenoprotein N (SelN) deficiency causes several inherited neuromuscular disorders collectively termed SEPN1-related myopathies, characterized by early onset, generalized muscle atrophy, and muscle weakness affecting especially axial muscles and leading to spine rigidity, severe scoliosis, and respiratory insufficiency. SelN is ubiquitously expressed and is located in the membrane of the endoplasmic reticulum; however, its function remains elusive. The predominant expression of SelN in human fetal tissues and the embryonic muscle phenotype reported in mutant zebrafish suggest that it is involved in myogenesis. In mice, SelN is also mostly expressed during embryogenesis and especially in the myotome, but no defect was detected in muscle development and growth in the Sepn1 knock-out mouse model. By contrast, we recently demonstrated that SelN is essential for muscle regeneration and satellite cell maintenance in mice and humans, hence opening new avenues regarding the pathomechanism(s) leading to SEPN1-related myopathies. At the cellular level, recent data suggested that SelN participates in oxidative and calcium homeostasis, with a potential role in the regulation of the ryanodine receptor activity. Despite the recent and exciting progress regarding the physiological function(s) of SelN in muscle tissue, the pathogenesis leading to SEPN1-related myopathies remains largely unknown, with several unsolved questions, and no treatment available. In this review, we introduce SelN, its properties and expression pattern in zebrafish, mice, and humans, and we discuss its potential roles in muscle tissue and the ensuing clues for the development of therapeutic options.

Selenoproteins and protection against oxidative stress: selenoprotein N as a novel player at the crossroads of redox signaling and calcium homeostasis

Healthy cells continually produce low levels of reactive oxygen species (ROS), which are buffered by multiple antioxidant systems. Imbalance between ROS production and elimination results in oxidative stress, which has been implicated in aging and in numerous human diseases, including cancer and diabetes. Selenoproteins are a family of proteins that contain the amino acid selenocysteine, encoded by an in-frame UGA. Those selenoproteins whose function is identified are catalytically active in redox processes, representing one of the main enzymatic antioxidant systems and important mediators of the beneficial role of selenium in human health. Nevertheless, the function of most selenoproteins remains unknown; this included Selenoprotein N (SelN), the only selenoprotein directly associated with a human genetic disease. Mutations of the SelN gene cause SEPN1-related myopathy, a particular early-onset muscle disorder. Recent studies have identified SelN as a key protein in cell protection against oxidative stress and redox-related calcium homeostasis. Furthermore, an effective ex vivo treatment of SelN deficiency has been identified, paving the way to a clinical therapy. In this review we discuss the physiological and pathophysiological role of SelN and the interest of SEPN1-related myopathy as a model paradigm to understand and target therapeutically other selenoproteins involved in human health and disease.

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.

The phenotype and long-term follow-up in 11 patients with juvenile selenoprotein N1-related myopathy

The selenoprotein N1-related myopathies comprise rigid spine muscular dystrophy, the "classical" form of multiminicore disease, a desmin-related myopathy with Mallory body like inclusions and a form of congenital fiber-type disproportion. To define the phenotype and long-term clinical course in juvenile Selenoprotein N1-related myopathies 11 juvenile patients from eight families with SEPN1 mutations were assessed over a mean period of 7.2 years. Clinical findings, histomorphological studies, respiratory investigations and genetic data were analyzed: age of manifestation varied within the first 2 years of life with muscle hypotonia, lag of head control and delayed motor development. Further gross motor development was normal in 9/11 patients. All patients were ambulant for at least 1000 m at a mean age of 13.7 years. Eight patients exhibited a rigid spine diagnosed at a mean age of 10 years. All patients had respiratory impairment with a vital capacity ranging from 18% to 65%. Four patients were intermittently nocturnally ventilated at a mean age of 11 years. Body mass index was below 20 (kgm(-2)) in all patients. Muscle biopsies of eight individuals revealed multiminicores (n=2), congenital fiber-type disproportion (n=1), myopathic changes with single cores (n=2) and unspecific myopathic features (n=3). Mutations were distributed throughout the entire SEPN1 gene. Although the phenotype of juvenile selenoprotein N1-related myopathies is homogenous regarding the main symptoms we describe a variable degree of clinical severity. Major complications were early respiratory failure, impaired increase in weight and orthopedic problems. There seems to be no correlation between skeletal muscle weakness and respiratory failure.

Respiratory involvement in inherited primary muscle conditions

Patients with inherited muscle disorders can develop respiratory muscle weakness leading to ventilatory failure. Predicting the extent of respiratory involvement in the different types of inherited muscle disorders is important, as it allows clinicians to impart prognostic information and offers an opportunity for early interventional management strategies. The approach to respiratory assessment in patients with muscle disorders, the current knowledge of respiratory impairment in different muscle disorders and advice on the management of respiratory complications are summarised.

Molecular mechanism of rigid spine with muscular dystrophy type 1 caused by novel mutations of selenoprotein N gene

Mutations of selenoprotein N, 1 gene (SEPN1) cause rigid spine with muscular dystrophy type 1 (RSMD1), multiminicore disease, and desmin-related myopathy. We found two novel SEPN1 mutations in two Japanese patients with RSMD1. To clarify the pathomechanism of RSMD1, we performed immunohistochemical studies using a newly developed antibody for selenoprotein N. Selenoprotein N was diffusely distributed in the cytoplasm of the control muscle, but was reduced and irregularly expressed in the cytoplasm of a patient with RSMD1. The expression pattern was very similar to that of calnexin, a transmembrane protein of the endoplasmic reticulum. Selenoprotein N seems to be an endoplasmic reticulum glycoprotein, and loss of this protein leads to disturbance of muscular function. One of the families had the SEPN1 homozygous mutation in the initiation codon 1_2 ins T in exon 1 and showed truncated protein expression. The other had a homozygous 20-base duplication mutation at 80 (80_99dup, frameshift at R27) which, in theory, should generate many nonsense mutations including TGA. These nonsense mutations are premature translation termination codons and they degrade immediately by the process of nonsense-mediated decay (NMD). However, truncated selenoprotein N was also expressed. A possible mechanism behind this observation is that SEPN1 mRNAs may be resistant to NMD. We report on the possible molecular mechanism behind these mutations in SEPN1. Our study clarifies molecular mechanisms of this muscular disorder.

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.

Selenoprotein N muscular dystrophy: differential diagnosis for early-onset limited mobility of the spine

Early spinal rigidity is a nonspecific feature reported in diseases such as neuromuscular and central movement disorders. We present a male patient with rigid spine muscular dystrophy caused by newly identified compound heterozygote mutations of the selenoprotein N gene and discuss this disease as a possible differential diagnosis for early-onset reduced spine mobility. Rigid spine muscular dystrophy is a rare myopathy presenting in childhood with a typical combination of stable or slowly progressive mild to moderate muscle weakness, limitation in flexion of the spine, and progressive restrictive ventilatory disorder. The clinical features of our patient include early-onset rigidity of his spine, scoliosis, mild muscular weakness predominantly of neck and trunk flexors, and restrictive ventilatory disorder. Biopsy of the biceps muscle revealed nonspecific myopathic changes, and molecular analysis confirmed the diagnosis of rigid spine muscular dystrophy. Thus, neuromuscular diseases such as muscular dystrophy must be considered in all patients presenting with early spinal rigidity, and genetic determination is a possible way to determine the diagnosis.

Understanding the importance of selenium and selenoproteins in muscle function

Selenium is an essential trace element. In cattle, selenium deficiency causes dysfunction of various organs, including skeletal and cardiac muscles. In humans as well, lack of selenium is associated with many disorders, but despite accumulation of clinical reports, muscle diseases are not generally considered on the list. The goal of this review is to establish the connection between clinical observations and the most recent advances obtained in selenium biology. Recent results about a possible role of selenium-containing proteins in muscle formation and repair have been collected. Selenoprotein N is the first selenoprotein linked to genetic disorders consisting of different forms of congenital muscular dystrophies. Understanding the muscle disorders associated with selenium deficiency or selenoprotein N dysfunction is an essential step in defining the causes of the disease and obtaining a better comprehension of the mechanisms involved in muscle formation and maintenance.

The congenital muscular dystrophies: recent advances and molecular insights

Over the past decade, molecular understanding of the congenital muscular dystrophies (CMDs) has greatly expanded. The diseases can be classified into 3 major groups based on the affected genes and the location of their expressed protein: abnormalities of extracellular matrix proteins (LAMA2, COL6A1, COL6A2, COL6A3), abnormalities of membrane receptors for the extracellular matrix (fukutin, POMGnT1, POMT1, POMT2, FKRP, LARGE, and ITGA7), and abnormal endoplasmic reticulum protein (SEPN1). The diseases begin in the perinatal period or shortly thereafter. A specific diagnosis can be challenging because the muscle pathology is usually not distinctive. Immunostaining of muscle using a battery of antibodies can help define a disorder that will need confirmation by gene testing. In muscle diseases with overlapping pathological features, such as CMD, careful attention to the clinical clues (e.g., family history, central nervous system features) can help guide the battery of immunostains necessary to target an unequivocal diagnosis.

Cognitive impairment in neuromuscular disorders

Several studies have suggested the presence of central nervous system involvement manifesting as cognitive impairment in diseases traditionally confined to the peripheral nervous system. The aim of this review is to highlight the character of clinical, genetic, neurofunctional, cognitive, and psychiatric deficits in neuromuscular disorders. A high correlation between cognitive features and cerebral protein expression or function is evident in Duchenne muscular dystrophy, myotonic dystrophy (Steinert disease), and mitochondrial encephalomyopathies; direct correlation between tissue-specific protein expression and cognitive deficits is still elusive in certain neuromuscular disorders presenting with or without a cerebral abnormality, such as congenital muscular dystrophies, congenital myopathies, amyotrophic lateral sclerosis, adult polyglucosan body disease, and limb-girdle muscular dystrophies. No clear cognitive deficits have been found in spinal muscular atrophy and facioscapulohumeral dystrophy.

Muscle function and dysfunction in health and disease

Skeletal muscles of the trunk and limbs developmentally originate from the cells of the dermomyotomal compartment of the somite. A wealth of knowledge has been accumulated with regard to understanding the molecular regulation of embryonic skeletal myogenesis. Myogenic induction is controlled through a complex series of spatiotemporal dependent signaling cascades. Secreted signaling molecules from surrounding structures not only initiate the myogenic program, but also influence proliferation and differentiation decisions. The proper coordination of these molecular events is thus critical for the formation of physiologically functional skeletal muscles. Hereditary congenital skeletal muscle defects arise due to genetics lesions in myogenic specific components. Understanding the mechanistic routes of congenital skeletal muscle disease therefore requires a comprehensive knowledge of the developmental system. Ultimately, the application of this knowledge will improve the diagnostic and therapeutic methodologies for such diseases. The aim of this review is to overview our current understanding of skeletal muscle development and associated human congenital diseases.

Scoliosis correction in an adolescent with a rigid spine syndrome: case report

STUDY DESIGN

Details of presentation and approach to the treatment of scoliosis in a case of a Rigid Spine Syndrome (RSS).

OBJECTIVE

To report on the results of conservative and operative treatment of scoliosis associated with RSS, and, based on this, to propose an assessment and treatment protocol for this condition.

SUMMARY OF BACKGROUND DATA

Congenital muscular dystrophies (CMD) are a group of disorders marked by hypotonia at birth and a generally nonprogressive course of muscle weakness. Spinal rigidity is present in a number of patients with CMD. RSS is classified as a CMD, and is characterized by early rigidity of the spine, limb contractures, and restrictive respiratory dysfunction. An approach to the treatment of scoliosis in RSS has not been established.

METHODS

Details of history, diagnostic tests, and treatment of an adolescent with RSS associated with progressive scoliosis and cervical spine extension contracture is presented. The role of brace treatment, Botox (Allergan, Inc., Irvine, CA), and details of operative correction, including histology of back muscles, is defined.

RESULTS

In this case of RSS with rigid scoliosis nonresponsive to brace therapy and Botox injections, an anterior thoracolumbar spine fusion with instrumentation was successfully performed for correction of the scoliosis, and the cervical spine was addressed through a posterior approach and an occiput-cervical fusion. We outline the details of surgical procedure and restoration of spinal balance in both sagittal and coronal planes.

CONCLUSIONS

The chromosomal bases of CMD and characteristic features of RSS, including diagnostic tests, have been reviewed. Surgical intervention with spinal deformity fusion, correction, and instrumentation is indicated in RSS with progressive spinal imbalance not responding to conservative therapy is safe and can give promising results.

Dysferlinopathy associated with rigid spine syndrome

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

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.

Desmin-related myopathy with mallory body-like inclusions is caused by mutations of the selenoprotein N gene

Desmin-related myopathies (DRMs) are a heterogeneous group of muscle disorders, morphologically defined by intrasarcoplasmic aggregates of desmin. Mutations in the desmin and the alpha-B crystallin genes account for approximately one third of the DRM cases. The genetic basis of the other forms remain unknown, including the early-onset, recessive form with Mallory body-like inclusions (MB-DRMs), first described in five related German patients. Recently, we identified the selenoprotein N gene (SEPN1) as responsible for SEPN-related myopathy (SEPN-RM), a unique early-onset myopathy formerly divided in two different nosological categories: rigid spine muscular dystrophy and the severe form of classical multiminicore disease. The finding of Mallory body-like inclusions in two cases of genetically documented SEPN-RM led us to suspect a relationship between MB-DRM and SEPN1. In the original MB-DRM German family, we demonstrated a linkage of the disease to the SEPN1 locus (1p36), and subsequently a homozygous SEPN1 deletion (del 92 nucleotide -19/+73) in the affected patients. A comparative reevaluation showed that MB-DRM and SEPN-RM share identical clinical features. Therefore, we propose that MB-DRM should be categorized as SEPN-RM. These findings substantiate the molecular heterogeneity of DRM, expand the morphological spectrum of SEPN-RM, and implicate a necessary reassessment of the nosological boundaries in early-onset myopathies.

Congenital myopathies

The congenital myopathies encompass a group of neuromuscular disorders with characteristic morphologic abnormalities in skeletal muscle, including nemaline myopathy, central core disease, multi-minicore disease, and myotubular myopathy. Giant steps have been made in our understanding of the molecular bases of these disorders, all of which show remarkable genetic heterogeneity. This review of congenital myopathies examines progress in defining clinical diagnostic criteria and novel genetic advances that have provided important clues regarding their pathogeneses.

A novel form of recessive limb girdle muscular dystrophy with mental retardation and abnormal expression of α-dystroglycan

The limb girdle muscular dystrophies are a heterogeneous group of conditions characterized by proximal muscle weakness and disease onset ranging from infancy to adulthood. We report here eight patients from seven unrelated families affected by a novel and relatively mild form of autosomal recessive limb girdle muscular dystrophy (LGMD2) with onset in the first decade of life and characterized by severe mental retardation but normal brain imaging. Immunocytochemical studies revealed a significant selective reduction of alpha-dystroglycan expression in the muscle biopsies. Linkage analysis excluded known loci for both limb girdle muscular dystrophy and congenital muscular dystrophies in the consanguineous families. We consider that this represents a novel form of muscular dystrophy with associated brain involvement. The biochemical studies suggest that it may belong to the growing number of muscular dystrophies with abnormal expression of alpha-dystroglycan.

Muscular dystrophy overview: genetics and diagnosis

A specific genetic diagnosis can be reached for most children with muscular dystrophy. Advanced diagnostics, including genetic testing and analysis of nonmuscle tissues, such as skin and blood, often allow the diagnosis to be reached using minimally invasive procedures. These diagnostic advances accompany improved understanding of pathophysiology and pave the way for specific and curative treatments.

Mutations of the selenoprotein N gene, which is implicated in rigid spine muscular dystrophy, cause the classical phenotype of multiminicore disease: reassessing the nosology of early-onset myopathies

Multiminicore disease (MmD) is an autosomal recessive congenital myopathy characterized by the presence of multiple, short core lesions (known as "minicores") in most muscle fibers. MmD is a clinically heterogeneous condition, in which four subgroups have been distinguished. Homozygous RYR1 mutations have been recently identified in the moderate form of MmD with hand involvement. The genes responsible for the three other forms (including the most prevalent phenotype, termed the "classical" phenotype) remained, so far, unknown. To further characterize the genetic basis of MmD, we analyzed a series of 62 patients through a combined positional/candidate-gene approach. On the basis of clinical and morphological data, we suspected a relationship between classical MmD and the selenoprotein N gene (SEPN1), which is located on chromosome 1p36 (RSMD1 locus) and is responsible for the congenital muscular dystrophy with rigid spine syndrome (RSMD). A genomewide screening, followed by the analysis of 1p36 microsatellite markers in 27 informative families with MmD, demonstrated linkage to RSMD1 in eight families. All showed an axial myopathy with scoliosis and respiratory failure, consistent with the most severe end of the classical MmD spectrum; spinal rigidity was evident in some, but not all, patients. We excluded linkage to RSMD1 in 19 families with MmD, including 9 with classical MmD. Screening of SEPN1 in the 8 families that showed linkage and in 14 patients with classical sporadic disease disclosed 9 mutations affecting 17 patients (12 families); 6 were novel mutations, and 3 had been described in patients with RSMD. Analysis of three deltoid biopsy specimens from patients with typical RSMD revealed a wide myopathological variability, ranging from a dystrophic to a congenital myopathy pattern. A variable proportion of minicores was found in all the samples. The present study represents the first identification of a gene responsible for classical MmD, demonstrates its genetic heterogeneity, and reassesses the nosological boundaries between MmD and RSMD.

Clinical and imaging findings in six cases of congenital muscular dystrophy with rigid spine syndrome linked to chromosome 1p (RSMD1)

We report clinical and imaging findings in six cases from five families affected by the form of congenital muscular dystrophy with rigid spine linked to the locus rigid spine muscular dystrophy 1 on chromosome 1p35-36. All cases showed rigidity of the spine, predominant neck and trunk weakness and frequent and severe thoracic scoliosis. Respiratory impairment was always observed in the first decade. Muscle imaging showed a marked involvement of adductors, sartorius and biceps femoris while rectus femoris and gracilis were relatively spared. This pattern of selective muscle involvement was consistent in all six cases and could be easily observed on either computerised tomography or magnetic resonance imaging. The results of this study suggest that muscle imaging, in combination with clinical assessment can help to identify the rigid spine muscular dystrophy 1 form of congenital muscular dystrophy and can help to target the appropriate genetic investigations.

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.

Autosomal dominant Emery-Dreifuss muscular dystrophy: a new family with late diagnosis

Emery-Dreifuss muscular dystrophy is characterized by the clinical triad of early onset contractures of elbows, Achilles tendons and spine, wasting and weakness with a predominantly humero-peroneal distribution and life-threatening cardiac conduction defects and/or cardiomyopathy. Two main types of inheritance have been described: the X-linked form is caused by mutations in the STA gene on locus Xq28 and the gene for the autosomal dominant form (LMNA gene) has been localized on chromosome 1q11-q23. Recently, mutations in this LMNA gene have been also found to be responsible for the less frequent autosomal recessive form of the disease. Although all forms share a similar clinical presentation, some differences appear to exist between them as has been described recently in a large number of patients. We present the first documented Spanish family genetically confirmed to have autosomal dominant Emery-Dreifuss muscular dystrophy. Clinical, pathological and genetic data are described. We emphasize the difficulties in diagnosis, especially in sporadic cases or young patients in whom the clinical picture is not completely established.

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.

Mice with a targeted deletion of the tetranectin gene exhibit a spinal deformity

Tetranectin is a plasminogen-binding, homotrimeric protein belonging to the C-type lectin family of proteins. Tetranectin has been suggested to play a role in tissue remodeling, due to its ability to stimulate plasminogen activation and its expression in developing tissues such as developing bone and muscle. To test the functional role of tetranectin directly, we have generated mice with a targeted disruption of the gene. We report that the tetranectin-deficient mice exhibit kyphosis, a type of spinal deformity characterized by an increased curvature of the thoracic spine. The kyphotic angles were measured on radiographs. In 6-month-old normal mice (n = 27), the thoracic angle was 73 degrees +/- 2 degrees, while in tetranectin-deficient 6-month-old mice (n = 35), it was 93 degrees +/- 2 degrees (P < 0.0001). In approximately one-third of the mutant mice, X-ray analysis revealed structural changes in the morphology of the vertebrae. Histological analysis of the spines of these mice revealed an apparently asymmetric development of the growth plate and of the intervertebral disks of the vertebrae. In the most advanced cases, the growth plates appeared disorganized and irregular, with the disk material protruding through the growth plate. Tetranectin-null mice had a normal peak bone mass density and were not more susceptible to ovariectomy-induced osteoporosis than were their littermates as determined by dual-emission X-ray absorptiometry scanning. These results demonstrate that tetranectin plays a role in tissue growth and remodeling. The tetranectin-deficient mouse is the first mouse model that resembles common human kyphotic disorders, which affect up to 8% of the population.

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.

Mutations in SEPN1 cause congenital muscular dystrophy with spinal rigidity and restrictive respiratory syndrome

One form of congenital muscular dystrophy, rigid spine syndrome (MIM 602771), is a rare neuromuscular disorder characterized by early rigidity of the spine and respiratory insufficiency. A locus on 1p35-36 (RSMD1) was recently found to segregate with rigid spine muscular dystrophy 1 (ref. 1). Here we refine the locus and find evidence of linkage disequilibrium associated with SEPN1, which encodes the recently described selenoprotein N (ref. 2). Our identification and analysis of mutations in SEPN1 is the first description of a selenoprotein implicated in a human disease.

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.

Revised genomic structure of the human MAGP1 gene and identification of alternate transcripts in human and mouse tissues

The human MAGP1 (or MFAP2) and mouse Magp1 genes code for the microfibril-associated glycoprotein-1 (MAGP-1), an extracellular matrix protein of microfibrillar structures. We report a revised 5' genomic structure including the use of a single transcription start site that gives rise to a 32-bp 5' exon spanning a segment of the previously described exon B. No evidence of heterogeneous 5' ends from the use of alternative promoters was found in human tissues and cell lines. We located the genetic marker D1S170 to a position 3 kb downstream of the polyadenylation site. Large-scale comparison of the human and mouse genes revealed conservation of sequence outside the coding exons. Although the 5' flanking regions were found to be divergent certain cis-elements for transcription factors are conserved, including Sp1, AP-2, AP-4, NF-kappaB, and c-ETS motifs. We identified a total of five splice variants in addition to the canonical MAGP1A/Magp1A form. These transcripts are species-specific and are generated by different processing mechanisms. The alternate forms MAGP1A', MAGP1B, and MAGP1C are expressed in human tissues; and the two variants Magp1A" and Magp1D were found only in mouse. The alternatively spliced forms show restricted patterns of expression relative to the canonical isoform.

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.

Structure and chromosomal localization of the human and mouse muscle fructose-1,6-bisphosphatase genes

Mammalian skeletal muscle contains fructose-1,6-bisphosphatase (Fru-1,6-P(2)ase), a key enzyme of glyconeogenesis. We have shown previously that muscle Fru-1,6-P(2)ase is encoded by a gene different from that coding for the liver isoenzyme. Starting with genomic YAC libraries and based on the cDNA sequences of human and mouse muscle Fru-1,6-P(2)ases together with the known gene structures of two mammalian liver fructose-1,6-bisphosphatases, we have PCR-amplified and sequenced all functional parts of the human and mouse muscle fructose-1,6-bisphosphatase genes and determined their chromosomal localization. The human gene (FBP2), localized at chromosome 1p36.1-2, spans about 30 kb, while the mouse gene (Fbp2) at chromosome 13B3-C1 is more compact (about 21 kb). Intron lengths are only poorly conserved between the two genes, while intron number and positions are identical in all hitherto analyzed mammalian fructose-1,6-bisphosphatase isoenzyme genes. Transcriptional start sites were found to be located 97 and 95bp before the start codon in the human gene and 35 bp before the start codon in the mouse homolog. A comparison of the 5'-flanking sequences of the two genes revealed a 56% homology up to human bp -607 before the first transcriptional start point, while upstream of this region we found no similarity. The data presented in this paper provide a basis for further studies of the mechanism of expression regulation and the elucidation of the physiological role of the enzyme.

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.