Merosin-deficient congenital muscular dystrophy: the spectrum of brain involvement on magnetic resonance imaging

Hydrocephalus: A Review of Etiology-Driven Treatment Strategies

Hydrocephalus is a broad term usually understood as cerebrospinal fluid (CSF) accumulation resulting in cerebral ventricular system expansion. The production of CSF is by the choroid plexus in lateral ventricles, flowing between the third and fourth ventricles and eventually to the subarachnoid space. It is critical for proper neuronal function. Hydrocephalus is a neurological pathology linked to high morbidity from neurocognitive and motor impairment. It is classified as either communicating or non-communicating. Communicating hydrocephalus is understood as a deficit at cranial arachnoid villi and granulation absorption sites. However, there has been evidence that extracranial lymphatic vessels in the ethmoid bone region also play a role, as indicated by decreased lymphatic absorption in rat models of hydrocephalus. Treatment typically involves surgical shunt placement or endoscopic third ventriculostomy (ETV) technique with or without choroid plexus cauterization (CPC). These surgical interventions have high failure risks and complications that require re-intervention, further increasing morbidity and mortality risks. To date, there are few nonsurgical treatment strategies, but many have proved limited benefit, and many patients still require surgery. This analysis lays out the typical treatments and explores new, innovative interventions by highlighting the active role of brain parenchymal tissue in the pathogenesis of hydrocephalus.

An International Retrospective Early Natural History Study of LAMA2-Related Dystrophies

Background

LAMA2-related dystrophies (LAMA2-RDs) represent one of the most common forms of congenital muscular dystrophy and have historically been classified into two subtypes: complete or partial deficiency of laminin-211 (merosin). Patients with LAMA2-RD with the typical congenital phenotype manifest severe muscle weakness, delayed motor milestones, joint contractures, failure to thrive, and progressive respiratory insufficiency.

Objective

While a comprehensive prospective natural history study has been performed in LAMA2-RD patients over 5 years of age, the early natural history of patients with LAMA2-RD 5 years and younger has not been comprehensively characterized.

Methods

We extracted retrospective data for patients with LAMA2-RD ages birth through 5 years via the Congenital Muscle Disease International Registry (CMDIR). We analyzed the data using a phenotypic classification based on maximal motor milestones to divide patients into two phenotypic groups: "Sit" for those patients who attained that ability to remain seated and "Walk" for those patients who attained the ability to walk independently by 3.5 years of age.

Results

Sixty patients with LAMA2-RD from 10 countries fulfilled the inclusion criteria. Twenty-four patients had initiated non-invasive ventilation by age 5 years. Hospitalizations during the first years of life were often related to respiratory insufficiency. Feeding/nutritional difficulties and orthopedic issues were commonly reported. Significant elevations of creatine kinase (CK) observed during the neonatal period declined rapidly within the first few months of life.

Conclusions

This is the largest international retrospective early natural history study of LAMA2-RD to date, contributing essential data for understanding early clinical findings in LAMA2-RD which, along with the data being collected in international, prospective early natural history studies, will help to establish clinical trial readiness. Our proposed nomenclature of LAMA2-RD1 for patients who attain the ability to sit (remain seated) and LAMA2-RD2 for patients who attain the ability to walk independently is aimed at further improving LAMA2-RD classification.

Phenotype-genotype spectrum of a cohort of congenital muscular dystrophies: a single-centre experience from India

Congenital Muscular Dystrophies (CMD) are phenotypically and genotypically heterogenous disorders with a prevalence of 0.68 to 2.5/100,000, contributing to significant morbidity and mortality. We aimed to study the phenotype-genotype spectrum of genetically confirmed cases of CMD. This was retrospective & descriptive study done at a quaternary care referral centre in south India. Genetically confirmed cases of CMDs seen between 2010 to 2020 were recruited. Detailed clinical history, including pedigree, MRI brain/muscle, next generation sequencing results of 61 CMD cases were collected. Collagen VI-related dystrophy (COL6-RD) (36%) was the most common subtype with variants frequently seen in COL6A1 gene. Other CMDs identified were LAMA2-RD (26%), alpha-dystroglycan-RD (19%), LMNA-RD (8%), CHKB-RD (7%) and SEPN1-RD (3%). Similar to previous cohorts, overall, missense variants were common in COL-6 RD. Variants in triple helical domain (THD) of COL6-RD were seen in 11/22 patients, 5 of whom were ambulatory contrary to previous literature citing severe disease with these variants. However, our follow-up period was shorter. In the LAMA2-RD, 2/16 patients were ambulatory & all 16 carried truncating variants. Among dystroglycanopathies, FKRP-RD was the commonest. Milder phenotype of FKRP- RD was observed with variant c.1343C > T, which was also a recurrent variant in our cohort. p.Arg249Trp variant in LMNA-CMD associated with early loss of ambulation was also identified in 1/5 of our patients who expired at age 2.8 years. The current retrospective series provides detailed clinical features and mutation patterns of genetically confirmed cases of CMD from a single center in India.

A Multicenter Cross-Sectional Study of the Swiss Cohort of LAMA2-Related Muscular Dystrophy

Background

LAMA2-related muscular dystrophy (LAMA2-RD) is an autosomal-recessive disorder and one of the most common congenital muscular dystrophies. Due to promising therapies in preclinical development, there is an increasing effort to better define the epidemiology and natural history of this disease.

Objective

The present study aimed to describe a well-characterized baseline cohort of patients with LAMA2-RD in Switzerland.

Methods

The study used data collected by the Swiss Registry for Neuromuscular Disorders (Swiss-Reg-NMD). Diagnostic findings were derived from genetics, muscle biopsy, creatine kinase-level and electrophysiological testing, as well as from brain MRIs. Further clinical information included motor assessments (CHOP INTEND, MFM20/32), joint contractures, scoliosis, ophthalmoplegia, weight gain, feeding difficulties, respiratory function, cardiac investigations, EEG findings, IQ and schooling.

Results

Eighteen patients with LAMA-RD were included in the Swiss-Reg-NMD as of May 2023 (age at inclusion into the registry: median age 8.7 years, range 1 month - 31 years F = 8, M = 10). Fourteen patients presented with the severe form of LAMA2-RD (were never able to walk; CMD), whereas four patients presented with the milder form (present or lost walking capability; LGMD). All patients classified as CMD had symptoms before 12 months of age and 11/14 before the age of six months. 15 carried homozygous or compound heterozygous pathogenic or likely pathogenic variants in LAMA2 and two were homozygous for a variant of unknown significance (one patient unknown). Brain MRI was available for 14 patients, 13 had white matter changes and 11 had additional structural abnormalities, including cobblestone malformations, pontine hypoplasia and an enlarged tegmento-vermial angle not reported before.

Conclusion

This study describes the Swiss cohort of patients with LAMA2-RD and gives insights into measuring disease severity and disease progression, which is important for future clinical trials, as well as for a better clinical understanding and management of patients with LAMA2-RD.

Pediatric Neuromuscular Diseases

The diagnostic and referral workflow for children with neuromuscular disorders is evolving, particularly as newborn screening programs are expanding in tandem with novel therapeutic developments. However, for the children who present with symptoms and signs of potential neuromuscular disorders, anatomic localization, guided initially by careful history and physical examination, continues to be the cardinal initial step in the diagnostic evaluation. It is important to consider whether the localization is more likely to be in the lower motor neuron, peripheral nerve, neuromuscular junction, or muscle. After that, disease etiologies can be divided broadly into inherited versus acquired categories. Considerations of localization and etiologies will help generate a differential diagnosis, which in turn will guide diagnostic testing. Once a diagnosis is made, it is important to be aware of current treatment options, as a number of new therapies for some of these disorders have been approved in recent years. Families are also increasingly interested in clinical research, which may include natural history studies and interventional clinical trials. Such research has proliferated for rare neuromuscular diseases, leading to exciting advances in diagnostic and therapeutic technologies, promising dramatic changes in the landscape of these disorders in the years to come.

Congenital Muscular Dystrophy Due to Merosin Deficiency: Report of a New Mutation

Congenital muscular dystrophy due to merosin deficiency is one of the most common congenital muscular dystrophies. It is characterized by a LAMA2 gene mutation and causes varied clinical symptoms depending on the type of presentation. In this case report, we identified the importance of the medical history and the autosomal recessive expression, which compromises the sequencing of the LAMA2 gene, with a mutation variant c. 1854_1861dup (p. Leu621Hisfs*7), in homozygosity not described so far. As well as the phenotypic characteristics of the evidenced mutation. A 13-year-old patient presented with a clinical history that began at 18 months of age. According to the mother, the patient had a delay in neurological development and could not walk since he was 7. In addition, contractures were observed in the lower extremity, elbows, and fingers of both hands. The patient also had scoliosis, bilateral hip dysplasia, and sleep apnea-hypopnea syndrome. However, cognitive function was unaffected. Extension studies revealed elevated creatine kinase levels, electromyography indicated muscle fiber involvement, and brain resonance imaging showed a hyperintense lesion at the periventricular level along with symmetrical supratentorial findings. Immunohistochemical studies of merosin showed incomplete reactivity and gene sequencing revealed evidence of a LAMA2 mutation: c. 1854_1861dup (p. Leu621Hisfs*7), in homozygosity. Congenital muscular dystrophy caused by merosin deficiency is characterized by the absence of laminin alpha-2. The clinical manifestation of this disease is a severe phenotype, mainly due to the early onset of the disease. In patients with mutations in the LAMA2 gene, the absence or partial reduction of laminin alpha-2 staining may allow some degree of ambulation, as it could indicate a partially functional protein. To complement clinical, immunohistochemical, and pathologic findings, ultrasound can be used as a potential tool for monitoring or assisting in the diagnosis of individuals with congenital muscular dystrophy. In this study, we performed sequencing of the LAMA2 gene, which revealed a homozygous c. 1854_1861dup (p. Leu621Hisfs*7) mutation. In addition, we describe the phenotypic features associated with this specific mutation.

LAMA2-Related Muscular Dystrophy: The Importance of Accurate Phenotyping and Brain Imaging in the Diagnosis of LGMD

We report three siblings from a non-consanguineous family presenting with contractural limb-girdle phenotype with intrafamilial variability. Muscle MRI showed posterior thigh and quadriceps involvement with a sandwich-like sign. Whole-exome sequencing identified two compound heterozygous missense TTN variants and one heterozygous LAMA2 variant. Brain MRI performed because of concentration difficulties in one of the siblings evidenced white-matter abnormalities, subsequently found in the others. The genetic analysis was re-oriented, revealing a novel pathogenic intronic LAMA2 variant which confirmed the LAMA2-RD diagnosis. This work highlights the importance of a thorough clinical phenotyping and the importance of brain imaging, in order to orientate and interpret the genetic analysis.

Cataract, abnormal electroretinogram and visual evoked potentials in a child with SMA-LED2 - extending the phenotype

This case report describes a girl who presented antenatal arthrogryposis and postnatal hypotonia, generalized and respiratory weakness, joint deformities particularly affecting the lower limbs and poor swallow. By 5 months, cataracts, abnormal electroretinograms, visual evoked potentials and global developmental impairments were recognized. No causative variants were identified on targeted gene panels. After her unexpected death at 11 months, gene-agnostic trio whole exome sequencing revealed a likely pathogenic de novo BICD2 missense variant, NM_001003800.1, c.593T>C, p.(Leu198Pro), confirming the diagnosis of spinal muscular atrophy lower extremity predominant type 2 (SMA-LED2). We propose that cataracts and abnormal electroretinograms are novel features of SMA-LED2.

LAMA2-Related Dystrophies: Clinical Phenotypes, Disease Biomarkers, and Clinical Trial Readiness

Mutations in the LAMA2 gene affect the production of the α2 subunit of laminin-211 (= merosin) and result in either partial or complete laminin-211 deficiency. Complete merosin deficiency is typically associated with a more severe congenital muscular dystrophy (CMD), clinically manifested by hypotonia and weakness at birth, the development of contractures of large joints, and progressive respiratory involvement. Muscle atrophy and severe weakness typically prevent independent ambulation. Partial merosin deficiency is mostly manifested by later onset limb-girdle weakness and joint contractures so that independent ambulation is typically achieved. Collectively, complete and partial merosin deficiency is referred to as LAMA2-related dystrophies (LAMA2-RDs) and represents one of the most common forms of congenital muscular dystrophies worldwide. LAMA2-RDs are classically characterized by both central and peripheral nervous system involvement with abnormal appearing white matter (WM) on brain MRI and dystrophic appearing muscle on muscle biopsy as well as creatine kinase (CK) levels commonly elevated to >1,000 IU/L. Next-generation sequencing (NGS) has greatly improved diagnostic abilities for LAMA2-RD, and the majority of patients with merosin deficiency carry recessive pathogenic variants in the LAMA2 gene. The existence of multiple animal models for LAMA2-RDs has helped to advance our understanding of laminin-211 and has been instrumental in preclinical research progress and translation to clinical trials. The first clinical trial for the LAMA2-RDs was a phase 1 pharmacokinetic and safety study of the anti-apoptotic compound omigapil, based on preclinical studies performed in the dy ^W/dy ^W and dy ^2J/dy ^2J mouse models. This phase 1 study enabled the collection of pulmonary and motor outcome measures and also provided the opportunity for investigating exploratory outcome measures including muscle ultrasound, muscle MRI and serum, and urine biomarker collection. Natural history studies, including a five-year prospective natural history and comparative outcome measures study in patients with LAMA2-RD, have helped to better delineate the natural history and identify viable outcome measures. Plans for further clinical trials for LAMA2-RDs are presently in progress, highlighting the necessity of identifying adequate, disease-relevant biomarkers, capable of reflecting potential therapeutic changes, in addition to refining the clinical outcome measures and time-to-event trajectory analysis of affected patients.

Brain Dysfunction in LAMA2-Related Congenital Muscular Dystrophy: Lessons From Human Case Reports and Mouse Models

Laminin α2 gene (LAMA2)-related Congenital Muscular Dystrophy (CMD) was distinguished by a defining central nervous system (CNS) abnormality—aberrant white matter signals by MRI—when first described in the 1990s. In the past 25 years, researchers and clinicians have expanded our knowledge of brain involvement in LAMA2-related CMD, also known as Congenital Muscular Dystrophy Type 1A (MDC1A). Neurological changes in MDC1A can be structural, including lissencephaly and agyria, as well as functional, including epilepsy and intellectual disability. Mouse models of MDC1A include both spontaneous and targeted LAMA2 mutations and range from a partial loss of LAMA2 function (e.g., dy^2J/dy^2J), to a complete loss of LAMA2 expression (dy^3K/dy^3K). Diverse cellular and molecular changes have been reported in the brains of MDC1A mouse models, including blood-brain barrier dysfunction, altered neuro- and gliogenesis, changes in synaptic plasticity, and decreased myelination, providing mechanistic insight into potential neurological dysfunction in MDC1A. In this review article, we discuss selected studies that illustrate the potential scope and complexity of disturbances in brain development in MDC1A, and as well as highlight mechanistic insights that are emerging from mouse models.

Epilepsy in LAMA2-related muscular dystrophy: An electro-clinico-radiological characterization

OBJECTIVE

To delineate the epileptic phenotype of LAMA2-related muscular dystrophy (MD) and correlate it with the neuroradiological and muscle biopsy findings, as well as the functional motor phenotype.

METHODS

Clinical, electrophysiological, neuroradiological, and histopathological data of 25 patients with diagnosis of LAMA2-related MD were analyzed.

RESULTS

Epilepsy occurred in 36% of patients with LAMA2-related MD. Mean age at first seizure was 8 years. The most common presenting seizure type was focal-onset seizures with or without impaired awareness. Visual aura and autonomic signs, including vomiting, were frequently reported. Despite a certain degree of variability, bilateral occipital or temporo-occipital epileptiform abnormalities were by far the most commonly observed. Refractory epilepsy was found in 75% of these patients. Epilepsy in LAMA2-related MD was significantly more prevalent in those patients in whom the cortical malformations were more extensive. In contrast, the occurrence of epilepsy was not found to be associated with the patients' motor ability, the size of their white matter abnormalities, or the amount of residual merosin expressed on muscle.

SIGNIFICANCE

The epileptic phenotype of LAMA2-related MD is characterized by focal seizures with prominent visual and autonomic features associated with EEG abnormalities that predominate in the posterior quadrants. A consistent correlation between epileptic phenotype and neuroimaging was identified, suggesting that the extension of the polymicrogyria may serve as a predictor of epilepsy occurrence.

Laminin α2 controls mouse and human stem cell behaviour during midbrain dopaminergic neuron development

Development of the central nervous system requires coordination of the proliferation and differentiation of neural stem cells. Here, we show that laminin alpha 2 (lm-α2) is a component of the midbrain dopaminergic neuron (mDA) progenitor niche in the ventral midbrain (VM) and identify a concentration-dependent role for laminin α2β1γ1 (lm211) in regulating mDA progenitor proliferation and survival via a distinct set of receptors. At high concentrations, lm211-rich environments maintain mDA progenitors in a proliferative state via integrins α6β1 and α7β1, whereas low concentrations of lm211 support mDA lineage survival via dystroglycan receptors. We confirmed our findings in vivo, demonstrating that the VM was smaller in the absence of lm-α2, with increased apoptosis; furthermore, the progenitor pool was depleted through premature differentiation, resulting in fewer mDA neurons. Examination of mDA neuron subtype composition showed a reduction in later-born mDA neurons of the ventral tegmental area, which control a range of cognitive behaviours. Our results identify a novel role for laminin in neural development and provide a possible mechanism for autism-like behaviours and the brainstem hypoplasia seen in some individuals with mutations of LAMA2.

Current understanding and treatment of cardiac and skeletal muscle pathology in laminin-α2 chain-deficient congenital muscular dystrophy

Congenital muscular dystrophy (CMD) is a class of severe early-onset muscular dystrophies affecting skeletal/cardiac muscles as well as the central nervous system (CNS). Laminin-α2 chain-deficient congenital muscular dystrophy (LAMA2 MD), also known as merosin-deficient congenital muscular dystrophy type 1A (MDC1A), is an autosomal recessive CMD characterized by severe muscle weakness and degeneration apparent at birth or in the first 6 months of life. LAMA2 MD is the most common congenital muscular dystrophy, affecting approximately 4 in 500,000 children. The most common cause of death in early-onset LAMA2 MD is respiratory tract infection, with 30% of them dying within the first decade of life. LAMA2 MD is caused by loss-of-function mutations in the LAMA2 gene encoding for the laminin-α2 chain, one of the subunits of laminin-211. Laminin-211 is an extracellular matrix protein that functions to stabilize the basement membrane and muscle fibers during contraction. Since laminin-α2 is expressed in many tissue types including skeletal muscle, cardiac muscle, Schwann cells, and trophoblasts, patients with LAMA2 MD experience a multi-systemic clinical presentation depending on the extent of laminin-α2 chain deficiency. Cardiac manifestations are typically associated with a complete absence of laminin-α2; however, recent case reports highlight cardiac involvement in partial laminin-α2 chain deficiency. Laminin-211 is also expressed in the brain, and many patients have abnormalities on brain imaging; however, mental retardation and/or seizures are rarely seen. Currently, there is no cure for LAMA2 MD, but various therapies are being investigated in an effort to lessen the severity of LAMA2 MD. For example, antisense oligonucleotide-mediated exon skipping and CRISPR-Cas9 genome editing have efficiently restored the laminin-α2 chain in mouse models in vivo. This review consolidates information on the clinical presentation, genetic basis, pathology, and current treatment approaches for LAMA2 MD.

Exome sequencing detects compound heterozygous nonsense LAMA2 mutations in two siblings with atypical phenotype and nearly normal brain MRI

LAMA2 mutations cause the most frequent congenital muscular dystrophy subtype MDC1A and a variety of milder phenotypes, characterized by total or partial laminin-α2 deficiency. In both severe and milder cases brain MRI invariably shows abnormal white matter signal intensity. We report clinical, histopathological, imaging and genetic data on two siblings with very subtle, and at first undetected, reduction in laminin-α2 expression, and brain MRI showing minor non-specific abnormalities. Clinical features in the female proband were characterized by muscle weakness involving neck and axial muscles, and pelvic girdle and distal lower limb muscles, reduced tendon reflexes and pes cavus. Clinical features in a younger brother were similar, and remained stable in both siblings during the follow up. Whole exome sequencing (WES) detected two heterozygous truncating LAMA2 mutations. Brain MRI in combination with laminin-α2 immunohistochemistry might not be sufficient and WES might be the only means to reach a diagnosis.

Genetic defects disrupting glial ion and water homeostasis in the brain

Electrical activity of neurons in the brain, caused by the movement of ions between intracellular and extracellular compartments, is the basis of all our thoughts and actions. Maintaining the correct ionic concentration gradients is therefore crucial for brain functioning. Ion fluxes are accompanied by the displacement of osmotically obliged water. Since even minor brain swelling leads to severe brain damage and even death, brain ion and water movement has to be tightly regulated. Glial cells, in particular astrocytes, play a key role in ion and water homeostasis. They are endowed with specific channels, pumps and carriers to regulate ion and water flow. Glial cells form a large panglial syncytium to aid the uptake and dispersal of ions and water, and make extensive contacts with brain fluid barriers for disposal of excess ions and water. Genetic defects in glial proteins involved in ion and water homeostasis disrupt brain functioning, thereby leading to neurological diseases. Since white matter edema is often a hallmark disease feature, many of these diseases are characterized as leukodystrophies. In this review we summarize our current understanding of inherited glial diseases characterized by disturbed brain ion and water homeostasis by integrating findings from MRI, genetics, neuropathology and animal models for disease. We discuss how mutations in different glial proteins lead to disease, and highlight the similarities and differences between these diseases. To come to effective therapies for this group of diseases, a better mechanistic understanding of how glial cells shape ion and water movement in the brain is crucial.

Neonatal hypotonia and neuromuscular conditions

The differential diagnosis of neonatal hypotonia is a complex task, as in newborns hypotonia can be the presenting sign of different underlying causes, including peripheral and central nervous system involvement and genetic and metabolic diseases. This chapter describes how a combined approach, based on the combination of clinical signs and new genetic techniques, can help not only to establish when the hypotonia is related to peripheral involvement but also to achieve an accurate and early diagnosis of the specific neuromuscular diseases with neonatal onset. The early identification of such disorders is important, as this allows early intervention with disease-specific standards of care and, more importantly, because of the possibility to treat some of them, such as spinal muscular atrophy, with therapeutic approaches that have recently become available.

LAMA2 gene mutation update: Toward a more comprehensive picture of the laminin-α2 variome and its related phenotypes

Congenital muscular dystrophy type 1A (MDC1A) is one of the main subtypes of early-onset muscle disease, caused by disease-associated variants in the laminin-α2 (LAMA2) gene. MDC1A usually presents as a severe neonatal hypotonia and failure to thrive. Muscle weakness compromises normal motor development, leading to the inability to sit unsupported or to walk independently. The phenotype associated with LAMA2 defects has been expanded to include milder and atypical cases, being now collectively known as LAMA2-related muscular dystrophies (LAMA2-MD). Through an international multicenter collaborative effort, 61 new LAMA2 disease-associated variants were identified in 86 patients, representing the largest number of patients and new disease-causing variants in a single report. The collaborative variant collection was supported by the LOVD-powered LAMA2 gene variant database (https://www.LOVD.nl/LAMA2), updated as part of this work. As of December 2017, the database contains 486 unique LAMA2 variants (309 disease-associated), obtained from direct submissions and literature reports. Database content was systematically reviewed and further insights concerning LAMA2-MD are presented. We focus on the impact of missense changes, especially the c.2461A > C (p.Thr821Pro) variant and its association with late-onset LAMA2-MD. Finally, we report diagnostically challenging cases, highlighting the relevance of modern genetic analysis in the characterization of clinically heterogeneous muscle diseases.

Extracellular matrix-driven congenital muscular dystrophies

Skeletal muscle function relies on the myofibrillar apparatus inside myofibers as well as an intact extracellular matrix surrounding each myofiber. Muscle extracellular matrix (ECM) plays several roles including but not limited to force transmission, regulation of growth factors and inflammatory responses, and influencing muscle stem cell (i.e. satellite cell) proliferation and differentiation. In most myopathies, muscle ECM undergoes remodeling and fibrotic changes that may be maladaptive for normal muscle function and recovery. In addition, mutations in skeletal muscle ECM and basement proteins can cause muscle disease. In this review, we summarize the clinical features of two of the most common congenital muscular dystrophies, COL6-related dystrophies and LAMA2-related dystrophies, which are caused by mutations in muscle ECM and basement membrane proteins. The study of clinical features of these diseases has helped to inform basic research and understanding of the biology of muscle ECM. In return, basic studies of muscle ECM have provided the conceptual framework to develop therapeutic interventions for these and other similar disorders of muscle.

Genetik der kortikalen Fehlbildungen

Kortikale Malformationen sind vielfältig und stellen eine wichtige Ursache der geistigen Entwicklungsstörung und der Epilepsie dar. Die Ätiologie der kortikalen Fehlbildungen ist sehr heterogen und beinhaltet sowohl rein exogene Ursachen als auch chromosomale und monogene Erkrankungen. Eine effiziente genetische Diagnostik bedarf der akkuraten Interpretation des Magnetresonanztomographie(MRT)-Musters. Bei einigen klinischen Formen kann eine zielgerichtete Einzelgendiagnostik erfolgen, die anderen klinischen Entitäten erfordern dagegen eine komplexe Stufendiagnostik und können nur mittels Hochdurchsatzsequenzierung aufgeklärt werden. In diesem Beitrag werden die 4 häufigsten kortikalen Fehlbildungen im Hinblick auf die typischen klinischen Symptome, MRT-Merkmale und den Algorithmus der genetischen Abklärung vorgestellt.

Clinical and neuroimaging findings in two brothers with limb girdle muscular dystrophy due to LAMA2 mutations

Recessive mutations in LAMA2 commonly cause congenital muscular dystrophy (MDC1A) and, rarely, limb girdle muscular dystrophy (LGMD). We report 2 brothers who presented in adulthood with LGMD due to novel mutations in LAMA2 identified by whole exome sequencing (WES). Muscle biopsy more than 30 years ago demonstrated dystrophic changes but was not available for immunoanalysis. Muscle MRI demonstrated involvement of peripheral muscle with internal sparing classically seen in collagen-VI related disorders. Extensive genetic testing, including COL6A1/2/3, was performed prior to WES. Subsequent skin biopsy immunoanalysis demonstrated laminin α2 partial absence. The phenotype of the patients was notable for novel central nervous system findings, namely bilateral signal changes in the globi pallidi, and presence of dilated cardiomyopathy (DCM). They also illustrate the similarity in muscle MRI in collagen VI and laminin α2-related disorders, both of which are due to mutations in genes encoding extracellular matrix proteins.

Laminin α2 Deficiency-Related Muscular Dystrophy Mimicking Emery-Dreifuss and Collagen VI related Diseases

Background: Laminin α2 deficient congenital muscular dystrophy, caused by mutations in the LAMA2 gene, is characterized by early muscle weakness associated with abnormal white matter signal on cerebral MRI.

Objective: To report on 4 patients with LAMA2 gene mutations whose original clinical features complicated the diagnosis strategy.

Methods: Clinical, electrophysiological, muscle imaging and histopathological data were retrospectively collected from all patients. DNA samples were analysed by next-generation sequencing or direct gene sequencing. Laminin α2 was analysed by western-blot and immunohistochemistry.

Results: The four patients achieved independent walking. All had proximal muscle weakness with scapular winging and prominent joint contractures without peripheral neuropathy. During follow-up, two patients suffered from refractory epilepsy associated with brain leukoencephalopathy in one, polymicrogyria and lissencephaly without white matter changes in the other. In two patients, the distribution of fatty infiltration resembles that of collagen-VI related myopathies. Dilated cardiomyopathy contstartabstractwith conduction defects, suggestive of Emery-Dreifuss myopathy, emerged in two of them within the 4th decade. Molecular diagnosis remained elusive for many years. Finally, targeted capture-DNA sequencing unveiled the involvement of the LAMA2 gene in two families, and led us to further identify LAMA2 mutations in the remaining family using Sanger sequencing.

Conclusions: This report extends the clinical and radiological features of partial Laminin α2 deficiency since patients showed atypical manifestations including dilated cardiomyopathy with conduction defects in 2, epilepsy in 2, one of whom also had sole cortical brain abnormalities. Importantly, clinical findings and muscle imaging initially pointed to collagen-VI related disorders and Emery-Dreifuss muscular dystrophy.

Dysregulation of matricellular proteins is an early signature of pathology in laminin-deficient muscular dystrophy

Background

MDC1A is a congenital neuromuscular disorder with developmentally complex and progressive pathologies that results from a deficiency in the protein laminin α₂. MDC1A is associated with a multitude of pathologies, including increased apoptosis, inflammation and fibrosis. In order to assess and treat a complicated disease such as MDC1A, we must understand the natural history of the disease so that we can identify early disease drivers and pinpoint critical time periods for implementing potential therapies.

Results

We found that DyW mice show significantly impaired myogenesis and high levels of apoptosis as early as postnatal week 1. We also saw a surge of inflammatory response at the first week, marked by high levels of infiltrating macrophages, nuclear factor κB activation, osteopontin expression and overexpression of inflammatory cytokines. Fibrosis markers and related pathways were also observed to be elevated throughout early postnatal development in these mice, including periostin, collagen and fibronectin gene expression, as well as transforming growth factor β signaling. Interestingly, fibronectin was found to be the predominant fibrous protein of the extracellular matrix in early postnatal development. Lastly, we observed upregulation in various genes related to angiotensin signaling.

Methods

We sought out to examine the dysregulation of various pathways throughout early development (postnatal weeks 1-4) in the DyW mouse, the most commonly used mouse model of laminin-deficient muscular dystrophy. Muscle function tests (stand-ups and retractions) as well as gene (qRT-PCR) and protein levels (western blot, ELISA), histology (H&E, picrosirius red staining) and immunohistochemistry (fibronectin, TUNEL assay) were used to assess dysregulation of matricelluar protieins.

Conclusions

Our results implicate the involvement of multiple signaling pathways in driving the earliest stages of pathology in DyW mice. As opposed to classical dystrophies, such as Duchenne muscular dystrophy, the dysregulation of various matricellular proteins appears to be a distinct feature of the early progression of DyW pathology. On the basis of our results, we believe that therapies that may reduce apoptosis and stabilize the homeostasis of extracellular matrix proteins may have increased efficacy if started at a very early age.

Diagnostic approach to the congenital muscular dystrophies

Congenital muscular dystrophies (CMDs) are early onset disorders of muscle with histological features suggesting a dystrophic process. The congenital muscular dystrophies as a group encompass great clinical and genetic heterogeneity so that achieving an accurate genetic diagnosis has become increasingly challenging, even in the age of next generation sequencing. In this document we review the diagnostic features, differential diagnostic considerations and available diagnostic tools for the various CMD subtypes and provide a systematic guide to the use of these resources for achieving an accurate molecular diagnosis. An International Committee on the Standard of Care for Congenital Muscular Dystrophies composed of experts on various aspects relevant to the CMDs performed a review of the available literature as well as of the unpublished expertise represented by the members of the committee and their contacts. This process was refined by two rounds of online surveys and followed by a three-day meeting at which the conclusions were presented and further refined. The combined consensus summarized in this document allows the physician to recognize the presence of a CMD in a child with weakness based on history, clinical examination, muscle biopsy results, and imaging. It will be helpful in suspecting a specific CMD subtype in order to prioritize testing to arrive at a final genetic diagnosis.

Congenital muscular dystrophies and congenital myopathies

PURPOSE OF REVIEW

The purpose of this review is to provide information regarding the diagnosis and natural history of some very rare disorders: congenital muscular dystrophies and congenital myopathies. Patients with these conditions share characteristics such as early onset of weakness and severe hypotonia. Other organs such as the brain, eyes, and skin may be involved. Diagnosis depends largely on recognition of phenotype, muscle biopsy, and mutation analysis.

RECENT FINDINGS

More than 30 genes have been associated with these diseases, most of which have only been recognized in the past decade. Increasing availability of DNA analysis has been important in decreasing delay in diagnosis.

SUMMARY

Patients with congenital muscular dystrophy or congenital myopathy are at high risk of complications including restrictive lung disease, orthopedic deformities, seizures, cardiomyopathy, and malignant hyperthermia. Life expectancy varies with the severity of complications. Having an accurate and specific diagnosis allows the neurologist to carry out anticipatory guidance and appropriate monitoring. New hope exists for experimental treatments for congenital muscular dystrophy and congenital myopathy as our understanding of pathogenesis evolves.

Laminin-111 improves muscle repair in a mouse model of merosin-deficient congenital muscular dystrophy

Merosin-deficient congenital muscular dystrophy type 1A (MDC1A) is a severe and fatal muscle-wasting disease with no cure. MDC1A patients and the dy(W-/-) mouse model exhibit severe muscle weakness, demyelinating neuropathy, failed muscle regeneration and premature death. We have recently shown that laminin-111, a form of laminin found in embryonic skeletal muscle, can substitute for the loss of laminin-211/221 and prevent muscle disease progression in the dy(W-/-) mouse model. What is unclear from these studies is whether laminin-111 can restore failed regeneration to laminin-α2-deficient muscle. To investigate the potential of laminin-111 protein therapy to improve muscle regeneration, laminin-111 or phosphate-buffered saline-treated laminin-α2-deficient muscle was damaged with cardiotoxin and muscle regeneration quantified. Our results show laminin-111 treatment promoted an increase in myofiber size and number, and an increased expression of α7β1 integrin, Pax7, myogenin and embryonic myosin heavy chain, indicating a restoration of the muscle regenerative program. Together, our results show laminin-111 restores muscle regeneration to laminin-α2-deficient muscle and further supports laminin-111 protein as a therapy for the treatment of MDC1A.

Triggering regeneration and tackling apoptosis: a combinatorial approach to treating congenital muscular dystrophy type 1 A

Merosin-deficient congenital muscular dystrophy type 1A (MDC1A) is an autosomal recessive disorder caused by mutations in the laminin-α2 gene (OMIM: 607855). Currently, no treatment other than palliative care exists for this disease. In our previous work, genetic interventions in the Lama2(Dy-w) mouse model for MDC1A demonstrated that limited regeneration and uncontrolled apoptosis are important drivers of this disease. However, targeting one of these disease drivers without addressing the other results in only partial rescue of the phenotype. The present study was designed to determine whether utilizing a combinatorial treatment approach can lead to a more profound amelioration of the disease pathology. To accomplish this task, we generated Bax-null Lama2(Dy-w)mice that overexpressed muscle-specific IGF-1 (Lama2(Dy-w)Bax(-/-)+IGF-1tg). Further to test the translational potential of IGF-1 administration in combination with Bax inhibition, we treated Lama2(Dy-w)Bax(-/-) mice postnatally with systemic recombinant human IGF-1 (IPLEX™). These two combinatorial treatments lead to similar, promising outcomes. In addition to increased body and muscle weights, both transgenic overexpression and systemic administration of IGF-1 combined with Bax-inhibition resulted in improved muscle phenotype and locomotory function that were nearly indistinguishable from wild-type mice. These results provide a fundamental proof of concept that justifies the use of a combination therapy as an effective treatment for MDC1A and highlights a compelling argument toward shifting the paradigm in treating multifaceted neuromuscular diseases.

Laminin regulates postnatal oligodendrocyte production by promoting oligodendrocyte progenitor survival in the subventricular zone

The laminin family of extracellular matrix proteins are expressed broadly during embryonic brain development, but are enriched at ventricular and pial surfaces where laminins mediate radial glial attachment during corticogenesis. In the adult brain, however, laminin distribution is restricted, yet is found within the vascular basal lamina and associated fractones of the ventricular zone (VZ)-subventricular zone (SVZ) stem cell niche, where laminins regulate adult neural progenitor cell proliferation. It remains unknown, however, if laminins regulate the wave of oligodendrogenesis that occurs in the neonatal/early postnatal VZ-SVZ. Here we report that Lama2, the gene that encodes the laminin α2-subunit, regulates postnatal oligodendrogenesis. At birth, Lama2-/- mice had significantly higher levels of dying oligodendrocyte progenitor cells (OPCs) in the OPC germinal zone of the dorsal SVZ. This translated into fewer OPCs, both in the dorsal SVZ well as in an adjacent developing white matter tract, the corpus callosum. In addition, intermediate progenitor cells that give rise to OPCs in the Lama2-/- VZ-SVZ were mislocalized and proliferated nearer to the ventricle surface. Later, delays in oligodendrocyte maturation (with accompanying OPC accumulation), were observed in the Lama2-/- corpus callosum, leading to dysmyelination by postnatal day 21. Together these data suggest that prosurvival laminin interactions in the developing postnatal VZ-SVZ germinal zone regulate the ability, or timing, of oligodendrocyte production to occur appropriately.

Spectrum of pontocerebellar hypoplasia in 13 girls and boys with CASK mutations: confirmation of a recognizable phenotype and first description of a male mosaic patient

Background

Pontocerebellar hypoplasia (PCH) is a heterogeneous group of diseases characterized by lack of development and/or early neurodegeneration of cerebellum and brainstem. According to clinical features, seven subtypes of PCH have been described, PCH type 2 related to TSEN54 mutations being the most frequent. PCH is most often autosomal recessive though de novo anomalies in the X-linked gene CASK have recently been identified in patients, mostly females, presenting with intellectual disability, microcephaly and PCH (MICPCH).

Methods

Fourteen patients (12 females and two males; aged 16 months-14 years) presenting with PCH at neuroimaging and with clinical characteristics unsuggestive of PCH1 or PCH2 were included. The CASK gene screening was performed using Array-CGH and sequencing. Clinical and neuroradiological features were collected.

Results

We observed a high frequency of patients with a CASK mutation (13/14). Ten patients (8 girls and 2 boys) had intragenic mutations and three female patients had a Xp11.4 submicroscopic deletion including the CASK gene. All were de novo mutations. Phenotype was variable in severity but highly similar among the 11 girls and was characterized by psychomotor retardation, severe intellectual disability, progressive microcephaly, dystonia, mild dysmorphism, and scoliosis. Other signs were frequently associated, such as growth retardation, ophthalmologic anomalies (glaucoma, megalocornea and optic atrophy), deafness and epilepsy. As expected in an X-linked disease manifesting mainly in females, the boy hemizygous for a splice mutation had a very severe phenotype with nearly no development and refractory epilepsy. We described a mild phenotype in a boy with a mosaic truncating mutation. We found some degree of correlation between severity of the vermis hypoplasia and clinical phenotype.

Conclusion

This study describes a new series of PCH female patients with CASK inactivating mutations and confirms that these patients have a recognizable although variable phenotype consisting of a specific form of pontocerebellar hypoplasia. In addition, we report the second male patient to present with a severe MICPCH phenotype and a de novo CASK mutation and describe for the first time a mildly affected male patient harboring a mosaic mutation. In our reference centre, CASK related PCH is the second most frequent cause of PCH. The identification of a de novo mutation in these patients enables accurate and reassuring genetic counselling.

Laminin-111 protein therapy reduces muscle pathology and improves viability of a mouse model of merosin-deficient congenital muscular dystrophy

Merosin-deficient congenital muscular dystrophy type 1A (MDC1A) is a lethal muscle-wasting disease that is caused by mutations in the LAMA2 gene, resulting in the loss of laminin-α2 protein. MDC1A patients exhibit severe muscle weakness from birth, are confined to a wheelchair, require ventilator assistance, and have reduced life expectancy. There are currently no effective treatments or cures for MDC1A. Laminin-α2 is required for the formation of heterotrimeric laminin-211 (ie, α2, β1, and γ1) and laminin-221 (ie, α2, β2, and γ1), which are major constituents of skeletal muscle basal lamina. Laminin-111 (ie, α1, β1, and γ1) is the predominant laminin isoform in embryonic skeletal muscle and supports normal skeletal muscle development in laminin-α2-deficient muscle but is absent from adult skeletal muscle. In this study, we determined whether treatment with Engelbreth-Holm-Swarm-derived mouse laminin-111 protein could rescue MDC1A in the dy(W-/-) mouse model. We demonstrate that laminin-111 protein systemically delivered to the muscles of laminin-α2-deficient mice prevents muscle pathology, improves muscle strength, and dramatically increases life expectancy. Laminin-111 also prevented apoptosis in laminin-α2-deficient mouse muscle and primary human MDC1A myogenic cells, which indicates a conserved mechanism of action and cross-reactivity between species. Our results demonstrate that laminin-111 can serve as an effective protein substitution therapy for the treatment of muscular dystrophy in the dy(W-/-) mouse model and establish the potential for its use in the treatment of MDC1A.

Congenital muscular dystrophies: a brief review

Congenital muscular dystrophies (CMDs) are clinically and genetically heterogeneous neuromuscular disorders with onset at birth or in infancy in which the muscle biopsy is compatible with a dystrophic myopathy. In the past 10 years, knowledge of neuromuscular disorders has dramatically increased, particularly with the exponential boost of disclosing the genetic background of CMDs. This review will highlight the clinical description of the most important forms of CMD, paying particular attention to the main keys for diagnostic approach. The diagnosis of CMDs requires the concurrence of expertise in multiple specialties (neurology, morphology, genetics, neuroradiology) available in a few centers worldwide that have achieved sufficient experience with the different CMD subtypes. Currently, molecular diagnosis is of paramount importance not only for phenotype-genotype correlations, genetic and prenatal counseling, and prognosis and aspects of management, but also concerning the imminent availability of clinical trials and treatments.

Transgenic overexpression of the α7 integrin reduces muscle pathology and improves viability in the dy(W) mouse model of merosin-deficient congenital muscular dystrophy type 1A

Merosin-deficient congenital muscular dystrophy 1A (MDC1A) is a devastating neuromuscular disease that results in children being confined to a wheelchair, requiring ventilator assistance to breathe and premature death. MDC1A is caused by mutations in the LAMA2 gene, which results in the partial or complete loss of laminin-211 and laminin-221, the major laminin isoforms found in the basal lamina of skeletal muscle. MDC1A patients exhibit reduced α7β1 integrin; however, it is unclear how the secondary loss of α7β1 integrin contributes to MDC1A disease progression. To investigate whether restoring α7 integrin expression can alleviate the myopathic phenotype observed in MDC1A, we produced transgenic mice that overexpressed the α7 integrin in the skeletal muscle of the dy(W⁻/⁻) mouse model of MDC1A. Enhanced expression of the α7 integrin restored sarcolemmal localization of the α7β1 integrin to laminin-α2-deficient myofibers, changed the composition of the muscle extracellular matrix, reduced muscle pathology, maintained muscle strength and function and improved the life expectancy of dy(W⁻/⁻) mice. Taken together, these results indicate that enhanced expression of α7 integrin prevents muscle disease progression through augmentation and/or stabilization of the existing extracellular matrix in laminin-α2-deficient mice, and strategies that increase α7 integrin in muscle might provide an innovative approach for the treatment of MDC1A.

CNS findings in congenital muscular dystrophy 1A (with laminin alpha-2-deficiency)

Congenital muscular dystrophy (MDC) is a group of rare hereditary myopathies with an early onset of progressive muscle weakness and dystrophic changes as evidenced by muscle biopsy. Some forms are associated with severe malformations of the brain. This study presented 2 pediatric patients with genetically diagnosed congenital muscular dystrophy 1A. The patients exhibited a typical combination of muscular hypotonia, joint contractures and elevated creatine kinase levels. Characteristic white matter lesions were not present in an early MRI scan of one patient, but could be detected at the age of 18 months. The second patient showed both severe white and grey matter abnormalities (pachy microgyria) in the MRI scan. In both cases, MRI findings did not correlate with the mental development of the patients.

Consensus statement on standard of care for congenital muscular dystrophies

Congenital muscular dystrophies are a group of rare neuromuscular disorders with a wide spectrum of clinical phenotypes. Recent advances in understanding the molecular pathogenesis of congenital muscular dystrophy have enabled better diagnosis. However, medical care for patients with congenital muscular dystrophy remains very diverse. Advances in many areas of medical technology have not been adopted in clinical practice. The International Standard of Care Committee for Congenital Muscular Dystrophy was established to identify current care issues, review literature for evidence-based practice, and achieve consensus on care recommendations in 7 areas: diagnosis, neurology, pulmonology, orthopedics/rehabilitation, gastroenterology/ nutrition/speech/oral care, cardiology, and palliative care. To achieve consensus on the care recommendations, 2 separate online surveys were conducted to poll opinions from experts in the field and from congenital muscular dystrophy families. The final consensus was achieved in a 3-day workshop conducted in Brussels, Belgium, in November 2009. This consensus statement describes the care recommendations from this committee.

Bilateral occipital cortical dysplasia and white matter T2 hyperintensity with mild non-specific myopathy: two sibling cases

We report two heterosexual sibling cases of mild non-specific myopathy, with bilateral occipital cortical dysplasia and diffuse white matter hyperintensity on brain magnetic resonance imaging (MRI). The histological examination of the muscle in the elder sister revealed non-specific myopathic changes and no reductions of alpha-dystroglycan and laminin alpha2 expressions. The characteristic findings in the occipital lobe on brain MRI in both cases suggested cobblestone lissencephaly. Disrupted structure of the glia limitans and pial basement membrane complex, by a cause other than an alpha-dystroglycan and laminin alpha2 abnormality, may be the cause of the cortical dysplasia in the sibling cases.

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.

Intraventricular injection of antibodies to β1-integrins generates pressure gradients in the brain favoring hydrocephalus development in rats

In some tissues, the injection of antibodies to the β1-integrins leads to a reduction in interstitial fluid pressure, indicating an active role for the extracellular matrix in tissue pressure regulation. If perturbations of the matrix occur in the periventricular area of the brain, a comparable lowering of interstitial pressures may induce transparenchymal pressure gradients favoring ventricular expansion. To examine this concept, we measured periventricular (parenchymal) and ventricular pressures with a servo-null micropipette system (2-μm tip) in adult Wistar rats before and after anti-integrin antibodies or IgG/IgM isotype controls were injected into a lateral ventricle. In a second group, the animals were kept for 2 wk after similar injections and after euthanization, the brains were removed and assessed for hydrocephalus. In experiments in which antibodies to β1-integrins ( n = 10) but not isotype control IgG/IgM ( n = 7) were injected, we observed a decline in periventricular pressures relative to the preinjection values. Under similar circumstances, ventricular pressures were elevated ( n = 10) and were significantly greater than those in the periventricular interstitium. We estimated ventricular to periventricular pressure gradients of up to 4.3 cmH2O. In the chronic preparations, we observed enlarged ventricles in many of the animals that received injections of anti-integrin antibodies (21 of 29 animals; 72%) but not in any animal receiving the isotype controls. We conclude that modulation/disruption of β1-integrin-matrix interactions in the brain generates pressure gradients favoring ventricular expansion, suggesting a novel mechanism for hydrocephalus development.

beta1 integrin maintains integrity of the embryonic neocortical stem cell niche

During embryogenesis, the neural stem cells (NSC) of the developing cerebral cortex are located in the ventricular zone (VZ) lining the cerebral ventricles. They exhibit apical and basal processes that contact the ventricular surface and the pial basement membrane, respectively. This unique architecture is important for VZ physical integrity and fate determination of NSC daughter cells. In addition, the shorter apical process is critical for interkinetic nuclear migration (INM), which enables VZ cell mitoses at the ventricular surface. Despite their importance, the mechanisms required for NSC adhesion to the ventricle are poorly understood. We have shown previously that one class of candidate adhesion molecules, laminins, are present in the ventricular region and that their integrin receptors are expressed by NSC. However, prior studies only demonstrate a role for their interaction in the attachment of the basal process to the overlying pial basement membrane. Here we use antibody-blocking and genetic experiments to reveal an additional and novel requirement for laminin/integrin interactions in apical process adhesion and NSC regulation. Transient abrogation of integrin binding and signalling using blocking antibodies to specifically target the ventricular region in utero results in abnormal INM and alterations in the orientation of NSC divisions. We found that these defects were also observed in laminin alpha2 deficient mice. More detailed analyses using a multidisciplinary approach to analyse stem cell behaviour by expression of fluorescent transgenes and multiphoton time-lapse imaging revealed that the transient embryonic disruption of laminin/integrin signalling at the VZ surface resulted in apical process detachment from the ventricular surface, dystrophic radial glia fibers, and substantial layering defects in the postnatal neocortex. Collectively, these data reveal novel roles for the laminin/integrin interaction in anchoring embryonic NSCs to the ventricular surface and maintaining the physical integrity of the neocortical niche, with even transient perturbations resulting in long-lasting cortical defects.

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 neurobiology of the dystrophin-associated glycoprotein complex

While the function of dystrophin in muscle disease has been thoroughly investigated, dystrophin and associated proteins also have important roles in the central nervous system. Many patients with Duchenne and Becker muscular dystrophies (D/BMD) have cognitive impairment, learning disability, and an increased incidence of some neuropsychiatric disorders. Accordingly, dystrophin and members of the dystrophin-associated glycoprotein complex (DGC) are found in the brain where they participate in macromolecular assemblies that anchor receptors to specialized sites within the membrane. In neurons, dystrophin and the DGC participate in the postsynaptic clustering and stabilization of some inhibitory GABAergic synapses. During development, alpha-dystroglycan functions as an extracellular matrix receptor controlling, amongst other things, neuronal migration in the developing cortex and cerebellum. Several types of congenital muscular dystrophy caused by impaired alpha-dystroglycan glycosylation cause neuronal migration abnormalities and mental retardation. In glial cells, the DGC is involved in the organization of protein complexes that target water-channels to the plasma membrane. Finally, mutations in the gene encoding epsilon-sarcoglycan cause the neurogenic movement disorder, myoclonus-dystonia syndrome implicating epsilon-sarcoglycan in dopaminergic neurotransmission. In this review we describe the recent progress in defining the role of the DGC and associated proteins in the brain.

LAMA2 stop-codon mutation: merosin-deficient congenital muscular dystrophy with occipital polymicrogyria, epilepsy and psychomotor regression

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

Cutis laxa with frontoparietal cortical malformation: a novel type of congenital disorder of glycosylation

This report describes a female infant with cutis laxa, short stature, microcephaly, wide anterior fontanel and bifrontal cortical malformation. Isoelectrofocusing of plasma transferrin and apolipoprotein C-III showed abnormal patterns suggesting defective N- and O-glycosylation. Together with recently reported patients, this patient represents a novel type of congenital disorder of glycosylation.