Neuromuscular disorders in zebrafish: state of the art and future perspectives.

Neuromuscular disorders are a broad group of inherited conditions affecting the structure and function of the motor system with polymorphic clinical presentation and disease severity. Although individually rare, collectively neuromuscular diseases have an incidence of 1 in 3,000 and represent a significant cause of disability of the motor system. The past decade has witnessed the identification of a large number of human genes causing muscular disorders, yet the underlying pathogenetic mechanisms remain largely unclear, limiting the developing of targeted therapeutic strategies. To overcome this barrier, model systems that replicate the different steps of human disorders are increasingly being developed. Among these, the zebrafish (Danio rerio) has emerged as an excellent organism for studying genetic disorders of the central and peripheral motor systems. In this review, we will encounter most of the available zebrafish models for childhood neuromuscular disorders, providing a brief overview of results and the techniques, mainly transgenesis and chemical biology, used for genetic manipulation. The amount of data collected in the past few years will lead zebrafish to became a common functional tool for assessing rapidly drug efficacy and off-target effects in neuromuscular diseases and, furthermore, to shed light on new etiologies emerging from large-scale massive sequencing studies.

Muscle ultrasound density in human fetuses with spina bifida aperta.

BACKGROUND: In fetal spina bifida aperta (SBA), leg movements caudal to the meningomyelocele (MMC) are transiently present, but they disappear shortly after birth. Insight in the underlying mechanism could help to improve treatment strategies. In fetal SBA, the pathogenesis of neuromuscular damage prior to movement loss is still unknown. We reasoned that prenatal assessment of muscle ultrasound density (fetal-MUD) could help to reveal whether progressive neuromuscular damage is present in fetal SBA, or not. AIM: To reveal whether prenatal neuromuscular damage is progressively present in SBA. PATIENTS/METHODS: In SBA fetuses (n=6; 22-37 weeks gestational age), we assessed fetal-MUD in myotomes caudal to the MMC and compared measurements between myotomes cranial to the MMC and controls (n=11; 17-36 weeks gestational age). Furthermore, we intra-individually compared MUD and muscle histology between the pre- and postnatal period. RESULTS: Despite persistently present fetal leg movements caudal to the MMC, fetal-MUD was higher caudal to the MMC than in controls (p<0.05). Fetal-MUD caudal to the MMC did not increase with gestational age, whereas fetal-MUD in controls and cranial to the MMC increased with gestational age (p<0.05). In 5 of 6 patients assessed, comparison between pre- and postnatal MUD and/or muscle histology indicated consistent findings. CONCLUSIONS: In fetal SBA, persistent leg movements concur with stable, non-progressively increased fetal-MUD. These data may implicate that early postnatal loss of leg movements is associated with the impact of additional neuromuscular damage after the prenatal period.

Diversity of neuromuscular pathology in lethal multiple pterygium syndrome.

Lethal multiple pterygium syndrome (LMPS) is an uncommon fetal-onset disorder of unknown etiology. The pathogenesis of LMPS has been suggested to be early-onset fetal akinesia, fragile collagen, or generalized edema. Information on the neuromuscular pathology of LMPS in the literature is generally scanty. We present the findings from a review of 14 fetuses with features of LMPS from the archives of the Hammersmith Hospital Perinatal Pathology Department. Autopsy reports, photographs, fetograms, and histological sections were examined, and additional special stains and immunostaining were performed on muscle sections. In five cases, there was evidence of autosomal recessive inheritance. One case was later shown to be due to glycogen storage disease type IV. The skeletal muscle bulk was reduced in all fetuses and the remaining muscle showed a range of histological appearances including vacuolar degeneration, dystrophy, a generalized or patchy myotubular appearance, and generalized hypotrophy. In one, the histological appearance was essentially normal. Two cases had abnormalities in the brain. Large motor neurons were present in the anterior spinal horns of all fetuses in whom the spinal cord could be examined. There was no evidence of cartilaginous joint fusion. We conclude that LMPS is the phenotype resulting from fetal akinesia commencing in the first or early second trimester. In the majority of cases, the precise underlying cause will not be identified, however, occasionally a metabolic or neurodevelopmental disorder or a specific primary myopathy may be demonstrated, providing adequate autopsy investigations are undertaken.

[Progress in pediatric neurology]. / Progrès en neurologie pédiatrique.

A central part of Pediatric Neurology is currently dominated by the search for genetic factors involved in developmental disorders of the nervous system, including cases where the cytogenetic examination remains uncontributive. The prerequisite for a good definition of the malformative phenotypes leads to distinguish: 1 cerebral malformations that can be identified at the macroscopic scale, by imaging. 2 polymalformative syndromes including mental retardation where cerebral imaging is not contributive, thus the syndromatic definition is based on associated somatic anomalies. 3 Non-syndromatic mental retardation, where a genetic origin is clear only in the familial forms. Various methodological approaches have included genetic linkage studies, search for inframicroscopic chromosomal rearrangements in the critical region and investigation of candidate genes. A great number of syndromes have been connected with a great diversity of genetic mechanisms, whose many examples are presented: genopathies with regular or variable expression, unstable mutations, contiguous gene syndromes or other complex infracytogenetic rearrangements, chromosomal or genic mosaicisms, mutations submitted to parental imprinting. New methods of genomic screening will be necessary to progress in this field, given the great number of genes involved in cerebral development. As for the early developmental disorders of the PNS and muscle, their diagnosis becomes frequent during the intrauterine life, raising the problem of a better definition of the fetopathological phenotypes.

Increased apoptosis of motoneurons and altered somatotopic maps in the brachial spinal cord of Hoxc-8-deficient mice.

Mice deficient for the homeotic gene Hoxc-8 suffer from a congenital prehension deficiency of the forepaw. During embryogenesis, Hoxc-8 is highly expressed in motoneurons within spinal cord segments C7 to T1. These motoneurons innervate forelimb distal muscles that move the forepaw. In Hoxc-8 mutant embryos, formation of these muscles is normal, but their innervation is perturbed. From E13.5 onwards, distal muscles normally supplied by C(7-8) MNs also receive ectopic projections from C(5-6) and T1 motoneurons. Coordinates of motor pools are altered along the rostrocaudal and also the mediolateral axes. Following this aberrant connectivity pattern and during the time of naturally occurring cell death, apoptosis is specifically enhanced in C7-T1 motoneurons. Loss of Hox-encoded regional specifications subsequently leads to a numerical deficit of motoneurons and an irreversible disorganization of motor pools. In Hoxc-8 null mutants, C(7-8) motoneurons lose their selective advantage in growth cone pathfinding behavior and/or target recognition, two essential steps in the establishment and maintenance of a functional nervous system.

[The importance of vitamin B 6 for development of the infant. Human medical and animal experiment studies]. / Die Bedeutung von Vitamin B6 für die Entwicklung des Säuglings. Humanmedizinische und tierexperimentelle Studien.

Vitamin B-6 is an important coenzyme in the biosynthesis of the neurotransmitters GABA, dopamine and serotonin and is therefore required for the normal perinatal development of the central nervous system. In rat studies, biochemical and morphological abnormalities (decreased dendritic arborization and reduced numbers of myelinated axons and synapses) in the brains of pups from vitamin B-6 deficient dams were associated with behavioral changes such as epileptiform seizures and movement disorders. In severely vitamin B-6 deficient human infants, similar behavioral abnormalities have been described. Marginally deficient neonates were found to have a lower birthweight and to display less mature reactive and adaptive behavior in the Brazleton Neonatal Assessment Scale than well-fed infants. While it is not yet possible to define the exact amount of vitamin B-6 required to support optimal brain development, pregnant and lactating women should be encouraged to consume a diet that is rich in vitamin B-6.

Neurogenic arthrogryposis multiplex congenita: clinical and MRI findings.

A clinical and magnetic resonance imaging (MRI) study on a selected group of 11 children, with a diagnosis of neurogenic arthrogryposis multiplex congenita (AMC) based on clinical, electromyographic, and muscle biopsy findings, is presented to determine the extent of central nervous system involvement in AMC. Family history, pregnancy, perinatal problems, other abnormalities, and epileptic seizures were reviewed. Neurologic examination, electroencephalography, intellectual assessment, and MRI study both of spinal cord and brain were performed. The clinical and laboratory findings disclosed evidence of spinal cord lesions with involvement of anterior horn cell function in all patients, and impairment of cerebral function in 5 patients. MRI revealed spinal cord atrophy in 3 patients, diffuse atrophy in 2 patients, and involved thoraco-lumbar segments in 1 patient. Cranial MRI studies demonstrated features of developmental brain abnormalities in 3 patients, cortical frontal atrophy in 2, and was normal in 4. In neurogenic AMC patients, MRI examination of the spinal cord and brain may help to clarify the pathogenesis of the disease and is helpful for prognostic and therapeutic purposes.

The Pena-Shokeir syndrome: report of nine Dutch cases.

We report on nine individuals with the Pena-Shokeir syndrome. Clinical findings are compared with data on patients from the literature. Emphasis is made on genetic background, neuropathological findings, and (in two cases) on prenatal data. Possible pathogenetic mechanisms are discussed.

Early effects in vitro of the muscular dysgenesis mutation on nervous tissue in the mouse.

Muscular dysgenesis (mdg), a disease expressed in embryonic mice, severely affects the formation and differentiation of skeletal musculature. The focus of this investigation was an analysis of dysgenic nervous tissue with special attention centered on interactions between muscle and nerve cells in vitro. Results indicate that mdg/mdg spinal cord cells can form functional neuromuscular junctions in nerve-muscle cocultures and induce contractions in dysgenic muscle. However, dysgenic spinal cord cells induce fewer myotubes to contract and result in a delayed induction of dysgenic myotube contractile activity. Furthermore, mdg/mdg nervous tissue, or its conditioned medium, is associated with a higher incidence of morphologically abnormal myotube contractures. The results from this investigation demonstrate that there are functional abnormalities in both dysgenic muscle and nervous tissues which are stable and expressed for up to 3 weeks in vitro.

Relationship of genotype and in vitro contractility in mdg/mdg in equilibrium +/+ "mosaic" myotubes.

Muscular dysgenesis (mdg) in the mouse is an autosomal recessive lethal disorder that is manifested by a gross failure of skeletal muscle development. In vitro mdg/mdg myoblasts proliferate normally and fuse successfully into myotubes, but these myotubes fail to contract either spontaneously or in response to physiological stimuli despite the presence of effective contractile elements and an ability to propagate action potentials normally. We have determined that mdg/mdg and +/+ myoblasts are capable of fusing in vitro to form "mosaic" myotubes which typically express an apparently normal contractile phenotype. Electrophoretic analysis of the relative activities of myotube glucosephosphate isomerase (GPI-1) isozymes provided a means of estimating the proportions of myonuclei of each genotype within individual myotubes. Only a very small proportion of genotypically normal myonuclei were required for expression of an apparently normal contractile phenotype.

Neurons induce contractions in myotubes containing only muscular dysgenic nuclei.

Muscular dysgenic (mdg/mdg) myotubes cultured alone do not contract. Glucosephosphate isomerase (GPI-1) isozymes were analyzed to determine the final genotype of cultured dysgenic (mdg/mdg, gpi-1a/a) myotubes to which normal embryonic spinal cord and limb cells (CBA/J +/+, gpi-1b/b) had been added. Although both myoblast and spinal cord cell additions caused induction of spontaneous contractions, only myoblasts fused with the myotubes to create functional heterokaryons. Spinal cord cells did not fuse with dysgenic myotubes, but formed functional synapses.

Collagen types in neuromuscular diseases.

The striking proliferation of connective tissue characteristic of the muscular dystrophies can be attributed predominantly to an increase in endomysial and perimysial type III collagen. Carriers of muscular dystrophy occasionally revealed a slight increase in anti-type III collagen fluorescence, but no abnormalities in collagen disposition were observed in foetuses "at risk" for DMD. In contrast, the proportion of collagen types in neurogenic atrophies appeared normal although anti-type IV and V staining, which delineated the basement membrane, was very intense around atrophied fibres, as was also the case in small fibres in myopathic diseases. The detection of staining with anti-type III, IV and V collagens in splits which are sometimes observed in hypertrophied fibres in the muscular dystrophies supports the suggestion that abnormalities in collagen production, perhaps involving a defective modulation of myoblast-fibroblast expression, may be involved in the pathogenesis of these diseases.

[Neuromuscular interactions--tendencies toward a biochemical-genetic analysis]. / Neuro-muskuläre Wechselwirkungen Ansätze zur biochemisch-genetischen Analyse.

The analysis of hereditary neuro-muscular diseases in the mouse and in other vertebrates may contribute to our understanding of the developmental interactions between spinal cord and sceletal muscle. Meaningful biochemical analysis must be preceded by "biological mixing experiments" to demonstrate whether a given mutation is cell-autonomous, and, if so, which cell type caries the primary defect. Techniques are available to carry out the critical experiment in vivo (artificial chimaeras) or in culture.