Molecular studies of spinal muscular atrophy.

Spinal muscular atrophy (SMA) is inherited as an autosomal recessive disorder which presents as a severe, intermediate or mild condition. The disease selectively affects the alpha motor neuron but nothing is as yet known about the underlying biochemical defect. Recent genetic studies have mapped all three types of SMA to the same region of human chromosome 5 (5q11.2-q13.3) raising the possibility that the mutations may be allelic. Polymorphic DNA markers have been characterised which are suitable for prenatal diagnosis. This is the first step in the isolation of the mutant gene (or genes) involved in this disorder.     

Treatment of Type I Spinal Muscular Atrophy With Noninvasive Ventilation and Gastrostomy Feeding

Type I spinal muscular atrophy (SMA) is a rapidly progressive, degenerative neuromuscular disease of infancy. In severe SMA, weakness, hypotonia, and bulbar involvement lead to progressive respiratory insufficiency and swallowing dysfunction, which are frequently complicated by aspirations. There are few studies reported in the literature that address the respiratory management of type I SMA. This article reports the results of treating four patients with infantile SMA with noninvasive positive pressure ventilation and gastrostomy feeding. All patients had gastroesophageal reflux disease, which was managed medically. Despite these therapies, survival was only 1 to 3.5 months after presenting with severe aspirations. The treatment strategy, which can be effective in less rapidly progressive neuromuscular diseases, did not alter the very poor prognosis of type I SMA. The treatment options are reviewed, and a strategy designed to optimize quality of life for infants with this fatal disease is presented.     

Spinal muscular atrophy combined with sporadic olivopontocerebellar atrophy

The combination of spinal muscular atrophy (SMA) with a variety of neural and extraneural defects, particularly pontocerebellar hypoplasia, has been reported. To date, all of the reported SMA with pontocerebellar hypoplasia was from infants; however, here we report a SMA with sporadic olivopontocerebellar atrophy (sOPCA) in an adult patient. The 68-year-old male patient displayed various clinical symptoms including progressive proximal muscle weakness, muscle atrophy and muscle fasciculation with a long course of disease. EMG demonstrated that amyotrophy was due to the impairment of lower motor neurons. The clinical symptoms and the EMG were consistent with the diagnosis of SMA. The presence of cerebellar ataxia, limb tremors, muscle atrophy and weakness in the patient led to the diagnosis of sOPCA that was confirmed by the MRI results. To our knowledge, this is the first case report of combination of SMA with sOPCA in an adult. It is yet unclear whether there is a common pathogenesis between the two diseases.     

Hybrid survival motor neuron genes in Japanese patients with spinal muscular atrophy

Spinal muscular atrophy (SMA) is a frequently occurring autosomal recessive disease, characterized by the degeneration of spinal cord anterior horn cells, leading to muscular atrophy. Most SMA patients carry homozygous deletions of the telomeric survival motor neuron gene (SMN) exons 7 and 8. In the study presented here, we examined 20 Japanese SMA patients and found that 4 of these patients were lacking in telomeric SMN exon 7, but retained exon 8. In these 4 patients, who exhibited all grades of disease severity, direct sequencing analysis demonstrated the presence of a hybrid SMN gene in which centromeric SMN exon 7 was adjacent to telomeric SMN exon 8. In an SMA family, a combination of polymerase chain reaction and enzyme-digestion analysis and haplotype analysis with the polymorphic multicopy marker Agl-CA indicated that the patient inherited the hybrid gene from her father. In conclusion, hybrid SMN genes can be present in all grades of disease severity and inherited from generation to generation in an SMA family.     

SMN2 copy number predicts acute or chronic spinal muscular atrophy but does not account for intrafamilial variability in siblings

Spinal muscular atrophy (SMA) is an autosomal recessive disorder that affects motor neurons. It is caused by mutations in the survival motor neuron gene 1 (SMN1). The SMN2 gene, which is the highly homologous SMN1 copy that is present in all the patients, is unable to prevent the disease. An SMN2 dosage method was applied to 45 patients with the three SMA types (I–III) and to four pairs of siblings with chronic SMA (II–III) and different phenotypes. Our results confirm that the SMN2 copy number plays a key role in predicting acute or chronic SMA. However, siblings with different SMA phenotypes show an identical SMN2 copy number and identical markers, indicating that the genetic background around the SMA locus is insufficient to account for the intrafamilial variability. In our results, age of onset appears to be the most important predictor of disease severity in affected members of the same family.Given that SMN2 is regarded as a target for potential pharmacological therapies in SMA, the identification of genetic factors other than the SMN genes is necessary to better understand the pathogenesis of the disease in order to implement additional therapeutic approaches.     

成人型脊髓性肌萎缩症临床分析(附46例报告)

目的总结分析成人型脊髓性肌萎缩症(SMA4)的临床特征。方法收集46例经肌肉活检证实的SMA4病例进行临床资料回顾性分析。结果SMA4起病隐袭,进展缓慢,肌无力以四肢近端为主,无锥体束受累。约四分之一患者血清CPK轻度升高;EMG示神经源性损害;肌活检主要为小群性肌萎缩,ATP酶染色见同型肌群化及肌纤维代偿性肥大。结论SMA4是病变影响下运动神经元的一组独立性疾病,并非为肌萎缩侧索硬化的某一发展阶段。预后相对良好。     

Chronic Pharmacological Increase of Neuronal Activity Improves Sensory-Motor Dysfunction in Spinal Muscular Atrophy Mice

Dysfunction of neuronal circuits is an important determinant of neurodegenerative diseases. Synaptic dysfunction, death, and intrinsic activity of neurons are thought to contribute to the demise of normal behavior in the disease state. However, the interplay between these major pathogenic events during disease progression is poorly understood. Spinal muscular atrophy (SMA) is a neurodegenerative disease caused by a deficiency in the ubiquitously expressed protein SMN and is characterized by motor neuron death, skeletal muscle atrophy, as well as dysfunction and loss of both central and peripheral excitatory synapses. These disease hallmarks result in an overall reduction of neuronal activity in the spinal sensory-motor circuit. Here, we show that increasing neuronal activity by chronic treatment with the FDA-approved potassium channel blocker 4-aminopyridine (4-AP) improves motor behavior in both sexes of a severe mouse model of SMA. 4-AP restores neurotransmission and number of proprioceptive synapses and neuromuscular junctions (NMJs), while having no effects on motor neuron death. In addition, 4-AP treatment with pharmacological inhibition of p53-dependent motor neuron death results in additive effects, leading to full correction of sensory-motor circuit pathology and enhanced phenotypic benefit in SMA mice. Our in vivo study reveals that 4-AP-induced increase of neuronal activity restores synaptic connectivity and function in the sensory-motor circuit to improve the SMA motor phenotype.SIGNIFICANCE STATEMENT Spinal muscular atrophy (SMA) is a neurodegenerative disease, characterized by synaptic loss, motor neuron death, and reduced neuronal activity in spinal sensory-motor circuits. However, whether these are parallel or dependent events is unclear. We show here that long-term increase of neuronal activity by the FDA-approved drug 4-aminopyridine (4-AP) rescues the number and function of central and peripheral synapses in a SMA mouse model, resulting in an improvement of the sensory-motor circuit and motor behavior. Combinatorial treatment of pharmacological inhibition of p53, which is responsible for motor neuron death and 4-AP, results in additive beneficial effects on the sensory-motor circuit in SMA. Thus, neuronal activity restores synaptic connections and improves significantly the severe SMA phenotype.     

Hypoperfusion in the supplementary motor area, dorsolateral prefrontal cortex and insular cortex in Parkinson's disease.

The changes of regional cerebral blood flow (rCBF) in Parkinson's disease (PD) were investigated. Because of individual differences in brain volume and the extent of brain atrophy, previous functional imaging studies involved potential methodological difficulties. In this study, using the statistical parametric mapping technique, 99mTechnetium-labeled hexamethylpropyleneamineoxime brain single-photon emission computed tomography images from 18 patients with PD were transformed into standard brain-based stereotaxic coordinate spaces and then compared with such images for 11 control subjects matched for age and extent of brain atrophy. A rCBF decrement in the supplementary motor area (SMA) and such decrement in the dorsolateral prefrontal cortex (DLPFC) were observed in the summarized PD images as compared with controls (p<0.005). In a subgroup in the Hoehn-Yahr III/IV stage (11 cases), the rCBF decrement was demonstrated not only in the SMA, but also in the DLPFC and insular cortex (p<0.001). There was a correlation between the degree of the rCBF decrement in the DLPFC or the insular cortex and the score of the unified Parkinson's disease rating scale (p<0.05), while the rCBF decrement in the SMA showed no relationship with the severity of disease. The function of the SMA is closely associated with the nigro-striatal pathway and its impairment can explain the basic akinetic symptoms in PD, which are responsive to L-DOPA treatment. On the other hand, the DLPFC and insular cortex may play key roles in specific symptoms of impairment at advanced stages, such as impaired working memory, postural instability and autonomic dysfunction. We hypothesize that the impairment of the DLPFC and insular function is correlated with the progression of the disease and is related to DOPA-refractory symptoms, which are major problems in the care of patients with advanced PD.     

Spinal muscular atrophy with progressive myoclonic epilepsy: report of new cases and review of the literature

Spinal muscular atrophy (SMA) is a clinically and genetically heterogeneous disease characterised by loss of motor function and muscle atrophy due to anterior horn cell degeneration. The most common variant is chromosome 5-linked proximal SMA, ranging in severity from congenital onset and infantile death to onset in adult life. Genetically separate variants with different distribution of weakness and/or additional features such as central nervous system involvement have been described. A rare variant with associated myoclonic epilepsy and lower motor neuron disease had been previously described in three families before the SMN gene, responsible for the common form of SMA, was isolated. We report four patients from two additional families affected by a syndrome characterised by severe and progressive myoclonic epilepsy and proximal weakness, tremor and lower motor neuron disease proven by electrophysiologic and muscle biopsy findings. Extensive metabolic investigations were normal and genetic analysis excluded the SMN gene. This study confirms that the association of myoclonic epilepsy and motor neuron disease represents a separate clinical and genetic entity from chromosome 5-linked SMA, the primary defect of which remains unknown.     

Establishing a standardized therapeutic testing protocol for spinal muscular atrophy

Several mice models have been created for spinal muscular atrophy (SMA); however, there is still no standard preclinical testing system for the disease. We previously generated type III-specific SMA model mice, which might be suitable for use as a preclinical therapeutic testing system for SMA. To establish such a system and test its applicability, we first created a testing protocol and then applied it as a means to investigate the use of valproic acid (VPA) as a possible treatment for SMA. These SMA mice revealed tail/ear/foot deformity, muscle atrophy, poorer motor performances, smaller compound muscle action potential and lower spinal motoneuron density at the age of 9 to 12 months in comparison with age-matched wild-type littermate mice. In addition, VPA attenuates motoneuron death, increases spinal SMN protein level and partially normalizes motor function in SMA mice. These results suggest that the testing protocol developed here is well suited for use as a standardized preclinical therapeutic testing system for SMA.     

Is Kugelberg-Welander spinal muscular atrophy a fetal defect?

Twelve children who had developed Kugelberg-Welander (K-W) spinal muscular atrophy (SMA) before the age of six years were investigated. Electrophysiological, histochemical, ultrastructural, and biochemical studies demonstrated features of immature muscle fibers suggesting a fetal defect as in the Werdnig-Hoffmann (W-H) form of SMA. Comparison with known patterns of human myogenesis and of experimental denervation of immature muscle suggested that the defect in K-W SMA probably takes place in fetal life at a stage later than in W-H SMA. In contrast to W-H SMA, a considerable percentage of mature fibers of normal structure and diameter were present. The immature fibers impair the normal development of muscle cells by preventing the increase in number of mature fibers and causing an overloading of the normal fibers with consequent hypertrophy and eventually destructive changes. This is the pattern in K-W disease that distinguishes the juvenile form of SMA from W-H disease.     

Spinal muscular atrophy: SMN protein deficiency

Spinal muscular atrophy is a heterogeneous group of disorders characterised by the loss of alfa motor neurons in spinal cord. Autosomal recessive infantile and juvenile proximal spinal muscular atrophy is the most common form of the disease. The identification of the disease gene-Survival of Motor Neuron (SMN) was a major advance in understanding of the molecular basis of SMA. 98% of SMA patients show the homozygous absence of at least exon 7 telomeric copy of SMN, the rest carry small intragenic mutations, usually in exon 6. Two different mechanisms seem to be responsible for the absence of the telomeric copy: deletion in severe form and gene conversion associated with mild phenotype. Recently, biochemical studies resulted in identification of the 38kDa survival motor neuron (SMN) protein, probably involved in the biogenesis of spliceosomal snRNP. The SMN protein level was shown to be 100-fold reduced in spinal cord of SMA 1 patients.     

Riluzole attenuates spinal muscular atrophy disease progression in a mouse model

Spinal muscular atrophy (SMA) is a motor neuron disease caused by mutations of the survival motor neuron 1 gene (SMN1). No curative treatment is available. Mutant mice carrying homozygous deletion of Smn exon 7 directed to neurons display a degenerative process of motor neurons similar to that found in human SMA. To test whether riluzole, which exhibits neurotrophic properties, might have a protective role in SMA, mutant mice were treated with it after the onset of the degenerative process. Riluzole improved median survival and exerted a protective effect against aberrant cytoskeletal organization of motor synaptic terminals but not against loss of proximal axons. These results demonstrate that the disease course of SMA can be attenuated after the onset of neuromuscular defects and may warrant further investigation in a therapeutic trial in SMA.     

Spinal muscular atrophy

Spinal muscular atrophies (SMA) are characterized by degeneration of lower motor neurons associated with muscle paralysis and atrophy. Childhood SMA is a common recessive autosomal disorder and represents one of the most common genetic causes of death in childhood. The pathophysiology remains unknown, and no curative treatment is available so far. The last 10 years have seen major advances in the field of SMA, which are starting points towards understanding the SMA pathogenesis and developing therapeutic strategies for this devastating neurodegenerative disease.     

Motor unit number index (MUNIX) in children and adults with 5q-spinal muscular atrophy: Variability and clinical correlations

Spinal muscular atrophy (SMA) is a motor neuron disease associated with progressive muscle weakness and motor disability. The motor unit number index (MUNIX) is a biomarker used to assess loss of motor units in later-onset SMA patients. Twenty SMA patients (SMA types 3 and 4), aged between 7 and 41 years, were clinically evaluated through the Hammersmith Motor Functional Scale Expanded and the Spinal Muscular Atrophy-Functional Rating Scale. The patients underwent compound motor action potential (CMAP) and MUNIX studies of the right abductor pollicis brevis, abductor digiti minimi and tibialis anterior (TA) muscles. Age-matched healthy controls (n = 20) were enrolled to obtain normative CMAP and MUNIX values from the same muscles. Compared to healthy controls, SMA patients showed significant reductions in MUNIX values among all muscles studied, whereas CMAP showed reductions only in the weaker muscles (abductor digiti minimi and TA). MUNIX variability was significantly higher in the SMA group than in the control group. MUNIX variability in TA correlated with CMAP variability. Motor functional scores correlated with TA MUNIX. The MUNIX study is feasible in later-onset SMA patients, and TA MUNIX values correlate with disease severity in patients with mild motor impairment.     

Spinal muscular atrophy: recent advances and future prospects

Spinal muscular atrophies (SMA) are characterized by degeneration of lower motor neurons associated with muscle paralysis and atrophy. Childhood SMA is a frequent recessive autosomal disorder and represents one of the most common genetic causes of death in childhood. Mutations of the SMN1 gene are responsible for SMA. The knowledge of the genetic basis of SMA, a better understanding of SMN function, and the recent generation of SMA mouse models represent major advances in the field of SMA. These are starting points towards understanding the pathophysiology of SMA and developing therapeutic strategies for this devastating neurodegenerative disease, for which no curative treatment is known so far.     

Degeneration of cocultures of spinal muscular atrophy muscle cells and rat spinal cord explants is not due to secreted factors and cannot be prevented by neurotrophins

We have shown recently that cocultures of muscle cells from infantile spinal muscular atrophy (SMA) patients innervated by motoneurons of normal rat spinal cord explants undergo a degeneration process, suggesting that muscle may play a role in this atrophy, which previously has been considered to be a pure motoneuron disease. Conditional media of SMA cocultures did not affect control healthy nerve muscle cocultures. Conversely, conditioned media of control cocultures were unable to prevent degeneration of SMA cocultures. Moreover, neurotrophic factors, thought to be of help in motoneuron disease treatment, did not protect SMA cocultures from premature death. Our results suggest that the abnormal phenotype observed in nerve-muscle coculture (1) is not due to the release of a toxic factor nor to the lack of a secreted survival factor; and (2) does not respond to neurotrophin treatment. © 1997 John Wiley & Sons, Inc. Muscle Nerve 20: 953–960, 1997     

Serum cholinesterase activity in infantile and juvenile spinal muscular atrophy

Serum acetylcholinesterase (AChE) and pseudocholinesterase (ChE) activity in infantile and juvenile spinal muscular atrophy (SMA) was determined. The total AChE activity was either normal or decreased in the childhood SMA (Type 1), the other SMA groups and disease controls (ALS, X-linked SMA). In the majority of SMA Type 1 cases (6/7 tested) an absence of the asymmetric A12 form was found. This was accompanied by changes in the other asymmetric and globular forms. The latter was, however, not specific for SMA Type 1 cases. The ChE activity was increased in the majority of SMA cases as well as disease controls. The asymmetric A12 ChE form was increased in all SMA Type 3 cases, the values of this form in SMA Type 1 was variable. A change in the ChE globular forms in SMA Type 1 and SMA Type 2 was a frequent finding. It is suggested that the absence of the asymmetric A12 AChE form in SMA Type 1 arises because of muscle cell immaturity and undeveloped muscle-nerve interactions. The reason of ChE changes is obscure.