Deletions in the survival motor neuron gene on 5q13 in autosomal recessive spinal muscular atrophy

A transcriptomics-based drug repositioning approach to identify drugs with similar activities for the treatment of muscle pathologies in spinal muscular atrophy (SMA) models

Spinal muscular atrophy (SMA) is a genetic neuromuscular disorder caused by the reduction of survival of motor neuron (SMN) protein levels. Although three SMN-augmentation therapies are clinically approved that significantly slow down disease progression, they are unfortunately not cures. Thus, complementary SMN-independent therapies that can target key SMA pathologies and that can support the clinically approved SMN-dependent drugs are the forefront of therapeutic development. We have previously demonstrated that prednisolone, a synthetic glucocorticoid (GC) improved muscle health and survival in severe Smn-/-;SMN2 and intermediate Smn2B/- SMA mice. However, long-term administration of prednisolone can promote myopathy. We thus wanted to identify genes and pathways targeted by prednisolone in skeletal muscle to discover clinically approved drugs that are predicted to emulate prednisolone's activities. Using an RNA-sequencing, bioinformatics, and drug repositioning pipeline on skeletal muscle from symptomatic prednisolone-treated and untreated Smn-/-; SMN2 SMA and Smn+/-; SMN2 healthy mice, we identified molecular targets linked to prednisolone's ameliorative effects and a list of 580 drug candidates with similar predicted activities. Two of these candidates, metformin and oxandrolone, were further investigated in SMA cellular and animal models, which highlighted that these compounds do not have the same ameliorative effects on SMA phenotypes as prednisolone; however, a number of other important drug targets remain. Overall, our work further supports the usefulness of prednisolone's potential as a second-generation therapy for SMA, identifies a list of potential SMA drug treatments and highlights improvements for future transcriptomic-based drug repositioning studies in SMA.

Potentiation of neuromuscular transmission by a small molecule calcium channel gating modifier improves motor function in a severe spinal muscular atrophy mouse model

Spinal muscular atrophy (SMA) is a monogenic disease that clinically manifests as severe muscle weakness owing to neurotransmission defects and motoneuron degeneration. Individuals affected by SMA experience neuromuscular weakness that impacts functional activities of daily living. We have used a mouse model of severe SMA (SMNΔ7) to test whether a calcium channel gating modifier (GV-58), alone or in combination with a potassium channel antagonist (3,4-diaminopyridine; 3,4-DAP), can improve neuromuscular function in this mouse model. Bath application of GV-58 alone or in combination with 3,4-DAP significantly restored neuromuscular transmission to control levels in both a mildly vulnerable forearm muscle and a strongly vulnerable trunk muscle in SMNΔ7 mice at postnatal days 10-12. Similarly, acute subcutaneous administration of GV-58 to postnatal day 10 SMNΔ7 mice, alone or in combination with 3,4-DAP, significantly increased a behavioral measure of muscle strength. These data suggest that GV-58 may be a promising treatment candidate that could address deficits in neuromuscular function and strength and that the addition of 3,4-DAP to GV-58 treatment could aid in restoring function in SMA.

Spinal muscular atrophy with hypoplasia of the corpus callosum: a case report

BACKGROUND

Spinal Muscular Atrophy (SMA) is a severe neuromuscular disorder due to a defect in the survival motor neuron 1 (SMN1) gene. Hypoplasia of the corpus callosum is underdevelopment or thinness of the corpus callosum. SMA and callosal hypoplasia are relatively rare, and there is limited information sharing the diagnosis and treatment for SMA patients with callosal hypoplasia.

CASE DESCRIPTION

A boy with callosal hypoplasia, small penis, and small testes had been perceived with motor regression at 5 months. He was referred to the rehabilitation department and neurology department at 7 months. Physical examination showed absent deep tendon reflexes, proximal weakness and significant hypotonia. He was recommended to perform trio whole-exome sequencing (WES) and array comparative genomic hybridization (aCGH) for his complicated conditions. The subsequent nerve conduction study revealed some characteristics of motor neuron diseases. We identified a homozygous deletion in exon 7 of the SMN1 gene by multiplex ligation-dependent probe amplification and failed to find further pathogenic variations responsible for multiple malformations by trio WES and aCGH. He was diagnosed as SMA. Despite some concerns, he received the therapy of nusinersen for nearly 2 years. He gained the milestone of sitting without support, which he had never accomplished, after the seventh injection, and he continued to improve. During follow-up, there were no adverse events reported and no signs of hydrocephalus.

CONCLUSIONS

Some extra features which could not belong to neuromuscular manifestation made the diagnosis and treatment of SMA more complicated.

The role of autophagy-lysosomal pathway in motor neuron diseases

Motor neuron diseases (MNDs) include a broad group of diseases in which neurodegeneration mainly affects upper and/or lower motor neurons (MNs). Although the involvement of specific MNs, symptoms, age of onset, and progression differ in MNDs, the main pathogenic mechanism common to most MNDs is represented by proteostasis alteration and proteotoxicity. This pathomechanism may be directly related to mutations in genes encoding proteins involved in the protein quality control system, particularly the autophagy-lysosomal pathway (ALP). Alternatively, proteostasis alteration can be caused by aberrant proteins that tend to misfold and to aggregate, two related processes that, over time, cannot be properly handled by the ALP. Here, we summarize the main ALP features, focusing on different routes utilized to deliver substrates to the lysosome and how the various ALP pathways intersect with the intracellular trafficking of membranes and vesicles. Next, we provide an overview of the mutated genes that have been found associated with MNDs, how these gene products are involved in different steps of ALP and related processes. Finally, we discuss how autophagy can be considered a valid therapeutic target for MNDs treatment focusing on traditional autophagy modulators and on emerging approaches to overcome their limitations.

Mouse models of SMA show divergent patterns of neuronal vulnerability and resilience

Background

Spinal muscular atrophy (SMA) is a form of motor neuron disease affecting primarily children characterised by the loss of lower motor neurons (MNs). Breakdown of the neuromuscular junctions (NMJs) is an early pathological event in SMA. However, not all motor neurons are equally vulnerable, with some populations being lost early in the disease while others remain intact at the disease end-stage. A thorough understanding of the basis of this selective vulnerability will give critical insight into the factors which prohibit pathology in certain motor neuron populations and consequently help identify novel neuroprotective strategies.

Methods

To retrieve a comprehensive understanding of motor neuron susceptibility in SMA, we mapped NMJ pathology in 20 muscles from the Smn^2B/- SMA mouse model and cross-compared these data with published data from three other commonly used mouse models. To gain insight into the molecular mechanisms regulating selective resilience and vulnerability, we analysed published RNA sequencing data acquired from differentially vulnerable motor neurons from two different SMA mouse models.

Results

In the Smn^2B/- mouse model of SMA, we identified substantial NMJ loss in the muscles from the core, neck, proximal hind limbs and proximal forelimbs, with a marked reduction in denervation in the distal limbs and head. Motor neuron cell body loss was greater at T5 and T11 compared with L5. We subsequently show that although widespread denervation is observed in each SMA mouse model (with the notable exception of the Taiwanese model), all models have a distinct pattern of selective vulnerability. A comparison of previously published data sets reveals novel transcripts upregulated with a disease in selectively resistant motor neurons, including genes involved in axonal transport, RNA processing and mitochondrial bioenergetics.

Conclusions

Our work demonstrates that the Smn^2B/- mouse model shows a pattern of selective vulnerability which bears resemblance to the regional pathology observed in SMA patients. We found drastic differences in patterns of selective vulnerability across the four SMA mouse models, which is critical to consider during experimental design. We also identified transcript groups that potentially contribute to the protection of certain motor neurons in SMA mouse models.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13395-022-00305-9.

Distribution of weight, stature, and growth status in children and adolescents with spinal muscular atrophy: An observational retrospective study in the United States

Introduction/Aims

Data regarding weight, height/length, and growth status of patients with spinal muscular atrophy (SMA) who have received only supportive care are limited. This cross‐sectional study describes these measurements in patients with Type 1 and Types 2/3 SMA and compares them with reference values from typically developing children.

Methods

Retrospective baseline data from three sites in the Pediatric Neuromuscular Clinical Research Network (Boston, New York, Philadelphia) were used. Descriptive statistics for weight, height/length, body mass index‐for‐age, as well as weight‐for‐length and absolute and relative deviations from reference values (ie, 50th percentile from World Health Organization/Centers for Disease Control growth charts) were calculated. Furthermore, growth status was reported.

Results

A total of 91 genetically confirmed patients with SMA receiving optimal supportive care and without any disease‐modifying treatment were stratified into Types 1 (n = 28) and 2/3 SMA (n = 63). Patients with Type 1 SMA weighed significantly less (median = −7.5%) compared with reference values and patients with Types 2/3 SMA were significantly shorter (mean = −3.0%) compared with reference values. The median weight was considerably below the 50th percentile in both groups of patients, even if they received a high standard of care and proactive feeding support.

Discussion

More research is needed to understand which factors influence growth longitudinally, and how to accurately capture growth in patients with SMA. Further research should investigate the best time to provide feeding support to avoid underweight, especially in patients with Type 1, and how to avoid the risk of overfeeding, especially in patients with Types 2/3 SMA.

Management of Spinal Muscular Atrophy in the Adult Population

Spinal muscular atrophy (SMA) is a group of neurodegenerative disorders resulting from the loss of spinal motor neurons. 95% of patients share a pathogenic mechanism of loss of survival motor neuron (SMN) 1 protein expression due to homozygous deletions or other mutations of the SMN1 gene, with the different phenotypes influenced by variable copy numbers of the SMN2 gene. Advances in supportive care, disease modifying treatment and novel gene therapies have led to an increase in the prevalence of SMA, with a third of SMA patients now represented by adults. Despite the growing number of adult patients, consensus on the management of SMA has focused primarily on the pediatric population. As the disease burden is vastly different in adult SMA, an approach to treatment must be tailored to their unique needs. This review will focus on the management of the adult SMA patient as they age and will discuss proper transition of care from a pediatric to adult center, including the need for continued monitoring for osteoporosis, scoliosis, malnutrition, and declining mobility and functioning. As in the pediatric population, multidisciplinary care remains the best approach to the management of adult SMA. Novel and emerging therapies such as nusinersen and risdiplam provide hope for these patients, though these medications are of uncertain efficacy in this population and require additional study.

Efficacy of nusinersen in type 1, 2 and 3 spinal muscular atrophy: Real world data from Hungarian patients

INTRODUCTION

Spinal muscular atrophy (SMA) is an autosomal recessive disorder caused by a homozygous deletion of the survival motor neuron (SMN) 1 gene. Nusinersen is an antisense oligonucleotide enhancing the production of the SMN protein. It has received approval by the European Medicines Agency (EMA) in 2017, based on the clinical trials demonstrating the effectiveness of nusinersen in several types of SMA. In Hungary, the first patient received nusinersen treatment in April 2018. Our aim is to summarize our experience regarding the efficacy, safety and tolerability of nusinersen in our patients.

METHODS

Data were collected retrospectively in all types of SMA patients (type 1-3) starting treatment with nusinersen in Hungary between April 2018 and December 2019. Motor functions were evaluated at baseline, at the fourth and all following injections.

RESULTS

By 31^st December 2019, nusinersen therapy was initiated in 54 patients at either of the two Hungarian treatment centres. Mean age of the patients at the start of the treatment was 6.3 years (±5,4 range 0.4-17.9). 13 patients are type 1 (mean 0.78 ± 0.27, range 0.4-1.5 yrs), 21 patients are type 2 (mean 4.5 ± 3.3, range 1.3-12 yrs), 23 patients are type 3 (mean 10.9 ± 5.2, range 2.9-17.9 yrs). Fourteen patients had severe scoliosis, four of them underwent spine stabilizing surgery. During the study period 340 injections were administered without any new safety concerns emerging. The data of 38 patients, who had completed the first six treatments, were included in the final statistical analysis. Motor function has improved in most of the children. By the 307th day visit, on average, a 14.9 (±5,1) point improvement was measured on the CHOP INTEND scale in type 1 patients (p = 0.016). All patients with type 1 SMA who performed the motor evaluation (7/10) have improved by more than four (7-21) points. Regarding type 2 patients, a 7.2 (range -2- 17) point increase from baseline (p < 0.001) on the Hammersmith Functional Motor Scale Expanded (HFMSE) and 4.3 (range: 2-9) point increase (p = 0.031) on the Revised Upper Limb Module (RULM) were found. The distance of the 6 min walk test also increased by 33.9 m on average (range -16 - 106), in type 3 patients.

CONCLUSION

According to our results nusinersen has the same safety and tolerability profile as in the clinical trials. In a heterogenic patient population of SMA type 1 and 2, nusinersen showed similar efficacy as seen in the pivotal studies. A clinically and statistically significant improvement of motor functions was also detectable in type 3 patients with heterogeneous age distribution.

Synaptic withdrawal following nerve injury is influenced by postnatal maturity, muscle-specific properties, and the presence of underlying pathology in mice

Axonal and synaptic degeneration occur following nerve injury and during disease. Traumatic nerve injury results in rapid fragmentation of the distal axon and loss of synaptic terminals, in a process known as Wallerian degeneration (WD). Identifying and understanding factors that influence the rate of WD is of significant biological and clinical importance, as it will facilitate understanding of the mechanisms of neurodegeneration and identification of novel therapeutic targets. Here, we investigate levels of synaptic loss following nerve injury under a range of conditions, including during postnatal development, in a range of anatomically distinct muscles and in a mouse model of motor neuron disease. By utilising an ex vivo model of nerve injury, we show that synaptic withdrawal is slower during early postnatal development. Significantly more neuromuscular junctions remained fully innervated in the cranial nerve/muscle preparations analysed at P15 than at P25. Furthermore, we demonstrate variability in the level of synaptic withdrawal in response to injury in different muscles, with retraction being slower in abdominal preparations than in cranial muscles across all time points analysed. Importantly, differences between the cranial and thoracoabdominal musculature seen here are not consistent with differences in muscle vulnerability that have been previously reported in mouse models of the childhood motor neuron disease, spinal muscular atrophy (SMA), caused by depletion of survival motor neuron protein (Smn). To further investigate the relationship between synaptic degeneration in SMA and WD, we induced WD in preparations from the Smn^2B/− mouse model of SMA. In a disease‐resistant muscle (rostral band of levator auris longus), where there is minimal denervation, there was no change in the level of synaptic loss, which suggests that the process of synaptic withdrawal following injury is Smn‐independent. However, in a muscle with ongoing degeneration (transvs. abdominis), the level of synaptic loss significantly increased, with the percentage of denervated endplates increasing by 33% following injury, compared to disease alone. We therefore conclude that the presence of a die‐back can accelerate synaptic loss after injury in Smn^2B/− mice.

Reduced P53 levels ameliorate neuromuscular junction loss without affecting motor neuron pathology in a mouse model of spinal muscular atrophy

Spinal Muscular Atrophy (SMA) is a childhood motor neuron disease caused by mutations or deletions within the SMN1 gene. At endstages of disease there is profound loss of motor neurons, loss of axons within ventral roots and defects at the neuromuscular junctions (NMJ), as evidenced by pathological features such as pre-synaptic loss and swelling and post-synaptic shrinkage. Although these motor unit defects have been widely described, the time course and interdependancy of these aspects of motor unit degeneration are unclear. Recent reports have also revealed an early upregulation of transcripts associated with the P53 signalling pathway. The relationship between the upregulation of these transcripts and pathology within the motor unit is also unclear. In this study, we exploit the prolonged disease timecourse and defined pre-symptomatic period in the Smn^2B/- mouse model to perform a temporal analysis of the different elements of motor unit pathology. We demonstrate that NMJ loss occurs prior to cell body loss, and coincides with the onset of symptoms. The onset of NMJ pathology also coincides with an increase in P53-related transcripts at the cell body. Finally, using a tamoxifen inducible P53 knockout, we demonstrate that post-natal reduction in P53 levels can reduce NMJ loss, but does not affect other aspects of NMJ pathology, motor neuron loss or the phenotype of the Smn^2B/- mouse model. Together this work provides a detailed temporal description of pathology within motor units of an SMA mouse model, and demonstrates that NMJ loss is a P53-dependant process. This work supports the role for P53 as an effector of synaptic and axonal degeneration in a die-back neuropathy.

Diagnosis and management of spinal muscular atrophy: Part 1: Recommendations for diagnosis, rehabilitation, orthopedic and nutritional care

Spinal muscular atrophy (SMA) is a severe neuromuscular disorder due to a defect in the survival motor neuron 1 (SMN1) gene. Its incidence is approximately 1 in 11,000 live births. In 2007, an International Conference on the Standard of Care for SMA published a consensus statement on SMA standard of care that has been widely used throughout the world. Here we report a two-part update of the topics covered in the previous recommendations. In part 1 we present the methods used to achieve these recommendations, and an update on diagnosis, rehabilitation, orthopedic and spinal management; and nutritional, swallowing and gastrointestinal management. Pulmonary management, acute care, other organ involvement, ethical issues, medications, and the impact of new treatments for SMA are discussed in part 2.

Comparison of independent screens on differentially vulnerable motor neurons reveals alpha-synuclein as a common modifier in motor neuron diseases

The term “motor neuron disease” encompasses a spectrum of disorders in which motor neurons are the primary pathological target. However, in both patients and animal models of these diseases, not all motor neurons are equally vulnerable, in that while some motor neurons are lost very early in disease, others remain comparatively intact, even at late stages. This creates a valuable system to investigate the factors that regulate motor neuron vulnerability. In this study, we aim to use this experimental paradigm to identify potential transcriptional modifiers. We have compared the transcriptome of motor neurons from healthy wild-type mice, which are differentially vulnerable in the childhood motor neuron disease Spinal Muscular Atrophy (SMA), and have identified 910 transcriptional changes. We have compared this data set with published microarray data sets on other differentially vulnerable motor neurons. These neurons were differentially vulnerable in the adult onset motor neuron disease Amyotrophic Lateral Sclerosis (ALS), but the screen was performed on the equivalent population of neurons from neurologically normal human, rat and mouse. This cross species comparison has generated a refined list of differentially expressed genes, including CELF5, Col5a2, PGEMN1, SNCA, Stmn1 and HOXa5, alongside a further enrichment for synaptic and axonal transcripts. As an in vivo validation, we demonstrate that the manipulation of a significant number of these transcripts can modify the neurodegenerative phenotype observed in a Drosophila line carrying an ALS causing mutation. Finally, we demonstrate that vector-mediated expression of alpha-synuclein (SNCA), a transcript decreased in selectively vulnerable motor neurons in all four screens, can extend life span, increase weight and decrease neuromuscular junction pathology in a mouse model of SMA. In summary, we have combined multiple data sets to identify transcripts, which are strong candidates for being phenotypic modifiers, and demonstrated SNCA is a modifier of pathology in motor neuron disease.

The term “motor neuron disease” refers to a group of disorders, causing progressive paralysis of affected patients due to the degeneration of motor neurons cells which control voluntary movements. Importantly, not all motor neurons appear to be affected in the same way, with those that control the face being affected less that those that control the abdomen. The reason why some motor neurons are more vulnerable is unknown; however, understanding this may provide new targets for therapeutics to slow motor neuron degeneration either as stand-alone therapeutics or in combination with SMN-inducing compounds. In this study, we analysed gene expression in different groups of motor neurons and compared this to previously published expression data to identify commonalities. One of the common transcripts was alpha-synuclein (SNCA), which was consistently expressed at lower levels in vulnerable motor neurons. Importantly, when SNCA levels were increased in a mouse model of motor neuron disease, the disease phenotype was significantly reduced, including an extension in survival and reduction in motor neuron pathology. Collectively, these results demonstrate that this approach can identify disease modifiers that can reduce disease severity in models of motor neuron disease and potentially identify new therapeutic targets.

Does the survival motor neuron copy number variation play a role in the onset and severity of sporadic amyotrophic lateral sclerosis in Malians?

Introduction

Spinal muscular atrophy (SMA) and sporadic amyotrophic lateral sclerosis (SALS) are both motor neuron disorders. SMA results from the deletion of the survival motor neuron (SMN) 1 gene. High or low SMN1 copy number and the absence of SMN2 have been reported as risk factors for the development or severity of SALS.

Objective

To investigate the role of SMN gene copy number in the onset and severity of SALS in Malians.

Material and Methods

We determined the SMN1 and SMN2 copy number in genomic DNA samples from 391 Malian adult volunteers, 120 Yoruba from Nigeria, 120 Luyha from Kenya and 74 U.S. Caucasians using a Taqman quantitative PCR assay. We evaluated the SALS risk based on the estimated SMA protein level using the Veldink formula (SMN1 copy number + 0.2 ∗ SMN2 copy number). We also characterized the disease natural history in 15 ALS patients at the teaching hospital of Point G, Bamako, Mali.

Results

We found that 131 of 391 (33.5%) had an estimated SMN protein expression of ≤ 2.2; 60 out of 391 (15.3%) had an estimated SMN protein expression < 2 and would be at risk of ALS and the disease onset was as early as 16 years old. All 15 patients were male and some were physically handicapped within 1-2 years in the disease course.

Conclusion

Because of the short survival time of our patients, family histories and sample DNA for testing were not done. However, our results show that sporadic ALS is of earlier onset and shorter survival time as compared to patients elsewhere. We plan to establish a network of neurologists and researchers for early screening of ALS.

Central and peripheral defects in motor units of the diaphragm of spinal muscular atrophy mice

Spinal muscular atrophy (SMA) is characterized by motoneuron loss and muscle weakness. However, the structural and functional deficits that lead to the impairment of the neuromuscular system remain poorly defined. By electron microscopy, we previously found that neuromuscular junctions (NMJs) and muscle fibres of the diaphragm are among the earliest affected structures in the severe mouse SMA model. Because of certain anatomical features, i.e. its thinness and its innervation from the cervical segments of the spinal cord, the diaphragm is particularly suitable to characterize both central and peripheral events. Here we show by immunohistochemistry that, at postnatal day 3, the cervical motoneurons of SMA mice receive less stimulatory synaptic inputs. Moreover, their mitochondria become less elongated which might represent an early stage of degeneration. The NMJs of the diaphragm of SMA mice show a loss of synaptic vesicles and active zones. Moreover, the partly innervated endplates lack S100 positive perisynaptic Schwann cells (PSCs). We also demonstrate the feasibility of comparing the proteomic composition between diaphragm regions enriched and poor in NMJs. By this approach we have identified two proteins that are significantly upregulated only in the NMJ-specific regions of SMA mice. These are apoptosis inducing factor 1 (AIFM1), a mitochondrial flavoprotein that initiates apoptosis in a caspase-independent pathway, and four and a half Lim domain protein 1 (FHL1), a regulator of skeletal muscle mass that has been implicated in several myopathies.

Autophagy dysregulation in cell culture and animals models of spinal muscular atrophy

Abnormal autophagy has become a central thread linking neurodegenerative diseases, particularly of the motor neuron. One such disease is spinal muscular atrophy (SMA), a genetic neuromuscular disorder caused by mutations in the SMN1 gene resulting in low levels of Survival Motor Neuron (SMN) protein. Despite knowing the causal protein, the exact intracellular processes that are involved in the selective loss of motor neurons remain unclear. Autophagy induction can be helpful or harmful depending on the situation, and we sought to understand the state of the autophagic response in SMA. We show that cell culture and animal models demonstrate induction of autophagy accompanied by attenuated autophagic flux, resulting in the accumulation of autophagosomes and their associated cargo. Expression of the SMN-binding protein a-COP, a known modulator of autophagic flux, can ameliorate this autophagic traffic jam.

Applicability of histone deacetylase inhibition for the treatment of spinal muscular atrophy

Spinal muscular atrophy (SMA), a neurodegenerative disease with potentially devastating and even deadly effects on affected individuals, was first described in the late nineteenth century. Although the survival of motor neuron (SMN) gene was identified nearly 2 decades ago to be causative of the disease, neither an effective treatment nor a cure are currently available. Yet efforts are on-going to test a multitude of treatment strategies with the potential to alleviate disease symptoms in human and clinical trials. Among the most studied compounds for the treatment of SMA are histone deacetylase inhibitors. Several of these epigenetic modifiers have been shown to increase expression of the crucial SMN gene in vitro and in vivo, an effect linked to increased histone acetylation and remodeling of the chromatin landscape surrounding the SMN gene promoter. Here, we review the history and current state of use of histone deacetylase inhibitors in SMA, as well as the success of clinical trials investigating the clinical applicability of these epigenetic modifiers in SMA treatment.

Molecular evolution of the moonlighting protein SMN in metazoans

The spinal muscular atrophy (SMA) associated protein survival of motor neuron (SMN) is known to be a moonlighting protein: having one primary, ancestral function (presumed to be involvement in U snRNP assembly) along with one or more secondary functions. One hypothesis for the evolution of moonlighting proteins is that regions of a structure under relatively weak negative selection could gain new functions without interfering with the primary function. To test this hypothesis, we investigated sequence conservation and dN/dS, which reflects the selection acting on a coding sequence, in SMN and a related protein, splicing factor 30 (SPF30), which is not currently known to be multifunctional. We found very different patterns of evolution in the two genes, with SPF30 characterized by strong sequence conservation and negative selection in most animal taxa investigated, and SMN with much lower sequence conservation, and much weaker negative selection at many sites. Evidence was found of positive selection acting on some sites in primate genes for SMN. SMN was also found to have been duplicated in a number of species, and with patterns that indicate reduced negative selection following some of these duplications. There were also several animal species lacking an SMN gene.

GStream: improving SNP and CNV coverage on genome-wide association studies

We present GStream, a method that combines genome-wide SNP and CNV genotyping in the Illumina microarray platform with unprecedented accuracy. This new method outperforms previous well-established SNP genotyping software. More importantly, the CNV calling algorithm of GStream dramatically improves the results obtained by previous state-of-the-art methods and yields an accuracy that is close to that obtained by purely CNV-oriented technologies like Comparative Genomic Hybridization (CGH). We demonstrate the superior performance of GStream using microarray data generated from HapMap samples. Using the reference CNV calls generated by the 1000 Genomes Project (1KGP) and well-known studies on whole genome CNV characterization based either on CGH or genotyping microarray technologies, we show that GStream can increase the number of reliably detected variants up to 25% compared to previously developed methods. Furthermore, the increased genome coverage provided by GStream allows the discovery of CNVs in close linkage disequilibrium with SNPs, previously associated with disease risk in published Genome-Wide Association Studies (GWAS). These results could provide important insights into the biological mechanism underlying the detected disease risk association. With GStream, large-scale GWAS will not only benefit from the combined genotyping of SNPs and CNVs at an unprecedented accuracy, but will also take advantage of the computational efficiency of the method.

Deletion analysis of SMN and NAIP genes in Tunisian patients with spinal muscular atrophy

Background:

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder involving degeneration of anterior horn cells of spinal cord, resulting in progressive muscle weakness and atrophy.

Aims:

The purpose of our study was to determine the frequency of SMN and NAIP deletions in Tunisian SMA patients.

Materials and Methods:

Polymerase chain reaction (PCR) combined with restriction fragment length polymorphism (RFLP) was used to detect the deletion of exon 7 and exon 8 of SMN1 gene, as well as multiplex PCR for exon 5 and 13 of NAIP gene.

Results:

Fifteen (45.4%) out of 33 SMA patients were homozygously deleted for exons 7 and/or 8 of SMN1. Homozygous deletion of NAIP gene was observed in 20% (3 / 15) of patients.

Conclusions:

The molecular diagnosis system based on PCR-RFLP analysis can conveniently be applied in the clinical testing, genetic counseling, prenatal diagnosis, and pre-implantation genetic diagnosis of SMA.

Clinical and Genetic Study of Algerian Patients with Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is the second most common lethal autosomal recessive disorder. It is divided into the acute Werdnig-Hoffmann disease (type I), the intermediate form (type II), the Kugelberg-Welander disease (type III), and the adult form (type IV). The gene involved in all four forms of SMA, the so-called survival motor neuron (SMN) gene, is duplicated, with a telomeric (tel SMN or SMN1) and a centromeric copy (cent SMN or SMN2). SMN1 is homozygously deleted in over 95% of SMA patients. Another candidate gene in SMA is the neuronal apoptosis inhibitory protein (NAIP) gene; it shows homozygous deletions in 45-67% of type I and 20-42% of type II/type III patients. Here we studied the SMN and NAIP genes in 92 Algerian SMA patients (20 type I, 16 type II, 53 type III, and 3 type IV) from 57 unrelated families, using a semiquantitative PCR approach. Homozygous deletions of SMN1 exons 7 and/or 8 were found in 75% of the families. Deletions of exon 4 and/or 5 of the NAIP gene were found in around 25%. Conversely, the quantitative analysis of SMN2 copies showed a significant correlation between SMN2 copy number and the type of SMA.

Sodium vanadate combined with L-ascorbic acid delays disease progression, enhances motor performance, and ameliorates muscle atrophy and weakness in mice with spinal muscular atrophy

BACKGROUND

Proximal spinal muscular atrophy (SMA), a neurodegenerative disorder that causes infant mortality, has no effective treatment. Sodium vanadate has shown potential for the treatment of SMA; however, vanadate-induced toxicity in vivo remains an obstacle for its clinical application. We evaluated the therapeutic potential of sodium vanadate combined with a vanadium detoxification agent, L-ascorbic acid, in a SMA mouse model.

METHODS

Sodium vanadate (200 μM), L-ascorbic acid (400 μM), or sodium vanadate combined with L-ascorbic acid (combined treatment) were applied to motor neuron-like NSC34 cells and fibroblasts derived from a healthy donor and a type II SMA patient to evaluate the cellular viability and the efficacy of each treatment in vitro. For the in vivo studies, sodium vanadate (20 mg/kg once daily) and L-ascorbic acid (40 mg/kg once daily) alone or in combination were orally administered daily on postnatal days 1 to 30. Motor performance, pathological studies, and the effects of each treatment (vehicle, L-ascorbic acid, sodium vanadate, and combined treatment) were assessed and compared on postnatal days (PNDs) 30 and 90. The Kaplan-Meier method was used to evaluate the survival rate, with P < 0.05 indicating significance. For other studies, one-way analysis of variance (ANOVA) and Student's t test for paired variables were used to measure significant differences (P < 0.05) between values.

RESULTS

Combined treatment protected cells against vanadate-induced cell death with decreasing B cell lymphoma 2-associated X protein (Bax) levels. A month of combined treatment in mice with late-onset SMA beginning on postnatal day 1 delayed disease progression, improved motor performance in adulthood, enhanced survival motor neuron (SMN) levels and motor neuron numbers, reduced muscle atrophy, and decreased Bax levels in the spinal cord. Most importantly, combined treatment preserved hepatic and renal function and substantially decreased vanadium accumulation in these organs.

CONCLUSIONS

Combined treatment beginning at birth and continuing for 1 month conferred protection against neuromuscular damage in mice with milder types of SMA. Further, these mice exhibited enhanced motor performance in adulthood. Therefore, combined treatment could present a feasible treatment option for patients with late-onset SMA.

The spinal muscular atrophy disease protein SMN is linked to the Golgi network

Proximal spinal muscular atrophy (SMA) is a neurodegenerative disorder caused by deficiency of the ubiquitous Survival of Motor Neuron (SMN) protein. SMN has been shown to be transported in granules along the axon and moved through cytoskeletal elements. However, the role and nature of SMN granules are still not well characterized. Here, using immunocytochemical methods and time-lapse studies we show that SMN granules colocalize with the Golgi apparatus in motor neuron-like NSC34 cells. Electron microscopy clearly revealed that SMN granules are transported into the Golgi stack and aggregate in the trans-Golgi apparatus. SMN granules are characterized as either coated or un-coated and behave like regulated secretory granules. Treatment of cells with monensin to disrupt Golgi-mediated granule secretion decreased SMN expression in neurites and caused growth cone defects similar to those seen in SMN knockdown cells. Knockdown of Cop-α, the protein that coats vesicles transporting proteins between the Golgi compartments, caused SMN granule accumulation in the Golgi apparatus. In addition to the well-studied role of SMN in small nuclear ribonucleoprotein (SnRNP) assembly, this work links SMN granules with the Golgi network and thus sheds light on Golgi-mediated SMN granule transport.

Spinal muscular atrophy pathogenic mutations impair the axonogenic properties of axonal-survival of motor neuron

The axonal survival of motor neuron (a-SMN) protein is a truncated isoform of SMN1, the spinal muscular atrophy (SMA) disease gene. a-SMN is selectively localized in axons and endowed with remarkable axonogenic properties. At present, the role of a-SMN in SMA is unknown. As a first step to verify a link between a-SMN and SMA, we investigated by means of over-expression experiments in neuroblastoma-spinal cord hybrid cell line (NSC34) whether SMA pathogenic mutations located in the N-terminal part of the protein affected a-SMN function. We demonstrated here that either SMN1 missense mutations or small intragenic re-arrangements located in the Tudor domain consistently altered the a-SMN capability of inducing axonal elongation in vitro. Mutated human a-SMN proteins determined in almost all NSC34 motor neurons the growth of short axons with prominent morphologic abnormalities. Our data indicate that the Tudor domain is critical in dictating a-SMN function possibly because it is an association domain for proteins involved in axon growth. They also indicate that Tudor domain mutations are functionally relevant not only for FL-SMN but also for a-SMN, raising the possibility that also a-SMN loss of function may contribute to the pathogenic steps leading to SMA.

Spinal muscular atrophy carrier frequency and estimated prevalence of the disease in Moroccan newborns

Spinal muscular atrophy (SMA) is one of the most common autosomal recessive diseases caused by homozygous deletion of exon 7 of the survival motor neuron 1 (SMN1) gene in approximately 95% of SMA patients. Carrier frequency studies of SMA have been reported for various populations. The aim of our study was to estimate the carrier frequency of the common SMN1 exon 7 deletion in the Moroccan population to achieve an insight into the prevalence of SMA in Morocco. In this study, we used a reliable quantitative real-time polymerase chain reaction assay with SYBR Green I dye to determine the copy number of the SMN1 gene. Analysis of 150 Moroccan newborns predicts a carrier frequency of approximately 1:25, which would mean a calculated SMA prevalence of 1:1800 after correction due to consanguinity. These results show as expected that the SMA carrier frequency in Morocco is higher than in the European populations and is close to those of Middle Eastern countries. Genetic carrier testing for genetic counseling should be recommended particularly to families with a clear clinical history of SMA.

Carboxylic acid derivatives of histone deacetylase inhibitors induce full length SMN2 transcripts: a promising target for spinal muscular atrophy therapeutics

INTRODUCTION

Proximal spinal muscular atrophy (SMA) is a common autosomal recessively inherited neuromuscular disorder. It is caused by homozygous absence of the survival motor neuron 1 (SMN1) gene. SMN2, which modulates the severity of the disease, represents a major target for therapy. The aim of this study was to investigate whether SMN2 expression can be increased by caffeic acid, chlorogenic acid and curcumin, which are designed by modifications of the carboxylic acid class of histone deacetylase (HDAC) inhibitors.

MATERIAL AND METHODS

Using quantitative real-time PCR, we analysed the levels of full-length SMN2 and Δ7SMN2 mRNA. We performed LDH cytotoxicity assay to analyse whether SMN2 activating concentrations of caffeic acid, chlorogenic acid and curcumin were cytotoxic to fibroblasts.

RESULTS

We found that caffeic acid and curcumin were more efficient than chlorogenic acid and increased full-length SMN2 mRNA levels 1.5 and 1.7-fold, respectively. Δ7SMN2 mRNA levels were measured to investigate alternative splicing of exon 7. We also found that cytotoxicity was not observed at SMN2 activating concentrations.

CONCLUSIONS

Our data suggest that carboxylic acid derivatives including phenolic structure and symmetry could be a good candidate for SMA treatment.

Spinal muscular atrophy due to double gene conversion event

Spinal muscular atrophy (SMA) is an autosomal recessive disease characterized by degeneration of the anterior horn cells of the spinal cord. The survival motor neuron (SMN) gene has been identified as an SMA-determining gene. SMN exists as two copies in 5q13, and deletions in exons 7 and 8 of the telomeric copy (SMN(T)) occur in 95% of patients, regardless of disease severity. In a minority of patients, exon 7 but not exon 8 of SMN(T) appears deleted. We now report a patient with typical features of SMA type II who carried homozygous deletions of SMN(T) exon 7 and centromeric SMN (SMN(C)) exon 8 but retained SMN(T) exon 8 and SMN(C) exon 7. Sequence analysis demonstrated that SMN(C) exon 7 was adjacent to SMN(T) exon 8 on both SMN copies, indicating a double conversion. We confirm that sequence conversion is a common event in SMA and is associated with the milder form of the disease. The severity, however, can be modified in either positive or negative direction by other factors.

Overview of paediatric neuromuscular disorders and related pulmonary issues: diagnostic and therapeutic considerations

Pulmonary compromise is common in neuromuscular disease. Respiratory failure may be a presenting feature of neuromuscular disease and remains a major cause of morbidity and mortality. This article will review the current understanding of the more commonly encountered neuromuscular disorders in childhood and emphasize related pulmonary issues.

Copy number variations in the human genome and strategies for analysis

The structure and sequence of the genome is immensely variable in the human population. Segmental copy number variants (CNVs) contribute to the extensive phenotypic diversity among humans and have been shown to associate with disease susceptibility. In this article, we provide a detailed review of human genetic variations and the experimental approaches used to discover, catalog, and genotype CNVs.

False homozygous deletions of SMN1 exon 7 using Dra I PCR-RFLP caused by a novel mutation in spinal muscular atrophy

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder, and about 95% of SMA patients are homozygous for deletions in the SMN1 gene. Herein, classical polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) using DraI yielded false homozygous deletions of SMN1 exon 7 in a patient with SMA, but multiple ligation-dependent probe amplification analysis revealed one remaining copy of SMN1 exon 7. Sequencing showed that this false deletion in the PCR-RFLP resulted from a novel mutation of one SMN1 copy that was not deleted (c.863G > T, p.R288M). This novel sequence variant introduced a mismatch that interfered with primer binding. These findings demonstrate that comprehensive analysis using PCR-RFLP, multiple ligation-dependent probe amplification, and sequencing can reliably and correctly diagnose SMA.

Molecular analysis of the SMN and NAIP genes in Iranian spinal muscular atrophy patients

BACKGROUND

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder characterized by degeneration of spinal cord anterior horn cells, leading to muscular atrophy. SMA is clinically classified into three subgroups based on the age of onset and severity. The majority of patients with SMA have homozygous deletions of exons 7 and 8 of the survival motor neuron (SMN) gene. The purpose of the present study was to determine the frequency of SMN and neuronal apoptosis inhibitory protein (NAIP) gene deletions in Iranian SMA patients. Experience in prenatal diagnosis of SMA in this population is also reported.

METHODS

To study the frequency of deletions of SMN and NAIP genes in an Iranian sample group, 75 unrelated SMA patients (54 type I, eight type II and 13 type III) were analyzed according to the methods described by van der Steege et al and Roy et al.

RESULTS

Homozygous deletion of SMN1 exons 7 and/or 8 were identified in 68 out of 75 patients (90%). Deletion of exon 5 of the NAIP gene was found in 40/54 of type I, 2/8 of type II and 1/13 of type III patients.

CONCLUSIONS

Deletion of the SMN1 gene is a major cause of SMA in Iran, and NAIP gene deletions were common in the present patients with type I SMA. Also, the incidence of NAIP deletion is higher in more severe SMA.

Deletions in the Survival Motor Neuron Gene in Iranian Patients with Spinal Muscular Atrophy

Introduction: Spinal muscular atrophy (SMA) is a common neuromuscular disorder with progressive paralysis caused by the loss of -motor neurons in the spinal cord. The survival motor neuron (SMN) protein is encoded by 2 genes, SMN1 and SMN2. The most frequent mutation is the biallelic deletion of exon 7 of the SMN1 gene. In SMA, SMN2 cannot compensate for the loss of SMN1, due to the exclusion of exon 7. The aim of our study was to estimate the frequency of the common SMN1 exon 7 deletion in patients referred to our centre for carrier detection and prenatal diagnosis. Materials and Methods: We performed the detection of exon 7 deletion of the SMN1 gene for the affected patients and fetuses suspected to have SMA. Results: Of 243 families, 195 were classified as SMA type I, 30 as type II, and 18 as type III according to their family histories. The analysis of exon 7 deletion among living affected children showed that 94% of the patients with SMA type I, 95% with type II families and 100% with type III had homozygous deletions. Of the prenatal diagnoses, 21 (22.8%) of the 92 fetuses were found to be affected and these pregnancies were terminated. Conclusions: The homozygosity frequency for the deletion of SMN1 exon 7 for all 3 types was (94%), similar to those of Western Europe, China, Japan and Kuwait. Key words: Iranian patients, SMN1

Prenatal diagnosis of spinal muscular atrophy in Macedonian families

Spinal muscular atrophy (SMA) is the second most common lethal autosomal recessive disorder of childhood, affecting approximately 1 in 6,000-10,000 births, with a carrier frequency of 1 in 40-60. There is no effective cure or treatment for this disease. Thus, the availability of prenatal testing is important. The aim of this study was to establish an efficient and rapid method for prenatal diagnosis of SMA and genetic counseling in families with risk for having a child with SMA. In this paper we present the results from prenatal diagnosis in Macedonian SMA families using direct analysis of fetal DNA. The probands of these families were previously found to be homozygous for a deletion of exons 7 and 8 of SMN1 gene. DNA obtained from chorionic villas samples and amniocytes was analyzed for deletions in SMN gene. SMN exon 7 and 8 deletion analysis was performed by polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP). Of the 12 prenatal diagnoses, DNA analysis showed normal results in eight fetuses. Four of the fetuses were homozygote for a deletion of exons 7 and 8 of SMN1. After genetic counseling, the parents of the eight normal fetuses decided to continue the pregnancy, while in the four families with affected fetuses, the pregnancy was terminated. The results were confirmed after birth.

Spinal muscular atrophy

Spinal muscular atrophy is an autosomal recessive neurodegenerative disease characterised by degeneration of spinal cord motor neurons, atrophy of skeletal muscles, and generalised weakness. It is caused by homozygous disruption of the survival motor neuron 1 (SMN1) gene by deletion, conversion, or mutation. Although no medical treatment is available, investigations have elucidated possible mechanisms underlying the molecular pathogenesis of the disease. Treatment strategies have been developed to use the unique genomic structure of the SMN1 gene region. Several candidate treatment agents have been identified and are in various stages of development. These and other advances in medical technology have changed the standard of care for patients with spinal muscular atrophy. In this Seminar, we provide a comprehensive review that integrates clinical manifestations, molecular pathogenesis, diagnostic strategy, therapeutic development, and evidence from clinical trials.

SMN2 and NAIP gene dosages in Vietnamese patients with spinal muscular atrophy

BACKGROUND

The SMN1 gene is now recognized as a spinal muscular atrophy (SMA)-causing gene, while SMN2 and NAIP have been characterized as a modifying factor of the clinical severity of SMA. Gene dosage of SMN2 is associated with clinical severity of SMA. But the relationship between gene dosage of NAIP and clinical severity of SMA remains to be clarified, although complete deletion of NAIP is frequent in type I patients.

METHODS

To evaluate the contribution of the SMN2 and NAIP gene dosages to SMA, quantitative real-time polymerase chain reaction was used to measure copy numbers of SMN2 and NAIP in 34 Vietnamese SMA patients lacking SMN1 (13 type I, 11 type II and 10 type III patients).

RESULTS

The SMN2 copy number in type I patients was significantly lower than that in type II-III patients, which was compatible with the previous reports. In contrast, 25 out of 34 patients had only zero or one copy of NAIP, while 50 out of 52 controls had two or more copies. For NAIP (+) genotype, six out of 13 type I patients, eight out of 11 type II patients and six out of 10 type III patients carried one NAIP copy.

CONCLUSIONS

The SMN2 copy number was related to the clinical severity of SMA among Vietnamese patients. The presence of one NAIP copy, that is, heterozygous NAIP deletion, was common in Vietnamese SMA, regardless of clinical phenotype.

A preliminary report on spinal muscular atrophy lymphoblastoid cell lines: are they an appropriate tool for drug screening?

INTRODUCTION

Spinal muscular atrophy (SMA) is a neurodegenerative disease of the motor neurons that results in progressive muscle weakness. It is also the leading hereditary cause of infant mortality. Homozygous loss of the survival motor neuron (SMN1) gene causes SMA, and the number of copies of the SMN2 gene modulates the severity of the disease. Increasing the expression of the SMN2 gene by pharmacological agents is one of the therapeutic approaches currently being implemented.

METHODS

In this preliminary study, we investigated the effect of phenylbutyrate, a histone deacetylase (HDAC) inhibitor, on SMN2 expression in two SMA type III Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines to understand the suitability of lymphoblastoid cell lines in drug screening. These cell lines are regarded as a good source as they can easily be established from the peripheral leucocytes of patients. Quantitative analysis of SMN2 mRNA was performed on established cell lines treated with various concentrations of phenylbutyrate and for a range of incubation periods using real-time polymerase chain reaction. Western blot analysis was used to determine SMN protein levels.

RESULTS

Real-time polymerase chain reaction and Western blot analysis demonstrated that the levels of SMN2 full-length (fl-SMN2) transcripts and protein were not increased in phenylbutyrate-treated cell lines compared to non-treated controls.

CONCLUSION

These results suggest that EBV-transformed lymphoblastoid cell lines are not suitable for studying the effect of certain HDAC inhibitors on SMN2 gene expression.

Amyotrophic lateral sclerosis: from current developments in the laboratory to clinical implications

Amyotrophic lateral sclerosis (ALS) is a late-onset progressive degeneration of motor neurons occurring both as a sporadic and a familial disease. The etiology of ALS remains unknown, but one fifth of instances are due to specific gene defects, the best characterized of which is point mutations in the gene coding for Cu/Zn superoxide dismutase (SOD1). Because sporadic and familial ALS affect the same neurons with similar pathology, it is hoped that understanding these gene defects will help in devising therapies effective in both forms. A wealth of evidence has been collected in rodents made transgenic for mutant SOD1, which represent the best available models for familial ALS. Mutant SOD1 likely induces selective vulnerability of motor neurons through a combination of several mechanisms, including protein misfolding, mitochondrial dysfunction, oxidative damage, cytoskeletal abnormalities and defective axonal transport, excitotoxicity, inadequate growth factor signaling, and inflammation. Damage within motor neurons is enhanced by noxious signals originating from nonneuronal neighboring cells, where mutant SOD1 induces an inflammatory response that accelerates disease progression. The clinical implication of these findings is that promising therapeutic approaches can be derived from multidrug treatments aimed at the simultaneous interception of damage in both motor neurons and nonmotor neuronal cells.

Exercise-induced activation of NMDA receptor promotes motor unit development and survival in a type 2 spinal muscular atrophy model mouse

Spinal muscular atrophy (SMA) is an inborn neuromuscular disorder caused by low levels of survival motor neuron protein, and for which no efficient therapy exists. Here, we show that the slower rate of postnatal motor-unit maturation observed in type 2 SMA-like mice is correlated with the motor neuron death. Physical exercise delays motor neuron death and leads to an increase in the postnatal maturation rate of the motor-units. Furthermore, exercise is capable of specifically enhancing the expression of the gene encoding the major activating subunit of the NMDA receptor in motor neurons, namely the NR2A subunit, which is dramatically downregulated in the spinal cord of type 2 SMA-like mice. Accordingly, inhibiting NMDA-receptor activity abolishes the exercise-induced effects on muscle development, motor neuron protection and life span gain. Thus, restoring NMDA-receptor function could be a promising therapeutic approach to SMA treatment.

Clinical and genetic study of spinal muscular atrophies in Oman

This article presents a retrospective study and a prospective study on spinal muscular atrophy in Oman. For the retrospective study, data were collected from neurophysiology records, from both inpatient and outpatient files. The prospective study was conducted on children as they presented to the hospital and was funded by Sultan Qaboos University. The patients of spinal muscular atrophy were classified into types I, II, and III based on their clinical features as per the International Spinal Muscular Atrophy Consortium classification. The incidence of spinal muscular atrophy was about 1 per 6000 live births. Spinal muscular atrophy type I formed 65% of the cases. Survival motor neuron deletion was seen in 70% of cases of all types of spinal muscular atrophy. The deletion was 83% in spinal muscular atrophy type I. A further study to look into the nondeletional cases is in progress.

Consensus statement for standard of care in spinal muscular atrophy

Spinal muscular atrophy is a neurodegenerative disease that requires multidisciplinary medical care. Recent progress in the understanding of molecular pathogenesis of spinal muscular atrophy and advances in medical technology have not been matched by similar developments in the care for spinal muscular atrophy patients. Variations in medical practice coupled with differences in family resources and values have resulted in variable clinical outcomes that are likely to compromise valid measure of treatment effects during clinical trials. The International Standard of Care Committee for Spinal Muscular Atrophy was formed in 2005, with a goal of establishing practice guidelines for clinical care of these patients. The 12 core committee members worked with more than 60 spinal muscular atrophy experts in the field through conference calls, e-mail communications, a Delphi survey, and 2 in-person meetings to achieve consensus on 5 care areas: diagnostic/new interventions, pulmonary, gastrointestinal/nutrition, orthopedics/rehabilitation, and palliative care. Consensus was achieved on several topics related to common medical problems in spinal muscular atrophy, diagnostic strategies, recommendations for assessment and monitoring, and therapeutic interventions in each care area. A consensus statement was drafted to address the 5 care areas according to 3 functional levels of the patients: nonsitter, sitter, and walker. The committee also identified several medical practices lacking consensus and warranting further investigation. It is the authors' intention that this document be used as a guideline, not as a practice standard for their care. A practice standard for spinal muscular atrophy is urgently needed to help with the multidisciplinary care of these patients.

Valproic acid promotes neurite outgrowth in PC12 cells independent from regulation of the survival of motoneuron protein

Spinal muscular atrophy (SMA) is a neurodegenerative disorder of motoneurons. The disease is caused by deletions or mutations of the survival of motoneuron gene 1 (SMN1). The amount of protein expressed from the second gene, SMN2, correlated with the severity of the clinical phenotype. The histone deacetylase inhibitor valproic acid (VPA) has been shown to increase the total cellular amount of functional SMN protein and is therefore considered as a drug candidate for treatment of SMA. In this study, we analyzed the effects of VPA in PC12 cells, a model system for neuronal differentiation, with regard to neurite outgrowth and SMN expression. VPA promoted neurite outgrowth in PC12 cells. However, this effect did not correlate with upregulation of SMN protein levels, suggesting a SMN-independent mechanism for VPA regulation of neurite outgrowth.

Expanding the phenotypes of the Pro56Ser VAPB mutation: proximal SMA with dysautonomia

The phenotype of 16 members of a family affected by a late-onset, dominant, progressive, motor and autonomic disorder is described. The VAPB (Pro56Ser) mutation was detected in Brazilian families with different phenotypes of motor neuron disorders. In this family, proximal and axial muscle weakness and atrophy, associated with abdominal protrusion, defined the motor phenotype. Death occurred in 10-15 years due to respiratory insufficiency. Tone and tendon reflexes were decreased and a distal tremor was common. Sensation was preserved. Autonomic abnormalities were also present, including choking, chronic intestinal constipation, sexual dysfunction, and sudomotor abnormalities, and on nerve morphology there was involvement of unmyelinated fibers. Electromyography disclosed ongoing denervation and reinnervation. Isolated dysfunction of motor and autonomic neurons is unusual among the spinal muscular atrophies. On this basis, this condition seems to represent a new category of disease.

Case report: birth after preimplantation genetic diagnosis of a subtle mutation in SMN1 gene

Spinal muscular atrophy (SMA) preimplantation genetic diagnosis (PGD) has been available since 1998. Protocols are based on the detection of the homozygous deletion of exon 7, which are present in 90-98% of SMA patients. A couple where the woman was a heterozygous carrier of the usual SMN1 Del7 mutation and the man was a heterozygous carrier of pMet263Arg substitution in exon 6 of SMN1 gene was referred for PGD. The usual PGD test being unsuitable for this couple, we developed a novel duplex polymerase chain reaction (PCR)-based PGD test for the detection of the mutation pMet263Arg by allele specific amplification, combined with the amplification of D5S641 extragenic polymorphic marker. PCR conditions were established using single control lymphoblasts and lymphocytes from the pMet263Arg substitution carrier. Amplification was obtained in 100% of the 86 single cells tested, amplification refractory mutation system (ARMS) PCR was specific in 100% of single cells tested and a complete genotype (mutation plus D5S641) was achieved in 88% of them. A PGD cycle was performed successfully and a pregnancy was obtained. An unaffected girl was born and postnatal diagnosis confirmed PGD results. This is the first PGD described for SMA because of another mutation than the major homozygous exon 7 deletion of SMN1. In the future, a similar strategy could be adopted for other subtle mutations of this gene.

The spinal muscular atrophy gene product regulates neurite outgrowth: importance of the C terminus

Spinal muscular atrophy is a neurodegenerative disease accompanied by a loss of motoneurons. Either mutations or deletions in the survival of motoneuron (SMN) gene are responsible for this defect. SMN is an assembly protein for RNA-protein complexes in the nucleus and is also found in axons of neurons. However, it is unclear which dysfunctions of SMN are important for disease progression. In this study we analyzed the contributions of different SMN regions for localization and neuronal differentiation associated with outgrowth of neurites. Suppression of endogenous SMN protein levels significantly decreased the growth of neurites. Down-regulation of the interacting protein gemin2 had the opposite effect. Surprisingly, selective overexpression of the SMN C-terminal domain promoted neurite outgrowth similar to full-length protein and could rescue the SMN knock-down effects. The knock-down led to a significant change in the G-/F-actin ratio, indicating a role for SMN in actin dynamics. Therefore, our data suggest a functional role for SMN in microfilament metabolism in axons of motoneurons.

Deletion analyses of SMN1 and NAIP genes in Malaysian spinal muscular atrophy patients

BACKGROUND

The survival motor neuron 1 (SMN1) gene has been recognized to be responsible for spinal muscular atrophy (SMA) because it is homozygously deleted in more than 90% of SMA patients, irrespective of their clinical severity, whereas the neuronal apoptosis inhibitory protein (NAIP) gene is now considered to be a modifying factor of the severity of SMA. In Malaysia, it remains to be elucidated whether deletion of the SMN1 gene is also a main cause of SMA or whether deletion of the NAIP gene is found in the SMA patients.

METHODS

To clarify the pathogenesis of SMA in Malaysia, a deletion analysis of the SMN1 and NAIP genes was performed in 24 Malaysian SMA patients. Deletion analysis of exons 7 and 8 of the SMN1 gene was performed according to the method described by van der Steege et al., while deletion analysis of exon 5 of the NAIP gene was performed according to a method described by Roy et al.

RESULTS

Homozygous deletion of SMN1 exon 7 and exon 8 were identified in 19 out of 24 patients (79%). As to the NAIP gene, deletion of exon 5 was detected in six out of 24 patients (25%). NAIP gene deletion was correlated with severity of the disease.

CONCLUSIONS

Deletion of the SMN1 exon 7 is a major cause of SMA in Malaysia, and NAIP gene deletions are not rare in type I SMA in Malaysia. The lower percentage of the SMN1 gene deletion may be due to the possibility that the present study included some patients without SMN1 gene abnormality and/or some patients with non-deletion type mutations in the SMN1 gene.