Spinal muscular atrophy

iPSCs and small molecules: a reciprocal effort towards better approaches for drug discovery

The revolutionary induced pluripotent stem cell (iPSC) technology provides a new path for cell replacement therapies and drug screening. Patient-specific iPSCs and subsequent differentiated cells manifesting disease phenotypes will finally position human disease pathology at the core of drug discovery. Cells used to test the toxic effects of drugs can also be generated from normal iPSCs and provide a much more accurate and cost-effective system than many animal models. Here, we highlight the recent progress in iPSC-based cell therapy, disease modeling and drug evaluations. In addition, we discuss the use of small molecule drugs to improve the generation of iPSCs and understand the reprogramming mechanism. It is foreseeable that the interplay between iPSC technology and small molecule compounds will push forward the applications of iPSC-based therapy and screening systems in the real world and eventually revolutionize the methods used to treat diseases.

A homozygous double mutation in SMN1: a complicated genetic diagnosis of SMA

Spinal muscular atrophy (SMA), the most common autosomal recessive cause of infant death, is typically diagnosed by determination of SMN1 copy number. Approximately 3–5% of patients with SMA retain at least one copy of the SMN1 gene carrying pathogenic insertions, deletions, or point mutations. We report a patient with SMA who is homozygous for two mutations carried in cis: an 8 bp duplication (c.48_55dupGGATTCCG; p.Val19fs*24) and a point mutation (c.662C>T; p.Pro221Leu). The consanguineous parents carry the same two mutations within one SMN1 gene copy. We demonstrate that a more accurate diagnosis of the disease is obtained through a novel diagnostic assay and development of a capillary electrophoresis method to determine the copy number of their mutant alleles. This illustrates the complexity of SMN mutations and suggests additional testing (gene sequencing) may be appropriate when based on family lines.

Small molecule screen reveals regulation of survival motor neuron protein abundance by Ras proteins

Small molecule modulators of protein activity have proven invaluable in the study of protein function and regulation. While inhibitors of protein activity are relatively common, small molecules that can increase protein abundance are rare. Small molecule protein upregulators with targeted activities would be of value in the study of the mechanisms underlying loss-of-function diseases. We developed a high-throughput screening approach to identify small molecule upregulators of the Survival of Motor Neuron protein (SMN), whose decreased levels cause the neurodegenerative disease spinal muscular atrophy (SMA). We screened 69,189 compounds for SMN upregulators and performed mechanistic studies on the most active compound, a bromobenzophenone analogue designated cuspin-1. Mechanistic studies of cuspin-1 revealed that increasing Ras signaling upregulates SMN protein abundance via an increase in translation rate. These findings suggest that controlled modulation of the Ras signaling pathway may benefit patients with SMA.

Type III spinal muscular atrophy mimicking muscular dystrophies

Types III and IV spinal muscular atrophy represent a diagnostic challenge due to the great variability in their presentation. We report a series of eight patients with type III spinal muscular atrophy who were followed for a long time for possible muscular dystrophy or myopathy, confirming its clinical heterogeneity and propensity to delayed diagnosis. Clinical examination revealed heterogeneous findings, where the diagnosis of type III spinal muscular atrophy was not immediately apparent in many patients as their clinical and laboratory abnormalities were consistent with muscular dystrophy or myopathy. The presence of dystrophic features such as hypertrophy of the calves, weakness of the limb girdle, high serum creatine kinase levels, and myopathic histopathology should not divert attention from the possibility of spinal muscular atrophy. It is strongly recommended to give variable presentations enough thought and to consider the autosomal recessive type III spinal muscular atrophy in the diagnostic evaluation.

Splicing therapy for neuromuscular disease

Duchenne muscular dystrophy (DMD) and spinal muscular atrophy (SMA) are two of the most common inherited neuromuscular diseases in humans. Both conditions are fatal and no clinically available treatments are able to significantly alter disease course in either case. However, by manipulation of pre-mRNA splicing using antisense oligonucleotides, defective transcripts from the DMD gene and from the SMN2 gene in SMA can be modified to once again produce protein and restore function. A large number of in vitro and in vivo studies have validated the applicability of this approach and an increasing number of preliminary clinical trials have either been completed or are under way. Several different oligonucleotide chemistries can be used for this purpose and various strategies are being developed to facilitate increased delivery efficiency and prolonged therapeutic effect. As these novel therapeutic compounds start to enter the clinical arena, attention must also be drawn to the question of how best to facilitate the clinical development of such personalised genetic therapies and how best to implement their provision.

SMA-EUROPE workshop report: Opportunities and challenges in developing clinical trials for spinal muscular atrophy in Europe

Spinal muscular atrophy (SMA) is the most common lethal recessive disease in childhood, and there is currently no effective treatment to halt disease progression. The translation of scientific advances into effective therapies is hampered by major roadblocks in clinical trials, including the complex regulatory environment in Europe, variations in standards of care, patient ascertainment and enrolment, a narrow therapeutic window and a lack of biomarkers of efficacy. In this context, SMA-Europe organized its first international workshop in July 2012 in Rome, gathering 34 scientists, clinicians and representatives of patient organizations to establish recommendations for improving clinical trials for SMAa.

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.

Actin isoforms in neuronal development and function

The actin cytoskeleton contributes directly or indirectly to nearly every aspect of neuronal development and function. This diversity of functions is often attributed to actin regulatory proteins, although how the composition of the actin cytoskeleton itself may influence its function is often overlooked. In neurons, the actin cytoskeleton is composed of two distinct isoforms, β- and γ-actin. Functions for β-actin have been investigated in axon guidance, synaptogenesis, and disease. Insight from loss-of-function in vivo studies has also revealed novel roles for β-actin in select brain structures and behaviors. Conversely, very little is known regarding functions of γ-actin in neurons. The dysregulation or mutation of both β- and γ-actin has been implicated in multiple human neurological disorders, however, demonstrating the critical importance of these still poorly understood proteins. This chapter highlights what is currently known regarding potential distinct functions for β- and γ-actin in neurons as well as the significant areas that remain unexplored.

Morphological characteristics of motor neurons do not determine their relative susceptibility to degeneration in a mouse model of severe spinal muscular atrophy

Spinal muscular atrophy (SMA) is a leading genetic cause of infant mortality, resulting primarily from the degeneration and loss of lower motor neurons. Studies using mouse models of SMA have revealed widespread heterogeneity in the susceptibility of individual motor neurons to neurodegeneration, but the underlying reasons remain unclear. Data from related motor neuron diseases, such as amyotrophic lateral sclerosis (ALS), suggest that morphological properties of motor neurons may regulate susceptibility: in ALS larger motor units innervating fast-twitch muscles degenerate first. We therefore set out to determine whether intrinsic morphological characteristics of motor neurons influenced their relative vulnerability to SMA. Motor neuron vulnerability was mapped across 10 muscle groups in SMA mice. Neither the position of the muscle in the body, nor the fibre type of the muscle innervated, influenced susceptibility. Morphological properties of vulnerable and disease-resistant motor neurons were then determined from single motor units reconstructed in Thy.1-YFP-H mice. None of the parameters we investigated in healthy young adult mice - including motor unit size, motor unit arbor length, branching patterns, motor endplate size, developmental pruning and numbers of terminal Schwann cells at neuromuscular junctions - correlated with vulnerability. We conclude that morphological characteristics of motor neurons are not a major determinant of disease-susceptibility in SMA, in stark contrast to related forms of motor neuron disease such as ALS. This suggests that subtle molecular differences between motor neurons, or extrinsic factors arising from other cell types, are more likely to determine relative susceptibility in SMA.

Electrophysiological and motor function scale association in a pre-symptomatic infant with spinal muscular atrophy type I

A term infant, at familial risk for spinal muscular atrophy (SMA), had the diagnosis genetically confirmed on day 3 of life. Clinical evaluation, the CHOP INTEND motor scale and the CMAP amplitude were obtained on days 5 (pre-symptomatic), 20 (mildly weak), 34 (moderately weak) and 63 (severely weak). Palliative care was provided and he expired of an acute pulmonary infection on day 81. The CMAP amplitude and INTEND scores were initially in the normal range, then followed a corresponding decline to a nadir at day 34 and remained so at the 4th assessment. A log-transformed plot of CMAP amplitude from days 5-34 was linear. These data suggest that early motor neuron loss in SMA type I may be logarithmic and demonstrates that the INTEND motor scale closely follows the CMAP electrophysiological biomarker. This single case report supports the consideration that early intervention with a potential therapy is necessary, before the pool of functional motor neurons has plummeted. Further study of these parameters in pre-symptomatic infants with SMA type I will help guide the design of future intervention studies.

Amyotrophic lateral sclerosis: new insights into underlying molecular mechanisms and opportunities for therapeutic intervention

Recent years have witnessed a renewed interest in the pathogenic mechanisms of amyotrophic lateral sclerosis (ALS), a late-onset progressive degeneration of motor neurons. The discovery of new genes associated with the familial form of the disease, along with a deeper insight into pathways already described for this disease, has led scientists to reconsider previous postulates. While protein misfolding, mitochondrial dysfunction, oxidative damage, defective axonal transport, and excitotoxicity have not been dismissed, they need to be re-examined as contributors to the onset or progression of ALS in the light of the current knowledge that the mutations of proteins involved in RNA processing, apparently unrelated to the previous "old partners," are causative of the same phenotype. Thus, newly envisaged models and tools may offer unforeseen clues on the etiology of this disease and hopefully provide the key to treatment.

TSUNAMI: an antisense method to phenocopy splicing-associated diseases in animals

Antisense oligonucleotides (ASOs) are versatile molecules that can be designed to specifically alter splicing patterns of target pre-mRNAs. Here we exploit this feature to phenocopy a genetic disease. Spinal muscular atrophy (SMA) is a motor neuron disease caused by loss-of-function mutations in the SMN1 gene. The related SMN2 gene expresses suboptimal levels of functional SMN protein due to alternative splicing that skips exon 7; correcting this defect-e.g., with ASOs-is a promising therapeutic approach. We describe the use of ASOs that exacerbate SMN2 missplicing and phenocopy SMA in a dose-dependent manner when administered to transgenic Smn(-/-) mice. Intracerebroventricular ASO injection in neonatal mice recapitulates SMA-like progressive motor dysfunction, growth impairment, and shortened life span, with α-motor neuron loss and abnormal neuromuscular junctions. These SMA-like phenotypes are prevented by a therapeutic ASO that restores correct SMN2 splicing. We uncovered starvation-induced splicing changes, particularly in SMN2, which likely accelerate disease progression. These results constitute proof of principle that ASOs designed to cause sustained splicing defects can be used to induce pathogenesis and rapidly and accurately model splicing-associated diseases in animals. This approach allows the dissection of pathogenesis mechanisms, including spatial and temporal features of disease onset and progression, as well as testing of candidate therapeutics.

Triptolide increases transcript and protein levels of survival motor neurons in human SMA fibroblasts and improves survival in SMA-like mice

BACKGROUND AND PURPOSE

Spinal muscular atrophy (SMA) is a progressive neuromuscular disease. Since disease severity is related to the amount of survival motor neuron (SMN) protein, up-regulated functional SMN protein levels from the SMN2 gene are considered a major SMA drug-discovery strategy. In this study, we investigated the possible effects of triptolide, a diterpene triepoxide purified from Tripterygium wilfordii Hook. F., as a new compound for increasing SMN protein.

EXPERIMENTAL APPROACH

The effects and mechanisms of triptolide on the production of SMA protein were determined by cell-based assays using the motor neuronal cell line NSC34 and skin fibroblasts from SMA patients. Wild-type (Smn(+/+) SMN2(-/-) , C57BL/6) and SMA-like (Smn(-/-) SMN2) mice were injected with triptolide (0.01 or 0.1 mg·kg(-1) ·day(-1) , i.p.) and their survival rate and level of change in SMN protein in neurons and muscle tissue measured.

KEY RESULTS

In NSC34 cells and human SMA fibroblasts, pM concentrations of triptolide significantly increased SMN protein expression and the levels of SMN complex component (Gemin2 and Gemin3). In human SMA fibroblasts, triptolide increased SMN-containing nuclear gems and the ratio of full-length transcripts (FL-SMN2) to SMN2 transcripts lacking exon 7 (SMN2Δ7). Furthermore, in SMA-like mice, triptolide significantly increased SMN protein levels in the brain, spinal cord and gastrocnemius muscle. Furthermore, triptolide treatment increased survival and reduced weight loss in SMA-like mice.

CONCLUSION AND IMPLICATIONS

Triptolide enhanced SMN protein production by promoting SMN2 activation, exon 7 inclusion and increasing nuclear gems, and increased survival in SMA mice, which suggests triptolide might be a potential candidate for SMA therapy.

Genome-wide approaches to dissect the roles of RNA binding proteins in translational control: implications for neurological diseases

Translational control of messenger RNAs (mRNAs) is a key aspect of neurobiology, defects of which can lead to neurological diseases. In response to stimuli, local translation of mRNAs is activated at synapses to facilitate long-lasting forms of synaptic plasticity, the cellular basis for learning, and memory formation. Translation, as well as all other aspects of RNA metabolism, is controlled in part by RNA binding proteins (RBPs) that directly interact with mRNAs to form mRNA-protein complexes. Disruption of RBP function is becoming widely recognized as a major cause of neurological diseases. Thus understanding the mechanisms that govern the interplay between translation control and RBP regulation in both normal and diseased neurons will provide new opportunities for novel diagnostics and therapeutic intervention. As a means of studying translational control, genome-wide methods are emerging as powerful tools that have already begun to unveil mechanisms that are missed by single-gene studies. Here, we describe the roles of RBPs in translational control, review genome-wide approaches to examine translational control, and discuss how the application of these approaches may provide mechanistic insight into the pathogenic underpinnings of RBPs in neurological diseases.

Solution structure of the core SMN-Gemin2 complex

In humans, assembly of spliceosomal snRNPs (small nuclear ribonucleoproteins) begins in the cytoplasm where the multi-protein SMN (survival of motor neuron) complex mediates the formation of a seven-membered ring of Sm proteins on to a conserved site of the snRNA (small nuclear RNA). The SMN complex contains the SMN protein Gemin2 and several additional Gemins that participate in snRNP biosynthesis. SMN was first identified as the product of a gene found to be deleted or mutated in patients with the neurodegenerative disease SMA (spinal muscular atrophy), the leading genetic cause of infant mortality. In the present study, we report the solution structure of Gemin2 bound to the Gemin2-binding domain of SMN determined by NMR spectroscopy. This complex reveals the structure of Gemin2, how Gemin2 binds to SMN and the roles of conserved SMN residues near the binding interface. Surprisingly, several conserved SMN residues, including the sites of two SMA patient mutations, are not required for binding to Gemin2. Instead, they form a conserved SMN/Gemin2 surface that may be functionally important for snRNP assembly. The SMN-Gemin2 structure explains how Gemin2 is stabilized by SMN and establishes a framework for structure-function studies to investigate snRNP biogenesis as well as biological processes involving Gemin2 that do not involve snRNP assembly.

Human pluripotent stem cells: applications and challenges in neurological diseases

The ability to generate human pluripotent stem cells (hPSCs) holds great promise for the understanding and the treatment of human neurological diseases in modern medicine. The hPSCs are considered for their in vitro use as research tools to provide relevant cellular model for human diseases, drug discovery, and toxicity assays and for their in vivo use in regenerative medicine applications. In this review, we highlight recent progress, promises, and challenges of hPSC applications in human neurological disease modeling and therapies.

Common pathways of autoimmune inflammatory myopathies and genetic neuromuscular disorders

It has been shown that many hereditary motor neuron diseases are caused by mutation of RNA processing enzymes. Survival of motor neuron 1 (SMN1) is well-known as a causative gene for spinal muscular atrophy (SMA) and mutations of glycyl- and tyrosyl-tRNA synthetases are identified as a cause of distal SMA and Charcot-Marie-Tooth disease. Why and how the dysfunction of these ubiquitously expressed genes involved in RNA processing can cause a specific neurological disorder is not well understood. Interestingly, SMN complex has been identified recently as a new target of autoantibodies in polymyositis (PM). Autoantibodies in systemic rheumatic diseases are clinically useful biomarkers associated with a particular diagnosis, subset of a disease, or certain clinical characteristics. Many autoantibodies produced in patients with polymyositis/dermatomyositis (PM/DM) target RNA-protein complexes such as aminoacyl tRNA synthetases. It is interesting to note these same RNA-protein complexes recognized by autoantibodies in PM/DM are also responsible for genetic neuromuscular disease. Certain RNA-protein complexes are also targets of autoantibodies in paraneoplastic neurological disorders. Thus, there are several interesting associations between RNA-processing enzymes and neuromuscular disorders. Although pathogenetic roles of autoantibodies to intracellular antigens are generally considered unlikely, understanding the mechanisms of antigen selection in a particular disease and specific neurological symptoms caused by disruption of ubiquitous RNA-processing enzyme may help identify a common path in genetic neuromuscular disorders and autoimmunity in inflammatory myopathies.

Activation of the stress proteome as a mechanism for small molecule therapeutics

Various small molecule pharmacologic agents with different known functions produce similar outcomes in diverse Mendelian and complex disorders, suggesting that they may induce common cellular effects. These molecules include histone deacetylase inhibitors, 4-phenylbutyrate (4PBA) and trichostatin A, and two small molecules without direct histone deacetylase inhibitor activity, hydroxyurea (HU) and sulforaphane. In some cases, the therapeutic effects of histone deacetylase inhibitors have been attributed to an increase in expression of genes related to the disease-causing gene. However, here we show that the pharmacological induction of mitochondrial biogenesis was necessary for the potentially therapeutic effects of 4PBA or HU in two distinct disease models, X-linked adrenoleukodystrophy and sickle cell disease. We hypothesized that a common cellular response to these four molecules is induction of mitochondrial biogenesis and peroxisome proliferation and activation of the stress proteome, or adaptive cell survival response. Treatment of human fibroblasts with these four agents induced mitochondrial and peroxisomal biogenesis as monitored by flow cytometry, immunofluorescence and/or western analyses. In treated normal human fibroblasts, all four agents induced the adaptive cell survival response: heat shock, unfolded protein, autophagic and antioxidant responses and the c-jun N-terminal kinase pathway, at the transcriptional and translational levels. Thus, activation of the evolutionarily conserved stress proteome and mitochondrial biogenesis may be a common cellular response to such small molecule therapy and a common basis of therapeutic action in various diseases. Modulation of this novel therapeutic target could broaden the range of treatable diseases without directly targeting the causative genetic abnormalities.

Assessing electrical impedance alterations in spinal muscular atrophy via the finite element method

Electrical impedance myography (EIM) is a surface-based, non-invasive technique of evaluation of muscle health, involving the application of high frequency, low-amplitude current to the skin over a muscle of interest. Results from a previous animal study suggest that the finite element method can relate disease-induced changes in electrical properties of the muscle to alterations in surface impedance measurements; however, whether such an approach will prove useful in human models is uncertain. Therefore, to further investigate this question, we have created a single finite element model of the human biceps muscle using data from one healthy subject and one with spinal muscular atrophy (SMA), each of whom had comparable age, limb girth, muscle size, and subcutaneous fat thickness. Since healthy human tissue was unavailable, permittivity and conductivity measurements were obtained from five healthy and five advanced amyotrophic lateral sclerosis rat gastrocnemius muscles immediately after sacrifice; their data were input into the human biceps model and the expected surface voltages calculated. We then compared the results of this model to the actual surface EIM data for both individuals. Although the actual resistance and reactance values varied and the peak values were displaced, the resulting maximum phase predicted by the model approximated that obtained with surface recordings. These results support that alterations in the primary characteristics of muscle impact the surface impedance measurements in meaningful and likely predictable ways.

Childhood spinal muscular atrophy: controversies and challenges

Spinal muscular atrophy is an autosomal recessive disorder characterised by degeneration of motor neurons in the spinal cord and is caused by mutations of the survival of motor neuron 1 gene SMN1. The severity of spinal muscular atrophy is highly variable and no cure is available at present. Consensus has been reached on several aspects of care, the availability of which can have a substantial effect on prognosis, but controversies remain. The development of standards of care for children with the disorder and the identification of promising treatment strategies have changed the natural history of spinal muscular atrophy, and the prospects are good for further improvements in function, quality of life, and survival. A long-term benefit for patients will be the development of effective interventions (such as antisense oligonucleotides), some of which are in clinical trials. The need to be prepared for clinical trials has been the impetus for a remarkable and unprecedented cooperation between clinicians, scientists, industry, government, and volunteer organisations on an international scale.

Human axonal survival of motor neuron (a-SMN) protein stimulates axon growth, cell motility, C-C motif ligand 2 (CCL2), and insulin-like growth factor-1 (IGF1) production

Spinal muscular atrophy is a fatal genetic disease of motoneurons due to loss of full-length survival of motor neuron protein, the main product of the disease gene SMN1. Axonal SMN (a-SMN) is an alternatively spliced isoform of SMN1, generated by retention of intron 3. To study a-SMN function, we generated cellular clones for the expression of the protein in mouse motoneuron-like NSC34 cells. The model was instrumental in providing evidence that a-SMN decreases cell growth and plays an important role in the processes of axon growth and cellular motility. In our conditions, low levels of a-SMN expression were sufficient to trigger the observed biological effects, which were not modified by further increasing the amounts of the expressed protein. Differential transcriptome analysis led to the identification of novel a-SMN-regulated factors, i.e. the transcripts coding for the two chemokines, C-C motif ligands 2 and 7 (CCL2 and CCL7), as well as the neuronal and myotrophic factor, insulin-like growth factor-1 (IGF1). a-SMN-dependent induction of CCL2 and IGF1 mRNAs resulted in increased intracellular levels and secretion of the respective protein products. Induction of CCL2 contributes to the a-SMN effects, mediating part of the action on axon growth and random cell motility, as indicated by chemokine knockdown and re-addition studies. Our results shed new light on a-SMN function and the underlying molecular mechanisms. The data provide a rational framework to understand the role of a-SMN deficiency in the etiopathogenesis of spinal muscular atrophy.

International survey of physician recommendation for tracheostomy for Spinal Muscular Atrophy Type I

The ethics of invasive mechanical ventilation for children with the neurodegenerative disease Spinal Muscular Atrophy Type I (SMA I) is highly debated, and wide variability in clinical outcomes exists internationally. We conducted this international survey to identify physician characteristics associated with recommendation for tracheostomy and ventilation for SMA I. A cross-sectional online survey was distributed to 1,772 pediatric pulmonologists and pediatric intensivists from online membership directories of American Thoracic Society, American College of Chest Physicians, and European Respiratory Society. Questions explored physician demographics, attitudes and experience with SMA and end-of-life care, knowledge of consensus guidelines, and recommendations for respiratory care of SMA I. A logistic regression model assessed the independent effects of physician variables on the recommendation for invasive ventilation for SMA I. A total of 367 (21%) physicians completed the survey; 82% were pediatric pulmonologists; and 16% pediatric intensivists. Seventy percent of respondents were from the U.S. Fifty percent of physicians were aware of SMA consensus guidelines. Physicians from Commonwealth countries (U.K., Canada, Australia, etc.) were less likely to recommend tracheostomy/ventilation than U.S. physicians (7% vs. 25%, P = 0.005). Logistic regression modeling identified years of experience, pediatric pulmonology specialty, agreement with a pro-life statement, and recommendation for non-invasive ventilation as predictive of recommendation for long-term invasive ventilation for SMA I. In the largest international survey on this topic, we identified regional differences in physician recommendation for invasive ventilation for children with SMA I. Our data demonstrate a need for increased awareness of consensus guidelines and further dialog about the physician role in variability of care for children with SMA I.

Inherited neuromuscular disorders: pathway to diagnosis

Muscle weakness in childhood can be caused by a lesion at any point extending from the motor cortex, brainstem and spinal cord to the anterior horn cell, peripheral nerve, neuromuscular junction and muscle. A comprehensive history and physical examination is essential to aid classification of the neuromuscular disorder and direct gene testing. The more common disorders such as spinal muscular atrophy, Duchenne muscular dystrophy, myotonic dystrophy and facioscapulohumeral dystrophy may be diagnosed on direct gene testing based on the history and clinical examination. The congenital myopathies are classified based on structural abnormalities on muscle biopsy, while protein abnormalities on immunohistochemistry and immunoblotting aid classification of the muscular dystrophies. In this review, we provide an approach to diagnosis of a child with weakness, with a focus on the inherited neuromuscular disorders, and the features on history, examination and investigation that help to distinguish between them.

Therapy development for spinal muscular atrophy in SMN independent targets

Spinal muscular atrophy (SMA) is an autosomal recessive neurodegenerative disorder, leading to progressive muscle weakness, atrophy, and sometimes premature death. SMA is caused by mutation or deletion of the survival motor neuron-1 (SMN1) gene. An effective treatment does not presently exist. Since the severity of the SMA phenotype is inversely correlated with expression levels of SMN, the SMN-encoded protein, SMN is the most important therapeutic target for development of an effective treatment for SMA. In recent years, numerous SMN independent targets and therapeutic strategies have been demonstrated to have potential roles in SMA treatment. For example, some neurotrophic, antiapoptotic, and myotrophic factors are able to promote survival of motor neurons or improve muscle strength shown in SMA mouse models or clinical trials. Plastin-3, cpg15, and a Rho-kinase inhibitor regulate axonal dynamics and might reduce the influences of SMN depletion in disarrangement of neuromuscular junction. Stem cell transplantation in SMA model mice resulted in improvement of motor behaviors and extension of survival, likely from trophic support. Although most therapies are still under investigation, these nonclassical treatments might provide an adjunctive method for future SMA therapy.

Altered gene expression, mitochondrial damage and oxidative stress: converging routes in motor neuron degeneration

Motor neuron diseases (MNDs) are a rather heterogeneous group of diseases, with either sporadic or genetic origin or both, all characterized by the progressive degeneration of motor neurons. At the cellular level, MNDs share features such as protein misfolding and aggregation, mitochondrial damage and energy deficit, and excitotoxicity and calcium mishandling. This is particularly well demonstrated in ALS, where both sporadic and familial forms share the same symptoms and pathological phenotype, with a prominent role for mitochondrial damage and resulting oxidative stress. Based on recent data, however, altered control of gene expression seems to be a most relevant, and previously overlooked, player in MNDs. Here we discuss which may be the links that make pathways apparently as different as altered gene expression, mitochondrial damage, and oxidative stress converge to generate a similar motoneuron-toxic phenotype.

Spinal muscular atrophy type 1: are proactive respiratory interventions associated with longer survival?

CONTEXT

Spinal muscular atrophy type 1, an autosomal recessive motor neuron disease, is a leading genetic cause of death in infancy and early childhood.

OBJECTIVE

To determine whether the early initiation of noninvasive respiratory interventions is associated with longer survival.

DESIGN

Single-institution retrospective cohort study identified children with spinal muscular atrophy type 1 from January 1, 2002 to May 1, 2009 who were followed for 2.3 mean yrs.

SETTING

Tertiary care children's hospital and outpatient clinics in a vertically integrated healthcare system.

PATIENTS OR OTHER PARTICIPANTS

Forty-nine children with spinal muscular atrophy type 1 were grouped according to the level of respiratory support their caregivers chose within the first 3 months after diagnosis: proactive respiratory care (n = 26) and supportive care (n = 23).

INTERVENTIONS

Proactive respiratory care included bilevel noninvasive ventilation during sleep and twice a day cough assist while supportive respiratory care included suctioning, with or without supplemental oxygen.

MEASUREMENTS AND MAIN RESULTS

Kaplan-Meier survival curves were assessed based on intention to treat. Children treated with early proactive respiratory support had statistically longer survival compared to supportive care (log rank 0.047); however, the adjusted hazard ratio for survival was not statistically different (2.44 [95% confidence interval 0.84-7.1]). Children in the proactive group were more likely to be hospitalized for respiratory insufficiency (83% vs. 46%) and had shortened time after diagnosis until first hospital admission for respiratory insufficiency (median 118 vs. 979 days).

CONCLUSION

Longer survival time with spinal muscular atrophy type 1 is associated with early, noninvasive respiratory care interventions after diagnosis.

Drug treatment for spinal muscular atrophy types II and III

BACKGROUND

Spinal muscular atrophy (SMA) is caused by degeneration of anterior horn cells, which leads to progressive muscle weakness. Children with SMA type II do not develop the ability to walk without support and have a shortened life expectancy, whereas children with SMA type III develop the ability to walk and have a normal life expectancy. There are no known efficacious drug treatments that influence the disease course of SMA. This is an update of a review first published in 2009.

OBJECTIVES

To evaluate whether drug treatment is able to slow or arrest the disease progression of SMA types II and III and to assess if such therapy can be given safely. Drug treatment for SMA type I is the topic of a separate updated Cochrane review.

SEARCH METHODS

We searched the Cochrane Neuromuscular Disease Group Specialized Register (8 March 2011), Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2011, Issue 1), MEDLINE (January 1991 to February 2011), EMBASE (January 1991 to February 2011) and ISI Web of Knowledge (January 1991 to March 8 2011). We also searched clinicaltrials.gov to identify as yet unpublished trials (8 March 2011).

SELECTION CRITERIA

We sought all randomised or quasi-randomised trials that examined the efficacy of drug treatment for SMA types II and III. Participants had to fulfil the clinical criteria and have a deletion or mutation of the survival motor neuron 1 (SMN1) gene (5q11.2-13.2) that was confirmed by genetic analysis.The primary outcome measure was to be change in disability score within one year after the onset of treatment. Secondary outcome measures within one year after the onset of treatment were to be change in muscle strength, ability to stand or walk, change in quality of life, time from the start of treatment until death or full time ventilation and adverse events attributable to treatment during the trial period.

DATA COLLECTION AND ANALYSIS

Two authors independently reviewed and extracted data from all potentially relevant trials. Pooled relative risks and pooled standardised mean differences were to be calculated to assess treatment efficacy. Risk of bias was systematically analysed.

MAIN RESULTS

Six randomised placebo-controlled trials on treatment for SMA types II and III were found and included in the review: the four in the original review and two trials added in this update. The treatments were creatine (55 participants), phenylbutyrate (107 participants), gabapentin (84 participants), thyrotropin releasing hormone (9 participants), hydroxyurea (57 participants), and combination therapy with valproate and acetyl-L-carnitine (61 participants). None of these studies were completely free of bias. All studies had adequate blinding, sequence generation and reports of primary outcomes.None of the included trials showed any statistically significant effects on the outcome measures in participants with SMA types II and III. One participant died due to suffocation in the hydroxyurea trial and one participant died in the creatine trial. No participants in any of the other four trials died or reached the state of full time ventilation. Serious side effects were infrequent.

AUTHORS' CONCLUSIONS

There is no proven efficacious drug treatment for SMA types II and III.

Drug treatment for spinal muscular atrophy type I

BACKGROUND

Spinal muscular atrophy (SMA) is caused by degeneration of anterior horn cells of the spinal cord, which leads to progressive muscle weakness. Children with SMA type I will never be able to sit without support and usually die by the age of two years. There are no known efficacious drug treatments that influence the course of the disease. This is an update of a review first published in 2009.

OBJECTIVES

To evaluate whether drug treatment is able to slow or arrest the disease progression of SMA type I, and to assess if such therapy can be given safely. Drug treatment for SMA types II and III is the topic of a separate updated Cochrane review.

SEARCH METHODS

We searched the Cochrane Neuromuscular Disease Group Specialized Register (8 March 2011), CENTRAL (The Cochrane Library 2011, Issue 1), MEDLINE (January 1991 to February 2011), EMBASE (January 1991 to February 2011) and ISI Web of Knowledge (January 1991 to 8 March 2011). We searched the Clinical Trials Registry of the U.S. National Institute of Health (www.ClinicalTrials.gov) (8 March 2011) to identify additional trials that had not yet been published.

SELECTION CRITERIA

We sought all randomised or quasi-randomised trials that examined the efficacy of drug treatment for SMA type I. Participants had to fulfil the clinical criteria and have a deletion or mutation of the SMN1 gene (5q11.2-13.2) confirmed by genetic analysis.The primary outcome measure was time from birth until death or full time ventilation. Secondary outcome measures were development of rolling, sitting or standing within one year after the onset of treatment, and adverse events attributable to treatment during the trial period.

DATA COLLECTION AND ANALYSIS

Two authors (RW and AV) independently reviewed and extracted data from all potentially relevant trials. For included studies, pooled relative risks and standardised mean differences were to be calculated to assess treatment efficacy.

MAIN RESULTS

One small randomised controlled study comparing riluzole treatment to placebo for 10 SMA type 1 children was identified and included in the original review. No further trials were identified for the update in 2011. Regarding the primary outcome measure, three of seven children treated with riluzole were still alive at the ages of 30, 48 and 64 months, whereas all three children in the placebo group died; but the difference was not statistically significant. Regarding the secondary outcome measures, none of the children in the riluzole or placebo group developed the ability to roll, sit or stand, and no adverse effects were observed. For several reasons the overall quality of the study was low, mainly because the study was too small to detect an effect and because of baseline differences. Follow-up of the 10 included children was complete.

AUTHORS' CONCLUSIONS

No drug treatment for SMA type I has been proven to have significant efficacy.

The natural history of infant spinal muscular atrophy in China: a study of 237 patients

The authors retrospectively studied the natural history of 237 patients with infantile spinal muscular atrophy in China. The onset ages (mean ± SD) for types I to III were 3.1 ± 2.7, 8.7 ± 3.8, and 21.1 ± 11.7 months, respectively. The survival probabilities for type I patients at 1, 2, and 5 years were 44.9%, 38.1%, and 29.3%, respectively, and for type II patients, the probabilities were 100%, 100%, and 97%, respectively. All type III patients were alive. Type I patients with onset age after 2 months had significantly increased survival than those with onset before 2 months (P < .05). It should be noticed that survival probability at 2 years in type I patients in our study was close to that in other Asian samples of spinal muscular atrophy, but slightly better than that among whites. Patients accepted minimal proactive interventions other than antibiotics for pulmonary infection, so our study provides reliable baseline data of natural history of spinal muscular atrophy in China.

Brief report: phenotypic rescue of induced pluripotent stem cell-derived motoneurons of a spinal muscular atrophy patient

Spinal muscular atrophy (SMA) is one of the most common autosomal recessive disorders in humans and is a common genetic cause of infant mortality. The disease is caused by loss of the survival of motoneuron (SMN) protein, resulting in the degeneration of alpha motoneurons in spinal cord and muscular atrophy in the limbs and trunk. One function of SMN involves RNA splicing. It is unclear why a deficiency in a housekeeping function such as RNA splicing causes profound effects only on motoneurons but not on other cell types. One difficulty in studying SMA is the scarcity of patient's samples. The discovery that somatic cells can be reprogrammed to become induced pluripotent stem cell (iPSCs) raises the intriguing possibility of modeling human diseases in vitro. We reported the establishment of five iPSC lines from the fibroblasts of a type 1 SMA patient. Neuronal cultures derived from these SMA iPSC lines exhibited a reduced capacity to form motoneurons and an abnormality in neurite outgrowth. Ectopic SMN expression in these iPSC lines restored normal motoneuron differentiation and rescued the phenotype of delayed neurite outgrowth. These results suggest that the observed abnormalities are indeed caused by SMN deficiency and not by iPSC clonal variability. Further characterization of the cellular and functional deficits in motoneurons derived from these iPSCs may accelerate the exploration of the underlying mechanisms of SMA pathogenesis.

Prevalence and risk factors for feeding and swallowing difficulties in spinal muscular atrophy types II and III

OBJECTIVE

To identify the prevalence and risk factors of feeding and swallowing problems in patients with type II and type III spinal muscular atrophy (SMA).

STUDY DESIGN

Cross-sectional data from 108 genetically confirmed patients with SMA (age range, 3-45 years; 60 with type II and 48 with type III) were analyzed. The questionnaire survey included demographic data, current motor function and respiratory status, feeding and swallowing difficulties, and consequences. The risk factors were analyzed via logistic regression.

RESULTS

The 3 most common feeding and swallowing difficulties in patients with type II and III SMA were choking (30.6%), difficulty conveying food to the mouth (20.4%), and difficulty chewing (20.4%). Current motor function status was an independent risk factor for feeding and swallowing difficulties (sitters vs walkers: OR, 7.59; 95% CI, 1.22-47.46). All 4 nonsitters (ie, patients with type II SMA who had lost their sitting ability) had feeding and swallowing difficulties. Patients with feeding and swallowing difficulties had significantly higher rates of underweight and aspiration pneumonia than those without these problems.

CONCLUSION

Patients with type II and III SMA have a high prevalence of risk factors for feeding and swallowing difficulties, suggesting that an individualized treatment plan should depend on current motor function status.

Using induced pluripotent stem cells (iPSC) to model human neuromuscular connectivity: promise or reality?

Motor neuron diseases (MND) such as amyotrophic lateral sclerosis and spinal muscular atrophy are devastating, progressive and ultimately fatal diseases for which there are no effective treatments. Recent evidence from systematic studies of animal models and human patients suggests that the neuromuscular junction (NMJ) is an important early target in MND, demonstrating functional and structural abnormalities in advance of pathological changes occurring in the motor neuron cell body. The ability to study pathological changes occurring at the NMJ in humans is therefore likely to be important for furthering our understanding of disease pathogenesis, and also for designing and testing new therapeutics. However, there are many practical and technical reasons why it is not possible to visualise or record from NMJs in pre- and early-symptomatic MND patients in vivo. Other approaches are therefore required. The development of stem cell technologies has opened up the possibility of creating human NMJs in vitro, using pluripotent cells generated from healthy individuals and patients with MND. This review covers historical attempts to develop mature and functional NMJs in vitro, using co-cultures of muscle and nerve from animals, and discusses how recent developments in the generation and specification of human induced pluripotent stem cells provides an opportunity to build on these previous successes to recapitulate human neuromuscular connectivity in vitro.

Clinical and experimental applications of sodium phenylbutyrate

Histone acetyltransferase and histone deacetylase are enzymes responsible for histone acetylation and deacetylation, respectively, in which the histones are acetylated and deacetylated on lysine residues in the N-terminal tail and on the surface of the nucleosome core. These processes are considered the most important epigenetic mechanisms for remodeling the chromatin structure and controlling the gene expression. Histone acetylation is associated with gene activation. Sodium phenylbutyrate is a histone deacetylase inhibitor that has been approved for treatement of urea cycle disorders and is under investigation in cancer, hemoglobinopathies, motor neuron diseases, and cystic fibrosis clinical trials. Due to its characteristics, not only of histone deacetylase inhibitor, but also of ammonia sink and chemical chaperone, the interest towards this molecule is growing worldwide. This review aims to update the current literature, involving the use of sodium phenylbutyrate in experimental studies and clinical trials.

Drug treatment for spinal muscular atrophy type I

BACKGROUND

Spinal muscular atrophy (SMA) is caused by degeneration of anterior horn cells of the spinal cord, which leads to progressive muscle weakness. Children with SMA type I will never be able to sit without support and usually die by the age of two years. There are no known efficacious drug treatments that influence the course of the disease. This is an update of a review first published in 2009.

OBJECTIVES

To evaluate whether drug treatment is able to slow or arrest the disease progression of SMA type I, and to assess if such therapy can be given safely. Drug treatment for SMA types II and III is the topic of a separate updated Cochrane review.

SEARCH METHODS

We searched the Cochrane Neuromuscular Disease Group Specialized Register (8 March 2011), CENTRAL (The Cochrane Library 2011, Issue 1), MEDLINE (January 1991 to February 2011), EMBASE (January 1991 to February 2011) and ISI Web of Knowledge (January 1991 to 8 March 2011). We searched the Clinical Trials Registry of the U.S. National Institute of Health (www.ClinicalTrials.gov) (8 March 2011) to identify additional trials that had not yet been published.

SELECTION CRITERIA

We sought all randomised or quasi-randomised trials that examined the efficacy of drug treatment for SMA type I. Participants had to fulfil the clinical criteria and have a deletion or mutation of the SMN1 gene (5q11.2-13.2) confirmed by genetic analysis.The primary outcome measure was time from birth until death or full time ventilation. Secondary outcome measures were development of rolling, sitting or standing within one year after the onset of treatment, and adverse events attributable to treatment during the trial period.

DATA COLLECTION AND ANALYSIS

Two authors (RW and AV) independently reviewed and extracted data from all potentially relevant trials. For included studies, pooled relative risks and standardised mean differences were to be calculated to assess treatment efficacy.

MAIN RESULTS

One small randomised controlled study comparing riluzole treatment to placebo for 10 SMA type 1 children was identified and included in the original review. No further trials were identified for the update in 2011. Regarding the primary outcome measure, three of seven children treated with riluzole were still alive at the ages of 30, 48 and 64 months, whereas all three children in the placebo group died; but the difference was not statistically significant. Regarding the secondary outcome measures, none of the children in the riluzole or placebo group developed the ability to roll, sit or stand, and no adverse effects were observed. For several reasons the overall quality of the study was low, mainly because the study was too small to detect an effect and because of baseline differences. Follow-up of the 10 included children was complete.

AUTHORS' CONCLUSIONS

No drug treatment for SMA type I has been proven to have significant efficacy.

Drug treatment for spinal muscular atrophy types II and III

BACKGROUND

Spinal muscular atrophy (SMA) is caused by degeneration of anterior horn cells, which leads to progressive muscle weakness. Children with SMA type II do not develop the ability to walk without support and have a shortened life expectancy, whereas children with SMA type III develop the ability to walk and have a normal life expectancy. There are no known efficacious drug treatments that influence the disease course of SMA. This is an update of a review first published in 2009.

OBJECTIVES

To evaluate whether drug treatment is able to slow or arrest the disease progression of SMA types II and III and to assess if such therapy can be given safely. Drug treatment for SMA type I is the topic of a separate updated Cochrane review.

SEARCH METHODS

We searched the Cochrane Neuromuscular Disease Group Specialized Register (8 March 2011), Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2011, Issue 1), MEDLINE (January 1991 to February 2011), EMBASE (January 1991 to February 2011) and ISI Web of Knowledge (January 1991 to March 8 2011). We also searched clinicaltrials.gov to identify as yet unpublished trials (8 March 2011).

SELECTION CRITERIA

We sought all randomised or quasi-randomised trials that examined the efficacy of drug treatment for SMA types II and III. Participants had to fulfil the clinical criteria and have a deletion or mutation of the survival motor neuron 1 (SMN1) gene (5q11.2-13.2) that was confirmed by genetic analysis.The primary outcome measure was to be change in disability score within one year after the onset of treatment. Secondary outcome measures within one year after the onset of treatment were to be change in muscle strength, ability to stand or walk, change in quality of life, time from the start of treatment until death or full time ventilation and adverse events attributable to treatment during the trial period.

DATA COLLECTION AND ANALYSIS

Two authors independently reviewed and extracted data from all potentially relevant trials. Pooled relative risks and pooled standardised mean differences were to be calculated to assess treatment efficacy. Risk of bias was systematically analysed.

MAIN RESULTS

Six randomised placebo-controlled trials on treatment for SMA types II and III were found and included in the review: the four in the original review and two trials added in this update. The treatments were creatine (55 participants), phenylbutyrate (107 participants), gabapentin (84 participants), thyrotropin releasing hormone (9 participants), hydroxyurea (57 participants), and combination therapy with valproate and acetyl-L-carnitine (61 participants). None of these studies were completely free of bias. All studies had adequate blinding, sequence generation and reports of primary outcomes.None of the included trials showed any statistically significant effects on the outcome measures in participants with SMA types II and III. One participant died due to suffocation in the hydroxyurea trial and one participant died in the creatine trial. No participants in any of the other four trials died or reached the state of full time ventilation. Serious side effects were infrequent.

AUTHORS' CONCLUSIONS

There is no proven efficacious drug treatment for SMA types II and III.

Therapeutic developments in spinal muscular atrophy

Spinal muscular atrophy (SMA), a potentially devastating disease marked by progressive weakness and muscle atrophy resulting from the dysfunction and loss of motor neurons of the spinal cord, has emerged in recent years as an attractive target for therapeutic intervention. Caused by a homozygous mutation to the Survival of Motor Neurons 1 (SMN1) gene on chromosome 5q, the severity of the clinical phenotype in SMA is modulated by the function of a related protein, Survival of Motor Neurons 2 (SMN2). SMN2 predominantly produces an unstable SMN transcript lacking exon 7; only about 10% of the transcription product produces a full-length, functional SMN protein. Several therapeutic strategies have targeted this gene with the goal of producing increased full-length SMN transcript, thereby modifying the underlying mechanism. Drugs that have increased SMN2 function, in vitro, are now explored for potential therapeutic benefit in this disease. Alternative approaches, including neuroprotective, muscle anabolic, gene and cell replacement strategies, also hold promise. The recent advances in preclinical research and the development of a wider range of animal models for SMA continue to provide cautious optimism that effective treatments for SMA will eventually emerge.

Spinal muscular atrophy

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disease characterized by degeneration of alpha motor neurons in the spinal cord, resulting in progressive proximal muscle weakness and paralysis. Estimated incidence is 1 in 6,000 to 1 in 10,000 live births and carrier frequency of 1/40-1/60. This disease is characterized by generalized muscle weakness and atrophy predominating in proximal limb muscles, and phenotype is classified into four grades of severity (SMA I, SMAII, SMAIII, SMA IV) based on age of onset and motor function achieved. This disease is caused by homozygous mutations of the survival motor neuron 1 (SMN1) gene, and the diagnostic test demonstrates in most patients the homozygous deletion of the SMN1 gene, generally showing the absence of SMN1 exon 7. The test achieves up to 95% sensitivity and nearly 100% specificity. Differential diagnosis should be considered with other neuromuscular disorders which are not associated with increased CK manifesting as infantile hypotonia or as limb girdle weakness starting later in life.

Considering the high carrier frequency, carrier testing is requested by siblings of patients or of parents of SMA children and are aimed at gaining information that may help with reproductive planning. Individuals at risk should be tested first and, in case of testing positive, the partner should be then analyzed. It is recommended that in case of a request on carrier testing on siblings of an affected SMA infant, a detailed neurological examination should be done and consideration given doing the direct test to exclude SMA. Prenatal diagnosis should be offered to couples who have previously had a child affected with SMA (recurrence risk 25%). The role of follow-up coordination has to be managed by an expert in neuromuscular disorders and in SMA who is able to plan a multidisciplinary intervention that includes pulmonary, gastroenterology/nutrition, and orthopedic care. Prognosis depends on the phenotypic severity going from high mortality within the first year for SMA type 1 to no mortality for the chronic and later onset forms.

Impaired mandibular function in spinal muscular atrophy type II: need for early recognition

The aim of the study is to assess mandibular function in young patients with spinal muscular atrophy type II. A total of 12 children and young adults with spinal muscular atrophy type II and 12 healthy matched controls participated. The mandibular function impairment was moderate to severe in 50% of patients. A limited mouth opening (≤30 mm) was observed in 75% of the patients. In patients with a severe reduction of the mandibular range of motion the temporomandibular joint mainly rotated during mouth opening instead of the usual combination of rotation and sliding. The severity of the limited active mouth opening correlated with the severity of the disease (motor function measure scores). This study shows that mandibular dysfunction is common among young patients with spinal muscular atrophy type II. Early recognition of mandibular dysfunction may help to prevent complications such as aspiration as a result of chewing problems.

A role for SMN exon 7 splicing in the selective vulnerability of motor neurons in spinal muscular atrophy

Spinal muscular atrophy (SMA) is an inherited motor neuron disease caused by homozygous loss of the Survival Motor Neuron 1 (SMN1) gene. In the absence of SMN1, inefficient inclusion of exon 7 in transcripts from the nearly identical SMN2 gene results in ubiquitous SMN decrease but selective motor neuron degeneration. Here we investigated whether cell type-specific differences in the efficiency of exon 7 splicing contribute to the vulnerability of SMA motor neurons. We show that normal motor neurons express markedly lower levels of full-length SMN mRNA from SMN2 than do other cells in the spinal cord. This is due to inefficient exon 7 splicing that is intrinsic to motor neurons under normal conditions. We also find that SMN depletion in mammalian cells decreases exon 7 inclusion through a negative feedback loop affecting the splicing of its own mRNA. This mechanism is active in vivo and further decreases the efficiency of exon 7 inclusion specifically in motor neurons of severe-SMA mice. Consistent with expression of lower levels of full-length SMN, we find that SMN-dependent downstream molecular defects are exacerbated in SMA motor neurons. These findings suggest a mechanism to explain the selective vulnerability of motor neurons to loss of SMN1.

Fungal Smn and Spf30 homologues are mainly present in filamentous fungi and genomes with many introns: implications for spinal muscular atrophy

Spinal muscular atrophy is an important rare genetic disease characterized by the loss of motor neurons, where the main gene responsible is smn1. Orthologous genes have only been characterized in a single fungal genome: Schizosaccharomyces pombe. We have searched for putative SMN orthologues in publically available fungal genomes, finding that they are predominately present in filamentous fungi. SMN binding partners and the SPF30 SMN paralogue, which are all involved in mRNA splicing, were found to be present in a similar but non-identical subset of fungal genomes. The Saccharomycces cerevisiae yeast genome contains neither smn1 orthologues nor paralogues and it has been suggested that this might be related to the low number of introns in this yeast. Here we have tested this hypothesis by looking at other fungal genomes. Significantly, we find that fungal genomes with high numbers of introns also possess an SMN orthologue or at least its paralogue, SPF30.

Stem cell transplantation for motor neuron disease: current approaches and future perspectives

Motor neuron degeneration leading to muscle atrophy and death is a pathological hallmark of disorders, such as amyotrophic lateral sclerosis or spinal muscular atrophy. No effective treatment is available for these devastating diseases. At present, cell-based therapies targeting motor neuron replacement, support, or as a vehicle for the delivery of neuroprotective molecules are being investigated. Although many challenges and questions remain, the beneficial effects observed following transplantation therapy in animal models of motor neuron disease has sparked hope and a number of clinical trials. Here, we provide a comprehensive review of cell-based therapeutics for motor neuron disorders, with a particular emphasis on amyotrophic lateral sclerosis.