Spinal Muscular Atrophy Symptoms Research Articles

A Systematic Literature Review of the Natural History of Respiratory, Swallowing, Feeding, and Speech Functions in Spinal Muscular Atrophy (SMA).

Respiratory and bulbar dysfunctions (including swallowing, feeding, and speech functions) are key symptoms of spinal muscular atrophy (SMA), especially in its most severe forms. Demonstrating the long-term efficacy of disease-modifying therapies (DMTs) necessitates an understanding of SMA natural history. This study summarizes published natural history data on respiratory, swallowing, feeding, and speech functions in patients with SMA not receiving DMTs. Electronic databases (Embase, MEDLINE, and Evidence-Based Medicine Reviews) were searched from database inception to June 27, 2022, for studies reporting data on respiratory and/or bulbar function outcomes in Types 1-3 SMA. Data were extracted into a predefined template and a descriptive summary of these data was provided. Ninety-one publications were included: 43 reported data on respiratory, swallowing, feeding, and/or speech function outcomes. Data highlighted early loss of respiratory function for patients with Type 1 SMA, with ventilatory support typically required by 12 months of age. Patients with Type 2 or 3 SMA were at risk of losing respiratory function over time, with ventilatory support initiated between the first and fifth decades of life. Swallowing and feeding difficulties, including choking, chewing problems, and aspiration, were reported in patients across the SMA spectrum. Swallowing and feeding difficulties, and a need for non-oral nutritional support, were reported before 1 year of age in Type 1 SMA, and before 10 years of age in Type 2 SMA. Limited data relating to other bulbar functions were collated. Natural history data demonstrate that untreated patients with SMA experience respiratory and bulbar function deterioration, with a more rapid decline associated with greater disease severity. This study provides a comprehensive repository of natural history data on bulbar function in SMA, and it highlights that consistent assessment of outcomes in this area is necessary to benefit understanding and approval of new treatments.

Potential of Cell-Penetrating Peptide-Conjugated Antisense Oligonucleotides for the Treatment of SMA.

Spinal muscular atrophy (SMA) is a severe neuromuscular disorder that is caused by mutations in the survival motor neuron 1 (SMN1) gene, hindering the production of functional survival motor neuron (SMN) proteins. Antisense oligonucleotides (ASOs), a versatile DNA-like drug, are adept at binding to target RNA to prevent translation or promote alternative splicing. Nusinersen is an FDA-approved ASO for the treatment of SMA. It effectively promotes alternative splicing in pre-mRNA transcribed from the SMN2 gene, an analog of the SMN1 gene, to produce a greater amount of full-length SMN protein, to compensate for the loss of functional protein translated from SMN1. Despite its efficacy in ameliorating SMA symptoms, the cellular uptake of these ASOs is suboptimal, and their inability to penetrate the CNS necessitates invasive lumbar punctures. Cell-penetrating peptides (CPPs), which can be conjugated to ASOs, represent a promising approach to improve the efficiency of these treatments for SMA and have the potential to transverse the blood-brain barrier to circumvent the need for intrusive intrathecal injections and their associated adverse effects. This review provides a comprehensive analysis of ASO therapies, their application for the treatment of SMA, and the encouraging potential of CPPs as delivery systems to improve ASO uptake and overall efficiency.

High-sensitive cardiac troponin I (hs-cTnI) concentrations in newborns diagnosed with spinal muscular atrophy.

Spinal muscular atrophy (SMA) is a genetic neurodegenerative disease leading to muscular weakness and premature death. Three therapeutic options are currently available including gene replacement therapy (GRT), which is potentially cardiotoxic. High-sensitive cardiac troponin I (hs-cTnI) is widely used to monitor potential cardiac contraindications or side effects of GRT, but reference data in healthy newborns are limited and lacking in neonates with SMA. The aim of this study is to determine the range of pre-therapeutic hs-cTnI concentrations in neonates with SMA and to provide guidance for the assessment of these values. Hs-cTnI levels, genetic and clinical data of 30 newborns (age range 2-26 days) with SMA were retrospectively collected from 6 German neuromuscular centers. In addition, hs-cTnI levels were measured in 16 neonates without SMA. The median hs-cTnI concentration in neonates with SMA was 39.5 ng/L (range: 4-1205). In 16 newborns with SMA, hs-cTnI levels were above the test-specific upper reference limit (URL). Exploratory statistical analysis revealed no relevant correlation between hs-cTnI levels and gender, gestational age, mode of delivery, SMN2 copy number, symptoms of SMA or abnormal cardiac findings. Our results suggest higher hs-cTnI plasma levels in newborns with and without SMA compared to assay-specific reference values generated in adults. Given the wide range of hs-cTnI values in neonates with SMA, hs-cTnI levels must be determined before treatment in each patient and post-treatment elevations should be interpreted in the context of the course rather than as individual values.

NADPH oxidase 4 inhibition is a complementary therapeutic strategy for spinal muscular atrophy.

Spinal muscular atrophy (SMA) is a fatal neurodegenerative disorder, characterized by motor neuron (MN) degeneration and severe muscular atrophy and caused by Survival of Motor Neuron (SMN) depletion. Therapies aimed at increasing SMN in patients have proven their efficiency in alleviating SMA symptoms but not for all patients. Thus, combinational therapies are warranted. Here, we investigated the involvement of NADPH oxidase 4 (NOX4) in SMA-induced spinal MN death and if the modulation of Nox4 activity could be beneficial for SMA patients. We analysed in the spinal cord of severe type SMA-like mice before and at the disease onset, the level of oxidative stress and Nox4 expression. Then, we tested the effect of Nox4 inhibition by GKT137831/Setanaxib, a drug presently in clinical development, by intrathecal injection on MN survival and motor behaviour. Finally, we tested if GKT137831/Setanaxib could act synergistically with FDA-validated SMN-upregulating treatment (nusinersen). We show that NOX4 is overexpressed in SMA and its inhibition by GKT137831/Setanaxib protected spinal MN from SMA-induced degeneration. These improvements were associated with a significant increase in lifespan and motor behaviour of the mice. At the molecular level, GKT137831 activated the pro-survival AKT/CREB signaling pathway, leading to an increase in SMN expression in SMA MNs. Most importantly, we found that the per os administration of GKT137831 acted synergistically with a FDA-validated SMN-upregulating treatment. The pharmacological inhibition of NOX4 by GKT137831/Setanaxib is neuroprotector and could represent a complementary therapeutic strategy to fight against SMA.

Prevalence of morbidities across the lifespan for adults with spinal muscular atrophy: a retrospective cohort study

BackgroundRecently approved treatments for spinal muscular atrophy (SMA) may shift clinical care priorities to secondary complications associated with SMA-related aging. To date, there is little knowledge about the natural history of morbidities across the adult lifespan for SMA. The objective of this study was to identify the prevalence and odds ratio (OR) of various morbidities among adults with vs. without SMA prior to SMA-related treatment.MethodsThis was a retrospective cohort study that accessed Medicare fee-for-service and commercial claims data from 01/01/2008-12/22/2016. Data from adults ≥ 18 years old with SMA and without SMA matched (1:200 case:control) on demographics, region, and study entry year were included. The prevalence of 30 morbidities across physiologic systems (e.g., cardiovascular, metabolic, musculoskeletal, urinary) and mental health disorders was examined. Age- and sex-adjusted OR was estimated using logistic regression for each morbidity and effect modification by age and sex was tested.ResultsThere were 2,427 adults with SMA (mean [SD] age, 59.7 [17.4] years; 49.0% female) and 484,528 matched adults without SMA. Adults with vs. without SMA had a higher prevalence and adjusted OR of all 30 morbidities, ranging from OR = 1.61 (95% CI = 1.45–1.80) for hypothyroidism to OR = 7.80 (95% CI = 7.10–8.57) for fluid/electrolyte disorders. There was effect modification by age for 24 morbidities. The OR was highest for the youngest age group (18–40 years; OR range, 2.38 to 117.7; all P < 0.05) and declined with older age groups, but still remained significantly elevated in the oldest age group (≥ 75 years; OR range, 1.30 to 5.96; all P < 0.05).ConclusionsThe limitations of this study are that evidence of morbidities were limited to diagnostic claims and information on SMA type and symptoms or onset were not available. In conclusion, adults with SMA had a higher and earlier prevalence of a variety of morbidities across physiological systems and mental health disorders.

Spinal Muscular Atrophy: A Rare but Treatable Disease of the Nervous System

When something is rare it means that it happens very infrequently. Did you know that most diseases are rare? There are more than 6,000 known rare diseases, each affecting fewer than 1 in every 2,000 people. But if we put all the rare diseases together, they affect about 1 in 17 of us! Given that they are individually uncommon, rare diseases are often poorly understood. However, rare diseases have a large impact on families and society, thus they require increased attention. In this article, we will explore a rare disease of the nervous system called spinal muscular atrophy (SMA). We will tell you about the symptoms of SMA and explain how it is inherited. SMA has led the way in the discovery of treatments for rare diseases. Finding treatments for rare diseases requires intensive research and commitment from many people, but the success of SMA treatments highlights the importance of studying other rare conditions.

Spinal muscular atrophy – the effectiveness of treatment and new therapeutic possibilities for selected groups of patients in Poland

Spinal muscular atrophy (SMA) is a rare hereditary neuromuscular disorder caused by a genetic mutation in the Survival of motor neuron 1 (SMN1) gene, which is responsible for the production of a protein essential to motor neurons’ survival. Insufficient levels of the SMN protein lead to the loss of motor neurons in the spinal cord, which manifests in progressive muscle wasting. Due to the absence of an effective treatment in the early years, the disease was taking its toll with the respiratory problems being the primary cause of death. Currently, there are multiple approved treatments for SMA, which help to manage the symptoms and to prevent complications, such as nusinersen, risdiplam, and onasemnogene abeparovec. In Poland, nusinersen treatment has been offered free of charge by the public health service since 2019. It wasn’t until September 2022 that the reimbursement procedure included the other two drugs. The recently published studies on the nusinersen treatment in Poland showed stabilization or slowdown in the progression of symptoms in all patients. In March 2022, Poland implemented an SMA screening program for newborns, which aimed to detect this fatal and disabling disease before the infant displayed any SMA symptoms. The program resulted so far in early diagnosis and intervention providing a better prognosis for patients. Combination of newborn screening and the drug reimbursement program has significantly increased the chances of SMA patients for effective treatment.

SPINAL MUSCULAR ATROPHY CLINICAL FEATURES, CLASSIFICATION, NATURAL HISTORY, GENETICS, DIAGNOSIS, COMPLICATIONS AND TREATMENT OF THE DISEASE

Introduction: Spinal muscular atrophy (SMA) is a complex neuromuscular disorder, it is the most usual autosomal recessively inherited lethal neuromuscular disease in pediatrics, it presents a defective alteration in the survival motor neuron 1 (SMN1) gene. Spinal muscular atrophy clinically shows progressive weakness of skeletal and respiratory muscles. In recent years, drugs with encouraging results from phase II and III clinical trials have been presented. Objective: to detail current information related to spinal muscular atrophy, clinical features, classification, natural history, genetics, diagnosis, complications and treatment of the disease. Methodology: a total of 40 articles were analyzed in this review, including review and original articles, as well as clinical cases, of which 31 bibliographies were used because the other articles were not relevant to this study. The sources of information were PubMed, Google Scholar and Cochrane; the terms used to search for information in Spanish, Portuguese and English were: spinal muscular atrophy, Spinal Muscular Atrophy, spinal muscular atrophy and spinal muscular atrophy. Results: About 95 % of the occurrences of spinal muscular atrophy are generated by homozygous deletions. Individuals with 5q mutation make up 95% of cases of spinal muscular atrophy and the remaining 5% are generated by mutations in 5q1-5. Targeted treatments may prevent or delay the progression of some symptoms of spinal muscular atrophy. Conclusions: Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disease characterized by muscle atrophy and weakness resulting from irreversible loss and progressive degeneration of the brainstem nuclei and anterior horn cells in the spinal cord (lower motor neurons). Clinically it presents with symmetrical proximal limb weakness that also impacts the axial muscles, intercostal and bulbar musculature and is progressive, and the classification protocol is important in genetics, as well as providing prognostic and clinical information. The natural history of the disease is variable and complicated. It is made by demonstrating a history of proximal muscle weakness, motor difficulties or regression, diminished or absent deep tendon reflexes. Among the most frequent complications in unsupported individuals are those previously mentioned such as poor weight gain with growth retardation, scoliosis, restrictive lung disease, joint contractures and sleep difficulties. In terms of treatment, several different compounds have been investigated in recent years, focused on increasing muscle strength and function. Proactive supportive treatment involving a multidisciplinary team is paramount to decrease the severity of symptoms. KEY WORDS: muscle atrophy, spine, spinal, spinal cord, motor neuron.

Real-world safety of nusinersen in Japan: results from an interim analysis of a post-marketing surveillance and safety database

Purpose Nusinersen is the first disease-modifying therapy to treat spinal muscular atrophy (SMA). This report describes the safety and effectiveness of nusinersen in Japanese clinical use using two data sources: an ongoing Japanese post-marketing surveillance (PMS) and the safety database of the marketing authorisation holder, Biogen . Materials and Methods The PMS is evaluating the safety and effectiveness of nusinersen in all patients treated with nusinersen in Japan between August 2017 and August 2025; this interim analysis included data up to May 30, 2019. Biogen safety database data up to June 30, 2019 were also included to capture adverse events (AEs) from after the interim analysis cutoff date. Collected data included medical history, dosage and administration, and AEs. Safety assessment included AEs and serious AEs (SAEs). Effectiveness analyses included motor function assessments and clinical global impressions of improvement. Results Of 271 patients in the PMS population, 94 had SMA type I (34.7%), and 177 had SMA types II–IV (65.3%). AEs occurred in 67 patients (24.7%) and SAEs in 23 patients (8.5%). The Biogen safety database contained reports of 345 AEs; the most common were pneumonia, headache, and pyrexia, consistent with symptoms of SMA and lumbar puncture. In the analysis set, 26.2% of patients receiving nusinersen showed motor function improvements and 99.6–100.0% showed overall improvement. Conclusion In this interim analysis of the PMS and Biogen safety database, nusinersen had a favourable benefit–risk profile in Japanese patients with SMA.

SMA – OUTCOME MEASURES AND REGISTRIES: EP.258 Health care resource utilization in pediatric patients with spinal muscular atrophy: Interim analysis of a US retrospective chart review study

Patients with spinal muscular atrophy (SMA) have greater health care resource utilization (HCRU) because of progressive muscle weakness, atrophy, and associated complications. No prior studies have assessed HCRU following the initiation of disease-modifying therapies (DMTs). We conducted a retrospective chart review in the United States for SMA patients aged ≥6 months treated with nusinersen monotherapy, onasemnogene abeparvovec (OA) monotherapy, or nusinersen switching to OA. Patient characteristics and outcomes, including major SMA-related HCRU (inpatient [IP] admissions, emergency room [ER] visits, consultation visits) were collected. The index date was the date of monotherapy initiation or switch to OA. The baseline period was the time from the onset of SMA symptoms or time of SMA diagnosis (whichever came earlier) until index. The follow-up period was the time from the index date until the end of data availability. HCRU was summarized per patient-year (PPY). This interim analysis of 20 patients included 8 who received nusinersen monotherapy, 4 who received OA monotherapy, and 8 who switched to OA from initial nusinersen. SMA type at diagnosis was type 1 (4/8; 1/4; 6/8), type 2 (3/8; 1/4; 1/8), type 3 (1/8; 2/4; 0/8), and undetermined (0/8; 0/4; 1/8), respectively. Mean age at index (±standard deviation) was 39.9±12.7, 17.3±7.8, and 18.3±8.6 months, respectively. Among patients treated with nusinersen monotherapy, OA monotherapy, and nusinersen switching to OA, rates of IP admissions in the baseline vs. follow-up period were 1.21 vs. 0.28, 0.52 vs. 0.00, and 1.32 vs. 0.12 PPY; rates of ER visits were 1.69 vs. 0.62, 0.00 vs. 0.00, and 1.73 vs. 0.12 PPY; and rates of SMA-related consultation visits were 3.64 vs. 6.93, 4.95 vs. 3.79, and 7.83 vs. 4.14 PPY, respectively. Patients treated with OA monotherapy or nusinersen switching to OA had lower SMA-related major HCRU following treatment compared with patients treated with nusinersen monotherapy.

SMN Protein Contributes to Skeletal Muscle Cell Maturation Via Caspase-3 and Akt Activation

In spinal muscular atrophy (SMA), systemic deficiency of survival motor neurons (SMN) caused by loss or mutation of SMN1 leads to SMA symptoms. SMA was, for a long time, considered as a selective motor-neuron disease. However, accumulated evidence suggests that skeletal muscle cells are affected by low levels of SMN protein. The purpose of this study was to elucidate the function of SMN protein in skeletal cell differentiation and maturation. In SMNΔ7 mice, which exhibit a systemic reduction of SMN protein, muscle atrophy was evaluated. To direct the effect of SMN against muscle cells, SMN functions were examined by knockdown of SMN in mouse myoblasts cell line C2C12 using siRNA. SMNΔ7 mice showed muscle atrophy accompanied by decreased both expression of a myogenesis marker and a proliferating marker. In SMN-knockdown myoblasts, early expression of myosin heavy chain and reduced multinuclear myotube formation were found. Decreased caspase-3 activity and reduced phosphorylation of Akt were observed at an early stage of differentiation in SMN-knockdown myoblasts. A critical role of SMN protein in muscle cell differentiation via caspase-3 and Akt activation was shown.

Fetal Gene Therapy Using a Single Injection of Recombinant AAV9 Rescued SMA Phenotype in Mice.

Symptoms of spinal muscular atrophy (SMA) disease typically begin in the late prenatal or the early postnatal period of life. The intrauterine (IU) correction of gene expression, fetal gene therapy, could offer effective gene therapy approach for early onset diseases. Hence, the overall goal of this study was to investigate the efficacy of human survival motor neuron (hSMN) gene expression after IU delivery in SMA mouse embryos. First, we found that IU-intracerebroventricular (i.c.v.) injection of adeno-associated virus serotype-9 (AAV9)-EGFP led to extensive expression of EGFP protein in different parts of the CNS with a great number of transduced neural stem cells. Then, to implement the fetal gene therapy, mouse fetuses received a single i.c.v. injection of a single-stranded (ss) or self-complementary (sc) AAV9-SMN vector that led to a lifespan of 93 (median of 63) or 171 (median 105) days for SMA mice. The muscle pathology and number of the motor neurons also improved in both study groups, with slightly better results coming from scAAV treatment. Consequently, fetal gene therapy may provide an alternative therapeutic approach for treating inherited diseases such as SMA that lead to prenatal death or lifelong irreversible damage.

B.06 Safety and efficacy of nusinersen in infants/children with spinal muscular atrophy (SMA): part 1 of the phase 2 EMBRACE study

Background: EMBRACE (NCT02462759) Part 1 is a randomized, double-blind, sham-procedure controlled study assessing safety/tolerability of intrathecal nusinersen (12-mg equivalent dose) in symptomatic infants/children with SMA who were not eligible to participate in ENDEAR or CHERISH. Methods: Eligible participants had onset of SMA symptoms at ≤6 months with 3 SMN2 copies; onset at ≤6 months, age &gt;7 months and 2 copies; or onset at &gt;6 months, age ≤18 months, and 2/3 copies. Safety/tolerability was the primary endpoint. Exploratory endpoints included Hammersmith Infant Neurological Examination Section 2 (HINE-2) motor milestone attainment, change in ventilator use, and growth. Results: EMBRACE Part 1 was terminated early based on positive results from ENDEAR. Safety/tolerability was similar to previous trials. More nusinersen-treated (11/14;79%) vs. sham–treated individuals (2/7;29%) were HINE-2 motor milestone responders. Between Day 183 and 302, mean (SD) hours of ventilator use changed by +1.236 (3.712) hours in nusinersen-treated (n=12) and +2.123 (3.023) hours in sham–treated individuals (n=7). Similar increases in weight and body length were observed in nusinersen-treated and sham–treated individuals by Day 183. Conclusions: In EMBRACE Part 1, nusinersen demonstrated a favorable benefit-risk profile. These results add to the aggregated efficacy, safety/tolerability data of nusinersen in SMA.Study Supported by: Ionis and Biogen

Valproic Acid Treatment for Spinal Muscular Atrophy Patient with Abnormal Electroencephalogram Findings

Background: Valproic Acid (VPA), an anticonvulsant, is a histone deacetylase inhibitor that can increase the Survival Motor Neuron (SMN) level in Spinal Muscular Atrophy (SMA) patients and anticipated to be an effective therapeutic agent for SMA.Patient description: VPA was administered for SMA to a 6-year-old female who showed non-symptomatic abnormal electroencephalogram findings, as well as SMA signs and symptoms. Although the VPA concentration of our patient remained in a low range, electroencephalogram abnormalities disappeared within 10 months after starting administration. On the other hand, clinical signs and symptoms of SMA, respiratory function values, and modified Hammersmith Functional Motor Scale results showed no remarkable changes. We also analyzed survival motor neuron (SMN) transcripts and splicing factor transcripts, such as splicing factor 2/alternative splicing factor (SF2/ASF) and heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1), using quantitative real-time PCR assays performed before and after VPA treatment. The amounts of the FL-SMN, total-SMN, ASF/SF2, and hnRNPA1 transcripts showed an increasing tendency, whereas that of Δ7-SMN was decreased.Conclusion: Our findings indicate a discrepancy between SMN transcript response, and improvements in SMA symptoms and signs following VPA administration in some SMA patients.

Effect of genetic background on the phenotype of the Smn2B/- mouse model of spinal muscular atrophy.

Spinal muscular atrophy (SMA) is caused by mutations or deletions in the Survival Motor Neuron 1 (SMN1) gene in humans. Modifiers of the SMA symptoms have been identified and genetic background has a substantial effect in the phenotype and survival of the severe mouse model of SMA. Previously, we generated the less severe Smn2B/- mice on a mixed genetic background. To assess the phenotype of Smn deficiency on a pure genetic background, we produced Smn2B/2B congenic mice on either the C57BL/6 (BL6) or FVB strain background and characterized them at the 6th generation by breeding to Smn+/- mice. Smn2B/- mice from these crosses were evaluated for growth, survival, muscle atrophy, motor neuron loss, motor behaviour, and neuromuscular junction pathology. FVB Smn2B/- mice had a shorter life span than BL6 Smn2B/- mice (median of 19 days vs. 25 days). Similarly, all other defects assessed occurred at earlier stages in FVB Smn2B/-mice when compared to BL6 Smn2B/-mice. However, there were no differences in Smn protein levels in the spinal cords of these mice. Interestingly, levels of Plastin 3, a putative modifier of SMA, were significantly induced in spinal cords of BL6 Smn2B/- mice but not of FVB Smn2B/-mice. Our studies demonstrate that the phenotype in Smn2B/-mice is more severe in the FVB background than in the BL6 background, which could potentially be explained by the differential induction of genetic modifiers.

Long‐term exercise‐specific neuroprotection in spinal muscular atrophy‐like mice

The real impact of physical exercise parameters, i.e. intensity, type of contraction and solicited energetic metabolism, on neuroprotection in the specific context of neurodegeneration remains poorly explored. In this study behavioural, biochemical and cellular analyses were conducted to compare the effects of two different long-term exercise protocols, high intensity swimming and low intensity running, on motor units of a type 3 spinal muscular atrophy (SMA)-like mouse model. Our data revealed a preferential SMA-induced death of intermediate and fast motor neurons which was limited by the swimming protocol only, suggesting a close relationship between neuron-specific protection and their activation levels by specific exercise. The exercise-induced neuroprotection was independent of SMN protein expression and associated with specific metabolic and behavioural adaptations with notably a swimming-induced reduction of muscle fatigability. Our results provide new insight into the motor units' adaptations to different physical exercise parameters and will contribute to the design of new active physiotherapy protocols for patient care. Spinal muscular atrophy (SMA) is a group of autosomal recessive neurodegenerative diseases differing in their clinical outcome, characterized by the specific loss of spinal motor neurons, caused by insufficient level of expression of the protein survival of motor neuron (SMN). No cure is at present available for SMA. While physical exercise might represent a promising approach for alleviating SMA symptoms, the lack of data dealing with the effects of different exercise types on diseased motor units still precludes the use of active physiotherapy in SMA patients. In the present study, we have evaluated the efficiency of two long-term physical exercise paradigms, based on either high intensity swimming or low intensity running, in alleviating SMA symptoms in a mild type 3 SMA-like mouse model. We found that 10months' physical training induced significant benefits in terms of resistance to muscle damage, energetic metabolism, muscle fatigue and motor behaviour. Both exercise types significantly enhanced motor neuron survival, independently of SMN expression, leading to the maintenance of neuromuscular junctions and skeletal muscle phenotypes, particularly in the soleus, plantaris and tibialis of trained mice. Most importantly, both exercises significantly improved neuromuscular excitability properties. Further, all these training-induced benefits were quantitatively and qualitatively related to the specific characteristics of each exercise, suggesting that the related neuroprotection is strongly dependent on the specific activation of some motor neuron subpopulations. Taken together, the present data show significant long-term exercise benefits in type 3 SMA-like mice providing important clues for designing rehabilitation programmes in patients.

A large animal model of spinal muscular atrophy and correction of phenotype.

Spinal muscular atrophy (SMA) is caused by reduced levels of survival motor neuron (SMN) protein, which results in motoneuron loss. Therapeutic strategies to increase SMN levels including drug compounds, antisense oligonucleotides, and scAAV9 gene therapy have proved effective in mice. We wished to determine whether reduction of SMN in postnatal motoneurons resulted in SMA in a large animal model, whether SMA could be corrected after development of muscle weakness, and the response of clinically relevant biomarkers. Using intrathecal delivery of scAAV9 expressing an shRNA targeting pig SMN1, SMN was knocked down in motoneurons postnatally to SMA levels. This resulted in an SMA phenotype representing the first large animal model of SMA. Restoration of SMN was performed at different time points with scAAV9 expressing human SMN (scAAV9-SMN), and electrophysiology measurements and pathology were performed. Knockdown of SMN in postnatal motoneurons results in overt proximal weakness, fibrillations on electromyography indicating active denervation, and reduced compound muscle action potential (CMAP) and motor unit number estimation (MUNE), as in human SMA. Neuropathology showed loss of motoneurons and motor axons. Presymptomatic delivery of scAAV9-SMN prevented SMA symptoms, indicating that all changes are SMN dependent. Delivery of scAAV9-SMN after symptom onset had a marked impact on phenotype, electrophysiological measures, and pathology. High SMN levels are critical in postnatal motoneurons, and reduction of SMN results in an SMA phenotype that is SMN dependent. Importantly, clinically relevant biomarkers including CMAP and MUNE are responsive to SMN restoration, and abrogation of phenotype can be achieved even after symptom onset.

A cell-autonomous defect in skeletal muscle satellite cells expressing low levels of survival of motor neuron protein

Mutations in the Survival of Motor Neuron (SMN) gene underlie the development of spinal muscular atrophy (SMA), which currently represents the leading genetic cause of mortality in infants and toddlers. SMA is characterized by degeneration of spinal cord motor neurons and muscle atrophy. Although SMA is often considered to be a motor neuron disease, accumulating evidence suggests that muscle cells themselves may be affected by low levels of SMN. Here, we examine satellite cells, tissue-resident stem cells that play an essential role in the growth and repair of skeletal muscle, isolated from a severe SMA mouse model (Smn−/−; SMN2+/+). We found similar numbers of satellite cells in the muscles of SMA and wild-type (Smn+/+; SMN2+/+) mice at postnatal day 2 (P2), and, when isolated from skeletal muscle using cell surface marker expression, these cells showed comparable survival and proliferative potential. However, SMA satellite cells differentiate abnormally, revealed by the premature expression of muscle differentiation markers, and, especially, by a reduced efficiency in forming myotubes. These phenotypes suggest a critical role of SMN protein in the intrinsic regulation of muscle differentiation and suggest that abnormal muscle development contributes to the manifestation of SMA symptoms.

Ultrastructural changes in diaphragm neuromuscular junctions in a severe mouse model for Spinal Muscular Atrophy and their prevention by bifunctional U7 snRNA correcting SMN2 splicing

In Spinal Muscular Atrophy (SMA), the SMN1 gene is deleted or inactivated. Because of a splicing problem, the second copy gene, SMN2, generates insufficient amounts of functional SMN protein, leading to the death of spinal cord motoneurons. For a “severe” mouse SMA model ( Smn −/−, hSMN2 +/+; with affected pups dying at 5–7 days), which most closely mimicks the genetic set-up in human SMA patients, we characterise SMA-related ultrastructural changes in neuromuscular junctions (NMJs) of two striated muscles with discrete functions. In the diaphragm, but not the soleus muscle of 4-days old SMA mice, mitochondria on both sides of the NMJs degenerate, and perisynaptic Schwann cells as well as endoneurial fibroblasts show striking changes in morphology. Importantly, NMJs of SMA mice in which a modified U7 snRNA corrects SMN2 splicing and delays or prevents SMA symptoms are normal. This ultrastructural study reveals novel features of NMJ alterations – in particular the involvement of perisynaptic Schwann cells – that may be relevant for human SMA pathogenesis.

Deletion analysis of SMN1 and NAIP genes in southern Chinese children with spinal muscular atrophy

Spinal muscular atrophy (SMA) is a disorder characterized by degeneration of lower motor neurons and occasionally bulbar motor neurons leading to progressive limb and trunk paralysis as well as muscular atrophy. Three types of SMA are recognized depending on the age of onset, the maximum muscular activity achieved, and survivorship: SMA1, SMA2, and SMA3. The survival of motor neuron (SMN) gene has been identified as an SMA determining gene, whereas the neuronal apoptosis inhibitory protein (NAIP) gene is considered to be a modifying factor of the severity of SMA. The main objective of this study was to analyze the deletion of SMN1 and NAIP genes in southern Chinese children with SMA. Here, polymerase chain reaction (PCR) combined with restriction fragment length polymorphism (RFLP) was performed to detect the deletion of both exon 7 and exon 8 of SMN1 and exon 5 of NAIP in 62 southern Chinese children with strongly suspected clinical symptoms of SMA. All the 32 SMA1 patients and 76% (13/17) of SMA2 patients showed homozygous deletions for exon 7 and exon 8, and all the 13 SMA3 patients showed single deletion of SMN1 exon 7 along with 24% (4/17) of SMA2 patients. Eleven out of 32 (34%) SMA1 patients showed NAIP deletion, and none of SMA2 and SMA3 patients was found to have NAIP deletion. The findings of homozygous deletions of exon 7 and/or exon 8 of SMN1 gene confirmed the diagnosis of SMA, and suggested that the deletion of SMN1 exon 7 is a major cause of SMA in southern Chinese children, and that the NAIP gene may be a modifying factor for disease severity of SMA1. The molecular diagnosis system based on PCR-RFLP analysis can conveniently be applied in the clinical testing, genetic counseling, prenatal diagnosis and preimplantation genetic diagnosis of SMA.