Survival Motor Neuron Research Articles

Experience with the use of risdiplam in a familial case of spinal muscular atrophy 5q in patients with a homozygous deletion of the SMN1 gene and the same copy number of the SMN2 gene

Advances in the treatment of spinal muscular atrophy (SMA) have revolutionized the field. SMA is a rare autosomal recessive neurodegenerative motor neuron disease in which wide phenotypic variability has been described. The rate of increase in neurological deficit and the severity of the disease is mainly determined by the amount of functional SMN (Survival of Motor Neuron) protein. However, the clinical picture may differ significantly in patients carrying homozygous deletions of the SMN1 gene (Survival of Motor Neuron 1) and an identical number of copies of the SMN2 gene (Survival of Motor Neuron 2). A family clinical case of adult patients with spinal muscular atrophy 5q with a homozygous deletion of the SMN1 gene and the same number of copies of the SMN2 gene, having a different clinical picture of the disease, is presented, and the dynamics of the condition against the background of oral pathogenetic therapy is presented.

Cognitive impairment in children with 5q-associated spinal muscular atrophy type 1: two case reports and the review of the literature.

Spinal muscular atrophy (SMA) is an autosomal recessive disease caused by mutations in the survival motor neuron 1 (SMN1) gene on chromosome 5, leading to the degeneration of lower motor neurons. There are few studies on cognitive impairment comorbid with SMA. Here, we report two cases of severe cognitive impairment in Chinese children with SMA type 1, marking the first such reports in this demographic. We propose that severe cognitive dysfunction may be a comorbidity of SMA. Clinicians should consider SMA in patients presenting with severe muscle weakness and atrophy accompanied by cognitive impairments, to avoid misdiagnosis and oversight.

Risdiplam for the treatment of spinal muscular atrophy

Spinal muscular atrophy (SMA) is a devastating disease that is the leading genetic cause of death in infants and young children. It includes a broad spectrum of phenotypes that are classified into clinical groups based on the age of onset and maximum motor function achieved. The most common form of SMA is due to a defect in the survival motor neuron 1 gene (SMN1) localized to 5q11.2-q13.3. The development of clinical symptoms and disease progression is thought to be due to decreased levels of survival motor neuron (SMN) protein. SMA type 1 results in almost inevitable mortality within the first 2 years of life. The first two drugs approved globally for the treatment of SMA were the antisense oligonucleotide nusinersen (Spinraza), and the gene therapy onasemnogene abeparvovec-xioi (Zolgensma). Both interventions have approval and restrictions on use in different countries around the world. Despite these approved therapies, the medical unmet need in SMA (the majority of patients with SMA are not on a disease-modifying therapy) remains high with therapies in the pipeline to address some of the remaining limitations. The third and more recently approved drug for SMA is risdiplam (Evrysdi), an orally administered, centrally and peripherally distributed small molecule that modulates SMN2 pre-mRNA splicing toward the production of full-length SMN2 mRNA to increase functional SMN protein levels. In Russia the drug risdiplam was approved for use on November 26, 2020 with indications for the treatment of SMA in patients aged 2 months and older, and in 2023 the indications were expanded - use is allowed starting from the birth. Risdiplam is widely distributed into the CNS and peripheral tissues including muscles. Following risdiplam administration, SMN protein levels compared with baseline levels increase between 2- and 6-fold depending on the SMA phenotype treated. The risdiplam clinical development program currently has four ongoing clinical trials assessing its safety and efficacy. Clinical trials included more than 450 patients receiving risdiplam to date, has been well tolerated and no treatment-related safety findings leading to study withdrawal have been observed. Data from real clinical practice - more than 11.000 patients worldwide receive therapy with risdiplam, also confirm the safety and good tolerability of the drug.

Synergistic Effect of an Antisense Oligonucleotide and Small Molecule on Splicing Correction of the Spinal Muscular Atrophy Gene.

Spinal muscular atrophy (SMA) is treated by increasing the level of Survival Motor Neuron (SMN) protein through correction of SMN2 exon 7 skipping or exogenous expression of SMN through gene therapy. Currently available therapies have multiple shortcomings, including poor body-wide distribution, invasive delivery, and potential negative consequences due to high doses needed for clinical efficacy. Here we test the effects of a combination treatment of a splice-correcting antisense oligonucleotide (ASO) Anti-N1 with the small compounds risdiplam and branaplam. We show that a low-dose treatment of Anti-N1 with either compound produces a synergistic effect on the inclusion of SMN2 exon 7 in SMA patient fibroblasts. Using RNA-Seq, we characterize the transcriptomes of cells treated with each compound as well as in combination. Although high doses of each individual treatment trigger widespread perturbations of the transcriptome, combination treatment of Anti-N1 with risdiplam and branaplam results in minimal disruption of gene expression. For individual genes targeted by the 3 compounds, we observe little to no additive effects of combination treatment. Overall, we conclude that the combination treatment of a splice-correcting ASO with small compounds represents a promising strategy for achieving a high level of SMN expression while minimizing the risk of off-target effects.

The SMA Modifier Plastin 3 Targets Cell Membrane-Associated Proteins in Motoneurons.

Loss of the Survival Motor Neuron (SMN) gene inevitably leads to spinal muscular atrophy (SMA), one of the most common fatal neuromuscular diseases in children with FDA and EMA approved therapies. However, the cellular mechanisms leading to neuromuscular junction (NMJ) dysfunction due to impaired Ca2+ homeostasis in the presynaptic compartment remain largely unexplained. In the last decade, the so-called SMA modifiers have gained attention. The F-actin bundler Plastin 3 (PLS3) is one of them and counteracts neurotransmission defects, including altered vesicle endocytosis, in Smn-deficient NMJs. Properly bundled F-actin is the basis for the translocation and arrangement of transmembrane proteins at the cell surface. Our recently published data by Hennlein et al., J Cell Biol. (2023) clearly showed that Smn deficiency impairs the F-actin dependent translocation of the high-affinity BDNF receptor TrkB to the cell surface resulting in reduced BDNF-mediated TrkB activation in motor axon terminals. Strikingly, the overexpression of PLS3 restores TrkB availability, and significantly improves the clustering of the active zone-associated voltage-gated calcium channel Cav2.2 in growth cones of Smn-deficient motoneurons. These observations raise the question of how PLS3 mediates the proper cell surface localization and cluster-like formation of Cav2.2 in motor axon terminals.

Carrier screening for spinal muscular atrophy in 22913 Chinese reproductive age women.

To determine the carrier frequency of, and evaluate a carrier screening program for, spinal muscular atrophy (SMA) in reproductive age women in Shenzhen area. A staged screening procedure was used to perform carrier screening for SMA in 22,913 Chinese reproductive age women between 2019 and 2022 in Shenzhen area of China. First, the copy number of exon 7 in the SMN1 gene were detected in women of reproductive age using real-time quantitative polymerase chain reaction. If SMA carriers were detected, their spouses were then recommended to test. Prenatal diagnosis was carried out in couples who were both carriers. A total of 389 women were found to be SMA carriers (1.70%, 95% CI: 1.53%-1.87%), indicating the carrier prevalence was approximately 1:59. Despite the proportion of nonpregnant women increased from 37.96% in 2019 to 58.18% in 2022 (p < 0.05) among the 22,913 reproductive age women, the recall rate of spouses was still not high (62.21%, 95% CI: 57.39%-67.03%). Eight partners were found to be SMA carriers and two fetuses were determined to have SMA with no copies of the SMN1 gene. Although the acceptability and awareness of SMA carrier screening in Chinese population has increased in recent years, it still fails to reach the ideal expectation. Our experience may provide a basis for and facilitate the popularization of SMA carrier screening in Shenzhen area.

Ptbp2 re-expression rescues axon growth defects in Smn-deficient motoneurons.

Spinal muscular atrophy (SMA) is a neuromuscular disorder caused by mutations or deletions in the survival motoneuron 1 (SMN1) gene, resulting in deficiency of the SMN protein that is essential for motoneuron function. Smn depletion in mice disturbs axonal RNA transport and translation, thereby contributing to axon growth impairment, muscle denervation, and motoneuron degeneration. However, the mechanisms whereby Smn loss causes axonal defects remain unclear. RNA localization and translation in axons are controlled by RNA-binding proteins (RBP) and we recently observed that the neuronal RBP Ptbp2 modulates axon growth in motoneurons. Here, we identify Smn as an interactor of Ptbp2 in the cytosolic compartments of motoneurons. We show that the expression level of Ptbp2 is reduced in axons but not in the somata of Smn-depleted motoneurons. This is accompanied by reduced synthesis of the RBP hnRNP R in axons. Re-expression of Ptbp2 in axons compensates for the deficiency of Smn and rescues the defects in axon elongation and growth cone maturation observed in Smn-deficient motoneurons. Our data suggest that Ptbp2 and Smn are components of cytosolic mRNP particles, contributing to the precise spatial and temporal control of protein synthesis within axons and axon terminals.

Experience of the treatment of spinal muscular atrophy type 3 Kugelberg-Welander with Nusinersen

Before the advent of pathogenetic therapy, the diagnosis of spinal muscular atrophy (SMA) meant the loss of all hopes for recovery and the patient's setting on the path of a steady decline in motor functions, a deterioration in the quality of life and, ultimately, inevitable early death. Currently, new methods of pathogenetic therapy with nusinersen and risdiplam, as well as etiological therapy with onasemnogene abeparvovec, are available in the Russia. Nusinersen is an antisense oligonucleotide that modifies splicing of the SMN2 gene to increase production of normal full-length motor neuron survival protein, which is deficient in SMA. The mechanism of action of Nusinersen is based on the activation of the disabled exon 7 of the SMN2 gene. The article describes an example of long-term effective treatment using pathogenetic therapy of a patient diagnosed with SMA type 3.

A rapid and easy-to-use spinal muscular atrophy screening tool based on primers with high specificity and amplification efficiency for SMN1 combined with single-stranded tag hybridization assay.

Spinal muscular atrophy (SMA) is an intractable neuromuscular disorder primarily caused by homozygous deletions in exon 7 of the SMN1 gene. Early diagnosis and prompt treatment of patients with SMA have a significant impact on prognosis, and several therapies have recently been developed. Current SMA screening tests require a significant turnaround time to identify patients with suspected SMA, due both to the interval between the birth of a newborn and the collection of blood for newborn mass screening and the difficulty in distinguishing between SMN1 and SMN2, a paralog gene that requires testing in specialized laboratories. The aim of this study was therefore to develop a novel SMA screening assay that can be rapidly performed in ordinary hospitals and clinics to overcome these issues. We designed over 100 combinations of forward and reverse primers with 3' ends targeting SMN1-specific sites around exon 7, and evaluated their specificity and amplification efficiency by quantitative PCR to identify the best primer pair. Furthermore, we performed a single-stranded tag hybridization assay after PCR. To evaluate the accuracy and practicality of the newly developed assay, we analyzed saliva specimens from five patients with SMA and two SMA carriers collected in an outpatient clinic and DNA specimens from three patients with SMA and four SMA carriers from a biobank, together with those from healthy individuals. DNA and raw saliva specimens from all patients with SMA demonstrated a biallelic loss of SMN1, whereas those from carriers and healthy individuals did not. The results of 50 independent experiments were consistent for all samples. The assay could be completed within one hour. This simple and convenient new screening tool has the potential to allow patients with SMA to receive disease-modifying therapies within a shorter timeframe.

Consensus from the Brazilian Academy of Neurology for the diagnosis, genetic counseling, and use of disease-modifying therapies in 5q spinal muscular atrophy.

Spinal muscular atrophy linked to chromosome 5 (SMA-5q) is an autosomal recessive genetic disease caused by mutations in the SMN1. SMA-5q is characterized by progressive degeneration of the spinal cord and bulbar motor neurons, causing severe motor and respiratory impairment with reduced survival, especially in its more severe clinical forms. In recent years, highly effective disease-modifying therapies have emerged, either acting by regulating the splicing of exon 7 of the SMN2 gene or adding a copy of the SMN1 gene through gene therapy, providing a drastic change in the natural history of the disease. In this way, developing therapeutic guides and expert consensus becomes essential to direct the use of these therapies in clinical practice. This consensus, prepared by Brazilian experts, aimed to review the main available disease-modifying therapies, critically analyze the results of clinical studies, and provide recommendations for their use in clinical practice for patients with SMA-5q. This consensus also addresses aspects related to diagnosis, genetic counseling, and follow-up of patients under drug treatment. Thus, this consensus provides valuable information regarding the current management of SMA-5q, helping therapeutic decisions in clinical practice and promoting additional gains in outcomes.

A high-fidelity long-read sequencing-based approach enables accurate and effective genetic diagnosis of spinal muscular atrophy

BackgroundWe aimed to develop a high-fidelity long-read sequencing (LRS)-based approach to detect SMN gene variants in one step. It is challenging for conventional step-wise methods to simultaneously detect all kinds of variations between homologous SMN1 and SMN2. MethodsIn this study, LRS was developed to analyze copy numbers (CNs), full sequences, and structure of SMN1 and SMN2. The results were compared with those from the step-wise methods in 202 samples from 67 families. ResultsLRS achieved 100% (202/202) and 99.5% (201/202) accuracy for SMN1 and SMN2 CNs, respectively. It corrected SMN1 CNs from MLPA, which was caused by SNVs/indels that located in probe-binding region. LRS identified 23 SNVs/indels distributing throughout SMN1, including c.22dup and c.884A > T in trans-configuration, and a de novo variant c.41_42delinsC for the first time. LRS also identified a SMN2 variant c.346A > G. Moreover, it successfully determined Alu-mediated 8978-bp deletion encompassing exon 2a-5 and 1415-bp deletion disrupting exon 1, and the exact breakpoints of large deletions. Through haplotype-based pedigree trio analysis, LRS identified SMN1 2 + 0 carriers, and determined the distribution of SMN1 and SMN2 on two chromosomes. ConclusionsLRS represents a more comprehensive and accurate diagnosis approach that is beneficial to early treatment and effective management of SMA.

Spinal Muscular Atrophy, Approved Therapies and Future Prospects

Spinal muscular atrophy (SMA) is a complex congenital myoneural disorder, noted for gradual muscle atrophy leading to increasing muscular weakness and significant disability. SMA manifests broad array of clinical severity and its clinical traits can be graded into four primary phenotypes -SMA type I, II, III and IV mainly based on the age of onset of symptoms and highest motor milestones attained. Over the past few years, numerous feasible interventions found on the commonly accepted precept of augmenting the translation of the survival motor neuron (SMN) protein have been tried. Gene therapies focusing on SMN include splicing modulation of SMN2 gene (nusinersen) and replacing SMN1 gene (onasemnogene abeparvovec), whereas therapies focusing SMN-independent factors involve treatments improving muscular function, treatment of spinal deformities and neuroprotection. A noted milestone in history of SMA was the approval of Nusinersen in 2016. It was followed by approval in 2019 and in 2020 to onasemnogene abeparvovec and risdiplam respectively. These three approved therapies offered hope to the patients and their families globally. But some of the weaknesses are also associated with these therapies. Deficiency of phase 4 clinical trial data, high price tag, nonavailability of guidelines for the selection of therapies for specific phenotypes and lack of data form clinical trial targeted to compare safety and efficacy of currently approved therapies are some of the issues that licensed therapies for SMA are suffering. In the face such challenges, initiation of intervention at an early age along with the utilization of adjunct therapies seems to be a sound approach to treat SMA patients. The review discusses the classification, clinical description, genetics, diagnostics and treatment of SMA along with SMN independent therapeutic targets that can utilised for the development of new therapies.

Effect of nusinersen after 3 years of treatment in 57 young children with SMA in terms of SMN2 copy number or type

BackgroundSpinal muscular atrophy (SMA) is a rare genetic neuromuscular disorder due to an autosomal recessive mutation in the survival motor neuron 1 gene (SMN1), causing degeneration of the anterior horn cells of the spinal cord and resulting in muscle atrophy. This study aimed to report on the 36-month follow-up of children with SMA treated with nusinersen before the age of 3 years. Changes in motor function, nutritional and ventilatory support, and orthopedic outcomes were evaluated at baseline and 36 months after intrathecal administration of nusinersen and correlated with SMA type and SMN2 copy number. ResultsWe found that 93% of the patients gained new motor skills during the 3 years—standing without help for 12 of 37 and walking with help for 11 of 37 patients harboring three SMN2 copies. No patients with two copies of SMN2 can stand alone or walk. Patients bearing three copies of SMN2 are more likely to be spared from respiratory, nutritional, and orthopedic complications than patients with two SMN2 copies. ConclusionChildren with SMA treated with nusinersen continue to make motor acquisitions at 3 years after initiation of treatment. Children with two SMN2 copies had worse motor, respiratory, and orthopedic outcomes after 3 years of treatment than children with three copies.

Lateral olfactory tract usher substance (LOTUS), an endogenous Nogo receptor antagonist, ameliorates disease progression in amyotrophic lateral sclerosis model mice

Nogo–Nogo receptor 1 (NgR1) signaling is significantly implicated in neurodegeneration in amyotrophic lateral sclerosis (ALS). We previously showed that lateral olfactory tract usher substance (LOTUS) is an endogenous antagonist of NgR1 that prevents all myelin-associated inhibitors (MAIs), including Nogo, from binding to NgR1. Here we investigated the role of LOTUS in ALS pathogenesis by analyzing G93A-mutated human superoxide dismutase 1 (SOD1) transgenic (Tg) mice, as an ALS model, as well as newly generated LOTUS-overexpressing SOD1 Tg mice. We examined expression profiles of LOTUS and MAIs and compared motor functions and survival periods in these mice. We also investigated motor neuron survival, glial proliferation in the lumbar spinal cord, and neuromuscular junction (NMJ) morphology. We analyzed downstream molecules of NgR1 signaling such as ROCK2, LIMK1, cofilin, and ataxin-2, and also neurotrophins. In addition, we investigated LOTUS protein levels in the ventral horn of ALS patients. We found significantly decreased LOTUS expression in both SOD1 Tg mice and ALS patients. LOTUS overexpression in SOD1 Tg mice increased lifespan and improved motor function, in association with prevention of motor neuron loss, reduced gliosis, increased NMJ innervation, maintenance of cofilin phosphorylation dynamics, decreased levels of ataxin-2, and increased levels of brain-derived neurotrophic factor (BDNF). Reduced LOTUS expression may enhance neurodegeneration in SOD1 Tg mice and ALS patients by activating NgR1 signaling, and in this study LOTUS overexpression significantly ameliorated ALS pathogenesis. LOTUS might serve as a promising therapeutic target for ALS.

Comparison of the accuracy of multiplex digital PCR versus multiplex ligation-dependent probe amplification in quantification of the survival of motor neuron genes copy numbers

For over two decades, multiplex ligation-dependent probe amplification (MLPA) has served as the gold standard for genetic testing of spinal muscular atrophy. However, there is emerging evidence questioning the reliability of MLPA in determining the copy numbers (CNs) of the survival of motor neuron (SMN) gene in certain cases. Recently, digital polymerase chain reaction (dPCR) has shown potential for better performance in copy number variant detection. This study aimed to compare MLPA and dPCR in quantifying SMN1 and SMN2 CNs, identify reasons for observed discrepancies, and explore the clinical implications of false results.A total of 733 DNA samples, previously subjected to MLPA analysis, were tested using multiplex droplet dPCR assays. Samples exhibiting inconsistent results between the two methods underwent repeated dPCR assays. When inconsistencies persisted, a third method was employed for verification. Digital PCR yielded results consistent with those of MLPA in 94.4% (692/733) of samples. Forty-one cases exhibited quantitative disparities in SMN1 and/or SMN2 CNs between the two methods. Confirmatory tests revealed that 37 inaccurate results were produced by the MLPA analysis, whereas four were attributed to the dPCR method. The dPCR technique exhibits better accuracy than MLPA and is qualified for SMA genetic testing across various clinical scenarios.

Hip Displacement in Spinal Muscular Atrophy: The Influences of Genetic Severity, Functional Level, and Disease-modifying Treatments.

Hip displacement (HD) is common in spinal muscular atrophy (SMA), but neither genetic severity nor gross motor function level have been investigated as risk factors. Although disease-modifying agents (DMA) have improved function and overall health, their effects on the prevention of HD are unknown. The purpose of this study was to determine risk factors for HD development in SMA. Retrospective cohort. Children with SMA presenting between January 2005 and August 2021, at least 1 hip radiograph, and a minimum 2-year follow-up were included. The primary outcome measure was the prevalence of HD (migration percentage ≥40%). Secondary outcomes included SMA type (I/II/III), survival motor neuron 2 copy number, Hammersmith Functional Motor Scale (HFMS, out of 66), ambulatory status (Functional Mobility Scale at 50m), clinically relevant scoliosis (>40 degrees and/or surgery), and DMA treatment (>1-year duration, nusinersen/risdiplam/onasemnogene abeparvovec) as risk factors. Univariate and multivariate logistic regression analyses were performed. Eighty-two patients (52% female) with SMA type I (n=32, 39%), II (n=36, 44%), and III (n=14, 17%) met the inclusion criteria, with a final follow-up of 4.5 (SD: 2.7) years. Age at first hip radiograph was 3.4 (SD: 2.9) years. The prevalence of HD was 75.6%, with a mean age of onset of 4.6 (SD: 2.7) years. When stratified by SMA type, the prevalence/age of onset (mean, years) was 84%/3.1 (SD: 1.7), 80%/5.8 (SD: 2.3), and 36%/9.0 (SD: 4.3), respectively. HFMS score >23 was protective against HD by receiver operating characteristic analysis ( P =0.008). Significant risk factors by univariate analysis were SMA type I ( P =0.002) and II ( P =0.002), HFMS ≤23 ( P =0.01), nonambulatory status (Functional Mobility Scale at 50m = 1, P =0.001), clinically relevant scoliosis ( P =0.01), and DMA treatment ( P =0.01). By multivariate analysis, only SMA type II ( P =0.04) and scoliosis ( P =0.04) were independent risk factors. The prevalence of HD in SMA is highly linked to disease severity. Identified risk factors can be used in the development of surveillance programs for early detection of HD in SMA, allowing for timely management. Level III.

Long term peripheral AAV9-SMN gene therapy promotes survival in a mouse model of spinal muscular atrophy.

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disease characterized by motor neuron loss and skeletal muscle atrophy. SMA is caused by the loss of the SMN1 gene and low SMN protein levels. Current SMA therapies work by increasing SMN protein in the body. Although SMA is regarded as a motor neuron disorder, growing evidence shows that several peripheral organs contribute to SMA pathology. A gene therapy treatment, onasemnogene abeparvovec, is being explored in clinical trials via both systemic and central nervous system (CNS) specific delivery, but the ideal route of delivery as well as the long-term effectiveness is unclear. To investigate the impact of gene therapy long term, we assessed SMA mice at 6months after treatment of either intravenous (IV) or intracerebroventricular (ICV) delivery of scAAV9-cba-SMN. Interestingly, we observed that SMN protein levels were restored in the peripheral tissues but not in the spinal cord at 6months of age. However, ICV injections provided better motor neuron and motor function protection than IV injection, while IV-injected mice demonstrated better protection of neuromuscular junctions and muscle fiber size. Surprisingly, both delivery routes resulted in an equal rescue on survival, weight, and liver and pancreatic defects. These results demonstrate that continued peripheral AAV9-SMN gene therapy is beneficial for disease improvement even in the absence of SMN restoration in the spinal cord.

Pharmacological inhibition of the integrated stress response accelerates disease progression in an amyotrophic lateral sclerosis mouse model.

The integrated stress response (ISR) regulates translation in response to diverse stresses. ISR activation has been documented in amyotrophic lateral sclerosis (ALS) patients and ALS experimental models. In experimental models, both ISR stimulation and inhibition prevented ALS neurodegeneration; however, which mode of ISR regulation would work in patients is still debated. We previously demonstrated that the ISR modulator ISRIB (Integrated Stress Response InhiBitor, an eIF2B activator) enhances survival of neurons expressing the ALS neurotoxic allele SOD1 G93A. Here, we tested the effect of two ISRIB-like eIF2B activators (2BAct and PRXS571) in the disease progression of transgenic SOD1G93A mice. After biochemical characterization in primary neurons, SOD1G93A mice were treated with 2BAct and PRXS571. Muscle denervation of vulnerable motor units was monitored with a longitudinal electromyographic test. We used a clinical score to document disease onset and progression; force loss was determined with the hanging wire motor test. Motor neuronal survival was assessed by immunohistochemistry. In primary neurons, 2BAct and PRXS571 relieve the ISR-imposed translational inhibition while maintaining high ATF4 levels. Electromyographic recordings evidenced an earlier and more dramatic muscle denervation in treated SOD1G93A mice that correlated with a decrease in motor neuron survival. Both compounds anticipated disease onset and shortened survival time. 2BAct and PRXS571 anticipate disease onset, aggravating muscle denervation and motor neuronal death of SOD1G93A mice. This study reveals that the ISR works as a neuroprotective pathway in ALS motor neurons and reveals the toxicity that eIF2B activators may display in ALS patients.

Motor fiber function in spinal muscular atrophy-analysis of conduction velocity distribution.

The motor neuron survival protein, which is deficient in spinal muscular atrophy (SMA), performs numerous cellular functions. Currently, SMA is believed to be a multi-organ disease, including lesion of various structures of the central and peripheral nervous systems. Motor nerve damage, especially in milder SMA types, is controversial. This prompted the conduct of the electrophysiological studies in adults with SMA types 2 and 3 presented in this paper. The study group consisted of 44 adult patients with SMA types 2 and 3. All patients underwent neurological examination with Hammersmith Functional Motor Scale-Expanded (HFMSE) assessment. Standard electrophysiological studies in the ulnar nerve and conduction velocity distribution (CVD) tests were performed in all patients and controls. A prolongation of the distal latency and lowering of the motor potential amplitude with no changes in CVD were found in the whole patient group. There were no dependencies on the number of gene copies. Patients with low HFSME value had slower standard conduction velocity, CVD in upper and median quartiles, and narrower CVD spread; in milder SMA, CVD spread was greater than in controls. The significant reduction in motor response amplitude in SMA seems to be primarily related to motor neuron loss and directly proportional to its severity. The coexisting rearrangement in the peripheral nerve structure is present in SMA, and this could be partially caused by a coexisting demyelinating process. Nerve remodeling mainly affects large fibers and occurs in more severe SMA types with significant disability.

Optimization of base editors for the functional correction of SMN2 as a treatment for spinal muscular atrophy.

Spinal muscular atrophy (SMA) is caused by mutations in SMN1. SMN2 is a paralogous gene with a C•G-to-T•A transition in exon 7, which causes this exon to be skipped in most SMN2 transcripts, and results in low levels of the protein survival motor neuron (SMN). Here we show, in fibroblasts derived from patients with SMA and in a mouse model of SMA that, irrespective of the mutations in SMN1, adenosine base editors can be optimized to target the SMN2 exon-7 mutation or nearby regulatory elements to restore the normal expression of SMN. After optimizing and testing more than 100 guide RNAs and base editors, and leveraging Cas9 variants with high editing fidelity that are tolerant of different protospacer-adjacent motifs, we achieved the reversion of the exon-7 mutation via an A•T-to-G•C edit in up to 99% of fibroblasts, with concomitant increases in the levels of the SMN2 exon-7 transcript and of SMN. Targeting the SMN2 exon-7 mutation via base editing or other CRISPR-based methods may provide long-lasting outcomes to patients with SMA.