Insights into spinal muscular atrophy from molecular biomarkers

Spinal muscular atrophy is a devastating motor neuron disease characterized by severe cases of fatal muscle weakness.It is one of the most common genetic causes of mortality among infants aged less than 2 years.Biomarker research is currently receiving more attention,and new candidate biomarkers are constantly being discovered.This review initially discusses the evaluation methods commonly used in clinical practice while briefly outlining their respective pros and cons.We also describe recent advancements in research and the clinical significance of molecular biomarkers for spinal muscular atrophy,which are classified as either specific or non-specific biomarkers.This review provides new insights into the pathogenesis of spinal muscular atrophy,the mechanism of biomarkers in response to drug-modified therapies,the selection of biomarker candidates,and would promote the development of future research.Furthermore,the successful utilization of biomarkers may facilitate the implementation of gene-targeting treatments for patients with spinal muscular atrophy.

Infantile Spinal Muscular Atrophy at the Albert Royer National Children’s Hospital Center in Dakar

Introduction: Infantile spinal muscular atrophy (ISA) is an autosomal recessive disease caused by primary degeneration of cells in the anterior horn of the spinal cord, leading to muscle weakness and hypotonia. Its incidence is estimated at 1 in 6000 births worldwide. In Africa, particularly in Senegal, there are few studies interested on this pathology. We therefore deemed this study necessary, which set itself the objective of describing the diagnostic, therapeutic and progressive aspects of infantile spinal muscular atrophy at the Albert Royer National Children’s Hospital Center in Dakar (CHNEAR). Methodology: We conducted a retrospective descriptive study over a period of two (2) years from December 2020 to December 2022. Included were all hospitalized patients in whom the diagnosis of spinal muscular atrophy was made with or without genetic confirmation. The data were collected on a pre-established form then entered and analyzed with the following software: Excel 2013 and R version 4.1.3. Results: During our study period, 2100 children were hospitalized, the annual incidence was 0.76%. The average age of our patients was 9 ± 9 months with a range of 3 months to 32 months and the median was 6.5 months. The sex ratio was 7. The notion of family consanguinity was found in 62.5% of cases and the notion of ISA in the family in 25% of cases. Hypotonia and respiratory distress were found at the forefront in equal proportions (50% of cases). Electromyogram (EMG) was performed in 3 patients (37.5%). Symptomatic medical treatment was administered in 100% of patients, 04 patients had benefited from respiratory physiotherapy, i.e. 50% of cases, and genetic counseling was carried out in one patient (12.5%). The evolution was immediately favorable in 2 patients or 25% of cases, unfavorable in 75% of cases with a death rate of 50% and the average age of death was 5.5 months ± 1 with extremes ranging from 3 to 7 months. Conclusion: The number of Infantile spinal muscular atrophy cases remains low in hospitals in Dakar. Diagnostic means are still difficult to access. The course is difficult to predict and is often marked in the long term by respiratory difficulties which can be fatal.

Anesthetic Management of a Patient with Spinal Muscular Atrophy Type III Undergoing Emergent Caesarean Section: A Case Report

In this case report, we describe the anesthetic management for a 36-year-old G2P0010 at 36 weeks gestation with Spinal Muscular Atrophy Type III who underwent an emergent caesarean section due to fetal footling breech position. The patient is a wheelchair-bound quadriplegic with kyphoscoliosis and a lack of cough reflex who required nasal continuous noninvasive ventilatory support (CNVS) for chronic hypercapnic respiratory failure. Surgery was done under general anesthesia due to its emergent nature, and the patient was successfully extubated and transitioned to nasal CNVS in the operating room at the end of the case. Postoperative care was provided in the medical intensive care unit for three days without complication and the patient was discharged home uneventfully.

Autophagy inhibition: a new therapeutic target in spinal muscular atrophy

Spinal muscular atrophy（SMA）is a hereditary pediatric motor neuron（MN）disease：survival motor neuron 1（SMN1）gene mutation determines MN degeneration and,consequently,muscle atrophy,breathing and swallowing difficulties,and,in the most severe cases,premature death.A second unaffected gene（SMN2）is present,but it can only produce a limited amount of functional protein,modulating the disease severity and progression.

Emerging concepts underlying selective neuromuscular dysfunction in infantile-onset spinal muscular atrophy

Infantile-onset spinal muscular atrophy is the quintessential example of a disorder characterized by a predominantly neurodegenerative phenotype that nevertheless stems from perturbations in a housekeeping protein.Resulting from low levels of the Survival of Motor Neuron(SMN)protein,spinal muscular atrophy manifests mainly as a lower motor neuron disease.Why this is so and whether other cell types contribute to the classic spinal muscular atrophy phenotype continue to be the subject of intense investigation and are only now gaining appreciation.Yet,what is emerging is sometimes as puzzling as it is instructive,arguing for a careful re-examination of recent study outcomes,raising questions about established dogma in the field and making the case for a greater focus on milder spinal muscular atrophy models as tools to identify key mechanisms driving selective neuromuscular dysfunction in the disease.This review examines the evidence for novel molecular and cellular mechanisms that have recently been implicated in spinal muscular atrophy,highlights breakthroughs,points out caveats and poses questions that ought to serve as the basis of new investigations to better understand and treat this and other more common neurodegenerative disorders.

Clinical features of adult spinal muscular atrophy:46 cases

BACKGROUND： Spinal muscular atrophy （SMA） is a kind of degenerative disease of nervous system. There are 4 types in clinic, especially types Ⅰ, Ⅱ and Ⅲ are common, and the researches on those 3 types are relative mature. Type IV is a kind of adult spinal muscular atrophy （ASMA）, which has low incidence rate and is often misdiagnosed as amyotrophic lateral sclerosis, muscular dystrophy, cervical syndrome, or others.OBJEETIVE： To observe the clinical features of 46 ASMA patients and analyze the relationship between course and activity of daily living. DESIGN ： Case analysis.SETTING： Departments of Neurology of the 81 Hospital of Chinese PLA, the Second Affiliated Hospital of Nanjing Medical College and General Hospital of Nanjing Military Area Command of Chinese PLA.PARTICIPANTS ： A total of 46 ASMA patients were selected from the Departments of Neurology of the 81 Hospital of Chinese PLA, the Second Affiliated Hospital of Nanjing Medical College and General Hospital of Nanjing Military Area Command of Chinese PLA between April 1998 and January 2002. All patients were consentient. Among 46 cases, there were 37 males and 9 females with the mean age of 42 years. The patients＇ courses in all ranged from 6 months to 23 years, concretely, courses of 37 cases were less than or equal to 5 years, and those of 9 cases were more than or equal to 6 years.METHODS： ① All the 46 ASMA patients were asked to check blood sedimentation, anti O, serum creatinine, creatine, blood creatine phosphokinase （CPK） and muscular biopsy as early as possible. ②X-ray was used to measure plain film of cervical vertebra borderline film of cranium and neck at proximal end of upper limb of 25 cases and plain film of abdominal vertebra at proximal end of lower limb of 17 cases. ③ Cerebrospinal fluid of lumbar puncture was checked on 42 cases, for routine examination, biochemical examination, and immunoglobulin examination. Electromyogram （EMG） was also examined to 42 cases. ④ Barthel index was used to evaluate activities of daily living （ADL） of patients with various courses. The index ranged from 1 to 100. The more the index of a ASMA was, the stronger his independence was. ⑤ The Barthel indexes of patients with courses ≤ 5 years and those ≥ 6 years were compared with univariate analysis of variance. MAIN OUTCOME MEASURES： ① Incidences of all patients at the first time; ② values of relative blood and blood biochemistry; ③results of muscular biopsy; ④ results of EMG and relative X-ray plain film of 42 cases; ⑤ results of cerebrospinal fluid of 42 cases; ⑥ comparisons of Barthel index of patients with various courses.RESULTS： A total of 46 ASMA patients were involved in the final analysis. ① Incidence on the first time： 25 patients had the disease at the proximal end of upper limb, 17 at the proximal end of lower limb, and 4 at the four limbs. ② Value of serum-blood CPK of one fourth patients was increased slightly （3.034-9.735 μkat/L; normal value： 0.400-3.001 μkat/L）, and other values of blood and blood biochemical indicator were normal. ③Results of muscle biopsy of all patients showed that a small group of muscular atrophy could be observed mostly, and muscle group in the same type and compensatory hypertrophy of muscle fibres were also observed with ATP enzyme staining. ④ Results of EMG of 42 cases suggested that 37 patients had mild and moderate nerve-derived injury and 3 had mild muscle-derived injury. Results of all the X-ray plain films in this study were normal. ⑤ Results of routine, biochemical and immunoglobulin examination in cerebrospinal fluid of lumbar puncture in 42 cases were all normal. ⑥The difference between Barthel indexes of patients with courses ≤ 5 years and those ≥ 6 years was not significant [（64.73±20.38） vs （68.89±21.76） points, P〉 0.05]. CONCLUSION ： ① Amyasthenia is mainly occurred at the proximal end of the four limbs of ASMA patients. A small group of muscular atrophy is its mostly pathological change, and the progression of the disease is slow. ② Most patients have mild and moderate nerve-derived injury under EMG examination.③ The duration of a patient suffered from the disease has no obvious effect on his ADL ability.

Large deletions within the spinal muscular atrophy gene region in a patient with spinal muscular atrophy type 3

Spinal muscular atrophy （SMA） is an autosomal recessive neuromuscular disorder characterized by degeneration and loss of anterior horn cells in the spinal cord and brain stem nuclei, leading to progressive limb and trunk paralysis and muscular atrophy. Depending on the age of onset and maximum muscular function achieved, SMA is recognized as SMA1, SMA2, SMA3 or SMA4, and most patients have a deletion or truncation of the survival motor neuron 1 （SMN1） gene. In this report, we present a patient with a mild SMA phenotype, SMA3, and define his genetic abnormality. Tetra-primer amplification refractory mutation system PCR combined with restriction fragment length polymorphism analysis and array comparative genomic hybridization were used to determine the genetic variations in this patient. A 500 kb deletion in chromosome 5q13.2, including homozygous deletion of neuronal apoptosis inhibitory protein, and heterozygous deletion of occludin and B-double prime 1 was identified. This SMA region deletion did not involve SMN, indicating that SMN was likely to function normally. The phenotype was dependent of the large deletion and neuronal apoptosis inhibitory protein, occludin and B-double prime 1 may be candidate genes for SMA3.

Nusinersen,an exon 7 inclusion drug for spinal muscular atrophy:A minireview

Spinal muscular atrophy is an autosomal recessive neuromuscular disease with incidence of 1 in 5000 to 10000 live births and is produced by homozygous deletion of exons 7 and 8 in the SMN1 gene.The SMN1 and SMN2 genes encode the survival motor neuron protein,a crucial protein for the preservation of motor neurons.Use of the newer drug,Nusinersen,from early infancy has shown improvement in clinical outcomes of spinal muscular atrophy patients.

Diagnosis of Progressive Spinal Muscular Atrophy by Using Polymerase Chain Reaction

Objective To understand the deletion in the survival motor neuron gene (SMN) of childhood onset spinal muscular atrophy (SMA) in Chinese, and the value of diagnosis of SMA using polymerase chain reaction restriction fragment length polymorphism (PCR RFLP)method. Methods\ Deletions of SMN gene of exon 7 and 8 in 10 cases of presumed SMA, and 20 normal controls from 6 families and 30 unrelated controls were performed by PCR RFLP analysis. Results\ Deletions of SMN gene detected in 9 of 10 (90%) cases of presumed SMA . No deletions of SMN in the telomere were found in the other members of families and controls.Conclusion\ PCR RFLP is a sensitive, specific and simple method in diagnosis of SMA.\;

Reduced mesencephalic astrocyte-derived neurotrophic factor expression by mutant androgen receptor contributes to neurodegeneration in a model of spinal and bulbar muscular atrophy pathology

Spinal and bulbar muscular atrophy is a neurodegenerative disease caused by extended CAG trinucleotide repeats in the androgen receptor gene,which encodes a ligand-dependent transcription facto r.The mutant androgen receptor protein,characterized by polyglutamine expansion,is prone to misfolding and forms aggregates in both the nucleus and cytoplasm in the brain in spinal and bulbar muscular atrophy patients.These aggregates alter protein-protein interactions and compromise transcriptional activity.In this study,we reported that in both cultured N2a cells and mouse brain,mutant androgen receptor with polyglutamine expansion causes reduced expression of mesencephalic astrocyte-de rived neurotrophic factor.Overexpressio n of mesencephalic astrocyte-derived neurotrophic factor amelio rated the neurotoxicity of mutant androgen receptor through the inhibition of mutant androgen receptor aggregation.Conversely.knocking down endogenous mesencephalic astrocyte-derived neurotrophic factor in the mouse brain exacerbated neuronal damage and mutant androgen receptor aggregation.Our findings suggest that inhibition of mesencephalic astrocyte-derived neurotrophic factor expression by mutant androgen receptor is a potential mechanism underlying neurodegeneration in spinal and bulbar muscular atrophy.

Nusinersen for spinal muscular atrophy types Ⅱ and Ⅲ:a retrospective single-center study in South Korea

Background This study investigated the efficacy and safety of nusinersen,an antisense oligonucleotide,in patients with spinal muscular atrophy(SMA)types II(OMIM:253,550)or III(OMIM:253,400),including those with severe scoliosis or requiring respiratory support via mechanical ventilation.Methods Data from 40 patients with genetically confirmed SMA who were treated with nusinersen at our institute from March 2019 to April 2022 were retrospectively analyzed.Of these,30 patients with an age of onset<3 years and not on permanent ventilation were selected.Clinical and genetic characteristics were investigated,and motor function was evaluated based on the Hammersmith Functional Motor Scale-Expanded(HFMSE)score.Results The mean age of symptom onset was 1.2 years.Most patients were diagnosed with SMA type II(27/30,90%).Nusinersen was administered via computed tomography-guided or direct intrathecal injection in 87%(26/30)and 13%(4/30)of the patients,respectively.At the 6-,14-,22-,and 26-month follow-ups,72%,71%,88%,and 86%of patients showed motor improvement,respectively,with mean changes in HFMSE scores of 2.10,2.88,4.21,and 5.29,respectively.Multivariable analysis showed that the use of noninvasive ventilation was associated with poorer outcomes of motor function.Conclusions Patients with SMA type II or III who received nusinersen treatment showed significant improvement in motor function.A longer treatment duration led to a higher number of patients with improved motor function.No significant side effects of nusinersen were observed.Patients with SMA,even those with severe scoliosis or on respiratory support,can be safely treated using nusinersen.

Compound heterozygous mutation in two unrelated cases of Chinese spinal muscular atrophy patients

Background Infantile proximal spinal muscular atrophy （SMA） is a common autosomal recessive neuromuscular disorder. Approximately 90-95% cases of SMA result from homozygous deletion of survival motor neuron gene 1（SMN1） and 5% cases are caused by compound heterozygous mutation （a SMN1 deletion on one allele and a subtle mutation on the other allele）.Methods In this research, two unrelated patients were clinically diagnosed according to the criteria of proximal SMA. Genetic diagnosis was performed to detect the homozygous deletion of exon 7 of SMN1 by PCR-restriction fragment length polymorphism （RFLP） and genomic sequencing. Multiplex ligation-dependent probe amplification （MLPA） analysis was carried out to measure copy numbers of SMN1, SMN2 and neuronal apoptosis inhibitor protein （NAIP） in the patients. Further sequencing of SMN1allele-specific PCR （AS-PCR） and SMN1 clones were also performed to analyze the point mutation of SMN1 gene. Additionally,the pedigree analysis of these two families was carried out to identify the transmission of the mutation.Results The inconsistent results using PCR-RFLP and genomic sequencing showed homozygous deletion of exon 7 of SMN1 and heterozygous deletion accompanied with a suspicious mutation in SMN1 gene, respectively. MLPA analysis of these two cases exhibited one SMN1 copy deletion. One identical c.863G〉T （p. Arg288Met） mutation was found in two cases by sequencing the SMN1 clones, which confirmed that both cases were SMA compound heterozygotes. One case showed partial conversion to form hybrid SMN （SMN2 17/SMN1 E8） identified by clones sequencing and another case carrying 3 SMN2 implied complete conversion from SMN1 to SMN2.Conclusion p. Arg288Met is more a disease-causing mutation than a polymorphism variation, and children with this mutation may have more severe phenotypes.

Clinical applications of MARSALA for preimplantation genetic diagnosis of spinal muscular atrophy

Conventional PCR methods combined with linkage analysis based on short tandem repeats （STRs） or Karyomapping with single nucleotide polymorphism （SNP） arrays, have been applied to preimplantation genetic diagnosis （PGD） for spinal muscular atrophy （SMA）, an autosome recessive disorder. However, it has limitations in SMA diagnosis by Karyomapping, and these methods are unable to distinguish wild- type embryos with carriers effectively. Mutated allele revealed by sequencing with aneuploidy and linkage analyses （MARSALA） is a new method allowing embryo selection by a one-step next-generation sequencing （NGS） procedure, which has been applied in PGD for both autosome dominant and X-linked diseases in our group previously. In this study, we carried out PGD based on MARSALA for two carrier families with SMA affected children. As a result, one of the couples has given birth to a healthy baby free of mutations in SMA-causing gene. It is the first time that MARSALA was applied to PGD for SMA, and we can distinguish the embryos with heterozygous deletion （carriers） from the wild-type （normal） ones accurately through this NGS-based method. In addition, direct mutation detection allows us to identify the affected embryos （homozygous deletion）, which can be regarded as probands for linkage analysis, in case that the affected family member is absent, In the future, the NGS-based MARSALA method is expected to be used in PGD for all monogenetic disorders with known pathogenic gene mutation.

Rapid genetic diagnosis and prenatal diagnosis of spinal muscular atrophy by denaturing high-performance liquid chromatography

Spinal muscular atrophy （SMA） is a common Pautosomal recessive neuromuscular disorder （1in 6000 to 10 000 births） caused by mutations in the SMN1 gene at 5q13. More than 90%-98% of SMA patients show homozygous deletion of SMN1, which has proved to be useful in the diagnosis of SMA. But it is hampered because of the existence of a highly homologous gene, SMN2. Based on nucleotide mismatches between SMN1 and SMN2, the following two DNA tests are usually performed： single-strand conformational polymorphism （SSCP） and polymerase chain reaction （PCR） followed by a restriction enzyme digestion.In this study we developed a new method for rapid genetic diagnosis of SMA by denaturing high-performance liquid chromatography （DHPLC）, which is based on different retention of homoduplexes and heteroduplexes in detecting the homozygous deletion of SMN1. Both genetic and prenatal diagnoses were performed successfully for a SMA family by DHPLC, which was confirmed as a rapid and effective technique for detecting the deletion of SMN1.

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 （NAlP） 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 SMNI 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 NA1P deletion. The findings of homozygous deletions ofexon 7 and/or exon 8 ofSMN1 gene confirmed the diagnosis of SMA, and suggested that the deletion ofSMN1 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 SMAI. 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.

Association between SMN2 methylation and disease severity in Chinese children with spinal muscular atrophy

The homozygous loss of the survival motor neuron 1 （SMN1） gene is the primary cause of spinal muscular atrophy （SMA）, a neuromuscular degenerative disease. A genetically similar gene, SMN2, which is not functionally equivalent in all SMA patients, modifies the clinical SMA phenotypes. We analyzed the methylation levels of 4 CpG islands （CGIs） in SMN2 in 35 Chinese children with SMA by MassARRAY. We found that three CpG units located in CGI 1 （nucleotides （nt） -871, -735） and CGI 4 （nt ＋999） are significantly hypomethylated in SMA type III compared with type I or II children after receiving Bonferroni correction. In addition to the differentially methylated CpG unit of nt -871, the methylation level of the nt -290/-288/-285 unit was negatively correlated with the expression of SMN2 full-length transcripts （SMN2-fl）. In addition, the methylation level at nt ＋938 was inversely proportional to the ratio of SMN2-fl and lacking exon 7 transcripts （SMN2-A7, fl/A7）, and was not associated with the SMN2 transcript levels. Thus, we can conclude that SMN2 methylation may regulate the SMA disease phenotype by modulating its transcription.

Total intravenous anesthesia for cesarean section in a pregnant woman with spinal muscular atrophy

Spinal muscular atrophy （SMA） is a genetic neuromuscular disorder characterized by progressive degeneration of the anterior horn cell leading to a lower motor neuron lesion. It is characterized by degeneration of alpha neurons in the anterior horn cells of the spinal cord leading to progressive muscle atrophy and premature death, usually from respiratory failure.1 There are four types according to the symptoms （Table 1）.

Prenatal diagnosis of spinal muscular atrophy in Chinese by genetic analysis of fetal cells

Background Spinal muscular atrophy （SMA） is an autosomal recessive disease characterized by degeneration of anterior horn cells of the spinal cord. The survival motor neuron gene is SMA-determining gene deleted in approximately 95% of SMA patients. This study was undertaken to predict prenatal SMA efficiently and rapidly in families with previously affected child. Methods Prenatal diagnosis was made in 8 fetuses with a family history of SMA. Polymerase （PCR） and restriction fragment length polymorphism （RFLP） were used for the detection of the neuron gene. Results The survival motor neuron fetuses were detected positive and the gene was not found in 6 fetuses, ruling out the diagnosis of SMA. Two fetuses were detected positive and the pregnancies were terminated. Conclusion Our method is effective and convenient in prenatal diagnosis of SMA.

Atrial Septal Defect, Neuromuscular Junction and Skeletal Abnormalities in Spinal Muscular Atrophy Type Ⅲ

Spinal muscular atrophy （SMA） is a genetic disorder which is clinically characterized by progressive muscle weakness and atrophy and is associated with the degeneration of spinal and lowers bulbar motor neurons. SMAis the most common genetic cause of infant mortality, and seems to be present in general populations. The clinical spectrum of SMA ranges from early infant death to normal adult life with only mild weakness. Approximately 81.2–95.0% of cases of SMA resulted from homozygous deletion of survival of motor neuron 1 （SMN1） and 5.0% were compound heterozygous patients.[1] SMA might manifest not only the dysfunction of pure motor neurons but also abnormalities in neuromuscular junction （NMJ）, osteoporotic bone formation, cardiac abnormalities, and vascular defects.[2] These phenomena have been described in severe SMA （Type I, II） patients and in mouse models while data from SMA Type III individuals are not available. Patients with SMA Type III demonstrate progressive proximal weakness affecting the legs more severely than the arms, and might ultimately end up in the wheelchair. Herein, we report one patient with SMA Type III manifesting an atrial septal defect （ASD）, NMJ defect, short stature, and thick toes.

Impaired dynamic interaction of axonal endoplasmic reticulum and ribosomes contributes to defective stimulus-response in spinal muscular atrophy

Background:Axonal degeneration and defects in neuromuscular neurotransmission represent a pathological hall-mark in spinal muscular atrophy(SMA)and other forms of motoneuron disease.These pathological changes do not only base on altered axonal and presynaptic architecture,but also on alterations in dynamic movements of organelles and subcellular structures that are not necessarily reflected by static histopathological changes.The dynamic inter-play between the axonal endoplasmic reticulum(ER)and ribosomes is essential for stimulus-induced local translation in motor axons and presynaptic terminals.However,it remains enigmatic whether the ER and ribosome crosstalk is impaired in the presynaptic compartment of motoneurons with Smn(survival of motor neuron)deficiency that could contribute to axonopathy and presynaptic dysfunction in SMA.Methods:Using super-resolution microscopy,proximity ligation assay(PLA)and live imaging of cultured motoneu-rons from a mouse model of SMA,we investigated the dynamics of the axonal ER and ribosome distribution and activation.Results:We observed that the dynamic remodeling of ER was impaired in axon terminals of Smn-deficient motoneu-rons.In addition,in axon terminals of Smn-deficient motoneurons,ribosomes failed to respond to the brain-derived neurotrophic factor stimulation,and did not undergo rapid association with the axonal ER in response to extracellular stimuli.Conclusions:These findings implicate impaired dynamic interplay between the ribosomes and ER in axon terminals of motoneurons as a contributor to the pathophysiology of SMA and possibly also other motoneuron diseases.