An autopsy case of spinal muscular atrophy type III (Kugelberg-Welander disease)

Muscular MRI and magnetic resonance neurography in spinal muscular atrophy

Spinal muscular atrophy (SMA) is an autosomal recessive genetic disease caused by the degeneration of the α-motor neurons in the anterior horn of the spinal cord. SMA is clinically characterized by progressive and symmetrical muscle weakness and muscle atrophy and ends up with systemic multisystem abnormalities. Quantitative MRI (qMRI) has the advantages of non-invasiveness, objective sensitivity, and high reproducibility, and has important clinical value in evaluating the severity of neuromuscular diseases and monitoring the efficacy of treatment. This article summarizes the clinical use of muscular MRI and magnetic resonance neurography in assessing the progress of SMA.

Disrupted individual-level morphological brain network in spinal muscular atrophy types 2 and 3

BACKGROUND AND OBJECTIVE

Spinal muscular atrophy (SMA) is one of the most common monogenic neuromuscular diseases, and the pathogenesis mechanisms, especially the brain network topological properties, remain unknown. This study aimed to use individual-level morphological brain network analysis to explore the brain neural network mechanisms in SMA.

METHODS

Individual-level gray matter (GM) networks were constructed by estimating the interregional similarity of GM volume distribution using both Kullback-Leibler divergence-based similarity (KLDs) and Jesen-Shannon divergence-based similarity (JSDs) measurements based on Automated Anatomical Labeling 116 and Hammersmith 83 atlases for 38 individuals with SMA types 2 and 3 and 38 age- and sex-matched healthy controls (HCs). The topological properties were analyzed by the graph theory approach and compared between groups by a nonparametric permutation test. Additionally, correlation analysis was used to assess the associations between altered topological metrics and clinical characteristics.

RESULTS

Compared with HCs, although global network topology remained preserved in individuals with SMA, brain regions with altered nodal properties mainly involved the right olfactory gyrus, right insula, bilateral parahippocampal gyrus, right amygdala, right thalamus, left superior temporal gyrus, left cerebellar lobule IV-V, bilateral cerebellar lobule VI, right cerebellar lobule VII, and vermis VII and IX. Further correlation analysis showed that the nodal degree of the right cerebellar lobule VII was positively correlated with the disease duration, and the right amygdala was negatively correlated with the Hammersmith Functional Motor Scale Expanded (HFMSE) scores.

CONCLUSIONS

Our findings demonstrated that topological reorganization may prioritize global properties over nodal properties, and disrupted topological properties in the cortical-limbic-cerebellum circuit in SMA may help to further understand the network pathogenesis underlying SMA.

Cell-mediated cytotoxicity within CSF and brain parenchyma in spinal muscular atrophy unaltered by nusinersen treatment

5q-associated spinal muscular atrophy (SMA) is a motoneuron disease caused by mutations in the survival motor neuron 1 (SMN1) gene. Adaptive immunity may contribute to SMA as described in other motoneuron diseases, yet mechanisms remain elusive. Nusinersen, an antisense treatment, enhances SMN2 expression, benefiting SMA patients. Here we have longitudinally investigated SMA and nusinersen effects on local immune responses in the cerebrospinal fluid (CSF) - a surrogate of central nervous system parenchyma. Single-cell transcriptomics (SMA: N = 9 versus Control: N = 9) reveal NK cell and CD8+ T cell expansions in untreated SMA CSF, exhibiting activation and degranulation markers. Spatial transcriptomics coupled with multiplex immunohistochemistry elucidate cytotoxicity near chromatolytic motoneurons (N = 4). Post-nusinersen treatment, CSF shows unaltered protein/transcriptional profiles. These findings underscore cytotoxicity's role in SMA pathogenesis and propose it as a therapeutic target. Our study illuminates cell-mediated cytotoxicity as shared features across motoneuron diseases, suggesting broader implications.

Respiratory function in adult patients with spinal muscular atrophy treated with nusinersen - a monocenter observational study

Background/objective

Insufficiency of respiratory muscles is the most important reason for mortality in the natural history of SMA. Thus, improvement or stabilization of respiratory function by disease-modifying therapies (DMT) is a very important issue.

Methods

We examined respiratory function using forced vital capacity (FVC) in 42 adult SMA patients (2 SMA type 1, 15 SMA type 2, 24 SMA type 3, 1 SMA type 4, median age 37 years, range 17-61 years) treated with nusinersen for a median of 22.1 months (range 2.1 to 46.7 months). Change in FVC was assessed using mixed effects linear regression models.

Results

Baseline FVC differed significantly between SMA type 1 (4.0, 8.0%), 2 (median 22.0%, IQR 18.0-44.0), 3 (median 81.0%, IQR 67.0-90.8) and, respectively, type 4 (84.0%) patients reflecting the heterogeneity of respiratory impairment based on the SMA type in adulthood (p < 0.0001). FVC remained stable during follow-up (mean -0.047, 95% CI -0.115 to 0.020, p = 0.17); however, subgroup analysis showed an increase in FVC of type 2 patients (mean 0.144, 95% CI 0.086 to 0.202, p < 0.0001) and a decrease in FVC of type 3/4 patients (-0.142, 95% CI -0.239 to -0.044, p = 0.005).

Conclusion

The observed improvement in FVC in patients with SMA type 2 can be seen as a therapeutic response differing from the progressive decline typically seen in the spontaneous course. For SMA type 3/4 patients approaching normal spirometry at baseline, FVC may only be of limited use as an outcome parameter due to ceiling effects.

Motor patterns of patients with spinal muscular atrophy suggestive of sensory and corticospinal contributions to the development of locomotor muscle synergies

Complex locomotor patterns are generated by combination of muscle synergies. How genetic processes, early sensorimotor experiences, and the developmental dynamics of neuronal circuits contribute to the expression of muscle synergies remains elusive. We shed light on the factors that influence development of muscle synergies by studying subjects with spinal muscular atrophy (SMA, types II/IIIa), a disorder associated with degeneration and deafferentation of motoneurons and possibly motor cortical and cerebellar abnormalities, from which the afflicted would have atypical sensorimotor histories around typical walking onset. Muscle synergies of children with SMA were identified from electromyographic signals recorded during active-assisted leg motions or walking, and compared with those of age-matched controls. We found that the earlier the SMA onset age, the more different the SMA synergies were from the normative. These alterations could not just be explained by the different degrees of uneven motoneuronal losses across muscles. The SMA-specific synergies had activations in muscles from multiple limb compartments, a finding reminiscent of the neonatal synergies of typically developing infants. Overall, while the synergies shared between SMA and control subjects may reflect components of a core modular infrastructure determined early in life, the SMA-specific synergies may be developmentally immature synergies that arise from inadequate activity-dependent interneuronal sculpting due to abnormal sensorimotor experience and other factors. Other mechanisms including SMA-induced intraspinal changes and altered cortical-spinal interactions may also contribute to synergy changes. Our interpretation highlights the roles of the sensory and descending systems to the typical and abnormal development of locomotor modules.NEW & NOTEWORTHY This is likely the first report of locomotor muscle synergies of children with spinal muscular atrophy (SMA), a subject group with atypical developmental sensorimotor experience. We found that the earlier the SMA onset age, the more the subjects' synergies deviated from those of age-matched controls. This result suggests contributions of the sensory/corticospinal activities to the typical expression of locomotor modules, and how their disruptions during a critical period of development may lead to abnormal motor modules.

Cognitive impairment in Chinese adult patients with type III spinal muscular atrophy without disease-modifying treatment

Objective

Spinal muscular atrophy (SMA) is a neurodegenerative disorder characterized by the degeneration of motor neurons in the spinal cord. It remains uncertain whether the cognitive performance of adult patients with SMA is impaired. The objective of this study was to assess the cognitive profile of adult Chinese patients with SMA and the association between clinical features and cognitive ability, particularly executive function.

Methods

This cross-sectional study included 22 untreated adult patients with type III SMA and 20 healthy subjects. The following variables were assessed: general intelligence, memory, attention, language, executive function, depression, anxiety, and other demographic and clinical parameters. In addition, physical function was evaluated using the Hammersmith Functional Motor Scale Expanded (HFMSE), the Revised Upper Limb Module (RULM), and the 6-Minute Walk Test (6MWT).

Results

SMA patients had lower scores than healthy subjects in the Verbal Fluency Test, Stroop effect, Total Errors, Perseverative Responses, Perseverative Errors, and Non-perseverative Errors in the Wisconsin Card Sorting Test, showing impaired abilities of SMA patients in executive function. In the Attention Network Test (ANT), the results indicated that the SMA patients also had selective deficits in their executive control networks. Ambulant patients had better executive function test performance than non-ambulant ones. Compromised executive abilities in patients with SMA were correlated with a younger age at onset, poorer motor function, and higher levels of anxiety and depression.

Conclusion

Our study presented the distribution of cognitive impairment in a Chinese cohort with SMA. Patients with type III SMA showed selective deficits in executive function, which may be associated with disease severity, physical impairment, depression and anxiety. Future cognitive studies, accounting for motor and emotional impairment, are needed to evaluate if executive impairment is driven by specific brain changes or by those confounding factors.

Cerebellar structural, astrocytic, and neuronal abnormalities in the SMNΔ7 mouse model of spinal muscular atrophy

Spinalmuscular atrophy (SMA) is a neuromuscular disease that affects as many as 1 in 6000 individuals at birth, making it the leading genetic cause of infant mortality. A growing number of studies indicate that SMA is a multi-system disease. The cerebellum has received little attention even though it plays an important role in motor function and widespread pathology has been reported in the cerebella of SMA patients. In this study, we assessed SMA pathology in the cerebellum using structural and diffusion magnetic resonance imaging, immunohistochemistry, and electrophysiology with the SMNΔ7 mouse model. We found a significant disproportionate loss in cerebellar volume, decrease in afferent cerebellar tracts, selective lobule-specific degeneration of Purkinje cells, abnormal lobule foliation and astrocyte integrity, and a decrease in spontaneous firing of cerebellar output neurons in the SMA mice compared to controls. Our data suggest that defects in cerebellar structure and function due to decreased survival motor neuron (SMN) levels impair the functional cerebellar output affecting motor control, and that cerebellar pathology should be addressed to achieve comprehensive treatment and therapy for SMA patients.

Brain Magnetic Resonance Imaging (MRI) in Spinal Muscular Atrophy: A Scoping Review

BACKGROUND

5q Spinal Muscular Atrophy (SMA) is a prototypical lower motor neuron disorder. However, the characteristic early motor impairment raises the question on the scope of brain involvement with implications for further investigations on the brain as a potential therapeutic target.

OBJECTIVE

To review changes across the SMA clinical spectrum reported on brain magnetic resonance imaging (MRI).

METHODS

We conducted a scoping review of existing literature on PubMed and EMBASE. Two reviewers searched and retrieved relevant articles on magnetic resonance brain imaging in individuals with SMA censoring to April 2022. Full-text articles published in peer-reviewed journals or abstracts accepted to conferences in English and French were included.

RESULTS

Twelve articles were identified describing a total of 39 patients [age range: 11 days to 41 years old, type 0 (n = 5), type 1 (n = 4), type 2 (n = 2), type 3 (n = 22), type 4 (n = 6)]. All reported structural changes and did not explore other MRI modalities. In individuals with infantile onset SMA, cortical and subcortical brain abnormalities in white matter, basal ganglia, thalamus, hippocampus, and high intensity areas around lateral ventricles and thalami were reported over time. In individuals with later-onset SMA, reduced cerebellar and lobular volume were observed as well as increased grey matter density in motor areas.

CONCLUSIONS

Limited data on brain imaging in SMA highlights both cortical and subcortical involvement in SMA, supporting the hypothesis that changes are not restricted to lower motor neuron pathways. Further studies are needed to determine the extent and prevalence of structural and functional brain changes across SMA types.

Redox Imbalance in Neurological Disorders in Adults and Children

Oxygen is a central molecule for numerous metabolic and cytophysiological processes, and, indeed, its imbalance can lead to numerous pathological consequences. In the human body, the brain is an aerobic organ and for this reason, it is very sensitive to oxygen equilibrium. The consequences of oxygen imbalance are especially devastating when occurring in this organ. Indeed, oxygen imbalance can lead to hypoxia, hyperoxia, protein misfolding, mitochondria dysfunction, alterations in heme metabolism and neuroinflammation. Consequently, these dysfunctions can cause numerous neurological alterations, both in the pediatric life and in the adult ages. These disorders share numerous common pathways, most of which are consequent to redox imbalance. In this review, we will focus on the dysfunctions present in neurodegenerative disorders (specifically Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis) and pediatric neurological disorders (X-adrenoleukodystrophies, spinal muscular atrophy, mucopolysaccharidoses and Pelizaeus-Merzbacher Disease), highlighting their underlining dysfunction in redox and identifying potential therapeutic strategies.

Sex and Gender Differences in Neurodegenerative Diseases: Challenges for Therapeutic Opportunities

The term “neurodegenerative diseases” (NDs) identifies a group of heterogeneous diseases characterized by progressive loss of selectively vulnerable populations of neurons, which progressively deteriorates over time, leading to neuronal dysfunction. Protein aggregation and neuronal loss have been considered the most characteristic hallmarks of NDs, but growing evidence confirms that significant dysregulation of innate immune pathways plays a crucial role as well. NDs vary from multiple sclerosis, in which the autoimmune inflammatory component is predominant, to more “classical” NDs, such as Parkinson’s disease, Alzheimer’s disease, amyotrophic lateral sclerosis, and spinal muscular atrophy. Of interest, many of the clinical differences reported in NDs seem to be closely linked to sex, which may be justified by the significant changes in immune mechanisms between affected females and males. In this review, we examined some of the most studied NDs by looking at their pathogenic and phenotypical features to highlight sex-related discrepancies, if any, with particular interest in the individuals’ responses to treatment. We believe that pointing out these differences in clinical practice may help achieve more successful precision and personalized care.

Mitochondrial Dysfunction in Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is a devastating neuromuscular disorder caused by recessive mutations in the SMN1 gene, globally affecting ~8-14 newborns per 100,000. The severity of the disease depends on the residual levels of functional survival of motor neuron protein, SMN. SMN is a ubiquitously expressed RNA binding protein involved in a plethora of cellular processes. In this review, we discuss the effects of SMN loss on mitochondrial functions in the neuronal and muscular systems that are the most affected in patients with spinal muscular atrophy. Our aim is to highlight how mitochondrial defects may contribute to disease progression and how restoring mitochondrial functionality may be a promising approach to develop new therapies. We also collected from previous studies a list of transcripts encoding mitochondrial proteins affected in various SMA models. Moreover, we speculate that in adulthood, when motor neurons require only very low SMN levels, the natural deterioration of mitochondria associated with aging may be a crucial triggering factor for adult spinal muscular atrophy, and this requires particular attention for therapeutic strategies.

Identification of a cytokine profile in serum and cerebrospinal fluid of pediatric and adult spinal muscular atrophy patients and its modulation upon nusinersen treatment

Background and objectives

Multisystem involvement in spinal muscular atrophy (SMA) is gaining prominence since different therapeutic options are emerging, making the way for new SMA phenotypes and consequent challenges in clinical care. Defective immune organs have been found in preclinical models of SMA, suggesting an involvement of the immune system in the disease. However, the immune state in SMA patients has not been investigated so far. Here, we aimed to evaluate the innate and adaptive immunity pattern in SMA type 1 to type 3 patients, before and after nusinersen treatment.

Methods

Twenty one pediatric SMA type 1, 2, and 3 patients and 12 adult SMA type 2 and 3 patients were included in this single-center retrospective study. A Bio-Plex Pro-Human Cytokine 13-plex Immunoassay was used to measure cytokines in serum and cerebrospinal fluid (CSF) of the study cohort before and after 6 months of therapy with nusinersen.

Results

We detected a significant increase in IL-1β, IL-4, IL-6, IL-10, IFN-γ, IL-17A, IL-22, IL-23, IL-31, and IL-33, in serum of pediatric and adult SMA patients at baseline, compared to pediatric reference ranges and to adult healthy controls. Pediatric patients showed also a significant increase in TNF-α and IL-17F levels at baseline. IL-4, IFN-γ, Il-22, IL-23, and IL-33 decreased in serum of pediatric SMA patients after 6 months of therapy when compared to baseline. A significant decrease in IL-4, IL-6, INF-γ, and IL-17A was detected in serum of adult SMA patients after treatment. CSF of both pediatric and adult SMA patients displayed detectable levels of all cytokines with no significant differences after 6 months of treatment with nusinersen. Notably, a higher baseline expression of IL-23 in serum correlated with a worse motor function outcome after treatment in pediatric patients. Moreover, after 6 months of treatment, patients presenting a higher IL-10 concentration in serum showed a better Hammersmith Functional Motor Scale Expanded (HFMSE) score.

Discussion

Pediatric and adult SMA patients show an inflammatory signature in serum that is reduced upon SMN2 modulating treatment, and the presence of inflammatory mediators in CSF. Our findings enhance SMA knowledge with potential clinical and therapeutic implications.

Glial fibrillary acidic protein in cerebrospinal fluid of patients with spinal muscular atrophy

Objective

Activated astroglia is involved in the pathophysiology of neurodegenerative diseases and has also been described in animal models of spinal muscular atrophy (SMA). Given the urgent need of biomarkers for treatment monitoring of new RNA‐modifying and gene replacement therapies in SMA, we examined glial fibrillary acidic protein concentrations in cerebrospinal fluid (cGFAP) as a marker of astrogliosis in SMA.

Methods

58 adult patients and 21 children with genetically confirmed 5q‐associated SMA from four German motor neuron disease specialist care centers and 30 age‐ and sex‐matched controls were prospectively included in this study. cGFAP was measured and correlated to motor performance and disease severity. Additionally, we compared cGFAP with neurofilament light chain concentrations in cerebrospinal fluid (cNfL).

Results

cGFAP concentrations did not differ from controls but showed higher levels in more severely affected patients after adjustment for patients' age. Normalized cNfL values were associated with disease severity. Within 14 months of nusinersen treatment, cGFAP concentrations did not change, while cNfL decreased significantly.

Interpretation

cGFAP is not an outstanding biomarker in SMA, but might support the hypothesis that glial activation is involved in SMA pathology. Unlike previously suggested, cNfL may be a promising biomarker also in adult patients with SMA, which should be subject to further investigations.

Spinal muscular atrophy type 2 patient who survived 61 years: an autopsy case report

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disease characterized by progressive muscle weakness due to degeneration of lower motor neurons in the anterior horn of the spinal cord. We analyzed autopsy findings of a male patient with SMA type 2 who survived until 61 years of age. Genetic analysis revealed a homozygous deletion of the survival motor neuron (SMN) gene 1 (SMN1) exon 7, confirming the diagnosis of SMA. Results of further analyses indicated that the patient had two copies of the genuine SMN gene 2 (SMN2) and one copy of a hybrid gene containing SMN2 exon 7 and SMN1 exon 8. Pathological examination revealed moderate neuronal loss of the anterior horn and appearance of heterotopic neurons in the lateral funiculus, whereas a few achromatic neurons were notably localized in the anterior horn of the lumbar segment. Microdysgenesis as a consequence of migration disturbance was found in the white matter of the frontal lobe, postulating the possibility of the maldevelopment of the nervous system.

Dual SMN inducing therapies can rescue survival and motor unit function in symptomatic ∆7SMA mice

Spinal muscular atrophy (SMA) is an autosomal recessive disease characterized by survival motor neuron (SMN) protein deficiency which results in motor neuron loss and muscle atrophy. SMA is caused by a mutation or deletion of the survival motor neuron 1 (SMN1) gene and retention of the nearly identical SMN2 gene. SMN2 contains a C to T change in exon 7 that results in exon 7 exclusion from 90% of transcripts. SMN protein lacking exon 7 is unstable and rapidly degraded. The remaining full-length transcripts from SMN2 are insufficient for normal motor neuron function leading to the development of SMA. Three different therapeutic approaches that increase full-length SMN (FL-SMN) protein production are approved for treatment of SMA patients. Studies in both animal models and humans have demonstrated increasing SMN levels prior to onset of symptoms provides the greatest therapeutic benefit. Treatment of SMA, after some motor neuron loss has occurred, is also effective but to a lesser degree. The SMN∆7 mouse model is a well characterized model of severe or type 1 SMA, dying at 14 days of age. Here we treated three groups of ∆7SMA mice starting before, roughly during, and after symptom onset to determine if combining two mechanistically distinct SMN inducing therapies could improve the therapeutic outcome both before and after motor neuron loss. We found, compared with individual therapies, that morpholino antisense oligonucleotide (ASO) directed against ISS-N1 combined with the small molecule compound RG7800 significantly increased FL-SMN transcript and protein production resulting in improved survival and weight of ∆7SMA mice. Moreover, when give late symptomatically, motor unit function was completely rescued with no loss in function at 100 days of age in the dual treatment group. We have therefore shown that this dual therapeutic approach successfully increases SMN protein and rescues motor function in symptomatic ∆7SMA mice.

Frontotemporal Pathology in Motor Neuron Disease Phenotypes: Insights From Neuroimaging

Frontotemporal involvement has been extensively investigated in amyotrophic lateral sclerosis (ALS) but remains relatively poorly characterized in other motor neuron disease (MND) phenotypes such as primary lateral sclerosis (PLS), progressive muscular atrophy (PMA), spinal muscular atrophy (SMA), spinal bulbar muscular atrophy (SBMA), post poliomyelitis syndrome (PPS), and hereditary spastic paraplegia (HSP). This review focuses on insights from structural, metabolic, and functional neuroimaging studies that have advanced our understanding of extra-motor disease burden in these phenotypes. The imaging literature is limited in the majority of these conditions and frontotemporal involvement has been primarily evaluated by neuropsychology and post mortem studies. Existing imaging studies reveal that frontotemporal degeneration can be readily detected in ALS and PLS, varying degree of frontotemporal pathology may be captured in PMA, SBMA, and HSP, SMA exhibits cerebral involvement without regional predilection, and there is limited evidence for cerebral changes in PPS. Our review confirms the heterogeneity extra-motor pathology across the spectrum of MNDs and highlights the role of neuroimaging in characterizing anatomical patterns of disease burden in vivo. Despite the contribution of neuroimaging to MND research, sample size limitations, inclusion bias, attrition rates in longitudinal studies, and methodological constraints need to be carefully considered. Frontotemporal involvement is a quintessential clinical facet of MND which has important implications for screening practices, individualized management strategies, participation in clinical trials, caregiver burden, and resource allocation. The academic relevance of imaging frontotemporal pathology in MND spans from the identification of genetic variants, through the ascertainment of presymptomatic changes to the design of future epidemiology studies.

A novel zebrafish model for intermediate type spinal muscular atrophy demonstrates importance of Smn for maintenance of mature motor neurons

A deficiency in Survival Motor Neuron (SMN) protein results in motor neuron loss in spinal muscular atrophy (SMA) patients. Human SMN is encoded by SMN1 and SMN2 that differ by a single C6T transition in a splice regulatory region of exon 7. In SMN2, exon 7 is skipped leading to an unstable protein, which cannot compensate for SMN1 loss in SMA patients. The disease severity of human SMA (Types 1 to 4) depends on the levels of SMN protein, with intermediate levels leading to delayed disease onset and extended life expectancy in Type 2 patients. We used homology directed repair (HDR) to generate a zebrafish mutant with intermediate Smn levels, to mimic intermediate, hSMN2 dependent forms of SMA. In the obtained smnA6Tind27 mutant zebrafish, Smn protein formed oligomers but protein levels dropped significantly at juvenile stages. Motor neurons and neuromuscular junctions (NMJ) also formed normally initially but motor neuron loss and locomotor deficiencies became evident at 21 days. Subsequent muscle wasting and early adult lethality also phenocopied intermediate forms of human SMA. Together, our findings are consistent with the interpretation that Smn is required for neuromuscular maintenance, and establish the smnA6Tind27 zebrafish mutant as a novel model for intermediate types of SMA. As this mutant allows studying the effect of late Smn loss on motor neurons, neuromuscular junctions, and muscle at advanced stages of the disease, it will be a valuable resource for testing new drugs targeted towards treating intermediate forms of SMA.

Spinal Muscular Atrophy: Autopsy Based Neuropathological Demonstration

Spinal muscular atrophy (SMA) encompasses a group of disorders with loss of spinal motor neurons.The report describes the neuropathological findings including brain and spinal cord at autopsy in a five-and-half-month-old boy with suspected type 1 SMA. The anterior motor neurons, Clarke's column at all the levels of spinal cord showed neuronal loss and degeneration while neurons at all the deep grey nuclei were preserved apart from variable degree anoxic changes. Skeletal muscle biopsy revealed features of neurogenic atrophy consistent with SMA. A differential diagnosis like storage disorders was excluded using electron microscopy. No extra-neural manifestations were seen. Neuropathological features at autopsy have seldom been reported in the literature.

Pilot Study on Quantitative Cervical Cord and Muscular MRI in Spinal Muscular Atrophy: Promising Biomarkers of Disease Evolution and Treatment?

Introduction: Nusinersen is a recent promising therapy approved for the treatment of spinal muscular atrophy (SMA), a rare disease characterized by the degeneration of alpha motor neurons (αMN) in the spinal cord (SC) leading to progressive muscle atrophy and dysfunction. Muscle and cervical SC quantitative magnetic resonance imaging (qMRI) has never been used to monitor drug treatment in SMA. The aim of this pilot study is to investigate whether qMRI can provide useful biomarkers for monitoring treatment efficacy in SMA.

Methods: Three adult SMA 3a patients under treatment with nusinersen underwent longitudinal clinical and qMRI examinations every 4 months from baseline to 21-month follow-up. The qMRI protocol aimed to quantify thigh muscle fat fraction (FF) and water-T2 (w-T2) and to characterize SC volumes and microstructure. Eleven healthy controls underwent the same SC protocol (single time point). We evaluated clinical and imaging outcomes of SMA patients longitudinally and compared SC data between groups transversally.

Results: Patient motor function was stable, with only Patient 2 showing moderate improvements. Average muscle FF was already high at baseline (50%) and progressed over time (57%). w-T2 was also slightly higher than previously published data at baseline and slightly decreased over time. Cross-sectional area of the whole SC, gray matter (GM), and ventral horns (VHs) of Patients 1 and 3 were reduced compared to controls and remained stable over time, while GM and VHs areas of Patient 2 slightly increased. We found altered diffusion and magnetization transfer parameters in SC structures of SMA patients compared to controls, thus suggesting changes in tissue microstructure and myelin content.

Conclusion: In this pilot study, we found a progression of FF in thigh muscles of SMA 3a patients during nusinersen therapy and a concurrent slight reduction of w-T2 over time. The SC qMRI analysis confirmed previous imaging and histopathological studies suggesting degeneration of αMN of the VHs, resulting in GM atrophy and demyelination. Our longitudinal data suggest that qMRI could represent a feasible technique for capturing microstructural changes induced by SMA in vivo and a candidate methodology for monitoring the effects of treatment, once replicated on a larger cohort.

Functional Abnormalities of Cerebellum and Motor Cortex in Spinal Muscular Atrophy Mice

Spinal muscular atrophy (SMA) is a devastating genetic neuromuscular disease. Diffuse neuropathology has been reported in SMA patients and mouse models, however, functional changes in brain regions have not been studied. In the SMNΔ7 mouse model, we identified three types of differences in neuronal function in the cerebellum and motor cortex from two age groups: P7-9 (P7) and P11-14 (P11). Microelectrode array studies revealed significantly lower spontaneous firing and network activity in the cerebellum of SMA mice in both age groups, but it was more profound in the P11 group. In the motor cortex, however, neural activity was not different in either age group. Whole-cell patch-clamp was used to study the function of output neurons in both brain regions. In cerebellar Purkinje cells (PCs) of SMA mice, the input resistance was larger at P7, while capacitance was smaller at P11. In the motor cortex, no difference was observed in the passive membrane properties of layer V pyramidal neurons (PN5s). The action potential threshold of both types of output neurons was depolarized in the P11 group. We also observed lower spontaneous excitatory and inhibitory synaptic activity in PN5s and PCs respectively from P11 SMA mice. Overall, these differences suggest functional alterations in the neural network in these motor regions that change during development. Our results also suggest that neuronal dysfunction in these brain regions may contribute to the pathology of SMA. Comprehensive treatment strategies may consider motor regions outside of the spinal cord for better outcomes.

Spinal muscular atrophy type III complicated by spinal superficial siderosis: a case report with molecular and neuropathological findings

Spinal muscular atrophy (SMA) is largely linked to deletion or mutation of the Survival motor neuron 1 (SMN1) gene located on chromosome 5q13. Type III (Kugelberg–Welander disease) is the mildest childhood form and patients may become ambulatory and have a normal life expectancy. We report the clinical history and morphological findings of a 55-year-old woman who began to experience motor problems at the age of two. She was never fully ambulatory, and her severe scoliosis required the insertion of surgical rod at age 19. Unexpectedly, around 35 years of age, she began to experience sensory symptoms best characterized as a myelo-radiculo-neuropathy with pain as the dominant symptom. Investigations never clarified the etiology of these symptoms. Molecular confirmation of SMA type III was done post-mortem. Neuropathological examination showed classic changes of lower motor neuron neurodegeneration, in line with those reported in the single molecularly confirmed case published so far, and with findings in rare cases reported prior to the discovery of the gene defect. A key autopsy finding was the presence of a severe superficial siderosis of the lower half of the spinal cord. In recent years, the concept of duropathy was put forward, associating superficial siderosis of the spinal cord with various spinal abnormalities, some of which were present in our patient. The presence of significant hemosiderin deposits in the spinal cord and sensory nerve roots with associated tissue and axonal damage provide a plausible explanation for the unexpected sensory symptomatology in this mild lower motor neurodegeneration.

Imaging of the thoracic spinal cord using radially sampled averaged magnetization inversion recovery acquisitions

BACKGROUND

Spinal cord (SC) gray and white matter atrophy quantification by advanced morphometric MRI can help to better characterize the course of neurodegenerative diseases in vivo, such as e.g. lower motor neuron disorders. Imaging the lower thoracic cord - containing those motor neurons that control leg function - could be particularly informative, however, is challenging due to tissue composition, physiological motion and large field of views.

NEW METHOD

An "averaged magnetization inversion recovery acquisitions" (AMIRA) approach with a radial k-space acquisition scheme was developed. The method is designed for morphometric SC imaging with a focus on the thoracic SC.

RESULTS

In a typical setting, radial AMIRA acquires transverse slices with a high 0.50 × 0.50mm² in-plane resolution and a pronounced positive contrast between thoracic gray and white matter, within typically 2:39 min. Additional proof-of-concept measurements in patients demonstrate that such contrast and resolving capability is indeed necessary to assess potential atrophy of the anterior horns.

COMPARISON WITH EXISTING METHOD(S)

Radial AMIRA utilizes two benefits of radial MRI techniques: being generally less prone to motion effects and that fold over artifacts can manifest less intrusively. These benefits are united with the original AMIRA approach which allows the contrast to be 'tuned' and improved based on the combination of five simultaneously acquired images of different tissue contrast.

CONCLUSIONS

Radial AMIRA is a promising approach for in vivo SC gray and white matter atrophy visualization and quantification in lower motor neuron diseases and other autoimmune or genetic diseases involving the entire (not only cervical) spinal cord.

Cerebellar degeneration in adult spinal muscular atrophy patients

BACKGROUND

Spinal muscular atrophy (SMA) is a genetic motor neuron disease related to deletions in the SMN1 gene. There is mounting evidence that the disease is not restricted to motor neurons. In this neuroimaging study, we aimed to investigate the presence of in-vivo cerebellar damage in adult SMA patients not treated with disease-modifying treatment.

METHODS

Twenty-five molecularly confirmed patients with SMA type III or IV and 25 healthy controls underwent MRI with cerebellar focused structural analysis by the CERES automated pipeline. Volumetry (total and gray matter-GM) as well as cortical thickness of the cerebellar lobules were compared in both groups. Full clinical and demographic data were then assessed for correlations with cerebellar imaging findings.

RESULTS

Volumes of cerebellar lobules VIIIB (right), IX and X were significantly smaller in patients with SMA. Lobule IX also had GM atrophy in comparison to controls. We found no significant correlation between clinical findings and cerebellar damage.

CONCLUSIONS

Neuroimaging detects cerebellar structural changes in adult SMA patients, suggesting that neurodegeneration is not confined to the lower motor neurons in the disease.

Glial cells involvement in spinal muscular atrophy: Could SMA be a neuroinflammatory disease?

Spinal muscular atrophy (SMA) is a severe, inherited disease characterized by the progressive degeneration and death of motor neurons of the anterior horns of the spinal cord, which results in muscular atrophy and weakness of variable severity. Its early-onset form is invariably fatal in early childhood, while milder forms lead to permanent disability, physical deformities and respiratory complications. Recently, two novel revolutionary therapies, antisense oligonucleotides and gene therapy, have been approved, and might prove successful in making long-term survival of these patients likely. In this perspective, a deep understanding of the pathogenic mechanisms and of their impact on the interactions between motor neurons and other cell types within the central nervous system (CNS) is crucial. Studies using SMA animal and cellular models have taught us that the survival and functionality of motor neurons is highly dependent on a whole range of other cell types, namely glial cells, which are responsible for a variety of different functions, such as neuronal trophic support, synaptic remodeling, and immune surveillance. Thus, it emerges that SMA is likely a non-cell autonomous, multifactorial disease in which the interaction of different cell types and disease mechanisms leads to motor neurons failure and loss. This review will introduce the different glial cell types in the CNS and provide an overview of the role of glial cells in motor neuron degeneration in SMA. Furthermore, we will discuss the relevance of these findings so far and the potential impact on the success of available therapies and on the development of novel ones.

Twenty-Five Years of Spinal Muscular Atrophy Research: From Phenotype to Genotype to Therapy, and What Comes Next

Twenty-five years ago, the underlying genetic cause for one of the most common and devastating inherited diseases in humans, spinal muscular atrophy (SMA), was identified. Homozygous deletions or, rarely, subtle mutations of SMN1 cause SMA, and the copy number of the nearly identical copy gene SMN2 inversely correlates with disease severity. SMA has become a paradigm and a prime example of a monogenic neurological disorder that can be efficiently ameliorated or nearly cured by novel therapeutic strategies, such as antisense oligonucleotide or gene replacement therapy. These therapies enable infants to survive who might otherwise have died before the age of two and allow individuals who have never been able to sit or walk to do both. The major milestones on the road to these therapies were to understand the genetic cause and splice regulation of SMN genes, the disease's phenotype-genotype variability, the function of the protein and the main affected cellular pathways and tissues, the disease's pathophysiology through research on animal models, the windows of opportunity for efficient treatment, and how and when to treat patients most effectively.This review aims to bridge our knowledge from phenotype to genotype to therapy, not only highlighting the significant advances so far but also speculating about the future of SMA screening and treatment.

Astrocytes in Motor Neuron Diseases

Motor neuron disorders are highly debilitating and mostly fatal conditions for which only limited therapeutic options are available. To overcome this limitation and develop more effective therapeutic strategies, it is critical to discover the pathogenic mechanisms that trigger and sustain motor neuron degeneration with the greatest accuracy and detail. In the case of Amyotrophic Lateral Sclerosis (ALS), several genes have been associated with familial forms of the disease, whilst the vast majority of cases develop sporadically and no defined cause can be held responsible. On the contrary, the huge majority of Spinal Muscular Atrophy (SMA) occurrences are caused by loss-of-function mutations in a single gene, SMN1. Although the typical hallmark of both diseases is the loss of motor neurons, there is increasing awareness that pathological lesions are also present in the neighbouring glia, whose dysfunction clearly contributes to generating a toxic environment in the central nervous system. Here, ALS and SMA are sequentially presented, each disease section having a brief introduction, followed by a focussed discussion on the role of the astrocytes in the disease pathogenesis. Such a dissertation is substantiated by the findings that built awareness on the glial involvement and how the glial-neuronal interplay is perturbed, along with the appraisal of this new cellular site for possible therapeutic intervention.

Magnetic resonance imaging of the cervical spinal cord in spinal muscular atrophy

Objective

In this study we investigated the potential value of magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) in characterizing changes in the cervical spinal cord and peripheral nerve roots in vivo in patients with spinal muscular atrophy (SMA).

Methods

We developed an MRI protocol with 4 sequences to investigate the cervical spinal cord and nerve roots on a 3 Tesla MRI system. We used 2 anatomical MRI sequences to investigate cross-sectional area (CSA) at each spinal segment and the diameter of ventral and dorsal nerve roots, and two diffusion tensor imaging (DTI) techniques to estimate the fractional anisotropy (FA), mean (MD), axial (AD) and radial diffusivity (RD) in 10 SMA patients and 20 healthy controls.

Results

There were no significant differences in CSA (p > .1), although an 8.5% reduction of CSA in patients compared to healthy controls was apparent at segment C7. DTI data showed a higher AD in grey matter of patients compared to healthy controls (p = .033). Significantly lower MD, AD and RD values were found in rostral nerve roots (C3-C5) in patients (p < .045).

Conclusions

We showed feasibility of an advanced 3 T MRI protocol that allowed differences to be determined between patients and healthy controls, confirming the potential of this technique to assess pathological mechanisms in SMA. After further development and confirmation of findings in a larger sample, these techniques may be used to study disease course of SMA in vivo and evaluate response to survival motor neuron (SMN) augmenting therapy.

•

The developed MRI sequences measure (micro)structural spinal cord changes in SMA.

•

cervical spinal cross-sectional area is overall (non-significantly) smaller in SMA.

•

In nerve roots C3-C8 all DTI parameters were lower in patients compared to controls.

•

Largest differences in DTI parameters were located at the rostral cervical segments.

Lumbosacral ventral spinal nerve root atrophy identified on MRI in a case of spinal muscular atrophy type II

Spinal muscular atrophies are rare genetic disorders most often caused by homozygous deletion mutations in SMN1 that lead to progressive neurodegeneration of anterior horn cells. Ventral spinal root atrophy is a consistent pathological finding in post-mortem examinations of patients who suffered from various subtypes of spinal muscular atrophy; however, corresponding radiographic findings have not been previously reported. We present a patient with hypotonia and weakness who was found to have ventral spinal root atrophy in the lumbosacral region on MRI and was subsequently diagnosed with spinal muscular atrophy. More systematic analyses of imaging studies in spinal muscular atrophy will help determine whether such findings have the potential to serve as reliable diagnostic markers for clinical evaluations or as outcome measure for clinical trials.

Mild SMN missense alleles are only functional in the presence of SMN2 in mammals

Spinal muscular atrophy (SMA) is caused by reduced levels of full-length SMN (FL-SMN). In SMA patients with one or two copies of the Survival Motor Neuron 2 (SMN2) gene there are a number of SMN missense mutations that result in milder-than-predicted SMA phenotypes. These mild SMN missense mutation alleles are often assumed to have partial function. However, it is important to consider the contribution of FL-SMN as these missense alleles never occur in the absence of SMN2. We propose that these patients contain a partially functional oligomeric SMN complex consisting of FL-SMN from SMN2 and mutant SMN protein produced from the missense allele. Here we show that mild SMN missense mutations SMND44V, SMNT74I or SMNQ282A alone do not rescue mice lacking wild-type FL-SMN. Thus, missense mutations are not functional in the absence of FL-SMN. In contrast, when the same mild SMN missense mutations are expressed in a mouse containing two SMN2 copies, functional SMN complexes are formed with the small amount of wild-type FL-SMN produced by SMN2 and the SMA phenotype is completely rescued. This contrasts with SMN missense alleles when studied in C. elegans, Drosophila and zebrafish. Here we demonstrate that the heteromeric SMN complex formed with FL-SMN is functional and sufficient to rescue small nuclear ribonucleoprotein assembly, motor neuron function and rescue the SMA mice. We conclude that mild SMN missense alleles are not partially functional but rather they are completely non-functional in the absence of wild-type SMN in mammals.

Glial Activation and Central Synapse Loss, but Not Motoneuron Degeneration, Are Prevented by the Sigma-1 Receptor Agonist PRE-084 in the Smn2B/- Mouse Model of Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is characterized by the loss of α-motoneurons (MNs) with concomitant muscle denervation. MN excitability and vulnerability to disease are particularly regulated by cholinergic synaptic afferents (C-boutons), in which Sigma-1 receptor (Sig1R) is concentrated. Alterations in Sig1R have been associated with MN degeneration. Here, we investigated whether a chronic treatment with the Sig1R agonist PRE-084 was able to exert beneficial effects on SMA. We used a model of intermediate SMA, the Smn2B/- mouse, in which we performed a detailed characterization of the histopathological changes that occur throughout the disease. We report that Smn2B/- mice exhibited qualitative differences in major alterations found in mouse models of severe SMA: Smn2B/- animals showed more prominent MN degeneration, early motor axon alterations, marked changes in sensory neurons, and later MN deafferentation that correlated with conspicuous reactive gliosis and altered neuroinflammatory M1/M2 microglial balance. PRE-084 attenuated reactive gliosis, mitigated M1/M2 imbalance, and prevented MN deafferentation in Smn2B/- mice. These effects were also observed in a severe SMA model, the SMNΔ7 mouse. However, the prevention of gliosis and MN deafferentation promoted by PRE-084 were not accompanied by any improvements in clinical outcome or other major pathological changes found in SMA mice.

Developmental and degenerative cardiac defects in the Taiwanese mouse model of severe spinal muscular atrophy

Spinal muscular atrophy (SMA), an autosomal recessive disease caused by a decrease in levels of the survival motor neuron (SMN) protein, is the most common genetic cause of infant mortality. Although neuromuscular pathology is the most severe feature of SMA, other organs and tissues, including the heart, are also known to be affected in both patients and animal models. Here, we provide new insights into changes occurring in the heart, predominantly at pre- and early symptomatic ages, in the Taiwanese mouse model of severe SMA. Thinning of the interventricular septum and dilation of the ventricles occurred at pre- and early symptomatic ages. However, the left ventricular wall was significantly thinner in SMA mice from birth, occurring prior to any overt neuromuscular symptoms. Alterations in collagen IV protein from birth indicated changes to the basement membrane and contributed to the abnormal arrangement of cardiomyocytes in SMA hearts. This raises the possibility that developmental defects, occurring prenatally, may contribute to cardiac pathology in SMA. In addition, cardiomyocytes in SMA hearts exhibited oxidative stress at pre-symptomatic ages and increased apoptosis during early symptomatic stages of disease. Heart microvasculature was similarly decreased at an early symptomatic age, likely contributing to the oxidative stress and apoptosis phenotypes observed. Finally, an increased incidence of blood retention in SMA hearts post-fixation suggests the likelihood of functional defects, resulting in blood pooling. These pathologies mirror dilated cardiomyopathy, with clear consequences for heart function that would likely contribute to potential heart failure. Our findings add significant additional experimental evidence in support of the requirement to develop systemic therapies for SMA capable of treating non-neuromuscular pathologies.

Pathogenic commonalities between spinal muscular atrophy and amyotrophic lateral sclerosis: Converging roads to therapeutic development

Spinal muscular atrophy (SMA) and amyotrophic lateral sclerosis (ALS) are the two most common motoneuron disorders, which share typical pathological hallmarks while remaining genetically distinct. Indeed, SMA is caused by deletions or mutations in the survival motor neuron 1 (SMN1) gene whilst ALS, albeit being mostly sporadic, can also be caused by mutations within genes, including superoxide dismutase 1 (SOD1), Fused in Sarcoma (FUS), TAR DNA-binding protein 43 (TDP-43) and chromosome 9 open reading frame 72 (C9ORF72). However, it has come to light that these two diseases may be more interlinked than previously thought. Indeed, it has recently been found that FUS directly interacts with an Smn-containing complex, mutant SOD1 perturbs Smn localization, Smn depletion aggravates disease progression of ALS mice, overexpression of SMN in ALS mice significantly improves their phenotype and lifespan, and duplications of SMN1 have been linked to sporadic ALS. Beyond genetic interactions, accumulating evidence further suggests that both diseases share common pathological identities such as intrinsic muscle defects, neuroinflammation, immune organ dysfunction, metabolic perturbations, defects in neuron excitability and selective motoneuron vulnerability. Identifying common molecular effectors that mediate shared pathologies in SMA and ALS would allow for the development of therapeutic strategies and targeted gene therapies that could potentially alleviate symptoms and be equally beneficial in both disorders. In the present review, we will examine our current knowledge of pathogenic commonalities between SMA and ALS, and discuss how furthering this understanding can lead to the establishment of novel therapeutic approaches with wide-reaching impact on multiple motoneuron diseases.

Free-Aspire: A new device for the management of airways clearance in patient with ineffective cough

A 3-year-old girl with Spinal Muscular Atrophy type I presented with a right pneumonia. On physical examination pulmonary auscultation revealed an asymmetry of breath sounds between the 2 hemithoraces, owing to decreased breath sounds in the right hemithorax. Blood tests were normal. The initial working diagnosis was a suspected area of mucus accumulation. A treatment with Free Aspire was started. Within a few days, the girl was discharged with a normal physical examination and X-ray study result. Spinal Muscular Atrophy is a rare neuromuscular disorder characterized by loss of motor neurons and progressive muscle wasting. Cough in these patients result ineffective. Free-Aspire is an electromedical machine for removing bronchoalveolar secretions. The case show that Free Aspire in patients with ineffective cough and impaired removal of secretions is a safe and effective device for the removal of bronchial secretions and could be an another help in the management of airway clearance.

New insights into SMA pathogenesis: immune dysfunction and neuroinflammation

Spinal muscular atrophy (SMA) is a neuromuscular disorder characterized by motor neuron degeneration, although defects in multiple cell types and tissues have also been implicated. Three independent laboratories recently identified immune organ defects in SMA. We therefore propose a novel pathogenic mechanism contributory to SMA, resulting in higher susceptibility to infection and exacerbated disease progression caused by neuroinflammation. Overall, compromised immune function could significantly affect survival and quality of life of SMA patients. We highlight the recent findings in immune organ defects, their potential consequences on patients, our understanding of neuroinflammation in SMA, and new research hypotheses in SMA pathogenesis.

Cardiac pathology in spinal muscular atrophy: a systematic review

Background

Hereditary proximal spinal muscular atrophy (SMA) is a severe neuromuscular disease of childhood caused by homozygous loss of function of the survival motor neuron (SMN) 1 gene. The presence of a second, nearly identical SMN gene (SMN2) in the human genome ensures production of residual levels of the ubiquitously expressed SMN protein. Alpha-motor neurons in the ventral horns of the spinal cord are most vulnerable to reduced SMN concentrations but the development or function of other tissues may also be affected, and cardiovascular abnormalities have frequently been reported both in patients and SMA mouse models.

Methods

We systematically reviewed reported cardiac pathology in relation to SMN deficiency. To investigate the relevance of the possible association in more detail, we used clinical classification systems to characterize structural cardiac defects and arrhythmias.

Conclusions

Seventy-two studies with a total of 264 SMA patients with reported cardiac pathology were identified, along with 14 publications on SMA mouse models with abnormalities of the heart. Structural cardiac pathology, mainly septal defects and abnormalities of the cardiac outflow tract, was reported predominantly in the most severely affected patients (i.e. SMA type 1). Cardiac rhythm disorders were most frequently reported in patients with milder SMA types (e.g. SMA type 3). All included studies lacked control groups and a standardized approach for cardiac evaluation.

The convergence to specific abnormalities of cardiac structure and function may indicate vulnerability of specific cell types or developmental processes relevant for cardiogenesis. Future studies would benefit from a controlled and standardized approach for cardiac evaluation in patients with SMA.

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-017-0613-5) contains supplementary material, which is available to authorized users.

Spinal Muscular Atrophy

Spinal muscular atrophy is an autosomal-recessive disorder characterized by degeneration of motor neurons in the spinal cord and caused by mutations in the survival motor neuron 1 gene, SMN1. The severity of SMA is variable. The SMN2 gene produces a fraction of the SMN messenger RNA (mRNA) transcript produced by the SMN1 gene. There is an inverse correlation between SMN2 gene copy number and clinical severity. Clinical management focuses on multidisciplinary care. Preclinical models of SMA have led to an explosion of SMA clinical trials that hold great promise of effective therapy in the future.

An Integrative Transcriptomic Analysis for Identifying Novel Target Genes Corresponding to Severity Spectrum in Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is an inherited neuromuscular disease resulting from a recessive mutation in the SMN1 gene. This disease affects multiple organ systems with varying degrees of severity. Exploration of the molecular pathological changes occurring in different cell types in SMA is crucial for developing new therapies. This study collected 39 human microarray datasets from ArrayExpress and GEO databases to build an integrative transcriptomic analysis for recognizing novel SMA targets. The transcriptomic analysis was conducted through combining weighted correlation network analysis (WGCNA) for gene module detection, gene set enrichment analysis (GSEA) for functional categorization and filtration, and Cytoscape (visual interaction gene network analysis) for target gene identification. Seven novel target genes (Bmp4, Serpine1, Gata6, Ptgs2, Bcl2, IL6 and Cntn1) of SMA were revealed, and are all known in the regulation of TNFα for controlling neural, cardiac and bone development. Sequentially, the differentially expressed patterns of these 7 target genes in mouse tissues (e.g., spinal cord, heart, muscles and bone) were validated in SMA mice of different severities (pre-symptomatic, mildly symptomatic, and severely symptomatic). In severely symptomatic SMA mice, TNFα was up-regulated with attenuation of Bmp4 and increase of Serpine1 and Gata6 (a pathway in neural and cardiac development), but not in pre-symptomatic and mildly symptomatic SMA mice. The severely symptomatic SMA mice also had the elevated levels of Ptgs2 and Bcl2 (a pathway in skeletal development) as well as IL6 and Cntn1 (a pathway in nervous system development). Thus, the 7 genes identified in this study might serve as potential target genes for future investigations of disease pathogenesis and SMA therapy.

Restoration of SMN in Schwann cells reverses myelination defects and improves neuromuscular function in spinal muscular atrophy

Spinal muscular atrophy (SMA) is a neuromuscular disease caused by low levels of SMN protein, primarily affecting lower motor neurons. Recent evidence from SMA and related conditions suggests that glial cells can influence disease severity. Here, we investigated the role of glial cells in the peripheral nervous system by creating SMA mice selectively overexpressing SMN in myelinating Schwann cells (Smn^−/−;SMN2^tg/0;SMN1^SC). Restoration of SMN protein levels restricted solely to Schwann cells reversed myelination defects, significantly improved neuromuscular function and ameliorated neuromuscular junction pathology in SMA mice. However, restoration of SMN in Schwann cells had no impact on motor neuron soma loss from the spinal cord or ongoing systemic and peripheral pathology. This study provides evidence for a defined, intrinsic contribution of glial cells to SMA disease pathogenesis and suggests that therapies designed to include Schwann cells in their target tissues are likely to be required in order to rescue myelination defects and associated disease symptoms.

Cervical Spinal Cord Atrophy Profile in Adult SMN1-Linked SMA

PURPOSE

The mechanisms underlying the topography of motor deficits in spinal muscular atrophy (SMA) remain unknown. We investigated the profile of spinal cord atrophy (SCA) in SMN1-linked SMA, and its correlation with the topography of muscle weakness.

MATERIALS AND METHODS

Eighteen SMN1-linked SMA patients type III/V and 18 age/gender-matched healthy volunteers were included. Patients were scored on manual muscle testing and functional scales. Spinal cord was imaged using 3T MRI system. Radial distance (RD) and cord cross-sectional area (CSA) measurements in SMA patients were compared to those in controls and correlated with strength and disability scores.

RESULTS

CSA measurements revealed a significant cord atrophy gradient mainly located between C3 and C6 vertebral levels with a SCA rate ranging from 5.4% to 23% in SMA patients compared to controls. RD was significantly lower in SMA patients compared to controls in the anterior-posterior direction with a maximum along C4 and C5 vertebral levels (p-values < 10-5). There were no correlations between atrophy measurements, strength and disability scores.

CONCLUSIONS

Spinal cord atrophy in adult SMN1-linked SMA predominates in the segments innervating the proximal muscles. Additional factors such as neuromuscular junction or intrinsic skeletal muscle defects may play a role in more complex mechanisms underlying weakness in these patients.

SMN deficiency does not induce oxidative stress in SMA iPSC-derived astrocytes or motor neurons

Spinal muscular atrophy (SMA) is a genetic disorder characterized by loss of motor neurons in the spinal cord leading to muscle atrophy and death. Although motor neurons (MNs) are the most obviously affected cells in SMA, recent evidence suggest dysfunction in multiple cell types. Astrocytes are a crucial component of the motor circuit and are intimately involved with MN health and maintenance. We have previously shown that SMA astrocytes are altered both morphologically and functionally early in disease progression, though it is unclear what causes astrocytes to become reactive. Oxidative stress is a common feature among neurodegenerative diseases. Oxidative stress can both induce apoptosis in neurons and can cause astrocytes to become reactive, which are features observed in the SMA induced pluripotent stem cell (iPSC) cultures. Therefore, we asked if oxidative stress contributes to SMA astrocyte pathology. We examined mitochondrial bioenergetics, transcript and protein levels of oxidative and anti-oxidant factors, and reactive oxygen species (ROS) production and found little evidence of oxidative stress. We did observe a significant increase in endogenous catalase expression in SMA iPSCs. While catalase knockdown in SMA iPSCs increased ROS production above basal levels, levels of ROS remained lower than in controls, further arguing against robust oxidative stress in this system. Viral delivery of survival motor neuron (SMN) reversed astrocyte activation and restored catalase levels to normal, without changing mitochondrial respiration or expression of oxidative stress markers. Taken together, these data indicate that SMN deficiency induces astrocyte reactivity, but does not do so through an oxidative stress-mediated process.

Astrocytes influence the severity of spinal muscular atrophy

Systemically low levels of survival motor neuron-1 (SMN1) protein cause spinal muscular atrophy (SMA). α-Motor neurons of the spinal cord are considered particularly vulnerable in this genetic disorder and their dysfunction and loss cause progressive muscle weakness, paralysis and eventually premature death of afflicted individuals. Historically, SMA was therefore considered a motor neuron-autonomous disease. However, depletion of SMN in motor neurons of normal mice elicited only a very mild phenotype. Conversely, restoration of SMN to motor neurons in an SMA mouse model had only modest effects on the SMA phenotype and survival. Collectively, these results suggested that additional cell types contribute to the pathogenesis of SMA, and understanding the non-autonomous requirements is crucial for developing effective therapies. Astrocytes are critical for regulating synapse formation and function as well as metabolic support for neurons. We hypothesized that astrocyte functions are disrupted in SMA, exacerbating disease progression. Using viral-based restoration of SMN specifically to astrocytes, survival in severe and intermediate SMA mice was observed. In addition, neuromuscular circuitry was improved. Astrogliosis was prominent in end-stage SMA mice and in post-mortem patient spinal cords. Increased expression of proinflammatory cytokines was partially normalized in treated mice, suggesting that astrocytes contribute to the pathogenesis of SMA.

Molecular mechanisms and animal models of spinal muscular atrophy

Spinal muscular atrophy (SMA), the leading genetic cause of infant mortality, is characterized by the degeneration of spinal motor neurons and muscle atrophy. Although the genetic cause of SMA has been mapped to the Survival Motor Neuron1 (SMN1) gene, mechanisms underlying selective motor neuron degeneration in SMA remain largely unknown. Here we review the latest developments and our current understanding of the molecular mechanisms underlying SMA pathogenesis, focusing on the animal model systems that have been developed, as well as new diagnostic and treatment strategies that have been identified using these model systems. This article is part of a special issue entitled: Neuromuscular Diseases: Pathology and Molecular Pathogenesis.

Spinal muscular atrophy: diagnosis and management in a new therapeutic era

Spinal muscular atrophy (SMA) describes a group of disorders associated with spinal motor neuron loss. In this review we provide an update regarding the most common form of SMA, proximal or 5q-SMA, and discuss the contemporary approach to diagnosis and treatment. Electromyography and muscle biopsy features of denervation were once the basis for diagnosis, but molecular testing for homozygous deletion or mutation of the SMN1 gene allows efficient and specific diagnosis. In combination with loss of SMN1, patients retain variable numbers of copies of a second similar gene, SMN2, which produces reduced levels of the survival motor neuron (SMN) protein that are insufficient for normal motor neuron function. Despite the fact that understanding of how ubiquitous reduction of SMN protein leads to motor neuron loss remains incomplete, several promising therapeutics are now being tested in early-phase clinical trials.

ROCK inhibition as a therapy for spinal muscular atrophy: understanding the repercussions on multiple cellular targets

Spinal muscular atrophy (SMA) is the most common genetic disease causing infant death, due to an extended loss of motoneurons. This neuromuscular disorder results from deletions and/or mutations within the Survival Motor Neuron 1 (SMN1) gene, leading to a pathological decreased expression of functional full-length SMN protein. Emerging studies suggest that the small GTPase RhoA and its major downstream effector Rho kinase (ROCK), which both play an instrumental role in cytoskeleton organization, contribute to the pathology of motoneuron diseases. Indeed, an enhanced activation of RhoA and ROCK has been reported in the spinal cord of an SMA mouse model. Moreover, the treatment of SMA mice with ROCK inhibitors leads to an increased lifespan as well as improved skeletal muscle and neuromuscular junction pathology, without preventing motoneuron degeneration. Although motoneurons are the primary target in SMA, an increasing number of reports show that other cell types inside and outside the central nervous system contribute to SMA pathogenesis. As administration of ROCK inhibitors to SMA mice was systemic, the improvement in survival and phenotype could therefore be attributed to specific effects on motoneurons and/or on other non-neuronal cell types. In the present review, we will present the various roles of the RhoA/ROCK pathway in several SMA cellular targets including neurons, myoblasts, glial cells, cardiomyocytes and pancreatic cells as well as discuss how ROCK inhibition may ameliorate their health and function. It is most likely a concerted influence of ROCK modulation on all these cell types that ultimately lead to the observed benefits of pharmacological ROCK inhibition in SMA mice.

Mechanisms involved in spinal cord central synapse loss in a mouse model of spinal muscular atrophy

Motoneuron (MN) cell death is the histopathologic hallmark of spinal muscular atrophy (SMA), although MN loss seems to be a late event. Conversely, disruption of afferent synapses on MNs has been shown to occur early in SMA. Using a mouse model of severe SMA (SMNΔ7), we examined the mechanisms involved in impairment of central synapses. We found that MNs underwent progressive degeneration in the course of SMA, with MN loss still occurring at late stages. Loss of afferent inputs to SMA MNs was detected at embryonic stages, long before MN death. Reactive microgliosis and astrogliosis were present in the spinal cord of diseased animals after the onset of MN loss. Ultrastructural observations indicate that dendrites and microglia phagocytose adjacent degenerating presynaptic terminals. Neuronal nitric oxide synthase was upregulated in SMNΔ7 MNs, and there was an increase in phosphorylated myosin light chain expression in synaptic afferents on MNs; these observations implicate nitric oxide in MN deafferentation and suggest that the RhoA/ROCK pathway is activated. Together, our observations suggest that the earliest change occurring in SMNΔ7 mice is the loss of excitatory glutamatergic synaptic inputs to MNs; reduced excitability may enhance their vulnerability to degeneration and death.

Spinal muscular atrophy: a motor neuron disorder or a multi-organ disease?

Spinal muscular atrophy (SMA) is an autosomal recessive disorder that is the leading genetic cause of infantile death. SMA is characterized by loss of motor neurons in the ventral horn of the spinal cord, leading to weakness and muscle atrophy. SMA occurs as a result of homozygous deletion or mutations in Survival Motor Neuron-1 (SMN1). Loss of SMN1 leads to a dramatic reduction in SMN protein, which is essential for motor neuron survival. SMA disease severity ranges from extremely severe to a relatively mild adult onset form of proximal muscle atrophy. Severe SMA patients typically die mostly within months or a few years as a consequence of respiratory insufficiency and bulbar paralysis. SMA is widely known as a motor neuron disease; however, there are numerous clinical reports indicating the involvement of additional peripheral organs contributing to the complete picture of the disease in severe cases. In this review, we have compiled clinical and experimental reports that demonstrate the association between the loss of SMN and peripheral organ deficiency and malfunction. Whether defective peripheral organs are a consequence of neuronal damage/muscle atrophy or a direct result of SMN loss will be discussed.

Notch signaling pathway is activated in motoneurons of spinal muscular atrophy

Spinal muscular atrophy (SMA) is a neurodegenerative disease produced by low levels of Survival Motor Neuron (SMN) protein that affects alpha motoneurons in the spinal cord. Notch signaling is a cell-cell communication system well known as a master regulator of neural development, but also with important roles in the adult central nervous system. Aberrant Notch function is associated with several developmental neurological disorders; however, the potential implication of the Notch pathway in SMA pathogenesis has not been studied yet. We report here that SMN deficiency, induced in the astroglioma cell line U87MG after lentiviral transduction with a shSMN construct, was associated with an increase in the expression of the main components of Notch signaling pathway, namely its ligands, Jagged1 and Delta1, the Notch receptor and its active intracellular form (NICD). In the SMNΔ7 mouse model of SMA we also found increased astrocyte processes positive for Jagged1 and Delta1 in intimate contact with lumbar spinal cord motoneurons. In these motoneurons an increased Notch signaling was found, as denoted by increased NICD levels and reduced expression of the proneural gene neurogenin 3, whose transcription is negatively regulated by Notch. Together, these findings may be relevant to understand some pathologic attributes of SMA motoneurons.