Natural history of denervation in SMA: relation to age, SMN2 copy number, and function

Spinal muscular atrophy - insights and challenges in the treatment era

Spinal muscular atrophy (SMA) is an autosomal recessive motor neuron disease caused by deletion or mutation of SMN1. Four subtypes exist, characterized by different clinical severities. New therapeutic approaches have become available in the past few years, dramatically changing the natural history of all SMA subtypes, including substantial clinical improvement with the severe and advanced SMA type 1 variant. Trials have now demonstrated that phenotypic rescue is even more dramatic when pre-symptomatic patients are treated, and emerging real-world data are demonstrating the benefits of intervention even in the chronic phase of the condition. Here, we critically review how the field is rapidly evolving in response to the new therapies and questions that the new treatments have posed, including the effects of treatment at different ages and stages of disease, new phenotypes and long-term outcomes in patients who would not have survived without treatment, and decisions of who to treat and when. We also discuss how the outcomes associated with different timing of therapeutic intervention are contributing to our understanding of the biology and pathogenesis of SMA.

CMAP changes upon symptom onset and during treatment in spinal muscular atrophy patients: lessons learned from newborn screening

PURPOSE

Early identification and treatment of spinal muscular atrophy (SMA) are crucial but difficult. In this study, we aimed to assess the significance of compound motor action potential (CMAP) amplitude in patients identified through a newborn screening program.

METHODS

We initiated a large-scale population newborn screening program for SMA in Taiwan in 2014. Patients had access to treatment through clinical trials or expanded use programs. Symptomatic patients were evaluated regularly, including CMAP exams.

RESULTS

Among 364,000 screened newborns, 21 were diagnosed with SMA. The incidence of SMA was around 1 in 17,000 live births, and 70% developed SMA type 1. All infants with two SMN2 copies became symptomatic before the age of 1 month. CMAP amplitudes of 12 newborns were available, including 6 who were subsequently treated with nusinersen. We found that a rapid decrease of CMAP amplitude was an early predictor of symptom onset. Pretreatment CMAP and rapid increment of post-treatment CMAP could predict better treatment outcomes.

CONCLUSION

This study prospectively demonstrated the incidence of SMA and its types. Our results imply the importance of pretreatment CMAP amplitude and rapid reversal of post-treatment CMAP amplitude with regard to disease presentation and also treatment outcomes.

Clinical Course in a Patient With Spinal Muscular Atrophy Type 0 Treated With Nusinersen and Onasemnogene Abeparvovec

Spinal muscular atrophy type 0 is the most severe phenotype of the disease, with patients presenting with contractures, weakness, and respiratory failure at birth, and is typically fatal within weeks. We describe the case of a patient with spinal muscular atrophy type 0 who was treated with both nusinersen and onasemnogene abeparvovec. She has made modest motor improvements since treatment initiation with a 30-point improvement in CHOP-INTEND score, and continues to make motor gains at age 13 months without regression of function, although she remains profoundly weak. Although she has had motor improvements, she has also had continued systemic complications from her spinal muscular atrophy, including chronic respiratory failure, dysphagia, congenital heart malformation, digit necrosis, and diffuse macular rash. This case highlights the challenges in treating those with more severe disease phenotypes and raises questions of how some systemic complications may respond to current SMN replacement therapies.

Subacute Liver Failure Following Gene Replacement Therapy for Spinal Muscular Atrophy Type 1

Spinal muscular atrophy is a neurodegenerative disease resulting from irreversible loss of anterior horn cells owing to biallelic deletions/mutations in the survival motor neuron (SMN) 1 gene. Gene replacement therapy using an adeno-associated virus vector containing the SMN gene was approved by the US Food and Drug Administration in May 2019. We report 2 cases of transient, drug-induced liver failure after this therapy.

Quantitative MRI of skeletal muscle in a cross-sectional cohort of patients with spinal muscular atrophy types 2 and 3

The aim of this study was to document upper leg involvement in spinal muscular atrophy (SMA) with quantitative MRI (qMRI) in a cross-sectional cohort of patients of varying type, disease severity and age. Thirty-one patients with SMA types 2 and 3 (aged 29.6 [7.6-73.9] years) and 20 healthy controls (aged 37.9 [17.7-71.6] years) were evaluated in a 3 T MRI with a protocol consisting of DIXON, T2 mapping and diffusion tensor imaging (DTI). qMRI measures were compared with clinical scores of motor function (Hammersmith Functional Motor Scale Expanded [HFMSE]) and muscle strength. Patients exhibited an increased fat fraction and fractional anisotropy (FA), and decreased mean diffusivity (MD) and T2 compared with controls (all P < .001). DTI parameters FA and MD manifest stronger effects than can be accounted for the effect of fatty replacement. Fat fraction, FA and MD show moderate correlation with muscle strength and motor function: FA is negatively associated with HFMSE and Medical Research Council sum score (τ = -0.56 and -0.59; both P < .001) whereas for fat fraction values are τ = -0.50 and -0.58, respectively (both P < .001). This study shows that DTI parameters correlate with muscle strength and motor function. DTI findings indirectly indicate cell atrophy and act as a measure independently of fat fraction. Combined these data suggest the potential of muscle DTI in monitoring disease progression and to study SMA pathogenesis in muscle.

Natural History of Type 1 Spinal Muscular Atrophy in a Series of Argentinian Children

Background: SMA1 natural history is characterized by early development of chronic respiratory failure. Respiratory interventions in type 1 SMA infants are subject to great practice variability. Nusinersen, has been recently approved in Argentina. The advent of novel treatments has highlighted the need for natural history studies reporting disease progression in type 1 SMA. Objective: To analyze the progression, respiratory interventions and survival based on the type of respiratory support in type 1SMA patients, in a third level pediatric hospital in Argentina. Methods: Cohort of SMA1 patients followed at the Interdisciplinary Program for the Study and Care of Neuromuscular Patients (IPNM). Patient survival was analyzed by using the Kaplan-Meier method. Log-rank test was performed to compare the survival curve for three respiratory intervention groups. Results: 59 patients. Mean age of symptom onset was 2.19 (±1.4) months, age at diagnosis was 3.9 (±2.1) months. Patients developed respiratory failure at 5.82 months (±2.32) and 13.8 months (±5.6) in Type 1B and Type 1C, respectively (p < 0.001) 53 p were SMA1B. Three copies were found in 1/6 SMA1C. Respiratory interventions: SRC 23 p (56.1%); SRC + NIV 8 p (19.5%); SRC + IV 10 p (24.4%). 8 patients were already on invasive ventilation when included in the IPNM. Patients with invasive ventilation showed longer survival. Conclusions: This series provides valuable information on respiratory intervention requirements and life expectancy in children with SMA1 before the implementation of novel treatments that increase the expression of the SMA protein.

Next-generation sequencing of newborn screening genes: the accuracy of short-read mapping

Newborn screening programs are an integral part of public health systems aiming to save lives and improve the quality of life for infants with treatable disorders. Technological advancements have driven the expansion of newborn screening programs in the last two decades and the development of fast, accurate next-generation sequencing technology has opened the door to a range of possibilities in the field. However, technological challenges with short-read next-generation sequencing technologies remain significant in highly homologous genomic regions such as pseudogenes or paralogous genes and need to be considered when implemented in screening programs. Here, we simulate 50 genomes from populations around the world to test the extent to which high homology regions affect short-read mapping of genes related to newborn screening disorders and the impact of differential read lengths and ethnic backgrounds. We examine a 158 gene screening panel directly relevant to newborn screening and identify gene regions where read mapping is affected by homologous genomic regions at different read lengths. We also determine that the patient’s ethnic background does not have a widespread impact on mapping accuracy or coverage. Additionally, we identify newborn screening genes where alternative forms of sequencing or variant calling pipelines should be considered and demonstrate that alterations to standard variant calling can retrieve some formerly uncalled variants.

Muscle strength and motor function in adolescents and adults with spinal muscular atrophy

OBJECTIVE

To assess longitudinal patterns of muscle strength, motor function, and maximal compound muscle action potential amplitudes (CMAP_MAX) in older patients with spinal muscular atrophy (SMA), hypothesizing a continued decline of motor function parameters throughout life.

METHODS

We measured muscle strength (Medical Research Council), motor function (Hammersmith Functional Motor Scale Expanded [HFMSE] and Motor Function Measure), and CMAP_MAX in treatment-naive patients. We used both longitudinal and cross-sectional data in mixed models to analyze natural history patterns.

RESULTS

We included 250 patients with SMA types 1c through 4. Median patient age at assessment was 26.8 years, the number of assessments per patient ranged from 1 to 6. Baseline muscle strength and motor function scores differed significantly between SMA types, but annual rates of decline were largely similar and mostly linear. HFMSE floor effects were present for all patients with SMA type 1c, and adolescents and adults with types 2 and 3a. CMAP_MAX differed significantly between SMA types but did not decline significantly with increasing age. Muscle strength correlated very strongly with motor function (τ ≥ 0.8) but only moderately with CMAP_MAX (τ ≈ 0.5-0.6).

CONCLUSION

Muscle strength and motor function decline in older patients with SMA are constant without periods of slower progression or a plateau phase. The floor effects of the HFMSE preclude its use for long-term follow-up of adult patients with SMA types 1c through 3a. Muscle strength sum scores represent an alternative, feasible outcome measure for adolescent and adult patients with SMA.

The Identification of Novel Biomarkers Is Required to Improve Adult SMA Patient Stratification, Diagnosis and Treatment

Spinal muscular atrophy (SMA) is currently classified into five different subtypes, from the most severe (type 0) to the mildest (type 4) depending on age at onset, best motor function achieved, and copy number of the SMN2 gene. The two recent approved treatments for SMA patients revolutionized their life quality and perspectives. However, upon treatment with Nusinersen, the most widely administered therapy up to date, a high degree of variability in therapeutic response was observed in adult SMA patients. These data, together with the lack of natural history information and the wide spectrum of disease phenotypes, suggest that further efforts are needed to develop precision medicine approaches for all SMA patients. Here, we compile the current methods for functional evaluation of adult SMA patients treated with Nusinersen. We also present an overview of the known molecular changes underpinning disease heterogeneity. We finally highlight the need for novel techniques, i.e., -omics approaches, to capture phenotypic differences and to understand the biological signature in order to revise the disease classification and device personalized treatments.

Incorporating Spinal Muscular Atrophy Analysis by Next-Generation Sequencing into a Comprehensive Multigene Panel for Neuromuscular Disorders

Background: Spinal muscular atrophy (SMA) is traditionally molecularly diagnosed by multiplex ligation-dependent probe amplification or quantitative polymerase chain reaction (qPCR). SMA analyses are not routinely incorporated into gene panel analyses for individuals with suspected SMA or broader neuromuscular indications. Aim: We sought to determine whether a next-generation sequencing (NGS) approach that integrates SMA analyses into a multigene neuromuscular disorders panel could detect undiagnosed SMA. Materials and Methods: Sequence and copy number variants of the SMN1/SMN2 genes were simultaneously analyzed in samples from 5304 unselected individuals referred for testing using an NGS-based 122-gene neuromuscular panel. This diagnostic approach was validated using DNA from 68 individuals who had been previously diagnosed with SMA via quantitative PCR for SMN1/SMN2. Results: Homozygous loss of SMN1 was detected in 47 unselected individuals. Heterozygous loss of SMN1 was detected in 118 individuals; 8 had an indeterminate variant in "SMN1 or SMN2" that supported an SMA diagnosis but required additional disambiguation. Of the remaining SMA carriers, 44 had pathogenic variants in other genes. Concordance rates between NGS and qPCR were 100% and 93% for SMN1 and SMN2 copy numbers, respectively. Where there was disagreement, phenotypes were more consistent with the SMN2 results from NGS. Conclusion: Integrating NGS-based SMA testing into a multigene neuromuscular panel allows a single assay to diagnose SMA while comprehensively assessing the spectrum of variants that can occur in individuals with broad differential diagnoses or nonspecific/overlapping neuromuscular features.

Lack of effect on ambulation of dalfampridine-ER (4-AP) treatment in adult SMA patients

SMA is a genetically determined motor system disorder that results in muscle weakness, selective motor neuron death, muscle atrophy, and impaired functional mobility. In SMA model systems, long-term treatment with 4-aminopyridine (4-AP) has been shown to improve motor function. To assess tolerability and preliminary efficacy of 4-AP on walking ability, endurance and EMG in adult ambulatory SMA patients, we conducted a double blind, placebo control, crossover pilot study with dalfampridine (4-AP, 10 mg BID). The study is comprised of a short-term (2 weeks) treatment arm with 1-week washout and a long-term (6 weeks) treatment arm with a 2-week washout. The primary outcome measure, for which the study was powered, was the 6 min walk test (6MWT, distance and percent fatigue); secondary outcome measures were the Hammersmith Functional Motor Scale Expanded (HFMSE), Manual Muscle Testing (MMT), Myometry with Hand held Dynamometry, HHD) and Quantitative Gait Analyses. We performed electrophysiology, including CMAP and H-reflex, during the short-term treatment trial. The mean age of the 11 participants enrolled was 37.7 ± 11.9 years; 54.5% were male. Dalfampridine was safe and well tolerated and no patient suffered a serious adverse event related to treatment. We observed no statistically significant positive effects of dalfampridine treatment on our primary functional motor outcome (6MWT distance, fatigue). Dalfampridine had a positive effects on H-reflex and H/M ratio but not on CMAP amplitude. The effect on the H-reflex is of interest, as it suggests dalfampridine may enhance neuronal activity, an effect observed in SMA Drosophila and mouse models at doses (mg/kg) not recommended for clinical use. Larger studies with dalfampridine in SMA patients are needed to confirm our findings, especially in light of studies in other populations showing drug effects in only a subset of patients.

Diagnostic Testing for Patients with Spinal Muscular Atrophy

Diagnostic genetic testing for spinal muscular atrophy is key in establishing early diagnosis for affected individuals. Prenatal carrier testing of parents with subsequent testing of the fetus for homozygous SMN1 gene deletion in those at risk of this autosomal recessive disorder as well as newborn screening can identify the vast majority of affected individuals before the onset of symptoms. Patients presenting symptomatically must be genetically confirmed as soon as possible because targeted treatments are now available that profoundly impact symptoms and improve quality of life.

Whole-blood dysregulation of actin-cytoskeleton pathway in adult spinal muscular atrophy patients

OBJECTIVE

Recent advances in therapeutics have improved prognosis for severely affected spinal muscular atrophy (SMA) type 1 and 2 patients, while the best method of treatment for SMA type 3 patients with later onset of disease is unknown. To better characterize the SMA type 3 population and provide potential therapeutic targets, we aimed to understand gene expression differences in whole blood of SMA type 3 patients (n = 31) and age- and gender-matched controls (n = 34).

METHODS

We performed the first large-scale whole blood transcriptomic screen with L1000, a rapid, high-throughput gene expression profiling technology that uses 978 landmark genes to capture a representation of the transcriptome and predict expression of 9196 additional genes.

RESULTS

The primary downregulated KEGG pathway in adult SMA type 3 patients was "Regulation of Actin Cytoskeleton," and downregulated expression of key genes in this pathway, including ROCK1, RHOA, and ACTB, was confirmed in the same whole blood samples using RT-qPCR. SMA type 3 patient-derived fibroblasts had lower expression of these genes compared to control fibroblasts from unaffected first-degree relatives. Overexpression of SMN levels using an AAV vector in fibroblasts did not normalize ROCK1, RHOA, and ACTB mRNA expression, indicating the involvement of additional genes in cytoskeleton dynamic regulation.

INTERPRETATION

Our findings from whole blood and patient-derived fibroblasts suggest SMA type 3 patients have decreased expression of actin cytoskeleton regulators. These observations provide new insights and potential therapeutic targets for SMA patients with longstanding denervation and secondary musculoskeletal pathophysiology.

Stander Use in Spinal Muscular Atrophy: Results From a Large Natural History Database

PURPOSE

The purpose of this study was to describe stander use in a natural history cohort of drug therapy-naïve children with spinal muscular atrophy (SMA) who are not walking and identify factors associated with consistent stander use.

METHODS

Data from 397 children with SMA types 1 and 2 characterized the prevalence and frequency of stander use. Predictors of consistent stander use explored were SMA type, survival motor neuron 2 gene (SMN2) copy number, respiratory support, and motor performance.

RESULTS

Prevalence of consistent stander use was 13% in type 1 and 68% in type 2. SMA type, SMN2 copy number, respiratory support, and head rotation control each predicted consistent stander use.

CONCLUSIONS

Findings characterize stander use in children with SMA who are not walking, address important safety considerations, identify factors that may inform physical therapists' clinical decision-making related to standing program prescription, and provide guidance for future prospective studies.

Motor neuron loss in SMA is not associated with somal stress-activated JNK/c-Jun signaling

A pathological hallmark of spinal muscular atrophy (SMA) is severe motor neuron (MN) loss, which results in muscle weakness and often infantile or childhood mortality. Although it is well established that deficient expression of survival motor neuron (SMN) protein causes SMA, the molecular pathways that execute MN cell death are poorly defined. The c-Jun NH2-terminal kinases (JNKs) are stress-activated kinases with multiple substrates including c-Jun, which can be activated during neuronal injury and neurodegenerative disease leading to neuronal apoptosis. Recently, increased JNK-c-Jun signaling was reported in SMA raising the possibility that JNK inhibitors could be a novel treatment for this disease. We examined JNK-c-Jun activity in SMA mouse and human cultured cells and tissues. Anisomycin treatment of human SMA fibroblasts and sciatic nerve ligation in SMA mice provoked robust phosphorylated-c-Jun (p-c-Jun) expression indicating that SMN-deficiency does not prevent activation of the stress-induced JNK-c-Jun signaling pathway. Despite retained capacity to activate JNK-c-Jun, we observed no basal increase of p-c-Jun levels in SMA compared to control cultured cells, human or mouse spinal cord tissues, or mouse MNs during the period of MN loss in severe SMA model mice. In both controls and SMA, ~50% of α-MN nuclei express p-c-Jun with decreasing expression during the early postnatal period. Together these studies reveal no evidence of stress-activated JNK-c-Jun signaling in MNs of SMA mice or human tissues, but do highlight the important role of JNK-c-Jun activity during normal MN development raising caution about JNK antagonism in this pediatric neuromuscular disease.

Treatment expectations and patient-reported outcomes of nusinersen therapy in adult spinal muscular atrophy

Background

The antisense-oligonucleotide (ASO) nusinersen has recently been approved as the first genetically modifying therapy for 5q-associated spinal muscular atrophy (SMA) based on randomized sham-controlled trials in infants and children. The efficacy in adults with long disease history and advanced disease status is still widely unknown; the same applies to specific expectations of adult SMA patients and to what extent they are met and may impact outcome measures.

Methods

In a longitudinal monocentric study in adult patients with SMA types 2–4, the Stanford Expectations of Treatment Scale (SETS) was assessed prior to and during nusinersen treatment. Treatment outcome was evaluated using patient-reported outcomes (PROs) as well as objectively quantifiable motor outcome measures.

Results

Adult SMA patients had high expectations of nusinersen treatment effectiveness regarding increase in muscle strength and disease stabilization. Via PROs, 75% stated improvements in muscle strength, endurance and independence under therapy which was in line with slight improvements in quantifiable motor scores during a  ten month observation period. In contrast, patients only expressed few negative expectations which further decreased during therapy.

Conclusions

This study showed mainly positive treatment expectations and PROs in patients undergoing nusinersen treatment along with measurable functional improvement in adult SMA patients. Moreover, treatment expectations did not significantly influence outcome measures.

Electronic supplementary material

The online version of this article (10.1007/s00415-020-09847-8) contains supplementary material, which is available to authorized users.

Spinal Muscular Atrophy: Past, Present, and Future

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disease caused by deletions or mutations in the survival motor neuron (SMN1) gene. SMA is characterized by loss of lower motor neurons (anterior horn cells) in the spinal cord and brainstem nuclei, leading to progressive symmetrical muscle weakness and atrophy. It affects approximately 1 in 6,000 to 1 in 10,000 individuals and is the most common inherited cause of childhood mortality, but this may soon change given recent developments. In December 2016, nusinersen, an antisense oligonucleotide drug, was approved by the United States Food and Drug Administration for the treatment of SMA, and in July 2018, SMA was added to the recommended uniform screening panel, a list of conditions that all states are encouraged to include in their newborn screening (NBS) panels. In this review, we begin with a brief clinical history of the diagnosis of SMA, discuss the current SMA clinical classification system, describe the current treatment, and discuss evolving treatment guidelines. We then discuss the path to include SMA in NBS programs as well as the controversies it engenders because the variability in age at symptom onset means early identification of asymptomatic patients who will not require therapy for years or decades. We also consider alternate population screening opportunities. Next, we consider experimental treatments. We conclude by supporting NBS for SMA with the caveat that a long-term follow-up registry is ethically essential to ensure that the benefits outweigh the harms for all screened infants, including those with milder and/or later-onset forms of SMA.

Diagnostic journey in Spinal Muscular Atrophy: Is it still an odyssey?

Background

The advent of new therapies has increased the need to achieve early diagnosis in Spinal Muscular Atrophy (SMA). The aim of the present study was to define the age of diagnosis in the three main types of SMA with pediatric-onset and the timing between the recognition of clinical signs and confirmed genetic diagnosis.

Methods

All patients with a confirmed diagnosis of type I, II, III SMA followed in 5 Italian centers were included in this study, assessing age at symptoms onset, presenting sign or symptom, age at diagnosis, interval between clinical onset and diagnosis and type of medical investigations conducted in order to obtain the diagnosis.

Results

The cohort included 480 patients, 191 affected by SMA type I, 210 by type II and 79 by type III. The mean age at diagnosis was 4.70 months (SD ±2.82) in type I, 15.6 months (SD±5.88) in type II, and 4.34 years (SD±4.01) in type III.

The mean time between symptom onset and diagnosis was 1.94 months (SD±1.84) in type I, 5.28 months (SD±4.68) in type II and 16.8 months (SD±18.72) in type III.

Conclusions

Our results suggest that despite improved care recommendations there is still a marked diagnostic delay, especially in type III. At the time new therapies are becoming available more attention should be devoted to reducing such delay as there is consistent evidence of the benefit of early treatment.

Trajectory of change in the swallowing status in spinal muscular atrophy type I

OBJECTIVES

This study aimed to elucidate the change in progressive swallowing dysfunction from birth up to 2 years of age to provide clinical insights into the management of swallowing difficulty in patients with spinal muscular atrophy (SMA) type I.

METHODS

Data of 11 patients with SMA type I were retrospectively reviewed. The Neuromuscular Disease Swallowing Status Scale (NdSSS) scores and videofluoroscopic swallowing study (VFSS) were used.

RESULTS

Swallowing function deteriorated in patients with SMA type I at an approximate age of 6 months. Tube feeding was initiated at the median age of 6 months (interquartile range, 3-7 months). The transition period for switching the feeding route from totally oral to tube feeding varied widely among patients (5-12 months). In four patients, aspiration was observed in VFSS, even when nutrition was provided orally. In two patients, the evidence of laryngeal aspiration was obtained via the VFSS during the very early stages of the disease at 3 and 4 months. Conversely, in one patient, total oral feeding was maintained for up to 12 months, and evidence of aspiration was not observed in the VFSS.

CONCLUSION

An individualized approach is essential, as the timeline of deterioration of swallowing function varies widely in patients with SMA type I.

Survival Motor Neuron Gene Copy Number Analysis by Exome Sequencing: Assisting Spinal Muscular Atrophy Diagnosis and Carrier Screening

Spinal muscular atrophy (SMA) is a leading genetic cause of infant death, influenced by the copy number of two highly homologous genes: SMN1 and SMN2. Although exome sequencing is widely applied for genetic testing, SMA diagnosis and carrier screening have not been incorporated in routine data analysis and lack evaluation in clinical applications. We established a workflow for the SMN gene copy number analysis through uniquely mapped reads on exon 7 of SMN genes and the control region. The workflow was applied retrospectively in the enrolled cohort and validated with multiple ligation-dependent probe amplification. The predictions of this method are completely consistent with a benchmark data set (n = 104). The retrospective analysis in the Neonatal Intensive Care Unit cohort detected and confirmed eight SMN1 homozygous deletions and 60 carriers (n = 3734). With experimental confirmation, the receiver operating characteristic curve analysis showed the area under the curve of 100% and 97.8%, respectively, in predicting SMN1 homozygous and heterozygous deletion events, and 99.2% and 96.2%, respectively, in SMN2 deletion and duplication events. The results showed favorable ability in SMN genes copy number status prediction based on real clinical sequencing data. This study provides a precise and portable workflow for SMN genes copy number analysis based on exome sequencing, assisting SMA diagnosing, carrier screening, and disease severity warning in clinical application.

Assessment of motor unit loss in patients with spinal muscular atrophy

OBJECTIVE

To assess motor unit (MU) changes in patients with spinal muscular atrophy (SMA) using compound muscle action potential (CMAP) scans.

METHODS

We performed CMAP scan recordings in median nerves of 24 treatment-naïve patients (median age 39; range 12-75 years) with SMA types 2-4. From each scan, we determined maximum CMAP amplitude (CMAP_max), a motor unit number estimate (MUNE), and D50 which quantifies the largest discontinuities within CMAP scans.

RESULTS

Median CMAP_max was 8.1 mV (range 0.9-14.6 mV), MUNE was 29 (range 6-131), and D50 was 25 (range 2-57). We found a reduced D50 (<25) in patients with normal CMAP_max (n = 12), indicating MU loss and enlarged MUs due to reinnervation. Lower D50 values were associated with decreased MUNE (P < 0.001, r = 0.68, n = 43). CMAP_max, MUNE and D50 values differed between SMA types (P < 0.001). Lower motor function scores were related to patients with lower CMAP_max, MUNE and D50 values (P < 0.001).

CONCLUSIONS

The CMAP scan is an easily applicable technique that is superior to routine assessment of CMAP_max in SMA.

SIGNIFICANCE

The detection of pathological MU changes across the spectrum of SMA may provide important biomarkers for evaluating disease course and monitoring treatment efficacy.

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.

Intrathecal nusinersen administration in adult spinal muscular atrophy patients with complex spinal anatomy

Background:

Intrathecal administration of nusinersen in adult spinal muscular atrophy (SMA) patients presents challenges owing to severe scoliosis and previous spinal surgery with metal implantation. In patients with a complex spinal situation, the potential risks of the intrathecal administration may lead to delayed treatment initiation.

Methods:

In this study, we analyzed 53 CT-guided lumbar punctures of 11 adult nonambulatory SMA type 2 and 3 patients. All patients had scoliosis and six patients had previously undergone metal implantation.

Results:

Drug administration was successful in 100% of the patients and none of the patients opted for treatment discontinuation. Complete osseous fusion precluded conventional posterior interlaminar access in eight lumbar punctures in four patients, which required alternative routes including transforaminal punctures and translaminar drilling. Median duration of all lumbar punctures was 9 min and median radiation exposure was 100 mGy* cm. The most common adverse event was post-lumbar puncture syndrome that occurred in five lumbar punctures (9.4%).

Conclusions:

Our data demonstrate that nusinersen can be successfully, safely, and rapidly administered in adult SMA patients with complex spinal conditions and suggest the translaminar drilling technique as an alternative delivery route. Therefore, intrathecal nusinersen treatment should not be withheld from patients because of severe spine deformities, however, drug efficacy in adult SMA patients needs to be investigated in further studies.

Drug treatment for spinal muscular atrophy types II and III

BACKGROUND

Spinal muscular atrophy (SMA) is caused by a homozygous deletion of the survival motor neuron 1 (SMN1) gene on chromosome 5, or a heterozygous deletion in combination with a (point) mutation in the second SMN1 allele. This results in degeneration of anterior horn cells, which leads to progressive muscle weakness. Children with SMA type II do not develop the ability to walk without support and have a shortened life expectancy, whereas children with SMA type III develop the ability to walk and have a normal life expectancy. This is an update of a review first published in 2009 and previously updated in 2011.

OBJECTIVES

To evaluate if drug treatment is able to slow or arrest the disease progression of SMA types II and III, and to assess if such therapy can be given safely.

SEARCH METHODS

We searched the Cochrane Neuromuscular Specialised Register, CENTRAL, MEDLINE, Embase, and ISI Web of Science conference proceedings in October 2018. In October 2018, we also searched two trials registries to identify unpublished trials.

SELECTION CRITERIA

We sought all randomised or quasi-randomised trials that examined the efficacy of drug treatment for SMA types II and III. Participants had to fulfil the clinical criteria and have a homozygous deletion or hemizygous deletion in combination with a point mutation in the second allele of the SMN1 gene (5q11.2-13.2) confirmed by genetic analysis. The primary outcome measure was change in disability score within one year after the onset of treatment. Secondary outcome measures within one year after the onset of treatment were change in muscle strength, ability to stand or walk, change in quality of life, time from the start of treatment until death or full-time ventilation and adverse events attributable to treatment during the trial period. Treatment strategies involving SMN1-replacement with viral vectors are out of the scope of this review, but a summary is given in Appendix 1. Drug treatment for SMA type I is the topic of a separate Cochrane Review.

DATA COLLECTION AND ANALYSIS

We followed standard Cochrane methodology.

MAIN RESULTS

The review authors found 10 randomised, placebo-controlled trials of treatments for SMA types II and III for inclusion in this review, with 717 participants. We added four of the trials at this update. The trials investigated creatine (55 participants), gabapentin (84 participants), hydroxyurea (57 participants), nusinersen (126 participants), olesoxime (165 participants), phenylbutyrate (107 participants), somatotropin (20 participants), thyrotropin-releasing hormone (TRH) (nine participants), valproic acid (33 participants), and combination therapy with valproic acid and acetyl-L-carnitine (ALC) (61 participants). Treatment duration was from three to 24 months. None of the studies investigated the same treatment and none was completely free of bias. All studies had adequate blinding, sequence generation and reporting of primary outcomes. Based on moderate-certainty evidence, intrathecal nusinersen improved motor function (disability) in children with SMA type II, with a 3.7-point improvement in the nusinersen group on the Hammersmith Functional Motor Scale Expanded (HFMSE; range of possible scores 0 to 66), compared to a 1.9-point decline on the HFMSE in the sham procedure group (P < 0.01; n = 126). On all motor function scales used, higher scores indicate better function. Based on moderate-certainty evidence from two studies, the following interventions had no clinically important effect on motor function scores in SMA types II or III (or both) in comparison to placebo: creatine (median change 1 higher, 95% confidence interval (CI) -1 to 2; on the Gross Motor Function Measure (GMFM), scale 0 to 264; n = 40); and combination therapy with valproic acid and carnitine (mean difference (MD) 0.64, 95% CI -1.1 to 2.38; on the Modified Hammersmith Functional Motor Scale (MHFMS), scale 0 to 40; n = 61). Based on low-certainty evidence from other single studies, the following interventions had no clinically important effect on motor function scores in SMA types II or III (or both) in comparison to placebo: gabapentin (median change 0 in the gabapentin group and -2 in the placebo group on the SMA Functional Rating Scale (SMAFRS), scale 0 to 50; n = 66); hydroxyurea (MD -1.88, 95% CI -3.89 to 0.13 on the GMFM, scale 0 to 264; n = 57), phenylbutyrate (MD -0.13, 95% CI -0.84 to 0.58 on the Hammersmith Functional Motor Scale (HFMS) scale 0 to 40; n = 90) and monotherapy of valproic acid (MD 0.06, 95% CI -1.32 to 1.44 on SMAFRS, scale 0 to 50; n = 31). Very low-certainty evidence suggested that the following interventions had little or no effect on motor function: olesoxime (MD 2, 95% -0.25 to 4.25 on the Motor Function Measure (MFM) D1 + D2, scale 0 to 75; n = 160) and somatotropin (median change at 3 months 0.25 higher, 95% CI -1 to 2.5 on the HFMSE, scale 0 to 66; n = 19). One small TRH trial did not report effects on motor function and the certainty of evidence for other outcomes from this trial were low or very low. Results of nine completed trials investigating 4-aminopyridine, acetyl-L-carnitine, CK-2127107, hydroxyurea, pyridostigmine, riluzole, RO6885247/RG7800, salbutamol and valproic acid were awaited and not available for analysis at the time of writing. Various trials and studies investigating treatment strategies other than nusinersen (e.g. SMN2-augmentation by small molecules), are currently ongoing.

AUTHORS' CONCLUSIONS

Nusinersen improves motor function in SMA type II, based on moderate-certainty evidence. Creatine, gabapentin, hydroxyurea, phenylbutyrate, valproic acid and the combination of valproic acid and ALC probably have no clinically important effect on motor function in SMA types II or III (or both) based on low-certainty evidence, and olesoxime and somatropin may also have little to no clinically important effect but evidence was of very low-certainty. One trial of TRH did not measure motor function.

Advances in Treatment of Spinal Muscular Atrophy - New Phenotypes, New Challenges, New Implications for Care

Spinal Muscular Atrophy (SMA) is caused by autosomal recessive mutations in SMN1 and results in the loss of motor neurons and progressive muscle weakness. The spectrum of disease severity ranges from early onset with respiratory failure during the first months of life to a mild, adult-onset type with slow rate of progression. Over the past decade, new treatment options such as splicing modulation of SMN2 and SMN1 gene replacement by gene therapy have been developed. First drugs have been approved for treatment of patients with SMA and if initiated early they can significantly modify the natural course of the disease. As a consequence, newborn screening for SMA is explored and implemented in an increasing number of countries. However, available evidence for these new treatments is often limited to a small spectrum of patients concerning age and disease stage. In this review we provide an overview of available and emerging therapies for spinal muscular atrophy and we discuss new phenotypes and associated challenges in clinical care. Collection of real-world data with standardized outcome measures will be essential to improve both the understanding of treatment effects in patients of all SMA subtypes and the basis for clinical decision-making in SMA.

Serum creatinine is a biomarker of progressive denervation in spinal muscular atrophy

OBJECTIVE

Identifying simple biomarkers that can predict or track disease progression in patients with spinal muscular atrophy (SMA) remains an unmet clinical need. To test the hypothesis that serum creatinine (Crn) could be a prognostic biomarker for monitoring progression of denervation in patients with SMA, we determined whether serum Crn concentration correlates with disease severity in patients with SMA.

METHODS

We examined a cohort of 238 patients with SMA with 1,130 Crn observations between 2000 and 2016. Analyses were corrected for age, and 156 patients with SMA had dual-energy x-ray absorptiometry data available for correction for lean mass. We investigated the relationship between Crn and SMA type, survival motor neuron 2 (SMN2) copies, and Hammersmith Functional Motor Scale (HFMS) score as primary outcomes. In addition, we tested for associations between Crn and maximum ulnar compound muscle action potential amplitude (CMAP) and motor unit number estimation (MUNE).

RESULTS

Patients with SMA type 3 had 2.2-fold (95% confidence interval [CI] 1.93-2.49; p < 0.0001) higher Crn levels compared to those with SMA type 1 and 1.7-fold (95% CI 1.52-1.82; p < 0.0001) higher Crn levels compared to patients with SMA type 2. Patients with SMA type 2 had 1.4-fold (95% CI 1.31-1.58; p < 0.0001) higher Crn levels than patients with SMA type 1. Patients with SMA with 4 SMN2 copies had 1.8-fold (95% CI 1.57-2.11; p < 0.0001) higher Crn levels compared to patients with SMA with 2 SMN2 copies and 1.4-fold (95% CI 1.24-1.58; p < 0.0001) higher Crn levels compared to patients with SMA with 3 SMN2 copies. Patients with SMA with 3 SMN2 copies had 1.4-fold (95% CI 1.21-1.56; p < 0.0001) higher Crn levels than patients with SMA with 2 SMN2 copies. Mixed-effect model revealed significant differences in Crn levels among walkers, sitters, and nonsitters (p < 0.0001) and positive associations between Crn and maximum CMAP (p < 0.0001) and between Crn and MUNE (p < 0.0001). After correction for lean mass, there were still significant associations between Crn and SMA type, SMN2 copies, HFMS, CMAP, and MUNE.

CONCLUSIONS

These findings indicate that decreased Crn levels reflect disease severity, suggesting that Crn is a candidate biomarker for SMA progression. We conclude that Crn measurements should be included in the routine analysis of all patients with SMA. In future studies, it will be important to determine whether Crn levels respond to molecular and gene therapies.

Drug treatment for spinal muscular atrophy type I

BACKGROUND

Spinal muscular atrophy (SMA) is caused by a homozygous deletion of the survival motor neuron 1 (SMN1) gene on chromosome 5, or a heterozygous deletion in combination with a point mutation in the second SMN1 allele. This results in degeneration of anterior horn cells, which leads to progressive muscle weakness. By definition, children with SMA type I are never able to sit without support and usually die or become ventilator dependent before the age of two years. There have until very recently been no drug treatments to influence the course of SMA. We undertook this updated review to evaluate new evidence on emerging treatments for SMA type I. The review was first published in 2009 and previously updated in 2011.

OBJECTIVES

To assess the efficacy and safety of any drug therapy designed to slow or arrest progression of spinal muscular atrophy (SMA) type I.

SEARCH METHODS

We searched the Cochrane Neuromuscular Specialised Register, CENTRAL, MEDLINE, Embase, and ISI Web of Science conference proceedings in October 2018. We also searched two trials registries to identify unpublished trials (October 2018).

SELECTION CRITERIA

We sought all randomised controlled trials (RCTs) or quasi-RCTs that examined the efficacy of drug treatment for SMA type I. Included participants had to fulfil clinical criteria and have a genetically confirmed deletion or mutation of the SMN1 gene (5q11.2-13.2). The primary outcome measure was age at death or full-time ventilation. Secondary outcome measures were acquisition of motor milestones, i.e. head control, rolling, sitting or standing, motor milestone response on disability scores within one year after the onset of treatment, and adverse events and serious adverse events attributable to treatment during the trial period. Treatment strategies involving SMN1 gene replacement with viral vectors are out of the scope of this review.

DATA COLLECTION AND ANALYSIS

We followed standard Cochrane methodology.

MAIN RESULTS

We identified two RCTs: one trial of intrathecal nusinersen in comparison to a sham (control) procedure in 121 randomised infants with SMA type I, which was newly included at this update, and one small trial comparing riluzole treatment to placebo in 10 children with SMA type I. The RCT of intrathecally-injected nusinersen was stopped early for efficacy (based on a predefined Hammersmith Infant Neurological Examination-Section 2 (HINE-2) response). At the interim analyses after 183 days of treatment, 41% (21/51) of nusinersen-treated infants showed a predefined improvement on HINE-2, compared to 0% (0/27) of participants in the control group. This trial was largely at low risk of bias. Final analyses (ranging from 6 months to 13 months of treatment), showed that fewer participants died or required full-time ventilation (defined as more than 16 hours daily for 21 days or more) in the nusinersen-treated group than the control group (hazard ratio (HR) 0.53, 95% confidence interval (CI) 0.32 to 0.89; N = 121; a 47% lower risk; moderate-certainty evidence). A proportion of infants in the nusinersen group and none of 37 infants in the control group achieved motor milestones: 37/73 nusinersen-treated infants (51%) achieved a motor milestone response on HINE-2 (risk ratio (RR) 38.51, 95% CI 2.43 to 610.14; N = 110; moderate-certainty evidence); 16/73 achieved head control (RR 16.95, 95% CI 1.04 to 274.84; moderate-certainty evidence); 6/73 achieved independent sitting (RR 6.68, 95% CI 0.39 to 115.38; moderate-certainty evidence); 7/73 achieved rolling over (RR 7.70, 95% CI 0.45 to 131.29); and 1/73 achieved standing (RR 1.54, 95% CI 0.06 to 36.92; moderate-certainty evidence). Seventy-one per cent of nusinersen-treated infants versus 3% of infants in the control group were responders on the Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP INTEND) measure of motor disability (RR 26.36, 95% CI 3.79 to 183.18; N = 110; moderate-certainty evidence). Adverse events and serious adverse events occurred in the majority of infants but were no more frequent in the nusinersen-treated group than the control group (RR 0.99, 95% CI 0.92 to 1.05 and RR 0.70, 95% CI 0.55 to 0.89, respectively; N = 121; moderate-certainty evidence). In the riluzole trial, three of seven children treated with riluzole were still alive at the ages of 30, 48, and 64 months, whereas all three children in the placebo group died. None of the children in the riluzole or placebo group developed the ability to sit, which was the only milestone reported. There were no adverse effects. The certainty of the evidence for all measured outcomes from this study was very low, because the study was too small to detect or rule out an effect, and had serious limitations, including baseline differences. This trial was stopped prematurely because the pharmaceutical company withdrew funding. Various trials and studies investigating treatment strategies other than nusinersen, such as SMN2 augmentation by small molecules, are ongoing.

AUTHORS' CONCLUSIONS

Based on the very limited evidence currently available regarding drug treatments for SMA type 1, intrathecal nusinersen probably prolongs ventilation-free and overall survival in infants with SMA type I. It is also probable that a greater proportion of infants treated with nusinersen than with a sham procedure achieve motor milestones and can be classed as responders to treatment on clinical assessments (HINE-2 and CHOP INTEND). The proportion of children experiencing adverse events and serious adverse events on nusinersen is no higher with nusinersen treatment than with a sham procedure, based on evidence of moderate certainty. It is uncertain whether riluzole has any effect in patients with SMA type I, based on the limited available evidence. Future trials could provide more high-certainty, longer-term evidence to confirm this result, or focus on comparing new treatments to nusinersen or evaluate them as an add-on therapy to nusinersen.

A Novel System for Spinal Muscular Atrophy Screening in Newborns: Japanese Pilot Study

Spinal muscular atrophy (SMA) is a neuromuscular disorder caused by SMN1 gene deletion/mutation. The drug nusinersen modifies SMN2 mRNA splicing, increasing the production of the full-length SMN protein. Recent studies have demonstrated the beneficial effects of nusinersen in patients with SMA, particularly when treated in early infancy. Because nusinersen treatment can alter disease trajectory, there is a strong rationale for newborn screening. In the current study, we validated the accuracy of a new system for detecting SMN1 deletion (Japanese patent application No. 2017-196967, PCT/JP2018/37732) using dried blood spots (DBS) from 50 patients with genetically confirmed SMA and 50 controls. Our system consists of two steps: (1) targeted pre-amplification of SMN genes by direct polymerase chain reaction (PCR) and (2) detection of SMN1 deletion by real-time modified competitive oligonucleotide priming-PCR (mCOP-PCR) using the pre-amplified products. Compared with PCR analysis results of freshly collected blood samples, our system exhibited a sensitivity of 1.00 (95% confidence interval [CI] 0.96-1.00) and a specificity of 1.00 (95% CI 0.96-1.00). We also conducted a prospective SMA screening study using DBS from 4157 Japanese newborns. All DBS tested negative, and there were no screening failures. Our results indicate that the new system can be reliably used in SMA newborn screening.

Assessing Rat Forelimb and Hindlimb Motor Unit Connectivity as Objective and Robust Biomarkers of Spinal Motor Neuron Function

Sensitive and objective biomarkers of neuronal injury, degeneration, and regeneration can help facilitate translation of experimental findings into clinical testing. Whereas measures of upper motor neuron connectivity have been readily established, functional assessments of lower motor neuron (LMN) innervation of forelimb muscles are lacking. Compound muscle action potential (CMAP) and motor unit (MU) number estimation (MUNE) are well-established methods that allow longitudinal MU integrity monitoring in patients. In analogy we refined CMAP and MUNE methods for assessing spinal MU input in the rat forelimb and hindlimb. Repeated CMAP and MUNE recordings are robust (coefficients of variability: 4.5-11.3%), and MUNE measurements from forelimb wrist flexor muscles (415 ± 8 [SEM]) align with back-traced anatomical LMN counts (336 ± 16 [SEM]). For disease validation, cross-sectional blinded electrophysiological and muscle contractility measurements were obtained in a cohort of G93A SOD1 mutant overexpressing rats and compared with controls. Longitudinal assessment of mutant animals demonstrated progressive motor unit decline in the hindlimb to a greater extent than the forelimb. Hindlimb CMAP and MUNE demonstrated strong correlations with plantarflexion muscle contractility. Cross-species assessment of upper/fore- limb and lower/hind- limb motor units using objective electrophysiological CMAP and MUNE values as biomarkers will guide and improve bi-directional translation.

Nusinersen initiated in infants during the presymptomatic stage of spinal muscular atrophy: Interim efficacy and safety results from the Phase 2 NURTURE study

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NURTURE is an ongoing study of nusinersen started in a presymptomatic stage of SMA.

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All infants were ≥25 months old, and alive without permanent ventilation.

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All infants achieved independent sitting and 88% (22/25) were walking alone.

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Nusinersen demonstrated durability of effect with a median 2.9 years of follow up.

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Nusinersen was well tolerated with no new safety concerns over extended follow up.

Spinal muscular atrophy (SMA) is a neurodegenerative disease associated with severe muscle atrophy and weakness in the limbs and trunk. We report interim efficacy and safety outcomes as of March 29, 2019 in 25 children with genetically diagnosed SMA who first received nusinersen in infancy while presymptomatic in the ongoing Phase 2, multisite, open-label, single-arm NURTURE trial. Fifteen children have two SMN2 copies and 10 have three SMN2 copies. At last visit, children were median (range) 34.8 [25.7–45.4] months of age and past the expected age of symptom onset for SMA Types I or II; all were alive and none required tracheostomy or permanent ventilation. Four (16%) participants with two SMN2 copies utilized respiratory support for ≥6 h/day for ≥7 consecutive days that was initiated during acute, reversible illnesses. All 25 participants achieved the ability to sit without support, 23/25 (92%) achieved walking with assistance, and 22/25 (88%) achieved walking independently. Eight infants had adverse events considered possibly related to nusinersen by the study investigators. These results, representing a median 2.9 years of follow up, emphasize the importance of proactive treatment with nusinersen immediately after establishing the genetic diagnosis of SMA in presymptomatic infants and emerging newborn screening efforts.

Biomarkers and the Development of a Personalized Medicine Approach in Spinal Muscular Atrophy

Recent unprecedented advances in treatment for spinal muscular atrophy (SMA) enabled patients to access the first approved disease modifying therapy for the condition. There are however many uncertainties, regarding timing of treatment initiation, response to intervention, treatment effects and long-term outcomes, which are complicated by the evolving phenotypes seen in the post-treatment era for patients with SMA. Biomarkers of disease, with diagnostic, prognostic, predictive, and pharmacodynamic value are thus urgently required, to facilitate a wider understanding in this dynamic landscape. A spectrum of these candidate biomarkers, will be evaluated in this review, including genetic, epigenetic, proteomic, electrophysiological, and imaging measures. Of these, SMN2 appears to be the most significant modifier of phenotype to date, and its use in prognostication shows considerable clinical utility. Longitudinal studies in patients with SMA highlight an emerging role of circulatory markers such as neurofilament, in tracking disease progression and response to treatment. Furthermore, neurophysiological biomarkers such as CMAP and MUNE values show considerable promise in the real word setting, in following the dynamic response and output of the motor unit to therapeutic intervention. The specific value for these possible biomarkers across diagnosis, prognosis, prediction of treatment response, efficacy, and safety will be central to guide future patient-targeted treatments, the design of clinical trials, and understanding of the pathophysiological mechanisms of disease and intervention.

Applying Deep Neural Network Analysis to High-Content Image-Based Assays

The etiological underpinnings of many CNS disorders are not well understood. This is likely due to the fact that individual diseases aggregate numerous pathological subtypes, each associated with a complex landscape of genetic risk factors. To overcome these challenges, researchers are integrating novel data types from numerous patients, including imaging studies capturing broadly applicable features from patient-derived materials. These datasets, when combined with machine learning, potentially hold the power to elucidate the subtle patterns that stratify patients by shared pathology. In this study, we interrogated whether high-content imaging of primary skin fibroblasts, using the Cell Painting method, could reveal disease-relevant information among patients. First, we showed that technical features such as batch/plate type, plate, and location within a plate lead to detectable nuisance signals, as revealed by a pre-trained deep neural network and analysis with deep image embeddings. Using a plate design and image acquisition strategy that accounts for these variables, we performed a pilot study with 12 healthy controls and 12 subjects affected by the severe genetic neurological disorder spinal muscular atrophy (SMA), and evaluated whether a convolutional neural network (CNN) generated using a subset of the cells could distinguish disease states on cells from the remaining unseen control–SMA pair. Our results indicate that these two populations could effectively be differentiated from one another and that model selectivity is insensitive to batch/plate type. One caveat is that the samples were also largely separated by source. These findings lay a foundation for how to conduct future studies exploring diseases with more complex genetic contributions and unknown subtypes.

Nusinersen in type 1 spinal muscular atrophy: Twelve-month real-world data

OBJECTIVE

The aim of the study was to report 12-month changes after treatment with nusinersen in a cohort of 85 type I spinal muscular atrophy patients of ages ranging from 2 months to 15 years and 11 months.

METHODS

All patients were assessed using the Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP INTEND) and the Hammersmith Infant Neurological Examination-Section 2 (HINE-2).

RESULTS

Two of the 85 patients had 1 SMN2 copy, 61 had 2 copies, and 18 had 3 copies. In 4 patients the SMN2 copy number was not available. At baseline, the mean CHOP INTEND scores ranged between 0 and 52 (mean = 15.66, standard deviation [SD] = ±13.48), and the mean HINE-2 score was between 0 and 5 (mean = 0.69, SD = ±1.23). There was a difference between baseline and the 12-month scores on both the CHOP INTEND and the HINE-2 for the whole group (p < 0.001), the subgroups with 2 SMN2 copies (p < 0.001), and those with 3 SMN2 copies (p < 0.001). The difference was found not only in patients younger than 210 days at baseline (p < 0.001) but also in those younger than 5 years on the CHOP INTEND and younger than 2 years on the HINE-2.

INTERPRETATION

Our results, expanding the age range and the severity of type I patients treated with nusinersen over 1 year, provide additional data on the range of efficacy of the drug that will be helpful in making an informed decision on whether to start treatment in patients of different ages and severity. ANN NEUROL 2019;86:443-451.

NCALD Antisense Oligonucleotide Therapy in Addition to Nusinersen further Ameliorates Spinal Muscular Atrophy in Mice

Spinal muscular atrophy (SMA) is a neuromuscular disease causing the most frequent genetic childhood lethality. Recently, nusinersen, an antisense oligonucleotide (ASO) that corrects SMN2 splicing and thereby increases full-length SMN protein, has been approved by the FDA and EMA for SMA therapy. However, the administration of nusinersen in severe and/or post-symptomatic SMA-affected individuals is insufficient to counteract the disease. Therefore, additional SMN-independent therapies are needed to support the function of motoneurons and neuromuscular junctions. We recently identified asymptomatic SMN1-deleted individuals who were protected against SMA by reduced expression of neurocalcin delta (NCALD). NCALD reduction is proven to be a protective modifier of SMA across species, including worm, zebrafish, and mice. Here, we identified Ncald-ASO3-out of 450 developed Ncald ASOs-as the most efficient and non-toxic ASO for the CNS, by applying a stepwise screening strategy in cortical neurons and adult and neonatal mice. In a randomized-blinded preclinical study, a single subcutaneous low-dose SMN-ASO and a single intracerebroventricular Ncald-ASO3 or control-ASO injection were presymptomatically administered in a severe SMA mouse model. NCALD reduction of >70% persisted for about 1 month. While low-dose SMN-ASO rescues multiorgan impairment, additional NCALD reduction significantly ameliorated SMA pathology including electrophysiological and histological properties of neuromuscular junctions and muscle at P21 and motoric deficits at 3 months. The present study shows the additional benefit of a combinatorial SMN-dependent and SMN-independent ASO-based therapy for SMA. This work illustrates how a modifying gene, identified in some asymptomatic individuals, helps to develop a therapy for all SMA-affected individuals.

Increased Single-Fiber Jitter Level Is Associated With Reduction in Motor Function With Aging

OBJECTIVE

Age-associated skeletal muscle weakness is a major contributing factor to an increased late life mortality and morbidity, but its neurobiology is poorly understood. Previously, we provided histological evidence of dying-back axonal degeneration of motor neurons and denervation of neuromuscular junctions in age-associated muscle weakness. Given this, we aimed to evaluate the relation between impaired neuromuscular transmission and various aspects of age-associated muscle weakness.

DESIGN

We compared two electrophysiological measures, single-fiber jitter and compound motor action potential in mice of different age groups, and correlated them with various physical performance measures, such as grip strength, standing and walking time, and treadmill performance.

RESULTS

Consistent with our previous histological data, single-fiber jitter, a measure of neuromuscular junction transmission, was significantly increased in older animals, whereas compound motor action potential shows no difference between young and old age groups. Neither jitter nor compound motor action potential correlated with any of physical performance measures, except for jitter and standing activity.

CONCLUSIONS

Impaired neuromuscular transmission-represented as increase in single-fiber electromyography jitter level-reflects decline in motor function with aging.

Challenges of gene delivery to the central nervous system and the growing use of biomaterial vectors

Gene therapy is a promising form of treatment for those suffering from neurological disorders or central nervous system (CNS) injury, however, obstacles remain that limit its translational potential. The CNS is protected by the blood brain barrier, and this barrier blocks genes from traversing into the CNS if administered outside of the CNS. Viral and non-viral gene delivery vehicles, commonly referred to as vectors, are modified to enhance delivery efficiency to target locations in the CNS. Still, there are few gene therapy approaches approved by the FDA for CNS disease or injury treatment. The lack of viable clinical approaches is due, in part, to the unpredictable nature of many vector systems. In particular, safety concerns exist with the use of viral vectors for CNS gene delivery. To seek some alternatives to viral vectors, development of new non-viral, biomaterial vectors is occurring at a rapid rate. This review discusses the challenges of delivering various forms of genetic material to the CNS, the use and limitations of current viral vector delivery systems, and the use of non-viral, biomaterial vectors for CNS applications.

Perspectives in genetic counseling for spinal muscular atrophy in the new therapeutic era: early pre-symptomatic intervention and test in minors

Spinal muscular atrophy (SMA) is an autosomal-recessive neuromuscular disorder representing a continuous spectrum of muscular weakness ranging from compromised neonates to adults with minimal manifestations. Patients show homozygous absence or disease-causing variants of the SMN1 gene (−/− or 0/0) and in carriers only one copy is absent or mutated (1/0). Genetic diagnosis and counseling in SMA present several challenges, including the existence of carriers (2/0) that are undistinguishable of non-carriers (1/1) with current genetic testing methods and the report of patients (0/0) with very mild manifestations and even asymptomatic that are discovered when a full symptomatic case appears in the family. Younger asymptomatic siblings of symptomatic SMA patients are usually never tested until adolescence or adult life. However, following regulatory approval of the first tailored treatment for SMA, the prospects for care of these patients have changed. Early testing, including pre-symptomatic newborn screening and confirmation of diagnosis would change proactive measures and opportunities for therapy based in the actual landscape of new treatments. This review discusses the challenges and new perspectives of genetic counseling in SMA.

Thoracic circumference: A new outcome measure in spinal muscular atrophy type 1?

Since respiratory insufficiency is the first cause of morbidity and mortality in spinal muscular atrophy type 1 (SMA 1), specific respiratory outcome measures are needed to evaluate changes and assess innovative therapies. In this study, thoracic circumference (TC) was used as a proxy for chest growth and an indirect measurement of respiratory function. The anthropometric parameters including TC and head-circumference (HC) were evaluated from birth to 13 months in 19 infants with SMA 1 and 124 control infants. TC was significantly decreased in the SMA 1 group from the first weeks of life. The control group TC/HC ratio = 1 (± 0.04), and was not found to be associated with age. By contrast, it decreased with time in all infants with SMA 1 and those with a TC/HC ratio <0.85 died within 3 months. TC is a simple measurement that provided an index of chest growth and was used as evidence of early, progressive respiratory failure and under-development of the rib-cage in SMA 1. The TC/HC ratio decreased in all patients over time, reflecting the progression of the disease suggesting that TC/HC ratio could be a new measure for SMA 1 for measuring disease severity and prognosis.

Nusinersen in later-onset spinal muscular atrophy: Long-term results from the phase 1/2 studies

Objective

To report results of intrathecal nusinersen in children with later-onset spinal muscular atrophy (SMA).

Methods

Analyses included children from a phase 1b/2a study (ISIS-396443-CS2; NCT01703988) who first received nusinersen during that study and were eligible to continue treatment in the extension study (ISIS-396443-CS12; NCT02052791). The phase 1b/2a study was a 253-day, ascending dose (3, 6, 9, 12 mg), multiple-dose, open-label, multicenter study that enrolled children with SMA aged 2–15 years. The extension study was a 715-day, single-dose level (12 mg) study. Time between studies varied by participant (196–413 days). Assessments included the Hammersmith Functional Motor Scale–Expanded (HFMSE), Upper Limb Module (ULM), 6-Minute Walk Test (6MWT), compound muscle action potential (CMAP), and quantitative multipoint incremental motor unit number estimation. Safety also was assessed.

Results

Twenty-eight children were included (SMA type II, n = 11; SMA type III, n = 17). Mean HFMSE scores, ULM scores, and 6MWT distances improved by the day 1,150 visit (HFMSE: SMA type II, +10.8 points; SMA type III, +1.8 points; ULM: SMA type II, +4.0 points; 6MWT: SMA type III, +92.0 meters). Mean CMAP values remained relatively stable. No children discontinued treatment due to adverse events.

Conclusions

Nusinersen treatment over ∼3 years resulted in motor function improvements and disease activity stabilization not observed in natural history cohorts. These results document the long-term benefit of nusinersen in later-onset SMA, including SMA type III.

Clinicaltrials.gov identifier

NCT01703988 (ISIS-396443-CS2); NCT02052791 (ISIS-396443-CS12).

Classification of evidence

This study provides Class IV evidence that nusinersen improves motor function in children with later-onset SMA.

Neurofilament as a potential biomarker for spinal muscular atrophy

Objective

To evaluate plasma phosphorylated neurofilament heavy chain (pNF‐H) as a biomarker in spinal muscular atrophy (SMA).

Methods

Levels of pNF‐H were measured using the ProteinSimple^® platform in plasma samples from infants with SMA enrolled in ENDEAR (NCT02193074) and infants/children without neurological disease.

Results

Median pNF‐H plasma level was 167.0 pg/mL (7.46–7,030; n = 34) in children without SMA (aged 7 weeks–18 years) and was higher in those aged < 1 versus 1–18 years (P = 0.0002). In ENDEAR participants with infantile‐onset SMA, median baseline pNF‐H level (15,400 pg/mL; 2390–50,100; n = 117) was ~10‐fold higher than that of age‐matched infants without SMA (P < 0.0001) and ~90‐fold higher than children without SMA (P < 0.0001). Higher pretreatment pNF‐H levels in infants with SMA were associated with younger age at symptom onset, diagnosis, and first dose; lower baseline Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders score; and lower peroneal compound muscle potential amplitude. Nusinersen treatment was associated with a rapid and greater decline in pNF‐H levels: nusinersen‐treated infants experienced a steep 71.9% decline at 2 months to 90.1% decline at 10 months; sham control–treated infants declined steadily by 16.2% at 2 months and 60.3% at 10 months.

Interpretation

Plasma pNF‐H levels are elevated in infants with SMA. Levels inversely correlate with age at first dose and several markers of disease severity. Nusinersen treatment is associated with a significant decline in pNF‐H levels followed by relative stabilization. Together these data suggest plasma pNF‐H is a promising marker of disease activity/treatment response in infants with SMA.

Specific inhibition of myostatin activation is beneficial in mouse models of SMA therapy

Spinal muscular atrophy (SMA) is a neuromuscular disease characterized by loss of α-motor neurons, leading to profound skeletal muscle atrophy. Patients also suffer from decreased bone mineral density and increased fracture risk. The majority of treatments for SMA, approved or in clinic trials, focus on addressing the underlying cause of disease, insufficient production of full-length SMN protein. While restoration of SMN has resulted in improvements in functional measures, significant deficits remain in both mice and SMA patients following treatment. Motor function in SMA patients may be additionally improved by targeting skeletal muscle to reduce atrophy and improve muscle strength. Inhibition of myostatin, a negative regulator of muscle mass, offers a promising approach to increase muscle function in SMA patients. Here we demonstrate that muSRK-015P, a monoclonal antibody which specifically inhibits myostatin activation, effectively increases muscle mass and function in two variants of the pharmacological mouse model of SMA in which pharmacologic restoration of SMN has taken place either 1 or 24 days after birth to reflect early or later therapeutic intervention. Additionally, muSRK-015P treatment improves the cortical and trabecular bone phenotypes in these mice. These data indicate that preventing myostatin activation has therapeutic potential in addressing muscle and bone deficiencies in SMA patients. An optimized variant of SRK-015P, SRK-015, is currently in clinical development for treatment of SMA.

Pico de fluxo de tosse em crianças e jovens com atrofia muscular espinhal tipo II e tipo III

RESUMO A atrofia muscular espinhal é uma doença neurodegenerativa, que pode cursar com insuficiência respiratória progressiva. O objetivo deste trabalho é descrever o pico de fluxo de tosse de crianças e jovens com atrofia muscular espinhal dos tipos II e III. Trata-se de um estudo transversal descritivo realizado em ambulatório de neuropediatria entre março de 2011 e maio de 2012, com pacientes com atrofia muscular e espinhal dos tipos II e III com mais de 5 anos de idade. Dos 53 pacientes elegíveis, 21 participaram da pesquisa. A medição do pico de fluxo de tosse foi realizada através do peak flow meter com os pacientes sentados e deitados. Após registradas três medidas, foi selecionada a maior entre elas. Os indivíduos do tipo III alcançaram valores de pico de fluxo de tosse superiores aos dos indivíduos do tipo II. As medidas tomadas em posição sentada (AME tipo II 159,4 l/min; AME tipo III 287,9 l/min) foram superiores às medidas em posição deitada (AME tipo II 146,9 l/min; AME tipo III 257,5 l/min), com diferença significativa (p-valor=0,008 posição sentada e p=0,033 posição deitada). Concluiu-se que indivíduos com AME tipo III apresentam maior PFT, principalmente quando sentados, em comparação com o tipo II.

Novel challenges in spinal muscular atrophy - How to screen and whom to treat?

In recent years, disease‐modifying and life‐prolonging therapies for spinal muscular atrophy (SMA) have been developed. However, patients are currently diagnosed with significant delay and therapies are often administered in advanced stages of motor neuron degeneration, showing limited effects. Methods to identify children in presymptomatic stages are currently evaluated in newborn screening programs. Yet, not all children develop symptoms shortly after birth raising the question whom to treat and when to initiate therapy. Finally, monitoring disease progression becomes essential to individualize management. Here, we review the literature on screening approaches, strategies to predict disease severity, and biomarkers to monitor therapy.

Treatment Algorithm for Infants Diagnosed with Spinal Muscular Atrophy through Newborn Screening

Background:

Spinal muscular atrophy (SMA) is an autosomal recessive disease characterized by the degeneration of alpha motor neurons in the spinal cord, leading to muscular atrophy. SMA is caused by deletions or mutations in the survival motor neuron 1 gene (SMN1). In humans, a nearly identical copy gene, SMN2, is present. Because SMN2 has been shown to decrease disease severity in a dose-dependent manner, SMN2 copy number is predictive of disease severity.

Objective:

To develop a treatment algorithm for SMA-positive infants identified through newborn screening based upon SMN2 copy number.

Methods:

A working group comprised of 15 SMA experts participated in a modified Delphi process, moderated by a neutral third-party expert, to develop treatment guidelines.

Results:

The overarching recommendation is that all infants with two or three copies of SMN2 should receive immediate treatment (n = 13). For those infants in which immediate treatment is not recommended, guidelines were developed that outline the timing and appropriate screens and tests to be used to determine the timing of treatment initiation.

Conclusions:

The identification SMA affected infants via newborn screening presents an unprecedented opportunity for achievement of maximal therapeutic benefit through the administration of treatment pre-symptomatically. The recommendations provided here are intended to help formulate treatment guidelines for infants who test positive during the newborn screening process.

Prenatal aspects in spinal muscular atrophy: From early detection to early presymptomatic intervention

With the recent advances in spinal muscular atrophy therapies, the complete scenario of standard of care and following up is changing not only in the clinical field with new phenotypes emerging but also with new expectations for patients, caregivers and health providers. The actual evidence indicates that early intervention and treatment is crucial for better response and prognosis. Knowledge of the prenatal and pre-symptomatic postnatal stages of the disease are becoming essential to consider the opportunities of timely diagnosis and to decide the earliest therapeutic intervention.

An overview of the Cure SMA membership database: Highlights of key demographic and clinical characteristics of SMA members

Background:

The Cure SMA database is one of the largest patient reported databases for people affected with SMA.

Objective:

The purpose of this study was to examine a subset of affected SMA persons with types I, II, and III from a patient reported database.

Methods:

Individuals with SMA were selected from the database using a date of first contact to Cure SMA between 2010 and 2016. Data analyzed included age at diagnosis, number of weeks from SMA diagnosis to contacting Cure SMA, and geographic distribution of individuals.

Results:

A total of 1,966 individuals with SMA were included in the analysis. Of these individuals, 51.9% had type I, 32.3% had type II, and 15.8% had type III. The average age of diagnosis for type I patients was 5.2 months, 22.1 months for type II, and 97.8 months for type III. From published incidence, about 59.0% of affected individuals in the US are registered in the Cure SMA database.

Conclusions:

The Cure SMA database is a unique and robust source of patient reported data that informs on the burden of illness and supports the development of new therapeutic modalities.

Evidence in focus: Nusinersen use in spinal muscular atrophy: Report of the Guideline Development, Dissemination, and Implementation Subcommittee of the American Academy of Neurology

OBJECTIVE

To identify the level of evidence for use of nusinersen to treat spinal muscular atrophy (SMA) and review clinical considerations regarding use.

METHODS

The author panel systematically reviewed nusinersen clinical trials for patients with SMA and assigned level of evidence statements based on the American Academy of Neurology's 2017 therapeutic classification of evidence scheme. Safety information, regulatory decisions, and clinical context were also reviewed.

RESULTS

Four published clinical trials were identified, 3 of which were rated above Class IV. There is Class III evidence that in infants with homozygous deletions or mutations of SMN1, nusinersen improves the probability of permanent ventilation-free survival at 24 months vs a well-defined historical cohort. There is Class I evidence that in term infants with SMA and 2 copies of SMN2, treatment with nusinersen started in individuals younger than 7 months results in a better motor milestone response and higher rates of event-free survival than sham control. There is Class I evidence that in children aged 2-12 years with SMA symptom onset after 6 months of age, nusinersen results in greater improvement in motor function at 15 months than sham control. Nusinersen was safe and well-tolerated.

CLINICAL CONTEXT

Evidence of efficacy is currently highest for treatment of infantile- and childhood-onset SMA in the early and middle symptomatic phases. While approved indications for nusinersen use in North America and Europe are broad, payer coverage for populations outside those in clinical trials remain variable. Evidence, availability, cost, and patient preferences all influence decision-making regarding nusinersen use.

Biomarkers of Spinal and Bulbar Muscle Atrophy (SBMA): A Comprehensive Review

Spinal and bulbar muscular atrophy (SBMA), also known as Kennedy's disease, is a rare, X-linked, late onset neuromuscular disorder. The disease is caused by a CAG trinucleotide repeat expansion in the first exon of the androgen receptor gene. It is characterized by slowly progressive lower motor neurons degeneration, primary myopathy and widespread multisystem involvement. Respiratory involvement is rare, and the condition is associated with a normal life expectancy. Despite a plethora of therapeutic studies in mouse models, no effective disease-modifying therapy has been licensed for clinical use to date. The development of sensitive monitoring markers for the particularly slowly progressing pathology of SBMA is urgently required to aid future clinical trials. A small number of outcome measures have been proposed recently, including promising biochemical markers, which show correlation with clinical disability and disease-stage and progression. Nevertheless, a paucity of SBMA-specific biomarker studies persists, delaying the development of monitoring markers for pharmaceutical trials. Collaborative efforts through international consortia and multicenter registries are likely to contribute to the characterization of the natural history of the condition, the establishment of disease-specific biomarker panels and ultimately contribute to the development of disease-modifying drugs.