Spinal muscular atrophy. 32nd ENMC International Workshop. Naarden, The Netherlands, 10-12 March 1995

Respiratory management of spinal muscular atrophy type 1 patients treated with Nusinersen

INTRODUCTION

The recent development of disease-modifying treatments in spinal muscular atrophy (SMA) type 1 shifted these patients' management from palliative to proactive. The aim of this study was to assess patients' nocturnal gas exchanges before noninvasive ventilation (NIV) initiation and their clinical evolution to determine if capnia is a good criterion to decide when to introduce respiratory support.

PATIENTS AND METHODS

This multicentric retrospective study reports the respiratory management and evolution of 17 SMA type 1 children (10 females) for whom treatment with Nusinersen was initiated between 2016 and 2018.

RESULTS

Median [interquartile range-IQR] age at diagnosis and at first Nusinersen injection was of 4 [3;8] and 4 [3;9] months, respectively. Patients were followed during 38 [24;44] months. Thirteen (76%) patients were started on NIV at a median [IQR] age of 12 [9;18] months. Repeated hospitalizations and intensive care unit admissions were needed for 11 of them. Blood gas and nocturnal gas exchange recordings performed before NIV initiation were always normal. 9/13 X-ray performed before NIV showed atelectasis and/or acute lower respiratory tract infections. There was a significant decrease in the total number of hospital admissions between the first and second year of treatment (p = 0.04).

CONCLUSION

This study shows that patients do not present with nocturnal hypoventilation before respiratory decompensations and NIV initiation, and suggests that a delay in NIV initiation might result in respiratory complications. There is a need for disease-centered guidelines for the respiratory management of these patients, including NIV indications.

An expanded access program of risdiplam for patients with Type 1 or 2 spinal muscular atrophy

Objective

The US risdiplam expanded access program (EAP; NCT04256265) was opened to provide individuals with Type 1 or 2 spinal muscular atrophy (SMA) who had no satisfactory treatment options access to risdiplam prior to commercial availability. The program was designed to collect safety data during risdiplam treatment.

Methods

Patients were enrolled from 23 non‐preselected sites across 17 states and treated with risdiplam orally once daily. Eligible patients had a 5q autosomal recessive Type 1 or 2 SMA diagnosis, were aged ≥2 months at enrollment, and were ineligible for available and approved SMA treatments or could not continue treatment due to a medical condition, lack/loss of efficacy, or the COVID‐19 pandemic.

Results

Overall, 155 patients with Type 1 (n = 73; 47.1%) or 2 SMA (n = 82; 52.9%) were enrolled and 149 patients (96.1%) completed the EAP (defined as obtaining access to commercial risdiplam, if desired). The median treatment duration was 4.8 months (range, 0.3–9.2 months). The median patient age was 11 years (range, 0–50 years), and most patients (n = 121; 78%) were previously treated with a disease‐modifying therapy. The most frequently reported adverse events were diarrhea (n = 10; 6.5%), pyrexia (n = 7; 4.5%), and upper respiratory tract infection (n = 5; 3.2%). The most frequently reported serious adverse event was pneumonia (n = 3; 1.9%). No deaths were reported.

Interpretation

In the EAP, the safety profile of risdiplam was similar to what was reported in pivotal risdiplam clinical trials. These safety data provide further support for the use of risdiplam in the treatment of adult and pediatric patients with SMA.

Sagittal Plane Deformities in Children with SMA2 following Posterior Spinal Instrumentation

This is a retrospective radiographic review to assess post-operative sagittal plane deformities in patients with Spinal Muscular Atrophy type 2 that had been treated with posterior spinal instrumentation. Thirty-two patients with a history of either spinal fusion (N = 20) or growing rods (N = 12) were identified with an average of 7.6 (2.1-16.6) years post-operative follow-up. Forty percent (13/32) of the patients were identified as having obvious "tucked chin" (N = 4), "tipped trunk" (N = 9), or both (N = 3). Sacral incidence was the only parameter that was statistically significant change between pre-operative or immediate post-operative measurements (66.9° vs. 55.2° p = 0.03). However, at final follow-up, the post-operative thoracic kyphosis had decreased over time in those that developed a subsequent sagittal deformity (24.2°) whereas it increased in those that did not (44.7°, p = 0.008). This decrease in thoracic kyphosis throughout the instrumented levels, resulted in a greater lordotic imbalance (30.4° vs. 5.6°, p = 0.001) throughout the instrumented levels in the group that developed the subsequent cervical or pelvic sagittal deformities. In conclusion, sagittal plane deformities commonly develop outside the instrumented levels in children with SMA type 2 following posterior spinal instrumentation and may be the result of lordotic imbalance that occurs through continued anterior growth following posterior instrumentation.

Prognostic Factors and Treatment-Effect Modifiers in Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is a rare, progressive neuromuscular disease characterized by loss of motor neurons and muscle atrophy. Untreated infants with type 1 SMA do not achieve major motor milestones, and death from respiratory failure typically occurs before 2 years of age. Individuals with types 2 and 3 SMA exhibit milder phenotypes and have better functional and survival outcomes. Herein, a systematic literature review was conducted to identify factors that influence the prognosis of types 1, 2, and 3 SMA. In untreated infants with type 1 SMA, absence of symptoms at birth, a later symptom onset, and a higher survival of motor neuron 2 (SMN2) copy number are all associated with increased survival. Disease duration, age at treatment initiation, and, to a lesser extent, baseline function were identified as potential treatment‐modifying factors for survival, emphasizing that early treatment with disease‐modifying therapies (DMT) is essential in type 1 SMA. In patients with types 2 and 3 SMA, factors considered prognostic of changes in motor function were SMN2 copy number, age, and ambulatory status. Individuals aged 6–15 years were particularly vulnerable to developing complications (scoliosis and progressive joint contractures) which negatively influence functional outcomes and may also affect the therapeutic response in patients. Age at the time of treatment initiation emerged as a treatment‐effect modifier on the outcome of DMTs. Factors identified in this review should be considered prior to designing or analyzing studies in an SMA population, conducting population matching, or summarizing results from different studies on the treatments for SMA.

Mathematical Disease Progression Modeling in Type 2/3 Spinal Muscular Atrophy

INTRODUCTION

We propose a mathematical model to empirically describe spinal muscular atrophy (SMA) progression assessed by the 3 domains of the motor function measure (MFM) scale. The model implements development and deterioration of muscle function.

METHODS

Nonlinear mixed-effects modeling was applied to data from 2 observational studies and 1 prospective clinical efficacy study comprising 190 healthy participants and 277 patients with type 2/3 SMA.

RESULTS

The model evidenced correlations between parameter estimates for different MFM domains. Slower development in MFM domain D1 (standing and transfers) was associated with faster deterioration for MFM domains D2 (proximal and axial motricity) and D3 (distal motor function).

DISCUSSION

The model describes all individual data well, although sparseness and variability of observational data prevented numerically stable estimation of parameters. Treatment duration in clinical studies was too limited to determine a proper drug-effect model that could differentiate between symptomatic and disease modifying effects. Muscle Nerve 58: 528-535, 2018.

Natural history of infantile-onset spinal muscular atrophy

OBJECTIVE

Infantile-onset spinal muscular atrophy (SMA) is the most common genetic cause of infant mortality, typically resulting in death preceding age 2. Clinical trials in this population require an understanding of disease progression and identification of meaningful biomarkers to hasten therapeutic development and predict outcomes.

METHODS

A longitudinal, multicenter, prospective natural history study enrolled 26 SMA infants and 27 control infants aged <6 months. Recruitment occurred at 14 centers over 21 months within the NINDS-sponsored NeuroNEXT (National Network for Excellence in Neuroscience Clinical Trials) Network. Infant motor function scales (Test of Infant Motor Performance Screening Items [TIMPSI], The Children's Hospital of Philadelphia Infant Test for Neuromuscular Disorders, and Alberta Infant Motor Score) and putative physiological and molecular biomarkers were assessed preceding age 6 months and at 6, 9, 12, 18, and 24 months with progression, correlations between motor function and biomarkers, and hazard ratios analyzed.

RESULTS

Motor function scores (MFS) and compound muscle action potential (CMAP) decreased rapidly in SMA infants, whereas MFS in all healthy infants rapidly increased. Correlations were identified between TIMPSI and CMAP in SMA infants. TIMPSI at first study visit was associated with risk of combined endpoint of death or permanent invasive ventilation in SMA infants. Post-hoc analysis of survival to combined endpoint in SMA infants with 2 copies of SMN2 indicated a median age of 8 months at death (95% confidence interval, 6, 17).

INTERPRETATION

These data of SMA and control outcome measures delineates meaningful change in clinical trials in infantile-onset SMA. The power and utility of NeuroNEXT to provide "real-world," prospective natural history data sets to accelerate public and private drug development programs for rare disease is demonstrated. Ann Neurol 2017;82:883-891.

Newborn genetic screening for spinal muscular atrophy in the UK: The views of the general population

Background

Spinal muscular atrophy (SMA) is an inherited neuromuscular disorder and a leading genetic cause of infant death worldwide. However, there is no routine screening program for SMA in the UK. Lack of treatments and the inability of screening tests to accurately predict disease severity are among the key reasons implementation of screening has faltered in the UK. With the recent release of the first therapy for SMA (Nusinersen), calls are being made for a reconsideration of this stance; however, very little is known about the views of the general public.

Methods

An online survey was administered to 232 individuals with no prior relationship with SMA to assess their attitudes toward a newborn screening program for it. Results are compared with previously gathered data on the views of SMA‐affected families toward screening.

Results

Eighty‐four percent of participants were in favor of newborn screening. Key reasons for support were a belief that it would lead to better healthcare and life expectancy for affected infants and facilitate informed decision‐making for future pregnancies. Key reasons for nonsupport were a belief in the potential for significant negative impact on the family unit in terms of bonding and stress.

Conclusions

Public acceptability is a key component in the evaluation of any potential screening program in the UK. This study demonstrates that newborn screening for SMA is viewed largely positively by people unfamiliar with the condition. The importance of early identification overrode all other social and ethical concerns about screening for the majority of participants.

Baseline results of the NeuroNEXT spinal muscular atrophy infant biomarker study

OBJECTIVE

This study prospectively assessed putative promising biomarkers for use in assessing infants with spinal muscular atrophy (SMA).

METHODS

This prospective, multi-center natural history study targeted the enrollment of SMA infants and healthy control infants less than 6 months of age. Recruitment occurred at 14 centers within the NINDS National Network for Excellence in Neuroscience Clinical Trials (NeuroNEXT) Network. Infant motor function scales and putative electrophysiological, protein and molecular biomarkers were assessed at baseline and subsequent visits.

RESULTS

Enrollment began November, 2012 and ended September, 2014 with 26 SMA infants and 27 healthy infants enrolled. Baseline demographic characteristics of the SMA and control infant cohorts aligned well. Motor function as assessed by the Test for Infant Motor Performance Items (TIMPSI) and the Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP-INTEND) revealed significant differences between the SMA and control infants at baseline. Ulnar compound muscle action potential amplitude (CMAP) in SMA infants (1.4 ± 2.2 mV) was significantly reduced compared to controls (5.5 ± 2.0 mV). Electrical impedance myography (EIM) high-frequency reactance slope (Ohms/MHz) was significantly higher in SMA infants than controls SMA infants had lower survival motor neuron (SMN) mRNA levels in blood than controls, and several serum protein analytes were altered between cohorts.

INTERPRETATION

By the time infants were recruited and presented for the baseline visit, SMA infants had reduced motor function compared to controls. Ulnar CMAP, EIM, blood SMN mRNA levels, and serum protein analytes were able to distinguish between cohorts at the enrollment visit.

Spinal muscular atrophies

Spinal muscular atrophies (SMAs) are hereditary degenerative disorders of lower motor neurons associated with progressive muscle weakness and atrophy. Proximal 5q SMA is caused by decreased levels of the survival of motor neuron (SMN) protein and is the most common genetic cause of infant mortality. Its inheritance pattern is autosomal recessive, resulting from mutations involving the SMN1 gene on chromosome 5q13. Unlike other autosomal recessive diseases, the SMN gene has a unique structure (an inverted duplication) that presents potential therapeutic targets. Although there is currently no effective treatment of SMA, the field of translational research in this disorder is active and clinical trials are ongoing. Advances in the multidisciplinary supportive care of children with SMA also offer hope for improved life expectancy and quality of life.

Spectrum of neuropathophysiology in spinal muscular atrophy type I

Neuropathologic findings within the central and peripheral nervous systems in patients with spinal muscular atrophy type I (SMA-I) were examined in relation to genetic, clinical, and electrophysiologic features. Five infants representing the full clinical spectrum of SMA-I were examined clinically for compound motor action potential amplitude and SMN2 gene copy number; morphologic analyses of postmortem central nervous system, neuromuscular junction, and muscle tissue samples were performed and SMN protein was assessed in muscle samples. The 2 clinically most severely affected patients had a single copy of the SMN2 gene; in addition to anterior horn cells, dorsal root ganglia, and thalamus, neuronal degeneration in them was widespread in the cerebral cortex, basal ganglia, pigmented nuclei, brainstem, and cerebellum. Two typical SMA-I patients and a milder case each had 2 copies of the SMN2 gene and more restricted neuropathologic abnormalities. Maturation of acetylcholine receptor subunits was delayed and the neuromuscular junctions were abnormally formed in the SMA-I patients. Thus, the neuropathologic findings in human SMA-I are similar to many findings in animal models; factors other than SMN2 copy number modify disease severity. We present a pathophysiologic model for SMA-I as a protein deficiency disease affecting a neuronal network with variable clinical thresholds. Because new treatment strategies improve survival of infants with SMA-I, a better understanding of these factors will guide future treatments.

Observational study of spinal muscular atrophy type I and implications for clinical trials

OBJECTIVES

Prospective cohort study to characterize the clinical features and course of spinal muscular atrophy type I (SMA-I).

METHODS

Patients were enrolled at 3 study sites and followed for up to 36 months with serial clinical, motor function, laboratory, and electrophysiologic outcome assessments. Intervention was determined by published standard of care guidelines. Palliative care options were offered.

RESULTS

Thirty-four of 54 eligible subjects with SMA-I (63%) enrolled and 50% of these completed at least 12 months of follow-up. The median age at reaching the combined endpoint of death or requiring at least 16 hours/day of ventilation support was 13.5 months (interquartile range 8.1-22.0 months). Requirement for nutritional support preceded that for ventilation support. The distribution of age at reaching the combined endpoint was similar for subjects with SMA-I who had symptom onset before 3 months and after 3 months of age (p=0.58). Having 2 SMN2 copies was associated with greater morbidity and mortality than having 3 copies. Baseline electrophysiologic measures indicated substantial motor neuron loss. By comparison, subjects with SMA-II who lost sitting ability (n=10) had higher motor function, motor unit number estimate and compound motor action potential, longer survival, and later age when feeding or ventilation support was required. The mean rate of decline in The Children's Hospital of Philadelphia Infant Test for Neuromuscular Disorders motor function scale was 1.27 points/year (95% confidence interval 0.21-2.33, p=0.02).

CONCLUSIONS

Infants with SMA-I can be effectively enrolled and retained in a 12-month natural history study until a majority reach the combined endpoint. These outcome data can be used for clinical trial design.

VPA response in SMA is suppressed by the fatty acid translocase CD36

Functional loss of SMN1 causes proximal spinal muscular atrophy (SMA), the most common genetic condition accounting for infant lethality. Hence, the hypomorphic copy gene SMN2 is the only resource of functional SMN protein in SMA patients and influences SMA severity in a dose-dependent manner. Consequently, current therapeutic approaches focus on SMN2. Histone deacetylase inhibitors (HDACi), such as the short chain fatty acid VPA (valproic acid), ameliorate the SMA phenotype by activating the SMN2 expression. By analyzing blood SMN2 expression in 16 VPA-treated SMA patients, about one-third of individuals were identified as positive responders presenting increased SMN2 transcript levels. In 66% of enrolled patients, a concordant response was detected in the respective fibroblasts. Most importantly, by taking the detour of reprograming SMA patients' fibroblasts, we showed that the VPA response was maintained even in GABAergic neurons derived from induced pluripotent stem cells (iPS) cells. Differential expression microarray analysis revealed a complete lack of response to VPA in non-responders, which was associated with an increased expression of the fatty acid translocase CD36. The pivotal role of CD36 as the cause of non-responsiveness was proven in various in vitro approaches. Most importantly, knockdown of CD36 in SMA fibroblasts converted non- into pos-responders. In summary, the concordant response from blood to the central nervous system (CNS) to VPA may allow selection of pos-responders prior to therapy. Increased CD36 expression accounts for VPA non-responsiveness. These findings may be essential not only for SMA but also for other diseases such as epilepsy or migraine frequently treated with VPA.

Candidate proteins, metabolites and transcripts in the Biomarkers for Spinal Muscular Atrophy (BforSMA) clinical study

Background

Spinal Muscular Atrophy (SMA) is a neurodegenerative motor neuron disorder resulting from a homozygous mutation of the survival of motor neuron 1 (SMN1) gene. The gene product, SMN protein, functions in RNA biosynthesis in all tissues. In humans, a nearly identical gene, SMN2, rescues an otherwise lethal phenotype by producing a small amount of full-length SMN protein. SMN2 copy number inversely correlates with disease severity. Identifying other novel biomarkers could inform clinical trial design and identify novel therapeutic targets.

Objective:

To identify novel candidate biomarkers associated with disease severity in SMA using unbiased proteomic, metabolomic and transcriptomic approaches.

Materials and Methods:

A cross-sectional single evaluation was performed in 108 children with genetically confirmed SMA, aged 2–12 years, manifesting a broad range of disease severity and selected to distinguish factors associated with SMA type and present functional ability independent of age. Blood and urine specimens from these and 22 age-matched healthy controls were interrogated using proteomic, metabolomic and transcriptomic discovery platforms. Analyte associations were evaluated against a primary measure of disease severity, the Modified Hammersmith Functional Motor Scale (MHFMS) and to a number of secondary clinical measures.

Results

A total of 200 candidate biomarkers correlate with MHFMS scores: 97 plasma proteins, 59 plasma metabolites (9 amino acids, 10 free fatty acids, 12 lipids and 28 GC/MS metabolites) and 44 urine metabolites. No transcripts correlated with MHFMS.

Discussion

In this cross-sectional study, “BforSMA” (Biomarkers for SMA), candidate protein and metabolite markers were identified. No transcript biomarker candidates were identified. Additional mining of this rich dataset may yield important insights into relevant SMA-related pathophysiology and biological network associations. Additional prospective studies are needed to confirm these findings, demonstrate sensitivity to change with disease progression, and assess potential impact on clinical trial design.

Trial Registry

Clinicaltrials.gov NCT00756821.

RNA-targeting approaches for neuromuscular diseases

Although most molecular therapy strategies for genetic diseases are based on gene replacement, interesting alternative approaches target RNA. These strategies rely on the modification of the mutated gene's expression in vivo by modulating pre-mRNA splicing, mRNA stability or mRNA translation. Here, we review recent progress using these RNA-based approaches in the field of muscle and muscle-related genetic diseases. Different molecular tools, including modified antisense oligonucleotides, pre-mRNA trans-splicing molecules, ribozymes or chemical compounds have been used successfully on patient cells or animal models of disease. These diverse strategies show tremendous therapeutic potential and several clinical trials have been initiated with Duchenne muscular dystrophy patients with promising results.

LBH589 induces up to 10-fold SMN protein levels by several independent mechanisms and is effective even in cells from SMA patients non-responsive to valproate

Histone deacetylase inhibitors (HDACi) are potential candidates for therapeutic approaches in cancer and neurodegenerative diseases such as spinal muscular atrophy (SMA)--a common autosomal recessive disorder and frequent cause of early childhood death. SMA is caused by homozygous absence of SMN1. Importantly, all SMA patients carry a nearly identical copy gene, SMN2, that produces only minor levels of correctly spliced full-length transcripts and SMN protein. Since an increased number of SMN2 copies strongly correlates with a milder SMA phenotype, activation or stabilization of SMN2 is considered as a therapeutic strategy. However, clinical trials demonstrated effectiveness of the HDACi valproate (VPA) and phenylbutyrate only in <50% of patients; therefore, identification of new drugs is of vital importance. Here we characterize the novel hydroxamic acid LBH589, an HDACi already widely used in cancer clinical trials. LBH589 treatment of human SMA fibroblasts induced up to 10-fold elevated SMN levels, the highest ever reported, accompanied by a markedly increased number of gems. FL-SMN2 levels were increased 2-3-fold by transcription activation via SMN2 promoter H3K9 hyperacetylation and restoration of correct splicing via elevated hTRA2-beta1 levels. Furthermore, LBH589 stabilizes SMN by reducing its ubiquitinylation as well as favouring incorporation into the SMN complex. Cytotoxic effects were not detectable at SMN2 activating concentrations. Notably, LBH589 also induces SMN2 expression in SMA fibroblasts inert to VPA, in human neural stem cells and in the spinal cord of SMN2-transgenic mice. Hence, LBH589, which is active already at nanomolar doses, is a highly promising candidate for SMA therapy.

Spinal muscular atrophy

Spinal muscular atrophy (SMA) is a potentially devastating and lethal neuromuscular disease frequently manifesting in infancy and childhood. The discovery of the underlying mutation in the survival of motor neurons 1 (SMN1) gene has accelerated preclinical research, leading to treatment targets and transgenic mouse models, but there is still no effective treatment. The clinical severity is inversely related to the copy number of SMN2, a modifying gene producing some full-length SMN transcript. Drugs shown to increase SMN2 function in vitro, therefore, have the potential to benefit patients with SMA. Because several drugs are now on the horizon of clinical investigation, we review recent clinical trials for SMA and discuss the challenges and opportunities associated with SMA drug development. Although an orphan disease, SMA is well-positioned for successful trials given that it has a common genetic etiology in most cases, that it can be readily diagnosed, that preclinical research in vitro and in transgenic animals has identified candidate compounds, and that trial networks have been established.

Plastin 3 is a protective modifier of autosomal recessive spinal muscular atrophy

Homozygous deletion of the survival motor neuron 1 gene (SMN1) causes spinal muscular atrophy (SMA), the most frequent genetic cause of early childhood lethality. In rare instances, however, individuals are asymptomatic despite carrying the same SMN1 mutations as their affected siblings, thereby suggesting the influence of modifier genes. We discovered that unaffected SMN1-deleted females exhibit significantly higher expression of plastin 3 (PLS3) than their SMA-affected counterparts. We demonstrated that PLS3 is important for axonogenesis through increasing the F-actin level. Overexpression of PLS3 rescued the axon length and outgrowth defects associated with SMN down-regulation in motor neurons of SMA mouse embryos and in zebrafish. Our study suggests that defects in axonogenesis are the major cause of SMA, thereby opening new therapeutic options for SMA and similar neuromuscular diseases.

Motor function-muscle strength relationship in spinal muscular atrophy

The relationship between motor function and muscle strength in patients with spinal muscular atrophy (SMA) is still controversial. In 120 genetically proven SMA patients, aged 5 years or older, we measured muscle strength in the arms and legs by a hand-held dynamometer, forced vital capacity by a spirometer, and the time needed to walk 10 m, arise from the floor, and climb steps. SMA patients had markedly reduced muscle strength, approximating 20% of that predicted from age- and gender-matched normative data. Knee extensors were the weakest muscles in SMA patients. The young ambulant SMA patients performed better than adults in all the timed tests and had greater muscle strength on knee extension. This study shows a good relationship between motor ability and muscle strength in SMA and confirms that age-related loss of function in SMA is due to loss of muscle strength.

Segmental distribution of muscle weakness in SMA III: implications for deterioration in muscle strength with time

We examined 26 spinal muscular atrophy type III (SMA III) patients with SMNt deletions, searching for possible segmental distribution of muscle weakness. In those with disease duration of < or = 11 years, the weakest muscles were upper lumbar innervated ones in the lower extremities. In the upper extremities, early involvement of triceps muscle suggested the possibility of lower cervical (C7) onset. Electrophysiologically, weaker muscles had a more severe reduction in the recruitment pattern, particularly in the lower extremities. However, severe reduction in recruitment was sometimes also observed in clinically strong muscles. In patients with disease duration of > or = 16 years and regardless of disease duration, in those with disease onset at < or = 3 years of age, weakness and severe electrophysiological changes were more widespread. These findings may suggest a progression in muscle weakness with time. When compared to 12 patients with Becker muscular dystrophy (BMD), early stage SMA III with weak iliopsoas-strong gluteus maximus stood in contrast to BMD with weak gluteus maximus-strong iliopsoas.