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

The motor unit number index (MUNIX) profile of patients with adult spinal muscular atrophy

OBJECTIVE

Objective of this study is the comprehensive characterisation of motor unit (MU) loss in type III and IV Spinal Muscular Atrophy (SMA) using motor unit number index (MUNIX), and evaluation of compensatory mechanisms based on MU size indices (MUSIX).

METHODS

Nineteen type III and IV SMA patients and 16 gender- and age-matched healthy controls were recruited. Neuromuscular performance was evaluated by muscle strength testing and functional scales. Compound motor action potential (CMAP), MUNIX and MUSIX were studied in the abductor pollicis brevis (APB), abductor digiti minimi (ADM), deltoid, tibialis anterior and trapezius muscles. A composite MUNIX score was also calculated.

RESULTS

SMA patients exhibited significantly reduced MUNIX values (p < 0.05) in all muscles, while MUSIX was increased, suggesting active re-innervation. Significant correlations were identified between MUNIX/MUSIX and muscle strength. Similarly, composite MUNIX scores correlated with disability scores. Interestingly, in SMA patients MUNIX was much lower in the ADM than in the ABP, a pattern which is distinctly different from that observed in Amyotrophic Lateral Sclerosis.

CONCLUSIONS

MUNIX is a sensitive measure of MU loss in adult forms of SMA and correlates with disability.

SIGNIFICANCE

MUNIX evaluation is a promising candidate biomarker for longitudinal studies and pharmacological trials in adult SMA patients.

Molecular Factors Involved in Spinal Muscular Atrophy Pathways as Possible Disease-modifying Candidates

Spinal Muscular Atrophy (SMA) is a neuromuscular disorder caused by mutations in the SMN1 gene. Being a monogenic disease, it is characterized by high clinical heterogeneity. Variations in penetrance and severity of symptoms, as well as clinical discrepancies between affected family members can result from modifier genes influence on disease manifestation. SMN2 gene copy number is known to be the main phenotype modifier and there is growing evidence of additional factors contributing to SMA severity. Potential modifiers of spinal muscular atrophy can be found among the wide variety of different factors, such as multiple proteins interacting with SMN or promoting motor neuron survival, epigenetic modifications, transcriptional or splicing factors influencing SMN2 expression. Study of these factors enables to reveal mechanisms underlying SMA pathology and can have pronounced clinical application.

Prospective and longitudinal natural history study of patients with Type 2 and 3 spinal muscular atrophy: Baseline data NatHis-SMA study

Spinal muscular atrophy (SMA) is a monogenic disorder caused by loss of function mutations in the survival motor neuron 1 gene, which results in a broad range of disease severity, from neonatal to adult onset. There is currently a concerted effort to define the natural history of the disease and develop outcome measures that accurately capture its complexity. As several therapeutic strategies are currently under investigation and both the FDA and EMA have recently approved the first medical treatment for SMA, there is a critical need to identify the right association of responsive outcome measures and biomarkers for individual patient follow-up. As an approved treatment becomes available, untreated patients will soon become rare, further intensifying the need for a rapid, prospective and longitudinal study of the natural history of SMA Type 2 and 3. Here we present the baseline assessments of 81 patients aged 2 to 30 years of which 19 are non-sitter SMA Type 2, 34 are sitter SMA Type 2, 9 non-ambulant SMA Type 3 and 19 ambulant SMA Type 3. Collecting these data at nine sites in France, Germany and Belgium established the feasibility of gathering consistent data from numerous and demanding assessments in a multicenter SMA study. Most assessments discriminated between the four groups well. This included the Motor Function Measure (MFM), pulmonary function testing, strength, electroneuromyography, muscle imaging and workspace volume. Additionally, all of the assessments showed good correlation with the MFM score. As the untreated patient population decreases, having reliable and valid multi-site data will be imperative for recruitment in clinical trials. The pending two-year study results will evaluate the sensitivity of the studied outcomes and biomarkers to disease progression.

Trial Registration: ClinicalTrials.gov (NCT02391831).

Nusinersen: A Treatment for Spinal Muscular Atrophy

OBJECTIVE

To review the efficacy and safety of nusinersen (Spinraza) in the treatment of spinal muscular atrophy (SMA).

DATA SOURCES

An English-language literature search of PubMed and MEDLINE (1946 to June 2018) was performed using the terms nusinersen, ISIS-SMN (Rx), and spinal muscular atrophy. Manufacturer prescribing information, abstracts, article bibliographies, and clinicaltrials.gov data were incorporated for additional materials.

STUDY SELECTION/DATA EXTRACTION

All clinical trials of nusinersen were identified and analyzed in the review.

DATA SYNTHESIS

Nusinersen is the first drug therapy approved for the treatment of SMA. It is a novel modified antisense oligonucleotide designed to treat SMA caused by mutations in chromosome 5q that lead to survival motor neuron protein deficiency. Nusinersen has been studied for safety, pharmacokinetics, and efficacy in both open-label and randomized controlled trials. The studies show improvement in motor function across SMA of all types. The most common adverse effects were respiratory tract infections, headache, back pain, constipation, and post-lumbar puncture syndrome. Relevance to Patient Care and Clinical Practice: Based on phase III trial data, nusinersen produced positive changes in the clinical course of patients with SMA. The acquisition and administration of nusinersen present a number of challenges in clinical practice. Its intrathecal delivery and costly price tag must be recognized.

CONCLUSION

Nusinersen is safe and effective in patients with SMA. It was well tolerated across all studied age groups.

Nusinersen in type 1 SMA infants, children and young adults: Preliminary results on motor function

We report preliminary data on the six month use of Nusinersen in 104 type 1 patients of age ranging from three months to 19 years, 9 months. Ten of the 104 were classified as 1.1, 58 as 1.5 and 36 as 1.9. Three patients had one SMN2 copy, 65 had two and 24 had three copies. In 12 the SMN2 copy number was not available. After six months an improvement of more than two points was found in 58 of the 104 (55.7%) on the CHOP INTEND and in 21 of the 104 (20.19%) on the Hammersmith Infant Neurological Examination (HINE). Changes more than two points were found in 26/71 patients older than two years, and in seven of the 20 older than 10 years. Changes ≥ four points were found in 20/71 older than two years, and in six of the 20 patients older than 10 years. The difference between baseline and six months on both CHOP INTEND and HINE was significant for the whole group (p < 0.001) as well as for the subgroups with two (p < 0.001), and three SMN2 copies (p < 0.001). Our preliminary results suggest that functional improvement can be observed in type 1 patients outside the range of the inclusion criteria used in the Endear study.

Increase of hyperpolarization-activated cyclic nucleotide-gated current in the aberrant excitability of spinal muscular atrophy

OBJECTIVE

The pathophysiology of spinal muscular atrophy (SMA) is still unclear.

METHODS

The nerve excitability test in SMA patients and a mouse model of SMA was carried out to explore the pathophysiology of nodal and internodal currents, and quantitative PCR, western blotting, and whole-cell patch-clamp recording were used for the identified hypothesis.

RESULTS

The nerve excitability test in SMA patients showed increased inward rectification in the current-threshold relationship and increased overshoot after hyperpolarizing threshold electrotonus, which indicates increased hyperpolarization-activated cyclic nucleotide-gated (HCN) current; these findings correlated with disease severity. Increased inward rectification in the current-threshold relationship was reproducible in a mouse model of mild SMA, and the abnormality preceded the decline of compound motor action potential amplitudes. Furthermore, quantitative PCR of spinal cord tissues and western blotting of the spinal cord and sciatic nerves showed increased HCN1 and HCN2 expression in SMA mice, and voltage-clamp recording in dissociated spinal motor neurons from SMA mice also showed increased HCN current density. Treatment with ZD7288, an HCN channel blocker, also reduced early mortality, improved motor function, and restored neuromuscular junction architecture in a mouse model of severe SMA.

INTERPRETATION

This study shows that increased HCN current underlies the pathophysiology of SMA and can be a novel non-SMN target for SMA therapy. Ann Neurol 2018;83:494-507.

Transforaminal intrathecal delivery of nusinersen using cone-beam computed tomography for children with spinal muscular atrophy and extensive surgical instrumentation: early results of technical success and safety

BACKGROUND

Nusinersen, the only treatment approved by the United States Food and Drug Administration for spinal muscular atrophy (SMA), is delivered intrathecally. Many children with SMA have extensive spinal instrumentation and deformities, often precluding the use of standard approaches for gaining intrathecal access. Furthermore the anatomical distortion that often occurs with rotoscoliosis can complicate the use of fluoroscopic guidance. Compared to fluoroscopy, CT affords superior guidance for complex needle placements. This opens up alternatives to the posterior (interlaminar) technique, including transforaminal and caudal approaches.

OBJECTIVE

This study describes the early results of technical success, complications and radiation dose of intrathecal delivery of nusinersen using cone-beam CT guidance with two-axis fluoroscopic navigational overlay.

MATERIALS AND METHODS

We conducted a retrospective review of 15 consecutive nusinersen injections performed in four children with SMA and extensive spinal hardware precluding standard posterior lumbar puncture techniques. These children were treated using transforaminal thecal access employing cone-beam CT with navigational overlay. We analyzed results including technical success, complications and total fluoroscopy time.

RESULTS

All procedures were technically successful. No major complications and one minor complication were reported; the minor complication was a post-procedural neuropathic headache that was attributed to procedural positioning and was treated successfully with gabapentin. The average procedural fluoroscopy time and air kerma were 1.9 min and 55.8 mGy, respectively.

CONCLUSION

Cone-beam CT guidance with two-axis navigational overlay is a safe, effective method for gaining transforaminal intrathecal access in children with spinal abnormalities and hardware precluding the use of standard techniques.

Alternative mRNA Splicing in the Pathogenesis of Obesity

Alternative mRNA splicing is an important mechanism in expansion of proteome diversity by production of multiple protein isoforms. However, emerging evidence indicates that only a limited number of annotated protein isoforms by alternative splicing are detected, and the coding sequence of alternative splice variants usually is only slightly different from that of the canonical sequence. Nevertheless, mis-splicing is associated with a large array of human diseases. Previous reviews mainly focused on hereditary and somatic mutations in cis-acting RNA sequence elements and trans-acting splicing factors. The importance of environmental perturbations contributed to mis-splicing is not assessed. As significant changes in exon skipping and splicing factors expression levels are observed with diet-induced obesity, this review focuses on several well-known alternatively spliced metabolic factors and discusses recent advances in the regulation of the expressions of splice variants under the pathophysiological conditions of obesity. The potential of targeting the alternative mRNA mis-splicing for obesity-associated diseases therapies will also be discussed.

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.

Single-Cell Analysis of SMN Reveals Its Broader Role in Neuromuscular Disease

The mechanism underlying selective motor neuron (MN) death remains an essential question in the MN disease field. The MN disease spinal muscular atrophy (SMA) is attributable to reduced levels of the ubiquitous protein SMN. Here, we report that SMN levels are widely variable in MNs within a single genetic background and that this heterogeneity is seen not only in SMA MNs but also in MNs derived from controls and amyotrophic lateral sclerosis (ALS) patients. Furthermore, cells with low SMN are more susceptible to cell death. These findings raise the important clinical implication that some SMN-elevating therapeutics might be effective in MN diseases besides SMA. Supporting this, we found that increasing SMN across all MN populations using an Nedd8-activating enzyme inhibitor promotes survival in both SMA and ALS-derived MNs. Altogether, our work demonstrates that examination of human neurons at the single-cell level can reveal alternative strategies to be explored in the treatment of degenerative diseases.

Two Cases of Spinal Muscular Atrophy Type II with Eosinophilic Oesophagitis

Although primarily characterised by loss of motor neurons from the anterior horn of spinal cord and muscle atrophy, spinal muscular atrophy (SMA) is now recognised as a multi-systemic disorder. Here, we report two SMA Type II patients with eosinophilic oesophagitis (EoE), a rare, chronic immune/antigen-mediated condition. One patient presented with dysphagia and poor weight gain, and the second patient had symptoms of gastro-oesophageal reflux (GOR) and poor weight gain. In both patients, macroscopic observations during gastroscopy indicated typical signs of EoE, which were verified during histological examination of oesophageal biopsies. Given that there is a specific treatment strategy for EoE, these cases highlight the importance of considering this condition in clinical investigations - especially for patients with SMA - who have GOR, discomfort, and oral aversion.

Diagnosis and management of spinal muscular atrophy: Part 1: Recommendations for diagnosis, rehabilitation, orthopedic and nutritional care

Spinal muscular atrophy (SMA) is a severe neuromuscular disorder due to a defect in the survival motor neuron 1 (SMN1) gene. Its incidence is approximately 1 in 11,000 live births. In 2007, an International Conference on the Standard of Care for SMA published a consensus statement on SMA standard of care that has been widely used throughout the world. Here we report a two-part update of the topics covered in the previous recommendations. In part 1 we present the methods used to achieve these recommendations, and an update on diagnosis, rehabilitation, orthopedic and spinal management; and nutritional, swallowing and gastrointestinal management. Pulmonary management, acute care, other organ involvement, ethical issues, medications, and the impact of new treatments for SMA are discussed in part 2.

Presymptomatic Diagnosis of Spinal Muscular Atrophy Through Newborn Screening

OBJECTIVE

To demonstrate the feasibility of presymptomatic diagnosis of spinal muscular atrophy (SMA) through newborn screening (NBS).

STUDY DESIGN

We performed a screening trial to assess all newborns who underwent routine newborn metabolic screening at the National Taiwan University Hospital newborn screening center between November 2014 and September 2016. A real-time polymerase chain reaction (RT-PCR) genotyping assay for the SMN1/SMN2 intron 7 c.888+100A/G polymorphism was performed to detect homozygous SMN1 deletion using dried blood spot (DBS) samples. Then the exon 7 c.840C>T mutation and SMN2 copy number were determined by both droplet digital PCR (ddPCR) using the original screening DBS and multiplex ligation-dependent probe amplification (MLPA) using a whole blood sample.

RESULTS

Of the 120 267 newborns, 15 tested positive according to the RT-PCR assay. The DBS ddPCR assay excluded 8 false-positives, and the other 7 patients were confirmed by the MLPA assay. Inclusion of the second-tier DBS ddPCR screening assay resulted in a positive prediction value of 100%. The incidence of SMA was 1 in 17 181 (95% CI, 1 in 8323 to 1 in 35 468). Two of the 3 patients with 2 copies of SMN2 and all 4 patients with 3 or 4 copies of SMN2 were asymptomatic at the time of diagnosis. Five of the 8 false-positives were caused by intragenic recombination between SMN1 and SMN2.

CONCLUSION

Newborn screening can detect patients affected by SMA before symptom onset and enable early therapeutic intervention. A combination of a RT-PCR and a second-tier ddPCR can accurately diagnose SMA from DBS samples with no false-positives.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02123186.

Clinical trial of L-Carnitine and valproic acid in spinal muscular atrophy type I

INTRODUCTION

The aim of this study was to determine the safety and therapeutic potential of L-carnitine and valproic acid (VPA) in infants with spinal muscular atrophy (SMA).

METHODS

Our investigation was an open-label phase 2 multicenter trial of L-carnitine and VPA in infants with SMA type I with retrospective comparison to an untreated, matched cohort. Primary outcomes were: safety and adverse events; secondary outcomes were survival, time to death/>16 hours/day of ventilator support; motor outcomes; and maximum ulnar compound motor action potential amplitude.

RESULTS

A total of 245 AEs were observed in 35 of the 37 treated subjects (95%). Respiratory events accounted for 49% of all adverse events, resulting in 14 deaths. Survival was not significantly different between treated and untreated cohorts.

DISCUSSION

This trial provides evidence that, in infants with SMA type I, L-carnitine/VPA is ineffective at altering survival. The substantial proportion of infants reaching end-points within 6 months of enrollment underscores the urgent need for pre-symptomatic treatment in SMA type I. Muscle Nerve 57: 193-199, 2018.

Nusinersen for the treatment of spinal muscular atrophy

INTRODUCTION

Spinal muscular atrophy (SMA) is an autosomal recessive degenerative neuromuscular disorder characterized by loss of spinal motor neurons leading to muscle weakness. This review article focuses on a novel antisense oligonucleotide treatment, first ever approved for SMA (nusinersen, Spinraza^TM) and describes the exciting journey from early ASO clinical trials to regulatory approval of the first ever known effective treatment for SMA. Areas covered: This article reviews the results of the published open label nusinersen studies in infants and children, and briefly covers the preliminary findings of the recently completed but as yet unpublished nusinersen-sham controlled trials, as well as the presymptomatic nusinersen trial known as Nurture. Clinical use of nusinersen is also reviewed. Expert commentary: Collectively, the studies show improvement in motor function across SMA of all types, including SMA type 3. Best motor response was observed with early treatment; presymptomatic treatment prevented disease manifestations. Nusinersen was found to be safe and well tolerated across all age groups studied. Nusinersen has irrevocably altered the natural history of SMA and allowed for the first time children to transition between SMA types. Nusinersen should be considered as standard of care for the treatment of SMA of all types.

Longitudinal assessments in discordant twins with SMA

We report longitudinal clinical and neurophysiological assessments in twins affected by spinal muscular atrophy (SMA) with discordant phenotypes. The boy had the homozygous deletion of SMN1, a typical type 1 SMA course, and died at the age of eight months. His twin sister, asymptomatic at the time of the diagnosis in her brother, had the same genetic defect but she developed clinical and electrophysiological signs of type 2 SMA. The reduction of tendon reflexes was the first clinical sign at the age of 4 months, followed within few weeks, by a mild decrement in the amplitude of the compound motor action potentials. After the age of 9 months, she showed a sudden clinical and electrophysiological deterioration. Among molecular tests, we determined SMN2 copy number, SMN2 and Plastin 3 transcript levels in peripheral blood, and observed no relevant differences between twins.

Motor milestone assessment of infants with spinal muscular atrophy using the hammersmith infant neurological Exam-Part 2: Experience from a nusinersen clinical study

INTRODUCTION

In this study we examined the feasibility of assessing motor milestone performance of infants with spinal muscular atrophy (SMA) using the Hammersmith Infant Neurological Exam-Part 2 (HINE-2) in a phase 2 study of nusinersen.

METHODS

Nineteen SMA infants were assessed using the HINE-2 at baseline (≤7 months of age), and periodically up to 39 months of age. We evaluated whether the HINE-2 was feasible, reliable, and sensitive to change.

RESULTS

Motor milestone assessments in SMA infants were feasible using the HINE-2. Baseline test-retest reliability was excellent (R = 0.987; P < 0.0001). SMA infants were extremely low functioning at baseline and the HINE-2 was able to detect changes over time in 16 of 19 infants within all 8 domains. HINE-2 improvements were correlated with changes in other neuromuscular outcome measures.

CONCLUSION

Results support the use of the HINE-2 motor milestone assessment in clinical trials of SMA infants. Muscle Nerve 57: 143-146, 2017.

The Actin Cytoskeleton in SMA and ALS: How Does It Contribute to Motoneuron Degeneration?

Amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA) are neurodegenerative diseases with overlapping clinical phenotypes based on impaired motoneuron function. However, the pathomechanisms of both diseases are largely unknown, and it is still unclear whether they converge on the molecular level. SMA is a monogenic disease caused by low levels of functional Survival of Motoneuron (SMN) protein, whereas ALS involves multiple genes as well as environmental factors. Recent evidence argues for involvement of actin regulation as a causative and dysregulated process in both diseases. ALS-causing mutations in the actin-binding protein profilin-1 as well as the ability of the SMN protein to directly bind to profilins argue in favor of a common molecular mechanism involving the actin cytoskeleton. Profilins are major regulat ors of actin-dynamics being involved in multiple neuronal motility and transport processes as well as modulation of synaptic functions that are impaired in models of both motoneuron diseases. In this article, we review the current literature in SMA and ALS research with a focus on the actin cytoskeleton. We propose a common molecular mechanism that explains the degeneration of motoneurons for SMA and some cases of ALS.

Emerging therapies and challenges in spinal muscular atrophy

Spinal muscular atrophy (SMA) is a hereditary neurodegenerative disease with severity ranging from progressive infantile paralysis and premature death (type I) to limited motor neuron loss and normal life expectancy (type IV). Without disease‐modifying therapies, the impact is profound for patients and their families. Improved understanding of the molecular basis of SMA, disease pathogenesis, natural history, and recognition of the impact of standardized care on outcomes has yielded progress toward the development of novel therapeutic strategies and are summarized. Therapeutic strategies in the pipeline are appraised, ranging from SMN1 gene replacement to modulation of SMN2 encoded transcripts, to neuroprotection, to an expanding repertoire of peripheral targets, including muscle. With the advent of preliminary trial data, it can be reasonably anticipated that the SMA treatment landscape will transform significantly. Advancement in presymptomatic diagnosis and screening programs will be critical, with pilot newborn screening studies underway to facilitate preclinical diagnosis. The development of disease‐modifying therapies will necessitate monitoring programs to determine the long‐term impact, careful evaluation of combined treatments, and further acceleration of improvements in supportive care. In advance of upcoming clinical trial results, we consider the challenges and controversies related to the implementation of novel therapies for all patients and set the scene as the field prepares to enter an era of novel therapies. Ann Neurol 2017;81:355–368

Spinal Muscular Atrophy Type I: Is It Ethical to Standardize Supportive Care Intervention in Clinical Trials?

The natural history of spinal muscular atrophy type I (SMA-I) has changed as improved medical support has become available. With investigational drugs for spinal muscular atrophy now in clinical trials, efficient trial design focuses on enrolling recently diagnosed infants, providing best available supportive care, and minimizing subject variation. The quandary has arisen whether it is ethically appropriate to specify a predefined level of nutritional and/or ventilation support for spinal muscular atrophy type I subjects while participating in these studies. We conducted a survey at 2 spinal muscular atrophy investigator meetings involving physician investigators, clinical evaluators, and study coordinators from North America, Europe, and Asia-Pacific. Each group endorsed the concept that having a predefined degree of nutritional and ventilation support was warranted in this context. We discuss how autonomy, beneficence/non-maleficence, noncoercion, social benefit, and equipoise can be maintained when a predefined level of supportive care is proposed, for participation in a clinical trial.

The next generation of population-based spinal muscular atrophy carrier screening: comprehensive pan-ethnic SMN1 copy-number and sequence variant analysis by massively parallel sequencing

PURPOSE

To investigate pan-ethnic SMN1 copy-number and sequence variation by hybridization-based target enrichment coupled with massively parallel sequencing or next-generation sequencing (NGS).

METHODS

NGS reads aligned to SMN1 and SMN2 exon 7 were quantified to determine the total combined copy number of SMN1 and SMN2. The ratio of SMN1 to SMN2 was calculated based on a single-nucleotide difference that distinguishes the two genes. SMN1 copy-number results were compared between the NGS and quantitative polymerase chain reaction and/or multiplex ligation-dependent probe amplification. The NGS data set was also queried for the g.27134T>G single-nucleotide polymorphism (SNP) and other SMN1 sequence pathogenic variants.

RESULTS

The sensitivity of the test to detect spinal muscular atrophy (SMA) carriers with one copy of SMN1 was 100% (95% confidence interval (CI): 95.9-100%; n = 90) and specificity was 99.6% (95% CI: 99.4-99.7%; n = 6,648). Detection of the g.27134T>G SNP by NGS was 100% concordant with an restriction fragment-length polymorphism method (n = 493). Ten single-nucleotide variants in SMN1 were detectable by NGS and confirmed by gene-specific amplicon-based sequencing. This comprehensive approach yielded SMA carrier detection rates of 90.3-95.0% in five ethnic groups studied.

CONCLUSION

We have developed a novel, comprehensive SMN1 copy-number and sequence variant analysis method by NGS that demonstrated improved SMA carrier detection rates across the entire population examined.Genet Med advance online publication 19 January 2017.

Muscle magnetic resonance imaging in spinal muscular atrophy type 3: Selective and progressive involvement

INTRODUCTION

In this study we sought to identify magnetic resonance imaging (MRI) signs of selective muscle involvement and disease progression in patients with spinal muscular atrophy type 3b (SMA3b).

METHODS

Twenty-five patients with genetically confirmed SMA3b underwent MRI on a 1.5-Tesla MR scanner.

RESULTS

MRI showed significantly more severe involvement of the iliopsoas than of the gluteus maximus muscles, and more severe involvement of the triceps brachii than of the biceps brachii muscles. The quadriceps femoris muscles were severely involved. The deltoid, adductor longus, portions of the hamstrings, gracilis, sartorius, and rectus abdominis muscles were well preserved. We found a significant positive correlation between MRI changes and disease duration for gluteus maximus and triceps brachii. Follow-up MRIs of 4 patients showed disease progression.

CONCLUSIONS

This study confirms the pattern of selective muscle involvement suggested by previous studies and further refines muscle MRI changes in SMA3b. Progressive muscle involvement is implicated. Muscle Nerve 55: 651-656, 2017.

Treatment of infantile-onset spinal muscular atrophy with nusinersen: a phase 2, open-label, dose-escalation study

BACKGROUND

Nusinersen is a 2'-O-methoxyethyl phosphorothioate-modified antisense drug being developed to treat spinal muscular atrophy. Nusinersen is specifically designed to alter splicing of SMN2 pre-mRNA and thus increase the amount of functional survival motor neuron (SMN) protein that is deficient in patients with spinal muscular atrophy.

METHODS

This open-label, phase 2, escalating dose clinical study assessed the safety and tolerability, pharmacokinetics, and clinical efficacy of multiple intrathecal doses of nusinersen (6 mg and 12 mg dose equivalents) in patients with infantile-onset spinal muscular atrophy. Eligible participants were of either gender aged between 3 weeks and 7 months old with onset of spinal muscular atrophy symptoms between 3 weeks and 6 months, who had SMN1 homozygous gene deletion or mutation. Safety assessments included adverse events, physical and neurological examinations, vital signs, clinical laboratory tests, cerebrospinal fluid laboratory tests, and electrocardiographs. Clinical efficacy assessments included event free survival, and change from baseline of two assessments of motor function: the motor milestones portion of the Hammersmith Infant Neurological Exam-Part 2 (HINE-2) and the Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP-INTEND) motor function test, and compound motor action potentials. Autopsy tissue was analysed for target engagement, drug concentrations, and pharmacological activity. HINE-2, CHOP-INTEND, and compound motor action potential were compared between baseline and last visit using the Wilcoxon signed-rank test. Age at death or permanent ventilation was compared with natural history using the log-rank test. The study is registered at ClinicalTrials.gov, number NCT01839656.

FINDINGS

20 participants were enrolled between May 3, 2013, and July 9, 2014, and assessed through to an interim analysis done on Jan 26, 2016. All participants experienced adverse events, with 77 serious adverse events reported in 16 participants, all considered by study investigators not related or unlikely related to the study drug. In the 12 mg dose group, incremental achievements of motor milestones (p<0·0001), improvements in CHOP-INTEND motor function scores (p=0·0013), and increased compound muscle action potential amplitude of the ulnar nerve (p=0·0103) and peroneal nerve (p<0·0001), compared with baseline, were observed. Median age at death or permanent ventilation was not reached and the Kaplan-Meier survival curve diverged from a published natural history case series (p=0·0014). Analysis of autopsy tissue from patients exposed to nusinersen showed drug uptake into motor neurons throughout the spinal cord and neurons and other cell types in the brainstem and other brain regions, exposure at therapeutic concentrations, and increased SMN2 mRNA exon 7 inclusion and SMN protein concentrations in the spinal cord.

INTERPRETATION

Administration of multiple intrathecal doses of nusinersen showed acceptable safety and tolerability, pharmacology consistent with its intended mechanism of action, and encouraging clinical efficacy. Results informed the design of an ongoing, sham-controlled, phase 3 clinical study of nusinersen in infantile-onset spinal muscular atrophy.

FUNDING

Ionis Pharmaceuticals, Inc and Biogen.

Normalization of Patient-Identified Plasma Biomarkers in SMNΔ7 Mice following Postnatal SMN Restoration

INTRODUCTION AND OBJECTIVE

Spinal muscular atrophy (SMA) is an autosomal recessive motor neuron disorder. SMA is caused by homozygous loss of the SMN1 gene and retention of the SMN2 gene resulting in reduced levels of full length SMN protein that are insufficient for motor neuron function. Various treatments that restore levels of SMN are currently in clinical trials and biomarkers are needed to determine the response to treatment. Here, we sought to investigate in SMA mice a set of plasma analytes, previously identified in patients with SMA to correlate with motor function. The goal was to determine whether levels of plasma markers were altered in the SMNΔ7 mouse model of SMA and whether postnatal SMN restoration resulted in normalization of the biomarkers.

METHODS

SMNΔ7 and control mice were treated with antisense oligonucleotides (ASO) targeting ISS-N1 to increase SMN protein from SMN2 or scramble ASO (sham treatment) via intracerebroventricular injection on postnatal day 1 (P1). Brain, spinal cord, quadriceps muscle, and liver were analyzed for SMN protein levels at P12 and P90. Ten plasma biomarkers (a subset of biomarkers in the SMA-MAP panel available for analysis in mice) were analyzed in plasma obtained at P12, P30, and P90.

RESULTS

Of the eight plasma biomarkers assessed, 5 were significantly changed in sham treated SMNΔ7 mice compared to control mice and were normalized in SMNΔ7 mice treated with ASO.

CONCLUSION

This study defines a subset of the SMA-MAP plasma biomarker panel that is abnormal in the most commonly used mouse model of SMA. Furthermore, some of these markers are responsive to postnatal SMN restoration. These findings support continued clinical development of these potential prognostic and pharmacodynamic biomarkers.

Genotype-phenotype correlation of SMN locus genes in spinal muscular atrophy children from Argentina

BACKGROUND/PURPOSE

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder, considered one of the leading causes of infant mortality. It is caused by mutations in the SMN1 gene. A highly homologous copy of this gene named SMN2 and other neighbouring genes, SERF1A and NAIP, are considered phenotypic modifiers of the disease. In recent years, notable advances have been made in SMA research regarding evaluation, prognosis, and therapeutic options. Thus, genotype-phenotype studies in SMA are important to stratify patients for motor function tests and for envisaged clinical trials. The aim of this study was to provide clinical and molecular data of a series of Argentinean children with SMA to establish a comprehensive genotype-phenotype correlation.

METHODS

144 Argentinean children with SMA (56 children with type I, 58 with type II, and 30 with type III) were evaluated. The copy number of SMN2, SERF1A, and NAIP genes was established using MLPA (Multiplex Ligation-dependent Probe Amplification) and then correlated with the patients clinical subtypes. To improve clinical characterization we considered the initial symptoms that prompted the consultation, age of acquisition of motor abilities to independent walking and age at loss of gait. We also evaluated clinical and molecular features of sibling pairs in seven families.

RESULTS

A strong correlation was observed between the SMN2 copy number and SMA phenotype while SERF1A and NAIP copy number showed a moderate correlation. We observed intra- and inter-family differences among the SMA types.

CONCLUSION

This first genotype-phenotype correlation study in Argentinean SMA children provides data to improve patient stratification and define more adequate follow-up parameters.

Developmental milestones in type I spinal muscular atrophy

The aim of this retrospective multicentric study was to assess developmental milestones longitudinally in type I SMA infants using the Hammersmith Infant Neurological Examination. Thirty-three type I SMA infants, who classically do not achieve the ability to sit unsupported, were included in the study. Our results confirmed that all patients had a score of 0 out of a scale of 4 on items assessing sitting, rolling, crawling, standing or walking. A score of more than 0 was only achieved in three items: head control (n = 13), kicking (n = 15) and hand grasp (n = 18). In these items, the maximal score achieved was 1 out of a scale of 4, indicating only partial achievement of the milestone. Infants with symptom onset after 6 months of age had longer preservation of a score of 1 when compared to those with onset before 6 months of age. Our results suggest that even when current standards of care are applied, developmental milestones are rarely even partially achieved as part of natural history in type I SMA infants. No infants in this study achieved a major milestone such as rolling over, or sitting independently, which would therefore represent robust outcomes in future interventional trials.

Commonality amid diversity: Multi-study proteomic identification of conserved disease mechanisms in spinal muscular atrophy

The neuromuscular disease spinal muscular atrophy (SMA) is a leading genetic cause of infant mortality, resulting from low levels of full-length survival motor neuron (SMN) protein. Despite having a good understanding of the underlying genetics of SMA, the molecular pathways downstream of SMN that regulate disease pathogenesis remain unclear. The identification of molecular perturbations downstream of SMN is required in order to fully understand the fundamental biological role(s) for SMN in cells and tissues of the body, as well as to develop a range of therapeutic targets for developing novel treatments for SMA. Recent developments in proteomic screening technologies have facilitated proteome-wide investigations of a range of SMA models and tissues, generating novel insights into disease mechanisms by highlighting conserved changes in a range of molecular pathways. Comparative analysis of distinct proteomic datasets reveals conserved changes in pathways converging on GAP43, GAPDH, NCAM, UBA1, LMNA, ANXA2 and COL6A3. Proteomic studies therefore represent a leading tool with which to dissect the molecular mechanisms of disease pathogenesis in SMA, serving to identify potentially attractive targets for the development of novel therapies.

Spinal Muscular Atrophy

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

Opening the window: The case for carrier and perinatal screening for spinal muscular atrophy

Spinal muscular atrophy (SMA) is the most common genetically inherited neurodegenerative disease that leads to infant mortality worldwide. SMA is caused by genetic deletion or mutation in the survival of motor neuron 1 (SMN1) gene, which results in a deficiency in SMN protein. For reasons that are still unclear, SMN protein deficiency predominantly affects α-motor neurons, resulting in their degeneration and subsequent paralysis of limb and trunk muscles, progressing to death in severe cases. Emerging evidence suggests that SMN protein deficiency also affects the heart, autonomic nervous system, skeletal muscle, liver, pancreas and perhaps many other organs. Currently, there is no cure for SMA. Patient treatment includes respiratory care, physiotherapy, and nutritional management, which can somewhat ameliorate disease symptoms and increase life span. Fortunately, several novel therapies have advanced to human clinical trials. However, data from studies in animal models of SMA indicate that the greatest therapeutic benefit is achieved through initiating treatment as early as possible, before widespread loss of motor neurons has occurred. In this review, we discuss the merit of carrier and perinatal patient screening for SMA considering the efficacy of emerging therapeutics and the physical, emotional and financial burden of the disease on affected families and society.

Protective effects of butyrate-based compounds on a mouse model for spinal muscular atrophy

Proximal spinal muscular atrophy (SMA) is a childhood-onset degenerative disease resulting from the selective loss of motor neurons in the spinal cord. SMA is caused by the loss of SMN1 (survival motor neuron 1) but retention of SMN2. The number of copies of SMN2 modifies disease severity in SMA patients as well as in mouse models, making SMN2 a target for therapeutics development. Sodium butyrate (BA) and its analog (4PBA) have been shown to increase SMN2 expression in SMA cultured cells. In this study, we examined the effects of BA, 4PBA as well as two BA prodrugs-glyceryl tributyrate (BA3G) and VX563-on the phenotype of SMNΔ7 SMA mice. Treatment with 4PBA, BA3G and VX563 but not BA beginning at PND04 significantly improved the lifespan and delayed disease end stage, with administration of VX563 also improving the growth rate of these mice. 4PBA and VX563 improved the motor phenotype of SMNΔ7 SMA mice and prevented spinal motor neuron loss. Interestingly, neither 4PBA nor VX563 had an effect on SMN expression in the spinal cords of treated SMNΔ7 SMA mice; however, they inhibited histone deacetylase (HDAC) activity and restored the normal phosphorylation states of Akt and glycogen synthase kinase 3β, both of which are altered by SMN deficiency in vivo. These observations show that BA-based compounds with favorable pharmacokinetics ameliorate SMA pathology possibly by modulating HDAC and Akt signaling.

Copy Number Variations in the Survival Motor Neuron Genes: Implications for Spinal Muscular Atrophy and Other Neurodegenerative Diseases

Proximal spinal muscular atrophy (SMA), a leading genetic cause of infant death worldwide, is an early-onset, autosomal recessive neurodegenerative disease characterized by the loss of spinal α-motor neurons. This loss of α-motor neurons is associated with muscle weakness and atrophy. SMA can be classified into five clinical grades based on age of onset and severity of the disease. Regardless of clinical grade, proximal SMA results from the loss or mutation of SMN1 (survival motor neuron 1) on chromosome 5q13. In humans a large tandem chromosomal duplication has lead to a second copy of the SMN gene locus known as SMN2. SMN2 is distinguishable from SMN1 by a single nucleotide difference that disrupts an exonic splice enhancer in exon 7. As a result, most of SMN2 mRNAs lack exon 7 (SMNΔ7) and produce a protein that is both unstable and less than fully functional. Although only 10–20% of the SMN2 gene product is fully functional, increased genomic copies of SMN2 inversely correlates with disease severity among individuals with SMA. Because SMN2 copy number influences disease severity in SMA, there is prognostic value in accurate measurement of SMN2 copy number from patients being evaluated for SMA. This prognostic value is especially important given that SMN2 copy number is now being used as an inclusion criterion for SMA clinical trials. In addition to SMA, copy number variations (CNVs) in the SMN genes can affect the clinical severity of other neurological disorders including amyotrophic lateral sclerosis (ALS) and progressive muscular atrophy (PMA). This review will discuss how SMN1 and SMN2 CNVs are detected and why accurate measurement of SMN1 and SMN2 copy numbers is relevant for SMA and other neurodegenerative diseases.

Is spinal muscular atrophy a disease of the motor neurons only: pathogenesis and therapeutic implications?

Spinal muscular atrophy (SMA) is a genetic neurological disease that causes infant mortality; no effective therapies are currently available. SMA is due to homozygous mutations and/or deletions in the survival motor neuron 1 gene and subsequent reduction of the SMN protein, leading to the death of motor neurons. However, there is increasing evidence that in addition to motor neurons, other cell types are contributing to SMA pathology. In this review, we will discuss the involvement of non-motor neuronal cells, located both inside and outside the central nervous system, in disease onset and progression. Even if SMN restoration in motor neurons is needed, it has been shown that optimal phenotypic amelioration in animal models of SMA requires a more widespread SMN correction. It has been demonstrated that non-motor neuronal cells are also involved in disease pathogenesis and could have important therapeutic implications. For these reasons it will be crucial to take this evidence into account for the clinical translation of the novel therapeutic approaches.

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.

The neuromuscular impact of symptomatic SMN restoration in a mouse model of spinal muscular atrophy

BACKGROUND

Significant advances in the development of SMN-restoring therapeutics have occurred since 2010 when very effective biological treatments were reported in mouse models of spinal muscular atrophy. As these treatments are applied in human clinical trials, there is pressing need to define quantitative assessments of disease progression, treatment stratification, and therapeutic efficacy. The electrophysiological measures Compound Muscle Action Potential and Motor Unit Number Estimation are reliable measures of nerve function. In both the SMN∆7 mouse and a pig model of spinal muscular atrophy, early SMN restoration results in preservation of electrophysiological measures. Currently, clinical trials are underway in patients at post-symptomatic stages of disease progression. In this study, we present results from both early and delayed SMN restoration using clinically-relevant measures including electrical impedance myography, compound muscle action potential, and motor unit number estimation to quantify the efficacy and time-sensitivity of SMN-restoring therapy.

METHODS

SMA∆7 mice were treated via intracerebroventricular injection with antisense oligonucleotides targeting ISS-N1 to increase SMN protein from the SMN2 gene on postnatal day 2, 4, or 6 and compared with sham-treated spinal muscular atrophy and control mice. Compound muscle action potential and motor unit number estimation of the triceps surae muscles were performed at day 12, 21, and 30 by a single evaluator blinded to genotype and treatment. Similarly, electrical impedance myography was measured on the biceps femoris muscle at 12days for comparison.

RESULTS

Electrophysiological measures and electrical impedance myography detected significant differences at 12days between control and late-treated (4 or 6days) and sham-treated spinal muscular atrophy mice, but not in mice treated at 2days (p<0.01). EIM findings paralleled and correlated with compound muscle action potential and motor unit number estimation (r=0.61 and r=0.50, respectively, p<0.01). Longitudinal measures at 21 and 30days show that symptomatic therapy results in reduced motor unit number estimation associated with delayed normalization of compound muscle action potential.

CONCLUSIONS

The incomplete effect of symptomatic treatment is accurately identified by both electrophysiological measures and electrical impedance myography. There is strong correlation between these measures and with weight and righting reflex. This study predicts that measures of compound muscle action potential, motor unit number estimation, and electrical impedance myography are promising biomarkers of treatment stratification and effect for future spinal muscular atrophy trials. The ease of application and simplicity of electrical impedance myography compared with standard electrophysiological measures may be particularly valuable in future pediatric clinical trials.

Systemic, postsymptomatic antisense oligonucleotide rescues motor unit maturation delay in a new mouse model for type II/III spinal muscular atrophy

Clinical presentation of spinal muscular atrophy (SMA) ranges from a neonatal-onset, very severe disease to an adult-onset, milder form. SMA is caused by the mutation of the Survival Motor Neuron 1 (SMN1) gene, and prognosis inversely correlates with the number of copies of the SMN2 gene, a human-specific homolog of SMN1. Despite progress in identifying potential therapies for the treatment of SMA, many questions remain including how late after onset treatments can still be effective and what the target tissues should be. These questions can be addressed in part with preclinical animal models; however, modeling the array of SMA severities in the mouse, which lacks SMN2, has proven challenging. We created a new mouse model for the intermediate forms of SMA presenting with a delay in neuromuscular junction maturation and a decrease in the number of functional motor units, all relevant to the clinical presentation of the disease. Using this new model, in combination with clinical electrophysiology methods, we found that administering systemically SMN-restoring antisense oligonucleotides (ASOs) at the age of onset can extend survival and rescue the neurological phenotypes. Furthermore, these effects were also achieved by administration of the ASOs late after onset, independent of the restoration of SMN in the spinal cord. Thus, by adding to the limited repertoire of existing mouse models for type II/III SMA, we demonstrate that ASO therapy can be effective even when administered after onset of the neurological symptoms, in young adult mice, and without being delivered into the central nervous system.

SMN expression is required in motor neurons to rescue electrophysiological deficits in the SMNΔ7 mouse model of SMA

Proximal spinal muscular atrophy (SMA) is the most frequent cause of hereditary infant mortality. SMA is an autosomal recessive neuromuscular disorder that results from the loss of the Survival Motor Neuron 1 (SMN1) gene and retention of the SMN2 gene. The SMN2 gene produces an insufficient amount of full-length SMN protein that results in loss of motor neurons in the spinal cord and subsequent muscle paralysis. Previously we have shown that overexpression of human SMN in neurons in the SMA mouse ameliorates the SMA phenotype while overexpression of human SMN in skeletal muscle had no effect. Using Cre recombinase, here we show that either deletion or replacement of Smn in motor neurons (ChAT-Cre) significantly alters the functional output of the motor unit as measured with compound muscle action potential and motor unit number estimation. However ChAT-Cre alone did not alter the survival of SMA mice by replacement and did not appreciably affect survival when used to deplete SMN. However replacement of Smn in both neurons and glia in addition to the motor neuron (Nestin-Cre and ChAT-Cre) resulted in the greatest improvement in survival of the mouse and in some instances complete rescue was achieved. These findings demonstrate that high expression of SMN in the motor neuron is both necessary and sufficient for proper function of the motor unit. Furthermore, in the mouse high expression of SMN in neurons and glia, in addition to motor neurons, has a major impact on survival.

Electrophysiological Motor Unit Number Estimation (MUNE) Measuring Compound Muscle Action Potential (CMAP) in Mouse Hindlimb Muscles

Compound muscle action potential (CMAP) and motor unit number estimation (MUNE) are electrophysiological techniques that can be used to monitor the functional status of a motor unit pool in vivo. These measures can provide insight into the normal development and degeneration of the neuromuscular system. These measures have clear translational potential because they are routinely applied in diagnostic and clinical human studies. We present electrophysiological techniques similar to those employed in humans to allow recordings of mouse sciatic nerve function. The CMAP response represents the electrophysiological output from a muscle or group of muscles following supramaximal stimulation of a peripheral nerve. MUNE is an electrophysiological technique that is based on modifications of the CMAP response. MUNE is a calculated value that represents the estimated number of motor neurons or axons (motor control input) supplying the muscle or group of muscles being tested. We present methods for recording CMAP responses from the proximal leg muscles using surface recording electrodes following the stimulation of the sciatic nerve in mice. An incremental MUNE technique is described using submaximal stimuli to determine the average single motor unit potential (SMUP) size. MUNE is calculated by dividing the CMAP amplitude (peak-to-peak) by the SMUP amplitude (peak-to-peak). These electrophysiological techniques allow repeated measures in both neonatal and adult mice in such a manner that facilitates rapid analysis and data collection while reducing the number of animals required for experimental testing. Furthermore, these measures are similar to those recorded in human studies allowing more direct comparisons.

Multiple effects of curcumin on promoting expression of the exon 7-containing SMN2 transcript

Survival of motor neuron 2 (SMN2) is a modifier gene for spinal muscular atrophy (SMA), a neurodegenerative disease caused by insufficient SMN protein mostly due to SMN1 defect. SMN2 is nearly identical to SMN1 but unfortunately only able to produce a small amount of SMN protein due to exon 7 skipping. The exon 7-containing SMN2 transcript (SMN2_E7+) can be increased by a dietary compound, curcumin, but the involved molecular changes are not clear. Here we have found that in fibroblast cells of a SMA type II patient, curcumin enhanced the inclusion of SMN2 exon 7. Examination of the potential splicing factors showed that curcumin specifically increased the protein and transcript levels of SRSF1. The increased SRSF1 protein was mainly nuclear and hyperphosphorylated. Interestingly, the curcumin effects on the SMN2 and SRSF1 transcripts were inhibited by a protein deacetylase inhibitor, trichostatin A. Moreover, in support of its role in the SMN2 splicing, knocking down SRSF1 reduced the inclusion of SMN2 exon 7. Thus, curcumin appears to have multiple effects on the SMN2 transcript and its splicing regulators, including the change of alternative splicing and transcript/protein level as well as phosphorylation. Protein deacetylases and phosphatases are likely involved in these effects. Interestingly, the effects all seem to favor production of the SMN2_E7+ transcript in SMA patient cells.

Quantitative muscle ultrasound measures rapid declines over time in children with SMA type 1

Muscles are small in spinal muscular atrophy (SMA). It is not known if muscle size changes over time in SMA type 1. We quantified changes over time in muscle size and echointensity during two repeated ultrasound examinations of unilateral proximal (biceps brachii/brachialis and quadriceps) and distal (anterior forearm flexors and tibialis anterior) muscles in three children with SMA type 1. We compared muscle thickness (MT) to body weight-dependent normal reference values. Children were 1, 6, and 11months old at baseline and had 2, 2 and 4 months between ultrasound examinations, respectively. At baseline, MT was normal for weight in all muscles except an atrophic quadriceps in the oldest child. MT decreased and echointensity increased (worsened) over time. At follow up, MT was below normal for weight in the quadriceps in all three children, in the biceps/brachioradialis in two, and in the anterior forearm in one. Tibialis anterior MT remained normal for weight in all three children. Muscle echointensity increased over time in all muscles and, on average, more than doubled in two children. In children with SMA type 1, muscle atrophies and becomes hyperechoic over time. Quantitative muscle ultrasound measures disease progression in SMA type 1 that warrants additional study in more children.

Disease mechanisms and therapeutic approaches in spinal muscular atrophy

Motor neuron diseases are neurological disorders characterized primarily by the degeneration of spinal motor neurons, skeletal muscle atrophy, and debilitating and often fatal motor dysfunction. Spinal muscular atrophy (SMA) is an autosomal-recessive motor neuron disease of high incidence and severity and the most common genetic cause of infant mortality. SMA is caused by homozygous mutations in the survival motor neuron 1 (SMN1) gene and retention of at least one copy of the hypomorphic gene paralog SMN2. Early studies established a loss-of-function disease mechanism involving ubiquitous SMN deficiency and suggested SMN upregulation as a possible therapeutic approach. In recent years, greater knowledge of the central role of SMN in RNA processing combined with deep characterization of animal models of SMA has significantly advanced our understanding of the cellular and molecular basis of the disease. SMA is emerging as an RNA disease not limited to motor neurons, but one that involves dysfunction of motor circuits that comprise multiple neuronal subpopulations and possibly other cell types. Advances in SMA research have also led to the development of several potential therapeutics shown to be effective in animal models of SMA that are now in clinical trials. These agents offer unprecedented promise for the treatment of this still incurable neurodegenerative disease.

Trinucleotide insertion in the SMN2 promoter may not be related to the clinical phenotype of SMA

BACKGROUND

More than 90% of spinal muscular atrophy (SMA) patients show homozygous deletion of SMN1 (survival motor neuron 1). They retain SMN2, a highly homologous gene to SMN1, which may partially compensate for deletion of SMN1. Although the promoter sequences of these two genes are almost identical, a GCC insertion polymorphism has been identified at c.-320_-321 in the SMN1 promoter. We have also found this insertion polymorphism in an SMN2 promoter in an SMA patient (Patient A) who has SMA type 2/3.

PURPOSE

The aims of this study were to determine the frequency of the GCC insertion polymorphism in SMA patients, and to evaluate its effect on SMN transcription efficiency.

PATIENTS AND METHODS

Fifty-one SMA patients, including Patient A, were involved in this study. SMN2 transcript levels in white blood cells were measured by real-time polymerase chain reaction. Screening of the GCC insertion polymorphism was performed using denaturing high-pressure liquid chromatography. The transcription efficiency of the promoter with the insertion mutation was evaluated using a reporter-gene assay.

RESULTS

All SMA patients in this study were homozygous for SMN1 deletion. Patient A retained two copies of SMN2, and showed only a small amount of SMN2 transcript in white blood cells. We detected a GCC insertion polymorphism at c.-320_-321 only in Patient A, and not in 50 other SMA patients. The polymorphism had a slight but significant negative effect on transcription efficiency.

DISCUSSION AND CONCLUSION

Patient A was judged to be an exceptional case of SMA, because the GCC insertion polymorphism rarely exists in SMN1-deleted SMA patients. The GCC insertion polymorphism did not enhance the transcriptional efficiency of SMN2. Thus, this GCC insertion polymorphism in the SMN2 promoter may not be associated with the milder phenotype of the patient. Patient A suggests that there are other unknown factors modifying the clinical phenotype of SMA.

SMN1 and SMN2 copy numbers in cell lines derived from patients with spinal muscular atrophy as measured by array digital PCR

Proximal spinal muscular atrophy (SMA) is an early-onset motor neuron disease characterized by loss of α-motor neurons and associated muscle atrophy. SMA is caused by deletion or other disabling mutation of survival motor neuron 1 (SMN1). In the human genome, a large duplication of the SMN-containing region gives rise to a second copy of this gene (SMN2) that is distinguishable by a single nucleotide change in exon 7. Within the SMA population, there is substantial variation in SMN2 copy number; in general, those individuals with SMA who have a high SMN2 copy number have a milder disease. Because SMN2 functions as a disease modifier, its accurate copy number determination may have clinical relevance. In this study, we describe the development of an assay to assess SMN1 and SMN2 copy numbers in DNA samples using an array-based digital PCR (dPCR) system. This dPCR assay can accurately and reliably measure the number of SMN1 and SMN2 copies in DNA samples. In a cohort of SMA patient-derived cell lines, the assay confirmed a strong inverse correlation between SMN2 copy number and disease severity. Array dPCR is a practical technique to determine, accurately and reliably, SMN1 and SMN2 copy numbers from SMA samples.

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.