Intrathecal Gene Therapy for Giant Axonal Neuropathy.

BACKGROUND: Giant axonal neuropathy is a rare, autosomal recessive, pediatric, polysymptomatic, neurodegenerative disorder caused by biallelic loss-of-function variants in GAN, the gene encoding gigaxonin. METHODS: We conducted an intrathecal dose-escalation study of scAAV9/JeT-GAN (a self-complementary adeno-associated virus-based gene therapy containing the GAN transgene) in children with giant axonal neuropathy. Safety was the primary end point. The key secondary clinical end point was at least a 95% posterior probability of slowing the rate of change (i.e., slope) in the 32-item Motor Function Measure total percent score at 1 year after treatment, as compared with the pretreatment slope. RESULTS: One of four intrathecal doses of scAAV9/JeT-GAN was administered to 14 participants - 3.5×1013 total vector genomes (vg) (in 2 participants), 1.2×1014 vg (in 4), 1.8×1014 vg (in 5), and 3.5×1014 vg (in 3). During a median observation period of 68.7 months (range, 8.6 to 90.5), of 48 serious adverse events that had occurred, 1 (fever) was possibly related to treatment; 129 of 682 adverse events were possibly related to treatment. The mean pretreatment slope in the total cohort was -7.17 percentage points per year (95% credible interval, -8.36 to -5.97). At 1 year after treatment, posterior mean changes in slope were -0.54 percentage points (95% credible interval, -7.48 to 6.28) with the 3.5×1013-vg dose, 3.23 percentage points (95% credible interval, -1.27 to 7.65) with the 1.2×1014-vg dose, 5.32 percentage points (95% credible interval, 1.07 to 9.57) with the 1.8×1014-vg dose, and 3.43 percentage points (95% credible interval, -1.89 to 8.82) with the 3.5×1014-vg dose. The corresponding posterior probabilities for slowing the slope were 44% (95% credible interval, 43 to 44); 92% (95% credible interval, 92 to 93); 99% (95% credible interval, 99 to 99), which was above the efficacy threshold; and 90% (95% credible interval, 89 to 90). Between 6 and 24 months after gene transfer, sensory-nerve action potential amplitudes increased, stopped declining, or became recordable after being absent in 6 participants but remained absent in 8. CONCLUSIONS: Intrathecal gene transfer with scAAV9/JeT-GAN for giant axonal neuropathy was associated with adverse events and resulted in a possible benefit in motor function scores and other measures at some vector doses over a year. Further studies are warranted to determine the safety and efficacy of intrathecal AAV-mediated gene therapy in this disorder. (Funded by the National Institute of Neurological Disorders and Stroke and others; ClinicalTrials.gov number, NCT02362438.).

Safety and Efficacy of Apitegromab in Patients With Spinal Muscular Atrophy Types 2 and 3: The Phase 2 TOPAZ Study.

BACKGROUND AND OBJECTIVES: Currently approved therapies for spinal muscular atrophy (SMA) reverse the degenerative course, leading to better functional outcome, but they do not address the impairment arising from preexisting neurodegeneration. Apitegromab, an investigational, fully human monoclonal antibody, inhibits activation of myostatin (a negative regulator of skeletal muscle growth), thereby preserving muscle mass. The phase 2 TOPAZ trial assessed the safety and efficacy of apitegromab in individuals with later-onset type 2 and type 3 SMA. METHODS: In this study, designed to investigate potential meaningful combinations of eligibility and treatment regimen for future studies, participants aged 2-21 years received IV apitegromab infusions every 4 weeks for 12 months in 1 of 3 cohorts. Cohort 1 stratified ambulatory participants aged 5-21 years into 2 arms (apitegromab 20 mg/kg alone or in combination with nusinersen); cohort 2 evaluated apitegromab 20 mg/kg combined with nusinersen in nonambulatory participants aged 5-21 years; and cohort 3 blindly evaluated 2 randomized apitegromab doses (2 and 20 mg/kg) combined with nusinersen in younger participants ≥2 years of age. The primary efficacy measure was mean change from baseline using the Hammersmith Functional Motor Scale version appropriate for each cohort. Data were analyzed using a paired t test with 2-sided 5% type 1 error for the mean change from baseline for predefined cohort-specific primary efficacy end points. RESULTS: Fifty-eight participants (mean age 9.4 years) were enrolled at 16 trial sites in the United States and Europe. Participants had been treated with nusinersen for a mean of 25.9 months before enrollment in any of the 3 trial cohorts. At month 12, the mean change from baseline in Hammersmith scale score was -0.3 points (95% CI -2.1 to 1.4) in cohort 1 (n = 23), 0.6 points (-1.4 to 2.7) in cohort 2 (n = 15), and in cohort 3 (n = 20), the mean scores were 5.3 (-1.5 to 12.2) and 7.1 (1.8 to 12.5) for the 2-mg/kg (n = 8) and 20-mg/kg (n = 9) arms, respectively. The 5 most frequently reported treatment-emergent adverse events were headache (24.1%), pyrexia (22.4%), upper respiratory tract infection (22.4%), cough (22.4%), and nasopharyngitis (20.7%). No deaths or serious adverse reactions were reported. DISCUSSION: Apitegromab led to improved motor function in participants with later-onset types 2 and 3 SMA. These results support a randomized, placebo-controlled phase 3 trial of apitegromab in participants with SMA. TRIAL REGISTRATION INFORMATION: This trial is registered with ClinicalTrials.gov (NCT03921528). CLASSIFICATION OF EVIDENCE: This study provides Class III evidence that apitegromab improves motor function in later-onset types 2 and 3 spinal muscular atrophy.

Identifying Biomarkers of Spinal Muscular Atrophy for Further Development.

BACKGROUND: Spinal muscular atrophy (SMA) is caused by bi-allelic, recessive mutations of the survival motor neuron 1 (SMN1) gene and reduced expression levels of the survival motor neuron (SMN) protein. Degeneration of alpha motor neurons in the spinal cord causes progressive skeletal muscle weakness. The wide range of disease severities, variable rates of decline, and heterogenous clinical responses to approved disease-modifying treatment remain poorly understood and limit the ability to optimize treatment for patients. Validation of a reliable biomarker(s) with the potential to support early diagnosis, inform disease prognosis and therapeutic suitability, and/or confirm response to treatment(s) represents a significant unmet need in SMA. OBJECTIVES: The SMA Multidisciplinary Biomarkers Working Group, comprising 11 experts in a variety of relevant fields, sought to determine the most promising candidate biomarker currently available, determine key knowledge gaps, and recommend next steps toward validating that biomarker for SMA. METHODS: The Working Group engaged in a modified Delphi process to answer questions about candidate SMA biomarkers. Members participated in six rounds of reiterative surveys that were designed to build upon previous discussions. RESULTS: The Working Group reached a consensus that neurofilament (NF) is the candidate biomarker best poised for further development. Several important knowledge gaps were identified, and the next steps toward filling these gaps were proposed. CONCLUSIONS: NF is a promising SMA biomarker with the potential for prognostic, predictive, and pharmacodynamic capabilities. The Working Group has identified needed information to continue efforts toward the validation of NF as a biomarker for SMA.

Continued benefit of nusinersen initiated in the presymptomatic stage of spinal muscular atrophy: 5-year update of the NURTURE study.

INTRODUCTION/AIMS: NURTURE (NCT02386553) is an open-label study of nusinersen in children (two SMN2 copies, n = 15; three SMN2 copies, n = 10) who initiated treatment in the presymptomatic stage of spinal muscular atrophy (SMA). A prior analysis after ~3 y showed benefits on survival, respiratory outcomes, motor milestone achievement, and a favorable safety profile. An additional 2 y of follow-up (data cut: February 15, 2021) are reported. METHODS: The primary endpoint is time to death or respiratory intervention (≥6 h/day continuously for ≥7 days or tracheostomy). Secondary outcomes include overall survival, motor function, and safety. RESULTS: Median age of children was 4.9 (3.8-5.5) y at last visit. No children have discontinued the study or treatment. All were alive. No additional children utilized respiratory intervention (defined per primary endpoint) since the prior data cut. Children with three SMN2 copies achieved all World Health Organization (WHO) motor milestones, with all but one milestone in one child within normal developmental timeframes. All 15 children with two SMN2 copies achieved sitting without support, 14/15 walking with assistance, and 13/15 walking alone. Mean Hammersmith Functional Motor Scale Expanded total scores showed continued improvement. Subgroups with two SMN2 copies, minimum baseline compound muscle action potential amplitude ≥2 mV, and no baseline areflexia had better motor and nonmotor outcomes versus all children with two SMN2 copies. DISCUSSION: These results demonstrate the value of early treatment, durability of treatment effect, and favorable safety profile after ~5 y of nusinersen treatment. Inclusion/exclusion criteria and baseline characteristics should be considered when interpreting presymptomatic SMA trial data.

Intrathecal Onasemnogene Abeparvovec for Sitting, Nonambulatory Patients with Spinal Muscular Atrophy: Phase I Ascending-Dose Study (STRONG).

BACKGROUND: Spinal muscular atrophy (SMA) is a neuromuscular disorder arising from biallelic non-functional survival motor neuron 1 (SMN1) genes with variable copies of partially functional SMN2 gene. Intrathecal onasemnogene abeparvovec administration, at fixed, low doses, may enable treatment of heavier patients ineligible for weight-based intravenous dosing. OBJECTIVE: STRONG (NCT03381729) assessed the safety/tolerability and efficacy of intrathecal onasemnogene abeparvovec for sitting, nonambulatory SMA patients. METHODS: Sitting, nonambulatory SMA patients (biallelic SMN1 loss, three SMN2 copies, aged 6-<60 months) received a single dose of intrathecal onasemnogene abeparvovec. Patients were enrolled sequentially into one of three (low, medium, and high) dose cohorts and stratified into two groups by age at dosing: younger (6-<24 months) and older (24-<60 months). Primary endpoints included safety/tolerability, independent standing ≥3 seconds (younger group), and change in Hammersmith Functional Motor Scale Expanded (HFMSE) from baseline (older group) compared with historic controls. RESULTS: Thirty-two patients were enrolled and completed the study (medium dose, n = 25). All patients had one or more treatment-emergent adverse events, with one serious and related to treatment (transaminase elevations). No deaths were reported. One of 13 patients (7.7%) in the younger group treated with the medium dose achieved independent standing. At Month 12 for the older group receiving the medium dose, change from baseline in HFMSE was significantly improved compared with the SMA historic control population (P < 0.01). CONCLUSIONS: Intrathecal onasemnogene abeparvovec was safe and well-tolerated. Older patients treated with the medium dose demonstrated increases in HFMSE score greater than commonly observed in natural history.

TRPV4 mutations causing mixed neuropathy and skeletal phenotypes result in severe gain of function.

OBJECTIVE: Distinct dominant mutations in the calcium-permeable ion channel TRPV4 (transient receptor potential vanilloid 4) typically cause nonoverlapping diseases of either the neuromuscular or skeletal systems. However, accumulating evidence suggests that some patients develop mixed phenotypes that include elements of both neuromuscular and skeletal disease. We sought to define the genetic and clinical features of these patients. METHODS: We report a 2-year-old with a novel R616G mutation in TRPV4 with a severe neuropathy phenotype and bilateral vocal cord paralysis. Interestingly, a different substitution at the same residue, R616Q, has been reported in families with isolated skeletal dysplasia. To gain insight into clinical features and potential genetic determinants of mixed phenotypes, we perform in-depth analysis of previously reported patients along with functional and structural assessment of selected mutations. RESULTS: We describe a wide range of neuromuscular and skeletal manifestations and highlight specific mutations that are more frequently associated with overlap syndromes. We find that mutations causing severe, mixed phenotypes have an earlier age of onset and result in more marked elevations of intracellular calcium, increased cytotoxicity, and reduced sensitivity to TRPV4 antagonism. Structural analysis of the two mutations with the most dramatic gain of ion channel function suggests that these mutants likely cause constitutive channel opening through disruption of the TRPV4 S5 transmembrane domain. INTERPRETATION: These findings demonstrate that the degree of baseline calcium elevation correlates with development of mixed phenotypes and sensitivity to pharmacologic channel inhibition, observations that will be critical for the design of future clinical trials for TRPV4 channelopathies.

Intron mutations and early transcription termination in Duchenne and Becker muscular dystrophy.

DMD pathogenic variants for Duchenne and Becker muscular dystrophy are detectable with high sensitivity by standard clinical exome analyses of genomic DNA. However, up to 7% of DMD mutations are deep intronic and analysis of muscle-derived RNA is an important diagnostic step for patients who have negative genomic testing but abnormal dystrophin expression in muscle. In this study, muscle biopsies were evaluated from 19 patients with clinical features of a dystrophinopathy, but negative clinical DMD mutation analysis. Reverse transcription-polymerase chain reaction or high-throughput RNA sequencing methods identified 19 mutations with one of three pathogenic pseudoexon types: deep intronic point mutations, deletions or insertions, and translocations. In association with point mutations creating intronic splice acceptor sites, we observed the first examples of DMD pseudo 3'-terminal exon mutations causing high efficiency transcription termination within introns. This connection between splicing and premature transcription termination is reminiscent of U1 snRNP-mediating telescripting in sustaining RNA polymerase II elongation across large genes, such as DMD. We propose a novel classification of three distinct types of mutations identifiable by muscle RNA analysis, each of which differ in potential treatment approaches. Recognition and appropriate characterization may lead to therapies directed toward full-length dystrophin expression for some patients.

Hip Pain in Patients With Spinal Muscular Atrophy: Prevalence, Intensity, Interference, and Factors Associated With Moderate to Severe Pain.

BACKGROUND: A subset of patients with spinal muscular atrophy (SMA) develop hip pain. We analyzed (1) the characteristics of hip pain in patients with SMA (prevalence, intensity, interference with activities, and responsiveness to treatment) and (2) factors (patient, clinical, and radiographic) associated with moderate to severe pain. METHODS: We performed a retrospective record review and telephone survey of 104 patients with SMA (77% response rate; 44% female; mean age, 22±13 y) who presented for treatment between 2010 and 2020. Patient, clinical, and radiographic characteristics (when available) were recorded. Patients with current or past hip pain were asked about pain characteristics. Pain intensity and interference were assessed with the Brief Pain Inventory, modified for SMA (scale, 0 to 10 with 0 indicating no pain/interference). We used univariate analysis and ordered logistic regression to determine associations between patient factors and hip pain (α=0.05). RESULTS: Hip pain occurred in 60/104 patients (58%), with 15 (14%) indicating moderate to severe pain. Compared with patients with normal body mass index values, patients who were obese had 5.4 times the odds [95% confidence interval (CI), 1.3-23] of moderate to severe pain. Hip contractures [adjusted odds ratio (aOR), 3.2; 95% CI, 1.2-8.8] and dislocations (aOR, 2.9; 95% CI, 1.1-7.9) were associated with greater odds of pain compared with hips without these presentations. Surgical correction for scoliosis (aOR, 2.6; 95% CI, 1.1-6.5) was also associated with greater odds of moderate to severe pain. Femoral head migration percentage was the only radiographic parameter associated with pain. Mean modified Brief Pain Inventory pain intensity was 2.1±2.3. Prolonged sitting, sleep, and transfers (eg, bed to wheelchair) were the activities most affected by pain. CONCLUSIONS: Hip pain was moderate to severe in 14% of patients with SMA. Obesity, hip contractures, surgical correction of scoliosis, and hip dislocations were independently associated with pain. Although mean pain intensity was low, hip pain interfered with daily activities, including prolonged sitting, sleep, and transfers. LEVEL OF EVIDENCE: Level III.

Clinical and genetic spectrum of a large cohort of patients with δ-sarcoglycan muscular dystrophy.

Sarcoglycanopathies include four subtypes of autosomal recessive limb-girdle muscular dystrophies (LGMDR3, LGMDR4, LGMDR5 and LGMDR6) that are caused, respectively, by mutations in the SGCA, SGCB, SGCG and SGCD genes. Delta-sarcoglycanopathy (LGMDR6) is the least frequent and is considered an ultra-rare disease. Our aim was to characterize the clinical and genetic spectrum of a large international cohort of LGMDR6 patients and to investigate whether or not genetic or protein expression data could predict a disease's severity. This is a retrospective study collecting demographic, genetic, clinical and histological data of patients with genetically confirmed LGMDR6 including protein expression data from muscle biopsies. We contacted 128 paediatric and adult neuromuscular units around the world that reviewed genetic data of patients with a clinical diagnosis of a neuromuscular disorder. We identified 30 patients with a confirmed diagnosis of LGMDR6 of which 23 patients were included in this study. Eighty-seven per cent of the patients had consanguineous parents. Ninety-one per cent of the patients were symptomatic at the time of the analysis. Proximal muscle weakness of the upper and lower limbs was the most common presenting symptom. Distal muscle weakness was observed early over the course of the disease in 56.5% of the patients. Cardiac involvement was reported in five patients (21.7%) and four patients (17.4%) required non-invasive ventilation. Sixty per cent of patients were wheelchair-bound since early teens (median age of 12.0 years). Patients with absent expression of the sarcoglycan complex on muscle biopsy had a significant earlier onset of symptoms and an earlier age of loss of ambulation compared to patients with residual protein expression. This study confirmed that delta-sarcoglycanopathy is an ultra-rare neuromuscular condition and described the clinical and molecular characteristics of the largest yet-reported collected cohort of patients. Our results showed that this is a very severe and quickly progressive disease characterized by generalized muscle weakness affecting predominantly proximal and distal muscles of the limbs. Similar to other forms of sarcoglycanopathies, the severity and rate of progressive weakness correlates inversely with the abundance of protein on muscle biopsy.

Association of Variants in the SPTLC1 Gene With Juvenile Amyotrophic Lateral Sclerosis.

Importance: Juvenile amyotrophic lateral sclerosis (ALS) is a rare form of ALS characterized by age of symptom onset less than 25 years and a variable presentation. Objective: To identify the genetic variants associated with juvenile ALS. Design, Setting, and Participants: In this multicenter family-based genetic study, trio whole-exome sequencing was performed to identify the disease-associated gene in a case series of unrelated patients diagnosed with juvenile ALS and severe growth retardation. The patients and their family members were enrolled at academic hospitals and a government research facility between March 1, 2016, and March 13, 2020, and were observed until October 1, 2020. Whole-exome sequencing was also performed in a series of patients with juvenile ALS. A total of 66 patients with juvenile ALS and 6258 adult patients with ALS participated in the study. Patients were selected for the study based on their diagnosis, and all eligible participants were enrolled in the study. None of the participants had a family history of neurological disorders, suggesting de novo variants as the underlying genetic mechanism. Main Outcomes and Measures: De novo variants present only in the index case and not in unaffected family members. Results: Trio whole-exome sequencing was performed in 3 patients diagnosed with juvenile ALS and their parents. An additional 63 patients with juvenile ALS and 6258 adult patients with ALS were subsequently screened for variants in the SPTLC1 gene. De novo variants in SPTLC1 (p.Ala20Ser in 2 patients and p.Ser331Tyr in 1 patient) were identified in 3 unrelated patients diagnosed with juvenile ALS and failure to thrive. A fourth variant (p.Leu39del) was identified in a patient with juvenile ALS where parental DNA was unavailable. Variants in this gene have been previously shown to be associated with autosomal-dominant hereditary sensory autonomic neuropathy, type 1A, by disrupting an essential enzyme complex in the sphingolipid synthesis pathway. Conclusions and Relevance: These data broaden the phenotype associated with SPTLC1 and suggest that patients presenting with juvenile ALS should be screened for variants in this gene.

Multidisciplinary Management of Ataxia Telangiectasia: Current Perspectives.

Ataxia telangiectasia (A-T) is a rare autosomal recessive disease caused by mutations in the ataxia telangiectasia mutated (ATM) gene. In the absence of a family history, the diagnosis of A-T is usually not made until the child is older and symptomatic. Classic A-T is characterized by a constellation of clinical symptoms including progressive ataxia, oculocutaneous telangiectasias and sinopulmonary disease and is usually associated with absence of ATM protein. Other laboratory features associated with A-T include elevated serum levels of alpha-fetoprotein (AFP) and increased chromosomal breakage with in vitro exposure to ionizing radiation. Sinopulmonary symptoms can occur to varying degrees across the lifespan. Some children will also have hypogammaglobulinemia and impaired antibody responses requiring supplemental gamma globulin. People with hypomorphic ATM mutations are often considered to have mild A-T with onset of ataxia and neurological progression occurring later in life with less impairment of the immune system. The risk of malignancy, however, is significantly increased in people with either classic or mild A-T. While hematological malignancies are most common in the first two decades of life, solid organ malignancies become increasingly common during young adulthood. Deterioration of neurologic function with age is associated with dysphagia with aspiration, growth faltering, loss of ambulation and decline in pulmonary function, morbidities that contribute to shortened life expectancy and decreased quality of life. Premature death is often due to malignancies or chronic respiratory insufficiency. A-T is currently managed with supportive care and symptomatic treatment. Current clinical trials, however, represent progress and hope towards disease-modifying therapies for A-T.

Improving the efficacy of exome sequencing at a quaternary care referral centre: novel mutations, clinical presentations and diagnostic challenges in rare neurogenetic diseases.

BACKGROUND: We used a multimodal approach including detailed phenotyping, whole exome sequencing (WES) and candidate gene filters to diagnose rare neurological diseases in individuals referred by tertiary neurology centres. METHODS: WES was performed on 66 individuals with neurogenetic diseases using candidate gene filters and stringent algorithms for assessing sequence variants. Pathogenic or likely pathogenic missense variants were interpreted using in silico prediction tools, family segregation analysis, previous publications of disease association and relevant biological assays. RESULTS: Molecular diagnosis was achieved in 39% (n=26) including 59% of childhood-onset cases and 27% of late-onset cases. Overall, 37% (10/27) of myopathy, 41% (9/22) of neuropathy, 22% (2/9) of MND and 63% (5/8) of complex phenotypes were given genetic diagnosis. Twenty-seven disease-associated variants were identified including ten novel variants in FBXO38, LAMA2, MFN2, MYH7, PNPLA6, SH3TC2 and SPTLC1. Single-nucleotide variants (n=10) affected conserved residues within functional domains and previously identified mutation hot-spots. Established pathogenic variants (n=16) presented with atypical features, such as optic neuropathy in adult polyglucosan body disease, facial dysmorphism and skeletal anomalies in cerebrotendinous xanthomatosis, steroid-responsive weakness in congenital myasthenia syndrome 10. Potentially treatable rare diseases were diagnosed, improving the quality of life in some patients. CONCLUSIONS: Integrating deep phenotyping, gene filter algorithms and biological assays increased diagnostic yield of exome sequencing, identified novel pathogenic variants and extended phenotypes of difficult to diagnose rare neurogenetic disorders in an outpatient clinic setting.

Growth in ataxia telangiectasia.

BACKGROUND: Ataxia telangiectasia (A-T) is a DNA repair disorder that affects multiple body systems. Neurological problems and immunodeficiency are two important features of this disease. At this time, two main severity groups are defined in A-T: classic (the more severe form) and mild. Poor growth is a common problem in classic A-T. An objective of this study was to develop growth references for classic A-T. Another objective was to compare growth patterns in classic A-T and mild A-T with each other and with the general population, using the CDC growth references. A final objective was to examine the effects of chronic infection on height. RESULTS: We found that classic A-T patients were smaller overall, and suffered from height and weight faltering that continued throughout childhood and adolescence. When compared to the CDC growth references, the median heights and weights for both male and female patients eventually fell to or below the 3rd centile on the CDC charts. Height faltering was more pronounced in females. Birthweight was lower in the classic A-T group compared to mild A-T and the general population, whereas birth length was not. Finally, we investigated height and BMI faltering in relation to number of infections and found no association. CONCLUSIONS: Classic A-T appears to affect growth in utero. Although children appear to grow well in very early life, faltering begins early, and is unrelenting.

Onasemnogene abeparvovec gene therapy for symptomatic infantile-onset spinal muscular atrophy in patients with two copies of SMN2 (STR1VE): an open-label, single-arm, multicentre, phase 3 trial.

BACKGROUND: Spinal muscular atrophy type 1 is a motor neuron disorder resulting in death or the need for permanent ventilation by age 2 years. We aimed to evaluate the safety and efficacy of onasemnogene abeparvovec (previously known as AVXS-101), a gene therapy delivering the survival motor neuron gene (SMN), in symptomatic patients (identified through clinical examination) with infantile-onset spinal muscular atrophy. METHODS: STR1VE was an open-label, single-arm, single-dose, phase 3 trial done at 12 hospitals and universities in the USA. Eligible patients had to be younger than 6 months and have spinal muscular atrophy with biallelic SMN1 mutations (deletion or point mutations) and one or two copies of SMN2. Patients received a one-time intravenous infusion of onasemnogene abeparvovec (1·1 × 1014 vector genomes per kg) for 30-60 min. During the outpatient follow-up, patients were assessed once per week, beginning at day 7 post-infusion for 4 weeks and then once per month until the end of the study (age 18 months or early termination). Coprimary efficacy outcomes were independent sitting for 30 s or longer (Bayley-III item 26) at the 18 month of age study visit and survival (absence of death or permanent ventilation) at age 14 months. Safety was assessed through evaluation of adverse events, concomitant medication usage, physical examinations, vital sign assessments, cardiac assessments, and laboratory evaluation. Primary efficacy endpoints for the intention-to-treat population were compared with untreated infants aged 6 months or younger (n=23) with spinal muscular atrophy type 1 (biallelic deletion of SMN1 and two copies of SMN2) from the Pediatric Neuromuscular Clinical Research (PNCR) dataset. This trial is registered with ClinicalTrials.gov, NCT03306277 (completed). FINDINGS: From Oct 24, 2017, to Nov 12, 2019, 22 patients with spinal muscular atrophy type 1 were eligible and received onasemnogene abeparvovec. 13 (59%, 97·5% CI 36-100) of 22 patients achieved functional independent sitting for 30 s or longer at the 18 month of age study visit (vs 0 of 23 patients in the untreated PNCR cohort; p<0·0001). 20 patients (91%, 79-100]) survived free from permanent ventilation at age 14 months (vs 6 [26%], 8-44; p<0·0001 in the untreated PNCR cohort). All patients who received onasemnogene abeparvovec had at least one adverse event (most common was pyrexia). The most frequently reported serious adverse events were bronchiolitis, pneumonia, respiratory distress, and respiratory syncytial virus bronchiolitis. Three serious adverse events were related or possibly related to the treatment (two patients had elevated hepatic aminotransferases, and one had hydrocephalus). INTERPRETATION: Results from this multicentre trial build on findings from the phase 1 START study by showing safety and efficacy of commercial grade onasemnogene abeparvovec. Onasemnogene abeparvovec showed statistical superiority and clinically meaningful responses when compared with observations from the PNCR natural history cohort. The favourable benefit-risk profile shown in this study supports the use of onasemnogene abeparvovec for treatment of symptomatic patients with genetic or clinical characteristics predictive of infantile-onset spinal muscular atrophy type 1. FUNDING: Novartis Gene Therapies.

Safety and efficacy of nusinersen in spinal muscular atrophy: The EMBRACE study.

INTRODUCTION: The EMBRACE study (Clinical Trials No. NCT02462759) evaluated nusinersen in infants/children with infantile- or later-onset spinal muscular atrophy (SMA) who were ineligible for the ENDEAR and CHERISH studies. METHODS: Participants were randomized to intrathecal nusinersen (12-mg scaled equivalent dose; n = 14) or sham procedure (n = 7) in part 1 (~14 months) and subsequently received open-label nusinersen for ~24 months in part 2 of the study. RESULTS: Part 1 was stopped early after the demonstration of motor function benefit with nusinersen in ENDEAR. There were no nusinersen-related adverse events (AEs) and no study discontinuations due to nusinersen-related AEs. The most common AEs included pyrexia, cough, pneumonia, and upper respiratory tract infections. Motor milestone responder rates were higher in those receiving nusinersen at last available assessment (93%) than in those receiving sham procedure in part 1 (29%) or transitioned from sham to nusinersen in part 2 (83%). This functional improvement was observed despite the small sample size and shortened part 1 trial duration that undermined the power of the study to demonstrate such treatment effects at a significant level. DISCUSSION: Nusinersen demonstrated a favorable long-term benefit-risk profile in this broad population of individuals with infantile- or later-onset SMA.

Impaired prenatal motor axon development necessitates early therapeutic intervention in severe SMA.

Gene replacement and pre-mRNA splicing modifier therapies represent breakthrough gene targeting treatments for the neuromuscular disease spinal muscular atrophy (SMA), but mechanisms underlying variable efficacy of treatment are incompletely understood. Our examination of severe infantile onset human SMA tissues obtained at expedited autopsy revealed persistence of developmentally immature motor neuron axons, many of which are actively degenerating. We identified similar features in a mouse model of severe SMA, in which impaired radial growth and Schwann cell ensheathment of motor axons began during embryogenesis and resulted in reduced acquisition of myelinated axons that impeded motor axon function neonatally. Axons that failed to ensheath degenerated rapidly postnatally, specifically releasing neurofilament light chain protein into the blood. Genetic restoration of survival motor neuron protein (SMN) expression in mouse motor neurons, but not in Schwann cells or muscle, improved SMA motor axon development and maintenance. Treatment with small-molecule SMN2 splice modifiers beginning immediately after birth in mice increased radial growth of the already myelinated axons, but in utero treatment was required to restore axonal growth and associated maturation, prevent subsequent neonatal axon degeneration, and enhance motor axon function. Together, these data reveal a cellular basis for the fulminant neonatal worsening of patients with infantile onset SMA and identify a temporal window for more effective treatment. These findings suggest that minimizing treatment delay is critical to achieve optimal therapeutic efficacy.

Detection of SMN1 to SMN2 gene conversion events and partial SMN1 gene deletions using array digital PCR.

Proximal spinal muscular atrophy (SMA), a leading genetic cause of infant death worldwide, 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 mutations of survival motor neuron 1 (SMN1) but retention of one or more copies of the paralog SMN2. Within the SMA population, there is substantial variation in SMN2 copy number (CN); in general, those individuals with SMA who have a high SMN2 CN have a milder disease. Because SMN2 functions as a disease modifier, its accurate CN determination may have clinical relevance. In this study, we describe the development of array digital PCR (dPCR) to quantify SMN1 and SMN2 CNs in DNA samples using probes that can distinguish the single nucleotide difference between SMN1 and SMN2 in exon 8. This set of dPCR assays 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 CN and disease severity. We can detect SMN1-SMN2 gene conversion events in DNA samples by comparing CNs at exon 7 and exon 8. Partial deletions of SMN1 can also be detected with dPCR by comparing CNs at exon 7 or exon 8 with those at intron 1. Array dPCR is a practical technique to determine, accurately and reliably, SMN1 and SMN2 CNs from SMA samples as well as identify gene conversion events and partial deletions of SMN1.