Risdiplam-Treated Infants with Type 1 Spinal Muscular Atrophy versus Historical Controls.

BACKGROUND: Type 1 spinal muscular atrophy (SMA) is a progressive neuromuscular disease characterized by an onset at 6 months of age or younger, an inability to sit without support, and deficient levels of survival of motor neuron (SMN) protein. Risdiplam is an orally administered small molecule that modifies SMN2 pre-messenger RNA splicing and increases levels of functional SMN protein in blood. METHODS: We conducted an open-label study of risdiplam in infants with type 1 SMA who were 1 to 7 months of age at enrollment. Part 1 of the study (published previously) determined the dose to be used in part 2 (reported here), which assessed the efficacy and safety of daily risdiplam as compared with no treatment in historical controls. The primary end point was the ability to sit without support for at least 5 seconds after 12 months of treatment. Key secondary end points were a score of 40 or higher on the Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP-INTEND; range, 0 to 64, with higher scores indicating better motor function), an increase of at least 4 points from baseline in the CHOP-INTEND score, a motor-milestone response as measured by Section 2 of the Hammersmith Infant Neurological Examination (HINE-2), and survival without permanent ventilation. For the secondary end points, comparisons were made with the upper boundary of 90% confidence intervals for natural-history data from 40 infants with type 1 SMA. RESULTS: A total of 41 infants were enrolled. After 12 months of treatment, 12 infants (29%) were able to sit without support for at least 5 seconds, a milestone not attained in this disorder. The percentages of infants in whom the key secondary end points were met as compared with the upper boundary of confidence intervals from historical controls were 56% as compared with 17% for a CHOP-INTEND score of 40 or higher, 90% as compared with 17% for an increase of at least 4 points from baseline in the CHOP-INTEND score, 78% as compared with 12% for a HINE-2 motor-milestone response, and 85% as compared with 42% for survival without permanent ventilation (P<0.001 for all comparisons). The most common serious adverse events were pneumonia, bronchiolitis, hypotonia, and respiratory failure. CONCLUSIONS: In this study involving infants with type 1 SMA, risdiplam resulted in higher percentages of infants who met motor milestones and who showed improvements in motor function than the percentages observed in historical cohorts. Longer and larger trials are required to determine the long-term safety and efficacy of risdiplam in infants with type 1 SMA. (Funded by F. Hoffmann-La Roche; FIREFISH ClinicalTrials.gov number, NCT02913482.).

Motor unit number estimation via MScanFit MUNE in spinal muscular atrophy.

INTRODUCTION/AIMS: MScanFit MUNE (MScanFit) is a novel tool to derive motor unit number estimates (MUNEs) from compound muscle action potential (CMAP) scans. Few studies have explored its utility in 5q spinal muscular atrophy (SMA5q) patients, assessing only the abductor pollicis brevis (APB) muscle. We aimed to assess different distal muscles in pediatric and adult SMA5q patients, further evaluating clinical-electrophysiological correlations. METHODS: We analyzed MScanFit parameters reflecting the extent of denervation (MUNE; N50) and parameters of collateral reinnervation in APB, abductor digiti minimi (ADM), and tibialis anterior (TA) muscles. SMA patients were clinically evaluated using standardized motor function clinical scales, including the Hammersmith Functional Motor Scale - Expanded and the Revised Upper Limb Module. RESULTS: A total of 23 SMA5q (9 SMA type 2 and 14 SMA type 3) and 12 age-matched healthy controls (HCs) were enrolled. SMA patients showed lower MUNE and N50 values and higher parameters of collateral sprouting in all muscles compared to HC (p < .001). SMA type 2 patients demonstrated lower MUNE and higher collateral reinnervation values in APB and TA compared to SMA type 3 (p < .05). Walker patients showed higher values of MUNE and N50, and lower parameters of reinnervation in all muscles compared to sitters (p < .05). MScanFit parameters showed strong correlations (Rho-values ranging from .72 to .83) with clinical measurements. MUNE values were abnormal in muscles that were not clinically affected. DISCUSSION: MScanFit parameters showed promise as an outcome measure. Further studies, particularly longitudinal ones, are needed to evaluate MScanFit in measuring response to treatments.

Determining minimal clinically important differences in the Hammersmith Functional Motor Scale Expanded for untreated spinal muscular atrophy patients: An international study.

BACKGROUND AND PURPOSE: Spinal muscular atrophy (SMA) is a rare and progressive neuromuscular disorder with varying severity levels. The aim of the study was to calculate minimal clinically important difference (MCID), minimal detectable change (MDC), and values for the Hammersmith Functional Motor Scale Expanded (HFMSE) in an untreated international SMA cohort. METHODS: The study employed two distinct methods. MDC was calculated using distribution-based approaches to consider standard error of measurement and effect size change in a population of 321 patients (176 SMA II and 145 SMA III), allowing for stratification based on age and function. MCID was assessed using anchor-based methods (receiver operating characteristic [ROC] curve analysis and standard error) on 76 patients (52 SMA II and 24 SMA III) for whom the 12-month HFMSE could be anchored to a caregiver-reported clinical perception questionnaire. RESULTS: With both approaches, SMA type II and type III patients had different profiles. The MCID, using ROC analysis, identified optimal cutoff points of -2 for type II and -4 for type III patients, whereas using the standard error we found the optimal cutoff points to be 1.5 for improvement and -3.2 for deterioration. Furthermore, distribution-based methods uncovered varying values across age and functional status subgroups within each SMA type. CONCLUSIONS: These results emphasize that the interpretation of a single MCID or MDC value obtained in large cohorts with different functional status needs to be made with caution, especially when these may be used to assess possible responses to new therapies.

Nusinersen in adults with type 3 spinal muscular atrophy: long-term outcomes on motor and respiratory function.

INTRODUCTION: Nusinersen was approved for 5q spinal muscular atrophy (SMA), irrespective of age, SMA type or functional status. Nonetheless, long-term data on adults with milder phenotypes are scarce. We aimed to characterize evolution on motor and respiratory function in our cohort of adults with type 3 SMA. METHODS: We conducted a longitudinal retrospective single-center study, including adults (≥18 years) with type 3 SMA under nusinersen for > 22 months. We reported on motor scores and spirometry parameters. RESULTS: Ten patients were included, with a median follow-up of 34 months (range = 22-46). Four patients (40%) were walkers. None used non-invasive ventilation. In Revised Upper Limb Module (RULM) and Expanded Hammersmith Functional Motor Scale (HFMSE), difference of medians increased at 6, 22 and 46 months comparing to baseline (-0.5 vs. + 1.5 vs. + 2.5 in RULM; + 4.0 vs. + 7.5 vs. + 6.0 in HFMSE). Two (50%) walkers presented a clinically meaningful improvement in 6-min walk distance. We did not report any clinically meaningful decrement in motor scores. Spirometry parameters showed an increasing difference of medians in maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) (-3 vs. + 13.4 vs. + 28.7 percentage points of predicted value for MIP; + 11.8 vs. + 13.1 vs. 13.3 percentage points of predicted value for MEP). DISCUSSION: Our cohort supports a sustained benefit of nusinersen in adults with type 3 SMA, in motor and respiratory function. Multicentric studies are still warranted.

Cardiac function evaluation in children with spinal muscular atrophy: A case-control study.

BACKGROUND: Spinal muscular atrophy (SMA) is an autosomal recessive disorder characterized by degeneration of lower motor neurons, resulting in progressive muscle weakness and atrophy. However, little is known regarding the cardiac function of children with SMA. METHODS: We recruited SMA patients younger than 18 years of age from January 1, 2022, to April 1, 2022, in the First Affiliated Hospital of Sun Yat-sen University. All patients underwent a comprehensive cardiac evaluation before treatment, including history taking, physical examination, blood tests of cardiac biomarkers, assessment of echocardiography and electrocardiogram. Age/gender-matched healthy volunteers were recruited as controls. RESULTS: A total of 36 SMA patients (26 with SMA type 2 and 10 with SMA type 3) and 40 controls were enrolled in the study. No patient was clinically diagnosed with heart failure. Blood tests showed elevated values of creatine kinase isoenzyme M and isoenzyme B (CK-MB) mass and high-sensitivity cardiac troponin T (hs-cTnT) in spinal muscular atrophy (SMA) patients. Regarding echocardiographic parameters, SMA children were detected with lower global left and right ventricular longitudinal strain, abnormal diastolic filling velocities of trans-mitral and trans-tricuspid flow. The results revealed no clinical heart dysfunction in SMA patients, but subclinical ventricular dysfunction was seen in SMA children including the diastolic function and myocardial performance. Some patients presented with elevated heart rate and abnormal echogenicity of aortic valve or wall. Among these SMA patients, seven patients (19.4%) had scoliosis. The Cobb's angles showed a significant negative correlation with LVEDd/BSA, but no correlation with other parameters, suggesting that mild scoliosis did not lead to significant cardiac dysfunction. CONCLUSIONS: Our findings warrant increased attention to the cardiac status and highlight the need to investigate cardiac interventions in SMA children.

Nusinersen Initiation After Onset of Weakness Does Not Prevent Progression of Hip Instability.

BACKGROUND: We report changes in the natural history of hip instability with nusinersen treatment among patients with spinal muscular atrophy (SMA) type II after onset of weakness, historically wheelchair-bound but now potentially ambulatory in the era of disease-modifying therapy. METHODS: Patients with genetically confirmed diagnoses of SMA type II who received intrathecal nusinersen from January 1, 2018, to June 30, 2022, were screened for inclusion. Patients with less than 6 months of follow-up, or prior hip surgeries were excluded. Primary clinical outcome measures included scores from Hammersmith motor functional scale expanded (HMFSE), revised upper limb module (RULM), 6-minute walk test (6MWT), and ambulatory status. Radiographic outcomes, including Reimer migration index, the presence of scoliosis, and pelvic obliquity, were also assessed. Secondary outcomes involved comparisons with a historical cohort of SMA type II patients treated at our institution who never received nusinersen. RESULTS: Twenty hips from 5 boys and 5 girls were included in the analysis, with a mean follow-up of 3 years and 8 months. The median age at time of nusinersen initiation was 6.8 years old, ranging between 2.5 and 10.3 years. All patients developed lower limb motor weakness before nusinersen initiation. After treatment with nusinersen, 1 previously stable hip (5%) developed subluxation, 15 hips (75%) remain subluxated, 3 hips (15%) remain dislocated, and 1 hip (5%) remained stable, with a statistically significant difference between the pretreatment and posttreatment groups ( P <0.01). Six patients (60%) were ambulatory at latest follow-up. Six patients (60%) had improved ambulatory ability; 2 had static ambulatory ability (20%); and 2 had deterioration in their walking ability. The median HFMSE score improved from 18.5 (range 0 to 46) to 22 (range 0 to 49) ( P =0.813), whereas the median RULM score improved from 17 (range 2 to 28) to 21.5 (range 5 to 37), which was statistically significant ( P =0.007). CONCLUSIONS: Hip instability persists despite treatment with nusinersen among patients with SMA type II who received nusinersen after onset of lower limb weakness. LEVEL OF EVIDENCE: Therapeutic Level IV.

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

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

Nusinersen versus Sham Control in Later-Onset Spinal Muscular Atrophy.

BACKGROUND: Nusinersen is an antisense oligonucleotide drug that modulates pre-messenger RNA splicing of the survival motor neuron 2 ( SMN2) gene. It has been developed for the treatment of spinal muscular atrophy (SMA). METHODS: We conducted a multicenter, double-blind, sham-controlled, phase 3 trial of nusinersen in 126 children with SMA who had symptom onset after 6 months of age. The children were randomly assigned, in a 2:1 ratio, to undergo intrathecal administration of nusinersen at a dose of 12 mg (nusinersen group) or a sham procedure (control group) on days 1, 29, 85, and 274. The primary end point was the least-squares mean change from baseline in the Hammersmith Functional Motor Scale-Expanded (HFMSE) score at 15 months of treatment; HFMSE scores range from 0 to 66, with higher scores indicating better motor function. Secondary end points included the percentage of children with a clinically meaningful increase from baseline in the HFMSE score (≥3 points), an outcome that indicates improvement in at least two motor skills. RESULTS: In the prespecified interim analysis, there was a least-squares mean increase from baseline to month 15 in the HFMSE score in the nusinersen group (by 4.0 points) and a least-squares mean decrease in the control group (by -1.9 points), with a significant between-group difference favoring nusinersen (least-squares mean difference in change, 5.9 points; 95% confidence interval, 3.7 to 8.1; P<0.001). This result prompted early termination of the trial. Results of the final analysis were consistent with results of the interim analysis. In the final analysis, 57% of the children in the nusinersen group as compared with 26% in the control group had an increase from baseline to month 15 in the HFMSE score of at least 3 points (P<0.001), and the overall incidence of adverse events was similar in the nusinersen group and the control group (93% and 100%, respectively). CONCLUSIONS: Among children with later-onset SMA, those who received nusinersen had significant and clinically meaningful improvement in motor function as compared with those in the control group. (Funded by Biogen and Ionis Pharmaceuticals; CHERISH ClinicalTrials.gov number, NCT02292537 .).

The Genotypic and Phenotypic Spectrum of BICD2 Variants in Spinal Muscular Atrophy.

The bicaudal D cargo adaptor 2 (BICD2) gene encodes a conserved cargo adaptor protein required for dynein-mediated transport. Inherited and de novo variants in BICD2 cause SMALED2 (spinal muscular atrophy lower extremity dominant 2), and a subset have recently been reported to cause severe, often lethal disease. However, a true genotype-phenotype correlation for BICD2 has not been performed, and cases described to date are scattered among at least 14 publications. In this review, we identify the characteristics of disease-causing variants in BICD2 that distinguish them from benign variation and perform genotype-phenotype correlations for 99 BICD2 variant carriers from 35 families. ANN NEUROL 2020;87:487-496.

Motor unit number index: A potential electrophysiological biomarker for pediatric spinal muscular atrophy.

INTRODUCTION/AIMS: In adult spinal muscular atrophy (SMA), the motor unit number index (MUNIX) has been shown to be an useful electrophysiological biomarker. This study evaluated the feasibility and the clinical relevance of using the MUNIX technique for patients with pediatric SMA (Ped-SMA) and correlated MUNIX results with clinical scores. METHODS: Fourteen patients with type II Ped-SMA (11 females; median age 11 y [interquartile range (IQR), 4.8-17 y]) and 14 controls (nine females; median age 10.75 y [IQR, 6.5-13.4 y]) were enrolled and matched by sex, age, height, weight, and body mass index. Clinical examination included manual muscle testing, dynamometry (grasp and pinch), and motor function measure (MFM). The MUNIX technique was evaluated in the abductor digiti minimi (ADM) and abductor pollicis brevis (APB) on two sides when possible. RESULTS: In the patients with Ped-SMA, the MUNIX and compound muscle action potential (CMAP) amplitudes were significantly decreased and the motor size unit index (MUSIX) was significantly increased in the ADM and APB when compared to controls. The intraclass correlation coefficient was good for the intrarater variability of the CMAP amplitude, MUNIX, and MUSIX in the ADM (0.95, 0.83, and 0.89, respectively) and the APB (0.98, 0.96, and 0.94, respectively). The total CMAP amplitude correlated with the grasp and pinch scores (P < .05), and the MUNIX measurements correlated with the MFM scores. DISCUSSION: The MUNIX technique, which accurately estimated lower motor neuron loss and the number of remaining functional motor units, was shown to be a useful electrophysiological biomarker for disease progression and a potential biomarker for treatment response.

Combination therapy with onasemnogene and risdiplam in spinal muscular atrophy type 1.

INTRODUCTION/AIMS: There are currently three medications approved for spinal muscular atrophy (SMA), but the use of these medications in combination has not been well described. METHODS: This is a retrospective report of four cases of SMA treated with dual onasemnogene and risdiplam therapy at our institution. RESULTS: Following onasemnogene therapy, all four patients experienced a perceived plateau of therapeutic benefit, at which time daily risdiplam was started. Transient fatigue and weakness was seen in two patients following risdiplam initiation, but this resolved within 1 mo. One patient was hospitalized with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and post-viral pneumonia, weeks following risdiplam initiation. No other adverse effects related to onasemnogene and risdiplam combination therapy were identified and all patients experienced objective and subjective improvement. DISCUSSION: Combination therapy with onasemnogene and risdiplam in patients with SMA appears to be well-tolerated. Further large prospective trials are needed to determine whether dual therapy is more efficacious than monotherapy, and to identify rare adverse events that may occur with the use of combination therapy.

Sensitivity and specificity of single and combined clouds analyses compared with quantitative motor unit potential analysis.

INTRODUCTION: Turns-amplitude, number of small segments (NSS)-activity, and envelope-activity clouds are three methods of electromyography (EMG) interference pattern analysis. Our objective was to evaluate the sensitivity and specificity of each individual cloud analysis and combined clouds analysis to compare with that of quantitative motor unit potential (QMUP) analysis. METHODS: A total of 379 muscles from 100 patients were analyzed by both QMUP and clouds analyses. Calculation of sensitivity and specificity was based on the clinical diagnosis as the "gold standard." RESULTS: For discrimination of abnormal vs normal and neuropathic vs non-neuropathic, combined clouds analysis had greater sensitivity than QMUP analysis and any single cloud analysis, but there were no differences in specificity. For discrimination of myopathic vs non-myopathic, combined clouds analysis and single cloud analysis had greater sensitivity than QMUP analysis, but there were no differences in specificity. DISCUSSION: Combined clouds analysis was superior to QMUP and each single cloud analysis for distinguishing normal, myopathic, and neuropathic muscles.

ZPR1 prevents R-loop accumulation, upregulates SMN2 expression and rescues spinal muscular atrophy.

Spinal muscular atrophy (SMA) is a neuromuscular disorder caused by homozygous mutation or deletion of the survival motor neuron 1 (SMN1) gene. A second copy, SMN2, is similar to SMN1 but produces ∼10% SMN protein because of a single-point mutation that causes splicing defects. Chronic low levels of SMN cause accumulation of co-transcriptional R-loops and DNA damage leading to genomic instability and neurodegeneration in SMA. Severity of SMA disease correlates inversely with SMN levels. SMN2 is a promising target to produce higher levels of SMN by enhancing its expression. Mechanisms that regulate expression of SMN genes are largely unknown. We report that zinc finger protein ZPR1 binds to RNA polymerase II, interacts in vivo with SMN locus and upregulates SMN2 expression in SMA mice and patient cells. Modulation of ZPR1 levels directly correlates and influences SMN2 expression levels in SMA patient cells. ZPR1 overexpression in vivo results in a systemic increase of SMN levels and rescues severe to moderate disease in SMA mice. ZPR1-dependent rescue improves growth and motor function and increases the lifespan of male and female SMA mice. ZPR1 reduces neurodegeneration in SMA mice and prevents degeneration of cultured primary spinal cord neurons derived from SMA mice. Further, we show that the low levels of ZPR1 associated with SMA pathogenesis cause accumulation of co-transcriptional RNA-DNA hybrids (R-loops) and DNA damage leading to genomic instability in SMA mice and patient cells. Complementation with ZPR1 elevates senataxin levels, reduces R-loop accumulation and rescues DNA damage in SMA mice, motor neurons and patient cells. In conclusion, ZPR1 is critical for preventing accumulation of co-transcriptional R-loops and DNA damage to avert genomic instability and neurodegeneration in SMA. ZPR1 enhances SMN2 expression and leads to SMN-dependent rescue of SMA. ZPR1 represents a protective modifier and a therapeutic target for developing a new method for the treatment of SMA.

miR-206 Reduces the Severity of Motor Neuron Degeneration in the Facial Nuclei of the Brainstem in a Mouse Model of SMA.

Spinal muscular atrophy (SMA) is a severe neuromuscular disease affecting infants caused by alterations of the survival motor neuron gene, which results in progressive degeneration of motor neurons (MNs). Although an effective treatment for SMA patients has been recently developed, the molecular pathway involved in selective MN degeneration has not been yet elucidated. In particular, miR-206 has been demonstrated to play a relevant role in the regeneration of neuromuscular junction in several MN diseases, and particularly it is upregulated in the quadriceps, tibialis anterior, spinal cord, and serum of SMA mice. In the present paper, we demonstrated that miR-206 was transiently upregulated also in the brainstem of the mouse model of SMA, SMAΔ7, in the early phase of the disease paralleling MN degeneration and was down-regulated in the late symptomatic phase. To prevent this downregulation, we intracerebroventricularly injected miR-206 in SMA pups, demonstrating that miR-206 reduced the severity of SMA pathology, slowing down disease progression, increasing survival rate, and improving behavioral performance of mice. Interestingly, exogenous miRNA-206-induced upregulation caused a reduction of the predicted target sodium calcium exchanger isoform 2, NCX2, one of the main regulators of intracellular [Ca2+] and [Na+]. Therefore, we hypothesized that miR-206 might exert part of its neuroprotective effect modulating NCX2 expression in SMA disease.

Improvement of Pulmonary Function Measured by Patient-reported Outcomes in Patients With Spinal Muscular Atrophy After Growth-friendly Instrumentation.

BACKGROUND: Children with spinal muscular atrophy (SMA) sustain a progressive reduction in pulmonary function (PF) related to both muscular weakness and the concomitant effects of spinal deformity on the thorax. Growth-friendly instrumentation is commonly utilized for younger patients with scoliosis and SMA to halt the progression of spinal curvature, but its effect on PF in these patients has not previously been investigated. Using the change in Early Onset Scoliosis 24-Item Questionnaire (EOSQ-24) PF subdomain scores, the authors will investigate whether PF improves in patients with SMA after a growth-friendly intervention. METHODS: This was a multicenter retrospective cohort study from 2 international registries of patients with SMA undergoing spinal deformity surgery from 2005 to 2015. Data collected were age, sex, degree of major coronal curve, type of growth-friendly construct, forced vital capacity (FVC), and EOSQ-24 scores at the patient's preoperative, 1-year postoperative, and 2-year postoperative visits. Differences in EOSQ-24 PF scores and FVC between baseline and postoperative assessment were examined by paired tests. RESULTS: A total of 74 patients were identified (mean age, 7.6±2.3 y, major curve 68.1±22.4 degrees, 51.4% female individuals). The mean EOSQ-24 PF scores improved significantly from 70.6 preoperatively to 83.6 at 1 year (P=0.092) and 86.5 at 2 years postoperatively (P=0.020). The scores in patients with rib-based constructs showed steeper increases at 1-year assessments than those in patients with spine-based constructs. The mean paired FVC value decreased from 63.9% predicted preoperatively, to 57.6% predicted at 1 year postoperatively (P=0.035), and 61.9% predicted preoperatively, to 56.3% predicted at 2 years postoperatively (P=0.178). CONCLUSIONS: Patients with SMA who received growth-friendly instrumentation did experience improvements in PF as measured by EOSQ-24 assessing the caregivers' perception. Given the uncertain reliability of PFTs in this young population, EOSQ-24 is an important tool for measuring improvements in health-related quality of life. LEVEL OF EVIDENCE: Level III-retrospective study.

Novel insights into SMALED2: BICD2 mutations increase microtubule stability and cause defects in axonal and NMJ development.

Bicaudal D2 (BICD2) encodes a highly conserved motor adaptor protein that regulates the dynein-dynactin complex in different cellular processes. Heterozygous mutations in BICD2 cause autosomal dominant lower extremity-predominant spinal muscular atrophy-2 (SMALED2). Although, various BICD2 mutations have been shown to alter interactions with different binding partners or the integrity of the Golgi apparatus, the specific pathological effects of BICD2 mutations underlying SMALED2 remain elusive. Here, we show that the fibroblasts derived from individuals with SMALED2 exhibit stable microtubules. Importantly, this effect was observed regardless of where the BICD2 mutation is located, which unifies the most likely cellular mechanism affecting microtubules. Significantly, overexpression of SMALED2-causing BICD2 mutations in the disease-relevant cell type, motor neurons, also results in an increased microtubule stability which is accompanied by axonal aberrations such as collateral branching and overgrowth. To study the pathological consequences of BICD2 mutations in vivo, and to address the controversial debate whether two of these mutations are neuron or muscle specific, we generated the first Drosophila model of SMALED2. Strikingly, neuron-specific expression of BICD2 mutants resulted in reduced neuromuscular junction size in larvae and impaired locomotion of adult flies. In contrast, expressing BICD2 mutations in muscles had no obvious effect on motor function, supporting a primarily neurological etiology of the disease. Thus, our findings contribute to the better understanding of SMALED2 pathology by providing evidence for a common pathomechanism of BICD2 mutations that increase microtubule stability in motor neurons leading to increased axonal branching and to impaired neuromuscular junction development.

Single-Dose Gene-Replacement Therapy for Spinal Muscular Atrophy.

BACKGROUND: Spinal muscular atrophy type 1 (SMA1) is a progressive, monogenic motor neuron disease with an onset during infancy that results in failure to achieve motor milestones and in death or the need for mechanical ventilation by 2 years of age. We studied functional replacement of the mutated gene encoding survival motor neuron 1 (SMN1) in this disease. METHODS: Fifteen patients with SMA1 received a single dose of intravenous adeno-associated virus serotype 9 carrying SMN complementary DNA encoding the missing SMN protein. Three of the patients received a low dose (6.7×1013 vg per kilogram of body weight), and 12 received a high dose (2.0×1014 vg per kilogram). The primary outcome was safety. The secondary outcome was the time until death or the need for permanent ventilatory assistance. In exploratory analyses, we compared scores on the CHOP INTEND (Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders) scale of motor function (ranging from 0 to 64, with higher scores indicating better function) in the two cohorts and motor milestones in the high-dose cohort with scores in studies of the natural history of the disease (historical cohorts). RESULTS: As of the data cutoff on August 7, 2017, all 15 patients were alive and event-free at 20 months of age, as compared with a rate of survival of 8% in a historical cohort. In the high-dose cohort, a rapid increase from baseline in the score on the CHOP INTEND scale followed gene delivery, with an increase of 9.8 points at 1 month and 15.4 points at 3 months, as compared with a decline in this score in a historical cohort. Of the 12 patients who had received the high dose, 11 sat unassisted, 9 rolled over, 11 fed orally and could speak, and 2 walked independently. Elevated serum aminotransferase levels occurred in 4 patients and were attenuated by prednisolone. CONCLUSIONS: In patients with SMA1, a single intravenous infusion of adeno-associated viral vector containing DNA coding for SMN resulted in longer survival, superior achievement of motor milestones, and better motor function than in historical cohorts. Further studies are necessary to confirm the safety and efficacy of this gene therapy. (Funded by AveXis and others; ClinicalTrials.gov number, NCT02122952 .).

Nusinersen versus Sham Control in Infantile-Onset Spinal Muscular Atrophy.

BACKGROUND: Spinal muscular atrophy is an autosomal recessive neuromuscular disorder that is caused by an insufficient level of survival motor neuron (SMN) protein. Nusinersen is an antisense oligonucleotide drug that modifies pre-messenger RNA splicing of the SMN2 gene and thus promotes increased production of full-length SMN protein. METHODS: We conducted a randomized, double-blind, sham-controlled, phase 3 efficacy and safety trial of nusinersen in infants with spinal muscular atrophy. The primary end points were a motor-milestone response (defined according to results on the Hammersmith Infant Neurological Examination) and event-free survival (time to death or the use of permanent assisted ventilation). Secondary end points included overall survival and subgroup analyses of event-free survival according to disease duration at screening. Only the first primary end point was tested in a prespecified interim analysis. To control the overall type I error rate at 0.05, a hierarchical testing strategy was used for the second primary end point and the secondary end points in the final analysis. RESULTS: In the interim analysis, a significantly higher percentage of infants in the nusinersen group than in the control group had a motor-milestone response (21 of 51 infants [41%] vs. 0 of 27 [0%], P<0.001), and this result prompted early termination of the trial. In the final analysis, a significantly higher percentage of infants in the nusinersen group than in the control group had a motor-milestone response (37 of 73 infants [51%] vs. 0 of 37 [0%]), and the likelihood of event-free survival was higher in the nusinersen group than in the control group (hazard ratio for death or the use of permanent assisted ventilation, 0.53; P=0.005). The likelihood of overall survival was higher in the nusinersen group than in the control group (hazard ratio for death, 0.37; P=0.004), and infants with a shorter disease duration at screening were more likely than those with a longer disease duration to benefit from nusinersen. The incidence and severity of adverse events were similar in the two groups. CONCLUSIONS: Among infants with spinal muscular atrophy, those who received nusinersen were more likely to be alive and have improvements in motor function than those in the control group. Early treatment may be necessary to maximize the benefit of the drug. (Funded by Biogen and Ionis Pharmaceuticals; ENDEAR ClinicalTrials.gov number, NCT02193074 .).

Respiratory Needs in Patients with Type 1 Spinal Muscular Atrophy Treated with Nusinersen.

OBJECTIVE: To evaluate the effects of nusinersen on respiratory function of patients with type 1 spinal muscular atrophy. STUDY DESIGN: Observational, longitudinal cohort study. We collected respiratory data from 118 children with type 1 spinal muscular atrophy and differing pulmonary requirements and conducted a semistructured qualitative interview among a subsample of caregivers at baseline, 6 months, and 10 months after the first nusinersen treatment. Patients were stratified according to ventilation modalities and age at study entry. RESULTS: Most patients in our cohort remained stable (84/109 = 77%). More than 80% of the children treated before age 2 years survived, in contrast to the lower survival reported in natural history studies, and did so without tracheostomy or noninvasive ventilation (NIV) ≥16 hours. In those less than 2 years old, only 3 patients shifted from NIV ≤10 hours to NIV >10 hours, and the other 3 reduced the hours of NIV required. Most of the older patients remained stable; this included not only those on tracheostomy or NIV >10 hours but also 75% of those on NIV ≤10 hours. CONCLUSIONS: Our results suggest that nusinersen may produce some improvement in the progression of respiratory impairment, both in terms of survival and need for respiratory support ≥16 hours, especially before the age of 2 years.

Nusinersen safety and effects on motor function in adult spinal muscular atrophy type 2 and 3.

OBJECTIVE: To retrospectively investigate safety and efficacy of nusinersen in a large cohort of adult Italian patients with spinal muscular atrophy (SMA). METHODS: Inclusion criteria were: (1) clinical and molecular diagnosis of SMA2 or SMA3; (2) nusinersen treatment started in adult age (>18 years); (3) clinical data available at least at baseline (T0-beginning of treatment) and 6 months (T6). RESULTS: We included 116 patients (13 SMA2 and 103 SMA3) with median age at first administration of 34 years (range 18-72). The Hammersmith Functional Rating Scale Expanded (HFMSE) in patients with SMA3 increased significantly from baseline to T6 (median change +1 point, p<0.0001), T10 (+2, p<0.0001) and T14 (+3, p<0.0001). HFMSE changes were independently significant in SMA3 sitter and walker subgroups. The Revised Upper Limb Module (RULM) in SMA3 significantly improved between T0 and T14 (median +0.5, p=0.012), with most of the benefit observed in sitters (+2, p=0.018). Conversely, patients with SMA2 had no significant changes of median HFMSE and RULM between T0 and the following time points, although a trend for improvement of RULM was observed in those with some residual baseline function. The rate of patients showing clinically meaningful improvements (as defined during clinical trials) increased from 53% to 69% from T6 to T14. CONCLUSIONS: Our data provide further evidence of nusinersen safety and efficacy in adult SMA2 and SMA3, with the latter appearing to be cumulative over time. In patients with extremely advanced disease, effects on residual motor function are less clear.