Differential impact on motor unit characteristics across severities of adult spinal muscular atrophy.

OBJECTIVE: To test the hypotheses that decomposition electromyography (dEMG) motor unit action potential (MUAP) amplitude and firing rate are altered in SMA; dEMG parameters are associated with strength and function; dEMG parameters are correlated with traditional electrophysiological assessments. METHODS: Ambulatory and non-ambulatory adults with SMA on nusinersen and healthy controls were enrolled. MUAPs were decomposed from multielectrode surface recordings during 30-s maximum contraction of the abductor digiti minimi (ADM). Isometric strength, upper limb function, patient-reported function, and standard electrophysiologic measures of the ADM (compound muscle action potential [CMAP], single motor unit potential [SMUP], motor unit number estimation [MUNE]) were collected. RESULTS: dEMG MUAP amplitudes were higher in ambulatory versus control and non-ambulatory groups and were higher in controls versus non-ambulatory SMA. In contrast, dEMG firing rates were higher in ambulatory versus non-ambulatory and control groups but similar between non-ambulatory and control. dEMG parameters showed moderate to strong positive correlation with strength and function whereas CMAP and MUNE better correlated with function than strength. SMUP did not correlate with strength, function, or dEMG MUAP amplitude. dEMG parameters show overall good test-retest reliability. INTERPRETATION: dEMG provided reliable, noninvasive measure of MUAP amplitude size and firing rate and revealed divergent patterns across disease severity in adults with SMA. Firing rate enhancement, as seen in milder SMA, may provide a therapeutic avenue for improving function in more severe SMA, where firing rates appear preserved. MUAP amplitude size and firing rate, quantified with dEMG, may be promising monitoring biomarker candidates for noninvasive assessment of SMA.

Psychometric evaluation of modified spinal muscular atrophy functional rating scale (SMAFRS) in adult patients using Rasch analysis.

INTRODUCTION/AIMS: The Spinal Muscular Atrophy Functional Rating Scale (SMAFRS) was first developed as a secondary functional outcome measure to detect changes over time in patients with spinal muscular atrophy (SMA) in clinical trials. Its modified version evaluates 10 activities of daily living. The aim of the study was to analyze modified SMAFRS data using item response theory psychometric models. METHODS: A total of 253 responses from 41 adult patients with ambulatory and non-ambulatory SMA types 2, 3, and 4 were analyzed. Rasch analysis was used to explore item-person targeting, fit statistics, category response functioning, dimensionality, and differential item functioning. RESULTS: Most items had good fitting with the exception of "toileting" and "respiratory." There were no major floor or ceiling effects, and most items covered a good range of disability with only a negligible breech of uni-dimensionality from eating, dressing, and respiratory items. Differential item function highlighted differences in toileting, turning, transferring, walking, and respiratory items between ambulatory and non-ambulatory populations. DISCUSSION: Despite subtle misfitting of certain items, mainly related to respiratory and bulbar function, overall modified SMAFRS remained a psychometrically stable and unidimensional outcome measure. There were some differences in measuring properties of certain functional items between ambulatory and non-ambulatory items that need to be taken into consideration in clinical trial design. Overall, the modified SMAFRS is a psychometrically reliable tool in assessment of adult patients with SMA.

CuATSM effectively ameliorates ALS patient astrocyte-mediated motor neuron toxicity in human in vitro models of amyotrophic lateral sclerosis.

Patient diversity and unknown disease cause are major challenges for drug development and clinical trial design for amyotrophic lateral sclerosis (ALS). Transgenic animal models do not adequately reflect the heterogeneity of ALS. Direct reprogramming of patient fibroblasts to neuronal progenitor cells and subsequent differentiation into patient astrocytes allows rapid generation of disease relevant cell types. Thus, this methodology can facilitate compound testing in a diverse genetic background resulting in a more representative population for therapeutic evaluation. Here, we used established co-culture assays with motor neurons and reprogrammed patient skin-derived astrocytes (iAs) to evaluate the effects of (SP-4-2)-[[2,2'-(1,2-dimethyl-1,2-ethanediylidene)bis[N-methylhydrazinecarbothioamidato-κN2 ,κS]](2-)]-copper (CuATSM), currently in clinical trial for ALS in Australia. Pretreatment of iAs with CuATSM had a differential effect on neuronal survival following co-culture with healthy motor neurons. Using this assay, we identified responding and non-responding cell lines for both sporadic and familial ALS (mutant SOD1 and C9ORF72). Importantly, elevated mitochondrial respiration was the common denominator in all CuATSM-responders, a metabolic phenotype not observed in non-responders. Pre-treatment of iAs with CuATSM restored mitochondrial activity to levels comparable to healthy controls. Hence, this metabolic parameter might allow selection of patient subpopulations best suited for CuATSM treatment. Moreover, CuATSM might have additional therapeutic value for mitochondrial disorders. Enhanced understanding of patient-specific cellular and molecular profiles could help improve clinical trial design in the future.

EphA4 targeting agents protect motor neurons from cell death induced by amyotrophic lateral sclerosis -astrocytes.

Amyotrophic lateral sclerosis (ALS) is a degenerative disease that progressively destroys motor neurons (MNs). Earlier studies identified EphA4, a receptor tyrosine kinase, as a possible disease-modifying gene. The complex interplay between the EphA4 receptor and its ephrin ligands in motor neurons and astrocytes has not yet been fully elucidated and includes a putative pro-apoptotic activity of the unbound receptor compared to ephrin-bound receptor. We recently reported that astrocytes from patients with ALS induce cell death in co-cultured MNs. Here we found that first-generation synthetic EphA4 agonistic agent 123C4, effectively protected MNs when co-cultured with reactive astrocytes from patients with ALS from multiple subgroups (sALS and mutant SOD1). Newer generation and more potent EphA4 agonistic agents 150D4, 150E8, and 150E7 provided effective protection at a lower therapeutic dose. Combined, the data suggest that the development of EphA4 agonistic agents provides potentially a promising therapeutic strategy for patients with ALS.

Neurofilament Levels in CSF and Serum in an Adult SMA Cohort Treated with Nusinersen.

OBJECTIVE: To retrospectively evaluate the utility of serum and cerebrospinal fluid (CSF) levels of neurofilament light chain (NfL) and phosphorylated neurofilament heavy chain (pNfH) as biomarkers for spinal muscular atrophy (SMA) progression and response to nusinersen treatment. METHODS: NfL and pNfH levels were quantified using single molecular array (SIMOA) in CSF of 33 adult SMA patients (SMN copy number 3-5) before and in response to nusinersen treatment. In 11 of the patients, blood serum samples were also collected. CSF NfL and pNfH from patients were compared to CSF Nfs from age-matched controls without neurological disease (n = 6). For patients, pearson correlation coefficients (r) were calculated to investigate associations between Nf levels and other functional outcome measures. RESULTS: Nf levels were similar between SMA and control adults and showed no change in response to nusinersen treatment in CSF or serum. Cross-sectional analyses showed an increase in CSF NfL and pNfH with age in patients (NfL p = 0.0013; pNfH p = 0.0035) and an increase in CSF NfL in controls (p = 0.002). In non-ambulatory patients, baseline serum pNfH showed a negative correlation with multiple strength and functional assessment metrics including Revised Upper Limb Module (r = -0.822, p = 0.04), upper extremity strength (r = -0.828, p = 0.042), lower extremity strength (r = -0.860, p = 0.028), and total strength (r = -0.870, p = 0.024). CONCLUSIONS: Nf levels did not change in response to nusinersen in adults with SMA and were not different from controls. In patients and controls, we detected an age-related increase in baseline CSF NfL and pNfH levels. Though some associations were identified, our results suggest Nf levels are not preditive or prognostic biomarkers in this population.

Persistent neuromuscular junction transmission defects in adults with spinal muscular atrophy treated with nusinersen.

OBJECTIVE: Spinal muscular atrophy (SMA) is a motor neuron disease caused by low levels of survival motor neuron (SMN) protein. Prior work in models and patients has demonstrated electrophysiological and morphological defects at the neuromuscular junction (NMJ). Therapeutic development has resulted in clinically available therapies to increase SMN protein levels in patients and improve muscle function. Here we aimed to investigate the effect of SMN restoration (via nusinersen) on NMJ transmission in adults with SMA. METHODS: Participants undergoing nusinersen treatment underwent 3 Hz repetitive nerve stimulation (RNS) of the spinal accessory nerve to assess compound muscle action potential amplitude decrement. Maximum voluntary isometric contraction (MVICT), Revised Upper Limb Module (RULM), and 6 min walk test (6MWT) were assessed for correlations with decrement. RESULTS: Data from 13 ambulatory (7 men/6 women, mean age 40±11 years) and 11 non-ambulatory (3 men/8 women, mean age 38±12 years) participants were analysed. Cross-sectional analyses of RNS decrement were similar at 14 months of nusinersen (-14.2%±11.5%, n=17) vs baseline (-11.9%±8.3%, n=15) (unpaired t-test, p=0.5202). Longitudinal comparison of decrement in eight participants showed no change at 14 months (-13.9%±6.7%) vs baseline (-16.9%±13.4%) (paired t-test, p=0.5863). Decrement showed strong correlations with measures of MVICT, RULM and 6MWT but not age or disease duration. CONCLUSION: Adults with SMA had significant NMJ transmission defects that were not corrected with 14 months of nusinersen treatment. NMJ defects were negatively associated with physical function, and thus may represent a promising target for additive or combinatorial treatments.

Safety, Tolerability, and Effect of Nusinersen Treatment in Ambulatory Adults With 5q-SMA.

Objective: To determine the safety and tolerability of nusinersen treatment in ambulatory adults with spinal muscular atrophy (SMA) and investigate the treatment effect on muscle strength, physical function, and motor unit physiology. Methods: Individuals aged 18 years or older with genetically confirmed 5q SMA, three or more copies of the SMN2 gene, and the ability to ambulate 30 feet were enrolled. Safety outcomes included the number of adverse events and serious adverse events, clinically significant vital sign or laboratory parameter abnormalities. Outcome assessments occurred at baseline (prior to the first dose of nusinersen) and then 2, 6, 10, and 14 months post-treatment. Results: Six women, seven men (mean age: 37 ± 11, range: 18-59 years) were included for analyses. The most common side effects were headache and back pain, but overall procedures and treatments were well-tolerated. No serious adverse events were reported. Maximal Voluntary Isometric Muscle Contraction Testing (MVICT) and 6-min walk test (6MWT) both showed overall stability with significant increases at 2, 6, and 10 months for the 6MWT. More consistent significant treatment effects were noted on the Hammersmith Functional Motor Scale Expanded, SMA-Functional Rating Scale, and forced vital capacity. Treatment resulted in progressively increased ulnar compound muscle action potential and average single motor unit potential amplitudes, but motor unit number estimation remained stable. Conclusions: Nusinersen treatment is safe and well-tolerated in ambulatory adults with SMA. Treatment resulted in improved motor function and electrophysiological findings suggest that this improvement may be occurring via improved motor unit reinnervation capacity.

Safety, Tolerability, and Effect of Nusinersen in Non-ambulatory Adults With Spinal Muscular Atrophy.

Objective: Investigation of the safety, tolerability, and treatment effect of nusinersen treatment in non-ambulatory adults with spinal muscular atrophy (SMA). Methods: Non-ambulatory individuals, aged 18 years or older with genetically confirmed 5q SMA were enrolled. In participants with spinal fusion, fluoroscopy guided cervical C1-C2 lateral approach was used. Outcomes at 2, 6, 10, and 14 months post-treatment were compared with baseline assessment. Forced vital capacity (FVC) was the primary outcome, and RULM, HFMSE, the modified SMA-FRS, and ulnar nerve electrophysiology [compound muscle action potential (CMAP), single motor unit size, and motor unit number] were secondary. Adverse and serious adverse events and clinically significant vital sign or lab abnormalities were recorded. Results: Results from 12 women and 7 men (mean age: 39.7 ± 13.9, range: 21-64 years) were analyzed. No clinically significant changes of vital signs or laboratory parameters were observed. Five participants were hospitalized for pneumonia. Other adverse events included headache, back pain, cervical injection site pain, and upper respiratory and urinary tract infections. High baseline protein/creatinine ratio without significant change on treatment noted in 4 participants. FVC was feasible in all participants. HFMSE and RULM were not feasible in the majority of participants. FVC and functional outcomes were stable without improvement. CMAP and single motor unit potential sizes showed enlargement while motor unit numbers were stable. Conclusions: Nusinersen, including C1/C2 delivery, was safe overall and well-tolerated. Several outcome measures were limited by floor effect. Overall, treatment resulted in stability of motor outcomes, but motor unit and CMAP size were increased.