Muscle & Nerve

Background and Objectives: Facioscapulohumeral muscular dystrophy (FSHD) is characterised by asynchronous muscle degeneration and marked pathological heterogeneity. While conventional MRI can detect fatty replacement and oedema-like abnormalities, it provides limited insight into other relevant biological processes such as extracellular matrix remodelling and tissue perfusion. This study investigated whether multispectral optoacoustic tomography (MSOT), an emerging imaging technique that non-invasively interrogates tissue composition through endogenous optical absorbers, can provide complementary molecular information on muscle involvement in FSHD. Methods: MSOT was performed on 568 muscles from 15 genetically confirmed FSHD patients and 9 healthy volunteers using a standardized protocol. The analysis included single-wavelength signal intensity and spectrally unmixed signals related to lipid, collagen, deoxygenated haemoglobin, oxygenated haemoglobin, total haemoglobin, and tissue oxygen saturation. Patients also underwent conventional muscle MRI together with clinical strength and disease severity assessments. Feasibility, reproducibility, discrimination between patients and controls, and associations with MRI and clinical measures were evaluated. Results: MSOT acquisition was well tolerated and highly reproducible (intra- and inter-rater ICC = 0.88). FSHD muscles displayed a distinct optoacoustic profile characterised by reduced signal intensity at wavelengths below 900 nm, increased lipid signal and reduced oxygenated and total haemoglobin signals. Lipid signal discriminated FSHD from control muscles (AUC 0.830, p = 0.008) and increased with MRI-defined fatty replacement (p < 0.0001). Short tau inversion recovery (STIR)-positive muscles on MRI exhibited a distinct molecular phenotype, with higher collagen-associated and lipid signals together with increased deoxygenated and total haemoglobin signals, consistent with active tissue remodelling. Although FSHD muscles classified as normal by conventional imaging showed group-level optoacoustic profiles comparable to controls, 13 of 141 (9%) demonstrated at least one abnormal MSOT-derived parameter. Reduced haemoglobin-related signals correlated with greater global disease severity, whereas increased lipid signal was associated with lower muscle strength. Discussion: MSOT is a feasible and reproducible imaging technique in FSHD that provides complementary molecular information beyond conventional structural imaging. Its ability to detect signatures related to fatty replacement, STIR positivity, functional impairment, and isolated abnormalities in radiologically normal muscles supports further longitudinal studies of MSOT-derived readouts as potential biomarkers of disease activity, progression, and therapeutic response.

Spinal muscular atrophy (SMA) is increasingly recognized as a multisystem disorder involving non-neuronal cells, yet the role of Schwann cells (SCs) in late-onset SMA (loSMA) remains unclear. We investigated age-dependent peripheral nerve pathology in a four-copy SMN2 mouse model of loSMA. Sciatic nerves from wild-type and loSMA mice were analyzed at postnatal (P) days 20, 35, 70, and >100 using semi-thin morphometry, immunofluorescence for MBP, Sox10, Sox2, and F4/80, and nerve conduction studies. loSMA nerves showed reduced myelin thickness at all time points and smaller axon diameters at P20 and P35. G- ratios were reduced at P20 but increased from P35 onward, indicating progressively altered axon-myelin relationships. MBP immunofluorescence intensity, compound muscle action potential amplitude, and nerve conduction velocity were reduced in loSMA mice at P>100. The proportion of Sox2+ SCs increased from P35 onward, while Sox10+ cell abundance increased at later stages. F4/80+ macrophages were transiently elevated at P35 and correlated with Sox2+ cell numbers at this stage. These findings demonstrate age-dependent myelin abnormalities, altered SC states, and transient accumulation of macrophages in loSMA peripheral nerves. Whether these changes are SC-autonomous or secondary to chronic axonal dysfunction remains to be determined.

Introduction/Aims To evaluate the usefulness of the Goal Attainment Scale (GAS) light for assessing response to risdiplam in patients with SMA aged [&ge;]15 years. Methods In this population-based, longitudinal, ambispective study, patients were evaluated before and at 12 and 24 months after risdiplam initiation using motor scales (SMA Functional Composite Score Revised [SMA-FCR]), pinch strength (MyoPinch), functional scales (EK2, ALSFRS-R), patient and clinician global impression of change (PGIC and CGIC), and GAS light. Longitudinal changes were assessed using linear mixed-effects models. The minimal detectable change (MDC) and minimal clinically important change (MCIC) of GAS light were calculated. Results Forty-four patients (median age 32 years; 56.8% female) were included: 31.8% non-sitters, 56.8% sitters, and 11.4% walkers. GAS light priorities differed across functional subgroups, with patients prioritising moderately affected domains. After 24 months of risdiplam treatment, motor outcomes showed non-significant improvements in walkers, whereas functional scales improved significantly only in non-sitters. In contrast, GAS light detected significant, increasing improvements across all functional subgroups. The MCIC and MDC for GAS light were 6.5 and 10.65 points, respectively. According to the CGIC, 58% of patients improved slightly, 29% remained stable, and 13% worsened slightly at 24 months. Using the MCIC threshold, 64.5% achieved clinically meaningful goal improvement. Discussion GAS light is a feasible, sensitive, patient-centred tool that may complement standardised outcome measures when evaluating treatment response in adults with SMA. These findings further support risdiplam as a valuable therapeutic option in this population.

Myasthenia gravis (MG) is an autoimmune disease caused by pathogenic autoantibodies against proteins at the neuromuscular junction (NMJ). The diagnosis and clinical management of MG patients largely relies on the detection of antigen-specific autoantibodies targeting acetylcholine receptor (AChR) or muscle-specific kinase (MuSK). Yet a subset of patients remains seronegative for known MG autoantibodies, highlighting a critical need for alternative approaches to identify pathogenic NMJ antibodies. We established a new human in vitro model of the NMJ based on primary human muscle cells that recapitulates key features of the NMJ: differentiation to myotubes, expression of key NMJ proteins and formation of postsynaptic AChR clusters in response to agrin stimulation. The model allows new insights into myogenesis and genetic muscle diseases, and the new muscle cell-based assay (CBA) detected autoantibodies in sera from patients with AChR- and MuSK-positive MG with 96.43% sensitivity and 100% specificity, while healthy control sera showed no reactivity. Incubation with patient sera significantly reduced AChR clustering compared to controls, demonstrating functional pathogenic effects. Thus, we established a physiologically relevant human NMJ model that enables detection and functional characterization of neuromuscular autoantibodies. This novel approach addresses a key limitation of current antigen-specific diagnostics and provides a method for improved detection and characterization of MG antibodies, independent of antigen specificity. One Sentence SummaryWe established a postsynaptic human in vitro neuromuscular junction model to assess binding and pathogenicity of MG autoantibodies. Key messagesO_ST_ABSWhat is already known on this topic?C_ST_ABSCurrent diagnosis of myasthenia gravis (MG) relies largely on the detection of antigen-specific autoantibodies against AChR and MuSK, leaving a clinically relevant subset of patients seronegative. What are the new findings?We established a physiologically relevant human in vitro neuromuscular junction model based on primary human muscle cells and developed a novel muscle cell-based assay (CBA) for the detection of neuromuscular autoantibodies. How might this impact on clinical practice or future developments?The CBA detected autoantibodies in patients with AChR- or MuSK-positive MG with high sensitivity and specificity and demonstrated their functional pathogenic effects on AChR clustering. This antigen-independent approach may improve the detection and functional characterization of MG autoantibodies, particularly in patients who are seronegative in current diagnostic assays. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=130 SRC="FIGDIR/small/743478v1_ufig1.gif" ALT="Figure 1000"> View larger version (38K): org.highwire.dtl.DTLVardef@18ed154org.highwire.dtl.DTLVardef@151036corg.highwire.dtl.DTLVardef@1b7ab34org.highwire.dtl.DTLVardef@1490fe9_HPS_FORMAT_FIGEXP M_FIG C_FIG

Severe peripheral nerve injuries result in incomplete recovery despite neurorrhaphy. Microsurgical suturing is technically demanding, time-intensive, and may produce variable fascicular alignment. Nerve Tape is an FDA-approved sutureless device enabling rapid, reproducible nerve coaptation. This study compared Nerve Tape with epineurial microsuturing following common peroneal nerve transection in Yucatan minipigs. Over 12 months, both groups demonstrated reinnervation of the tibialis anterior and extensor digitorum brevis, representing proximal and distal muscle targets, respectively. Tibialis anterior recovery was comparable between groups. In contrast, Nerve Tape produced greater distal motor recovery in the extensor digitorum brevis, with approximately 1.8-fold higher compound muscle action potential amplitude and 74.3% versus 46.0% recovery compared with microsutures. Compound nerve action potential amplitudes recorded from the motor branch of the deep peroneal nerve were also greater with Nerve Tape, whereas conduction velocities were comparable. Histological analysis demonstrated preserved fascicular architecture distal to the repair in both groups, with no significant differences in axon count, mean myelinated axon diameter, or g-ratio in the terminal common peroneal nerve or its distal motor branch. Clinical use was demonstrated in a representative case with progressive recovery. Nerve Tape supported durable structural and functional recovery and improved distal motor reinnervation compared with microsuturing.

Background: Force production reflects neuromuscular capacity, central regulation, and sensory feedback, making performance-based testing vulnerable when disease-related limitations could be interpreted as reduced effort. Repeated handgrip strength (HGS) testing may quantify neuromuscular fatigability in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), but interpretation of within-subject variability as an effort-validity marker remains controversial. We tested whether the coefficient of variation (CV) distinguishes ME/CFS-related impairment from deliberate submaximal performance and compared it with the sum of residuals (SR), a trajectory-aware metric. Methods: We analyzed three cohorts using the same repeated-HGS protocol: two 10-trial sessions separated by one hour. We included 211 ME/CFS participants and 170 controls, including 28 instructed to perform at 50% perceived maximum force. CV and SR were determined as HGS variability measures and compared by probability-density overlap and receiver operating characteristic analyses. The primary comparison was ME/CFS versus deliberately submaximal controls. Results: CV distributions showed substantial overlap between groups. SR improved group-level separation, increasing non-overlapping fractions from 0.217 to 0.326 in the Jaekel cohort and from 0.180 to 0.361 in the MIRACLE cohort. In ROC analyses, SR consistently yielded higher discrimination than CV across cohorts, sessions, and sex strata. A commonly used 15% CV cutoff classified 42-48% of ME/CFS participants as submaximal, while correctly identifying only 57-64% of deliberately submaximal controls. Conclusions: CV may conflate ME/CFS-related fatigability with irregular force modulation and should not be used as stand-alone evidence of submaximal effort. Trajectory-aware SR partly reduced this bias and indicated that ME/CFS-related force impairment is distinguishable from deliberate submaximal force production at the group level. However, neither metric should be used alone to diagnose ME/CFS or evaluate sincerity of effort.

Background: Duchenne muscular dystrophy (DMD) results from absence of dystrophin, causing sarcolemmal instability, progressive muscle and mitochondrial dysfunction and reduced cardiorespiratory fitness and bone density. Exercise may target these multisystem abnormalities but remains underutilized due to historical safety concerns and lack of disease specific guidelines for optimal dosing. We conducted an exploratory trial using personalized exercise prescription to assess adherence, safety and preliminary efficacy in DMD. Methods: Six ambulatory boys underwent 6-months of home-based, remotely-supervised leg cycling and isometric strengthening using individualized frequency, intensity and time parameters. Cycling was set to 40-60% of heart rate and strengthening to 50% maximal voluntary contraction (MVC). Safety was assessed by creatine kinase (CK), muscle MRS T2, and adverse events. Primary outcomes were 6-month change in peak oxygen uptake (VO2) and submaximal-cycling HR; secondary outcomes included muscle fat fraction, cross-sectional area (CSA) and peak strength; exploratory outcomes included bone density, pulmonary function and quality-of-life. Peak VO2 and CSA were contextualized against untreated DMD controls. Results: All participants completed the intervention with high adherence (88.5%) and no adverse events. Cycling averaged 2-3 times/week at HR 148+8 bpm for 21.9+3.9 minutes; strengthening averaged 1.8+0.6 sessions/week at 50% MVC. CK and MRS T2 remained stable. Peak VO2 and submaximal-cycling HR improved, CSA increased relative to controls, and hamstring strength increased. Bone density, forced vital capacity and quality-of-life scores showed favorable trends. Discussion: Appropriately dosed exercise is feasible, safe and may produce multisystem physiological benefits in boys with DMD, supporting personalized, physiologically monitored training as a complementary therapeutic strategy.

Background: Post-stroke spasticity is commonly assessed using the Modified Ashworth Scale (MAS), despite its limited objectivity and variable reliability. This study introduces ScoreE, a novel isokinetic dynamometry-derived metric designed to quantify elbow and wrist flexor hyper-resistance by comparing patients torque-angle profiles with a healthy reference corridor. Methods: Thirty-five post-stroke patients and twenty-one healthy controls were included. Elbow and wrist hyper-resistance was assessed using the MAS and an isokinetic dynamometer in two testing conditions: seated on the dynamometer chair (ergo chair) and seated in the patient wheelchair. Two dynamometer-derived metrics were analyzed: ScoreE and peak torque (PeakT). Feasibility, inter-rater and test-retest reliability, and associations with MAS grades were assessed. Exploratory PRE-POST changes following a 10-min local vibration session were also described. Results: ScoreE showed good to excellent inter-rater and test-retest reliability across joints and testing conditions. Inter-rater ICCs ranged from 0.81 to 0.89, and test-retest ICCs from 0.76 to 0.93. PeakT showed moderate to good reliability. In contrast, MAS agreement was lower and more variable. ScoreE showed moderate associations with MAS grades, particularly at the elbow, with weaker and less consistent associations at the wrist. MAS assessment was faster, but all assessments were well tolerated, with median pain ratings of 0/10 in all testing conditions. PRE-POST vibration changes were small and heterogeneous, preventing formal assessment of responsiveness. Conclusion: ScoreE provides a reliable, objective, and visually interpretable quantification of post-stroke elbow and wrist flexor hyper-resistance. By comparing the full torque-angle profile with normative data, this approach preserves information on both the magnitude and angular span of abnormal resistance, supporting its potential for targeted longitudinal monitoring.

Introduction. Skeletal muscle loss in sarcopenia and neuromuscular disorders remains a major unmet medical need. AAV9-delivered follistatin (FST), a myostatin/activin antagonist, induces muscle hypertrophy; however, fibre growth without adequate vascular adaptation may limit therapeutic efficacy. We evaluated whether co-administration of a VEGF-A165 plasmid enhances the hypertrophic and angiogenic effects of intramuscular AAV-FST gene transfer in C57BL/6 mice. Methods. Thirty-six C57BL/6 mice (18 males, 18 females) were assigned to PBS vehicle (n=10), AAV-FST (1 x 10^11 vg; n=10), VEGF plasmid (100 ug; n=6), or combination treatment (VEGF plus AAV-FST; n=10). The contralateral hindlimb served as an internal control. Endpoints at Day 115 included hindlimb muscle mass ratio (R/L), transgene expression, FST protein levels, muscle fibre morphometry, capillary density, and safety assessments. Results. Combination therapy produced the highest R/L ratio (1.176 +/- 0.091; p=0.004; d=2.04), whereas AAV-FST alone showed a borderline effect (R/L=1.113; p=0.050). Compared with AAV-FST monotherapy, combination treatment increased muscle FST mRNA approximately 2.1-fold, protein levels approximately 2.0-fold, and the muscle-to-liver expression ratio 2.6-fold. It also induced larger muscle fibres and doubled CD31+ vessel counts versus AAV-FST alone, indicating simultaneous hypertrophy and angiogenesis. No adverse haematological, biochemical, or histopathological findings were observed. Discussion. Combined AAV-FST and VEGF therapy enhanced local muscle hypertrophy, increased capillary density, and improved the muscle-to-liver transgene expression profile compared with AAV-FST monotherapy. The regimen was well tolerated and supports further evaluation of angiogenic preconditioning as a strategy to improve muscle-directed gene therapy for muscle-wasting disorders.

Facioscapulohumeral muscular dystrophy (FSHD) is one of the most common dominant muscular dystrophies and remains without an approved disease modifying therapy. Caused by the aberrant expression of the cytotoxic gene DUX4, FSHD is typically diagnosed in adulthood, however clinical onset in children (<18 years of age) is often associated with a more severe and rapid disease. While clinical trials are underway, a lack of human-specific pre-clinical models limit effective testing of potential therapies, particularly in children. To fill this gap, we describe here the development of induced pluripotent stem cell-derived 2-and 3-dimensional skeletal muscle models of children with clinically defined mild, moderate, and severe FSHD. These iPSC-derived muscle models replicate key features of FSHD, including aberrant DUX4 mRNA expression, muscle atrophy, and weakness, which correlate with the individuals specific disease severity. Next, we assessed the efficacy of adenine base editing (ABE) as a potential gene therapy approach to treat FSHD. DUX4-targeted ABE reduced DUX4 mRNA expression, improved muscle area and force generation in the most severe individual. Together this work supports the use of iPSC-derived skeletal muscle models as a less invasive method to study childhood-onset FSHD and establishes targeted DUX4 gene editing therapies as a potential treatment approach.

Background: Hereditary spastic paraplegia (HSP) comprises a heterogeneous group of neurodegenerative disorders characterized by progressive lower-extremity weakness and spasticity, with or without additional neurological symptoms. Objectives: To characterize the molecular genetic spectrum, inheritance patterns, molecular finding rate, and clinical characteristics of HSP within a multicenter Canadian cohort. Methods: We investigated 671 patients from 423 families who met clinical criteria for HSP identified through the Canadian HSP (CanHSP) registry from 7 medical centers across Canada. Patients were evaluated using known HSP and HSP mimic gene panels, whereas unsolved and more recent patients underwent whole-exome sequencing (WES). 435 individuals underwent gene-panel testing and 485 underwent WES. Copy-number variants (CNVs) were assessed using ExomeDepth, and candidate CNVs using multiplex ligation-dependent probe amplification (MLPA). Results: Molecular findings were identified in 426 of 671 individuals (63.5%): 351 (52.3%) had HSP-associated findings, 70 (10.4%) HSP-mimicking disorders, and five (0.7%) other molecular findings; 245 (36.5%) remained unresolved. Candidate variants were found in 80 relevant genes, 36 of which were HSP-associated genes. The most frequently implicated genes were SPAST (22.5%), SPG7 (5.7%), ATL1 (5.2%), SPG11 (3.6%), and SPG8 (3.3%). Phenotypically, SPAST, ATL1, and SPG8 w[zg1.1]ere predominantly associated with pure HSP, whereas SPG7 and SPG11 more often showed complicated phenotypes, with prominent cerebellar involvement in SPG7 and cognitive and developmental features in SPG11. Conclusion: Patients in CanHSP present with genetic and phenotypic heterogeneity. Reanalysis and complementary approaches, including whole-genome, RNA, and long-read sequencing, may increase diagnostic yield.

Background: Tremor is a repetitive, oscillatory movement with multiple subtypes requiring accurate characterization for diagnosis and treatment. While frequency, amplitude, and context are routinely used to describe tremor, recent recommendations have emphasized oscillation shape and regularity. However, these descriptors lack strict operational definitions, and differences in how clinicians interpret them introduce inconsistency into tremor classification. Objective: We quantified inter-rater reliability for commonly used tremor descriptors and determined which objectively measured signal parameters: peak amplitude, peak frequency, and frequency variability best explained inconsistency in rater assessments. Methods: We developed the Tremor Waveform Morphology Questionnaire (TWMQ) and obtained standardized video recordings of 34 individuals with upper-extremity tremor performing rest, postural, and kinetic tasks, with simultaneous kinematic recordings using an inertial sensor. Movement disorder experts rated tremor presence, shape, symmetry, regularity, rhythmicity, and diagnosis. We assessed inter-rater reliability, cross-feature dependencies, and modeled the influence of objective signal parameters on each subjective rating. Results: Tremor presence and symmetry showed high agreement, whereas jerkiness, rhythmicity, amplitude stability, and clinical diagnosis showed lower reliability. Modeling revealed that peak amplitude primarily influenced judgments of tremor presence, jerkiness, and diagnosis, while frequency variability drove ratings of rhythmicity and amplitude stability. Conclusions: Morphology-based descriptors remain subjective, but disagreement systematically reflects measurable signal properties. Objective definitions based on peak amplitude and frequency variability may improve the reliability and reproducibility of tremor characterization.

Corticospinal-motoneuronal connections are more prominent in distal than proximal upper-limb muscles, but whether this anatomical specialization influences the capacity for activity-dependent plasticity remains unknown. Here, we tested whether Hebbian stimulation targeting corticospinal-motoneuronal connections, induces muscle-specific plasticity in proximal and distal arm muscles in healthy humans. We applied a spike-timing-dependent stimulation protocol comprising 180 paired stimuli, with transcranial magnetic stimulation timed to evoke corticospinal volleys 1-2 ms before motoneurons were antidromically activated by electrical stimulation of the brachial plexus for the biceps brachii or the ulnar nerve for the first dorsal interosseous (FDI). Corticospinal excitability was assessed by measuring motor-evoked potentials (MEPs) before and 30 min after stimulation. Hebbian stimulation increased MEP amplitudes in both muscles, but facilitation was greater in the FDI than in the biceps. Because resting motor threshold was higher for the biceps than for the FDI, in a control experiment we matched stimulation intensities between muscles. Under these conditions, Hebbian stimulation continued producing greater facilitation in the FDI than in the biceps, indicating that the difference was not attributable to stimulation intensity. Moreover, changes in MEP amplitude were associated with maximal MEP size in the FDI but not in the biceps, whereas no muscle-specific association was observed with peripheral responses (M-max), supporting a stronger relationship between corticospinal drive and Hebbian plasticity in the distal than in the proximal arm muscle. Together, these findings identify a distal-to-proximal gradient in Hebbian plasticity across arm muscles, which may contribute to optimizing targeted neuromodulation approaches for upper-limb rehabilitation.

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a complex multisystem disorder. Its hallmark feature, post-exertional malaise (PEM), is a delayed and prolonged worsening of symptoms following even minor exertion. As PEM commonly includes muscle pain, weakness, exercise intolerance and impaired recovery, skeletal muscle dysfunction may contribute to its pathophysiology, but the underlying molecular processes remain poorly understood. We generated induced pluripotent stem cell-derived skeletal muscle myotubes from individuals with ME/CFS (n = 6) and healthy controls (n = 7) to investigate disease-associated transcriptomic alterations and identify potential therapeutic candidates. Myogenic progenitor cells from both groups differentiated into elongated, multinucleated myotubes expressing titin and myosin heavy chain, while qPCR profiling of myogenic differentiation markers further supported successful differentiation. Gene-level analysis identified three differentially expressed genes at an FDR-adjusted p < 0.05: ERVH48-1, CDX4 and SLC2A14. Isoform-switching analysis identified 16 genes with significant differential isoform usage, including CACNA1H, MIEF2, SMAD2 and CHD4. Gene set enrichment analysis identified broader pathway-level alterations involving RNA processing, protein synthesis, proteostasis, mitochondrial quality control, metabolism and muscle-related processes. Library of Integrated Network-based Cellular Signatures Phase 2 (LINCS2) analysis further prioritised 14 compounds associated with mitochondrial metabolism, glucose and lipid regulation, PPAR signalling, calcium and excitatory signalling, neuroimmune activity and cellular stress responses. Overall, ME/CFS iPSC-derived myotubes showed modest gene-level differences alongside broader isoform- and pathway-level alterations, supporting their use for investigating skeletal muscle biology and prioritising candidates for functional validation.

BackgroundLMNA-related congenital muscular dystrophy (L-CMD) is a rare, life-threatening genetic disorder caused by point mutations in the LMNA gene, for which no effective treatment currently exists. It is characterized by early-onset muscle weakness, dropped-head syndrome, hypotonia, cardiac complications, and restrictive lung disease, frequently leading to premature death. The LMNA c.745C>T (p.R249W) mutation is the most prevalent amongst L-CMD patients. Given its monogenic nature, L-CMD represents a compelling candidate for gene therapy approaches. ResultsIn this study, we investigated the therapeutic potential of adenine base editing (ABE) to correct the pathogenic LMNA c.745C>T (p.R249W) mutation in human myoblasts. We evaluated multiple ABE variants and single-guide RNAs (sgRNAs), identifying optimal combinations that achieved efficient and specific correction of the mutant allele. However, we found that editing can also introduce an adjacent bystander mutation, c.743T>C (p.L248P). To determine the functional consequences of base editing, we established clonal cell lines reverted to wild type or harboring the p.L248P variant. Whereas wild-type edited cells showed a clear correction for all the studied parameters that were abnormal in R249W myoblasts, we found that L248P cells show nuclear abnormalities resembling those of R249W mutant cells, and their cellular function is partially compromised. These results demonstrate that ABE can effectively target the LMNA c.745C>T mutation but also reveal the significant impact of bystander edits on cellular physiology. ConclusionsOur findings provide proof-of-concept for the application of base editing as a therapeutic strategy for L-CMD, while underscoring the necessity of precise editing technologies to ensure both efficacy and safety in future clinical translation.

Introduction/Aims: The e-norms method derives reference values from a laboratory's own mixed patient data, without recruiting healthy volunteers. A decade of use exposed three things the original description did not address: a dependence on how finely measurements are recorded, a minimum sample size below which derived limits are systematically too permissive, and an extension of the method to engineered composite features. This work characterizes the first two and describes a corrected plateau rule. Methods: Twenty-six sensory amplitude datasets (18 to 3,301 measurements), three sensory conduction velocity datasets, nine median-nerve datasets and a 2,000-measurement peroneal file were analyzed. Amplitudes were progressively rounded; velocities were made finer by adding noise of 0.05 m/s. Subsamples of 50 to 750 were drawn from thirteen large datasets on raw, logarithmic and square-root scales. The corrected rule was validated against expert visual plateau selection and against the plateau proportions reported in 2015, and limit stability was estimated by resampling. Results: At n = 50, amplitudes as recorded returned 0.28 of the full-sample limit with 73.1% failing; rounded to whole numbers they returned 1.03 with none failing. Integer velocities returned 1.03 with no failures, but failed in all 300 draws once noise was added. Derived limits were systematically too low below 250 to 300 measurements. The corrected rule returned 1.00 with 0.1% failures and left integer velocities essentially unchanged. Discussion: The dependence is intrinsic to locating the plateau from gaps between sorted values. Obtaining 250 normal studies means accumulating 530 to 1,250, depending on a laboratory's normal rate.

Objectives: We developed and evaluated ArchSpiral, an iPad application that digitizes the International Cooperative Ataxia Rating Scale (ICARS) spiral tracing task to address the need for portable rare disease assessment while preserving clinical scoring and generating quantitative digital biomarkers. Materials and Methods: ArchSpiral (Swift/SwiftUI/PencilKit) captures Apple Pencil or finger tracings and computes tracing accuracy, root mean squared error, duration, average speed, pen lifts, pauses, steadiness, and an automated ICARS-compatible morphology score. Twelve participants with congenital disorders of glycosylation completed paired paper-digital assessments. Results: Digital ICARS scores spanned the scoring range (1-4). Paper and digital scores agreed exactly in 11 of 12 assessments (linear weighted {kappa} = 0.91). Steadiness showed the strongest association with paper-based ICARS scores ({rho} = -0.82, FDR-adjusted P = 0.008). Discussion: ArchSpiral enables standardized digital spiral assessment, while preserving compatibility with conventional ICARS scoring and adding objective quantitative measures for longitudinal rare disease research and clinical care.

Background Cervical spondylotic myelopathy (CSM) is the most common cause of nontraumatic spinal cord dysfunction in adults. For mild disease, guidelines recommend shared decision-making between surgery and structured rehabilitation on the basis of clinical equipoise, yet no comparative effectiveness study has reported outcomes in this population. Whether a randomized trial is feasible is unknown. Methods We conducted two cross-sectional surveys between December 2025 and July 2026: one of patients with surgeon-confirmed CSM recruited from academic outpatient spine clinics, and one of practicing neurosurgical and orthopedic spine surgeons. Respondents rated willingness to participate in (1) a randomized trial of early surgery versus observation and (2) a prospective observational study in which treatment was patient-selected. Responses of likely or very likely were classified as willing. Groups were compared using Fisher exact tests, designs within respondents using exact McNemar tests, and predictors using univariable logistic regression. Results Fifty-four patients and 52 surgeons completed the surveys. Patients were markedly less willing than surgeons to accept randomization (15 of 54, 27.8% versus 44 of 52, 84.6%; p < 0.001). Both groups accepted the observational design (39 of 54, 72.2% versus 51 of 52, 98.1%; p < 0.001), and 26 of 39 patients unwilling to be randomized were willing to enroll in an observational study (p < 0.001). Willingness to be randomized did not differ across mJOA severity (mild 30.4%, moderate 25.0%, severe 27.3%; p = 0.93). Among patients declining randomization, 85.2% cited a wish to retain control over treatment, whereas fear of surgery was cited by one respondent. Forty-five surgeons (86.5%) considered both surgery and observation reasonable, and preference was divided (46.2% favoring early surgery, 48.1% favoring initial observation). Conclusions Surgeons report equipoise and high willingness to randomize, but most patients would decline random allocation, citing a wish to retain treatment choice rather than fear or distrust. A prospective observational study appears the more feasible route to comparative evidence in mild CSM. Feasibility assessments restricted to clinicians may substantially overestimate attainable accrual.

Background: Pseudo-orthostatic tremor (psOT) is a rare form of tremor of the lower body, triggered by standing, at frequencies lower than 13 Hz. It is believed to be secondary to other neurological disorders in a large proportion of cases. Surface electromyography (sEMG) can identify its core characteristics and differentiate it from other similar disorders such as primary orthostatic tremor (POT) and orthostatic myoclonus (OM). Objectives: Our study aims to illustrate the clinical and neurophysiological features as well as the outcomes and final diagnoses of patients with psOT in a retrospective two-centre cohort. Methods: We retrospectively examined the available clinical and neurophysiological records of 35 consecutive patients with a diagnosis of psOT in the 2022-2026 period. Data on demographics, clinical characteristics, sEMG findings, pharmacological treatments, ancillary investigations and patient reported outcomes were collected. Results: 35 patients with psOT were identified, of which 6 (17%) displayed features consistent with a functional neurological disorder (FND). Among the 29 patients with organic psOT, 21 (72.4%) fulfilled the diagnostic criteria for essential tremor (ET), while an identifiable neurological cause was established in four (13.8%). sEMG findings differed between functional and organic psOT, with the latter often displaying features consistent with weight-bearing hyperkinesias. Conclusions: Our retrospective study suggests that psOT is most often associated with ET, while an identifiable neurological cause was found in a relatively small proportion of patients. We also describe functional psOT as a previously unrecognized clinical presentation of FND.

Sex-related differences in force steadiness are often attributed to maximal strength and motor unit (MU) properties, but their independent contributions remain unclear. This study strength-matched females and males to remove the influence of maximal strength and determine whether MU properties are associated with sex-related differences in force steadiness. Twelve young adults (6 females) were matched for elbow flexion strength (females, 188.6{+/-}15.6 N; males, 199.7{+/-}24.8 N, p=0.4). Both groups performed submaximal isometric elbow flexion contractions at 2.5%, 5%, 10%, 15%, and 25% MVC. The MU recruitment thresholds (RT), discharge rates (MUDR), and coefficient of variation of interspike intervals (CVISI) were measured from intramuscular fine wire electromyography (EMG) electrodes. Force steadiness was quantified as the standard deviation (SD) and coefficient of variation (CV) of force. Across forces, SD and CV of force did not differ between females and males (p>0.05). Females had a higher recruitment threshold than males (p<0.05). Females had higher MUDR at 15% and 25% MVC (p<0.02), while males were higher at 5% MVC (p=0.02). The CVISI was greater in females (p<0.001) and positively correlated with SD of force (r=0.2) and negatively with CV of force (r=-0.2) in females and males. When strength was matched, sex-related differences in force steadiness were not evident. However, females exhibited higher MU recruitment thresholds, MUDR and CVISI. Despite greater CVISI in females, these differences did not translate into greater force fluctuations, suggesting that individual MU discharge variability is not a primary predictor of force steadiness when maximal strength is controlled. NEW & NOTEWORTHYO_LIStrength matching eliminated sex-related differences in elbow flexor force steadiness. C_LIO_LIFemales achieved similar force steadiness using higher MU recruitment thresholds and discharge rates, particularly in the short head of the biceps brachii. C_LIO_LIIn females, the greater variability in motor unit discharge was not associated with reduced force steadiness. C_LI