Disease-associated comorbidities, medication records and anthropometric measures in adults with Duchenne muscular dystrophy.

We investigated the comorbidities, associated factors, and the relationship between anthropometric measures and respiratory function and functional abilities in adults with Duchenne muscular dystrophy (DMD). This was a single-centre cross-sectional study in genetically diagnosed adults with DMD (>16 years old). Univariate and multivariate analyses identified factors associated with dysphagia, constipation, Body Mass Index (BMI), and weight. Regression analysis explored associations between BMI, weight, and respiratory/motor abilities. We included 112 individuals (23.4 ± 5.2 years old), glucocorticoid-treated 66.1 %. The comorbidities frequency was 61.6 % scoliosis (61.0 % of them had spinal surgery), 36.6 % dysphagia, 36.6 % constipation, and 27.8 % urinary conditions. The use of glucocorticoids delayed the time to spinal surgery. The univariate analysis revealed associations between dysphagia and constipation with age, lack of glucocorticoid treatment, and lower respiratory and motor function. In the multivariate analysis, impaired cough ability remained as the factor consistently linked to both conditions. Constipation associated with lower BMI and weight. BMI and weight positively correlated with respiratory parameters, but they did not associate with functional abilities. Glucocorticoids reduce the frequency of comorbidities in adults with DMD. The ability to cough can help identifying dysphagia and constipation. Lower BMI and weight in individuals with DMD with compromised respiratory function may suggest a higher calories requirement.

Start, switch and stop (triple-S) criteria for enzyme replacement therapy of late-onset Pompe disease: European Pompe Consortium recommendation update 2024.

BACKGROUND AND PURPOSE: Two novel enzyme replacement therapies (ERTs), studied in phase 3 trials in late-onset Pompe patients, reached marketing authorization by the European Medicines Agency in 2022 and 2023. The European Pompe Consortium (EPOC) updates and extends the scope of the 2017 recommendations for starting, switching and stopping ERT. METHODS: The European Pompe Consortium consists of 25 neuromuscular and metabolic experts from eight European countries. This update was performed after an in-person meeting, three rounds of discussion and voting to provide a consensus recommendation. RESULTS: The patient should be symptomatic, that is, should have skeletal muscle weakness or respiratory muscle involvement. Muscle magnetic resonance imaging findings showing substantial fat replacement can support the decision to start in a patient-by-patient scenario. Limited evidence supports switching ERT if there is no indication that skeletal muscle and/or respiratory function have stabilized or improved during standard ERT of 12 months or after severe infusion-associated reactions. Switching of ERT should be discussed on a patient-by-patient shared-decision basis. If there are severe, unmanageable infusion-associated reactions and no stabilization in skeletal muscle function during the first 2 years after starting or switching treatment, stopping ERT should be considered. After stopping ERT for inefficacy, restarting ERT can be considered. Six-monthly European Pompe Consortium muscle function assessments are recommended. CONCLUSIONS: The triple-S criteria on ERT start, switch and stop include muscle magnetic resonance imaging as a supportive finding and the potential option of home infusion therapy. Six-monthly long-term monitoring of muscle function is highly recommended to cover insights into the patient's trajectory under ERT.

Functional abilities, respiratory and cardiac function in a large cohort of adults with Duchenne muscular dystrophy treated with glucocorticoids.

BACKGROUND AND PURPOSE: The transition to adult services, and subsequent glucocorticoid management, is critical in adults with Duchenne muscular dystrophy. This study aims (1) to describe treatment, functional abilities, respiratory and cardiac status during transition to adulthood and adult stages; and (2) to explore the association between glucocorticoid treatment after loss of ambulation (LOA) and late-stage clinical outcomes. METHODS: This was a retrospective single-centre study on individuals with Duchenne muscular dystrophy (≥16 years old) between 1986 and 2022. Logistic regression, Cox proportional hazards models and survival analyses were conducted utilizing data from clinical records. RESULTS: In all, 112 individuals were included. Mean age was 23.4 ± 5.2 years and mean follow-up was 18.5 ± 5.5 years. At last assessment, 47.2% were on glucocorticoids; the mean dose of prednisone was 0.38 ± 0.13 mg/kg/day and of deflazacort 0.43 ± 0.16 mg/kg/day. At age 16 years, motor function limitations included using a manual wheelchair (89.7%), standing (87.9%), transferring from a wheelchair (86.2%) and turning in bed (53.4%); 77.5% had a peak cough flow <270 L/min, 53.3% a forced vital capacity percentage of predicted <50% and 40.3% a left ventricular ejection fraction <50%. Glucocorticoids after LOA reduced the risk and delayed the time to difficulties balancing in the wheelchair, loss of hand to mouth function, forced vital capacity percentage of predicted <30% and forced vital capacity <1 L and were associated with lower frequency of left ventricular ejection fraction <50%, without differences between prednisone and deflazacort. Glucocorticoid dose did not differ by functional, respiratory or cardiac status. CONCLUSION: Glucocorticoids after LOA preserve late-stage functional abilities, respiratory and cardiac function. It is suggested using functional abilities, respiratory and cardiac status at transition stages for adult services planning.

Safety and efficacy of losmapimod in facioscapulohumeral muscular dystrophy (ReDUX4): a randomised, double-blind, placebo-controlled phase 2b trial.

BACKGROUND: Facioscapulohumeral muscular dystrophy is a hereditary progressive myopathy caused by aberrant expression of the transcription factor DUX4 in skeletal muscle. No approved disease-modifying treatments are available for this disorder. We aimed to assess the safety and efficacy of losmapimod (a small molecule that inhibits p38α MAPK, a regulator of DUX4 expression, and p38ß MAPK) for the treatment of facioscapulohumeral muscular dystrophy. METHODS: We did a randomised, double-blind, placebo-controlled phase 2b trial at 17 neurology centres in Canada, France, Spain, and the USA. We included adults aged 18-65 years with type 1 facioscapulohumeral muscular dystrophy (ie, with loss of repression of DUX4 expression, as ascertained by genotyping), a Ricci clinical severity score of 2-4, and at least one skeletal muscle judged using MRI to be suitable for biopsy. Participants were randomly allocated (1:1) to either oral losmapimod (15 mg twice a day) or matching placebo for 48 weeks, via an interactive response technology system. The investigator, study staff, participants, sponsor, primary outcome assessors, and study monitor were masked to the treatment allocation until study closure. The primary endpoint was change from baseline to either week 16 or 36 in DUX4-driven gene expression in skeletal muscle biopsy samples, as measured by quantitative RT-PCR. The primary efficacy analysis was done in all participants who were randomly assigned and who had available data for assessment, according to the modified intention-to-treat principle. Safety and tolerability were assessed as secondary endpoints. This study is registered at ClinicalTrials.gov, number NCT04003974. The phase 2b trial is complete; an open-label extension is ongoing. FINDINGS: Between Aug 27, 2019, and Feb 27, 2020, 80 people were enrolled. 40 were randomly allocated to losmapimod and 40 to placebo. 54 (68%) participants were male and 26 (33%) were female, 70 (88%) were White, and mean age was 45·7 (SD 12·5) years. Least squares mean changes from baseline in DUX4-driven gene expression did not differ significantly between the losmapimod (0·83 [SE 0·61]) and placebo (0·40 [0·65]) groups (difference 0·43 [SE 0·56; 95% CI -1·04 to 1·89]; p=0·56). Losmapimod was well tolerated. 29 treatment-emergent adverse events (nine drug-related) were reported in the losmapimod group compared with 23 (two drug-related) in the placebo group. Two participants in the losmapimod group had serious adverse events that were deemed unrelated to losmapimod by the investigators (alcohol poisoning and suicide attempt; postoperative wound infection) compared with none in the placebo group. No treatment discontinuations due to adverse events occurred and no participants died during the study. INTERPRETATION: Although losmapimod did not significantly change DUX4-driven gene expression, it was associated with potential improvements in prespecified structural outcomes (muscle fat infiltration), functional outcomes (reachable workspace, a measure of shoulder girdle function), and patient-reported global impression of change compared with placebo. These findings have informed the design and choice of efficacy endpoints for a phase 3 study of losmapimod in adults with facioscapulohumeral muscular dystrophy. FUNDING: Fulcrum Therapeutics.

Defining clinical endpoints in limb girdle muscular dystrophy: a GRASP-LGMD study.

BACKGROUND: The Limb Girdle Muscular Dystrophies (LGMDs) are characterized by progressive weakness of the shoulder and hip girdle muscles as a result of over 30 different genetic mutations. This study is designed to develop clinical outcome assessments across the group of disorders. METHODS/DESIGN: The primary goal of this study is to evaluate the utility of a set of outcome measures on a wide range of LGMD phenotypes and ability levels to determine if it would be possible to use similar outcomes between individuals with different phenotypes. We will perform a multi-center, 12-month study of 188 LGMD patients within the established Genetic Resolution and Assessments Solving Phenotypes in LGMD (GRASP-LGMD) Research Consortium, which is comprised of 11 sites in the United States and 2 sites in Europe. Enrolled patients will be clinically affected and have mutations in CAPN3 (LGMDR1), ANO5 (LGMDR12), DYSF (LGMDR2), DNAJB6 (LGMDD1), SGCA (LGMDR3), SGCB (LGMDR4), SGCD (LGMDR6), or SGCG (LGMDR5, or FKRP-related (LGMDR9). DISCUSSION: To the best of our knowledge, this will be the largest consortium organized to prospectively validate clinical outcome assessments (COAs) in LGMD at its completion. These assessments will help clinical trial readiness by identifying reliable, valid, and responsive outcome measures as well as providing data driven clinical trial decision making for future clinical trials on therapeutic agents for LGMD. The results of this study will permit more efficient clinical trial design. All relevant data will be made available for investigators or companies involved in LGMD therapeutic development upon conclusion of this study as applicable. TRIAL REGISTRATION: Clinicaltrials.gov NCT03981289; Date of registration: 6/10/2019.

Digenic inheritance involving a muscle-specific protein kinase and the giant titin protein causes a skeletal muscle myopathy.

In digenic inheritance, pathogenic variants in two genes must be inherited together to cause disease. Only very few examples of digenic inheritance have been described in the neuromuscular disease field. Here we show that predicted deleterious variants in SRPK3, encoding the X-linked serine/argenine protein kinase 3, lead to a progressive early onset skeletal muscle myopathy only when in combination with heterozygous variants in the TTN gene. The co-occurrence of predicted deleterious SRPK3/TTN variants was not seen among 76,702 healthy male individuals, and statistical modeling strongly supported digenic inheritance as the best-fitting model. Furthermore, double-mutant zebrafish (srpk3-/-; ttn.1+/-) replicated the myopathic phenotype and showed myofibrillar disorganization. Transcriptome data suggest that the interaction of srpk3 and ttn.1 in zebrafish occurs at a post-transcriptional level. We propose that digenic inheritance of deleterious changes impacting both the protein kinase SRPK3 and the giant muscle protein titin causes a skeletal myopathy and might serve as a model for other genetic diseases.

104-week efficacy and safety of cipaglucosidase alfa plus miglustat in adults with late-onset Pompe disease: a phase III open-label extension study (ATB200-07).

The phase III double-blind PROPEL study compared the novel two-component therapy cipaglucosidase alfa + miglustat (cipa + mig) with alglucosidase alfa + placebo (alg + pbo) in adults with late-onset Pompe disease (LOPD). This ongoing open-label extension (OLE; NCT04138277) evaluates long-term safety and efficacy of cipa + mig. Outcomes include 6-min walk distance (6MWD), forced vital capacity (FVC), creatine kinase (CK) and hexose tetrasaccharide (Hex4) levels, patient-reported outcomes and safety. Data are reported as change from PROPEL baseline to OLE week 52 (104 weeks post-PROPEL baseline). Of 118 patients treated in the OLE, 81 continued cipa + mig treatment from PROPEL (cipa + mig group; 61 enzyme replacement therapy [ERT] experienced prior to PROPEL; 20 ERT naïve) and 37 switched from alg + pbo to cipa + mig (switch group; 29 ERT experienced; 8 ERT naive). Mean (standard deviation [SD]) change in % predicted 6MWD from baseline to week 104 was + 3.1 (8.1) for cipa + mig and - 0.5 (7.8) for the ERT-experienced switch group, and + 8.6 (8.6) for cipa + mig and + 8.9 (11.7) for the ERT-naïve switch group. Mean (SD) change in % predicted FVC was - 0.6 (7.5) for cipa + mig and - 3.8 (6.2) for the ERT-experienced switch group, and - 4.8 (6.5) and - 3.1 (6.7), respectively, in ERT-naïve patients. CK and Hex4 levels improved in both treatment groups by week 104 with cipa + mig treatment. Three patients discontinued the OLE due to infusion-associated reactions. No new safety signals were identified. Cipa + mig treatment up to 104 weeks was associated with overall maintained improvements (6MWD, biomarkers) or stabilization (FVC) from baseline with continued durability, and was well tolerated, supporting long-term benefits for patients with LOPD.Trial registration number: NCT04138277; trial start date: December 18, 2019.

Imaging mass cytometry analysis of Becker muscular dystrophy muscle samples reveals different stages of muscle degeneration.

Becker muscular dystrophy (BMD) is characterised by fiber loss and expansion of fibrotic and adipose tissue. Several cells interact locally in what is known as the degenerative niche. We analysed muscle biopsies of controls and BMD patients at early, moderate and advanced stages of progression using Hyperion imaging mass cytometry (IMC) by labelling single sections with 17 markers identifying different components of the muscle. We developed a software for analysing IMC images and studied changes in the muscle composition and spatial correlations between markers across disease progression. We found a strong correlation between collagen-I and the area of stroma, collagen-VI, adipose tissue, and M2-macrophages number. There was a negative correlation between the area of collagen-I and the number of satellite cells (SCs), fibres and blood vessels. The comparison between fibrotic and non-fibrotic areas allowed to study the disease process in detail. We found structural differences among non-fibrotic areas from control and patients, being these latter characterized by increase in CTGF and in M2-macrophages and decrease in fibers and blood vessels. IMC enables to study of changes in tissue structure along disease progression, spatio-temporal correlations and opening the door to better understand new potential pathogenic pathways in human samples.

Facioscapulohumeral Muscular Dystrophy European Patient Survey: Assessing Patient Reported Disease Burden and Preferences in Clinical Trial Participation.

Background: Facioscapulohumeral muscular dystrophy (FSHD) is a genetic disorder characterized by progressive muscle weakness leading to permanent disability. There are no curative treatments, however, there are several upcoming clinical trials testing new therapies in FSHD. Objective: This study aimed to explore the disease burden and patient preferences of people with FSHD to ensure that clinical trials can be designed to include outcome measures that are relevant and important to patients. Methods: A survey was developed with a steering committee clinicians and physiotherapists with relevant experience in the disease, patient representatives, a registry expert and industry consultants. Themes of the survey included; participant demographics, disease progression and impact on function, factors encouraging or discouraging clinical trial participation, and positive outcomes of a clinical trial. Results: 1147 participants responded to the online survey, representing 26 countries across Europe and a range of disease severities. The study highlighted the key symptoms causing concern for FSHD patients - muscle weakness and mobility issues - reflecting what participants want targeted for future therapies. The need for clear information and communication throughout clinical trials was emphasised. Factors most encouraging trial participation included access to new investigational therapies, access to trial results and benefits for the FSHD community. Factors most discouraging trial participation included travel related issues and fear of side effects. Conclusions: The results from this study identify the patient reported burden of FSHD and should provide researchers and industry with areas of therapeutic research that would be meaningful to patients, as well as supporting the development of patient centric outcome measures in clinical trials.

Applying the win ratio method in clinical trials of orphan drugs: an analysis of data from the COMET trial of avalglucosidase alfa in patients with late-onset Pompe disease.

BACKGROUND: Clinical trials for rare diseases often include multiple endpoints that capture the effects of treatment on different disease domains. In many rare diseases, the primary endpoint is not standardized across trials. The win ratio approach was designed to analyze multiple endpoints of interest in clinical trials and has mostly been applied in cardiovascular trials. Here, we applied the win ratio approach to data from COMET, a phase 3 trial in late-onset Pompe disease, to illustrate how this approach can be used to analyze multiple endpoints in the orphan drug context. METHODS: All possible participant pairings from both arms of COMET were compared sequentially on changes at week 49 in upright forced vital capacity (FVC) % predicted and six-minute walk test (6MWT). Each participant's response for the two endpoints was first classified as a meaningful improvement, no meaningful change, or a meaningful decline using thresholds based on published minimal clinically important differences (FVC ± 4% predicted, 6MWT ± 39 m). Each comparison assessed whether the outcome with avalglucosidase alfa (AVA) was better than (win), worse than (loss), or equivalent to (tie) the outcome with alglucosidase alfa (ALG). If tied on FVC, 6MWT was compared. In this approach, the treatment effect is the ratio of wins to losses ("win ratio"), with ties excluded. RESULTS: In the 2499 possible pairings (51 receiving AVA × 49 receiving ALG), the win ratio was 2.37 (95% confidence interval [CI], 1.30-4.29, p = 0.005) when FVC was compared before 6MWT. When the order was reversed, the win ratio was 2.02 (95% CI, 1.13-3.62, p = 0.018). CONCLUSION: The win ratio approach can be used in clinical trials of rare diseases to provide meaningful insight on treatment benefits from multiple endpoints and across disease domains.

Description of clinical and genetic features of 122 patients included in the Spanish Pompe registry.

Pompe disease is a rare genetic disorder with an estimated prevalence of 1:60.000. The two main phenotypes are Infantile Onset Pompe Disease (IOPD) and Late Onset Pompe Disease (LOPD). There is no published data from Spain regarding the existing number of cases, regional distribution, clinical features or, access and response to the treatment. We created a registry to collect all these data from patients with Pompe in Spain. Here, we report the data of the 122 patients registered including nine IOPD and 113 LOPD patients. There was a high variability in how the diagnosis was obtained and how the follow-up was performed among different centres. Seven IOPD patients were still alive being all treated with enzymatic replacement therapy (ERT) at last visit. Ninety four of the 113 LOPD patients had muscle weakness of which 81 were receiving ERT. We observed a progressive decline in the results of muscle function tests during follow-up. Overall, the Spanish Pompe Registry is a valuable resource for understanding the demographics, patient's journey and clinical characteristics of patients in Spain. Our data supports the development of agreed guidelines to ensure that the care provided to the patients is standardized across the country.

Magnetic resonance imaging-based criteria to differentiate dysferlinopathy from other genetic muscle diseases.

The identification of disease-characteristic patterns of muscle fatty replacement in magnetic resonance imaging (MRI) is helpful for diagnosing neuromuscular diseases. In the Clinical Outcome Study of Dysferlinopathy, eight diagnostic rules were described based on MRI findings. Our aim is to confirm that they are useful to differentiate dysferlinopathy (DYSF) from other genetic muscle diseases (GMD). The rules were applied to 182 MRIs of dysferlinopathy patients and 1000 MRIs of patients with 10 other GMD. We calculated sensitivity (S), specificity (Sp), positive and negative predictive values (PPV/NPV) and accuracy (Ac) for each rule. Five of the rules were more frequently met by the DYSF group. Patterns observed in patients with FKRP, ANO5 and CAPN3 myopathies were similar to the DYSF pattern, whereas patterns observed in patients with OPMD, laminopathy and dystrophinopathy were clearly different. We built a model using the five criteria more frequently met by DYSF patients that obtained a S 95.9%, Sp 46.1%, Ac 66.8%, PPV 56% and NPV 94% to distinguish dysferlinopathies from other diseases. Our findings support the use of MRI in the diagnosis of dysferlinopathy, but also identify the need to externally validate "disease-specific" MRI-based diagnostic criteria using MRIs of other GMD patients.

Post-hoc Nonparametric Analysis of Forced Vital Capacity in the COMET Trial Demonstrates Superiority of Avalglucosidase Alfa vs Alglucosidase Alfa.

In the COMET trial of patients with late-onset Pompe disease, greater improvement in upright forced vital capacity (FVC) % predicted was observed with avalglucosidase alfa (AVA) vs alglucosidase alfa (ALGLU) (estimated treatment difference: 2.43%). The pre-specified mixed model repeated measures (MMRM) analysis demonstrated non-inferiority of AVA (P = 0.0074) and narrowly missed superiority (P = 0.063; 95% CI: -0.13-4.99). We report superiority of AVA in two post-hoc analyses that account for an extreme outlier participant with low FVC and severe chronic obstructive pulmonary disease at baseline: MMRM excluding the outlier (P = 0.013) and non-parametric analysis of all data with repeated measures analysis of covariance (P = 0.019).

Defining Clinical Endpoints in Limb Girdle Muscular Dystrophy: A GRASP-LGMD study.

Background: The Limb Girdle Muscular Dystrophies (LGMDs) are characterized by progressive weakness of the shoulder and hip girdle muscles as a result of over 30 different genetic mutations. This study is designed to develop clinical outcome assessments across the group of disorders. Methods/design: The primary goal of this study is to evaluate the utility of a set of outcome measures on a wide range of LGMD phenotypes and ability levels to determine if it would be possible to use similar outcomes between individuals with different phenotypes. We will perform a multi-center, 12-month study of 188 LGMD patients within the established Genetic Resolution and Assessments Solving Phenotypes in LGMD (GRASP-LGMD) Research Consortium, which is comprised of 11 sites in the United States and 2 sites in Europe. Enrolled patients will be clinically affected and have mutations in CAPN3 (LGMDR1), ANO5 (LGMDR12), DYSF (LGMDR2), DNAJB6 (LGMDD1), SGCA (LGMDR3), SGCB (LGMDR4), SGCD (LGMDR6), or SGCG (LGMDR5, or FKRP-related (LGMDR9). Discussion: To the best of our knowledge, this will be the largest consortium organized to prospectively validate clinical outcome assessments (COAs) in LGMD at its completion. These assessments will help clinical trial readiness by identifying reliable, valid, and responsive outcome measures as well as providing data driven clinical trial decision making for future clinical trials on therapeutic agents for LGMD. The results of this study will permit more efficient clinical trial design. All relevant data will be made available for investigators or companies involved in LGMD therapeutic development upon conclusion of this study as applicable. Trial registration: clinicaltrials.gov NCT03981289; Date of registration: 6/10/2019.

Muscle magnetic resonance imaging of a large cohort of distal hereditary motor neuropathies reveals characteristic features useful for diagnosis.

Distal motor neuropathies (dHMN) are an heterogenous group of diseases characterized by progressive muscle weakness affecting predominantly the distal muscles of the lower and upper limbs. Our aim was to study the imaging features and pattern of muscle involvement in muscle magnetic resonance imaging (MRI) in dHMN patients of suspected genetic origin (dHMN). We conducted a retrospective study collecting clinical, genetic and muscle imaging data. Muscle MRI included T1-weighted and T2 weighted Short Tau Inversion Recovery images (STIR-T2w) sequences. Muscle replacement by fat was quantified using the Mercuri score. Identification of selective patterns of involvement was performed using hierarchical clustering. Eighty-four patients with diagnosis of dHMN were studied. Fat replacement was predominant in the distal lower leg muscles (82/84 cases), although also affected thigh and pelvis muscles. Asymmetric involvement was present in 29% of patients. The superficial posterior compartment of the leg, including the soleus and gastrocnemius muscles, was the most affected area (77/84). We observed a reticular pattern of fatty replacement progressing towards what is commonly known as "muscle islands" in 79.8%. Hyperintensities in STIR-T2w were observed in 78.6% patients mainly in distal leg muscles. Besides features common to all individuals, we identified and describe a pattern of muscle fat replacement characteristic of BICD2, HSPB1 and DYNC1H1 patients. We conclude that muscle MRI of patients with suspected dHMN reveals common features helpful in diagnosis process.

Decoding the transcriptome of Duchenne muscular dystrophy to the single nuclei level reveals clinical-genetic correlations.

Duchenne muscular dystrophy is a genetic disease produced by mutations in the dystrophin gene characterized by early onset muscle weakness leading to severe and irreversible disability. The cellular and molecular consequences of the lack of dystrophin in humans are only partially known, which is crucial for the development of new therapies aiming to slow or stop the progression of the disease. Here we have analyzed quadriceps muscle biopsies of seven DMD patients aged 2 to 4 years old and five age and gender matched controls using single nuclei RNA sequencing (snRNAseq) and correlated the results obtained with clinical data. SnRNAseq identified significant differences in the proportion of cell population present in the muscle samples, including an increase in the number of regenerative fibers, satellite cells, and fibro-adipogenic progenitor cells (FAPs) and a decrease in the number of slow fibers and smooth muscle cells. Muscle samples from the younger patients with stable mild weakness were characterized by an increase in regenerative fibers, while older patients with moderate and progressive weakness were characterized by loss of muscle fibers and an increase in FAPs. An analysis of the gene expression profile in muscle fibers identified a strong regenerative signature in DMD samples characterized by the upregulation of genes involved in myogenesis and muscle hypertrophy. In the case of FAPs, we observed upregulation of genes involved in the extracellular matrix regeneration but also several signaling pathways. Indeed, further analysis of the potential intercellular communication profile showed a dysregulation of the communication profile in DMD samples identifying FAPs as a key regulator of cell signaling in DMD muscle samples. In conclusion, our study has identified significant differences at the cellular and molecular levels in the different cell populations present in skeletal muscle samples of patients with DMD compared to controls.

Clinical Classification of Variants in the Valosin-Containing Protein Gene Associated With Multisystem Proteinopathy.

Background and Objectives: Pathogenic variants in the valosin-containing protein (VCP) gene cause a phenotypically heterogeneous disorder that includes myopathy, motor neuron disease, Paget disease of the bone, frontotemporal dementia, and parkinsonism termed multisystem proteinopathy. This hallmark pleiotropy makes the classification of novel VCP variants challenging. This retrospective study describes and assesses the effect of 19 novel or nonpreviously clinically characterized VCP variants identified in 28 patients (26 unrelated families) in the retrospective VCP International Multicenter Study. Methods: A 6-item clinical score was developed to evaluate the phenotypic level of evidence to support the pathogenicity of the novel variants. Each item is allocated a value, a score ranging from 0.5 to 5.5 points. A receiver-operating characteristic curve was used to identify a cutoff value of 3 to consider a variant as high likelihood disease associated. The scoring system results were confronted with results of in vitro ATPase activity assays and with in silico analysis. Results: All variants were missense, except for one small deletion-insertion, 18 led to amino acid changes within the N and D1 domains, and 13 increased the enzymatic activity. The clinical score coincided with the functional studies in 17 of 19 variants and with the in silico analysis in 12 of 19. For 12 variants, the 3 predictive tools agreed, and for 7 variants, the predictive tools disagreed. The pooled data supported the pathogenicity of 13 of 19 novel VCP variants identified in the study. Discussion: This study provides data to support pathogenicity of 14 of 19 novel VCP variants and provides guidance for clinicians in the evaluation of novel variants in the VCP gene.

Longitudinal Analysis of Respiratory Function of Different Types of Limb Girdle Muscular Dystrophies Reveals Independent Trajectories.

Background and Objectives: The prevalence and progression of respiratory muscle dysfunction in patients with limb girdle muscular dystrophies (LGMDs) has been only partially described to date. Most reports include cross-sectional data on a limited number of patients making it difficult to gain a wider perspective on respiratory involvement throughout the course of the disease and to compare the most prevalent LGMD subtypes. Methods: We reviewed the results of spirometry studies collected longitudinally in our cohort of patients in routine clinical visits from 2002 to 2020 along with additional clinical and genetic data. A linear mixed model was used to investigate the factors associated with the progression of respiratory dysfunction. Results: We followed up 156 patients with 5 different forms of LGMDs for a median of 8 years (range 1-25 years). Of them, 53 patients had pathogenic variants in the Capn3 gene, 47 patients in the Dysf gene, 24 patients in the Fkrp gene, 19 in the Ano5 gene, and 13 in one of the sarcoglycan genes (SCG). At baseline, 58 patients (37.1%) had a forced vital capacity percentage predicted (FVCpp) below 80%, while 14 patients (8.9%) had peak cough flow (PCF) values below 270 L/min. As a subgroup, FKRP was the group with a higher number of patients having FVC <80% and/or PCF <270 L/min at initial assessment (66%). We observed a progressive decline in FVCpp and PCF measurements over time, being age, use of wheelchair, and LGMD subtype independent factors associated with this decline. Fkrp and sarcoglycan patients had a quicker decline in their FVC (Kaplan-Meier curve, F test, p < 0.001 and p = 0.02, respectively). Only 7 of the 58 patients with low FVCpp values reported symptoms of respiratory dysfunction, which are commonly reported by patients with FVCpp below 50%-60%. The number of patients ventilated increased from 2 to 8 during follow-up. Discussion: Respiratory dysfunction is a frequent complication of patients with LGMDs that needs to be carefully studied and has direct implications in the care offered in daily clinics. Respiratory dysfunction is associated with disease progression because it is especially seen in patients who are full-time wheelchair users, being more frequent in patients with mutations in the Fkrp and sarcoglycan genes.

Neurofilament Light and Its Association With CNS Involvement in Patients With Classic Infantile Pompe Disease.

BACKGROUND AND OBJECTIVES: Enzyme replacement therapy (ERT) has substantially improved the outcome of classic infantile Pompe disease, an inheritable muscle disease previously fatal at infancy. However, under treatment, patients develop white matter abnormalities and neurocognitive problems. Therefore, upcoming therapies also target the brain. Currently, biomarkers reflecting CNS involvement are lacking. We aimed to study the association of neurofilament light (NfL) and CNS involvement. METHODS: To investigate the potential of NfL, we analyzed serum samples of patients with classic infantile Pompe disease who were treated with ERT. The samples were collected at ages of <1, 5, and 10 years, as well as around MRI scans. We compared the outcomes with levels in age- and sex-matched peers. Control samples were originally collected as part of routine blood work in children who underwent small surgeries and stored in the biobank of the Erasmus MC/Sophia Children's Hospital. RESULTS: We analyzed 74 serum samples of 17 patients collected at ages ranging from 22 days to 21.2 years (1-8 samples per patient) and compared these with outcomes of 71 matched peers. In the first year of age, NfL levels in patients and controls were similar (10.3 vs 11.0 pg/mL), but mixed linear model analysis showed a yearly increase of NfL of 6.0% in patients, compared with a decrease of 8.8% in controls (p < 0.001). Higher NfL was associated with lower IQ scores (p = 0.009) and lower processing speed scores (p = 0.001). DISCUSSION: We found significant differences in NfL levels between patients and controls and a good association between NfL and cognition. NfL deserves further exploration as a biomarker for CNS involvement in patients with classic infantile Pompe disease.

Comprehensive functional characterization of SGCB coding variants predicts pathogenicity in limb-girdle muscular dystrophy type R4/2E.

Genetic testing is essential for patients with a suspected hereditary myopathy. More than 50% of patients clinically diagnosed with a myopathy carry a variant of unknown significance in a myopathy gene, often leaving them without a genetic diagnosis. Limb-girdle muscular dystrophy (LGMD) type R4/2E is caused by mutations in ß-sarcoglycan (SGCB). Together, ß-, α-, γ-, and δ-sarcoglycan form a 4-protein transmembrane complex (SGC) that localizes to the sarcolemma. Biallelic loss-of-function mutations in any subunit can lead to LGMD. To provide functional evidence for the pathogenicity of missense variants, we performed deep mutational scanning of SGCB and assessed SGC cell surface localization for all 6,340 possible amino acid changes. Variant functional scores were bimodally distributed and perfectly predicted pathogenicity of known variants. Variants with less severe functional scores more often appeared in patients with slower disease progression, implying a relationship between variant function and disease severity. Amino acid positions intolerant to variation mapped to points of predicted SGC interactions, validated in silico structural models, and enabled accurate prediction of pathogenic variants in other SGC genes. These results will be useful for clinical interpretation of SGCB variants and improving diagnosis of LGMD; we hope they enable wider use of potentially life-saving gene therapy.