Decoding the muscle transcriptome of patients with late onset Pompe disease reveals markers of disease progression.

Late-onset Pompe Disease (LOPD) is a rare genetic disorder caused by the deficiency of acid alpha-glucosidase leading to progressive cellular dysfunction due to the accumulation of glycogen in the lysosome. The mechanism of relentless muscle damage - a classic manifestation of the disease - has been extensively studied by analysing the whole muscle tissue; however, little, if any, is known about transcriptional heterogeneity among nuclei within the multinucleated skeletal muscle cells. This is the first report of application of single nuclei RNA sequencing to uncover changes in the gene expression profile in muscle biopsies from eight patients with LOPD and four muscle samples from age and gender matched healthy controls. We matched these changes with histology findings using GeoMx Spatial Transcriptomics to compare the transcriptome of control myofibers from healthy individuals with non-vacuolated (histologically unaffected) and vacuolated (histologically affected) myofibers of LODP patients. We observed an increase in the proportion of slow and regenerative muscle fibers and macrophages in LOPD muscles. The expression of the genes involved in glycolysis was reduced, whereas the expression of the genes involved in the metabolism of lipids and amino acids was increased in non-vacuolated fibers, indicating early metabolic abnormalities. Additionally, we detected upregulation of autophagy genes, and downregulation of the genes involved in ribosomal and mitochondrial function leading to defective oxidative phosphorylation. The upregulation of the genes associated with inflammation, apoptosis and muscle regeneration was observed only in vacuolated fibers. Notably, enzyme replacement therapy - the only available therapy for the disease - showed a tendency to restore metabolism dysregulation, particularly within slow fibers. A combination of single nuclei RNA sequencing and spatial transcriptomics revealed the landscape of normal and the diseased muscle, and highlighted the early abnormalities associated with the disease progression. Thus, the application of these two new cutting-edge technologies provided insight into the molecular pathophysiology of muscle damage in LOPD and identified potential avenues for therapeutic intervention.

A Laing distal myopathy-associated proline substitution in the ß-myosin rod perturbs myosin cross-bridging activity.

Proline substitutions within the coiled-coil rod region of the ß-myosin gene (MYH7) are the predominant mutations causing Laing distal myopathy (MPD1), an autosomal dominant disorder characterized by progressive weakness of distal/proximal muscles. We report that the MDP1 mutation R1500P, studied in what we believe to be the first mouse model for the disease, adversely affected myosin motor activity despite being in the structural rod domain that directs thick filament assembly. Contractility experiments carried out on isolated mutant muscles, myofibrils, and myofibers identified muscle fatigue and weakness phenotypes, an increased rate of actin-myosin detachment, and a conformational shift of the myosin heads toward the more reactive disordered relaxed (DRX) state, causing hypercontractility and greater ATP consumption. Similarly, molecular analysis of muscle biopsies from patients with MPD1 revealed a significant increase in sarcomeric DRX content, as observed in a subset of myosin motor domain mutations causing hypertrophic cardiomyopathy. Finally, oral administration of MYK-581, a small molecule that decreases the population of heads in the DRX configuration, significantly improved the limited running capacity of the R1500P-transgenic mice and corrected the increased DRX state of the myofibrils from patients. These studies provide evidence of the molecular pathogenesis of proline rod mutations and lay the groundwork for the therapeutic advancement of myosin modulators.

Clinical and Genetic Analysis of Patients With TK2 Deficiency.

Objectives: Thymidine kinase 2 deficiency (TK2d) is a rare autosomal recessive disorder that stems from a perturbation of the mitochondrial DNA maintenance. Nucleoside treatment has recently shown promise as a disease-modifying therapy. TK2d was initially associated with rapidly progressive fatal myopathy in children featuring mitochondrial DNA depletion. Subsequently, less severe variants of the disease were described, with onset of symptoms during adolescence or adulthood and associated with the presence of multiple mtDNA deletions. These less severe phenotypes have been reported in only 15% of the approximately 120 patients described worldwide. However, some reports suggest that these juvenile and adult-onset presentations may be more common. The objective of this study was to describe the clinical phenotype in a sample of patients from Spain. Methods: This study includes 53 patients harboring biallelic TK2 pathogenic variants, compiling data retrospectively from 7 Spanish centers. We analyzed allele frequency, investigated the most recent common ancestor of core haplotypes, and used the Runs of Homozygosity approach to investigate variant coalescence. Results: Symptom onset distribution revealed that 32 patients (60%) experienced symptoms beyond 12 years of age. Approximately 30% of patients died of respiratory insufficiency, while 56% of surviving patients needed mechanical ventilation. Genetic analysis identified 16 distinct variants in TK2. Two variants, p.Lys202del and p.Thr108Met, exhibited significantly higher prevalence in the Spanish population than that reported in gnomAD database (86-fold and 13-fold, respectively). These variants are estimated to have originated approximately 16.8 generations ago for p.Thr108Met and 95.2 generations ago for p.Lys202del within the Spanish population, with the increase in frequency attributed to various forms of inbreeding. In late-onset cases, 46.9% carried the p.Lys202del variant. Discussion: The higher frequency of TK2d in Spain can be partially attributed to the increased prevalence of 2 variants and consanguinity. Notably, in 60% of the cohort, the disease was late-onset, emphasizing the potential underdiagnosis of this subgroup of patients in other regions. Raising awareness of this potentially treatable disorder is of utmost importance because early interventions can significantly affect the quality of life and survival of affected individuals.

EURO-NMD registry: federated FAIR infrastructure, innovative technologies and concepts of a patient-centred registry for rare neuromuscular disorders.

BACKGROUND: The EURO-NMD Registry collects data from all neuromuscular patients seen at EURO-NMD's expert centres. In-kind contributions from three patient organisations have ensured that the registry is patient-centred, meaningful, and impactful. The consenting process covers other uses, such as research, cohort finding and trial readiness. RESULTS: The registry has three-layered datasets, with European Commission-mandated data elements (EU-CDEs), a set of cross-neuromuscular data elements (NMD-CDEs) and a dataset of disease-specific data elements that function modularly (DS-DEs). The registry captures clinical, neuromuscular imaging, neuromuscular histopathology, biological and genetic data and patient-reported outcomes in a computer-interpretable format using selected ontologies and classifications. The EURO-NMD registry is connected to the EURO-NMD Registry Hub through an interoperability layer. The Hub provides an entry point to other neuromuscular registries that follow the FAIR data stewardship principles and enable GDPR-compliant information exchange. Four national or disease-specific patient registries are interoperable with the EURO-NMD Registry, allowing for federated analysis across these different resources. CONCLUSIONS: Collectively, the Registry Hub brings together data that are currently siloed and fragmented to improve healthcare and advance research for neuromuscular diseases.