Metabolomics Reveals Multiple Metabolic Alterations and Biomarkers of Disease Severity in Facioscapulohumeral Muscle Dystrophy

Background Facioscapulohumeral muscular dystrophy type 1 (FSHD1) is one of the most common adult‐onset myopathies and is causally associated with a contraction of the D4Z4 macrosatellite repeat array on chromosome 4. It presents with a variable pattern of progressive muscle weakness affecting the face, shoulder girdle and lower limbs. Pathophysiological mechanisms remain incompletely understood, and no effective treatments are available. Moreover, the lack of validated biomarkers limits the assessment of disease progression and therapeutic effects in clinical trials. Metabolic dysfunction has been hypothesized as a contributing factor, yet remains poorly explored. Methods In this multicentre, observational, cross‐sectional case–control study, we performed quantitative plasma metabolomics by mass spectrometry in 57 patients (age: 41.8 ± 11.9; females/males ratio: 1.04) with mild to moderate facioscapulohumeral muscular dystrophy (FSHD clinical score 6.4 ± 2.6) and age‐ and sex‐comparable controls (age: 41.1 ± 11.2; females/males ratio: 1.13) recruited from three tertiary neuromuscular reference centres. We restricted inclusion to patients with preserved ambulatory capacity to better capture systemic metabolic alterations not primarily driven by advanced disability. We analysed the data using an integrative framework combining univariate and multivariate analyses with five machine‐learning classifiers. Results We identified 57 circulating metabolites discriminating patients from controls, suggesting systemic perturbations in nitric oxide, mitochondrial and one‐carbon metabolism, as well as oxidative stress, muscle mass maintenance and lipid membrane remodelling. Notably, decreased creatinine (fold change in patients vs. controls: 0.754; FDR‐corrected p = 0.000003) and increased asymmetric dimethylarginine (ADMA; fold change in patients vs. controls: 1.168; FDR‐corrected p = 0.000704) emerged as the most significantly altered metabolites, both showing strong correlations with clinical neuromuscular functional scores, including muscle strength (creatinine ρ = 0.62, p = 0.0001; ADMA ρ = 0.34, p = 0.0124), facioscapulohumeral muscular dystrophy severity score (creatinine ρ = 0.53, p = 0.0001; ADMA ρ = 0.32, p = 0.0145) and the daily activity limitation ACTIVLIM scale (creatinine ρ = 0.38, p = 0.0035; ADMA ρ = 0.35, p = 0.008). Plasma levels of GDF15, a biomarker commonly used to support the diagnosis of mitochondrial diseases, were modestly but significantly elevated in patients versus controls (542.3 pg/mL ± 277.2 vs. 444.4 pg/mL ± 164.5, p = 0.043). Further analysis of a predefined mitochondria‐related metabolite panel showed coordinated alterations involving mitochondrial metabolic pathways and discriminated FSHD1 patients from controls (best AUC = 0.83). Conclusions These findings highlight systemic metabolic disturbances already detectable in mild‐to‐moderate stages of facioscapulohumeral muscular dystrophy, identifying creatinine and ADMA as promising biomarkers of disease severity, and expand current knowledge of disease pathophysiology. Trial Registration: ClinicalTrials.gov identifier: NCT06086548