Background/Aims: Facioscapulohumeral muscular dystrophy (FSHD) is one of the most prevalent muscular dystrophies. It is marked by progressive and asymmetric weakness and atrophy predominant in facial, shoulder girdle and upper arm muscles. FSHD is driven by the abnormal activation of DUX4 in skeletal muscle. Abnormal DUX4 expression disrupts muscle cell function through processes like apoptosis, oxidative stress, and inflammation, yet its full impact remains incompletely understood, with limited in vivo validation.    This study aims to understand the biological pathways involved in FSHD by single-nuclei RNA sequencing (snRNA-seq) on human skeletal muscle biopsies. Through this approach, we intend to identify disease-specific gene signatures and dysregulated pathways. This can inform new biomarkers for disease monitoring and discovery of new therapeutic targets.     Skeletal muscle biopsy samples have been collected from healthy individuals and FSHD patients, followed by snRNA-seq performed to explore the transcriptomic landscape of individual muscle cells. FSHD muscles are stratified according to their magnetic resonance signal, showing either active (STIR+) or inactive (STIR-) disease.   

Conclusions: Preliminary analyses have shown an increased prevalence of slow-twitch myonuclei, alongside endothelial cells and fibro-adipogenic progenitor cells (FAPs) in FSHD patients compared to healthy individuals.  This study is the initial step towards understanding the molecular and cellular mechanisms driving FSHD using a multi-omic approach. Preliminary findings indicate a higher amount of slow-twitch myonuclei and FAPs, which implies a shift in cell-type in the disease. Using this approach, this research intends to understand disease-specific biomarkers at different stages and aid in treatment development.