Symptom onset and cellular pathology in facioscapulohumeral muscular dystrophy is accelerated by cigarette smoking

Facioscapulohumeral muscular dystrophy (FSHD) is an incurable skeletal myopathy. In absence of therapy, lifestyle factors impacting disease progression are important for clinical management. Monozygotic twins with FSHD often exhibit dramatically different disease progression, indicating existence of environmental disease modifiers. Here we analyse the USA National Registry for Myotonic Dystrophy & Facioscapulohumeral Dystrophy, comprising 511 FSHD1 patients followed up annually for an average of 8 years. This multimodal, longitudinal dataset comprises 189 baseline and 37 annually assessed features. We developed a workflow for prospective cohort analysis and identify cigarette smoking as associated with a two-fold increase in risk of facial and lower limb involvement in FSHD1 patients. Our definition of lower limb involvement includes inability to run and climb steps unaided, important functional outcomes for FSHD patients. We then employed an assay to test the effects of cigarette smoke extract on human myoblasts in vitro. Cigarette smoke extract drove disproportionate defects in proliferation and myogenic differentiation of FSHD1 patient-derived myoblasts, compared to matched controls. Mitochondrial function was also inordinately affected in FSHD1 myoblasts exposed to cigarette smoke extract, with increased mitochondrial membrane potential and mitochondrial radical oxygen species (mitoROS) generation. Our findings support recommending smoking cessation in clinical management of FSHD. ### Competing Interest Statement JS is a consultant or serves on advisory board for Fulcrum, Dyne, Acceleron, Avidity, MT Pharma, Arrowhead, Vectiv Bio, and Sarepta. The other authors declare no conflicts of interest. ### Funding Statement We acknowledge support of the FSHD Society (FSHDFall2019-05482908070 to CRSB and PSZ). CRSB was supported by the Turing-Roche Partnership. PH was funded by the Medical Research Council (MR/P023215/1) and then by an Erwin Schroedinger post-doctoral fellowship awarded by the Austrian Science Fund (FWF, J4435-B), supported by Friends of FSH Research (Project 936270) and the FSHD Society (FSHD-Fall2020-3308289076), and is currently funded by the Medical Research Council (MR/X001520/1). The Zammit laboratory also receives support from Muscular Dystrophy UK, SOLVE FSHD and the Wellcome Trust. JS is supported by NINDS, FSHD Society, Friends of FSH Research, MDA, and FSHD Canada. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The USA FSHD data has been previously described (26, 72). Briefly de-identified data was collected on individuals participating in USA FSHD Registry located at the University of Rochester Medical Center in Rochester, New York (https://www.urmc.rochester.edu/neurology/national-registry.aspx). All de-identified data used in this study are available upon request from the USA FSHD Registry. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All de-identified data used in this study are available upon request from the USA FSHD Registry within the remit of informed consent (https://www.urmc.rochester.edu/neurology/national-registry.aspx). All anonymised data, code, and materials used in this study will be made available on reasonable request subject to suitable materials transfer agreements (MTAs).