DUX4 and Facioscapulohumeral dystrophy: However, as pathways that associate DUX4 expression to the FSHD muscle pathogenesis are not defined, identification of biomarkers of FSHD muscle function remain critical for understanding the process leading to the pathology but also for the definition of readouts to be used for drug design, outcome measures, and monitoring of therapies aimed at correcting the functional defect.