ACTA1 and facioscapulohumeral muscular dystrophy: By contrast, our aged chronic FSHD-like mouse models based on the ACTA1-MCM;FLExD/+ bi-transgenic animals more accurately recapitulate FSHD pathogenic mechanisms and pathophysiology, and are thus ideally suited to identify disease biomarkers, study potential disease mechanisms and determine the effects of potential therapeutics.