DUX4 and Facioscapulohumeral dystrophy: In order to investigate the cell intrinsic phenotype of FSHD myocytes, we compared previously characterized two healthy control (CTRL1 and CTRL2) and two representative patient immortalized skeletal myoblast lines (FSHD1 and FSHD2) with robust DUX4 target induction at the late myotube stage (day 11 differentiation) in vitro (Supplemental Fig. S1A)11.