We also showed sensitivity of the assay to detect comparatively low levels of endogenous DUX4 transcript in patient-derived myotubes, and again confirmed probe specificity in these cells as demonstrated by reduced DUX4 signal, as well as DUX4-activated biomarkers (MBD3L2 and PRAMEF12) in FSHD patient cells transfected with U6.miDUX4.405 plasmids. Here, DUX4 is linked to facioscapulohumeral muscular dystrophy.