SMCHD1 and facioscapulohumeral muscular dystrophy: We found that most of the repeat-initiated transcripts we tested are expressed in myotube cells derived from an FSHD2 patient where disease-causing mutations result in de-repression of endogenous DUX4, whereas we did not observe these transcripts in control myotubes that do not express DUX4. This indicates that the low level of endogenous DUX4 present in FSHD muscle cells is sufficient to transcriptionally activate the same endogenous repetitive elements identified by our over-expression studies described above.