DUX4 and Facioscapulohumeral dystrophy: MDC1A is due to mutation of an extracellular protein (laminin-a2), whereas LGMD2D is due to mutation of a sarcolemmal protein (a-sarcoglycan) and FSHD is due to genetic and epigenetic alterations that lead to aberrant expression of a nuclear transcription factor (DUX4-FL).