A subsequent study [61] designed to measure the relative abundance of the DUX4-fl and DUX4-s mRNAs in skeletal muscle cells and muscle biopsies showed that the control biopsies expressed very low amounts of the DUX4-s transcript encoding the truncated protein, whereas the FSHD samples expressed very low amounts of the DUX4-fl and sometimes the DUX4-s as well, indicating that the DUX4-fl mRNA was correlated with FSHD and might be a cause for FSHD. Here, DUX4 is linked to facioscapulohumeral muscular dystrophy.