DUX4 and Facioscapulohumeral dystrophy: The first study to demonstrate the potential of CRISPR/cas9 for the treatment of FSHD utilized a repurposed Cas9, namely the dead Cas9 (dCas9) (Table 2), fused to the Krüppel-associated box (KRAB, a potent transcriptional repressor that can be fused to heterologous DNA-binding protein repressor (Margolin et al., 1994)) to decrease DUX4 expression (Himeda et al., 2016).