Proof of concept that targeted exon removal could restore dystrophin expression in vivo was demonstrated in mdx mice (Mann et al. 2001), a dog model of DMD (Yokota et al. 2009) and more recently in DMD patients (van Deutekom et al. 2007; Kinali et al. 2009; Cirak et al. 2011; Goemans et al. 2011). This evidence concerns the gene DMD and Duchenne muscular dystrophy.