They started by characterizing natural mutations in F9 exon 5, CFTR exon 12 and SMN2 exon 7 associated with exon skipping in Hemophilia B, Cystic fibrosis (CF), and Spinal muscular atrophy (SMA), respectively and then tried its therapeutic splicing rescue by using different ExSpeU1s. This evidence concerns the gene SMN2 and proximal spinal muscular atrophy.