SMN2 and proximal spinal muscular atrophy: One of the first report about this mechanism is the study by Singh et al., 2013 who, by using cells from patients affected by spinal muscular atrophy (SMA), demonstrated the effectiveness of an ASO in correcting SMN2 exon 7 splicing, via the sequestration of the 3′ strand of an unique intra-intronic structure termed internal stem through LDI-1 (ISTL1) (Singh et al., 2013).