SMN2 and proximal spinal muscular atrophy: Importantly, these findings were replicated in human SMA patient fibroblasts, as well as in the Taiwanese severe SMA mouse model (Smn-/-; SMN2tg/0) – animals carrying the Hung targeted deletion of murine Smn and a human SMN2 transgene (Hsieh-Li et al., 2000; Custer and Androphy, 2014).