To investigate in vivo activity, severe SMA mice were generated according to the breeding scheme that produces severe SMA mice (Tg(SMN2)2Hungtg/0; Smn1tm1Hung/tm1Hung) and heterozygous (Het, Tg(SMN2)2Hungtg/0; Smn1tm1Hung/wt) control siblings as described by Gogliotti et al (2010). This evidence concerns the gene SMN2 and proximal spinal muscular atrophy.