SMN2 and proximal spinal muscular atrophy: Moreover, severe SMA mice (Smn−/−; SMN2+/+) had a very modest increase in the survival (16.7%) and bw (33.3% increase from post natal day 2 to post natal day 5) and this could be for many reasons: low ASO doses, multiple cerebral cannulations, delayed initial treatment and potential CNS toxicity from this chemistry 18.