SMN2 and proximal spinal muscular atrophy: Risdiplam — a small-molecule splice-switcher and the most recently approved SMN-augmenting agent to be added to the arsenal of SMA therapies — is reported to modulate SMN2 splicing systemically but has only relatively modest effects on boosting the protein, raising plasma SMN levels in treated types I and II patients by approximately 2.5-fold (66, 67) and muscle SMN of mutant mice by 210% (68).