St. Jude Children's Research Hospital Aug 13 2025 Spinal muscular atrophy (SMA) is a rare genetic condition that causes progressive muscle weakness, which, when untreated, prevents infants with the most severe form from gaining motor development - never gaining the ability to sit - and typically leads to death before 2 years of age. The oral drug risdiplam benefits symptomatic patients with improved motor function and increased survival, but had only been Food and Drug Administration–approved