Exploring the Physiologic, Pharmacodynamic, and Clinical Responses of Skeletal Muscle in Patients With Spinal Muscular Atrophy Treated With SMN-Directed Therapies

In this observational study, researchers are looking at the effects of spinal muscular atrophy (SMA) drugs on the muscles and nerve cells in patients with SMA. Primary Objectives * To evaluate the feasibility and reliability of performing MR functional imaging in exercising muscle in patients with SMA. * To evaluate patients with SMA types 2 and 3 at baseline and longitudinally at 6 and 12 months Secondary Objectives * To describe the MR functional bioenergetics response in muscles in five potential groups of patients with spinal muscular atrophy: untreated, actively treated with nusinersen (Spinraza®) or onasemnogene abeparvovec (Zolgensma®), actively treated with risdiplam (Evrysdi®), switching from Spinraza or Zolgensma to Evrysdi and initiating combination therapy of Spinraza or Zolgensma with Evrysdi . * To identify changes in motor function in patients with SMA types 2 and 3 who initiate treatment with risdiplam. * To obtain biomarkers in blood, urine, and muscle tissue to provide proof-of-concept support for risdiplam effect on skeletal muscle. * To obtain quality of life and disability data from participants in this study.