RecruitingPhase 4Drug trialA Study Evaluating the Effectiveness and Safety of Risdiplam Administered in Pediatric Patients With Spinal Muscular Atrophy Who Experienced a Plateau or Decline in Function After Gene TherapyThis is an open-label, single-arm, multicenter clinical study to evaluate the effectiveness and safety of risdiplam administered in pediatric participants with SMA and 2 SMN2 copies who previously received onasemnogene abeparvovec and experience a plateau or decline in function. Participants to be enrolled are children \<2 years of age genetically diagnosed with SMA.