An Active Treatment Study of SRK-015 in Patients With Type 2 or Type 3 Spinal Muscular Atrophy

Inclusion Criteria: * Age 5 through 21 years old at the time of screening for Cohorts 1 and 2; Age ≥2 years old at the time of screening for Cohort 3. * Documented diagnosis of 5q SMA. * Diagnosed as later-onset (e.g., Type 2 or Type 3) SMA prior to receiving any treatment with therapy approved for SMA. * Non-ambulatory patients must be able to sit independently (sits up straight with head erect for at least 10 seconds; does not use arms or hands to balance body or support position) per World Health Organization (WHO) motor milestones definition at screening. * Ambulatory patients must have the ability to independently ambulate without aids or orthotics over 10 meters in 30 seconds or less at screening. * Receiving the same background SMA therapy (e.g., on an approved survival motor neuron (SMN) upregulator therapy such as nusinersen, or not on any SMA therapy) for at least 6 months prior to screening and anticipated to remain on that therapy throughout the duration of the study. * If receiving the SMN upregulator therapy nusinersen, must have completed the loading regimen and initiated maintenance dosing (i.e., completed at least one maintenance dose) with at least 4 weeks after the first maintenance dose having elapsed prior to screening. * Nutritional status stable over the past 6 months and anticipated to be stable throughout the duration of the study. * Have no physical limitations that would prevent the patient from undergoing motor function outcome measures through…