SRK-015 is a fully human anti-proMyostatin monoclonal antibody (mAb) that selectively binds to pro-/latent myostatin with high affinity, inhibiting the proteolytic activation of the growth factor. SRK-015 is being developed for the treatment of spinal muscular atrophy (SMA) by targeting muscle atrophy and improving muscle strength, with the aim of offering clinically meaningful improvements in motor function. Pre-clinical studies demonstrated selective inhibition of myostatin activation, effectively increasing muscle mass and function in a SMA mouse model. No toxicologically significant findings were observed for SRK-015 in rats and non-human primates. A Phase 1, healthy volunteer study demonstrated a favorable safety profile of SRK-015 administered intravenously (IV) at all doses tested. The ongoing Phase 2 study evaluates the safety and efficacy of SRK-015 dosed IV every four weeks over a 12-month treatment period; Three distinct and parallel cohorts were enrolled. Cohort 1 enrolled 20 patients (5-21 years old) with ambulatory Type 3 SMA and were treated with 20 mg/kg of SRK-015 as monotherapy or in conjunction with an approved SMN up-regulator. The primary objectives are to assess safety and the mean change from baseline in the Revised Hammersmith Scale (RHS). Cohort 2 enrolled 15 patients (5-21 years old) with Type 2 or non-ambulatory Type 3 SMA, who were already treated with an approved SMN up-regulator. Patients were treated with 20 mg/kg of SRK-015. The primary objectives are to assess safety and the mean change from baseline in Hammersmith Functional Motor Scale Expanded (HFMSE). Cohort 3 enrolled 20 patients with Type 2 SMA, who were at least 2 years old and initiated treatment with an approved SMA up-regulator before turning five. Patients were randomized 1:1 to either 2 mg/kg or 20 mg/kg of SRK-015. The primary objectives are to assess safety and the mean change from baseline in HFMSE.