The purpose of this 52-week phase 2 study is to evaluate the safety and efficacy of SRK-015 on motor function in individuals with SMA Types 2 and 3 who are 2-21 years old. 

SRK-015 is a fully human anti-proMyostatin monoclonal antibody under investigation for the treatment of later-onset SMA. 

This multicenter study includes three Cohorts at 16 study sites in the United States and Europe. Cohort 1 (n=23) enrolled ambulatory Type 3 subjects, some of whom were not receiving any approved SMN up-regulator and some receiving an approved SMA treatment that was started after the subject turned 5 years old. Cohort 2 (n=15) enrolled Type 2 and non-ambulatory Type 3 subjects receiving an approved SMN up-regulator that was started after the subject turned 5 years old. Cohort 3 (n=20) enrolled Type 2 subjects who started on an approved SMN up-regulator before they turned 5 years old. Subjects receive SRK-015 every 4 weeks via intravenous infusion. Cohorts 1 and 2 receive 20 mg/kg SRK-015 and Cohort 3 subjects are randomized 1:1 in double-blind manner to 2 mg/kg or 20 mg/kg SRK-015. The primary efficacy endpoint for Cohort 1 is change in baseline Revised Hammersmith Scale scores. The primary efficacy endpoint for Cohorts 2 and 3 is change in baseline Hammersmith Functional Motor Scale Expanded scores. Safety is assessed throughout the trial by a Safety Surveillance Team. Blood samples are being obtained for measuring plasma SRK-015 concentrations and circulating latent myostatin concentrations.

The results of an interim analysis will include the safety, efficacy,  pharmacokinetics and pharmacodynamics of SRK-015, along with demographic and baseline characteristics of enrolled subjects.

Final conclusions will be based on data from the 12 month treatment period, which are anticipated in the first half of 2021.