


Diagnosed with later-onset SMA (i.e., Type 2 and Type 3 SMA) before receiving an approved SMN upregulator therapy (i.e., either nusinersen or risdiplam).Males and females 2 through 21 years old at Screening.Main Efficacy Population and Exploratory Subpopulation combined: Presence or absence of ADA against apitegromab in serum from blood samples.

Main Efficacy Population and Exploratory Subpopulation combined: Circulating latent myostatin concentrations in blood samples.Main Efficacy Population and Exploratory Subpopulation combined: Apitegromab concentrations in serum from blood samples.Main Efficacy Population and Exploratory Subpopulation combined: Incidence of Treatment Emergent Adverse Events (TEAEs) and Severe Adverse Events (SAEs) by severity.Main Efficacy Population: Change from Baseline in number of WHO motor development milestones attained at 12 months.Higher scores increased great upper limb function. The 19 scored items assess functions that relate to everyday life, such as pressing a button and picking up a token these items are scored 0, 1, or 2, where 0 denotes unable, 1 denotes able with modification, and 2 denotes able with no modification. The RULM is a 20 item assessment of upper limb function in nonambulatory patients with SMA that was performed for patients who were 30 months of age or older at baseline. Why Should I Register and Submit Results?.
