A Phase 3 interventional study of Apitegromab and Placebo in Spinal Muscular Atrophy, Spinal Muscular Atrophy Type 3 and Spinal Muscular Atrophy Type 2, sponsored by Scholar Rock, Inc.. Completed at 50 sites in 9 countries. Open to participants aged 2 Years to 21 Years. Per ClinicalTrials.gov, last updated 2026-01-22.
Sponsored by Scholar Rock, Inc. · Phase 3, Interventional, and Treatment
This Phase 3 trial (Study SRK-015-003) was conducted in patients ≥2 years old at Screening, who were previously diagnosed with later-onset spinal muscular atrophy (SMA) (i.e., Type 2 and Type 3 SMA) and were receiving an approved survival motor neuron (SMN) upregulator therapy (i.e., either nusinersen or risdiplam), to confirm the efficacy and safety of apitegromab as an adjunctive therapy to nusinersen and evaluate the efficacy and safety of apitegromab as an adjunctive therapy to risdiplam.
Receiving one background therapy for SMA (i.e., either nusinersen or risdiplam) for the time period specified below and anticipated to remain on that same treatment throughout the trial:
Exclusion Criteria:
Aged 2-12 years at Screening. Participants were randomized to receive apitegromab 10 mg/kg for up to 52 weeks.
Drug: Apitegromab
Aged 2-12 years at Screening. Participants were randomized to receive apitegromab 20 mg/kg for up to 52 weeks.
Drug: Apitegromab
Aged 2-12 years at Screening. Participants were randomized to receive placebo for up to 52 weeks.
Drug: Placebo
Aged 13-21 years at Screening. Participants were randomized to receive apitegromab 20 mg/kg for up to 52 weeks.
Drug: Apitegromab
Aged 13-21 years at Screening. Participants were randomized to receive placebo for up to 52 weeks.
Drug: Placebo
Apitegromab is a fully human anti-proMyostatin monoclonal antibody (mAb) of the immunoglobulin G4 (IgG4)/lambda isotype that specifically binds to human pro/latent myostatin with high affinity inhibiting myostatin activation. SRK-015 was administered every 4 weeks by intravenous (IV) infusion.
Also known as: SRK-015
Placebo was administered every 4 weeks by intravenous (IV) infusion.
Main Efficacy Population: Change from Baseline in Hammersmith Functional Motor Scale Expanded (HFMSE) total score.
The HFMSE assesses the physical abilities of patients with Type 2 and Type 3 SMA. It comprises of 33 items graded on a scale of 0, 1, or 2, where 0 denotes unable, 1 denotes performed with modification or adaptation, and 2 denotes performed without modification or adaptation. The overall score is the sum of the scores for all activities with a maximum achievable score of 66. Higher scores indicate increased motor function.
Time frame: Baseline up to 12 months.
Main Efficacy Population: Change from Baseline in Revised Upper Limb Module (RULM) total score.
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. 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 maximum score achievable is 37. Higher scores increased great upper limb function.
Time frame: Baseline up to 12 months.
Main Efficacy Population: Proportion of patients with ≥3-point change from Baseline in Hammersmith Functional Motor Scale Expanded (HFMSE) total score.
The HFMSE assesses the physical abilities of patients with Type 2 and Type 3 SMA. It comprises of 33 items graded on a scale of 0, 1, or 2, where 0 denotes unable, 1 denotes performed with modification or adaptation, and 2 denotes performed without modification or adaptation. The overall score is the sum of the scores for all activities with a maximum achievable score of 66. Higher scores indicate increased motor function.
Time frame: Baseline up to 12 months.
Main Efficacy Population: Change from Baseline in number of WHO motor development milestones attained at 12 months.
Time frame: Baseline up to 12 months.
Main Efficacy Population and Exploratory Subpopulation combined: Incidence of Treatment Emergent Adverse Events (TEAEs) and Severe Adverse Events (SAEs) by severity.
Time frame: Baseline up to 12 months.
Main Efficacy Population and Exploratory Subpopulation combined: Apitegromab concentrations in serum from blood samples.
Time frame: Baseline up to 12 months.
Main Efficacy Population and Exploratory Subpopulation combined: Circulating latent myostatin concentrations in blood samples.
Time frame: Baseline up to 12 months.
Main Efficacy Population and Exploratory Subpopulation combined: Presence or absence of Antidrug Antibody (ADA) against apitegromab in serum from blood samples.
Time frame: Baseline up to 12 months.
Plan to share: No
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Scholar Rock, Inc.