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.
61 studies on the registry are indexed under Spinal Muscular Atrophies of Childhood; 18 are open to participants now.
This study's enrollment of 188 is above the median of 15 across 41 interventional studies indexed under Spinal Muscular Atrophies of Childhood.
Browse Spinal Muscular Atrophies of Childhood studies →Scholar Rock, Inc. is the lead sponsor of 9 studies on the registry; 3 are open to participants now.
Compared within Spinal Muscular Atrophies of Childhood, this study's primary condition as ClinicalTrials.gg classifies it; the registry's first condition term is Muscular Atrophy, Spinal. The counts are of registry records indexed under each term, refreshed daily. How we classify →
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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:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Ways of preventing pregnancy. “Highly effective” methods fail less than 1% of the time a year when used correctly — for example an IUD or an implant.
Criteria usually say which methods count and how long to keep using them after the last dose, sometimes for male participants too. Some studies accept a partner’s vasectomy if it was confirmed successful and that person is the participant’s only sexual partner.
An allergy, or another reaction of the immune system, to a substance. “Hypersensitivity to the study drug” means a known allergic reaction to it — not every side effect a medicine can have.
The other ingredients in a medicine besides the active drug, such as fillers, colours or preservatives.
A drug or device being studied in a clinical trial.
It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.
Contraception
Ways of preventing pregnancy. “Highly effective” methods fail less than 1% of the time a year when used correctly — for example an IUD or an implant.
Criteria usually say which methods count and how long to keep using them after the last dose, sometimes for male participants too. Some studies accept a partner’s vasectomy if it was confirmed successful and that person is the participant’s only sexual partner.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Hypersensitivity
An allergy, or another reaction of the immune system, to a substance. “Hypersensitivity to the study drug” means a known allergic reaction to it — not every side effect a medicine can have.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Excipients
The other ingredients in a medicine besides the active drug, such as fillers, colours or preservatives.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Investigational drug or device
A drug or device being studied in a clinical trial.
It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
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
Ran from Apr 2022 to primary completion in Dec 2024, 32 months.
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Studies of the drug tested here: Apitegromab
Spinal Muscular Atrophies of Childhood →
Scholar Rock, Inc.