This double-blind, Phase 2, multiple-dose study will be conducted to evaluate the PK/PD, efficacy, safety, and tolerability of apitegromab in subjects \<2 years old with 5q autosomal recessive SMA who have delayed motor milestones for their age attributed to SMA at the discretion of the Investigator or a Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP-INTEND) score \<55.
Is <2 years old at the time of the informed consent
Had a gestational age of ≥35 weeks and gestational body weight ≥2.0 kg at birth
Has confirmed diagnosis of 5q autosomal recessive SMA
Has confirmed presence of SMN2 gene copy(ies)
Nutritional status that is not anticipated to be stable throughout the study or medical necessity for a gastric feeding tube, where most feeds are administered by this route
Major orthopedic issues such as severe scoliosis or severe contractures or interventional procedure, including spine or hip surgery, which is considered to have the potential to substantially limit the ability of the subject to be evaluated on any motor function outcome measures, within 6 months before Screening or anticipated during the study
Any other physical limitations (eg, the subject requires cast for contractures) that would prevent the subject from undergoing motor function outcome measures throughout the study.
Parallel
Apitegromab
DrugApitegromab 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 will be administered every 4 weeks by intravenous (IV) infusion.
Nusinersen
DrugNusinersen is a current standard-of-care SMN therapy that targets the SMN2 gene. It will be administered intrathecally per the prescribing information.
Risdiplam
DrugRisdiplam is a current standard-of-care SMN therapy that targets the SMN2 gene. It will be administered orally per the prescribing information.
Evaluate the PK of apitegromab in subjects <2 years old with SMA
Apitegromab concentrations in serum
Evaluate the PD of apitegromab in subjects <2 years old with SMA
Total latent myostatin concentrations in serum
Evaluate the motor function outcomes (ie, efficacy) due to apitegromab treatment
Change from baseline in the raw score of the Bayley Scale of Infant and Toddler Development, Fourth Edition - Gross Motor Subscale (BSID-4 GMS) at 48 weeks. BSID-4 GMS is a standardized assessment commonly used to evaluate development across 5 domains in infants and young children. It consists of 58 items, scored from 0 to 2 for each item, with higher scores indicating better gross motor development.
Assess the safety and tolerability of apitegromab administered to subjects receiving an SMN therapy
Incidence of TEAEs and SAEs by severity
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