The primary endpoint was safety, assessed by the number of patients reporting adverse events, treatment-related adverse events, severe adverse events, and adverse events of special interest.¹ 

The secondary endpoint was efficacy, which included change from baseline in Hammersmith Functional Motor Scale — Expanded (HFMSE) total score and change in Revised Upper Limb Module (RULM) total score at 52 weeks.¹ 

HFMSE is a 66-point scale that measures gross motor functions like sitting, standing, rolling, crawling, and walking. It’s an expanded version of HFMS, which was developed specifically for SMA types 2 and 3.^2,3 RULM is a 37-point assessment of motor function performance in the upper limbs for individuals with SMA.¹

Key inclusion criteria¹:

• Genetic confirmation of SMA based on biallelic loss of function due to SMN1 deletion or mutations and any number of copies of SMN2 

• 2 to <18 years of age 

• Able to sit independently* but have never taken steps

• Diagnosed through newborn screening or onset of signs and symptoms at <18 months of age 

• Received at least 4 loading doses of nusinersen or at least 3 months of treatment with risdiplam at screening

Key exclusion criteria¹:

• Elevated anti-AAV9 antibody titers (>1:50) or any validated result consistent with being elevated

• Clinically significant abnormalities in test results during screening 

• Contraindications for lumbar puncture procedure 

• Nusinersen dose within 4 months, or risdiplam dose within 15 days, prior to baseline

• Presence of an infection or febrile illness up to 30 days prior to administration

*Independent sitting is defined as sitting up straight with the head erect for at least 10 seconds without using arms or hands to balance the body or support the position.¹