Gene Therapy Shows Promise for Spinal Muscular Atrophy in Children and Teens
Phase 3 trial demonstrates significant motor function improvements with single intrathecal dose of onasemnogene abeparvovec.
Summary
The STEER phase 3 trial evaluated a one-time gene therapy for spinal muscular atrophy (SMA) in 126 treatment-naive patients aged 2-18 years who could sit but never walked independently. Participants received either intrathecal onasemnogene abeparvovec (OAV101 IT) or a sham procedure. After 52 weeks, those receiving gene therapy showed significantly improved motor function scores compared to controls, with similar safety profiles between groups.
Detailed Summary
Spinal muscular atrophy (SMA) is a devastating genetic neuromuscular disease caused by mutations in the SMN1 gene, leading to progressive muscle weakness and motor neuron loss. While existing treatments like nusinersen and risdiplam require lifelong administration, researchers have been developing one-time gene therapies that could provide sustained benefits.
The STEER trial was a 52-week, randomized, double-blind study conducted across 29 sites in 14 countries. It enrolled 126 treatment-naive patients aged 2-18 years with SMA who could sit independently but had never walked. Participants were randomly assigned to receive either a single intrathecal injection of onasemnogene abeparvovec (OAV101 IT) at a dose of 1.2 × 10^14 vector genomes (n=75) or a sham procedure (n=51).
The primary endpoint was the change in Hammersmith Functional Motor Scale-Expanded (HFMSE) scores from baseline to week 52. Results showed that patients receiving OAV101 IT demonstrated a statistically significant improvement in motor function compared to the sham group, with a least squares mean difference of 1.88 points (95% CI: 0.51-3.25; P=0.0074).
Safety analysis revealed similar rates of adverse events, serious adverse events, and adverse events of special interest between the two groups. Transaminase elevations were infrequent and mostly low-grade and transient. Notably, only two participants in the treatment group and one in the sham group developed sensory symptoms, addressing previous concerns about potential dorsal root ganglia effects observed in animal studies.
These findings represent a significant advancement in SMA treatment, offering the potential for a one-time therapeutic intervention that could provide sustained motor function benefits across a broader age range than currently available gene therapies. The fixed intrathecal dosing approach may overcome weight and age limitations of existing treatments while reducing systemic exposure to viral vectors.
Key Findings
- Single intrathecal gene therapy dose significantly improved motor function scores by 1.88 points vs sham
- Treatment showed similar safety profile to sham procedure with acceptable adverse event rates
- Transaminase elevations were infrequent, low-grade, and transient in most cases
- Only 2 treatment patients vs 1 sham patient developed sensory symptoms
- 122 of 126 participants completed the full 52-week study period
Methodology
Phase 3, randomized, double-blind, sham-controlled trial with 126 treatment-naive SMA patients aged 2-18 years across 29 international sites. Primary endpoint was change in Hammersmith Functional Motor Scale-Expanded scores over 52 weeks.
Study Limitations
Study limited to treatment-naive patients who could sit but never walked independently. Long-term durability beyond 52 weeks requires further investigation. Generalizability to other SMA phenotypes remains to be established.
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