What was reported

At the 5th International Scientific Congress on SMA (Budapest, 11–14 March 2026), Crawford, Sansone, Hagenacker and colleagues from Biogen presented Phase 1 interim safety + exploratory efficacy data for salanersen (BIIB115), an investigational antisense oligonucleotide for SMA.

Mechanism

Salanersen modifies splicing of the SMN2 gene by binding the ISS-N1 region — the same target as nusinersen. The novelty is a redesigned ASO backbone that supports once-per-year intrathecal dosing (vs four times per year for nusinersen).

Phase 1 readout (NCT05575011 / EU CT 2023-505643-39)

• Pediatric participants (0.5–12 y) previously treated with onasemnogene abeparvovec with suboptimal clinical status
• Doses tested: 40 mg and 80 mg
• 70% reduction in plasma neurofilament light by Day 180, sustained over time (in those with elevated baseline)
• 4 of 8 participants (50%) achieved new WHO motor milestones beyond what would be expected
• Mean improvements: HFMSE +3.3 points · RULM +5.3 points

Salanersen was generally well tolerated at both dose levels.

Phase 3 design

The presenters described Phase 3 studies being initiated to evaluate the 80 mg dose (once-yearly).

Why this matters

If Phase 3 confirms Phase 1 trends, salanersen could replace four-times-yearly nusinersen administration with a single annual procedure — substantially reducing the procedure burden on children and adults receiving intrathecal SMA therapy. It would also expand the SMN-restoring options available post-Zolgensma.

This is a third-party report of investigational data presented at the congress. Salanersen is not approved.