Regenxbio (RGNX) Study result summary

Study design and patient population

• AFFINITY DUCHENNE pivotal phase III trial enrolled 31 ambulatory boys aged one year or older, with broad mutation eligibility except exons 8–10 deletions or point mutations.

• Participants included 11 aged 1–3, 9 aged 4–7, and 11 aged 8+, with mean age at dosing from 3.3 to 10.7 years.

• Over 50 patients have been dosed across pivotal and confirmatory studies, aiming for 60 by mid-year.

• Baseline functional scores (NSAA, time to stand, walk, climb) were recorded for all age groups.

• Confirmatory study enrollment is ongoing, targeting a robust safety and efficacy database for regulatory submission.

Efficacy and biomarker results

• RGX-202 met its primary endpoint: 93% of patients achieved >10% microdystrophin expression at Week 12 (p<0.0001).

• 80% achieved >40% microdystrophin expression; mean expression was 71.1% overall and 41.6% in boys aged 8+.

• Statistically significant correlation (coefficient >0.9) between microdystrophin expression and functional improvement (NSAA) was observed.

• Functional improvements at 12 months exceeded external controls on NSAA and timed function tests, including in older patients.

• RGX-202 is the first gene therapy for Duchenne to show strong, statistically significant biomarker-function correlation.

Safety profile and immunosuppression

• RGX-202 was well-tolerated; two treatment-related serious adverse events (subacute myocarditis, liver injury) resolved without sequelae.

• No drug-related thrombocytopenia, myositis, or neurotoxicity reported; liver safety profile was favorable with stable enzyme levels.

• Most common adverse events were mild to moderate and resolved fully.

• Immunosuppression regimen, including eculizumab and sirolimus, was proactively implemented and well-tolerated.

• Safety database is expected to exceed 50 patients by filing, meeting regulatory expectations.