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 balanced age distribution and broad mutation eligibility, excluding only exons 8, 9, or 10 deletions or point mutations.

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

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

• Microdystrophin biomarker data was collected from 30 patients, interim safety from 31, and 12-month functional data from nine patients aged four and older.

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

Efficacy and biomarker results

• The trial met its primary endpoint: 93% of patients achieved >10% microdystrophin expression at week 12 (p<0.0001), with 80% exceeding 40%.

• Average microdystrophin expression was 71.1% overall and 41.6% in boys aged eight and older, the highest reported for this age group.

• Statistically significant correlation (coefficient >0.9) between microdystrophin expression and functional improvement on NSAA and other functional tests.

• Functional improvements at 12 months were observed in all age groups, outperforming external controls on NSAA and timed function tests.

• Caregivers reported improved function in daily activities and home/community settings at 12 months.

Safety profile

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

• No drug-related thrombocytopenia, myositis, or neurotoxicity reported; most adverse events were mild or moderate and resolved.

• Liver safety profile was favorable, with mean GGT and bilirubin levels stable and below upper limits of normal up to 12 months.

• Proactive immunosuppressive regimen, including eculizumab and sirolimus, was well-tolerated and considered a differentiator for safety.

• Investigators expressed confidence in the safety and predictability of the regimen, noting positive experiences for patients and families.