Neurogene Inc.

Efficacy Data

•100% of participants improved on the Clinical Global Impression-Improvement (CGI-I) scale and gained ≥1 developmental milestone, consistent with the composite endpoint used to evaluate efficacy in the Embolden™ registrational trial

•47 total developmental milestones were gained across participants, averaging 4.7 milestones per participant

•All participants gained ≥1 developmental milestone in the past 12 months

•Participants gained milestones in a progressive, developmentally ordered stepwise sequence, suggesting a restart of developmental progression

•Rapid onset of treatment effect, with median time to first clinical improvement of 2 months post-treatment

•Milestone gains deepened over time, increasing by 95% from 6 to 12 months and 147% from 6 to ≥12 months

•7 of 10 participants gained ≥2 developmental milestones and demonstrated improvements across ≥2 core Rett syndrome domains; both of these improvements were observed in pediatric and adolescent/adult participants

•Continued improvement through 30 months post-dose, with no plateau observed and no milestones lost

•Participants experienced clinically meaningful improvements across additional validated Rett syndrome scales, including the Rett Syndrome Gross Motor Scale (RSGMS) and Rett Syndrome Hand Function Scale (RSHFS) (p<0.001)