In Q4 2025, Taysha Gene Therapies reported dosing the first of 15 female patients (aged 6 to <22 years) in its open-label REVEAL pivotal trial of TSHA-102 for Rett syndrome. The single intrathecal administration delivers 1×10^15 vector genomes and targets the developmental plateau population. Enrollment is ongoing at multiple U.S. and European sites, and a six-month interim analysis of response rate—defined as gain or recovery of at least one of 28 standardized developmental milestones—is designed to support a Biologics License Application (BLA).

Taysha secured written agreement from the FDA to include a minimum of three months of safety data from its ASPIRE trial (N=3 females, aged 2 to <4 years) in the planned BLA. ASPIRE will evaluate high-dose TSHA-102 scaled for lower brain volume in younger patients, with efficacy extrapolated from REVEAL data. This alignment supports a label covering patients aged ≥2 years and reflects Agency concurrence on trial design and data package composition following a Type D meeting.

The Company expects to complete dosing in both REVEAL and ASPIRE in Q2 2026. Additionally, longer-term safety and efficacy results from Part A of its Phase 1/2 REVEAL trial are slated for release in H1 2026. These readouts will include six-month follow-up on developmental milestone gains and safety endpoints, providing critical evidence for TSHA-102’s risk-benefit profile ahead of BLA submission.

With an estimated 15,000–20,000 Rett syndrome patients across the U.S., EU and U.K., Taysha sees a significant opportunity to redefine the treatment paradigm for this severe monogenic disorder. TSHA-102’s novel miRARE technology aims to regulate MECP2 expression cell-by-cell, reducing overexpression risk. The program’s multiple FDA designations—Breakthrough Therapy, Regenerative Medicine Advanced Therapy, Fast Track, Orphan Drug and Rare Pediatric Disease—underscore the potential for accelerated development and broad regulatory support.