In the fourth quarter of 2025, Taysha dosed the first patient in its single-arm, open-label REVEAL pivotal trial of TSHA-102 in Rett syndrome. The trial is evaluating a one-time intrathecal administration of high-dose TSHA-102 (1×1015 vector genomes) in 15 female patients aged 6 to under 22 years who have reached the developmental plateau phase of the disease. Enrollment is underway across multiple U.S. and European clinical sites, with each patient serving as their own control. The primary endpoint—a response rate defined by gain or regain of at least one of 28 natural history–defined developmental milestones—is supported by a planned six-month interim analysis that may form the basis of a Biologics License Application submission.

Taysha secured written alignment from the FDA to include a minimum of three months of safety data from its ASPIRE trial in the planned BLA submission. ASPIRE is a safety-focused study enrolling three females aged 2 to under 4 years, evaluating the same high-dose TSHA-102 formulation scaled for lower brain volume. While efficacy in this younger cohort will be extrapolated from REVEAL pivotal trial outcomes, the FDA’s agreement enables Taysha to seek a label covering patients aged two years and older, potentially broadening access to an estimated 15,000–20,000 Rett syndrome patients in the U.S., EU and U.K.

Taysha anticipates completing dosing in both the REVEAL pivotal trial and the ASPIRE safety trial by the second quarter of 2026. In parallel, the company plans to report longer-term safety and efficacy results from Part A of its Phase 1/2 REVEAL study during the first half of 2026. These data will inform the timing and content of the BLA submission, supported by breakthrough therapy, RMAT, fast track, orphan drug and rare pediatric disease designations granted by the FDA, and corresponding regulatory recognitions in Europe and the U.K.