Taysha Gene Therapy Shows Lasting Gains in All 12 Rett Syndrome Trial Patients

All 12 girls and women with Rett syndrome who received the gene therapy candidate TSHA-102 in a clinical trial gained or regained at least one developmental milestone within one year, according to new data from the REVEAL Phase 1/2 clinical trial. Longer-term follow-up data from Part A of the trial show a lasting, deepening treatment-related effect for all patients, with functional gains continuing for those with the longest follow-up at 30 months, or 2.5 years.

Taysha Gene Therapies, the treatment's developer, reported that improvements were seen in walking and speaking abilities, as well as in skills such as using utensils without assistance. Developmental milestone gains increased by 69% between six and 12 months, and by 94% between six months and the latest follow-up of 12 months or more. In total, at a year or more post-treatment, 310 functional gains were observed across the 12 participants, averaging about 26 per patient. These comprised 31 developmental milestones and 279 additional skill gains and improvements.

Responses were consistent regardless of age, disease severity, or the patients' specific MECP2 mutations. Improvements were also observed on several clinician-assessed outcome measures: the Revised Motor Behavior Assessment (R-MBA); the Clinician Global Impression-Improvement (CGI-I); and the Clinical Global Impression-Severity (CGI-S).

Taysha has completed dosing in Part B — the pivotal Phase 3 portion — of REVEAL, enrolling girls and women with Rett, ages 6-21. Six-month top-line data from this Phase 3 part, along with feedback from the U.S. Food and Drug Administration toward the submission of an approval application, are expected early in 2027.

TSHA-102 is administered as a one-time treatment that delivers a functional copy of the MECP2 gene to cells in the nervous system. Most cases of Rett, a rare neurodevelopmental disorder that primarily affects girls, are caused by mutations in the MECP2 gene, which plays an essential role in regulating brain cell function. The therapy features a technology called miRARE, which helps manage MECP2 activity levels on a cell-by-cell basis to avoid toxic overactivity.

Interim data from Part A of REVEAL, along with results from a pediatric version of the trial with Rett girls, ages 5 to 8, showed that the gene therapy was generally safe and led to improvements in motor function, communication, and social skills.