Taysha Gene Therapies' investigational gene therapy TSHA-102 is showing promising results in Rett syndrome, a rare neurological disorder with no approved treatment targeting its underlying genetic cause. In the phase 1/2 REVEAL Part A trial, all 10 participants — ages 6 to 21 — who received a single intrathecal dose gained or regained at least one developmental milestone, a feat that has less than a 6.7% chance of occurring naturally after age 6.

Gains spanned multiple domains: patients showed improvements in communication (like using phrases), fine motor skills (such as purposeful hand use and finger feeding), gross motor function, and autonomic symptoms including reduced breath-holding, hyperventilation, and seizures. Notably, improvements deepened over time — the opposite of what natural history would predict. The therapy was well tolerated, with no treatment-related serious adverse events or dose-limiting toxicities reported.

By the Numbers:

• 10/10 participants gained or regained ≥1 developmental milestone
• 22 developmental milestones achieved, plus 165 additional skills or improvements
• <6.7% natural probability of milestone gains after age 6
• 25% reduction in seizure events at week 36 in one early patient
• 15,000–20,000 estimated patients living with Rett syndrome across the US, EU, and UK

Why it matters: TSHA-102 received FDA Breakthrough Therapy Designation in October 2025, and the pivotal REVEAL Part B trial is now underway. If results hold, this could become the first disease-modifying treatment for Rett syndrome — a condition that currently has no genetic-level therapy options.