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Taysha Completes Dosing in Pivotal Trial of Rett Syndrome Gene Therapy TSHA-102 as Longer-Term Data Show Sustained Developmental Gains

Taysha Gene Therapies has finished dosing 17 patients in the pivotal REVEAL trial of its Rett syndrome gene therapy TSHA-102 and reported longer-term Phase 1/2 data, setting up a planned BLA filing after a six-month interim analysis.

Biotech & Medicine Gene Therapy
gene therapy Rett syndrome TSHA-102 Taysha clinical trials FDA
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Overview

Taysha Gene Therapies said on June 22, 2026 that it had completed dosing in the pivotal portion of its REVEAL trial of TSHA-102, an investigational gene therapy for Rett syndrome, and reported longer-term follow-up data from earlier Phase 1/2 patients, according to GlobeNewswire. The company dosed 17 females in the developmental plateau population of Rett syndrome in the overenrolled pivotal trial and said the results position it to pursue a Biologics License Application (BLA) after a six-month interim analysis, according to GlobeNewswire.

Rett syndrome is a rare neurodevelopmental disorder caused by mutations in the MECP2 gene and is estimated to affect between 15,000 and 20,000 patients across the U.S., EU and U.K., with no approved disease-modifying therapies that treat the genetic root cause of the disease, according to GlobeNewswire.

What We Know

  • The pivotal REVEAL trial is a single-arm, open-label study evaluating a single intrathecal administration of high-dose TSHA-102 (1x10^15 total vector genomes) in females with Rett syndrome between the ages of 6 to under 22 years, according to GlobeNewswire. The company dosed the first patient in the pivotal trial in late 2025, as reported by CGTLive.
  • TSHA-102 is a self-complementary, intrathecally delivered AAV9 gene transfer therapy designed to deliver a functional form of MECP2 to cells in the central nervous system, using a technology Taysha calls a miRNA-Responsive Auto-Regulatory Element (miRARE), according to GlobeNewswire.
  • In the Phase 1/2 REVEAL Part A cohort (N=12, ages 6 to 21), 100% of patients gained or regained at least one developmental milestone by 12 months after treatment, according to GlobeNewswire.
  • At 12 months or longer after dosing, those patients showed 310 total functional gains, or about 26 per patient, comprising 31 developmental milestones and 279 additional skill gains, according to GlobeNewswire. Developmental milestone gains increased by 69% from 6 to 12 months and by 94% from 6 to 12 months or more after treatment, according to GlobeNewswire.
  • Across the Phase 1/2 and pivotal trials (N=29), Taysha reported no treatment-related serious adverse events or dose-limiting toxicities as of a June 2026 data cutoff, according to BioSpace.
  • “TSHA-102 consistently drove early, durable functional gains across the core domains of the disease, including communicating with words or phrases, eating with utensils without assistance and walking with support, which continue to accumulate over time,” said Dr. Elsa Rossignol, principal investigator of the REVEAL trial and a professor in neuroscience and pediatrics at the Université de Montréal, according to GlobeNewswire.
  • The FDA has granted TSHA-102 Breakthrough Therapy Designation, as reported by CGTLive.

Regulatory Path

The interim analysis intended to support the planned BLA is expected once all 17 pivotal patients complete six months of post-treatment follow-up, according to GlobeNewswire. “In early 2027, we plan to engage with the FDA to review the interim data and discuss next steps toward submitting the BLA, with topline results and regulatory feedback expected in the first half of 2027,” said Sean P. Nolan, Taysha’s chairman and chief executive officer, according to GlobeNewswire.

Separately, Taysha’s ASPIRE trial in younger children is ongoing; the company said it expects to dose a total of four females aged 2 to under 4 years, according to GlobeNewswire.

What We Don’t Know

  • Efficacy results from the pivotal trial itself have not yet been reported; the milestone and functional-gain figures come from the earlier Phase 1/2 Part A cohort, not the 17 pivotal patients, according to GlobeNewswire.
  • Because the pivotal study is single-arm and open-label with no concurrent control group, it is benchmarked against external natural-history data, where fewer than 6.7% of comparable patients would be expected to gain a milestone, as reported by CGTLive.
  • The timing of any FDA decision, and whether the six-month interim data will be sufficient to support a filing, remain uncertain pending the company’s planned early-2027 discussions with the agency, according to GlobeNewswire.