Taysha Gene Therapies Announces Completion of Dosing in REVEAL Pivotal Trial and Reports Longer-Term Clinical Data from Part A of REVEAL Phase 1/2 Trials Evaluating TSHA-102 for Rett Syndrome

About this update from Taysha Gene Therapies, Inc.

Completed dosing of 17 patients in REVEAL pivotal trial; topline data from 6 ‑ month interim analysis and FDA feedback on next steps toward BLA submission pathway expected 1H 2027 TSHA-102 was generally well-tolerated with no treatment-related SAEs or DLTs reported as of the June 2026 data cutoff across REVEAL Phase 1/2 and pivotal trials (N=29) 100% of REVEAL Part A patients (N=12, 6-21 years) gained/regained ≥one developmental milestone by 12 months post-TSHA-102, with consistent responses across ages and disease severity Longer-term follow ‑ up showed a durable and deepening treatment effect ≥12 months post-TSHA-102, with functional gains accumulating over time across core disease domains 310 total functional gains demonstrated ≥12 months post-TSHA-102 (~26 per patient), comprising 31 developmental milestones and 279 additional skill gains/improvements Robust and clinically meaningful responses at both 6 and ≥12 months in REVEAL Part A further support potential for BLA submission based on REVEAL pivotal trial 6-month interim analysis Conference call and webcast today at 8:30 AM ET DALLAS , June 22, 2026 (GLOBE NEWSWIRE) -- Taysha Gene Therapies, Inc. (Nasdaq: TSHA) (Taysha or the Company), a clinical-stage biotechnology company focused on advancing adeno-associated virus (AAV)-based gene therapies for severe monogenic diseases of the central nervous system (CNS), today announced the completion of dosing in the REVEAL pivotal trial and reported positive longer-term clinical data from Part A of the REVEAL Phase 1/2 trials evaluating TSHA-102 for the treatment of Rett syndrome. “As we advance toward a potential BLA submission for TSHA-102, we remain committed to developing a comprehensive, scientifically rigorous data package informed by our ongoing discussions with the FDA. We are pleased to report the completion of dosing in our REVEAL pivotal trial and positive longer-term follow-up data from our REVEAL Phase 1/2 trials. The data demonstrated early, durable treatment effect across all 12 pediatric, adolescent and adult patients, with responses continuing to deepen over time. On average, patients achieved 26 functional gains across core disease domains that impact activities of daily living at ≥12 months post-treatment, with consistent benefits observed regardless of age or disease severity,” said Sean P. Nolan , Chairman and Chief Executive Officer of Taysha. Mr. Nolan continued, “We believe the robust, clinically meaningful responses observed at both 6 and ≥12 months post-treatment continue to demonstrate the potential for TSHA-102 to transform the treatment paradigm for this devastating disease and further support the potential for a BLA submission based on the six-month interim analysis from our pivotal trial. 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.” REVEAL Pivotal Trial and ASPIRE Trial Updates: Completed dosing in the overenrolled REVEAL pivotal trial, with a total of 17 females in the developmental plateau population of Rett syndrome dosed with TSHA-102 The single-arm, open-label trial is evaluating a single intrathecal (IT) administration of high dose TSHA-102 (1x1015 total vector genomes (vg)) in females with Rett syndrome between the ages of 6 to

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