Taysha Gene Therapies Presents New Supplemental Data Analysis from Part A of the REVEAL Phase 1/2 Trials for TSHA-102 in Rett Syndrome at the 54th CNS Annual Meeting

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Previously disclosed 100% response rate across all 10 patients in Part A for pivotal trial primary endpoint of gain/regain of ≥ one natural history defined developmental milestone assessed via video-evidenced review by independent central raters New supplemental analysis of validated, structured efficacy scales provides supportive evidence of additional functional gains, with 100% of patients demonstrating multiple skill gains/improvements outside the natural history defined developmental milestones Findings reinforce the broad and consistent functional gains seen across the core domains that impact activities of daily living, with 22 developmental milestones and 165 additional skills/improvements achieved across the 10 patients post-TSHA-102 DALLAS , Oct. 09, 2025 (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 results from a new supplemental data analysis from Part A of the REVEAL Phase 1/2 adult/adolescent and pediatric trials evaluating TSHA-102 in females with Rett syndrome at the 54th Child Neurology Society (CNS) Annual Meeting. The analysis provides supportive evidence of additional functional gains in skills and improvements across core disease characteristics that are outside of the natural history defined developmental milestones, further highlighting the consistent, multi-domain impact of TSHA-102 on activities of daily living. “To assess the broad therapeutic impact of TSHA-102 on functional aspects of Rett syndrome, systematic evaluation criteria were applied to REVEAL Part A data,” said Elsa Rossignol , M.D., FRCP, FAAP, Associate Professor in Neuroscience and Pediatrics at the Université de Montréal, Director of the Rett Multidisciplinary Clinic of the CHU Sainte-Justine and a Principal Investigator of the REVEAL trials. “This included the pivotal trial primary endpoint of developmental milestone achievements not expected without treatment based on natural history data, assessed by independent raters through video-evidenced evaluation. Importantly, this approach enabled the reliable and objective measure of TSHA-102’s efficacy. The supplemental analysis of validated, structured efficacy scales was also conducted to capture supportive evidence of additional skill gains and improvements outside of the 28 natural history defined milestones.” Sukumar Nagendran , M.D., President and Head of R&D of Taysha added, “The new supplemental analysis of Part A data further underscores the potential consistency and breadth of TSHA-102’s impact across the core domains of Rett syndrome, including communication, fine motor, gross motor and autonomic function. In addition to the developmental milestones achieved across the treatment cohort in Part A, patients consistently gained additional skills and improvements across core disease characteristics. We believe this reinforces the potential therapeutic impact of TSHA-102 on activities of daily living that are important to caregivers and clinicians.” Supplemental Analysis of Previously Disclosed Part A REVEAL Phase 1/2 Data Reinforces the Broad, Multi-domain Functional Gains/Improvements Consistently Demonstrated Post-TSHA-102 Pivotal trial primary endpoint of the gain/regain of ≥ one of the 28 developmental milestones defined in the natural history study assessed independently via video-evidenced evaluation by multiple independent central raters 100% of patients in Part A (N=10) gained/regained ≥ one defined developmental milestone across the core functional domains of communication, fine motor and gross motor post-TSHA-102, with 0% to

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