Taysha Gene Therapies Reports Second Quarter 2025 Financial Results and Provides Corporate Update

About this update from Taysha Gene Therapies, Inc.

Commenced site activation for REVEAL pivotal trial in accordance with previously aligned upon key design elements, following receipt of No Objection Letter (NOL) from Health Canada and feedback from the FDA; patient enrollment anticipated to begin in Q4 2025 High dose and low dose TSHA-102 continue to be generally well tolerated with no treatment-related SAEs or DLTs in the 12 patients treated in Part A of REVEAL Phase 1/2 trials as of August 2025 data cutoff Part A data from REVEAL Phase 1/2 trials presented at IRSF Scientific Meeting showed 100% response rate for pivotal trial primary endpoint of gain/regain of ≥ one developmental milestone, corroborated by improvements in key secondary endpoints post-TSHA-102 Company anticipates reporting new supplemental REVEAL Part A clinical data supporting TSHA-102 therapeutic impact in Q4 2025 Gross proceeds of $230 million public follow-on offering, including full exercise of the underwriters’ option to purchase additional shares, strengthen balance sheet and extend cash runway into 2028 Conference call and webcast today at 8:30 AM Eastern Time DALLAS , Aug. 12, 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 reported financial results for the second quarter ended June 30, 2025, and provided a corporate update. “We have made strong progress across the Company supporting the advancement of our TSHA-102 development program toward potential registration for females two years and older with Rett syndrome. In May, we announced alignment with the FDA on key design elements of our REVEAL pivotal trial, and subsequently, submitted our IND application and CTA amendments to both the FDA and Health Canada . I’m pleased to share we have commenced site activation in accordance with the key design elements previously aligned on with the FDA, based on feedback recently received from these regulatory agencies. As a result, we anticipate beginning patient enrollment in the fourth quarter of this year,” said Sean P. Nolan , Chairman and Chief Executive Officer of Taysha. “Our frequent and constructive dialogue with the FDA through the Regenerative Medicine Advanced Therapy (RMAT) mechanism has been instrumental in enabling us to navigate this novel regulatory pathway. With a strengthened balance sheet, our pivotal trial underway and a clear path to registration, we believe we are well positioned to advance TSHA-102 to benefit patients living with this devastating disease.” 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, added, “The enthusiasm generated by the REVEAL Phase 1/2 clinical data presented at the IRSF Scientific Meeting was inspiring and highlights the therapeutic potential of TSHA-102. The developmental milestones achieved across all pediatric, adolescent and adult patients treated with TSHA-102, combined with the positive safety profile to date and minimally invasive intrathecal delivery, reinforces my belief in the potential of TSHA-102 to redefine the treatment landscape for Rett syndrome. I’m pleased to participate in the REVEAL pivotal trial and to contribute to the advancement of a potential therapy for individuals living with Rett syndrome, who continue to face profound unmet need.” Recent Corporate and TSHA-102 Program Highlights Commenced Site Activation for REVEAL Pivotal Trial Following Regulatory Feedback. In May 2025 , Taysha announced alignment with the U.S. Food and Drug Administration (FDA) on key elements of the REVEAL pivotal Part B trial design and next steps for enabling study initiation. Subsequently, the Company submitted its Investigational New Drug (IND) application amendment to the FDA and Clinical Trial Application Amendment (CTA-A) to Health Canada . Taysha commenced site activation for the REVEAL pivotal trial in accordance with previously aligned upon key design elements, following receipt of a NOL from Health Canada and written feedback from the FDA Trial Design: Single-arm, open-label trial, with each patient serving as their own control Dose and Administration: Single administration of high dose of TSHA-102 (1x1015 total vector genomes (vg)) delivered by lumbar intrathecal (IT) injection Patient Population: Enrolling 15 females aged 6 to

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