<img src="https://ml.globenewswire.com/Resource/Download/a88cd5f5-0b05-416c-a56b-e4130c10cfca?size=2" nborder="0" align="left" hspace="5" vspace="5" title="New taysha_inline_fullcolor_rgb_12in@300ppi.jpg" alt="Taysha Gene Therapies, Inc."/>Recently disclosed longer-term REVEAL Part A data demonstrated broad, multi-domain functional impact that deepened over time through ≥12 months post-TSHA-102 regardless of age or disease severity Rett syndrome natural history data analysis shows a clear developmental plateau after 6 years of age, supporting a stable, well-defined population to evaluate TSHA-102 in the REVEAL pivotal trial New data support the developmental milestone assessment (DMA) as a psychometrically valid, FDA-supported primary endpoint for single-arm interventional studies Preclinical data demonstrated superior MeCP2 expression of self-complementary AAV9 compared to single-stranded, supporting effective CNS delivery of TSHA-102 by intrathecal administration DALLAS, June 25, 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 multiple presentations highlighting its TSHA-102 program in clinical evaluation for Rett syndrome at the 2026 International Rett Syndrome Foundation (IRSF) Rett Syndrome Scientific Meeting, taking place in Prior Lake, MN, from June 29 – July 1, 2026. Additional details on the meeting can be found at IRSF’s <a href="https://www.globenewswire.com/Tracker?data=gFPr88F3CKRZNC-3PSBhDnSGiJbfJh11Xr6TKAn7SfAoMJKjaVGki22KrOQEk1_NGRTvXgaICr7MS9RcKlvwi_pdq2Am4AgW15lhrHdwZkgmhslVsP7P6rSwtoxfLQ8nA_JDr_pSRmdgbKJj4VtZQxuZltMJN_esQp3qOOmniks=" rel="nofollow" target="_blank" title="website">website</a>. Oral Presentation: Title: Safety and Efficacy Results from the REVEAL Part A Phase 1/2 Trial of TSHA-102 in Pediatric and Adolescent/Adult Cohorts Date/Time: Tuesday, June 30, 2026, at 9:00-9:20 AM CT Presenter: Elsa Rossignol, M.D., FRCP, FAAP, 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 trial Poster Presentations: Presentations will be held on Monday, June 29, and Tuesday, June 30, 2026, from 5:00-7:00 PM CT. Title: Safety and Efficacy Results from the REVEAL Part A Phase 1/2 Trial of TSHA-102 in Pediatric and Adolescent/Adult Cohorts Flash Talk Date/Time: Tuesday, June 30, 2026, at 3:40 PM CT Poster Number: 59 Presenter: Elsa Rossignol, M.D., FRCP, FAAP, 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 trial Title: The Developmental Plateau in Rett Syndrome: New Insights from the Natural History Study Inform Novel Interventional Study Designs Flash Talk Date/Time: Monday, June 29, 2026, at 3:10 PM CT Poster Number: 39 Presenter: Minna Montgomery, Medical Office Chief of Staff, Taysha Gene Therapies Title: Establishing the Rett Syndrome Developmental Milestone Assessment (RS-DMA) as a Primary Endpoint for Interventional Studies Flash Talk Date/Time: Monday, June 29, 2026, at 10:45 AM CT Poster Number: 7 Presenter: Tessa Clarkson, Ph.D., Co-Founder and CEO, Psychlomere, LLC Title: Superior Expression of Self-complementary AAV and Comparable Functionality of Mini and Full-length MECP2 Support the Design of TSHA-102 Gene Therapy for Rett Syndrome Flash Talk Date/Time: Tuesday, June 30, 2026, at 3:40 PM CT Poster Number: 54 Presenter: Fred Porter, Ph.D., Chief of Staff and Technical Operations Officer, Taysha Gene Therapies Company Hosted Symposium: Title: Establishing the Rett Syndrome Developmental Milestone Assessment (RS-DMA) as a Primary Endpoint for Interventional Studies Date/Time: Wednesday, July 1, 2026, 8:10-8:20 AM CT Presenter: Tessa Clarkson, Ph.D., Co-Founder and CEO, Psychlomere, LLC About TSHA-102 TSHA-102 is a self-complementary intrathecally delivered AAV9 investigational gene transfer therapy in clinical evaluation for Rett syndrome. Designed as a one-time treatment, TSHA-102 aims to address the genetic root cause of the disease by delivering a functional form of MECP2 to cells in the CNS. TSHA-102 utilizes a novel miRNA-Responsive Auto-Regulatory Element (miRARE) technology designed to mediate levels of MECP2 in the CNS on a cell-by-cell basis without risk of overexpression. TSHA-102 has received Breakthrough Therapy, Regenerative Medicine Advanced Therapy, Fast Track and Orphan Drug and Rare Pediatric Disease designations from the FDA, Orphan Drug designation from the European Commission and Innovative Licensing and Access Pathway designation from the Medicines and Healthcare products Regulatory Agency. About Rett Syndrome Rett syndrome is a rare neurodevelopmental disorder caused by mutations in the X-linked MECP2 gene encoding methyl CpG-binding protein 2 (MeCP2), which is essential for regulating neuronal and synaptic function in the brain. The disorder is characterized by loss of communication and hand function, slowing and/or regression of development, motor and respiratory impairment, seizures, intellectual disabilities and shortened life expectancy. Rett syndrome progression is divided into four key stages, beginning with early onset stagnation at 6 to 18 months of age followed by rapid regression, plateau and late motor deterioration. Rett syndrome primarily occurs in females and is one of the most common genetic causes of severe intellectual disability. Currently, there are no approved disease-modifying therapies that treat the genetic root cause of the disease. Rett syndrome caused by a pathogenic/likely pathogenic MECP2 mutation is estimated to affect between 15,000 and 20,000 patients in the U.S., EU, and U.K. About Taysha Gene Therapies Taysha Gene Therapies (Nasdaq: TSHA) is a clinical-stage biotechnology company focused on advancing adeno-associated virus (AAV)-based gene therapies for severe monogenic diseases of the central nervous system. Its lead clinical program TSHA-102 is in development for Rett syndrome, a rare neurodevelopmental disorder with no approved disease-modifying therapies that address the genetic root cause of the disease. With a singular focus on developing transformative medicines, Taysha aims to address severe unmet medical needs and dramatically improve the lives of patients and their caregivers. The Company’s management team has proven experience in gene therapy development and commercialization. Taysha leverages this experience, its manufacturing process and a clinically and commercially proven AAV9 capsid in an effort to rapidly translate treatments from bench to bedside. For more information, please visit <a href="https://www.globenewswire.com/Tracker?data=4eEEo9Dsfi1ibMh1mFlyzLdi-KtUF0tHj-3R8T6dj7Zt6AMx664QDHcTJ9MUxCPoiOj7dkFE_7wV4baSYJnEjTdlnwZUnR5AGRiZ22wyxj8=" rel="nofollow" target="_blank" title="www.tayshagtx.com">www.tayshagtx.com</a>. Forward-Looking Statements This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Words such as “anticipates,” “believes,” “expects,” “intends,” “projects,” “plans,” and “future” or similar expressions are intended to identify forward-looking statements. Forward-looking statements include, but are not limited to, statements concerning the potential of TSHA-102, including the reproducibility and durability of any favorable results initially seen in patients dosed to date in clinical trials, including with respect to functional milestones, and Taysha’s other product candidates to positively impact quality of life and alter the course of disease in the patients Taysha seeks to treat, Taysha’s research, development and regulatory plans for its product candidates, communications with the FDA, including with respect to the BLA for TSHA-102, the potential for Taysha’s product candidates to receive regulatory approval from the FDA or equivalent foreign regulatory agencies, and whether, if approved, these product candidates will be successfully distributed and marketed and the potential market opportunity for Taysha’s product candidates, including anticipated clinician and caregiver demand. Forward-looking statements are based on management’s current expectations and are subject to various risks and uncertainties that could cause actual results to differ materially and adversely from those expressed or implied by such forward-looking statements. Accordingly, these forward-looking statements do not constitute guarantees of future performance, and you are cautioned not to place undue reliance on these forward-looking statements. Risks regarding Taysha’s business are described in detail in Taysha’s Securities and Exchange Commission (“SEC”) filings, including in our Annual Report on Form 10-K for the full-year ended December 31, 2025, which are available on the SEC’s website at <a href="https://www.globenewswire.com/Tracker?data=BxvxmQG6KJkBksaDaMKJQgfEDcELIDPrR0R9akKUuAAAnvOiCRc4tYx7NDYz0Dz3ry7_0NmichtGMHELQXu0Ow==" rel="nofollow" target="_blank" title="www.sec.gov">www.sec.gov</a>. Additional information will be made available in other filings that Taysha makes from time to time with the SEC. These forward-looking statements speak only as of the date hereof, and Taysha disclaims any obligation to update these statements except as may be required by law. Company Contact: Hayleigh Collins Senior Director, Corporate Communications and Investor Relations Taysha Gene Therapies, Inc. <a href="https://www.globenewswire.com/Tracker?data=bBmKc7YUVSRF_MNQxYZk2ubJqaBEN2qokZF13Il8LBEiV-LyhvgJSIm3wVMHBJp0foLoyNPJo6DepZdJIWV2d1BFTx0s0QIsobVq2Y2qtwg=" rel="nofollow" target="_blank" title="hcollins@tayshagtx.com">hcollins@tayshagtx.com</a> Media Contact: Carolyn Hawley Inizio Evoke <a href="https://www.globenewswire.com/Tracker?data=2YCQ9VhrgGX1fLkYFRUhT2xRiR_bFDu0DjqrTfgU_8xVm4RT_hMPPIHj34XgeW9ho-aEPXIcn3zVLhqXTUj5mKNKwVLsK3W-rmz-CMKpiVvCliMYax4I0yWfFRa1Vy_-" rel="nofollow" target="_blank" title="Carolyn.hawley@inizioevoke.com">Carolyn.hawley@inizioevoke.com</a> <img alt="" src='https://ml.globenewswire.com/media/YjY3N2QwZWQtY2MxOC00NmU4LThiMDItMGJiYzA4ZjkzZWY0LTEyMTM5NjYtMjAyNi0wNi0yNS1lbg==/tiny/Taysha-Gene-Therapies-Inc-.png' referrerpolicy='no-referrer-when-downgrade' />

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Taysha Gene Therapies Announces Multiple Presentations Highlighting its TSHA-102 Clinical Program at the 2026 IRSF Rett Syndrome Scientific Meeting

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