Taysha Gene Therapies Shares Letter to the Rett Syndrome Community

September 24, 2021

Dear Rett Syndrome Community,

During the September 22 educational event on Rett syndrome for the investment community, Taysha mentioned that, pending submission, review and approval from regulatory agencies, our goal is to enroll patients ages 18 and over in the first planned clinical trial for TSHA-102, our investigational gene therapy for Rett syndrome.

We must work closely with regulatory agencies to advance TSHA-102 towards an Investigational New Drug (IND) application in the US and Clinical Trial Applications (CTA) outside of the US. These application processes and regulatory approvals are required before any clinical trials can begin. If the IND and CTA applications are accepted, we will have permission to start a clinical trial in patients. We plan to share more information about the clinical trial at that time.

We are also pleased to share that Taysha has been granted Orphan Drug Designation (ODD) from the European Commission for TSHA-102 for the treatment of Rett syndrome. The European Commission grants orphan designation for medicines intended to be developed for the diagnosis, prevention or treatment of disorders affecting fewer than five in 10,000 people in the European Union. TSHA-102 was also previously granted both Rare Pediatric Disease Designation (RPDD) and Orphan Drug Designation (ODD) from the US Food and Drug Administration (FDA).

These designations are not associated with the start of clinical trials and do not represent any regulatory approval or validation of our approach. However, this is an important step and milestone to emerge from our Rett syndrome program. For more information regarding this designation and TSHA-102, please read our press release.

We are committed to the Rett syndrome community and are grateful for the support from advocates and caregivers. We look forward to continuing to provide you with updates related to Taysha’s Rett syndrome program through our Rett syndrome advocacy partners.

Your Rare Ally,
The Taysha Team

This communication contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Forward-looking statements are based on Taysha's current expectations and are subject to various risks and uncertainties that could cause actual results to differ materially and adversely, including those described in our filings with the Securities and Exchange Commission , which is available at www.sec.gov. These forward-looking statements speak only as of the date hereof, and we disclaim any obligation to update these statements except as may be required by law.

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