Dear Tay-Sachs and Sandhoff Community,

We are pleased to announce that a Phase 1/2 clinical trial of TSHA-101 is currently enrolling patients with infantile GM2 gangliosidosis, also known as Tay-Sachs and Sandhoff diseases. The clinical trial will be conducted by the Kingston Health Sciences Centre at Queen's University in Ontario, Canada. The trial received financial support from the Canadian Glycomics Network (GlycoNet) and Taysha Gene Therapies, Inc., a patient-centric gene therapy company focused on monogenic diseases of the central nervous system.

First and foremost, the purpose of this clinical trial is to evaluate the safety of TSHA-101, an investigational AAV9-based gene therapy. The trial will also help determine if there is an improvement in symptoms and overall survival in children who have received TSHA-101.

Children 12 months and younger who have been diagnosed with GM2 gangliosidosis may be eligible to enroll in this study. The trial will enroll children wherever they and their caregivers reside, including outside Canada. However, all clinical trial visits will be conducted in person at Kingston Health Sciences Center at Queen's University in Kingston, Ontario, Canada.

TSHA-101 is an innovative approach to gene therapy as it is designed to deliver both HEX genes (Hex A and Hex B) at the same time in the same cell. TSHA-101 is delivered as a single injection through the spinal fluid, known as intrathecal delivery. We are hopeful for the outcomes in this initial study of TSHA-101, but the safety of our patients continues to be our highest priority.

We encourage you to visit http://www.tsd-sdgtxtrial.com/ for more information regarding the TSHA-101 clinical trial. If interested in learning more about eligibility criteria, you may contact the research team at info@TSD-SDGtxtrial.com.

We are grateful for the support of the GM2 gangliosidosis communities and for Queen's University for their continued efforts to advance TSHA-101 into the clinic. We look forward to providing updates about the TSHA- 101 clinical trial and its progress.

Warm regards,

The Taysha Team

GRANT ANNOUNCEMENT!!!!

The CTSF is very pleased to announce our latest grant in support of future clinical trials for Tay-Sachs and Sandhoff disease. This is your donation money at work!!

The CTSF proudly awards the labs of Queens University in Ontario, Canada $154,660 USD. This money will support and pay for the already initiated work to best understand the methodology and volume of Vector (medicine) to administer to children Intrathecally. This work is part of the complicated journey leading to the safe administration of gene therapy to children.

We will keep you posted on the progress on this work right here.

Donations to the CTSF are fully tax deductible and can be made in any amount by credit card at: www.curetay-sachs.org

Thank you for your continuing interest in FINDING THE CURE!!!!!

Dear Tay Sachs and Sandhoff patient communities,

On behalf of Sio Gene Therapies, it is our privilege to share an exciting update. Today, we are delighted to announce that the first patient has been dosed in a Phase 1/2 trial evaluating AXO-AAV-GM2, an investigational gene therapy for the treatment of GM2 gangliosidosis, also known as Tay-Sachs or Sandhoff Disease.

The two-part AXO-AAV-GM2 study consists of (1) a dose ranging cohort evaluating the safety and efficacy of various doses of the gene therapy, followed by (2) a confirmatory cohort treated with the optimal dose identified from the dose ranging cohort. Both infantile and juvenile patients with GM2 gangliosidosis will be enrolled in the study which is being conducted in partnership between the University of Massachusetts Medical School and Massachusetts General Hospital (MGH)under the direction of Dr. Terence Flotte and Dr. Florian Eichler respectively, who work together to provide the treatment and follow-up of the patients enrolled in the study.

Information about the study, including inclusion/exclusion criteria, are posted on clinicaltrials.gov (NCT04669535): A Dose-escalation and Safety & Efficacy Study of AXO-AAV-GM2 in Tay-Sachs or Sandhoff Disease - Full Text View - ClinicalTrials.gov. As with all clinical trials, enrollment is dependent upon the study investigator's medical assessment of the patient meeting the inclusion criteria for the study, and as such, Sio will play no role in the selection of patients for the trial. A few of the criteria are listed below:

• Must have a genetically confirmed diagnosis of Tay Sachs Disease or Sandhoff disease
• Age at the time of gene transfer is 2-12 years for juvenile-onset patients and 6-20 months for infantile-onset patients
• There are also factors assessed by the study investigator that will impact whether your child is eligible for the trial such as disease severity, surgical readiness for the gene transfer route of administration, and medical conditions that could interfere with conduct of the study or assessments

As always, your treating physician will serve as the best source of information for ongoing medical treatment and management of your child's disease. To learn more about this study, you or your doctor may contact the Clinical Research Coordinator at MGH, Haley Andonian(handonian@partners.org).

This is an important milestone for the entire GM2 community made possible by the many families, researchers and patient organizations committed to finding new treatments for Tay-Sachs and Sandhoff disease, and we look forward to enrollment of additional patients in this program. If you would like to reach out directly with any questions or feedback, you can contact us at patients@siogtx.com.

Sincerely,

Gavin Corcoran, MD

Chief R&D Officer

Erika De Boever

VP, Clinical Development