Mahzi Therapeutics Announces First Patient Dosed in Phase 1/2 UNITE Study of MZ-1866 for Pitt Hopkins Syndrome

First Investigational Gene Therapy for Pitt Hopkins Syndrome Intended to Address Underlying Disease Biology

SOUTH SAN FRANCISCO, Calif., Feb. 25, 2026 /PRNewswire/ -- Mahzi Therapeutics Inc., a clinical-stage biotechnology company developing precision therapies for neurogenetic disorders, today announced that the first patient has been dosed in its Phase 1/2 UNITE study evaluating MZ-1866, an investigational gene therapy for the treatment of Pitt Hopkins syndrome.

The Phase 1/2 study is a global, multicenter, open‑label trial designed to assess the safety, tolerability, and preliminary efficacy of a single administration of MZ‑1866 in participants with genetically confirmed Pitt Hopkins syndrome. This rare condition, affecting approximately 1 in 34,000-41,000 individuals and translating to an estimated 8,000 people living with Pitt Hopkins in the Unites States, results from mutations in the TCF4 gene. Affected individuals present with a combination of autism, developmental delay, hypotonia, ataxia, apnea/hyperventilation, severe gastrointestinal issues, and, less frequently, epilepsy. MZ‑1866 aims to address the underlying disease biology by providing functional copies of the TCF4 gene.

"Dosing the first patient is a significant achievement for the MZ-1866 program and for Mahzi's evolution as a clinical-stage company," said Yael Weiss, M.D., Ph.D., Chief Executive Officer of Mahzi. "We look forward to advancing this program to address a significant unmet medical need for patients with Pitt Hopkins syndrome and their families."

"The launch of the first investigational gene therapy trial for Pitt Hopkins syndrome represents a truly historic milestone for our community," said Audrey Davidow, President of the Pitt Hopkins Research Foundation. "For families who have waited years for meaningful therapeutic progress, this moment reflects countless hours of advocacy, collaboration, and perseverance. This Phase 1/2 trial brings long-held hope closer to reality and marks a critical step toward transforming the future of care for individuals living with Pitt Hopkins."

MZ-1866 was developed in collaboration with the Muotri Lab at the University of California San Diego, and the Phase 1/2 study was made possible by funding from the California Institute for Regenerative Medicine (CIRM), a state of California Agency that funds regenerative medicine, stem cell, and gene therapy research (Grant Number TRAN1-13997).

About the Phase 1/2 UNITE Study
The Phase 1/2 UNITE clinical trial is an open-label study evaluating a single administration of MZ-1866 in participants with genetically confirmed Pitt Hopkins syndrome. The study is designed to enroll approximately 12 participants across 5 sites in the United States, Israel, and Spain and evaluate a single dose of MZ-1866 delivered via intracerebroventricular administration. In addition to its primary safety objectives, the trial will evaluate developmental, communication, cognitive, and motor function exploratory endpoints.

Additional information on the Phase 1/2 UNITE study can be found at: https://clinicaltrials.gov/study/NCT07135050

About MZ-1866
MZ-1866 is a novel AAV9-TCF4 gene replacement therapy, constructed by inserting TCF4 isoform B (the longest known isoform and one of the most abundant brain isoforms) into an AAV9 expression cassette under the regulation of multimer E box sequences.

About Mahzi Therapeutics
Mahzi Therapeutics is a clinical-stage biotechnology company developing precision therapies for neurogenetic disorders in partnership with patient organizations and academic collaborators. For more information, visit www.mahzi.com.

About the California Institute for Regenerative Medicine (CIRM)
CIRM was created by the people of California to fund stem cell and gene therapy research with the goal of accelerating treatments for patients with unmet medical needs. With $8.5 billion in funding allocated through both Proposition 71 in 2004 and Proposition 14 in 2020, CIRM supports stem cell and gene therapy discoveries from inception through clinical trials, trains a workforce in California to fill jobs in the state's thriving biotech and biomedical research industry, and creates infrastructure to make clinical trials accessible for people throughout California. All of CIRM's research, workforce development, and infrastructure programs are designed to benefit the people of California, whose vision created the agency. For more information, visit www.cirm.ca.gov.

About the Pitt Hopkins Research Foundation
The Pitt Hopkins Research Foundation (PHRF) is a nonprofit organization dedicated to accelerating research and advancing treatments for Pitt Hopkins syndrome. Working in close partnership with leading scientists, clinicians, and families worldwide, PHRF funds innovative research, supports natural history and clinical studies, and builds the infrastructure needed to translate laboratory discoveries into clinical practice. Through strategic investment, collaborative leadership, and an unwavering commitment to the community it serves, PHRF is driving progress toward meaningful therapies and an eventual cure for Pitt Hopkins syndrome. For more information, visit www.pitthopkins.org.

Forward-Looking Statements
This press release contains forward-looking statements regarding the Company's clinical development programs and future operations. These statements are subject to inherent risks and uncertainties and results may differ materially. The Company assumes no obligation to update these statements except as required by law.

SOURCE MAHZI Therapeutics