First Gene Therapy Trial for Pitt Hopkins Syndrome Ignites Hope

SOUTH SAN FRANCISCO, CA – February 25, 2026 – A significant milestone has been reached in the fight against Pitt Hopkins syndrome (PTHS), a rare and severe neurogenetic disorder. Mahzi Therapeutics announced today that the first patient has been dosed in its Phase 1/2 UNITE clinical trial for MZ-1866. The announcement marks the launch of the first-ever investigational gene therapy trial for PTHS, a moment of profound hope for patients and families who have long awaited a treatment that could address the condition's underlying cause.

A Devastating Diagnosis, A Glimmer of Hope

Pitt Hopkins syndrome, caused by mutations in the TCF4 gene, is an unforgiving condition. Affecting an estimated 1 in 34,000 to 41,000 individuals, it imposes a lifetime of severe challenges. Individuals with PTHS typically face moderate-to-severe intellectual disability, significant developmental delays, and are often nonverbal. One of the most frightening symptoms is a distinctive breathing pattern characterized by episodes of rapid breathing (hyperventilation) followed by periods of apnea, or breath-holding, which can lead to a lack of oxygen.

Beyond these core issues, the majority of patients also experience seizures, chronic constipation, low muscle tone, and motor impairments. While often described as having a happy and excitable demeanor, they can also struggle with anxiety and features of autism spectrum disorder. Until now, the standard of care has been purely supportive, relying on a combination of physical, occupational, and speech therapies, along with medications to manage symptoms like seizures and constipation. No treatments exist to modify the course of the disease itself, leaving families to navigate a complex and demanding care regimen with no prospect of a cure.

"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."

Targeting the Genetic Root of the Disorder

Unlike therapies that only manage symptoms, MZ-1866 is designed to be a disease-modifying treatment that targets the genetic root of PTHS. The disorder arises from TCF4 haploinsufficiency, a state where individuals have only one functional copy of the gene instead of the necessary two. This deficiency impairs the production of a critical protein essential for brain development and function.

MZ-1866 is a novel gene replacement therapy that uses a well-studied and non-pathogenic delivery vehicle, the adeno-associated virus serotype 9 (AAV9). This vector is known for its ability to cross the blood-brain barrier and deliver its genetic payload to cells within the central nervous system. The therapy is constructed to carry a functional copy of the TCF4 gene—specifically isoform B, one of the most abundant versions in the brain—into the patient's neurons. The treatment is administered via a single intracerebroventricular injection, a direct delivery into the brain's fluid-filled spaces to ensure the therapy efficiently reaches its target.

The goal is to restore the deficient TCF4 protein, thereby correcting the underlying biological deficit and, hopefully, improving or even reversing the clinical symptoms of the syndrome. This groundbreaking approach was developed in close collaboration with the Muotri Lab at the University of California San Diego, where foundational research using brain organoids grown from patient skin cells helped pave the way for the therapy's creation.

The 'UNITE' Study and the Path Forward

The Phase 1/2 UNITE study is a global, multicenter, open-label trial designed to rigorously assess the safety and tolerability of MZ-1866. Approximately 12 participants with a genetically confirmed diagnosis of Pitt Hopkins syndrome will be enrolled across five sites in the United States, Israel, and Spain. While the primary objective is to ensure the single-dose therapy is safe, the trial will also gather crucial preliminary data on its efficacy.

Researchers will use a range of exploratory endpoints to measure potential improvements in developmental, communication, cognitive, and motor functions. This data will be critical for understanding the therapy's potential impact and designing future, larger-scale studies. The trial represents a major step for Mahzi Therapeutics, a clinical-stage biotechnology company whose name, derived from the Greek word for "together," reflects its collaborative ethos.

"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."

A New Model for Rare Disease Innovation

Bringing a therapy to trial for an ultra-rare disease like PTHS is a monumental undertaking fraught with scientific and financial challenges. The small patient population makes traditional large-scale clinical trials difficult, and the high cost of development can be a deterrent. The advancement of MZ-1866 showcases a modern, collaborative model that is becoming essential for progress in the rare disease space.

This effort has been a powerful synergy between a focused biotech company (Mahzi), pioneering academic research (Muotri Lab), a dedicated patient advocacy group (Pitt Hopkins Research Foundation), and crucial public funding. The California Institute for Regenerative Medicine (CIRM), a state agency created by California voters, provided a key grant that helped fund the IND-enabling toxicity studies and manufacturing necessary to launch the clinical trial. This ecosystem approach helps de-risk innovation and ensures that promising science for underserved populations can move from the laboratory to the clinic.

An Evolving Treatment Landscape

While the initiation of the UNITE study is a landmark event, it is part of a broader, encouraging trend of growing therapeutic interest in Pitt Hopkins syndrome. Other companies are also making strides with different approaches. Neuren Pharmaceuticals recently reported positive results from a Phase 2 trial of its drug candidate, NNZ-2591, which showed improvements in communication, social interaction, and motor abilities. Meanwhile, other researchers are exploring drug repurposing and alternative genetic treatments like CRISPR and antisense oligonucleotides (ASOs) to enhance TCF4 production.

This multi-pronged attack on the disorder signals a new era for the Pitt Hopkins community. After years with only supportive care options, the pipeline of potential treatments is finally beginning to grow, fueled by scientific advances, dedicated advocacy, and collaborative funding. For the thousands of families affected by Pitt Hopkins syndrome worldwide, the dosing of the first patient with a gene therapy is more than just a clinical event; it is the tangible arrival of hope.