More than 30 million Americans are living with a rare disease. For many of them, there's little doctors can do.
In fact, there are more than 10,000 known rare diseases. Yet fewer than 500 have an approved treatment.
Mahzi Therapeutics aims to change that. This biotech startup is developing genetic therapies for rare neurological disorders that can cause seizures, developmental disabilities, and autism-related symptoms. Unlike treatments that simply manage symptoms, Mahzi's goal is to address the underlying genetic cause of these conditions.
The company has attracted significant financial backing. It's raised $60 million from leading biotech investors including Venrock, HealthCap, Droia Ventures, and HBM Partners. It's also received $16 million in grant awards from the California Institute for Regenerative Medicine.
Mahzi's first target is Pitt Hopkins Syndrome, a rare genetic disorder that affects brain development. Children with the condition often experience severe developmental delays, difficulty speaking, breathing problems, and seizures. Currently, there's no approved treatment that addresses the disease itself.
Mahzi is developing a gene therapy designed to change that. Here's how it works:
Pitt Hopkins Syndrome is caused by a problem with a gene called TCF4. This prevents the body from producing enough of a protein that's essential for normal brain development.
Mahzi's treatment uses a modified, non-disease-causing virus to deliver a working copy of the gene into cells. The goal is to restore production of the missing protein and improve neurological function.
Early results have been encouraging. In animal studies, Mahzi's treatment improved learning, memory, and behavior in mice with the disorder. And in January 2026, Mahzi reached a major milestone: it became the first company to treat a patient with gene therapy for Pitt Hopkins Syndrome.
Its first human clinical trial is now underway, with additional patients expected to receive treatment before the end of 2026. But Pitt Hopkins is just the beginning.
Mahzi is also developing a gene therapy for WOREE Syndrome, another severe genetic disorder that causes seizures and developmental disabilities. It aims to advance this treatment into clinical testing in 2027.
The company is also developing several additional therapies using technology designed to influence how genes produce proteins. Ultimately, Mahzi believes its approach could be applied to more than 800 rare neurological disorders.
That represents a sizable opportunity. Mahzi estimates the market for rare neurological disease treatments exceeds $16 billion annually, within a broader rare-disease therapeutics market worth more than $200 billion. While these diseases affect relatively small numbers of patients, successful treatments can generate substantial revenue.
For example, FDA-approved gene therapies such as Zolgensma and Luxturna have demonstrated that one-time treatments for serious genetic disorders can command premium prices. Mahzi estimates that each successful treatment in its pipeline could eventually generate $200 million to $600 million in annual revenue.
Its business model centers on developing these therapies, obtaining regulatory approval, and commercializing them. It may also partner with larger pharmaceutical companies to help fund development and bring treatments to market.
Leading Mahzi is founder and CEO Dr. Yael Weiss, who has more than 20 years of pharmaceutical-industry experience. Yael previously held leadership positions at Merck and rare-disease specialists Genzyme and Ultragenyx. During her career, she contributed to four FDA drug approvals, including Januvia and Gardasil.
She's joined by CFO Aaron Olsen, who previously spent more than a decade at Ultragenyx and held a finance leadership role at BioMarin.