A Ray of Hope Pierces the Darkness: FDA Fast-Tracks Pioneering Gene Therapy for Devastating STXBP1 Brain Disorder

The FDA has granted Fast Track designation to CAP-002, a potential first-in-class gene therapy for STXBP1-DEE, a severe neurological disorder.
CAP-002 is the first IV-delivered, AAV blood-brain barrier-crossing genetic medicine poised to enter human clinical trials, offering hope where no approved treatments exist.
Capsida Biotherapeutics is initiating a Phase 1/2a clinical trial, aiming to provide a disease-modifying treatment for children and families devastated by STXBP1-DEE.

For families battling the relentless grip of STXBP1 developmental and epileptic encephalopathy (STXBP1-DEE), a rare and profoundly debilitating genetic condition, a new dawn may be breaking. Capsida Biotherapeutics today announced a pivotal milestone: the U.S. Food and Drug Administration (FDA) has granted Fast Track designation to CAP-002, its groundbreaking investigational gene therapy. This designation underscores the desperate unmet need for treatments for STXBP1-DEE, a disorder that plunges children into a world of severe developmental delays, intractable epilepsy, intellectual disability, and movement disorders, with many requiring lifelong care and less than half achieving independent walking or expressive language^{1, 3, 5, 8}.

CAP-002 isn't just another drug; it's a potential game-changer. It stands as the first-ever intravenously administered gene therapy engineered to cross the formidable blood-brain barrier and is now advancing into human clinical trials. "FDA’s granting of Fast Track designation for CAP-002 highlights the significant unmet need...and the potential of CAP-002 to be a first-in-class treatment," stated Dr. Swati Tole, Chief Medical Officer of Capsida.

The science is revolutionary. CAP-002, born from Capsida’s proprietary engineered capsids, aims to deliver a functional copy of the STXBP1 gene directly to the brain. In remarkable non-human primate studies, CAP-002 achieved over 70% neuron transduction across critical brain areas with a single IV infusion, while cleverly avoiding the liver and dorsal root ganglia. This unprecedented brain-wide expression offers the tantalizing potential to correct seizures, developmental disabilities, and motor abnormalities⁶. With Orphan Drug Designation secured in October 2024 and IND clearance in May 2025, Capsida is set to dose the first patient in its SYNRGY Phase 1/2a clinical trial in the third quarter of this year. For countless families, this pioneering therapy represents more than just medicine; it represents a profound hope for a brighter future. For more information about the SYNRGY clinical trial, please visit ( ).

A Ray of Hope Pierces the Darkness: FDA Fast-Tracks Pioneering Gene Therapy for Devastating STXBP1 Brain Disorder

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