Sentynl Therapeutics and Fortress Biotech have received approval from the U.S. Food and Drug Administration (FDA) for Zycubo, a copper replacement therapy for Menkes disease. This comes after an earlier rejection in October 2025 due to issues at the drug's manufacturing facility. At that time, Sentynl and Fortress stated that the FDA did not identify other problems with their application.
Menkes disease is a rare genetic disorder caused by mutations in the ATP7A gene, which is responsible for regulating copper levels in the body. According to the FDA, approximately one in every 100,000 to 250,000 babies worldwide are born with this condition. The disease leads to symptoms such as seizures, developmental delays, intellectual disabilities, and nervous system deterioration. Many patients do not live past three years of age.
Zycubo is administered through subcutaneous injection and functions by replacing copper in patients with Menkes disease. Results from a Phase II trial released in October 2021 showed nearly an 80% reduction in risk of death among patients treated within four weeks of birth compared to untreated historical controls. Later treatment reduced efficacy but still resulted in a 75% decrease in risk of death compared to those who did not receive treatment.
Reported side effects of Zycubo include infections, seizures, fever, vomiting, anemia, and respiratory problems. The FDA recommends monitoring patients for potential toxicity due to copper accumulation.
The approval of Zycubo follows closely behind the FDA’s authorization of Waskyra for Wiskott-Aldrich syndrome—a first gene therapy approval for this indication and also the first genetic medicine sponsored by a nonprofit organization to be approved by the agency. Waskyra was supported by Fondazione Telethon ETS from Italy.
These recent approvals come amid challenges in the rare disease sector. In December, Denali Therapeutics reported that its Pompe disease therapy was placed under clinical hold by the FDA because of hypersensitivity reactions observed during animal testing. Around the same period, Ultragenyx announced its osteogenesis imperfecta therapy failed to significantly reduce fracture rates in two late-stage studies.
"Zycubo’s approval represents an important advancement for children affected by Menkes disease," said representatives from Sentynl Therapeutics and Fortress Biotech.
