The FDA previously rejected Zycubo for Menkes disease in October last year, citing issues with the drug’s manufacturing facility.
After suffering a rejection late last year, Sentynl Therapeutics and Fortress Biotech have now picked up an FDA approval for their copper replacement therapy for Menkes disease, which will carry the brand name Zycubo.
One in every 100,000 to 250,000 babies born worldwide has Menkes disease, a rare genetic disorder, according to the FDA’s press announcement on Monday. The condition arises from mutations to the ATP7A gene, which encodes for a protein that helps sustain copper levels and its healthy distribution throughout the body.
Symptoms include seizures, developmental delays, intellectual disabilities and deterioration of the nervous system. According to the FDA, patients with Menkes disease often do not live past three years of age.
Zycubo is delivered via a subcutaneous injection and works by replacing copper levels. A Phase II readout in October 2021 demonstrated an almost 80% reduction in the risk of death in patients given the drug within four weeks of birth versus untreated historical controls.
Later intervention dampened the efficacy of Zycubo, but the drug remained significantly better than untreated historical controls, with a 75% decrease in the risk of death.
Despite these supportive findings, the FDA in October 2025 rejected Zycubo, citing problems with the manufacturing facility where the drug was slated to be produced. Sentynl and Fortress at the time noted that the regulator had not identified other issues with the application.
Zycubo’s side effects included infections, seizures, fever, vomiting, anemia and respiratory problems. The FDA recommends that patients be monitored for toxicity associated with copper accumulation.
Zycubo’s approval comes just over a month after the FDA greenlit Waskyra for Wiskott-Aldrich syndrome—marking the first gene therapy nod for this indication, and the first genetic medicine sponsored by a nonprofit to win the agency’s approval. Waskyra was backed by Fondazione Telethon ETS, based in Italy, which supports research and development for rare diseases.
Zycubo and Waskyra represent encouraging bright spots in a rare disease space that in recent weeks has seen a series of setbacks. In early December, Denali Therapeutics announced that the FDA placed its investigational Pompe disease therapy under clinical hold due to some hypersensitivity reactions observed in mouse models. Later that month, Ultragenyx revealed that its osteogenesis imperfecta therapy was unable to significantly lower fracture rates in two Phase III studies, wiping some $1 billion off its market value.
