GSK has received a significant regulatory boost for its investigational efforts in rare diseases after both the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA) granted Orphan Drug Designation (ODD) to momelotinib for the treatment of VEXAS syndrome, a rare and life-threatening inflammatory blood disorder with no approved therapies.
The designation marks an important milestone in the development of momelotinib for a disease that remains poorly understood and difficult to treat. VEXAS syndrome, which stands for Vacuoles, E1 enzyme, X-linked, Autoinflammatory, Somatic syndrome, is a recently identified clonal myeloid disorder characterized by severe inflammatory, rheumatologic, and hematologic manifestations. Patients often experience debilitating symptoms, progressive disease, and a poor prognosis, with studies indicating a five-year mortality rate of between 30% and 40%.
Orphan Drug Designation is granted to medicines intended to treat rare diseases and provides incentives aimed at supporting clinical development and regulatory review. These incentives can include market exclusivity, regulatory assistance, and financial benefits designed to encourage investment in treatments for underserved patient populations.
The FDA and EMA decisions were supported by emerging clinical evidence suggesting that Janus kinase (JAK) inhibitors may offer therapeutic benefits for patients with VEXAS syndrome. Retrospective analyses and case studies have indicated that JAK inhibition can help control disease activity and reduce inflammatory symptoms. In particular, evidence from an individual case report suggested that treatment with momelotinib may improve both inflammatory and hematologic manifestations associated with the disorder.
Momelotinib is a differentiated JAK inhibitor currently marketed under the brand names Ojjaara and Omjjara for specific forms of myelofibrosis. The drug is approved in the United States for adults with intermediate- or high-risk myelofibrosis and anemia. It is also approved in the European Union, the United Kingdom, and Japan for the treatment of myelofibrosis, further supporting its established safety and efficacy profile in hematologic diseases.
To further investigate its potential in VEXAS syndrome, GSK is preparing to launch the Phase II/III ATLAS clinical trial. The study will evaluate the efficacy and safety of momelotinib in patients with the rare condition and is expected to serve as the foundation for future global regulatory submissions. Details of the trial design are scheduled to be presented at the 2026 European Hematology Association (EHA) Congress taking place from June 11 to June 14.
The ATLAS study forms part of GSK’s broader development program for momelotinib, which continues to explore the medicine’s potential across multiple hematological and inflammatory disorders.
The orphan drug designations underscore growing interest in addressing rare diseases with high unmet medical need. For patients living with VEXAS syndrome, the recognition by both U.S. and European regulators offers hope that a targeted treatment option may eventually become available for a condition that currently lacks approved therapies.
If successful in clinical trials, momelotinib could become one of the first therapies specifically developed for VEXAS syndrome, potentially transforming the treatment landscape for this severe and often fatal disorder.