GSK gains transatlantic orphan drug designations for myelofibrosis asset in rare disease pivot

GSK (NYSE:GSK) announced that momelotinib, its approved Janus kinase (JAK) inhibitor, has received Orphan Drug Designation from both the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for the treatment of VEXAS syndrome.

The dual regulatory milestones mark a significant pipeline expansion for the asset into the underserved ultra-rare disease market.

VEXAS (Vacuoles, E1 enzyme, X-linked, Autoinflammatory, Somatic) syndrome is a progressive, life-threatening clonal myeloid disorder that manifests through severe rheumatologic and hematologic inflammation.

The disease carries a poor clinical prognosis, showing a 30% to 40% mortality rate within five years of onset.

There are currently no regulatory-approved targeted therapies available for patients diagnosed with the condition.

The regulatory incentives were granted based on retrospective clinical datasets and specific case history evaluations.

These initial files demonstrated that the unique, multi-pathway signaling inhibition profile of JAK inhibitors can modify the severe autoinflammatory loops native to VEXAS.

Published case reports highlighted that momelotinib administration yielded measurable improvements in baseline constitutional symptoms, localized inflammation, and secondary hematological abnormalities.

GSK plans to leverage these designations to accelerate its upcoming clinical trial framework.

The company will outline the study parameters for its planned Phase II/III ATLAS trial during a presentation at the European Hematology Association (EHA) 2026 Congress in Stockholm.

The global, multi-center study is designed to establish safety and efficacy margins to support future international regulatory filings.

Momelotinib—marketed commercially as Ojjaara in the US and Omjjara in Europe—is currently approved to treat intermediate- or high-risk myelofibrosis in adults presenting with disease-related anemia.