Regulatory officials from the U.S., UK, EU and Japan said their agencies should harmonize rules for clinical trials targeting rare diseases because patient populations in some study areas number only in the hundreds worldwide. If enacted, such a strategy could lead to faster development of advanced therapy medicinal products used to treat ultra-rare diseases.

Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, said there were plenty of diseases with patient populations so small that it may be difficult to field a viable trial in just one regulatory jurisdiction.

Marks suggested that the four regulators begin any global harmonization efforts with a focus on ultra-orphan drugs. He and other top regulators made the comments at last week’s Alliance for Regenerative Medicines’ Meeting on the Med.