The FDA has added another regulatory coup for Alexion’s ($ALXN) late-stage program for asfotase alfa, an enzyme replacement therapy for extremely rare cases of a metabolic disease known as hypophosphatasia. Already handed an orphan drug designation alongside fast-track status, the agency has added the highly sought after “breakthrough drug” designation for the therapy, which could further shave some time off the development schedule. 

Alexion–which has been cheered and jeered for its success marketing Soliris, the most expensive drug in the world–acquired the therapy in a $1.08 billion deal to buy Enobia at the beginning of 2012, paying $610 million in cash and offering $470 million in milestones to buy the biotech. The bulk of that money was paid for asfotase alfa, which had already demonstrated positive mid-stage data ahead of the buyout.

The FDA has been rapidly adding to its roster of breakthrough drugs, demonstrating a clear preference for experienced and successful drug developers with late-stage oncology and rare-disease treatments. It’s still early days for this designation, but the agency has been signaling that it’s willing to open its doors to drug development teams which have won the designation, potentially carving out a shortcut to an approval.