RARE ▲ +12.2% - Ultragenyx Pharmaceutical Inc. $RARE - Ultragenyx Announces Approval of FAYUVI™ Gene Therapy, the First-Ever FDA-Approved Treatment for Sanfilippo Syndrome Type A (MPS IIIA) Ultragenyx Pharmaceutical surged 12.2% after announcing FDA approval of FAYUVI, a gene therapy marking the first-ever treatment for Sanfilippo Syndrome Type A (MPS IIIA). The approval represents a significant milestone for the company's rare disease pipeline and opens a new market for treatment of this previously untreatable genetic disorder. 17-SEP-2026 03:48 PM ET