How the FDA Response on UX111
In late July 2025, Ultragenyx Pharmaceutical announced that its Phase 3 Aspire study for GTX-102 in Angelman syndrome fully enrolled 129 participants, while also receiving a Complete Response Letter from the FDA for its gene therapy UX111 targeting Sanfilippo syndrome type A, citing chemistry, manufacturing, and controls issues that require resubmission.
While the FDA acknowledged positive efficacy data for UX111, the focus now shifts to addressing manufacturing concerns, even as pipeline progress continues with strong community support in other rare disease programs.
We'll now explore how the FDA's Complete Response Letter for UX111 may affect Ultragenyx's investment narrative and future approval timelines.
To believe in Ultragenyx Pharmaceutical as a shareholder, you need confidence in its ability to bring rare disease therapies to market, especially gene therapies like UX111. The recent FDA Complete Response Letter for UX111 introduces added uncertainty to the approval timeline, but it does not materially shift the main short-term catalyst, the pending Phase 3 Aspire readout for GTX-102, nor does it fundamentally change the key risk around execution in late-stage programs.
Among recent announcements, the full enrollment of the Phase 3 Aspire study of GTX-102 for Angelman syndrome is most relevant. This milestone keeps Ultragenyx on track for topline results in 2026, reinforcing a pipeline-driven catalyst while the company works through regulatory feedback for UX111, highlighting both momentum and ongoing risk tied to late-stage clinical and regulatory execution.
Ultragenyx Pharmaceutical's outlook projects $1.3 billion in revenue and $140.6 million in earnings by 2028. This requires a 31.2% annual revenue growth rate and an earnings increase of $690.2 million from current earnings of -$549.6 million.
