Ultragenyx Pharmaceuticals Inc. surged 6.7% in after-hours trading on Wednesday after the U.S. Food and Drug Administration approved its gene therapy GENGLYCOS for patients aged eight and older with glycogen storage disease type Ia (GSDIa).
The approval, granted ahead of the assigned PDUFA action date of August 23, 2026, marks Ultragenyx’s first FDA-approved gene therapy and fifth overall product clearance. The therapy, pariglasgene brecaparvovec-opnr, targets an estimated 1,500 to 2,500 U.S. patients, offering a reduction in daily cornstarch management requirements. Regulatory clearance was supported by data from the 48-week Phase 3 GlucoGene study, which enrolled 46 participants and demonstrated a statistically significant reduction in cornstarch use.
The stock, which had traded well below its 52-week high of $39.89 ahead of the session, reached $28.48 in extended trading. Shares of the Novato, California-based biotech have gained roughly 15% over the past month, outperforming the broader biotech sector amid a backdrop of muted market activity. The S&P 500, Dow Jones Industrial Average, and Nasdaq Composite each ended the regular session within 0.1% of flat, with no major central bank announcements or macroeconomic releases materially influencing biotech sentiment.
Analysts covering Ultragenyx maintained a predominantly bullish stance, with the majority of ratings remaining at Buy. The company’s pipeline remains a focal point, with an additional FDA decision on UX111 for Sanfilippo syndrome Type A scheduled for September 19, 2026. GENGLYCOS’ approval underscores Ultragenyx’s expanding presence in rare disease therapeutics, a segment increasingly viewed as a high-growth opportunity within biotech.
