RARE Stock Jumps 6% After-Hours On First Gene Therapy Approval, New Priority Review Voucher

• GENGLYCOS is the first treatment to address the underlying genetic cause of GSDIa rather than only managing symptoms.
• Ultragenyx also received a Priority Review Voucher with the approval, which can be used to secure a faster review of a different future drug application.
• The approval sets the stage for a second potential approval later in September for another gene therapy targeting Sanfilippo syndrome.

Shares of Ultragenyx (RARE) jumped 6% in after-hours trading on Wednesday after the company announced U.S. Food and Drug Administration (FDA) accelerated approval of its first gene therapy, GENGLYCOS.

The FDA granted accelerated approval to GENGLYCOS, also called DTX401, for patients aged eight and older with glycogen storage disease type Ia (GSDIa), an ultra-rare inherited metabolic disorder.

The one-time gene therapy is designed to help the liver produce the missing enzyme needed to release stored sugar into the blood. Without the proper enzyme, the liver cannot maintain normal blood sugar, putting patients at risk of severe or life-threatening low blood sugar, especially during fasting or overnight. Families currently manage it with strict, around-the-clock regimens of raw cornstarch as a glucose replacement, plus careful diet monitoring.

GENGLYCOS approval rests on a late-stage trial showing treated patients needed significantly less daily cornstarch than those on placebo. As with any FDA accelerated approval, continued approval will depend on confirmatory data confirming longer-term benefit.

Why Does It Matter?

GENGLYCOS is the first treatment to address the underlying genetic cause of GSDIa rather than only managing symptoms. Ultragenyx also received a Priority Review Voucher with the approval, which can be used to secure a faster review of a different future drug application. The company can either use it itself or sell it to a peer.

This is Ultragenyx’s first gene therapy approval and its fifth overall FDA green light. The company already sells medicines such as Crysvita and Dojolvi. Success with DTX401 adds a new growth driver in a condition affecting 1,500–2,500 people in the United States, according to company estimates.

The approval also sets the stage for a second potential approval later in September for another gene therapy targeting Sanfilippo syndrome. Together, these could accelerate Ultragenyx's path toward profitability outlined for 2027.

How Did RARE Retail Traders React?

On Stocktwits, retail sentiment around RARE stock improved from ‘bullish’ to ‘extremely bullish’ over the past 24 hours, while message volume stayed at ‘normal’ levels.

A Stocktwits user sees the stock rising as high as $30 following the approval.

Another user noted that the priority review voucher Ultragenyx got with the approval alone is worth about $200 million.

A third user voiced hopes of a big-pharma buyout of Ultragenyx.

RARE stock has gained 14% year-to-date. 

Read More: AUPH Stock Rallies 6% After-Hours — Here’s Why

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