Here's a number that tells a story: 61%. That's how much daily cornstarch intake dropped, on average, for patients with glycogen storage disease type Ia (GSDIa) after 96 weeks on Ultragenyx's gene therapy. And it's not just a one-off result; it's sustained.
Ultragenyx Pharmaceutical Inc. (Ultragenyx (RARE)) on Wednesday shared the long-term data from its Phase 3 trial of GENGLYCOS, also known as DTX401, published in The Journal of Inherited Metabolic Disease. The therapy, which was recently approved by the FDA for patients eight and older, is designed to tackle the root cause of GSDIa, a condition where the body can't properly release glucose from glycogen, forcing patients to constantly consume cornstarch to keep blood sugar stable.
From 41% to 61%: The Improvement Keeps Coming
The trial had already hit its primary endpoint at Week 48, with a 41% mean reduction in cornstarch intake for DTX401 patients versus just 10% for placebo. But the new data shows the benefit deepens over time. By Week 96, both the original participants and those who crossed over from placebo achieved a 61% mean reduction in daily cornstarch intake.
And it's not just about the average. A significant chunk of patients saw major gains: 67% of initial participants and 72% of crossover participants cut their daily cornstarch reliance by at least half.
Perhaps the most life-changing effect was on nighttime routines. At baseline, nighttime cornstarch accounted for roughly half of participants' daily calories. Imagine having to wake up multiple times a night just to eat cornstarch to avoid dangerous drops in blood sugar. By Week 96, two-thirds of all participants had eliminated at least one overnight dose. Even better, 33% of original patients and 42% of crossover patients completely stopped nighttime cornstarch use while keeping their blood sugar stable.
Patients Feel Better, and Safety Looks Good
The benefits weren't just measured in lab values. Patient-reported outcomes showed that 83% of DTX401-dosed participants met or exceeded their baseline threshold for meaningful reduction by Week 48. By Week 96, up to 95% reported their overall condition had improved. That's allowing patients to transition toward more balanced diets that align with U.S. Dietary Guidelines, a huge quality-of-life win.
On the safety front, the therapy maintained a manageable profile through two years. The most common treatment-related adverse events were temporary liver enzyme spikes, which were managed with prophylactic corticosteroids. Importantly, researchers recorded no class-related toxicity, malignancy, or thrombotic microangiopathy.
As for the stock, Ultragenyx shares were down a hair, 0.08%, to $25.79 at the time of publication Wednesday.
This is the kind of data that reinforces why gene therapy is so exciting: a one-time treatment that keeps working and lets patients live more normal lives. For GSDIa patients, that means fewer alarms at 2 a.m. and more freedom to eat like everyone else.
