Ultragenyx shares tumble lower after rare disease drug fails PhII trial

Emil Kakkis, Ultragenyx

Shares of Ultragenyx $RARE tumbled close to 10% after the rare disease biotech reported that one of its drugs failed a Phase II trial.

UX007 was tested as a treatment for glucose transporter type-1 deficiency syndrome—or Glut1 DS—among a small group of patients. But it only cut the rate of seizures in the drug arm by 13.4% compared to the placebo arm, falling short of statistical significance.

Investigators, though, teased out a clinically, though not statistically, significant benefit for patients experiencing what are called “absence seizures,” or periods of unresponsiveness. And that is what Ultragenyx now intends to focus on in a Phase III pivotal trial.

The researchers said that they tracked a 47.3% drop in absence seizure frequency relative to the baseline. There was a 9.1% drop in observable seizures.

There were no serious adverse events recorded in the trial, but 14 of 36 patients dropped out due to adverse events. 18 patients in the drug arm — 72% — reported an adverse event compared to 45% in the placebo arm.

The drug converts into glucose in the brain, treating a genetic disease that interrupts the supply of glucose, triggering an energy deficiency with severe side effects. There are no approved therapies for Glut1 DS, which is generally currently treated with a ketogenic diet.

“These data suggest that UX007 has a clinically meaningful effect in Glut1DS patients with absence seizures,” said Ultragenyx CEO Emil Kakkis in a statement. “We look forward to studying UX007 in our Phase 3 study in Glut1 DS patients with movement disorders, and continue to evaluate our plans in the seizure indication.”

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