Rare Diseases, Results, Setbacks

Ultragenyx stumbles with UX007 PhIII, shares plunge

Rare disease specialist Ultragenyx Pharma $RARE has abandoned its experimental drug, UX007, as a treatment for Glut1 DS – a debilitating disease characterized by seizures, developmental delay, and movement disorders. The drugmaker, whose stock fell sharply in early trading, said the drug failed to demonstrate a statistically significant improvements in a Phase III trial.

UX007, also dubbed triheptanoinwas designed to address glucose transporter type-1 deficiency syndrome — or Glut1 DS — by getting glucose into the brains of the genetically afflicted group. Without adequate glucose, patients have a tendency to suffer from repeated seizures. Roughly 500 cases have been reported worldwide since the disorder was first identified in 1991, according to the NIH.

The late-stage, placebo-controlled trial included 44 children and adults with Glut1 DS that were experiencing distinct episodes of abnormal movements. The main goal was to achieve a significant reduction in the frequency of so-called disabling paroxysmal movement disorders, while secondary endpoints included reducing the duration of of the movement disorder events; walking capacity and endurance; patient-reported assessments of physical function, upper extremity function, fatigue and pain. Neither the primary nor the secondary endpoints were met, Ultragenyx said.

The announcement sent the biotech’s shares tumbling about 16% in early trading. Many investors were cautious on Glut1DS prospects, so “we are surprised by the stock market reaction, the challenging tape notwithstanding,” Leerink’s Joseph Schwartz wrote in a note. 

But all is not lost. Despite a failed mid-stage study, Ultragenyx in August said the FDA was willing to consider an accelerated pathway for UX007 as a treatment for LC-FAOD — a group of conditions that prevent the body from breaking down long-chain fatty acids into energy — after the drugmaker cobbled together data underscoring a fall in major clinical events for LC-FAOD.

On Friday, the maker of the $200,000 rare disease treatment burosumab said the FDA had accepted its proposal to submit an application to market UX007 for LC-FAOD based on existing data. Ultragenyx, which also sells Mepsevii, is also talking to regulators at the EMA, and will provide an update on those discussions later this year.

“Triheptanoin seems likely to obtain FDA approval in…LC-FAOD – which together with other progress at the company suggests to us downside for RARE is limited at current levels,” Schwartz added.


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