Ultragenyx's rare disease drug fails in late-stage trial; shares plunge

Ultragenyx Pharmaceutical said on Wednesday its experimental drug for a rare genetic neurodevelopmental disorder did not meet the main goal in a late-stage trial, sending its shares down 45% in aftermarket trading.

The drug, apazunersen, was tested as a treatment for Angelman syndrome, a condition that affects the nervous system and impairs typical brain development in childhood.

In the trial, the drug did not show meaningful improvement on a test of young children's cognitive and nonverbal reasoning abilities or on an overall measure of response across multiple developmental areas.

There were no differences between the treated and control groups that could support efficacy, the company said, adding it will evaluate the apazunersen program in light of this outcome and make a decision on its disposition.

Angelman syndrome currently has no approved disease-modifying treatment. Care focuses on controlling seizures, improving sleep, supporting communication and development, and managing movement, feeding, and other medical complications.

The condition occurs in about 1 in 15,000 live births. It is usually caused by a loss of function in the UBE3A gene on the 15th chromosome, specifically the copy inherited from the mother.

Last month, the company's gene therapy, Genglycos, became the first to receive the U.S. Food and Drug Administration's approval to treat a rare metabolic disorder called Von Gierke disease.