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

Sept. 2 (Reuters) - 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 40% 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.

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

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.