Gene therapy data weigh on Ultragenyx shares

Ultragenyx shed more than $350 million in market cap on Wednesday as investors digested additional data from a Phase I/II trial of gene therapy DTX401 for glycogen storage disease and news that the company would add more patients to the trial to confirm the dose.

Data from the study’s second, higher dose cohort of three glycogen storage disease type Ia patients showed less improvement on two efficacy endpoints than observed in patients in the study’s first cohort...