Sarepta Therapeutics Inc. shares plummeted as much as 20% in after-hours trading Thursday, after the company reported that a study had been put on hold by the Food and Drug Administration. Sarepta disclosed that a patient in a study of a proposed drug for Duchenne muscular dystrophy suffered a "serious adverse event of hypomagnesemia," or seriously low levels of magnesium in blood. The FDA put the study on clinical hold and requested more information about cases of hypomagnesemia; Sarepta said there had been more non-serious cases. "We will work to share information with FDA with the goal of resuming screening and dosing in the U.S. as quickly as possible," Chief Scientific Officer Louise Rodino-Klapac said in a statement. Executives planned a conference call for 4:15 Eastern time to discuss the announcement. Sarepta's stock has declined 20.2% so far this year, in line with a 21.1% decline in the S&P 500 index. [s:spx]
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