Correction: A previous version of this story stated incorrectly that beloranib was the only drug in Zafgen's pipeline. The company is also developing two other preclinical compounds.
Zafgen shares plunged 53% to $7.38 in premarket trading on concerns the U.S. Food and Drug Administration might step in to halt all clinical development of beloranib for patient-safety reasons.
The FDA placed a partial clinical hold on beloranib, after the first treated patient died in October.
Both patients suffered from a rare disease, Prader-Willi Syndrome, causing compulsive overeating and severe obesity. Both patients also died, due to blood clots in the lungs while taking beloranib. A direct tie between the blood clots and beloranib has not been established, but other beloranib-treated patients have also reported blood clots, forcing Zafgen to enact stricter screening methods and safety precautions.
Ever since the first Prader-Willi patient died in October, Zafgen's challenge has been to find a way to prove beloranib to help these patients without putting them at increased safety risk.
Wednesday's report of a second patient death makes Zafgen's job even more difficult, perhaps impossible.
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