A patient with Prader-Willi syndrome who was receiving Zafgen's experimental obesity drug beloranib was diagnosed with blood clots in the lung and died, according to a statement.
Prader-Willi syndrome causes constant hunger that leads those affected to gain excessive weight.
Two months prior, U.S. regulators had stopped part of the clinical trial to investigate the first patient's death, the Wall Street Journal reports. The second patient who died was involved in the open-label extension portion of the late-stage trial, which hadn't been stopped.
"Patient safety remains our top priority and we are investigating the circumstances around this event. We are also engaging in discussions with the FDA while we determine the next steps with the beloranib program," CEO Dr. Thomas Hughes said in a statement. "We are also engaging in discussions with the FDA while we determine the next steps with the beloranib program."
The biopharmaceutical company reiterated its expectations for top-line results of the randomized portion of the study in the fiscal 2016 first quarter.
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