Shares of Zafgen (ZFGN) are down 32% today after the FDA announced a partial clinical hold on the company's obesity trials. The FDA partial clinical hold is for a compound known as beloranib, it is being used to treat patients with obesity. The clinical trials placed on hold are known as ZAF-311 and ZAF-312. 

Once the FDA enacts the partial clinical hold, the trials are temporarily suspended pending further investigation. The reason for the FDA putting Zafgen's trials on partial clinical hold was due too a patient death in one of the trials. The patient death had occurred in the clinical trial known as ZAF-311 which used beloranib to treat patients with Prader-Willi Syndrome - PWS. 

The ZAF-311 trial is a phase 3 clinical trial and one patient data was "unblinded", where investigators found that the patient had died while on the beloranib drug. Now the FDA must investigate the data and the results from the company to determine the cause of death. The company also noted that some patients taking beloranib saw thromboembolic events. 

The FDA stated that the company must screen all patients in the ZAF-311 study for thrombotic disease prior to receiving additional drug therapy. Whether or not the FDA ultimately removes this clinical hold remains to be seen, and it is mainly dependent upon how long it takes for the investigation to conclude.