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New findings Thursday showing that Zafgen Inc.’s embattled drug candidate led to substantial weight loss among severely obese patients with type 2 diabetes lifted the Boston biotech’s shares.

While the clinical results amounted to a vote of confidence for the experimental drug, Beloranib, the study testing the drug in its target population — patients with the rare condition Prader-Willi Syndrome — remains on a clinical hold imposed by the Food and Drug Administration.

FDA regulators placed a hold on that late-stage study after the deaths last year of two Prader-Willi patients who had taken Beloranib in the study. Zafgen is working on a “risk mitigation” plan to monitor patients at most risk of developing the blood-clotting that led to the deaths.

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Company execututives hope that plan will help persuade the FDA to let the program go forward. Zafgen last month reported that, despite the deaths, other Prader-Willi patients in the clinical trial lost weight and engaged in less binge-eating after taking the experimental drug.

Thursday’s data involved a separate mid-stage study of Beloranib in severely obese patients with type 2 diabetes, a larger population group.

Those patients, who do not suffer from Prader-Willi Syndrome, the most common genetic cause of life-threatening obesity, lost between 12.7 percent and 13.5 percent of body weight, depending on the dosage they took, compared to a 3.1 percent weight loss for other patients in the trial who were given a placebo.

In an interview Thursday, however, Zafgen chief executive Thomas Hughes said the company is working on a second-generation drug to treat patients with severe obesity and type 2 diabetes.

He said the Zafgen ran the Beloranib trial on these patients to generate more data about the drug candidate because it was difficult to enroll as many patients with the rarer condition.

“This provides additional data on the safety and efficacy of Beloranib that will support our package for Prader-Willi patients,” Hughes said. “And it shows how powerful our approach is to reducing body weight in (obese) patients.”

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At the same time, he said, “our focus is to identify a path forward for beloranib in Prader-Willi patients.”

Hughes declined to comment on the New York hedge fund Kerrisdale Capital, which disclosed last month that it had taken a short position in Zafgen.

Shares of Zafgen closed up 2.1 percent at $7.60, a gain of 16 cents on the Nasdaq stock exchange Thursday.


Robert Weisman can be reached at robert.weisman@globe.com. Follow him on Twitter @GlobeRobW.