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In February, four months after the first patient in a trial of a designer CRISPR therapy suddenly died, around 100 researchers gathered in a Tucson, Ariz., conference hall to hear investigators in the study walk through the results of an autopsy.

Few details had been made public about the death of Terry Horgan, a 27-year-old man born with Duchenne muscular dystrophy, as the investigators worked to pinpoint a cause. There was dismay over his death and wide speculation. Some people wondered if he had even gotten the drug. Others feared that CRISPR-Cas9, a technology researchers hoped to deploy against many diseases, had played a role.


At the presentation, STAT has learned, leaders of the study put that fear to rest. Terence Flotte, provost and executive deputy chancellor of UMass Chan Medical School, where the study was conducted, did not yet know what killed Terry. But it wasn’t CRISPR.

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