NEW YORK (AP) — Alnylam Pharmaceuticals Inc. shares plunged by nearly half on Thursday after the company said it will stop development of a late-stage drug candidate because of potential safety issues.

Alnylam Pharmaceuticals was developing revusiran as a treatment for a hereditary condition called ATTR amyloidosis, which can lead to nervous and cardiovascular conditions. The study was focusing on patients suffering from heart issues because of the condition, but data pointed to the potential for peripheral nerve damage, prompting the study shutdown.

“Patient safety comes first,” CEO John Maraganore said in a statement. “We have stopped all dosing and are actively monitoring patients across revusiran studies to ensure their safety.”

The move to suspend development of revusiran does not affect development of patisiran, which is aimed at treating a similar condition.

Alnylam is a development-stage biotechnology company, focusing on RNAi technology. The goal is to target specific genes responsible for medical conditions and shut them down without harming healthy genes and cells.

Its stock dropped $34.50, or 49 percent, to $35.80 in morning trading.

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