U.S. FDA puts Avidity's muscle disorder drug trial on partial hold

Avidity Biosciences Inc said on Tuesday the U.S. Food and Drug Administration has put a hold on patient enrollment in an early-to-mid-stage trial of its drug to treat a genetic muscle disorder, sending the company's shares down over 15%.

The agency put the partial hold after a serious adverse event seen in a patient during the study.

California-based Avidity did not disclose any details about the event, but said it was working closely with the health regulator and a trial investigator to assess the cause, and taking steps to resolve the hold as quickly as possible.

Nearly 40 participants are currently enrolled in the trial for the drug, which seeks to treat myotonic dystrophy type 1 (MD1) - an inherited type of muscle-wasting disorder that affects muscles in the lower legs, hands and neck.