 Shares of Avidity Biosciences Inc. RNA, -4.52 soared 39 in premarket trading on Wednesday after the company said its experimental RNA therapy, when injected into the muscle, has potential as a treatment for myotonic dystrophy type 1, a sometimes fatal neuromuscular disease. The Phase 12 clinical trial is the first time that RNA has been delivered into the muscle in humans, Avidity said. 