Shares of Sarepta Therapeutics (NASDAQ: SRPT), which focuses on genetic treatments for rare diseases, were down 11.5% Wednesday afternoon after the Food and Drug Administration (FDA) pushed back its Prescription Drug User Fee Act (PDUFA) date on a Duchenne muscular dystrophy therapy candidate. The biotech stock is up less than 1% so far this year. The FDA gave Sarepta good news and bad news on Wednesday regarding the company's gene transfer therapy, SRP-9001 (delandistrogene moxeparvovec), designed to treat ambulatory patients with Duchenne muscular dystrophy (DMD) who have a mutation of the DMD gene.