NEW YORK (AP) — Shares of Sarepta Therapeutics Inc. fell Wednesday after the company said it will file for marketing approval of its most advanced experimental drug in the first half of 2014.

Sarepta is studying eteplirsen as a treatment for Duchenne muscular dystrophy, a rare and fatal genetic disease that causes increasing muscle weakness and affects one of every 3,500 boys worldwide. The company plans to file for marketing approval of eteplirsen by the end of June 2014, which means the drug could receive Food and Drug Administration clearance in late 2014 or early 2015. A standard FDA review takes 10 months.

Its shares lost $8.46, or 18.2 percent, to $37.97 in afternoon trading. The price of Sarepta shares has climbed sixfold over the last year and is currently at its highest level in seven years.

Deutsche Bank analyst Robyn Karnauskas downgraded Sarepta shares to “Hold” from “Buy,” saying the company is making progress but the shares have been strong. Karnauskas said in a research note the stock has advanced in the last few months because Wall Street expects accelerated approval for eteplirsen, but it’s not clear that Sarepta will be able to win a quicker approval. The analyst kept a $45 price target on the stock.

The Cambridge, Mass., company does not have any drugs on the market.