European regulators have delayed PTC Therapeutics' (PTCT - Get Report) request for permanent approval of its Duchenne muscular dystrophy drug Translarna.

Instead, Translarna will remain available to Duchenne patients in Europe under a conditional approval secured by the company in 2014, PTC Therapeutics said Monday.

The company didn't provide a timetable for a final decision but said a commitment to conduct a new clinical trial might be enough to persuade European regulators to allow Translarna to remain on the market.

PTC Therapeutics shares fell 6% to $6.77 after the company's Translarna regulatory update announcement.

PTC Therapeutics is also no closer to securing U.S. approval of Translarna. Last year, the U.S. Food and Drug Administration issued a "refuse to file" letter to the company -- turning back the Translarna approval application without a review. Monday, the company said efforts to appeal the FDA's decision have not yet been successful.

Translarna treats patients with Duchenne caused by a so-called nonsense mutation. This is a different patient population than what's targeted by Sarepta Therapeutics  (SRPT - Get Report) with eteplirsen. The PTC drug is approved on a conditional basis in Europe despite a failed phase III study in Duchenne patients.

For the past several months, the company has submitted various post-hoc analyses from the failed Duchenne study to European regulators in an attempt to win permanent approval. A decision was expected in September, following recent meetings between PTC Therapeutics and European regulators.

PTC Therapeutics is also developing Translarna to treat cystic fibrosis patients with nonsense mutations. An ongoing phase III study of Translarna in cystic fibrosis is expected to read out in early 2017.

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