* Data statistically significant in less advanced patients
* Findings enough to win U.S. approval - analyst
* Stock falls 16 pct in extended trade (Adds analyst comment)
By Natalie Grover
Oct 15 (Reuters) - PTC Therapeutics Inc's experimental muscle disorder drug failed to meet the main goal in a keenly watched late-stage study, sending its shares down about 16 percent after the bell.
The drug failed to show a statistically significant benefit over a placebo in patients with Duchenne muscular dystrophy (DMD), for which there is no therapy approved by the U.S. Food and Drug Administration.
However, in a sub-group of patients with less advanced DMD, the effect of the drug, Translarna, was deemed clinically meaningful.
PTC said the new data, combined with findings from previous trials on the drug, supported a U.S. marketing application for Translarna, which won conditional European approval last year.
"Without a doubt these results confirm - from the totality of data - Translarna's ability to slow disease progression, and we are actively planning for a U.S. launch in 2016," Chief Financial Officer Shane Kovacs told Reuters on Thursday.
DMD is a progressive degenerative disorder that hampers muscle movement and affects one in 3,600 newborn boys, most of whom die by the age of 30.
Oppenheimer's Christopher Marai said the findings were positive enough to support an FDA approval and allow for the continued sale of the treatment in the European Union.
"It was always difficult to show results on the primary endpoint in the first place and that's the because of the nature of the endpoint and disease progression," he said.
PTC conducted the trial on 228 boys, the largest-ever study on DMD patients, and aimed to show Translarna was more effective than a placebo in helping patients walk 30 meters more than they could without any medication.
However, data showed the drug helped patents walk only 15 meters more on average, but in less advanced patients it was able to induce a highly significant benefit of 47 meters.
Translarna met all secondary and tertiary endpoints with a robust safety profile in the trial.
Translarna targets DMD caused by nonsense mutations. This form of DMD affects roughly 7,000 boys globally, including about 2,000 in the United States and Canada.
PTC said data from its late-stage study will be presented to the European Medicines Agency in the near term and to the FDA, as part of its rolling marketing application, by the end of the year.
Oppenheimer's Marai estimates the drug represents a $1.2 billion global opportunity.
The company's shares were down 8 percent at $29.21 in extended trading, having recovered some of their losses. (Reporting by Natalie Grover in Bengaluru; Editing by Savio D'Souza)