UPDATE 2-US FDA questions Actelion rare disease drug data

* Company seeking wider approval of Zavesca

* Efficacy main issue for advisory panel -FDA staff

* Actelion says overall data show benefit (Adds company, FDA comments, updates shares)

By Lisa Richwine

WASHINGTON, Jan 8 (Reuters) - Questions about effectiveness are the main issue surrounding Actelion Ltd's (ATLN.VX) bid to sell a drug for treating a rare disease affecting the brain, U.S. drug reviewers said in documents released on Friday.

Europe's largest biotech company is seeking Food and Drug Administration approval of Zavesca for adults and children with neurological problems from a fatal disorder called Niemann-Pick type C disease (NP-C).

The main issue confronting the FDA is whether the overall data provide "sufficient evidence" of a "clinically meaningful effect" in treating the disease, Dr. Donna Griebel, head of the FDA's gastroenterology products division, said in a memo for an advisory panel that meets Tuesday.

Zavesca failed to meet the main goal in a study meant to back its use in NP-C, Griebel said. No difference was seen between Zavesca and a placebo regarding changes in eye movement. But Actelion submitted other data that should be considered, she said.

In a separate memo, FDA reviewers said some findings showed improvements in swallowing, language and other symptoms.

While "deficiencies exist, the body of data cannot be completely discounted because some patients treated with Zavesca did improve," they wrote.

Actelion is trying to cut its dependence on the drug Tracleer, which treats a rare heart and lung disorder and brings in more than $1 billion a year.

The company, in a summary released by the FDA, said the overall evidence in its Zavesca application "shows a relevant clinical benefit of (Zavesca) treatment in patients with this currently untreatable and invariably progressive disorder."

NP-C causes accumulation of cholesterol and other fats in the brain and other organs. It can cause impaired brain function, lack of muscle control and other problems.

Symptoms usually develop around age 10, and most patients die within five to 10 years of diagnosis. Several hundred to a few thousand patients worldwide have the disease, Actelion spokesman Roland Haefeli said.

He said the small population made the disease difficult to study, but Actelion had generated the largest amount of data for NP-C. The company wants the advisory panel to "look at different aspects of our different data sets that altogether allow you to form a judgment," Haefeli said. "We are pleased the FDA has called for an advisory panel."

Known generically as miglustat, Zavesca already is approved for treating adults with a rare disorder called type 1 Gaucher disease. Zavesca sales through the first nine months of 2009 were 38.3 million Swiss francs ($37 million).

The FDA's Griebel said potential risks were "an important secondary issue" for the advisory panel. Actelion has proposed new warnings about growth and platelet effects, she said.

The agency will consider recommendations from the panel before deciding whether to approve Actelion's application. The agency usually follows panel advice.

Actelion shares rose 0.35 percent in Swiss trading. (Reporting by Lisa Richwine; Editing by Steve Orlofsky and John Wallace)