PTC Therapeutics will need to carry out at least one further trial to demonstrate the effectiveness of its Duchenne Muscular Dystrophy therapy Translarna if it is to have a chance of bagging its approval in the US.

Translarna (ataluren) is a protein restoration therapy designed to enable the formation of a functioning protein in patients with genetic disorders caused by a nonsense mutation, an alteration in the genetic code that prematurely halts the synthesis of an essential protein.

The resulting disorder is determined by which protein cannot be expressed in its entirety and is no longer functional, such as dystrophin in Duchenne muscular dystrophy.

The US Food and Drug Administration has turned down PTC’s application to market the therapy for nonsense mutation dystrophinopathies, issuing a Complete Response Letter stating that it is unable to approve the application in its current form.

Specifically, the letter indicated that evidence of effectiveness from an additional adequate and well-controlled clinical trial(s) will be necessary at a minimum to provide substantial evidence of effectiveness, and also touched other nonclinical and CMC matters that PTC said it is in the process of addressing.

"We are extremely disappointed for the Duchenne community and strongly disagree with the agency's conclusions," said Stuart Peltz, the firm’s chief executive, commenting on the move. "We believe that this decision fails to consider the benefit-risk of ataluren and the high unmet medical need. Therefore, we plan to file a formal dispute resolution request next week."

Translarna has been given a conditional approval in the European Union, but background information prepared by the FDA ahead of an advisory committee meeting last month said studies were inconclusive, and highlighted several issues with the data.

Back in 2016 the FDA issued a Refusal to File on grounds that the application for Translarna “was not sufficiently complete to permit a substantive review”.