For more than a decade, PTC Therapeutics has been going back and forth with the FDA to find a path forward for a Duchenne muscular dystrophy drug with a spotty track record in clinical testing. That effort has come to an end.
PTC has withdrawn its application seeking regulatory approval for the drug ataluren, brand name Translarna, the company announced after Thursday’s market close. According to PTC, the FDA said that based on its review to date, the data in the submission are unlikely to show enough efficacy to support regulatory approval. The rare disease drug developer elaborated a bit more in a letter to the U.S. Duchenne community, saying there were differences in the interpretation of the data submitted for the drug and these differences cannot be resolved.
“Despite the evidence of safety and effectiveness demonstrated across several clinical studies, FDA has shared that they view the data as insufficient to meet their threshold for approval,” the letter said. “Accordingly, PTC has made the difficult decision to withdraw the resubmission of the New Drug Application for ataluren.”
The progressive muscle weakness of Duchenne stems from an inherited lack of dystrophin, a protein key to muscle function. A so-called nonsense mutation in the gene that codes for dystrophin prematurely stops production of the protein, leading to a shortened and non-functional version. Translarna, which was internally discovered by PTC, was developed as a protein restoration therapy. This oral small molecule is intended to enable a cell’s protein-making machinery to read through the premature stop signal, enabling formation of functioning dystrophin. At least, that’s how it’s supposed to work.
Translarna failed in Phase 2 testing. Nevertheless, PTC advanced Translarna to Phase 3. In 2015, PTC announced the drug failed this placebo-controlled study. Still, the company pressed forward with an FDA submission based on “the totality of the data.” The FDA turned down PTC’s submission in 2017 and has rebuffed the drugmaker’s subsequent efforts to seek approval.
For a while, Translarna had better luck in Europe. In 2014, European regulators granted the drug conditional marketing authorization, which requires annual renewal until there is sufficient data to support a standard marketing authorization. In 2023 and 2024, PTC disputed a negative opinion by the European Commission’s Committee on Medicinal Products for Human Use, which had concluded the drug’s benefit was not confirmed and authorization should not be renewed. Last March, the commission finally adopted the opinion and declined renewal.
Even though Translarna has not been commercially available in the U.S., a limited number of patients have had access to this drug under the FDA’s expanded access program. PTC’s letter said that in the coming weeks, the company will determine the next steps for the remaining supply of the drug for those currently receiving it.
Translarna is one of two PTC drugs for Duchenne. The company also markets Emflaza, which is approved in the U.S. but not in Europe. The way Emflaza works in Duchenne is not understood but this drug is a corticosteroid that reduces inflammation. Translarna and Emflaza are PTC’s top products, together accounting for $315.6 million in revenue through the first three quarters of 2025. But PTC faces financial challenges ahead. Translarna will provide marginal revenue from the remaining markets where the drug is still available and Emflaza has already lost market exclusivity.
The next highest contributor to PTC’s revenue is a new product, Sephience. Last summer, this drug was approved first in Europe and then the U.S. as a treatment for the rare metabolic disease phenylketonuria. Sephience accounted for $19.5 million in revenue in the third quarter of 2025. Kebilidi (Upstaza in Europe), a gene therapy approved in 2024 as a treatment for an ultra-rare enzyme deficiency, accounted for $15.7 million in revenue in the first nine months of 2025.
As for PTC’s pipeline, the company is still trying to find a path forward for vatiquinone, a drug developed for the rare neuromuscular disorder Friedreich’s ataxia. The FDA issued a complete response letter for this drug last August. PTC had submitted a new drug application despite the small molecule’s failure in Phase 3 testing.
Photo by Flickr user Nimble Photography via a Creative Commons license
