Sarepta Therapeutics announced Monday that it will move forward with an NDA filing for its rare-disease muscular dystrophy drug by the end of this year.

The Cambridge, MA, had a setback in November when the FDA told the company it needed more data before considering the Duchenne Muscular Dystrophy drug’s risks and benefits. Among its objections were that the data excluded “both younger boys who cannot perform such a demanding test, and older boys who are no longer ambulatory.”

Sarepta said in a statement that FDA discussions between November 2013 and March 2014 have shaped how it will move forward, including initiating several new studies  which “will include a clinical trial with predefined efficacy endpoints for ambulatory patients between the ages of 7 and 16 years who can walk a minimum distance, and two additional clinical trials that will evaluate safety and biomarkers in DMD patients younger than 7 years old.” Tests will also include patients who can no longer walk.

The drugmaker’s announcement also includes a substantial amount of caution that goes beyond the typical “safe harbor” provisions that are attached to corporate projections. Sarepta is careful to note that FDA has stated that it “remains skeptical about the persuasiveness of the (dystrophin) data” and “is uncertain whether the existing dystorphin biomarker data will be persuasive enough to serve as a surrogate endpoint that is reasonably likely to predict clinical benefit.”

The FDA also urged Sarepta to begin confirmatory studies that show clinical benefit.

The rare disease is a genetic disorder that is expressed by low- or no production of the protein dystrophin. The Centers of Disease Control describes the protein as a glue that holds muscles together “by keeping the structure of muscle cells,” without which “muscles weaken over time and become unable to work properly.” The progressive disease generally effects more boys than girls and is diagnosed between the ages of 3 and 6. Most patients require wheelchairs by their early teens.