FDA rejects BioMarin's muscle wasting drug; Sarepta drug in focus

Sarepta's eteplirsen, like BioMarin's Kyndrisa, skips a faulty section of the gene to produce dystrophin, the lack of which is believed to cause DMD.

Both drugs target a particular subset of DMD patients, which translates into an addressable population of about 1,800 boys in the United States and about 5,000 outside, according to Wedbush Securities analyst Heather Behanna.

The U.S. rejection, however, is not end of the road for Kyndrisa. BioMarin expects to hear back from the European regulatory advisory committee in April or May, with a final decision in the third quarter.

While a U.S. approval would have given BioMarin first-mover advantage in the market, a European approval is perhaps more significant as the drug will target a larger patient population.

Evercore ISI's Mark Schoenebaum expects BioMarin make its next move only after the FDA's decision on Sarepta, and European regulators' decision on Kyndrisa.

BioMarin said on Thursday it would work with the FDA to determine its next step.

PTC Therapeutics Inc's DMD drug, Translarna, won conditional European approval in 2014, to treat a different subset of patients.

Last year, PTC said it had enough data to submit a U.S. marketing application, despite the drug failing a U.S. late-stage study.