The US Food and Drug Administration (FDA) has rejected BioMarin Pharmaceutical Inc's drug for treating an uncommon muscle-wasting disorder. The agency’s rejection has shifted investor focus to Sarepta Therapeutics Inc's rival drug, which is presently in development.

The rejection has come after months of uncertainty around the drug, Kyndrisa, which was called to be the United States’ first treatment for Duchenne muscular dystrophy (DMD).

A progressive, degenerative genetic disorder, DMD hinders muscle movement and affects one in 3,600 infant boys. Mostly DMD patients lose their battle against the disease by the age of 30. It has no cure.

In November, a panel of independent advisers suggested the FDA that effectiveness of Kyndrisa in trials wasn’t sufficient to warrant approval. Sarepta's drug, eteplirsen will be reviewed in the coming week.

WBB Securities analyst Steve Brozak said that the rejection of Kyndrisa has effectively crowned Sarepta the US DMD winner. Brozak added that the pressure for the treatment approval is going to mount.

According to analysts, BioMarin will probably require another late-stage study for its drug in the United States. Europe is also reviewing Kyndrisa. Sarepta's eteplirsen, like BioMarin's Kyndrisa, has skipped a defective part of the gene for the production of dystrophin, the lack of which has been believed to have resulted into DMD.

The two drugs target a specific subset of DMD patients, which as per Wedbush Securities analyst Heather Behanna translates into an addressable population of nearly 1,800 US boys and around 5,000 outside.

However, the US rejection doesn’t mean the road has come to an end for Kyndrisa as BioMarin is looking forward to a response from the European regulatory advisory committee in April or May, with a last decision in Q3.