The U.S. Food and Drug Administration said on Thursday it had approved Biomarin Pharmaceutical Inc’s drug to treat a type of Batten disease, an extremely rare disorder that mainly impacts the nervous system.

The drug, Brineura, is an enzyme replacement therapy designed to slow loss of walking ability in patients, three years or older, with CLN2 disease. (

CLN2 disease is a rapidly progressive fatal brain condition, which affects less than one in one million U.S. residents many of whom are undiagnosed.

Biomarin said Brineura is expected to be available in the United States by early June and the company will begin promotion of the drug immediately.

The company said every year about 20 children are born in the U.S. with CLN2 disease, which is one of a group of disorders collectively referred to as Batten disease.

The FDA said it had issued Biomarin a rare pediatric disease priority review voucher, which would help a drug to get rapid approval.

Biomarin shares were up 1.4 percent in afternoon trading on Thursday.

(Reporting by Akankshita Mukhopadhyay in Bengaluru; Editing by Shounak Dasgupta)