By Deena Beasley

(Reuters) – U.S. regulators on Thursday approved BioMarin Pharmaceutical Inc’s Palynziq for adults with phenylketonuria, a rare metabolic disorder, sending shares of the biotechnology company up 3 percent after hours.

The drug, an injected enzyme replacement therapy, will have a list price of $267,000 a year, but after discounts mandated by government health plans and other concessions the net price will be $192,000, the company said in an emailed statement.

BioMarin said the drug will be available in the United States by the end of June.

Shares of BioMarin, which closed at $88.28 in regular trading, were up $2.72 at $91 after hours.

The FDA approval is “an important vote of confidence” for BioMarin, which could see significant growth potential driven by new products, J.P. Morgan analyst Cory Kasimov said in a research note.

BioMarin said Palynziq is the first approved enzyme substitution therapy to target the underlying cause of phenylketonuria, or PKU, by helping the body to break down phenylalanine, an amino acid found in protein-rich foods such as meat, dairy and eggs.

The FDA approved Palynziq for adults who have unontrolled concentrations of phenylalanine above a specific threshold despite other treatments. The drug can cause a severe allergic reaction, the company said.

About 11,000 people are living with PKU in the United States, according to BioMarin. Infants are screened at birth for the condition to make sure they are diagnosed and treated early.

If left untreated, the inherited disease can cause brain damage, leading to seizures, mental disorders and other neurological complications. Patients are treated throughout their lives, including a restricted diet.

Wall Street analysts, on average, expected sales of Palynziq to reach $620 million a year by 2024, according to Thomson Reuters I/B/E/S.

An older BioMarin drug for PKU, Kuvan, works by increasing activity of an enzyme that helps to reduce levels of phenylalanine in the blood.

(Reporting By Deena Beasley; Editing by Darren Schuettler)