BioMarin Pharmaceutical Inc. (Nasdaq: BMRN) has received Food and Drug Administration approval to a drug to treat the lack of an enzyme in adults that, unchecked, can damage the brain.

The condition could lead to severe intellectual disability, seizures, tremors, behavioral problems and psychiatric symptoms, the San Rafael-based company said in the announcement Thursday.

The company expects to market Palynziq (pegvaliase-pqpz) for use by the end of June. An injection, the drug is designed to reduce blood levels of the enzyme phenylalanine (Phe) in adults who have phenylketonuria, or PKU, also known as PAH deficiency. It is a genetic disorder caused by Phe deficiency. About 50,000 patients are diagnosed with it in the regions of the world where BioMarin operates.

The drug is said to be the first approved "enzyme substitution therapy." Phe is an amino acid that is found in all forms of protein. The disease is tested for in infants, occurring in one in every 12,000 live births in the U.S.

It is treated by restricting diets but is considered more difficult to treat in adults. Palynziq would help those adults whose levels are not controllable by other means. Unchecked, it can show up with severe intellectual disability, seizures, tremors, behavioral problems and psychiatric symptoms.

“The approval of Palynziq is the culmination of more than a decade of perseverance by BioMarin employees dedicated to bringing treatments to PKU adult patients,” said Jean-Jacques Bienaimé, chairman and CEO, in the announcement. “We are proud of this medical achievement and appreciate the FDA’s thoughtful review of our application. We also are grateful to the PKU patients and medical communities for their continued partnership and participation in the clinical program that led to the approval of this effective therapy.”

Christine Brown, M.S., executive director of the National PKU Alliance, is quoted as calling Palynziq potentially a "game-changing therapy" for adults "who have struggled throughout their lives to control their Phe levels, despite rigorous management."