Serono and BioMarin Pharmaceutical said they are on track to file for approval of an investigational drug for the genetic disorder phenylketonuria, or PKU, next year after reporting encouraging Phase III trial results.

The orally-bioavailable small molecule, Phenoptin (sapropterin dihydrochloride), was able to cut levels of the amino acid phenylalanine in the blood of PKU patients compared to placebo.

PKU is caused by a deficiency in an enzyme that metabolises phenylalanine, which is ingested in the diet. Patients with the disease must avoid eating foods containing the amino acid, otherwise levels of phenylalanine can accumulate in the blood and tissues and over time can cause nervous system damage, mental retardation and seizures.

Dietary restriction is currently used to control PKU, but an oral agent would help patients reach the treatment target of a blood level of phenylalanine of between 2mg/dl and 10mg/dl. This is enough to support normal growth, but avoids accumulation of the amino acid.

Emil Kakkis, chief medical officer of BioMarin said, "This is an exciting day for PKU patients worldwide as a simple oral treatment that could potentially help them reach their treatment goals is now one step closer to becoming a reality.”

BioMarin has licensed to Serono exclusive rights for Phenoptin outside of the USA and Japan. The two companies estimate that Phenoptin could be a potential treatment option for approximately 30% to 50% of the estimated 50,000 individuals in the developed world who have been diagnosed with PKU.

Phenoptin has been granted orphan drug status to treat PKU by both the Food and Drug Administration and the European Medicines Agency. If it becomes the first drug approved for treating the disease, it would have seven years of market exclusivity in the USA and 10 years in the EU.