Phenylketonuria (PKU) and mild hyperphenylalaninemia (HPA) are genetic disorders characterized by a deficiency in phenylalanine hydroxylase (PAH), resulting in intellectual impairment if not treated with dietary restriction of phenylalanine intake. Sapropterin dihydrochloride (Kuvan) is an orally active synthetic form of (6R)-L-erythro-5,6,7,8-tetrahydrobiopterin (BH4; a cofactor for PAH) that has received Orphan Drug status and Fast Track designation for the treatment of PKU. Phase II and III clinical data demonstrated that Kuvan was a safe and effective therapy in selected patients with HPA and mild-to-moderate PKU who responded to a BH4 loading test. Based on the clinical data, BioMarin Pharmaceutical Inc has estimated that Kuvan could be a potential treatment option for 30 to 50% of the estimated 50,000 patients in the developed world who have been diagnosed with PKU. According to Thomson Scientific's Strategic Drugs Database (SDdb), the worldwide consensus forecast values for Kuvan are approximately US $120, 190 and 260 million for 2008, 2009 and 2010, respectively.