BH4 is a cofactor for phenylalanine hydroxylase (PAH). Sapropterin dihydrochloride (Kuvan, 6R-BH4) acts a chaperone that can stabilize the PAH molecule and improve its function. Therapy with sapropterin allows some patients to tolerate more phenylalanine in the diet, but this benefit is not seen with all patients with phenylketonuria.
