ChEBI: Sapropterin dihydrochloride is the dihydrochloride salt of sapropterin. It is used for the diagnosis and treatment of variant forms of phenylketonuria (hyperphenylalaninaemia) associated with tetrahydrobiopterin deficiency. Natural cofactor for phenylalanine hydroxylase, tyrosine hydroxylase, tryptophan hydroxylase, and nitric oxide synthetase. It has a role as a diagnostic agent and a coenzyme. It contains a sapropterin.