Tetrahydrobiopterin Deficiency Causes, Symptoms, and Treatment

What is tetrahydrobiopterin deficiency? Tetrahydrobiopterin deficiency is a rare disorder that increases the levels of several substances, including phenylalanine, in the blood. Phenylalanine is a building block of proteins (an amino acid) that is obtained through the diet. It is found in all proteins and in some artificial sweeteners. If tetrahydrobiopterin deficiency is not treated,