Tetrahydrobiopterin Deficiency

Tetrahydrobiopterin deficiency (THBD, BH₄D), also called THB or BH₄ deficiency, is a rare metabolic disorder that increases the blood levels of phenylalanine. Phenylalanine is an amino acid obtained through the diet. It is found in all proteins and in some artificial sweeteners. If tetrahydrobiopterin deficiency is not treated, excess phenylalanine can build up to harmful levels in the body, causing mental retardation and other serious health problems.

High levels of phenylalanine are present from infancy in people with untreated tetrahydrobiopterin (THB, BH₄) deficiency. The resulting signs and symptoms range from mild to severe. Mild complications may include temporary low muscle tone. Severe complications include mental retardation, movement disorders, difficulty swallowing, seizures, behavioral problems, progressive problems with development, and an inability to control body temperature.

It was first characterized in 1975.