Tetrahydrobiopterin deficiency can be caused by defects in four different genes.

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.

Mutations in the QDPR gene are a common cause of tetrahydrobiopterin deficiency.

Tetrahydrobiopterin deficiency (THBD, BHD)

Tetrahydrobiopterin deficiency (THBD, BHD), also called THB or BH deficiency, is a rare metabolic disorder that increases the blood levels of phenylalanine.

Atypical Hyperphenylalaninemia BH4 Deficiency Malignant Hyperphenylalaninemia Atypical PKU Malignant PKU Tetrahydrobiopterin Synthesis Tetrahydrobiopterin Regeneration Tetrahydrobiopterin Deficiency is a rare genetic, neurological disorder present at birth.

Tetrahydrobiopterin deficiency also disrupts the levels of certain neurotransmitters in the brain, which affects the function of the central nervous system (CNS), and dysregulation of the nitric oxide cycle leads to a buildup of peroxynitrite, an inflammatory oxidant that further degrades BH4 and perpetuates a state of inflammation.