<unk>  (THBD, BH4D) is a rare metabolic disorder that increases the blood levels of phenylalanine. Phenylalanine is an amino acid obtained normally through the diet, but can be harmful if excess levels build up, causing intellectual disability and other serious health problems. In healthy individuals, it is metabolised (hydroxylated) into tyrosine, another amino acid, by phenylalanine hydroxylase. However, this enzyme requires<unk>  as a cofactor and thus its deficiency slows phenylalanine metabolism. High levels of phenylalanine are present from infancy in people with untreated<unk>  (THB, BH4) deficiency. The resulting signs and symptoms range from mild to severe. Mild complications may include temporary low muscle tone. Severe complications include intellectual disability, movement disorders, difficulty swallowing, seizures, behavioral problems, progressive problems with development, and an inability to control body temperature. It was first characterized in 1975.
Tetrahydrobiopterin deficiency
Cerebral folate deficiency
Cytochrome b5 deficiency
Adenine phosphoribosyltransferase deficiency
Molybdenum cofactor deficiency
Methylenetetrahydrofolate reductase deficiency
Dihydropyrimidine dehydrogenase deficiency
Biotin deficiency