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Tetrahydrobiopterin deficiency

Other Names for this Disease
  • BH4 deficiency
  • Hyperphenylalaninemia caused by a defect in biopterin metabolism
  • Hyperphenylalaninemia, non-phenylketonuric
  • Non-phenylketonuric hyperphenylalaninemia
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Tetrahydrobiopterin (BH4) deficiency is a neurological condition caused by an inborn error of metabolism. BH4 is a substance in the body that enhances the action of other enzymes. Deficiency of BH4 leads to abnormally high blood levels of the amino acid phenylalanine, and low levels of certain neurotransmitters.[1] Signs and symptoms can range from very mild to severe.[2] Affected newborns appear normal at birth, but may begin to experience neurological symptoms such as abnormal muscle tone; poor sucking and coordination; seizures; and delayed motor development. Without early, appropriate treatment, the condition can cause permanent intellectual disability and even death.[1] BH4 deficiency is caused by mutations in any one of several genes including the GCH1, PCBD1, PTS, and QDPR genes. It is inherited in an autosomal recessive manner.[3]Treatment depends on the genetic cause and severity, and may include a low phenylalanine diet; oral BH4 supplementation; and neurotransmitter replacement.[1]
Last updated: 11/2/2012


  1. Tetrahydrobiopterin Deficiency. NORD. May 23, 2008; Accessed 10/31/2012.
  2. Noah S Scheinfeld. Tetrahydrobiopterin Deficiency. Medscape Reference. June 27, 2012; Accessed 11/2/2012.
  3. Tetrahydrobiopterin deficiency. Genetics Home Reference. July 2011; Accessed 11/2/2012.
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Basic Information

  • Genetics Home Reference (GHR) contains information on Tetrahydrobiopterin deficiency. This website is maintained by the National Library of Medicine.
  • The National Organization for Rare Disorders (NORD) is a federation of more than 130 nonprofit voluntary health organizations serving people with rare disorders. Click on the link to view information on this topic.

In Depth Information

  • Medscape Reference provides information on this topic. Click on the link to view this information. You may need to register to view the medical textbook, but registration is free.
  • The Online Mendelian Inheritance in Man (OMIM) is an catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
  • PubMed is a searchable database of medical literature and lists journal articles that discuss Tetrahydrobiopterin deficiency. Click on the link to view a sample search on this topic.