Tetrahydrobiopterin Deficiency (BH4 Deficiency)

What is tetrahydrobiopterin deficiency?

Tetrahydrobiopterin (also known as BH4) deficiency is a rare disorder that increases the blood levels of a substance called phenylalanine. Phenylalanine is an amino acid (a building block of proteins) 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 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, behavioural problems, progressive problems with development, and an inability to control body temperature.

How common is tetrahydrobiopterin deficiency?

This condition is very rare; approximately 450 cases have been reported worldwide. In most parts of the world, only 1 percent to 2 percent of all infants with high phenylalanine levels have this disorder. In China, about 30 percent of newborns with elevated levels of phenylalanine have a deficiency of tetrahydrobiopterin.

What genes are related to tetrahydrobiopterin deficiency?

Mutations in the GCH1, PCBD1, PTS, and QDPR genes cause tetrahydrobiopterin deficiency.

Tetrahydrobiopterin is a compound that helps convert several amino acids, including phenylalanine, to other essential molecules in the body. It is also involved in the production of chemicals called neurotransmitters that transmit signals between nerve cells in the brain. Tetrahydrobiopterin deficiency can be caused by mutations in one of several genes, including GCH1, PCBD1, PTS, and QDPR. These genes make enzymes that are critical for producing and recycling tetrahydrobiopterin. If one of the enzymes fails to function correctly because of a gene mutation, little or no tetrahydrobiopterin is produced. As a result, phenylalanine from the diet builds up in the bloodstream and other tissues and can damage nerve cells in the brain. Tetrahydrobiopterin deficiency also disrupts the levels of certain neurotransmitters in the brain, which affects the function of the central nervous system.

How do people inherit tetrahydrobiopterin deficiency?

This condition is inherited in an autosomal recessive pattern, which means two copies of a specific gene in each cell are altered. Most often, the parents of an individual with an autosomal recessive disorder are carriers of one copy of the altered gene but do not show signs and symptoms of the disorder.

What other names do people use for tetrahydrobiopterin deficiency?

  • BH4 Deficiency
  • Hyperphenylalaninemia caused by a defect in biopterin metabolism
  • Hyperphenylalaninemia, Non-Phenylketonuric
  • Non-Phenylketonuric Hyperphenylalaninemia

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