Tetrahydrobiopterin Deficiency (cont.)

What are the symptoms of tetrahydrobiopterin deficiency?

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High levels of phenylalanine are present from early infancy in people with untreated tetrahydrobiopterin deficiency. Infants with this condition appear normal at birth, but medical problems ranging from mild to severe become apparent over time.

The signs and symptoms of this condition can include:

  • intellectual disability,

  • progressive problems with development,

  • movement disorders,

  • difficulty swallowing,

  • seizures,

  • behavioral problems, and

  • an inability to control body temperature.

How common is tetrahydrobiopterin deficiency?

This condition is very rare, affecting about 1 per million newborns. In most parts of the world, tetrahydrobiopterin deficiency accounts for only 1 percent to 2 percent of all cases of elevated phenylalanine levels. The remaining cases are caused by a similar condition called phenylketonuria (PKU). In certain countries, including Saudi Arabia, Taiwan, China, and Turkey, it is more common for elevated levels of phenylalanine to be caused by tetrahydrobiopterin deficiency.

What genes are related to tetrahydrobiopterin deficiency?

Tetrahydrobiopterin deficiency can be caused by mutations in one of several genes, including GCH1, PCBD1, PTS, and QDPR. These genes provide instructions for making enzymes that help produce and recycle tetrahydrobiopterin in the body. Tetrahydrobiopterin (also known as BH4) is a molecule that helps process several amino acids, including phenylalanine. It is also involved in the production of chemicals called neurotransmitters, which transmit signals between nerve cells in the brain.

If one of the enzymes fails to function correctly because of a gene mutation, little or no tetrahydrobiopterin is available to help process phenylalanine. As a result, phenylalanine can build up in the blood and other tissues. Because nerve cells in the brain are particularly sensitive to phenylalanine levels, excessive amounts of this substance can cause brain damage. Tetrahydrobiopterin deficiency can also alter the levels of certain neurotransmitters, which disrupts normal brain function.


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Tetrahydrobiopterin Deficiency - Symptoms Question: Please describe the symptoms associated with tetrahydrobiopterin deficiency in your child or relative.

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