Tetrahydrobiopterin deficiency

Tetrahydrobiopterin deficiency (also known as BH4 deficiency) is a rare inherited disorder that increases the levels of several substances, including phenylalanine, in the blood. Phenylalanine is a building block of proteins (an amino acid) that is obtained through the diet. It is found in all proteins and in some artificial sweeteners. If untreated, this condition can lead to intellectual disability and other serious health problems.

Signs and Symptoms

The signs and symptoms of tetrahydrobiopterin deficiency can vary widely. Newborns with this disorder appear healthy at birth, but medical problems ranging from mild to severe can become apparent over time. These problems can include intellectual disability, movement disorders, difficulty swallowing, seizures, behavioral problems, and progressive problems with development.

Causes

Tetrahydrobiopterin deficiency is caused by mutations in the GCH1, PCBD1, PTS, or QDPR gene. These genes provide instructions for making enzymes that are involved in the production of a molecule called tetrahydrobiopterin (BH4). BH4 helps convert several amino acids, including phenylalanine, to other essential molecules in the body. It is also involved in the production of neurotransmitters, which transmit signals between nerve cells in the brain.

Diagnosis

Tetrahydrobiopterin deficiency is diagnosed through newborn screening tests. These tests measure the amount of phenylalanine in a baby's blood. If the levels are too high, additional tests are done to determine if it is due to a BH4 deficiency or another condition called phenylketonuria (PKU).

Treatment

The treatment for tetrahydrobiopterin deficiency is lifelong and involves a diet low in phenylalanine. This includes a special medical formula and carefully chosen foods. Some individuals may also need to take BH4 supplements or other medications to help their body use BH4 more effectively.

Prognosis

The prognosis for individuals with tetrahydrobiopterin deficiency varies. With early diagnosis and treatment, many individuals can lead healthy lives. However, without treatment, this disorder can lead to severe intellectual disability and other health problems.

See Also

• Phenylketonuria
• Amino acid
• Neurotransmitter

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