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PCBD1 gene

Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

PCBD1 gene

The PCBD1 gene provides instructions for an enzyme that helps recycle tetrahydrobiopterin, a critical cofactor for processing amino acids and producing neurotransmitters.

Normal Function

The PCBD1 gene provides instructions for making an enzyme called pterin-4 alpha-carbinolamine dehydratase. This enzyme helps carry out one step in the chemical pathway that recycles a molecule called tetrahydrobiopterin (BH4).

Tetrahydrobiopterin plays a critical role in processing several protein building blocks (amino acids) in the body. For example, it works with the enzyme phenylalanine hydroxylase to convert an amino acid called phenylalanine into another amino acid, tyrosine. Tetrahydrobiopterin is also involved in reactions that produce chemicals called neurotransmitters, which transmit signals between nerve cells in the brain. Because it helps enzymes carry out chemical reactions, tetrahydrobiopterin is known as a cofactor.

When tetrahydrobiopterin interacts with enzymes during chemical reactions, the cofactor is altered and must be recycled to a usable form. Pterin-4 alpha-carbinolamine dehydratase is one of two enzymes that help recycle tetrahydrobiopterin in the body.

Health Conditions Related to Genetic Changes

Tetrahydrobiopterin deficiency

At least nine mutations in the PCBD1 gene have been found to cause tetrahydrobiopterin deficiency. When this condition results from PCBD1 gene mutations, it is known as pterin-4 alpha-carbinolamine dehydratase (PCD) deficiency. PCD deficiency accounts for about 5 percent of all cases of tetrahydrobiopterin deficiency.

Some mutations in the PCBD1 gene change single amino acids in pterin-4 alpha-carbinolamine dehydratase, while other mutations introduce a premature stop signal in the instructions for making this enzyme. Changes in pterin-4 alpha-carbinolamine dehydratase reduce the enzyme's activity, which affects the body's ability to recycle tetrahydrobiopterin. As a result, less of this cofactor is available to participate in chemical reactions such as the conversion of phenylalanine to tyrosine. If phenylalanine is not converted to tyrosine, the excess can build up in the bloodstream and other tissues.

Although people with PCD deficiency usually have elevated levels of phenylalanine in the blood, this form of tetrahydrobiopterin deficiency rarely causes significant medical problems. Researchers believe that other enzymes may compensate for the reduced activity of pterin-4 alpha-carbinolamine dehydratase in people with PCBD1 gene mutations.

Other Names for This Gene

  • 4-alpha-hydroxy-tetrahydropterin dehydratase
  • 6-pyruvoyl-tetrahydropterin synthase/dimerization cofactor of hepatocyte nuclear factor 1 alpha (TCF1)
  • Carbinolamine-4a-dehydratase
  • DCOH
  • Dimerization cofactor of hepatocyte nuclear factor 1-alpha
  • Dimerization cofactor of HNF1
  • PCBD
  • PCD
  • Phenylalanine hydroxylase-stimulating protein
  • PHS_HUMAN
  • Pterin carbinolamine dehydratase
  • pterin-4 alpha-carbinolamine dehydratase/dimerization cofactor of hepatocyte nuclear factor 1 alpha
  • pterin-4 alpha-carbinolamine dehydratase/dimerization cofactor of hepatocyte nuclear factor 1 alpha (TCF1)
  • Pterin-4-alpha-carbinolamine dehydratase
  • Pterin-4a-carbinolamine dehydratase (dimerization cofactor of hepatic nuclear factor 1-alpha)

Frequently Asked Questions

Many state newborn screening programs include a measurement of phenylalanine levels; an elevated phenylalanine with normal dihydropteridine reductase activity can prompt a specific BH4 loading test and genetic sequencing of PCBD1.
The mainstay is oral supplementation with sapropterin (synthetic BH4) to bypass the recycling defect, combined with a low‑phenylalanine diet to keep blood phenylalanine in the target range; regular neurodevelopmental assessments are also recommended.
PCBD1 deficiency follows an autosomal‑recessive pattern; both parents must carry one pathogenic variant. If one partner is a known carrier, the other should undergo carrier testing to determine the risk (25 % affected, 50 % carrier, 25 % unaffected) for each pregnancy.
cute worsening of lethargy, vomiting, seizures, or a sudden rise in blood phenylalanine (>360 µmol/L) are red‑flag signs that require immediate medical attention and possible adjustment of BH4 or dietary therapy.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.