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

QDPR gene

The QDPR gene provides instructions for making an enzyme essential for recycling tetrahydrobiopterin, a molecule critical for neurotransmitter production and amino acid processing.

Normal Function

The QDPR gene provides instructions for making an enzyme called quinoid dihydropteridine reductase. 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. Quinoid dihydropteridine reductase is one of two enzymes that help recycle tetrahydrobiopterin in the body.

Health Conditions Related to Genetic Changes

Tetrahydrobiopterin deficiency

More than 30 mutations in the QDPR gene have been found to cause tetrahydrobiopterin deficiency. When this condition results from QDPR gene mutations, it is known as dihydropteridine reductase (DHPR) deficiency, which accounts for about one-third of all cases of tetrahydrobiopterin deficiency.

Most QDPR gene mutations change single amino acids in quinoid dihydropteridine reductase, although some mutations insert small amounts of DNA or disrupt the gene's instructions. These changes greatly reduce or eliminate the enzyme's activity, preventing the proper recycling of tetrahydrobiopterin. Consequences include:

  • Phenylalanine buildup: Without sufficient tetrahydrobiopterin, phenylalanine cannot be converted to tyrosine. It can build up to toxic levels in the blood and tissues, potentially causing brain damage as nerve cells are highly sensitive to these levels.
  • Neurotransmitter disruption: Reduced enzyme activity disrupts the production of certain neurotransmitters, contributing to intellectual disability.

Other Names for This Gene

  • DHPR
  • DHPR_HUMAN
  • Dihydropteridine reductase
  • PKU2
  • SDR33C1

Frequently Asked Questions

BH4 is a cofactor because it is required by enzymes to catalyze chemical reactions, specifically the conversion of phenylalanine to tyrosine and the synthesis of neurotransmitters. During these reactions, BH4 is oxidized and becomes inactive. The QDPR enzyme is responsible for reducing it back to its active form. When QDPR is defective, BH4 cannot be recycled, leading to a depletion of the active cofactor. This results in the toxic buildup of phenylalanine and a deficiency in neurotransmitters like dopamine and serotonin.
While both conditions involve elevated phenylalanine levels, DHPR deficiency (caused by QDPR mutations) also affects neurotransmitter production because tetrahydrobiopterin (BH4) is a cofactor for dopamine and serotonin synthesis. Therefore, DHPR deficiency often presents with neurological symptoms such as developmental delay, seizures, and movement disorders, which are not typical of classic PKU. Treatment for DHPR deficiency usually requires BH4 supplementation in addition to a low-phenylalanine diet, whereas classic PKU is managed primarily through diet alone.
No, a low-phenylalanine diet addresses the toxic buildup of phenylalanine but does not correct the underlying neurotransmitter deficiency. Since the QDPR mutation prevents the recycling of BH4, patients often require pharmacological supplementation with BH4 (sapropterin) to support neurotransmitter synthesis. Without BH4 supplementation, neurological symptoms such as movement disorders and cognitive delays may persist despite normalizing phenylalanine levels.
Early signs often appear in the first few months of life and may include feeding difficulties, poor weight gain, and hypotonia (low muscle tone). As the condition progresses, infants may develop seizures, developmental delays, and movement disorders such as dystonia. Because elevated phenylalanine can be detected on newborn screening, early diagnosis is critical to prevent permanent neurological damage.
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.

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