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The official name of this gene is “quinoid dihydropteridine reductase.”
QDPR is the gene's official symbol. The QDPR gene is also known by other names, listed below.
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.
The QDPR gene belongs to a family of genes called SDR (short chain dehydrogenase/reductase superfamily).
A gene family is a group of genes that share important characteristics. Classifying individual genes into families helps researchers describe how genes are related to each other. For more information, see What are gene families? (http://ghr.nlm.nih.gov/handbook/howgeneswork/genefamilies) in the Handbook.
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. DHPR deficiency 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 into the QDPR gene or disrupt the way the gene's instructions are used to make the enzyme. Changes in quinoid dihydropteridine reductase greatly reduce or eliminate the enzyme's activity. Without enough of this enzyme, tetrahydrobiopterin is not recycled properly. As a result, this cofactor is not available to participate in chemical reactions such as the conversion of phenylalanine to tyrosine. If phenylalanine is not converted to tyrosine, it can build up to toxic levels in the blood and other tissues. Nerve cells in the brain are particularly sensitive to phenylalanine levels, which is why excessive amounts of this substance can cause brain damage.
Additionally, a reduction in quinoid dihydropteridine reductase activity disrupts the production of certain neurotransmitters in the brain. Because neurotransmitters are necessary for normal brain function, changes in the levels of these brain chemicals contribute to intellectual disability in people with DHPR deficiency.
Cytogenetic Location: 4p15.31
Molecular Location on chromosome 4: base pairs 17,488,015 to 17,513,856
The QDPR gene is located on the short (p) arm of chromosome 4 at position 15.31.
More precisely, the QDPR gene is located from base pair 17,488,015 to base pair 17,513,856 on chromosome 4.
See How do geneticists indicate the location of a gene? (http://ghr.nlm.nih.gov/handbook/howgeneswork/genelocation) in the Handbook.
You and your healthcare professional may find the following resources about QDPR helpful.
You may also be interested in these resources, which are designed for genetics professionals and researchers.
See How are genetic conditions and genes named? (http://ghr.nlm.nih.gov/handbook/mutationsanddisorders/naming) in the Handbook.
acids ; amino acid ; cofactor ; deficiency ; DNA ; enzyme ; gene ; molecule ; neurotransmitters ; phenylalanine ; protein ; toxic ; tyrosine
You may find definitions for these and many other terms in the Genetics Home Reference Glossary (http://www.ghr.nlm.nih.gov/glossary).
The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? (http://ghr.nlm.nih.gov/handbook/consult/findingprofessional) in the Handbook.