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VKORC1 gene

vitamin K epoxide reductase complex subunit 1

Normal Function

The VKORC1 gene provides instructions for making a vitamin K epoxide reductase enzyme. The VKORC1 enzyme is made primarily in the liver. It spans the membrane of a cellular structure called the endoplasmic reticulum, which is involved with protein processing and transport. The VKORC1 enzyme helps turn on (activate) clotting proteins in the pathway that forms blood clots. Specifically, the VKORC1 enzyme converts one form of vitamin K into a different form of vitamin K that assists in activating clotting proteins.

Health Conditions Related to Genetic Changes

Warfarin resistance

Multiple variations (polymorphisms) in the VKORC1 gene have been associated with warfarin resistance, a condition in which individuals require higher doses of the drug warfarin than are usually prescribed. Warfarin is an anticoagulant, which means that it thins the blood and prevents blood clots from forming. It acts by attaching (binding) to the VKORC1 enzyme and blocking (inhibiting) the activation of the clotting proteins.

The most common VKORC1 gene polymorphism in people with warfarin resistance changes a single protein building block (amino acid) in the VKORC1 enzyme. Specifically, the amino acid aspartic acid is replaced with the amino acid tyrosine at position 36 (written as Asp36Tyr or D36Y). This polymorphism leads to the formation of a VKORC1 enzyme with a decreased ability to bind to warfarin. As a result, a higher dose of warfarin is needed to inhibit the VKORC1 enzyme and stop the clotting process. If people with warfarin resistance require anticoagulant treatment and take the average warfarin dose (or less), they will remain at risk of developing a potentially harmful blood clot.

More About This Health Condition

Warfarin sensitivity

Multiple polymorphisms in the VKORC1 gene have been associated with warfarin sensitivity, a condition in which individuals require lower doses of the drug warfarin than are usually prescribed.

The most common VKORC1 gene polymorphism in people with warfarin sensitivity, known as VKORC1A, changes a single DNA building block (nucleotide) in an area near the VKORC1 gene, which controls the production of the enzyme. Specifically, the nucleotide guanine is replaced with the nucleotide adenine (written as -1639G>A). The VKORC1A polymorphism is particularly common in individuals of Asian and European descent. This change reduces the amount of VKORC1 enzyme that is available to convert vitamin K into a form that can activate clotting proteins. Because there is a decreased amount of VKORC1 enzyme, a lower dose of warfarin is needed to inhibit the actions of the enzyme, resulting in warfarin sensitivity. If people with warfarin sensitivity take the average warfarin dose (or more), they are at risk of an overdose, which can cause abnormal bleeding in the brain, gastrointestinal tract, or other tissues, and may lead to serious health problems or death.

More About This Health Condition

Other Names for This Gene

  • FLJ00289
  • vitamin K 1 2,3-epoxide reductase subunit 1
  • vitamin K epoxide reductase complex, subunit 1
  • VKOR

Additional Information & Resources

Tests Listed in the Genetic Testing Registry

Scientific Articles on PubMed

Catalog of Genes and Diseases from OMIM

Gene and Variant Databases


  • Ferder NS, Eby CS, Deych E, Harris JK, Ridker PM, Milligan PE, Goldhaber SZ, King CR, Giri T, McLeod HL, Glynn RJ, Gage BF. Ability of VKORC1 and CYP2C9 to predict therapeutic warfarin dose during the initial weeks of therapy. J Thromb Haemost. 2010 Jan;8(1):95-100. doi: 10.1111/j.1538-7836.2009.03677.x. Epub 2009 Oct 30. Citation on PubMed or Free article on PubMed Central
  • Flockhart DA, O'Kane D, Williams MS, Watson MS, Flockhart DA, Gage B, Gandolfi R, King R, Lyon E, Nussbaum R, O'Kane D, Schulman K, Veenstra D, Williams MS, Watson MS; ACMG Working Group on Pharmacogenetic Testing of CYP2C9, VKORC1 Alleles for Warfarin Use. Pharmacogenetic testing of CYP2C9 and VKORC1 alleles for warfarin. Genet Med. 2008 Feb;10(2):139-50. doi: 10.1097/GIM.0b013e318163c35f. Citation on PubMed
  • Kaye JB, Schultz LE, Steiner HE, Kittles RA, Cavallari LH, Karnes JH. Warfarin Pharmacogenomics in Diverse Populations. Pharmacotherapy. 2017 Sep;37(9):1150-1163. doi: 10.1002/phar.1982. Epub 2017 Sep 6. Citation on PubMed
  • Kurnik D, Qasim H, Sominsky S, Lubetsky A, Markovits N, Li C, Stein CM, Halkin H, Gak E, Loebstein R. Effect of the VKORC1 D36Y variant on warfarin dose requirement and pharmacogenetic dose prediction. Thromb Haemost. 2012 Oct;108(4):781-8. doi: 10.1160/TH12-03-0151. Epub 2012 Aug 7. Citation on PubMed or Free article on PubMed Central
  • Li T, Chang CY, Jin DY, Lin PJ, Khvorova A, Stafford DW. Identification of the gene for vitamin K epoxide reductase. Nature. 2004 Feb 5;427(6974):541-4. doi: 10.1038/nature02254. Citation on PubMed
  • Lund K, Gaffney D, Spooner R, Etherington AM, Tansey P, Tait RC. Polymorphisms in VKORC1 have more impact than CYP2C9 polymorphisms on early warfarin International Normalized Ratio control and bleeding rates. Br J Haematol. 2012 Jul;158(2):256-261. doi: 10.1111/j.1365-2141.2012.09150.x. Epub 2012 May 10. Citation on PubMed
  • Watzka M, Geisen C, Bevans CG, Sittinger K, Spohn G, Rost S, Seifried E, Muller CR, Oldenburg J. Thirteen novel VKORC1 mutations associated with oral anticoagulant resistance: insights into improved patient diagnosis and treatment. J Thromb Haemost. 2011 Jan;9(1):109-18. doi: 10.1111/j.1538-7836.2010.04095.x. Citation on PubMed

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.