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Vol. LVII, No. 15
July 29, 2005

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Genetic Variation Alters Response to Warfarin

By looking at the genetic makeup of people taking warfarin, researchers show that variations in a gene involved in blood clotting may explain why certain people require a lower or higher dose of the commonly prescribed anti-clotting drug. The finding ultimately could help doctors determine each patient's warfarin dose more quickly and precisely.

The proper dose of warfarin (Coumadin) can vary greatly between people and be hard for doctors to predict. To understand what accounts for some of this variability, researchers from the University of Washington in Seattle and Washington University in St. Louis analyzed the genetic makeup of people taking warfarin. They looked for variations in the gene vitamin K epoxide reductase (VKORC1), which makes a protein that helps control clotting and is the key target of warfarin.

The researchers found that the gene accounted for 25 percent of the overall variation in warfarin dose, suggesting that information about the gene could predict a person's response to the anti-clotting drug. Although genetic screening for the gene could lead to more precise dosing, the researchers agreed more research needs to be done first.

"This research points to the value of pharmacogenetics, the study of how genetic variations can alter people's responses to medicines," said NIH director Dr. Elias Zerhouni. "It shows one important way in which we are beginning to apply knowledge about the human genome for treating disease and improving human health."

The study, part of the NIH Pharmacogenetics Research Network, was supported by NIGMS, NHLBI and NIEHS.