Rs9923231

Several SNPs in the VKORC1 gene have been linked to warfarin sensitivity, with perhaps the most common being this SNP rs9923231. Note that the orientation as published in scientific articles is often on the opposite strand compared to the orientation in dbSNP, so you will sometimes see it as a G>T snp. It is also known as
 * -1639G>A with the minus indicating that this is in an upstream promoter
 * 3673 based on its position in GenBank accession number AY587020.
 * VKORC1*2.

The main findings related to the treatment of venous thromboembolism (aka VTE; from hypercoagulability) with the blood thinner warfarin for this SNP are that carriers of the rs9923231(T) allele require significantly reduced doses of warfarin, and are (otherwise) at a higher risk of serious bleeding.

Clinical studies demonstrate that rs9923231(A), and the tightly linked intron1 SNP rs9934438(T) predict warfarin dose more accurately than intron 2 SNP 1542G>C in blacks. Increased warfarin dose requirement in blacks was accounted for by lower frequency of the rs9923231(T) allele. Therefore, the T allele at rs9923231 is a suitable biomarker for warfarin dosing across ethnic populations.