The VKORC1 gene encodes Vitamin K Epoxide Reductase Complex 1 (VKORC1), which is responsible for reducing vitamin K 2,3-epoxide to the enzymatically active form of vitamin K that is essential for blood clotting. This protein comprises of 163 amino acids, with a molecular mass of 18.235 kDa. Variants in the VKORC1 gene appear to be the most important genetic factor determining variability in warfarin dose.
The VKORC1 gene is localized on chromosome 16p11.2. It is about 5 kb long, consists of three coding exons, and has two alternatively spliced transcripts encoding different isoforms. Individuals with an A allele (haplotype) in the VKORC1 1639 (or 3673) polymorphism need lower warfarin doses to inhibit VKORC1 and to produce an anticoagulant effect, because A allele carriers produce less VKORC1 than do those with G (non-A haplotype) allele. The prevalence of A allele varies by race; 37% of Caucasians and 14% of Africans have this allele.