|(C;C)||0.1||normal; no change in warfarin metabolism|
|(C;T)||CYP2C9*2 carrier; average 20% reduction in warfarin metabolism|
|(T;T)||2.1||CYP2C9*2 homozygote; average 40% reduction in warfarin metabolism|
rs1799853 is a SNP in the CYP2C9 gene and is linked to poor warfarin metabolism. Advanced knowledge of this may influence initial warfarin dosing by physicians. Warfarin is monitored through INR (international normalized ratio) and proper dosing is influenced by a variety of factors including warfarin metabolism and diet.[PMID 1305837]
rs1799853 is a SNP in the CYP2C9 gene. The rs1799853(T) allele encodes a variant amino acid, cysteine, which has been linked to poor metabolism of warfarin and thus sensitivity [PMID 15608560]. The common nomenclature for this polymorphism is CYP2C9*2 (Cys amino acid, T allele; the SNP is also known as C430T or Cys144Arg).
The CYP2C9*2 allele is also associated with higher sensitivity to the anti-epileptic drug phenytoin. Note however that the CPIC (and FDA) mention concurrent testing for the HLA-B*15:02 allele, since carriers are at significantly increased risk of Stevens-Johnson syndrome (SJS/PTEN).
The effect of CYP2C9 variants on drug metabolism should not be predicted without also considering CYP2C9*3, defined as the common loss of function variant rs1057910(C)  (NM_000771:c.430C>T, NP_000762:p.144R>C) [PMID 8004131] .
Individuals carrying this SNP may show increased risk of developing acute gastrointestinal bleeding during the use of nonsteroidal anti-inflammatory drugs (NSAIDs) that are CYP2C8 or CYP2C9 substrates, such as aceclofenac, celecoxib, diclofenac, ibuprofen, indomethazine, lornoxicam, meloxicam, naproxen, piroxicam, tenoxicam and valdecoxib.[PMID 19422321]
|Trait||Warfarin maintenance dose|
|Title||A Genome-Wide Association Study Confirms VKORC1, CYP2C9, and CYP4F2 as Principal Genetic Determinants of Warfarin Dose|
|Odds Ratio||0.54 [0.45-0.63] mg/week decrease|
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|Disease||Warfarin response warfarin response - Dosage not specified|
|CLNDBN||Warfarin response warfarin response - Dosage not specified|
|CLNSRC||OMIM Allelic Variant PharmGKB Clinical Annotation UniProtKB (protein)|
|CLNACC||RCV000150377.1, RCV000150378.1, RCV000008920.1, RCV000154312.1, RCV000211223.1, RCV000309101.1,|
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|qualified_impact||Moderate clinical importance, pharmacogenetic|
|summary||This variant, also called CYP2C9*2, is a pharmacogenetic variant that modulates sensitivity for Warfarin (due to reduced metabolism). This variant is associated with Caucasians. The FDA has approved reduced recommended Warfarin dosage based on the presence of this variant.|
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