Association of the GGCX (CAA)16/17 repeat polymorphism with higher warfarin dose requirements in African Americans

Pharmacogenet Genomics. 2012 Feb;22(2):152-8. doi: 10.1097/FPC.0b013e32834f288f.


Objective: Little is known about genetic contributors to higher than usual warfarin dose requirements, particularly for African Americans. This study tested the hypothesis that the γ-glutamyl carboxylase (GGCX) genotype contributes to warfarin dose requirements greater than 7.5 mg/day in an African American population.

Methods: A total of 338 African Americans on a stable dose of warfarin were enrolled. The GGCX rs10654848 (CAA)n, rs12714145 (G>A), and rs699664 (p.R325Q); VKORC1 c.-1639G>A and rs61162043; and CYP2C9*2, *3, *5, *8, *11, and rs7089580 genotypes were tested for their association with dose requirements greater than 7.5 mg/day alone and in the context of other variables known to influence dose variability.

Results: The GGCX rs10654848 (CAA)16 or 17 repeat occurred at a frequency of 2.6% in African Americans and was overrepresented among patients requiring greater than 7.5 mg/day versus those who required lower doses (12 vs. 3%, P=0.003; odds ratio 4.0, 95% confidence interval, 1.5-10.5). The GGCX rs10654848 genotype remained associated with high dose requirements on regression analysis including age, body size, and VKORC1 genotype. On linear regression, the GGCX rs10654848 genotype explained 2% of the overall variability in warfarin dose in African Americans. An examination of the GGCX rs10654848 genotype in warfarin-treated Caucasians revealed a (CAA)16 repeat frequency of only 0.27% (P=0.008 compared with African Americans).

Conclusion: These data support the GGCX rs10654848 genotype as a predictor of higher than usual warfarin doses in African Americans, who have a 10-fold higher frequency of the (CAA)16/17 repeat compared with Caucasians.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Anticoagulants / administration & dosage
  • Anticoagulants / therapeutic use*
  • Black or African American*
  • Carbon-Carbon Ligases / genetics*
  • Female
  • Genotype
  • Humans
  • Linear Models
  • Male
  • Middle Aged
  • Polymorphism, Genetic*
  • Warfarin / administration & dosage
  • Warfarin / therapeutic use*


  • Anticoagulants
  • Warfarin
  • Carbon-Carbon Ligases
  • glutamyl carboxylase