Researchers report a new genetic variant that contributes to warfarin dose requirement in African American individuals. In a genome-wide association study of adult African Americans, Perera et al. identified a novel CYP2C single nucleotide polymorphism (SNP) that is associated with warfarin dose requirement. The researchers confirmed the association in a validation cohort and say that including this variant in pharmacogenetic dosing algorithms could improve warfarin dose prediction in this patient population.