In a multi-center study involving Washington University, Intermountain, New York Presbyterian, and other centers, the GIFT trial, genotype-guided warfarin dosing was found to have clinical benefits.
GIFT randomized over 1600 patients undergoing either hip or knee arthroplasty. Composite adverse events fell from 15% to 11%.
Studying the value of genetic guidance in RCTs is problematic, because hospital based RCTs always insure that standard of care is optimally applied in the non-genetic arm. Genetic dose guidance might have more impact in the real world where standard of care is less monitored and controlled in typical patients. Some prior RCTs have been inconsistent; for one entry point, here.
The study by Gage et al. is online here; see also an Op Ed by Emery, here. Open access coverage at Genomeweb, here.
For a 2013 review at Genomeweb [subscription], here.