Below is an instruction from Human. Write a response.
    ### Instruction:
    What are the genetic changes related to warfarin resistance ?
    ### Response:
    Many genes are involved in the metabolism of warfarin and in determining the drug's effects in the body. Certain common changes (polymorphisms) in the VKORC1 gene account for 20 percent of the variation in warfarin metabolism due to genetic factors. Polymorphisms in other genes, some of which have not been identified, have a smaller effect on warfarin metabolism.
    