Below is an instruction from Human. Write a response.
    ### Instruction:
    What are the genetic changes related to warfarin sensitivity ?
    ### 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 CYP2C9 and VKORC1 genes account for 30 percent of the variation in warfarin metabolism due to genetic factors.
    