josie has leukemia and her doctor is thinking about giving her the chemotherapy drug purinethol, which is the best drug for this type of leukemia. tpmt is an enzyme that breaks down purinethol in the body so that it doesn't become toxic. josie's doctor does a genetic test and finds out she has a version of tpmt that has very little or no activity and is not really functional. what do you expect josie's doctor will do?