Robert's counts have been slow to recover, so the doctor has ordered TPMT Genotype testing. TPMT stands for Thiopurine Methyltransferase. The test measures TPMT gene related enzyme activity in the red blood cells. If a person has too low of TPMT activity, they can develop more severe side effects to Thiopurine drugs, such as sever drops in blood counts. Thiopurine drugs include many antimetabolites used in Leukemia, crohns, arthritis, and organ transplant patients. The Mercaptopurine that Robert has been taking over the last year is one of these drugs. The thought is that Robert may have low TPMT activity, and the recent daily doses of mercaptopurine along with the cumulative amounts from the year previous are keeping his counts low. It may not have been an issue before now due to the regular amounts of blood transfusions he has received, likely with blood with out the TPMT gene deficiency. Now that he he is living off of only blood produced in his own body, the condition may finally be coming to fruition.
What does this all mean? From what I understand, if the tests confirm the above condition, all that has to be done is switching to a non Thiopurine chemotherapy for the remainder of his maintenance. All this has caused is some extension of the period of somewhat compromised immunity that he is in currently, as well as just making it take longer to get him "dialed in" to the specific therapies he'll use during the next three years. Once they sort this all out and get him paired to the best therapies for his body, we will resume chemo.
Robert is feeling fairly well, aside from the side effects he is having from the week long round of steroids he is currently taking. But to be honest, the rest of us suffer those side effects more that he does. They turn kids into little over emotional eating machines in an instant. I'm thankful that hes almost done with this dose. He is enjoying being back in school, and really cares about his friends. There is one new boy who is giving him a hard time and calling him "baldy" which is really hurting his feelings. I'm trying to teach him to deal with it properly, but it seams to be escalating. Its just a part of life, and he will learn a lot from it. I fear he's too young for the punch a bully square in the nose program, so I'm taking the "take the high road" position. We'll see how it shakes out, there's no doubt it will help make him even stronger.