Preponderance of Thiopurine S-Methyltransferase Deficiency and Heterozygosity Among Patients Intolerant to Mercaptopurine or Azathioprine

There is a significant (> six-fold) overrepresentation of TPMT deficiency or heterozygosity among patients developing dose-limiting hematopoietic toxicity from therapy containing thiopurines. However, with appropriate dosage adjustments, TPMT-deficient and heterozygous patients can be treated with thiopurines, without acute dose-limiting toxicity.