Abstract
Objective: Individuals with decreased thiopurine methyltransferase (TPMT) activity are at risk of adverse effects of thiopurine administration whereas its increased activity may inactivate drugs faster. We evaluated genotype-phenotype correlations in patients with suspected hematological malignancies and inflammatory bowel disease from our region based on findings of nonlinear TPMT enzyme kinetics previously unreported.
Patients and Methods: The study group comprised 267 individuals. They were screened for the most common variants of low TPMT activity.
TPMT activity was measured in erythrocytes using the HPLC rate-blanked method. Results: Thirty-three patients (12.4%) were heterozygous (26 were TPMT*1/*3A, 5 TPMT*1/*2, 2 TPMT*1/*3C) and 1 was a compound heterozygote (*2/*3A).
Normal and low normal TPMT activities substantially overlapped in wildtype and heterozygous individuals, whereas high activities were found in 29 wild-type genotyped patients. Extreme and life-threatening toxicity was observed in the compound heterozygote patient.
Conclusion: Activity measurement performed at diagnosis provides clinicians with information on immediate pharmacokinetic-related adverse events and/or hypermetabolism, and genotyping may indicate the rate of pharmacodynamic thioguanine nucleotide accumulation due to slower overall thiopurine metabolism. (C) 2014 S. Karger AG, Basel