ERYTHROCYTE THIOPURINE METHYLTRANSFERASE ACTIVITY IN A KOREAN POPULATION

Thiopurine methyltransferase (TPMT) is the enzyme responsible for the S-methylation of thiopurine drugs. The enzyme, present in human red bl ood cells (RBC), is known to exhibit genetic polymorphism and intereth nic differences in its activity have been demonstrated. We have studie d the role of TPMT polymorphism in Koreans and compared enzyme activit y between this and other ethnic groups. In a population of 350 unrelat ed healthy Korean subjects TPMT activity showed a large interindividua l variation ranging from 3.2 to 22.9 nmol ml(-1) packed RBC h(-1) with a median value of 12.0 and mode of 11.0 nmol ml(-1) packed RBC h(-1). The enzyme activity was higher in male subjects than that in female ( median values; 12.2 vs 11.2, 95% confidence interval of the difference ; -2.1, 4.0 nmol ml(-1) packed RBC h(-1)). All subjects had detectable TPMT activity, but contrary to previous reports in other ethnic group s, this was distributed unimodally. The median RBC TPMT activity was v ery similar to values found in Caucasian populations, higher than in F loridian blacks and lower than that of a Norwegian Saami population.