Thiopurine methyltransferase activity in the Jewish population of Israel

Objective: 6-Mercaptopurine is used therapeutically for its immunosuppressant and cytotoxic properties. It is deactivated by thiopurine methyltransferase (TPMT), which shows genetic polymorphism in many populations. In North American populations, TMPT activity exhibits a trimodal activity pattern. In Oriental populations, TPMT shows almost a unimodal pattern of activity. The purpose of the present study was to assess the activity of TPMT in a Jewish male population sample in Israel. Methods: The study was approved by the Israeli Ministry of Health. Blood samples of 2.5 mi were collected in heparinized tubes from 134 males. The red blood cell (RBC) fraction of each individual was washed and hemolyzed. TPMT activity in the RBC hemolysate was determined using a radioactive assay with tritiated S-adenosyl methionine as a methyl donor. Results: The activity of TPMT ranged from 3.2 nmol/h/ml to 42.9 nmol/h/ml packed RBCs with mean and median activities of 18.6 nmol/h/ml and 17.9 nmol/h/ml packed RBCs, respectively. The distribution frequency of TPMT was very close to the unimodal by analysis of normal distribution. Conclusion: The pattern of distribution of TPMT in the Jewish population of Israel is closer to that of East Asian populations than European and Worth American populations. This observation may have relevance for the usage of 6-mercaptopurine and azathioprine as therapeutic agents in the Jewish population.