Review Article
Maciej Jankowski, Piotr Lan
Abstract
Inflammatory Bowel Disease (IBD) is more prevalent in children than adults, and the incidence is increasing. IBD is treated with thiopurines, metabolized by thiopurine S-methyltransferase (TPMT) and inter-individual variability in activity of TPMT affecting therapy efficiency and drug toxicity arises from genetic polymorphisms, mainly TPMT*2, *3A, and *3C. The aim was to investigate the frequency distribution of TPMT activity, determine the penetration rate of TPMT*2, *3A, and *3C alleles in children, and compare TPMT activity in children and adults with IBD. The study included 85 children, 45% with Crohn’s disease (CD) and 55% with ulcerative colitis (UC), and 31 adults with IBD. TPMT activity was measured with radiochemistry. TPMT*2, *3A, and *3C alleles were investigated with PCR and restriction fragment length polymorphism analyses. Children showed median TPMT activities of 13.12 and 13.19 U/ml RBC in CD and UC, respectively, with 4.8-fold variability (range, 4.74 - 22.56 U/ml RBC). TPMT activity was similar in children and adults; ranges: 5.56-21.34 vs. 9.61-17.84 U/ml RBC, respectively, in CD; and 4.74-22.56 vs. 5.19-21.98 U/ml RBC, respectively, in UC. Patients with CD and UC treated with azathioprine displayed similar TPMT activities, similar adverse event frequencies, and similar numbers of non-responders. One out of 85 patients (1.18%) was heterozygous with TPMT*1/TPMT*2 (TPMT activity: 5.19 ± 0.05 U/ml RBC). Individuals with low-intermediate TPMT activity (<8 U/ ml RBC) did not carry mutant alleles *3A or *3C. TPMT phenotypes were similar in children and adults with inflammatory bowel disease.