The association between thiopurine S-methultransferase *3C polymorphism and azathioprine induced myslosuppression in Thai patients with rheumatologic diseases

Abstract

Rheumatic diseases are of unknown pathogenic origin; during of the molecular and cellular processes that lead to disease pathology. Drugs used of treatment include azathioprine as immunosuppressants. Thiopurine S-methyltransferase (TPMT) is an enzyme important in drug metabolism which located in cytoplasm and genetic variation. Patients inheriting TPMT deficiency is at high risk of myelosuppression. The aim of this study was to characterize the TPMT*3C polymorphism. TPMT genotypes were determined using PCR-RFLP assays and TPMT activity RBC using HPLC method in 112 Rheumatogic patients taking azathioprine treatment. Biochemical and clinical data were retrospective. The results of genotyping analysis that found eight patients (7.14%) were heterozygous (TPMT*1/*3C) and one-hundred and four patients (92.86%) were homozygous TPMT*1 (A/A). The allele frequencies were 3.57% for “G” allele and 96.43% for “A” allele. The result show TPMT*1/*3C polymorphism are statistic significantly different (P < 0.001) and odd ratio 26.0, 95%CI 4.783 – 141.333 higher risk for AZA-induced leucopenia. Both patients groups taking azathioprine dose between 0.65 – 2.50 mg/kg/day that mean 1.54 ± 0.51 (SD) between azathioprine dose that result show not significantly different (P = 0.186). But not significantly different induced neutropenia (P = 0.06, odd ratio 8.889, 95%CI 1.237 – 63.878) and lymphopenia (P = 0.085, odd ratio 6.583, 95%CI 0.995 – 43.553). The mean of TPMT activity between TPMT*1/*1 (37.90 ± 12.64) and TPMT*1/*3C genotypes (17.53 ± 4.96) that found both groups were significantly difference (P<0.001). Base on the enzyme activity in RBCs which the optimal cut-off activities for TPMT activity calculated intermediate activity was ≤ 23.01 nmol 6-MTG/gHb/hr and high activity was > 23.01 nmol 6-MTG/gHb/hr with AUC. The statistical represent association between leucopenia (P = 0.003, odd ratio 21.5, 95%CI 2.961 – 156.128). But not significantly different induced T neutropenia (P = 0.059, odd ratio 11.25, 95%CI 1.233 – 102.623) and lymphopenia (P = 0.391, odd ratio 2.933, 95%CI 0.254 – 33.823) same as compared with genotype.