| Abstract |
Introduction: There is evidence that genotyping for Thiopurine methyl-transferase (TPMT) gene variants is useful for the prediction of response to thiopurine analogues (azathioprine and 6-mercaptopurine) in patients with inflammatory bowel disease (IBD). Polymorphisms of the ABCB1 gene (coding for p-glycoprotein 170) have been associated with inflammatory bowel disease (IBD) and resistance to treatment but the reported results are conflicting. The aim of the present study was to determine the prevalence of TPMT gene polymorphisms in a genetic homogenous population of IBD patients in Crete and to correlate results with adverse reactions to thiopurine drugs and to determine the frequency and role of ABCB1 gene polymorphisms in Cretan IBD patients and study any possible association with susceptibility to Inflammatory bowel disease (ulcerative colitis and Crohn’s disease), as well as resistance to medical treatment (need for surgical intervention).
Methods: A total of 223 consecutive IBD patients [111 Crohn’s disease (CD) and 112 ulcerative colitis (UC)] were reviewed for disease phenotype, response to treatment and need for colectomy. Genotyping for the commonest TPMT variants, TPMT*3A, TPMT3*C, TPMT*3B using PCR-RFLP method as well as allele-specific PCR for TPMT*2 was performed in 223 consecutive IBD patients and 119 age and sex matched healthy controls. The hospital medical records were reviewed for thiopurine use in these patients and related adverse events. All patients and the control group were genotyped for ABCB1 gene polymorphisms (G2677T/A and C3435T) by using the PCR-RFLPs method.
Results: The prevalence of TPMT variants TPMT*2, TPMT*3A, TPMT*3B and TPMT*3C was 1.8%, 2.7%, 1.3% and 1.8% respectively. G238C mutation was detected in 4 out of 223 (1.8%) patients, 3 (1.3%) patients were carriers of G460A mutation, 4 (1.8%) of A719G mutation and 6 (2.7%) of both G460A and A719G mutation. In healthy controls only one (0.8%) carried both the G460A and A719G mutation whereas TPMT*2, TPMT*3C and TPMT*3B were not detected. None of the genotypes was homozygous. A statistically significant correlation between the presence of G460A mutation and the development of leucopenia after thiopurines administration was observed (p=0.048).
Allele and genotype frequencies of G2677T/A and C3435T polymorphisms were found to be similar in IBD patients and healthy controls. There was no statistically significant correlation between any of the mutant variants studied and IBD or CD. A statistically significant correlation between the presence of 2677T mutation and UC was observed (p=0.049). No association of G2677T/A or C3435T with clinical phenotype, or resistance to treatment was also found. However, 59% of 34/223 patients who did not respond to therapy and required surgery, where found to carry both the C3434T and the G2677T alleles.
Conclusion: This study showed lower frequency of total TPMT variants and higher frequency of TPMT*3B in Cretan IBD patients compared to other Caucasian populations. The presence of G460A mutation is associated with the development of leucopenia. Furtermore, our study showed correlation of the G2677T polymorphism and UC, while failed to demonstrate any correlation between the C3435T and G2677A polymorphisms of ABCB1/MDR1 and the development of IBD, CD, disease phenotype or response to treatment. There was a trend towards association of the combined carriage of G2677T and C3435T mutations with disease refractory to treatment.
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Μελέτη των γενετικών παραγόντων της ιδιοπαθούς φλεγμονώδους νόσου του εντέρου
