TPMT and Decreased total leukocyte count: Allelic and genotypic frequencies of the TMPT and NUDT15 SNPs showed no statistically significant correlation with the treatment response, and the distribution of TMPT haplotypes was similar between non-responder patients and those experiencing adverse events compared to the responders; however, when the distribution of TPMT haplotypes and NUDT15*3 variant carriers was examined in relation to the types of adverse events in intolerant patients versus those who achieved benefit from treatment, leukopenia was observed more often in CD patients with at least one haplotype of the TPMT gene.