A study from Colombel showed that three-quarters of leucopenia were not explained by TPMT gene mutations.13 Meanwhile, only 8% of patients with leucopenia had TPMT∗3C gene mutations in this present study, which corroborates our previous pilot study on IBD.5 The distribution of TPMT polymorphism is different significantly in different population. Here, TPMT is linked to inflammatory bowel disease.