A retrospective cohort study that investigated the association of the risk for AZA-induced pancreatitis with the single nucleotide polymorphism mapped to the class II HLA gene, including the HLA-DQA1 and HLA-DRB1 haplotypes, in 373 IBD patients exposed to AZA showed that the class II HLA region was an important marker of the risk for AZA-induced pancreatitis [61]. This evidence concerns the gene HLA-DRB1 and pancreatitis.