HLA-DRB1 and Crohn disease: It is also interesting that HLA-DQA1*05:01 remains in linkage disequilibrium with HLA-DRB1*03:01 (D’ = 0.75 according to LDpair; European populations), which is associated with an increased risk of Crohn’s disease in a study focusing on four-digit HLA typing by microarrays in over 30,000 IBD patients [15].