IBD1 and IBD3 determine location of Crohn's disease in the Spanish population

Background: Crohn's disease is a heterogeneous disease from both genetic and clinical points of view. Aims: To look for associations between distinct genetic polymorphisms and clinical subgroups of the disease. Subjects: A total of 210 patients and 343 healthy control subjects, all adult, unrelated, white, Spanish individuals. Methods: DNA was purified from peripheral blood samples and was typed by sequence‐specific oligonucleotide polymerase chain reaction (PCR) method for human leukocyte antigen (HLA)‐DRB1 alleles (IBD3) and by allele‐specific PCR for NOD2/CARD15 (IBD1) polymorphisms. Results: NOD2/CARD15 mutations and HLA‐DRB1*07 confer susceptibility only to the ileal location of the disease, whereas HLA‐DRB1*0103 is associated only with the colonic location of the disease. The IBD3 effect was overshadowed by IBD1 mutations when present. Conclusion: The studied genetic polymorphisms of Crohn's disease basically determine the location of the disease and, only secondarily, the clinical form of the disease. This appears to be true for both inflammatory bowel diseases as HLA‐DRB1*0103 is associated both with colonic Crohn's disease and ulcerative colitis.