Very recently, a large genotype-phenotype study, carried out by the International IBD Genetic Consortium, highlighted that three loci namely 16q12/NOD2, 6p21/MHC and 3p21/MST1 were of some guide in conditioning the site of CD within the gastrointestinal tract, with the 16q12/NOD2 locus as a major determinant of ileal disease, and the 6p21/MHC locus mainly associated with colonic disease [15]. This evidence concerns the gene HLA-C and inflammatory bowel disease.