Ileal and Colonic Crohn Disease Are Two Different Diseases

In many studies, variations in the NOD2 gene are associated with small bowel Crohn disease and certain HLA alleles with colonic disease.

The current study of genes and subtypes of inflammatory bowel disease is the largest to date, involving nearly 35,000 patients. NOD2 was confirmed as strongly associated with ileal location and age at diagnosis. HLA alleles were associated with overall inflammatory bowel disease risk, age of onset, Crohn disease location, extent of ulcerative colitis, and surgery. A new gene locus called 3p21/MST1 was associated with age at diagnosis.

No other individual genetic markers were strongly associated with phenotype. Using a genetic score based on combinations of a large number of markers that were individually wea…