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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®

Crohn disease

Reviewed August 2007

What is Crohn disease?

Crohn disease is a complex, chronic disorder that primarily affects the digestive system. This condition typically involves abnormal inflammation of the intestinal walls, particularly in the lower part of the small intestine (the ileum) and portions of the large intestine (the colon). Inflammation can occur in any part of the digestive system, however. The inflamed tissues become thick and swollen, and the inner surface of the intestine may develop open sores (ulcers).

Crohn disease most commonly appears in a person's late teens or twenties, although the disease can appear at any age. Signs and symptoms tend to flare up multiple times throughout life. The most common features of this condition are persistent diarrhea, abdominal pain and cramping, loss of appetite, weight loss, and fever. Some people with Crohn disease have chronic bleeding from inflamed tissues in the intestine; over time, this bleeding can lead to a low number of red blood cells (anemia). In some cases, Crohn disease can also cause medical problems affecting the joints, eyes, or skin.

Intestinal blockage is a common complication of Crohn disease. Blockages are caused by swelling or a buildup of scar tissue in the intestinal walls. Some affected individuals also develop fistulae, which are abnormal connections between the intestine and other tissues. Fistulae occur when ulcers break through the intestinal wall to form passages between loops of the intestine or between the intestine and nearby structures (such as the bladder, vagina, or skin).

Crohn disease is one common form of inflammatory bowel disease (IBD). Another type of IBD, ulcerative colitis, also causes chronic inflammation of the intestinal lining. Unlike Crohn disease, which can affect any part of the digestive system, ulcerative colitis typically causes inflammation only in the colon. In addition, the two disorders involve different patterns of inflammation.

How common is Crohn disease?

Crohn disease is most common in western Europe and North America, where it affects 100 to 150 in 100,000 people. About one million Americans are currently affected by this disorder. Crohn disease occurs more often in whites and people of eastern and central European (Ashkenazi) Jewish descent than among people of other ethnic backgrounds.

What are the genetic changes related to Crohn disease?

Crohn disease is related to chromosomes 5 and 10.

Variations of the ATG16L1, IRGM, and NOD2 genes increase the risk of developing Crohn disease.

The IL23R gene is associated with Crohn disease.

A variety of genetic and environmental factors likely play a role in causing Crohn disease. Although researchers are studying risk factors that may contribute to this complex disorder, many of these factors remain unknown. Cigarette smoking is thought to increase the risk of developing this disease, and it may also play a role in periodic flare-ups of signs and symptoms.

Studies suggest that Crohn disease may result from a combination of certain genetic variations, changes in the immune system, and the presence of bacteria in the digestive tract. Recent studies have identified variations in specific genes, including ATG16L1, IL23R, IRGM, and NOD2, that influence the risk of developing Crohn disease. These genes provide instructions for making proteins that are involved in immune system function. Variations in any of these genes may disrupt the ability of cells in the intestine to respond normally to bacteria. An abnormal immune response to bacteria in the intestinal walls may lead to chronic inflammation and the digestive problems characteristic of Crohn disease.

Researchers have also discovered genetic variations in certain regions of chromosome 5 and chromosome 10 that appear to contribute to Crohn disease risk. One area of chromosome 5, known as the IBD5 locus, contains several genetic changes that may increase the risk of developing this condition. Other regions of chromosome 5 and chromosome 10 identified in studies of Crohn disease risk are known as "gene deserts" because they include no known genes. Instead, these regions may contain stretches of DNA that regulate nearby genes. Additional research is needed to determine how genetic variations in these chromosomal regions are related to a person's chance of developing Crohn disease.

Related Chromosome(s)

Changes involving these chromosomes are associated with Crohn disease.

  • chromosome 5
  • chromosome 10

Related Gene(s)

Changes in these genes are associated with Crohn disease.

  • ATG16L1
  • IL23R
  • IRGM
  • NOD2

Can Crohn disease be inherited?

The inheritance pattern of Crohn disease is unclear because many genetic and environmental factors are likely to be involved. This condition tends to cluster in families, however, and having an affected family member is a significant risk factor for the disease.

Where can I find information about diagnosis or management of Crohn disease?

These resources address the diagnosis or management of Crohn disease and may include treatment providers.

  • Genetic Testing Registry: Inflammatory bowel disease 1 (
  • MedlinePlus Encyclopedia: Crohn's disease (

You might also find information on the diagnosis or management of Crohn disease in Educational resources and Patient support.

General information about the diagnosis ( and management ( of genetic conditions is available in the Handbook. Read more about genetic testing (, particularly the difference between clinical tests and research tests (

To locate a healthcare provider, see How can I find a genetics professional in my area? ( in the Handbook.

Where can I find additional information about Crohn disease?

You may find the following resources about Crohn disease helpful. These materials are written for the general public.

You may also be interested in these resources, which are designed for healthcare professionals and researchers.

What other names do people use for Crohn disease?

  • Colitis, Granulomatous
  • Crohn's Disease
  • Crohn's enteritis
  • Enteritis, Granulomatous
  • Enteritis, Regional
  • Ileitis
  • Ileocolitis

For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines ( and How are genetic conditions and genes named? ( in the Handbook.

What if I still have specific questions about Crohn disease?

Ask the Genetic and Rare Diseases Information Center (

What glossary definitions help with understanding Crohn disease?

anemia ; autoimmune ; bacteria ; chromosome ; chronic ; colitis ; colon ; complication ; digestive ; digestive system ; DNA ; fever ; gene ; granulomatous ; ileum ; immune response ; immune system ; inflammation ; inheritance ; inheritance pattern ; intestine ; locus ; risk factors ; tissue

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


  • Chamberlin WM, Naser SA. Integrating theories of the etiology of Crohn's disease. On the etiology of Crohn's disease: questioning the hypotheses. Med Sci Monit. 2006 Feb;12(2):RA27-33. Epub 2006 Jan 26. Review. (
  • Gasche C, Grundtner P. Genotypes and phenotypes in Crohn's disease: do they help in clinical management? Gut. 2005 Jan;54(1):162-7. Review. Erratum in: Gut. 2005 Mar;54(3):442. (
  • Gaya DR, Russell RK, Nimmo ER, Satsangi J. New genes in inflammatory bowel disease: lessons for complex diseases? Lancet. 2006 Apr 15;367(9518):1271-84. Review. (
  • Marks DJ, Harbord MW, MacAllister R, Rahman FZ, Young J, Al-Lazikani B, Lees W, Novelli M, Bloom S, Segal AW. Defective acute inflammation in Crohn's disease: a clinical investigation. Lancet. 2006 Feb 25;367(9511):668-78. Erratum in: Lancet. 2007 Jul 28;370(9584):318. (
  • Parkes M, Barrett JC, Prescott NJ, Tremelling M, Anderson CA, Fisher SA, Roberts RG, Nimmo ER, Cummings FR, Soars D, Drummond H, Lees CW, Khawaja SA, Bagnall R, Burke DA, Todhunter CE, Ahmad T, Onnie CM, McArdle W, Strachan D, Bethel G, Bryan C, Lewis CM, Deloukas P, Forbes A, Sanderson J, Jewell DP, Satsangi J, Mansfield JC; Wellcome Trust Case Control Consortium, Cardon L, Mathew CG. Sequence variants in the autophagy gene IRGM and multiple other replicating loci contribute to Crohn's disease susceptibility. Nat Genet. 2007 Jul;39(7):830-2. Epub 2007 Jun 6. (
  • Podolsky DK. Inflammatory bowel disease. N Engl J Med. 2002 Aug 8;347(6):417-29. Review. (
  • Rioux JD, Xavier RJ, Taylor KD, Silverberg MS, Goyette P, Huett A, Green T, Kuballa P, Barmada MM, Datta LW, Shugart YY, Griffiths AM, Targan SR, Ippoliti AF, Bernard EJ, Mei L, Nicolae DL, Regueiro M, Schumm LP, Steinhart AH, Rotter JI, Duerr RH, Cho JH, Daly MJ, Brant SR. Genome-wide association study identifies new susceptibility loci for Crohn disease and implicates autophagy in disease pathogenesis. Nat Genet. 2007 May;39(5):596-604. Epub 2007 Apr 15. (
  • Russell RK, Nimmo ER, Satsangi J. Molecular genetics of Crohn's disease. Curr Opin Genet Dev. 2004 Jun;14(3):264-70. Review. (
  • Schreiber S, Rosenstiel P, Albrecht M, Hampe J, Krawczak M. Genetics of Crohn disease, an archetypal inflammatory barrier disease. Nat Rev Genet. 2005 May;6(5):376-88. Review. (
  • Stange EF, Travis SP, Vermeire S, Beglinger C, Kupcinkas L, Geboes K, Barakauskiene A, Villanacci V, Von Herbay A, Warren BF, Gasche C, Tilg H, Schreiber SW, Schölmerich J, Reinisch W; European Crohn's and Colitis Organisation. European evidence based consensus on the diagnosis and management of Crohn's disease: definitions and diagnosis. Gut. 2006 Mar;55 Suppl 1:i1-15. (
  • Vermeire S, Rutgeerts P. Current status of genetics research in inflammatory bowel disease. Genes Immun. 2005 Dec;6(8):637-45. Review. (
  • Xavier RJ, Podolsky DK. Unravelling the pathogenesis of inflammatory bowel disease. Nature. 2007 Jul 26;448(7152):427-34. Review. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: August 2007
Published: February 1, 2016