Ulcerative Colitis is one of two major forms of Inflammatory Bowel Disease, the other being Crohn’s disease. Colitis literally means inflammation of the colon and ulcerative refers to the presence of ulcers. Colitis is primarily a disease of the large intestine (colon and rectum). The inflammation and ulcers are the cause of the common symptoms of diarrhoea mixed with blood and mucus seen with Ulcerative Colitis. Other symptoms include crampy pain in the abdomen, pain when passing stool and inflammation of the rectum. If flare ups persist then Ulcerative Colitis may be accompanied by fever, weight loss and feeling sick. Onset of Ulcerative Colitis is typically between the ages of 15 and 35 with a population prevalence of around 200 per 100,000 persons in Western populations.
The most consistently replicated association of Ulcerative Colitis is with the HLA class II allele HLA-DRB1*01:03. This association is particularly strong in patients with severe disease, as defined by a need to colectomy. Among patients who do require colectomy, HLA-DRB1*01:03 may be associated with a shorter mean time to surgery. HLA-DRB1*15:02 but not HLA-DRB1*15:01, has also been shown to be associated with Ulcerative Colitis in some populations though the strength of the association varies in different populations. In some populations HLA-DRB1*04 has some protective effect. HLA risk alleles however only contribute a minor part of the overall genetic picture. The advent of genome wide association studies have identified a large number of potential candidate genes which are being studied for association with Ulcerative Colitis, including the Interleukin-23 Receptor (IL23R).
The association between HLA and Ulcerative Colitis is of low specificity and sensitivity, limiting the value of genetic testing for diagnostic purposes. However HLA-DRB1*01:03 typing may be of value in predicting patients who may potentially require colectomy as potential candidates for more aggressive treatment in a bid to spare the colon.
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