Heritability of Appendicitis

A longitudinal section of an acutely inflamed and enlarged appendix.

Appendicitis is the inflammation of the appendix. If the appendix bursts, its infected contents will spread throughout the abdominal cavity resulting in infection of the lining of the abdominal cavity (peritonitis). In only 30-40% of appendicitis cases food or faecal matter is lodged in the lumen of the appendix causing a bacterial infection. Epidemiological studies have identified gender, age, year of birth, socio-economic status, low-fibre diet and smoking status as risk factors for the disease.

Resent research about the nature of acute appendicitis indicates that it may be a result of an inappropriate immune response which may have a genetic basis. The innate immune system has been highly conserved over evolutionary time and there is evidence that variations in a gene that governs the inflammatory response are associated with acute appendicitis.

The genetics of appendicitis are not well understood and so a heritability analysis and genome wide linkage analysis of a large twin dataset was undertaken. This revealed some evidence of an age-dependent genetic predisposition to appendicitis. Monozygotic twins had a higher correlation in appendectomy status at age 20 than dizygotic twins which suggests that genetic factors may be involved in appendicitis leading to appendectomy. Treating age of onset of appendicitis as a censored survival trait revealed heritability of 0.21 and found evidence of linkage to chromosome 1p37.3.

Inflamed appendix removal by open surgery

References:
Oldmedow, C, Mengersen, K, Martin, N & Duffy, DL 2009, ‘Heritability and Linkage Analysis of Apendicitis Utilizing Age at Onset’, Twin Research and Human Genetics, vol. 12, no. 2, pp150-157.

Better Health Channel 2007, Appendicitis, viewed 5 May 2009, http://betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Appendicitis?OpenDocument

Images:
Wikipedia 2009, viewed 6 May 2009,
http://en.wikipedia.org/wiki/Appendicitis