Hereditary nonpolyposis colorectal cancer (HNPCC), also known as Lynch syndrome, is characterised by a risk of colorectal cancer and other cancers of the endometrium, ovary, stomach, small intestine, hepatobiliary tract, upper urinary tract, brain, and skin. HNPCC is subdivided into Lynch Syndrome I (familial colon cancer) and Lynch Syndrome II (other cancer of the gastrointestinal system or the reproductive system). The increased risk for these cancers is due to inherited mutations that degrade the self-repair capability of DNA.
Colon Cancer
Variations in the MLH1, MSH2, MSH6, and PMS2 genes increase the risk of developing Lynch syndrome. All of these genes are involved in the repair of mistakes made when DNA is copied (DNA replication) in preparation for cell division. Mutations in any of these genes prevent the proper repair of DNA replication mistakes. As the abnormal cells continue to divide, the accumulated mistakes can lead to uncontrolled cell growth and possibly cancer. Although mutations in these genes predispose individuals to cancer, not all people who carry these mutations develop cancerous tumors.
Lynch syndrome cancer risk is inherited in an autosomal dominant pattern, which means one inherited copy of the altered gene in each cell is sufficient to increase cancer risk. It is important to note that people inherit an increased risk of cancer, not the disease itself. Not all people who inherit mutations in these genes will develop cancer.
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