When normal repeated sequences of DNA are mutated and become abnormally long or shorter, genetic scientists refer to the condition as “microsatellite instability” or MSI. In technical terms, this instability results from defects in the normal DNA repair process and has been shown to be a key factor in colorectal, endometrial, ovarian, and gastric cancers.
Lynch Syndrome or hereditary nonpolyposis colorectal cancer (HNPCC) is a type of inherited cancer of the digestive tract that especially affects the rectum and colon. How common is Lynch Syndrome in the US? An estimated 143,000 new cases of colorectal cancer are expected to be diagnoised in 2012, 3% of which will be caused by Lynch Syndrome [1,2].
In particular, Lynch Syndrome is one manifestation of MSI occurrence that has been indicated by colorectal studies. The mutation involved in MSI inactivates major tumor suppressor genes. These are genes that play a key role in the prevention of cancer through regulation of the cell cycle. According to the National Institute of Health Genetics Home Reference article on the subject (http://ghr.nlm.nih.gov/condition/lynch-syndrome), “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.”
 Ann Intern Med. 2011;155:69-79