Uses of Microsatellites for Instability Testing

In each of our cells, there are genes that are responsible for repairing damaged DNA. Sometimes these genes undergo mutations. This causes regions called microsatellites (repeating strands of DNA) to become longer or shorter than they should be. This is what is referred to as microsatellite instability. Testing for microsatellite instability allows medical professionals to figure out whether or not a person is likely to undergo a genetic mutation that is responsible for hereditary nonpolyposis colorectal cancer (HNPCC), also known as Lynch Syndrome.

HNPCC

• The genes responsible for causing HNPCC are genes responsible for repair DNA. In people with HNPCC, there is a mutated copy of one of these genes. This can impair the person's ability to repair his own DNA. When this occurs, many mutations can accumulate over time and a tumor can result. Also when this occurs, microsatellite instability results much of the time. Approximately 90 percent of subjects that have tumors that have resulted from HNPCC also have microsatellite instability. This is why testing for microsatellite instability can help diagnose HNPCC-related tumors.

When to Test

• Testing for microsatellite instability is often one of the first tests medical professionals conduct in families that have a history of HNPCC. The types of tissue usually tested at this point are commonly colon and endometrial tissue.

Success Rate

• While this will not catch all cases of HNPCC-related tumors, a relatively few will escape this screening process (about 10 percent). When combined with other screening methods, microsatellite instability testing can be very effective in catching cancers early on in their development.

Strong HNPCC History

• If a person's family history shows strong susceptibility to HNPCC, medical professionals will often conduct genetic tests for DNA repair gene mutations on the person in question as well as his family even if the microsatellite instability test comes back negative. This helps account for the 10 percent of cases that slip through this screening technique.

Retro-testing

• This screening techniques is especially helpful in cases where all of a person's HNPCC-affected family members have died, leaving no one behind to test for DNA repair gene mutations. Microsatellite instability testing can be conducted on brain tissue taken from family members before they died with permission from the next of kin. This increases the likelihood that the cancer will be caught early.