MSI mutation, or Microsatellite Instability mutation, refers to a state of increased genetic mutability due to defects in DNA mismatch repair (MMR). In essence, it means the cell's ability to correct errors during DNA replication is compromised, leading to a higher rate of mutations. According to the provided reference, microsatellite instability (MSI) is the condition of genetic hypermutability (predisposition to mutation) that results from impaired DNA mismatch repair (MMR). The presence of MSI represents phenotypic evidence that MMR is not functioning normally.
Understanding Microsatellites
Microsatellites are short, repetitive DNA sequences scattered throughout the genome. Because of their repetitive nature, they are prone to errors during DNA replication.
The Role of Mismatch Repair (MMR)
The MMR system acts as a proofreading mechanism, identifying and correcting these errors. When MMR is impaired, these errors accumulate, leading to MSI.
Implications of MSI
MSI is commonly found in certain types of cancer, particularly colorectal cancer, endometrial cancer, and gastric cancer. It can have implications for:
- Cancer Diagnosis: MSI status can be used as a diagnostic marker.
- Prognosis: In some cancers, MSI-high tumors have been associated with better outcomes.
- Treatment: MSI-high tumors are more likely to respond to immunotherapy.
How MSI is Detected
MSI is typically detected through laboratory testing of tumor tissue. This involves comparing the lengths of microsatellites in tumor DNA to those in normal DNA from the same individual. If the microsatellite lengths are different in the tumor DNA, it indicates MSI.
Examples of Cancers with MSI
Several cancers exhibit MSI. These include:
- Colorectal cancer
- Endometrial cancer
- Gastric cancer
- Ovarian cancer
