Microsatellite instability

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In microsatellite instability ( MSI ), there is longitudinal changes in a short, repetitive DNA sequences as a result of defective DNA repair .

Repair proteins, such as DNA polymerase , normally detect and correct the incorporation of incorrect bases (“mismatch”) in newly produced DNA strands during DNA replication . They carry out the so-called mismatch repair . If the genes for these repair proteins (hMLH1, hMSH2, hMSH6, hPMS1, hPMS2) are defective, the repair system can fail and mutations gradually accumulate in the newly replicated DNA .

Since DNA is replicated more frequently in tumors than in other cells , microsatellite instability can be demonstrated by comparing DNA sequences (microsatellite markers) from a tumor and other DNA from the same organism (in humans, that of leukocytes). If it actually occurs in the examined tumor, it can be assumed that the patient has a genetic defect in the DNA repair system and that this is the reason for the cancer. Since this genetic defect can be inherited, genetic counseling and extended preventive care are advisable for the person affected and their relatives.

The examination for microsatellite instability is common in hereditary non-polypous colorectal cancer .

literature

  • Karl Heinimann: Molecular genetic diagnosis in HNPCC (hereditary colorectal carcinoma without generalized polyposis). Swiss Medical Journal No. 36, 2000, pp. 2009–2012 ( online, PDF, 620 kB ).