Fragment analysis
Following amplification of certain DNA fragments, fragment analysis makes it possible to visualise their length by means of capillary electrophoresis. This technique is used in the diagnosis of lymphoproliferative diseases (clonality analyses) and to determine microsatellite instability.
Microsatellite instability (MSI)
Microsatellites are short, non-coding DNA sequences of 2 to 6 base pairs in length, which are often repeated in the genome of an organism. In the case of microsatellite instability (MSI), length changes occur within these microsatellites as a result of defective DNA repair proteins (hMLH1, hMSH2, hMSH6, hPMS1, hPMS2). If microsatellite instability occurs in the tumour under investigation, it may be assumed that the patient has a genetic defect in the DNA repair system. This genetic defect may be present in the tumour alone (sporadic) or may, in rare cases, be inherited (mutation in the germline). In such cases, genetic counselling and precautionary measures for the person's extended family are advisable.
Microsatellite instability testing is often performed in the case of colorectal cancers, including to rule out hereditary non-polyposis colorectal cancers (Lynch syndrome).
Clonality analyses
Clonality analysis is used to help diagnose B-cell or T-cell lymphomas. This method is based on the unique rearrangements of B-cell receptors (Ig) and T-cell receptors (TCR) in B and T lymphocytes. The length of the modification varies between rearranged gene combinations of different lymphocytes in reactive processes (polyclonal pattern), but not in neoplastic lymphocytes, which are clonal descendants of a single transformed cell (monoclonal pattern).