Microsatellite instability in mononuclear cells from non-tumorigenic human tonsils and its use in forensic evaluation

Abstract Microsatellite instability (MSI) is characterized by small deletions or expansions within short tandem repeats in tumor DNA as compared with matching normal DNA. The additional bands (also called stutter bands or shadow bands) are observed in genetic mapping studies by PCR amplification of the loci with mono-, di-, tri- and sometimes tetra-nucleotide repeats. In addition, it is very difficult to distinguish the mutation events that have occurred during DNA replication or repair in vivo from those that occurred during PCR. To determine the origin of the stutter bands, TH01 typing was performed by semi-nested PCR using single somatic cells isolated from non-tumorigenic tonsils. One out of 178 cells (0.56%) examined had a product 4 bp shorter than the major band. These results indicate that the typing data from PCR amplification may reflect somatic mosaicism in the individual. However, we conclude that the existence of the mutated cells in this proportion may have no effect on forensic examination.