Fig. 1

The definitions of Type A and B MSI. The electrophoretic profiles of PCR amplified dinucleotide microsatellites are comprised of four peaks: + 2, 0, − 2 and − 4, and peak 0 corresponds to the correct size of template microsatellite sequence (Ref. 19) (a). When MSI occurs, there are several new minor microsatellite alleles with altered number of dinucleotide repeats, and the electrophoretic profiles are modified by them. Type A MSI is defined as an (i) appearance of new peaks within 6-bp (three repeats) (b, right and left) or a change in (ii) peak height ratio (PHR) above 0.15 between peak 0 and + 2 (b, left) or (iii) over 0.40 between peak 0 and − 2 (b, right). On the other hand, Type B is defined as an (i) appearance of new peaks over the length range of 6-bp (four or more repeat units) and/or an (ii) appearance of a new apex (c). Blue lines indicate parental (homozygous) alleles, and red lines altered MSI alleles. Observed electrophoretic profiles are shown by black interrupted lines.