ALLELIC PROFILES OF MONONUCLEOTIDE REPEAT MICROSATELLITES IN CONTROL INDIVIDUALS AND IN COLORECTAL TUMORS WITH AND WITHOUT REPLICATION ERRORS

We have recently shown that analysis of BAT-26, was sufficient to esta blish the Replication Error status of colorectal tumors and cell lines without the need for matching normal DNA, BAT-26, a poly(A) tract in the 5th intron of the hMSH2 gene, does not present significant size va riation either between the allleles of one individual or between allel es of different individuals, In colorectal tumors without defects in t he replication error system (RER- phenotype), BAT-26 is also quasi-mon omorphic, On the contrary, in RER+ colorectal tumors, BAT-26 shows uns table shortened alleles, In order to see whether this behaviour was sp ecific for BAT-26, or was a more general phenomenon for mononucleotide repeat microsatellites, we analysed eight other mononucleotide repeat s, In control individuals (72 samples) and in RER- colorectal tumors a nd cell lines (55 samples), these microsatellites were polymorphic, di morphic, quasi-monomorphic or monomorphic, indicating that the quasi-m onomorphic nature of BAT-26 was not a general rule, All of them showed a tendency to be shorter in RER+ colorectal tumors and cell lines (19 samples), but only quasi-monomorphic and monomorphic mononucleotide r epeats could be used to determine the RER status of tumors without mat ching normal DNA, although with a lower efficiency than BAT-26 due to either a smaller range of shortening in RER+ tumors or to a larger num ber of false negative cases.