The aim of this work is to introduce new possibilities of molecular genetics in the determination of Lynch syndrome patients and their relatives to the clinician society. The focus is given on Lynch syndrome cases where strict ICG Amsterdam criteria do not fit properly and therefore a genomic microsatellite instability (MSI) and/or qualitative/quantitative analyses of circulating DNA in blood plasma may be useful. In practical part of the work, among forty-one patients with histologically confirmed colorectal carcinoma diagnosis 15 patients were selected, those with at least one sibling aged less than sixty years. Next, their lymphocyte DNA samples were compared with paired DNA isolated from paraffin embedded samples of excissed tumors. The tumor Growth Factor receptor beta (TGFR
) microsatellite decaadenosine tract has been tested and the difference found in 2 (13%) cases. The finding should be followed by mutation analysis in mismatch repair (MMR) genes.

        Key words: Lynch syndrome – DNA diagnosis – chromosomal instability