Mutational landscape of normal epithelial cells in Lynch Syndrome patients

Lynch Syndrome (LS) is an autosomal dominant disease conferring a high risk of colorectal cancer due to germline heterozygous mutations in a DNA mismatch repair (MMR) gene. Although cancers in LS patients show elevated somatic mutation burdens, information on mutation rates in normal tissues and understanding of the trajectory from normal to cancer cell is limited. Here we whole-genome sequenced 152 crypts from normal and neoplastic epithelial tissues from LS patients. In normal tissues the repertoire of mutational processes and mutation rates were similar to those found in wild type individuals. A morphologically normal colonic crypt with an increased mutation burden and mutational signatures consistent with MMR deficiency was identified, which may represent a very early stage of LS pathogenesis. Phylogenetic tress of tumour crypts indicated that the most recent ancestor cell of each tumour was already MMR deficient and had experienced multiple clonal evolution cycles. This study demonstrates the genomic stability of epithelial cells with heterozygous germline MMR gene mutations and highlights important differences in the pathogenesis of LS from other colorectal cancer predisposition syndromes.

• 161 samples
• DAC: EGAC00001000000
• Technology: Illumina NovaSeq 6000