Comprehensive Constitutional Genetic and Epigenetic Characterization of Lynch-Like Individuals

Abstract

Síndrome de Lynch; Panell de gens del càncer; Epimutació

Síndrome de Lynch; Panel de genes del cáncer; Epimutación

Lynch syndrome; Cancer genes panel; Epimutation

The causal mechanism for cancer predisposition in Lynch-like syndrome (LLS) remains unknown. Our aim was to elucidate the constitutional basis of mismatch repair (MMR) deficiency in LLS patients throughout a comprehensive (epi)genetic analysis. One hundred and fifteen LLS patients harboring MMR-deficient tumors and no germline MMR mutations were included. Mutational analysis of 26 colorectal cancer (CRC)-associated genes was performed. Pathogenicity of MMR variants was assessed by splicing and multifactorial likelihood analyses. Genome-wide methylome analysis was performed by the Infinium Human Methylation 450K Bead Chip. The multigene panel analysis revealed the presence of two MMR gene truncating mutations not previously found. Of a total of 15 additional MMR variants identified, five -present in 6 unrelated individuals- were reclassified as pathogenic. In addition, 13 predicted deleterious variants in other CRC-predisposing genes were found in 12 probands. Methylome analysis detected one constitutional MLH1 epimutation, but no additional differentially methylated regions were identified in LLS compared to LS patients or cancer-free individuals. In conclusion, the use of an ad-hoc designed gene panel combined with pathogenicity assessment of variants allowed the identification of deleterious MMR mutations as well as new LLS candidate causal genes. Constitutional epimutations in non-LS-associated genes are not responsible for LLS.

This work was funded by the Spanish Ministry of Economy and Competitiveness and cofunded by FEDER funds -a way to build Europe- (grants SAF2012-33636, SAF2015-68016-R and SAF2016-80888-R), CIBERONC, RTICC Network (RD12/0036/0031 and RD12/0036/0008), the Spanish Association Against Cancer (AECC) (080253), the Government of Catalonia (grant 2014SGR338, 2017SGR1282 and PERIS SLT002/16/0037), Fundación Mutua Madrileña (grant AP114252013). We thank CERCA Programme for institutional support. ED was supported by a grant from the Spanish Ministry of Economy and Competitiveness. The AECC fellowship to MG-A. AF was supported by a grant from the Catalonian Health Department (SLT002/16/00409). FM was supported by CIBERONC. The Mexican National Council for Science and Technology (CONACyT) fellowship to GV.