A double primary colorectal cancer (CRC) in a familial setting signals a high risk of CRC. In order to identify novel CRC susceptibility genes, we whole-exome sequenced germline DNA from nine persons with a double primary CRC and a family history of CRC. The detected variants were processed by bioinformatics filtering and prioritization, including STRING protein-protein interaction and pathway analysis. A total of 150 missense, 19 stop-gain, 22 frameshift and 13 canonical splice site variants fulfilled our filtering criteria. The STRING analysis identified 20 DNA repair/cell cycle proteins as the main cluster, related to genes CHEK2, EXO1, FAAP24, FANCI, MCPH1, POLL, PRC1, RECQL, RECQL5, RRM2, SHCBP1, SMC2, XRCC1, in addition to CDK18, ENDOV, ZW10 and the known mismatch repair genes. Another STRING network included extracellular matrix genes and TGFβ signaling genes. In the nine whole-exome sequenced patients, eight harbored at least two candidate DNA repair/cell cycle/TGFβ signaling gene variants. The number of families is too small to provide evidence for individual variants but, considering the known role of DNA repair/cell cycle genes in CRC, the clustering of multiple deleterious variants in the present families suggests that these, perhaps jointly, contributed to CRC development in these families.

Biomedical Center Faculty of Medicine Charles University Pilsen Pilsen Czech Republic

Department of Genetics and Pathology International Hereditary Cancer Center Pomeranian Medical University in Szczecin Szczecin Poland

Division of Cancer Epidemiology German Cancer Research Center Heidelberg Germany

Division of Pediatric Neurooncology German Cancer Research Center Heidelberg Germany

Hopp Children's Cancer Center Heidelberg Germany

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