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.

• Keywords
• familial colorectal cancer, germline variant, multiple primaries, whole‐exome sequencing,
• MeSH
• Adult MeSH
• Genetic Predisposition to Disease MeSH
• Colorectal Neoplasms * genetics   pathology   MeSH
• Middle Aged MeSH
• Humans MeSH
• DNA Repair genetics   MeSH
• Pedigree MeSH
• Exome Sequencing MeSH
• Aged MeSH
• Germ-Line Mutation * MeSH
• Check Tag
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Male MeSH
• Aged MeSH
• Female MeSH
• Publication type
• Journal Article MeSH

About 15% of colorectal cancer (CRC) patients have first-degree relatives affected by the same malignancy. However, for most families the cause of familial aggregation of CRC is unknown. To identify novel high-to-moderate-penetrance germline variants underlying CRC susceptibility, we performed whole exome sequencing (WES) on four CRC cases and two unaffected members of a Polish family without any mutation in known CRC predisposition genes. After WES, we used our in-house developed Familial Cancer Variant Prioritization Pipeline and identified two novel variants in the solute carrier family 15 member 4 (SLC15A4) gene. The heterozygous missense variant, p. Y444C, was predicted to affect the phylogenetically conserved PTR2/POT domain and to have a deleterious effect on the function of the encoded peptide/histidine transporter. The other variant was located in the upstream region of the same gene (GRCh37.p13, 12_129308531_C_T; 43 bp upstream of transcription start site, ENST00000266771.5) and it was annotated to affect the promoter region of SLC15A4 as well as binding sites of 17 different transcription factors. Our findings of two distinct variants in the same gene may indicate a synergistic up-regulation of SLC15A4 as the underlying genetic cause and implicate this gene for the first time in genetic inheritance of familial CRC.

• Keywords
• Familial colorectal cancer, Germline variant, SLC15A4, Whole exome sequencing,
• MeSH
• Genetic Predisposition to Disease MeSH
• Colorectal Neoplasms * genetics   pathology   MeSH
• Humans MeSH
• Membrane Transport Proteins genetics   MeSH
• Nerve Tissue Proteins genetics   MeSH
• Pedigree MeSH
• Exome Sequencing MeSH
• Germ Cells pathology   MeSH
• Germ-Line Mutation * MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Membrane Transport Proteins MeSH
• Nerve Tissue Proteins MeSH
• SLC15A4 protein, human MeSH Browser