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Population-wide Screening for Germline Variants of Hereditary Cancer Genes in 12K Unselected Japanese Colorectal Cancers and 27K Controls

By Masashi Fujita, Xiaoxi Liu, Yusuke Iwasaki, Chikashi Terao, Sadaaki Takata, Chihiro Inai, Tomomi Aoi, Kazuhiro Maejima, Makoto Hirata, Yoshinori Murakami, Yoichiro Kamatani, Michiaki Kubo, Kiwamu Akagi, Koichi Matsuda, Hidewaki Nakagawa, Yukihide Momozawa

Posted 17 Mar 2020
bioRxiv DOI: 10.1101/2020.03.15.989947

Background & Aims: Colorectal cancer (CRC) is one of the most common cancers in Western countries and Japan. Currently, a few % of CRCs can be attributed to recognizable hereditary germline variants of known CRC susceptibility genes, predominantly the DNA mismatch repair genes. To establish a universal screening strategy for hereditary CRCs, it is necessary to explore the prevalence of hereditary CRC and pathogenic variants of multiple cancer-predisposing genes in non-European populations. Methods: We analyzed the coding regions of 27 cancer-predisposing genes, including mismatch repair genes, APC , and BRCA1/2 , in 12,503 unselected Japanese CRC patients and 23,705 controls aged ≥ 60 years without any personal or family history of cancer by target sequencing and genome-wide SNP chip data. Their clinical significance was assessed using ClinVar and the guidelines by the American College of Medical Genetics and Genomics and the Association for Molecular Pathology (ACMG/AMP). Results: We identified 4,804 variants in the 27 genes and annotated them as 397 pathogenic variants, 941 benign variants, and 3,466 variants of uncertain significance, of which 43.6% were registered in neither ClinVar nor dbSNP. In total, 3.3% of the unselected CRC patients and 1.5% of the controls had a pathogenic variant of the 27 genes. The pathogenic variants of MSH2 (odds ratio (OR) =18.1), MLH1 (OR=8.6), MSH6 (OR=4.9), APC (OR=49.4), BRIP1 (OR=3.6), BRCA1 (OR=2.6), BRCA2 (OR=1.9), and TP53 (OR=1.7) were significantly associated with CRC development in the Japanese population (P-values < 0.01, FDR<0.05). Furthermore, we confirmed copy number variants (CNVs) of MSH2/EPCAM , MLH1 , and APC by multiplex ligation-dependent probe amplification (MLPA) and quantitative PCR in this cohort (n = 23), including whole gene duplications of MSH2 and APC . These pathogenic variants were significantly associated with the diagnostic age and personal/family history of other types of cancer. In total, at least 3.5% of the Japanese CRC population had a pathogenic variant or CNV of the 27 cancer-predisposing genes. Conclusions: This is the largest study of CRC heredity in the Asian population and would contribute to the development of guidelines for genetic testing and variant interpretation for heritable CRCs. Universal screening for CRC risk should be assessed in multiple genes, including BRCA1/2 and BRIP1 . These data would facilitate risk assessment of cancer and optimize the screening strategy.

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