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Background and Objectives: Checkpoint kinase 2 ( CHEK2 ) is a tumor suppressor gene involved in DNA repair and cell cycle regulation. Pathogenic or likely pathogenic (P/LP) variants in CHEK2 are associated with increased cancer risk. Conversely, recent large cohort studies have identified certain variants that, despite being classified as P/LP by in silico analysis, are considered low risk. Thus, the genotype-phenotype correlations of CHEK2 require a better understanding. In this study, we aimed to characterize germline CHEK2 variants from a group of individuals who applied to cancer genetic clinics in the Marmara Region of Türkiye. We also aimed to assess the phenotypic impacts of these variants by using a new score of statistically significant in silico predictors (SSIPs). Methods: We analyzed 1707 individuals with high risk cancer predisposition, focusing on germline CHEK2 variants, using SSIP scores and population-specific data. Results: CHEK2 variants appeared in approximately 8% of cases. The SSIP scores indicated that the missense mutation, p.Arg117Gly, significantly impairs DNA repair. Almost half of the variants had higher allele frequencies than the variants listed in the Genome Aggregation Database (gnomAD), and three variants had significantly higher frequencies compared to the variants listed on the Turkish Variome database (p.Thr476Met, p.Arg137Gln, c.592+3A>T), emphasizing the importance of population-specific data. Conclusions: This comprehensive analysis of CHEK2 variants in the Turkish population provides crucial insights for cancer geneticists and oncologists. Our findings will help to enhance the evaluation and management of cancer predisposition associated with CHEK2 in Türkiye and other regions that have significant Turkish populations.

Concurrent pathogenic variants (PVs) in cancer predisposition genes have been reported in 0.1-2% of hereditary cancer (HC) patients. Determining concurrent PVs is crucial for the diagnosis, treatment, and risk assessment of unaffected family members. Next generation sequencing based diagnostic tests, which are widely used in HCs, enable the evaluation of multiple genes in parallel. We have screened the family members of a patient with bilateral breast cancer who was found to have concurrent PVs in BRCA1 (NM_007294.3;c.5102_5103del, p.Leu1701Glnfs*14) and MUTYH (NM_001128425.1;c.884C>T, p.Pro295Leu). Further analysis revealed concurrent PVs in CHEK2 (NM_007194.4;c.1427C>T, p.Thr476Met) and MUTYH (NM_001128425.1;c.884C>T, p.Pro295Leu) in the maternal uncle of the index case. Eight additional family members were found to have PVs in BRCA1 and MUTYH among 26 tested relatives. The sister and the brother of the index case who were diagnosed with breast and colon cancers, respectively, presented with the same genotype as the index case. Each family member was evaluated individually for clinical care and surveillance. This is the first report describing a family with BRCA1, MUTYH and CHEK2 concurrent PVs. Our findings provide valuable information for the assessment and management considerations for families with concurrent PVs., Competing Interests: Declaration of Competing Interest H.Q.R. reports research collaboration with Ambry Genetics (no compensation). The other authors declare no conflict of interest., (Copyright © 2022. Published by Elsevier Inc.)