Germline variants associated with breast cancer in Khakass women of North Asia.

INTRODUCTION: Variants in the BRCA1/2 genes are responsible for familial breast cancer. Numerous studies showed a different spectrum of BRCA variants among breast cancer patients of different Ethnicity origin. In the available literature, no previous research has focused on breast cancer-associated variants among the Khakass people (the indigenous people of the Russian Federation). METHODS: Twenty-six Khakass breast cancer patients were enrolled in the study. Genomic DNA was isolated from blood samples and used to prepare libraries using a Hereditary Cancer Solution kit. Next-generation sequencing (NGS) was performed using the MiSeq System (Illumina, USA). RESULTS: In our study, 12% of patients (3/26) carried a single pathogenic variant; 54% of patients (14/26) carried variants of uncertain significance (VUS) or conflicting variants; and 35% of patients (9/26) did not carry any clinically significant variants. Germline pathogenic variant in the ATM gene (rs780619951, NC_000011.10:g.108259022C > T) was identified in two unrelated patients with a family history of cancer (7.6%, 2/26). The pathogenic truncating variant in the ATM gene (p. R805* or c.2413C > T) leads to the nonfunctional version of the protein. This variant has been earlier reported in individuals with a family history of breast cancer. CONCLUSIONS: Our pilot study describes the germline variant in the ATM gene associated with breast cancer in Khakass women of North Asia.

Pathogenicity Reclassification of Genetic Variants Related to Early-Onset Breast Cancer among Women of Mongoloid Origin.

BACKGROUND: Germline alterations in BRCA1, BRCA2, and other genes are responsible for early-onset breast cancer. However, up to 20% of molecular tests report genetic variant of unknown significance (VUS) or novel variants that have never been previously described and their clinical significance are unknown. This study aimed to reclassify variant of unknown significance (VUS) or novel variants by using the ActiveDriveDB database that annotates variants through the lens of sites of post-translational modifications (PTM). METHODS: Our study included thirty-eighth young Buryat BC patients, belonging to the Mongoloid race and anthropologically to the Central Asia. Genomic DNA was extracted from the peripheral blood lymphocytes using the phenol/chloroform method. DNA library were prepared using the Hereditary Cancer SolutionTM kit (Sophia GENETICS, Switzerland) to cover 27 genes, such as ATM, APC, BARD1, BRCA1, BRCA2, BRIP1, CDH1, CHEK2, EPCAM, FAM175A, MLH1, MRE11A, MSH2, MSH6, MUTYH, NBN, PALB2, PIK3CA, PMS2, PMS2CL, PTEN, RAD50, RAD51C, RAD51D, STK11, TP53, and XRCC2. Paired-end sequencing (2 x 150 bp) was conducted using NextSeq 500 system (Illumina, USA). RESULTS: We re-examined 135 rare variants (41 VUS, 25 conflicting, 64 benign and 5 new variants). We identified 10 out of 135 (7.4%) mutations that affected the sites of post-translational modification in proteins. Of 135 rare mutations, 1 benign variant was reclassified as network-rewiring - motif loss mutation, 3 VUS and 1 new variant were reclassified as distal PTM- mutations, 2 new and 1 benign variant were classified as proximal PTM- mutations and 1 benign and 1 conflicting variant were classified as direct PTM- mutations. CONCLUSIONS: For the first time, 7.4% (10 out of 135) of mutations that affected the sites of post-translational modification in proteins were identified among early-onset breast cancer women of Mongoloid origin.

New germline mutations in non-BRCA genes among breast cancer women of Mongoloid origin.

In accordance with the Asian BRCA Consortium data, there is a significant difference in incidence rate of breast cancer depending on age, as well as spectrum and prevalence of BRCA1/2 mutations between Mongoloid (East Asian) and Caucasoid (European) people. However, European strategies to identify familial BC are still applied to the Asian population, including Russian Mongoloids (Khakas, Buryats, Tyvans and Yakuts and others). The main purpose of the study was to identify molecular changes associated with hereditary BC in Russian Mongoloid BC patients (Buryats). Thirty-nine patients were included in the study. Genomic DNA extracted from lymphocytes was used to prepare DNA-libraries. Target sequencing was designed to cover 27 genes, such as ATM, APC, BARD1, BRCA1, BRCA2, BRIP1, CDH1, CHEK2 and others. Paired-end sequencing (2 × 150 bp) was conducted on a NextSeq 500 system (Illumina, USA). Three pathogenic mutations in non-BRCA genes were found (prevalence of 8%). The pathogenic mutations were found in the RAD51D and PTEN genes. The pathogenic variant in the RAD51D gene (rs137886232, NC_000017.10:g.33428366G>A, p.R141X) was observed in two unrelated individuals aged under 40. One of these patients had a family history of late-onset stomach cancer in second-degree relatives. The pathogenic mutation in the PTEN gene (rs786201044, NC_000010.10:g.89692922T>C, p.C136R) was observed in a 38 years old breast cancer patient with no family history. In our study, we first describe pathogenic mutations in RAD51D and PTEN genes found in young Buryat patients.

New germline BRCA2 gene variant in the Tuvinian Mongol breast cancer patients.

To date, there are a limited number of reports on inherited gene mutations associated with breast cancer (BC) among Mongoloid indigenous people in Russia. The present study aimed at identifying the BC-associated genes in 26 Russian Mongoloid BC patients (Buryats, Tuvinians and others). The median age of the patients at the time of breast cancer diagnosis was 41 years (range 25-51 years). Genomic DNA isolated from blood samples was used to prepare libraries using a capture-based target enrichment kit (Hereditary Cancer Solution™, SOPHiA GENETICS, Switzerland) covering 27 genes (ATM, APC, BARD1, BRCA1, BRCA2, BRIP1, CDH1, CHEK2, EPCAM, FAM175A, MLH1, MRE11A, MSH2, MSH6, MUTYH, NBN, PALB2, PIK3CA, PMS2, PMS2CL, PTEN, RAD50, RAD51C, RAD51D, STK11, TP53 and XRCC2). Next-generation sequencing (NGS) was performed on an Illumina NextSeq 500 System (Illumina, USA). In our study, we found 1 Indel and 11 SNPs that passed filters during variant calling. We identified a highly pathogenic germline rs483353122 (c.8208_8209insAG, p.Leu2737Serfs*2) in the BRCA2 gene in six unrelated Tuvinian Mongol BC patients. We also identified a likely damaging germline rs35352891 in the MUTYH gene (c.1118C>T, p.Ala373Val) in one Buryat Mongol BC patient. Other SNPs were classified as variants of uncertain significance. To the best of our knowledge, this report is the first to describe the highly pathogenic variant in the BRCA2 gene (rs483353122) and the likely damaging germline variant in the MUTYH gene (rs35352891) in Russian Mongoloid BC patients with young-onset and/or bilateral and/or familial BC. Further studies are therefore necessary to evaluate the contributions of novel sequence variants to hereditary BC.

New variants in the BRCA1 gene in Buryat Mongol breast cancer patients: Report from two families.

BACKGROUND: The BRCA1 mutations that are endemic to the Slavic population of Russia have not been identified among indigenous peoples, including the Buryats, Tuvinians and Altaians with hereditary breast cancer. OBJECTIVE: This study was aimed to identify the mutations that are responsible for the occurrence of hereditary breast cancer in the indigenous population of the Republic of Buryatia. METHODS: Mutations in the BRCA1 gene were identified in blood samples by Sanger-based sequencing. RESULTS: We identified 11 polymorphisms (10 SNPs and 1 Indel) and 6 new unclassified sequence variants in the BRCA1 gene. In our study three new sequence variants (c.321T>A, c.366T>A, c.4357+2T>A) were found in position of previously described polymorphisms in dbSNPs: rs80357544 (c.321delT), rs190900046 (c.366T>G), and rs80358152 (c.4357+2T>C), respectively. Other three new sequence variants (c.3605A>G, c.1998A>C, and c.80+13A>C) have not been previously described in dbSNP, BIC and Human Gene Mutation Databases. CONCLUSIONS: We described six new sequence variants that have never been published in the literature or databases. Further studies are required to confirm the impact of new sequence variants on the risk of breast cancer in the Buryat Mongol population.