A Systematic Review of the Prevalence of Germline BRCA mutations in North Asia Breast Cancer Patients

Objective: The BRCA1/2 mutation status testing is the global standard of care for breast cancer patients with a family history of cancer. BRCA1/2 mutations are known to be ethno-specific. For some ethnic groups of the Northern Asia (Buryats, Yakuts, Altaians, Tuvans, Khakasses, etc.) the founder mutations in the BRCA1/2 genes have not been revealed. This systematic review was conducted to assess the prevalence of BRCA1/2 mutation in breast cancer patients inhabiting Eastern Europe and Northern Asia (or Siberia). Methods: A total of 23,561 studies published between 2014 and 2024 were analyzed, of which 55 were included in the review. The literature search was conducted using RusMed, Cyberleninka, Google Scholar, eLibrary, NCBI databases (n=5) and conference papers. Results: The founder mutations (c.5266dupC and/or c.181T>G) of BRCA1 gene that were frequently observed in the Slav peoples were also identified in Chechens, Armenians, Bashkirs, Ukrainians, Mordovians, Mari, Kabardians, Tatars, Uzbeks, Kyrgyz, Ossetians, Khanty indigenous peoples and Adygs. For Chechens, Kabardians, Ingush, Buryats, Khakasses, Sakha, Tuvans and Armenians, rare pathogenic variants of the BRCA1/2, ATM, СНЕК2, BRIP1, NBN, PTEN, TP53, PMS1, XPA, LGR4, BRWD1 and PALB2 genes were found. No data are available about the frequency of pathogenic BRCA1/2 mutations for ethnic groups, such as the Udmurts, Komi, Tajiks, Tabasarans, and Nogais indigenous people. Conclusion: This is the first systematic review that provides the spectrum of BRCA mutations in ethnic groups of breast cancer patients inhabiting Eastern Europe and Northern Asia. It has been shown that the mutations are ethnospecific (varied widely within groups) and not all groups are equally well studied. Further studies on the ethnic specificity of BRCA gene mutations are required.


Introduction
Globally, more than two million cases of breast cancer (BC) are diagnosed annually [1].Up to 10% of all BC cases are caused by accumulation of BRCA1/2 mutations, which increase the risk of developing BC to 99% [2].There are significant differences in the type and frequency of BRCA1/2 mutations depending on the geographical region and race/ethnicity.

BRCA1 and BRCA2 mutations across race and ethnicity
For some racial/ethnic groups, the founder mutations, such as the Ashkenazi Jews variant BRCA1 c.5266dup indigenous population of Siberia (Northern Asia, Russian Federation) remain poorly understood.

Indigenous peoples in Northern Asia (or Siberia)
BC is the most common malignancy among women in the transcontinental region, spanning Eastern Europe and Northern Asia (or Siberia).According to the 2010 census, more than 80 ethnic groups live in Eastern Europe and Northern Asia (or Siberia).The largest minorities include Tatars, Belarusians, Ukrainians, Bashkirs, Chuvashs, Chechens, and Armenians.The Kazakhs, Yakuts, Buryats, Ingush, Udmurts, Ossetians, etc. make up about 0.5% of the population (Table 1 and Figure 1) [5,6].
Siberia is a geographical area that includes all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east and covers an area of at least 13,100,000 km 2 [7].Northern Asia is one of the largest regions in Asia, while simultaneously being the least populated region.In 2020, the highest BC incidence was observed in Northern Asia (Siberia) among the Buryats (42.50 cases per 100,000 population), and Khakasses (42.26cases per 100,000), while the lowest among Tuvans (26.49cases per 100,000), Yakuts (27.84 cases per 100,000) and Altaians (29.61 cases per 100,000).The highest mortality was observed in Buryats (13.18 deaths per 100,000), Khakasses (10.89 deaths per 100,000) and Tuvans (10.06 deaths per 100,000), while the lowest one was observed in Yakuts (6.94 cases per 100,000), and Altaians (7.06 deaths per 100,000 population) [8].
A minority of the current population are descendants mainly of Mongol (Buryats) or Turkic indigenous people (Yakuts, Tuvans, Altaians, Tatars and Khakasses) and northern indigenous people (Samodeic people, Finno-Ugric peoples and others).Historically, the indigenous peoples of Siberia (Buryats, Tuvans, Altaians) live also in Mongolia, China and other countries.For example, Yakuts live also in Kazakhstan, Ukraine, Belarus, Kyrgyzstan, Latvia, Estonia and other countries.The Buryats live in China in the historical region of Barga (Inner Mongolia).The Tuvans live in China in Xinjiang Autonomous Region.The Altai people live in the Mongolia (the Mongolian Altai Mountains), in China (Altai Prefecture, northern Xinjiang) and in Kazakhstan [9][10][11][12][13].
Given recent achievements in the management of patients with BRCA1/2 mutations in breast cancer (PARPi) it is important that worldwide healthcare providers and decision makers are kept informed about of BRCA1/2 mutations ethnospecificity.Further research into the ethnic specificity of BRCA1/2 gene mutations will allow more patients with BRCA1/2 mutations around the world to receive the correct treatment.In this systematic review, we summarize the data on the spectrum of BC-associated gene mutations in ethnic groups of Siberia or Northern Asia, mainly focusing on mutation testing in different ethnic groups.

Materials and Methods
This systematic review was conducted in accordance with PRISMA guidelines (the Preferred Reporting Items for Systematic Reviews and Meta-Analyses) [14].A range of electronic databases was searched (N=5), including RusMed, Cyberleninka, Google Scholar, eLIBRARY.RU, and NCBI db PubMed.Searches of conference abstracts were also conducted.Details of resources and strategies used are available in the Supplement (Appendix 1).
This manuscript includes studies reporting on the prevalence of germline BRCA mutations in BC patients.The prevalence of any mutation was included regardless of whether the mutation was a founder mutation or not.Study inclusion was not limited by language.Only data that were available and reported from 2014 to 2024 were eligible for inclusion.Data from the included studies were extracted, stored, and analyzed.Studies were grouped by Figure 1.Map of Siberia and Eastern Europe, Genome Res.2017;27:1-14.[5] DOI:10.31557/APJCP.2024.25.6.1891Germline BRCA Mutation in Siberia c.T40G).For Tuvans rare variant of the BRCA2 gene (c.8208_8209insAG) was found.No pathogenic BRCA1/2 mutations were found in Buryats, Altaians, and Yakuts, probably due to the small sample size for the studied groups.
Rare pathogenic mutations of BRCA2, RAD51D, ATM genes that were previously found in Asians, were found in the ethnic groups of Siberia.The pathogenic variant of BRCA2 gene (c.8208_8209insAG,p.Leu2737Serfs*2, rs483353122) was observed in young Tuvan BC patients.The frameshift variant (c.8208_8209insAG, p.Leu2737Serfs*2, rs483353122), which was previously mentioned in the dbSNP, was also identified as germline in the Chinese population of the Hksar geographic origin.The pathogenic variant of RAD51D gene (rs137886232) was observed in young Buryat BC patients.The rs137886232 variant was identified as a founder mutation in Chinese population [57].Loveday C. et al. [58] indicated that RAD51D -deficient tumor cells were found to be sensitive to PARP inhibitors, suggesting a possible therapeutic approach for the anti-cancer treatment of RAD51D variant carriers [58].The germline pathogenic variant of the ATM gene was identified (rs780619951, NC_000011.10:g.108259022C>T) in a Khakass BC patient with a family history of cancer.The pathogenic truncating variant in the ATM gene (p.R805* or c.2413C>T) leads to nonfunctional version of the protein.
The pathogenic variant of the PTEN gene (rs786201044) was described in a young Buryat BC patient.This mutation affects the protein-tyrosine phosphatase-like domain and is associated with Cowden syndrome [59][60][61][62].

The spectrum of germline variants (conflicting or uncertain significance) in the BC-related genes among the ethnic groups inhabiting Eastern Europe and Northern Asia
There are many reports pointing to the need for a more thorough study of the clinical significance of germline variants (conflicting or uncertain significance) ethnic groups inhabiting Eastern Europe and Northern Asia.Data were highlighted and discussed separately for subgroups of patients that were of particular interest.

Study selection
A total of 23,561 papers and abstracts were retrieved from the literature searches and background papers, and systematic reviews.From these, full papers were obtained for 55 citations.After further review, 13 papers were excluded (Supplement, Appendix 2).A summary of the study selection process is reported in Figure 2.

The spectrum of pathogenic variants in the BC genes in ethnic groups inhabiting Eastern Europe and Northern Asia
The existence of ethno-specific mutations is well established.Here, we report detailed information from some studies (Tables 2 and 3).According to the literature data, the molecular features of BC in 32 ethnic groups inhabiting Eastern Europe and Northern Asia were studied .The founder mutations (c.5266dupC and/or c.181T>G) of BRCA1 gene that were frequently observed in the Slav peoples were also identified in Chechens, Armenians, Bashkirs, Ukrainians, Mordovians, Mari, Kabardians, Tatars, Uzbeks, Kyrgyz, Ossetians, Khanty and Adygs.For Chechens, Kabardians, Ingush, Buryats, Khakasses, Sakha, Tuvans and Armenians, rare pathogenic variants of the BRCA1/2, ATM, СНЕК2, BRIP1, NBN, PTEN, TP53, PMS1, XPA, LGR4, BRWD1 and PALB2 genes were found.No data are available about the frequency of pathogenic BRCA1/2 mutations for ethnic groups, such as Udmurts, Komi, Tajiks, Tabasarans, Turks, and Nogais indigenous people.
In ethnic groups of Siberia, the founder variants of BRCA1/2 gene, that were observed in Slav, were identified in Khanty (BRCA1 5382insС), Tuvans (BRCA2 c.3875_3878delGTCT) and Khakasses (BRCA1 gene   [34].A reduced activity of MTHFR (methylenetetrahydrofolate reductase) due to C677T variant affects DNA synthesis, repair and methylation and may be involved in BC risk [64].
According to the PubMed ClinVar database, the variants of conflicting significance were found in the ethnic groups of Northern Asia (or Siberia).For example, variants of conflicting significance of the PALB2 and TP53 genes were described in the Yakuts and Tuvans, respectively [54,56].A never-before-reported variant in the PALB2 gene (frameshift deletion, NM_024675:exon1:c.47delA:p.K16fs) was described in a young BC Yakut woman with a family history of pancreatic cancer.In accordance with db PubMed ClinVar, a new variant is located in codon of the PALB2 gene, where the likely pathogenic donor splice site variant (NM_024675.3:c.48+1delG)associated with hereditary cancer-predisposing syndrome has been earlier described.The variant of the TP53 gene (LRg_321t1: c.80C>T, rs397516438) was found in a young Tuvinian woman with a family history of BC.In accordance with ProteinPaint tool, the lRg_321t1: c.80 C>T mutation is located in codon of the TP53 gene, where the pathogenic mutation associated with Li-Fraumeni syndrome has been earlier described.Conflicting variants of MUTYH, ATM, RAD51D genes that were previously found in Chinese populations were found in Buryats, Khakasses and Tuvans [55].Further research into the genetic variants of BC-associated genes is required to bring us closer to understanding the pathogenesis of hereditary BC in ethnic groups of the Eastern Europe and Northern Asia.

Discussion
Although the mortality rates have declined in developed countries, hereditary reproductive system cancer remains socially significant and requires improved approaches to prevention, early detection, and effective therapy.Mutations in the BRCA1/2 genes lead to the loss of function of the proteins encoded by these genes, as well as disruption of the major DNA double-strand breakage repair mechanism [2,4].Curation technologies based on the data about the presence of BRCA1/2 gene mutations have currently been developed for BC patients.The presence of BRCA1/2 mutations makes it possible to assess the BC risk in healthy mutation carriers, as well as improve the existing approaches to prevention (prophylactic mastectomy), early detection of BC and making an accurate diagnosis [65].The importance of the BRCA1/2 status has increased manifold with the advent of PARP inhibitors, a group of targeted antitumor drugs blocking poly(ADP-ribose) polymerase enzymes (PARP) and participating in the repair of damaged DNA in BC patients.A total of 72.5-73.2% of patients with BC and BRCA mutations respond to PARP inhibition therapy [66].
Table 3. Germline Variants in BRCA1/2 and Other Genes that were Found in Ethnic Groups of Nothern Asian (or Siberia) Over the recent decades, BC has been the most common malignancy in the Eastern Europe and Northern Asia.The population is primarily descended from newcomers (Slavs) and indigenous population (Asian peoples).More than 13.8 million women inhabit these regions.More than 45 ethnic groups live in Northern Asia (Buryats, Evenks, Altaians, Tuvans, and Khakasses).The incidence of BC among the newcomers is significantly higher than that among the indigenous peoples.The indigenous population has an earlier age of disease onset, and the peak incidence occurs almost 10 years earlier than that for the newcomers.Previous studies have shown that the indigenous peoples of Siberia have short stature, the brachymorphic body type, a high degree of muscle and bone components with a slight development of adipose tissue, a later onset of biological maturity and an early onset of menopause.Moreover, body mass index (grade I-II obesity are classified as a risk for the BC) is significantly lower among the indigenous women (25.6 ± 0.4 kg/m 2 ) than among newcomers (p = 0.015) [67].For the indigenous population of Eastern Europe and Northern Asia, molecular factors determining the risk of developing hereditary BC remain poorly understood.
BC-associated mutation testing in the ethnic groups all over the world is challenging: 1) in some medical centers collecting information on race and ethnicity during BRCA1/2 mutation testing is forbidden; 2) populations of non-white ancestry are still underrepresented in studies of genes associated with BC; 3) genetic testing in the developing countries remains insufficient [3].For the ethnic groups of Siberia, the problems of testing for mutations in genes involved in BC pathogenesis are presented below.
First, BRCA1/2 mutation testing is carried out without taking into account the origin of BC patients.In order to identify the molecular abnormalities responsible for the genetic predisposition to BС in various ethnic groups, it is necessary at least to take into account the challenges, such as the ethnic diversity (more than 200 ethnic groups), demographic situation and special climatic and geographic conditions.
Second, for Asian ethnic groups the determination of eight Slavic mutations (by RT-PCR) is inappropriate because of the significant difference in the spectrum of mutations between the newcomers (Slavs) and the indigenous population (being of the Asian origin).In Siberia, the frequency of the 5382insC variant of the BRCA1 among newcomers with Slavic ancestry is 3.5%; no mutations in the BRCA1/2 genes have been identified among indigenous people [68].The search for ethnospecific molecular genetic disorders by high-throughput sequencing is needed for the ethnic groups.Moreover, studying the genome of ethnic patients with BC during mass screening does not reveal their inherent genetic features, since they are lost in the mass of the NGS data from patients not selected according to the ethnicity parameter.
Third, the enormous amount of data obtained during high-throughput sequencing requires detailed and extensive annotation to identify clinically significant changes in genes.This problem has been widely discussed all over the world.Special attention should be paid to reclassifying the new mutations, as well as the variants of uncertain and conflicting significance to determine the clinical (pathogenic) significance.In poorly studied populations the proportion of variants of uncertain significance is up to 30-50%.The presence of these variants makes it difficult to make an accurate diagnosis and, therefore, prescribe the adequate therapy [69].To reclassify variants of an unknown significance, it is necessary to use available tools, for example, PolyPhen2, Mutation Taster, SIFT or ActiveDriverDB and ProteinPaint tool.Open-source database https://www.ActiveDriverDB.org(Ontario Institute for Cancer Research), which annotates mutations through the prism of post-translational modification sites (PTMs).It was reported that up to 30% of mutations in post-translational modification sites were considered as benign by PolyPhen2, SIFT and others [70].ProteinPaint tool was created to expand an existing cancer genome portal and provide a comprehensive and intuitive view of cancer genomic data with advanced visualization features (https://pecan.stjude.cloud/proteinpaint)[71].
Fourth, the BRCA databases obtained using the data mainly from the Caucasians are used as reference materials for the diagnosis, treatment and prevention of BC all over the world.In the CIMBA study, which collected data on BRCA mutations of about 50 countries across six continents, there were very few data on these mutations among the non-Caucasians.Therefore, a disproportionately large transfer of genomic data of the Caucasian population to the poorly studied ethnic minorities around the world is currently observed.Openaccess databases (ClinVar, the BIC, ENIGMA and other) that used widely for the interpretation of VUS are not suitable for variants found in Asian ancestry populations.The caution also should be exercised when analyzing data of Asian populations sush as Chinese, Koreans, Japanese.For example, the use of ExAC EAS (East Asian), which is mainly composed of Chinese and Japanese, led to misleadingly in assessing the frequency of variants found among Koreans.It became apparent when an extended own control group consisting of Korean population was used [72].
Finally, very little is known about the penetrance of BRCA1 and BRCA2 mutations in the development of BC in ethnic minorities due to short follow-up duration and smaller cohort sizes.For example, in Korea, the BC penetrance for BRCA1 and BRCA2 carriers to age 70 years was 49 and 35%, respectively [73].
Therefore, because of the aforementioned challenges, there exist neither risk assessment models for BRCA1/2 mutation carriers nor guidelines for prevention and surveillance strategies in BC patients belonging to ethnic minorities.In order to meet these challenges, genomic research specialists believe that it is essential to facilitate the exchange of experience, technology and information between countries of all income levels and all the major populations of the world, as well as to create a registry of rare mutations or genetic variants found in BC patients belonging to ethnic minorities [73].This is the first systematic review that provides the spectrum of BRCA mutations in ethnic groups of BC patients inhabiting Eastern Europe and Northern Asia.Our study had some limitations arising due to the fact that some ethnic groups were studied in more details (Tatars, Armenians, Kazakhs, Tuvans) while others remained poorly studied (Mari, Mordovians, Uzbeks) or not studied (Komi, Tajiks, Tabasarans, Nogais).The studies also varied in methods (from PCR to high-throughput sequencing) and sample sizes, which made data analysis difficult.In addition, a significant part of the studies were excluded due to the fact that they studied the prevalence of mutations in any territory or region without taking into account the ethnic composition.In addition, there was no data on the frequency of mutations depending on the clinical and morphological characteristics of the tumor (triple negative cancer, hormonal status, etc.) and the anamnestic data of patients (family history of cancer, age of breast cancer manifestation, etc.).
In conclusion, this is the first systematic review that provides the spectrum of BRCA mutations in ethnic groups of BC patients inhabiting Eastern Europe and Northern Asia.It has been shown that the mutations are ethnospecific (varied widely within groups) and not all groups are equally well studied.Further studies on the ethnic specificity of BRCA gene mutations are required.

Figure 2 .
Figure 2. Flow Chart Detailing Literature Searches and Inclusion Screening

Table 1 .
The Largest Minorities Live in Eastern Europe and Northern Asia [42]ense, deletion, insertion, and InDels.The list of the most important germline variants in ethnic groups inhabiting Eastern Europe and Northern Asia introduced in Tables2 and 3. Some authors have found that germline variants of the genes such as cyclin-dependent kinase 12 and folate cycle gene are involved in the pathogenesis of BC.Bogdanova N., et al.[42]revealed the c.1047-2A>G

Table 2 .
Germline variants in BRCA1/2 and Others Genes that were Found in Ethnic Groups Inhabiting Eastern Europe (excluding Northern Asia or Siberia)

Table 2 .
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