The rise of technologies such as whole genome sequencing has expanded our knowledge of genes involved in various diseases. However, identifying new causative genes and mutations is a complex process, often requiring multiple procedures to determine the role of a mutation in a specific disease. Typically, the pathogenic variant's occurrence needs to be examined in both patients and healthy individuals, within family members, and across the population. However, there are challenges, such as the rarity of the variant, limited participation from relatives, and lack of prior descriptions of the variant in similar patient groups. Additionally, there can be differences in mutation frequency based on ethnic groups.
The LGR4 gene, which is involved in the Wnt/β-catenin signaling pathway related to tumors, has been the focus of recent attention in BC research [7]. Studies have shown that LGR4 knockdown mice exhibit delayed development of mammary ducts, reduced collateral formation, and impaired mammary stem cell function. For example, Mancini et al. (2020) found mutations in the LGR4 gene associated with delayed puberty [8]. Thus, three rare missense variants in the LGR4 gene were identified in six unrelated families with delayed puberty (17 patients) by autosomal dominant inheritance (NM_018490.3: c.286 A > G (rs757351670) p.Ile96Val; NM_018490.3: c.1087G > T (rs117543292) p.Gly363Cys and NM_018490.3: c.2531A > G (rs34804482) p.Asp844Gly). Six male probands exhibited delayed testicular development and decreased serum levels of LH/FSH and androgens, consistent with the low levels of free testosterone in heterozygous individuals with the inactivating p.R126X mutation of the LGR4 gene. It should be noted that all probands identified by Mancini et al. were male. Women with LGR4 gene mutations have not been extensively studied, although, in two families, the mutations were detected in women. The deCODE study indicated that women carrying the p.R126X mutation of the LGR4 gene experienced delayed menarche (by approximately 0.4 years). Further research is needed to understand the impact of these mutations on women's fertility.
The frequency of the alternative allele of the LGR4 rs34804482 gene has been extensively investigated across multiple projects, such as 1000Genomes, ExAc, Allele Frequency Aggregator, gnomAD - Exomes, the PAGE Study, and the ALFA project. According to dbPubMed, these studies have shown notable variations among diverse populations. The ALFA project reported the overall frequency of the alternative allele of the LGR4 gene (rs34804482) to be 0.021, 0.02 in Caucasians, 0.006 in Africans, 0.0000 in Asians, and 0.0008 in African Americans, indicating significant differences of this allele in terms of ethnicity [9].
This research investigated the prevalence of a specific genetic allele in the population of Western Siberia, focusing on the Russians, Buryats, Tuvans, Altaians, and Yakuts, both among healthy individuals and those diagnosed with breast cancer, using real-time PCR. The study revealed that the frequency of the LGR4 gene (rs34804482) in the overall patient group is 0.027. Among different ethnic groups, the frequency was 0.015 in Russians, 0.022 in Buryats, and 0.069 in Tuvans. The gene variant was not found in Khakassians and Yakuts. Interestingly, the occurrence of the pathogenic variant of the LGR4 gene in Tuvinians with BC was significantly higher than in Russians with breast cancer (X2 = 6.368, p = 0.012).
However, the study did not find a clear association between this gene variant and BC in either Russians or Tuvans, as the frequency in BC patients and healthy individuals was comparable within each group. For healthy individuals, the frequency of the pathogenic variant of the LGR4 gene (rs34804482) was 0.066 in Tuvans, significantly higher than the 0.016 found in healthy Russians (X2 = 4.46, p = 0.03). This suggests that the observed frequency of the pathogenic variant of the LGR4 gene (rs34804482) in the population of Western Siberia (healthy individuals) is mainly driven by the high occurrence of this gene variant in Tuvans.
Comparing the frequency of occurrence of the pathogenic variant of the LGR4 gene (rs34804482) with other populations worldwide revealed that the 0.016 frequency in Russians is similar to that of Europeans (0.0219). Tuvans, on the other hand, exhibited the highest incidence of this pathogenic variant at 0.066, which was statistically significantly higher compared to Americans and other ethnic groups (Table 4).
Our study, while providing valuable insights, had some limitations. The small size of our study groups was a significant constraint. To overcome this, we used dbPubMed data from samples that were not significantly larger than the size of our groups to obtain statistical differences. Despite the lack of data supporting the connection between the germinal pathogenic variant of the LGR4 gene and BC, our findings, particularly our real-time PCR test system, can be used by other scientists to examine the frequency of this variant in more diverse cohorts. This highlights the potential for further research in this area.
To sum up, we have conducted the first investigation of the frequency occurrence of the pathogenic variant of the LGR4 gene in BC patients and healthy individuals in Western Siberia. We discovered significant differences in the frequency of occurrence of the LGR4 gene variant based on the ethnicity of the subjects we studied. Notably, we found a high frequency of occurrence of this pathogenic germinal variant among the Tuvan population compared to other populations worldwide.