ZBRK1/ZNF350 is located on chromosome 19 GRCh37.p2; 52,490,079–52,467,593 [18], covering about 10 kb and containing 4 exons [13], which encodes a protein of 60-kDa [15]. This protein contains the highly conserved KRAB domain at the NH2 end, 8 continuous C2H2 zinc finger motifs at the COOH end, and the CTRD domain. ZBRK1/ZNF350 protein inhibits transcription through CTRD with independent DNA binding [19]. The N-terminal KRAB domain of ZBRK1/ZNF350 protein binds to the repressor protein to form a transcriptional repression domain [20]. ZBRK1/ZNF350 protein is related to the occurrence of various human tumors [21]. Garcia-Closas et al. [22] have conducted a meta-analysis based on the population of the United States (3368 cases and 2880 controls) and Poland (1995 cases and 2296 controls). They have found that there may be a weak link between the ZBRK1/ZNF350 rs4986771 locus and the risk of breast cancer. In the American population, compared to the wild-type homozygous genotype, heterozygotes at the ZBRK1/ZNF350 rs4986771 locus would suffer from increased risk of breast cancer, and the same genotype does not have significantly increased risk in the Polish population. A meta-analysis has showed that the rs4986771 gene mutation may have a protective effect on breast cancer [23]. However, in this study, our results showed that there was no statistically significant difference in the rs4986771 genotype frequency distribution between the case and control groups. The main reason for the difference between our conclusions and the meta-analysis [23] may be the sample size and study design. Their study was a meta-analysis performed on the population from the US (3368 cases and 2880 controls) and Poland (1995 cases and 2296 controls) with large sample size. However, the sample size in our original article was small. Further studies are needed.
In this study, through the direct sequencing of the exon region of the ZBRK1/ZNF350 gene in 80 cases of early-onset (30–40 years old) breast cancer who were admitted to our hospital, a total of 9 sequence variants were detected. Garcia et al. [11] have performed the ZBRK1/ZNF350 gene sequencing on patients with primary breast cancer and have found 9 polymorphic sites, among which 7 sites were consistent with the sites found herein, namely rs2278420, rs2278415, rs4986771, rs4986773, rs4988334, rs3764538, and rs4986772. The SIFT software was used to predict the protein function, and our results showed that the sequence variants rs4987241 and rs2278415 in the breast cancer patients were harmful mutations, and one of the patients was the carrier of c.111G > A in rs4987241 aged 34 years old, who suffered from bilateral breast cancers (axillary lymph node metastasis at both sides, 3/22 right breast and 1/26 left breast; the left breast was triple negative breast cancer). Another breast cancer patient also suffered from bilateral breast cancer, who was aged 37 years old, and both breasts were triple-negative breast cancers. However, in this study, there were no significant differences in the genotype frequencies of rs4987241 and rs2278415 distribution between the case and control groups. However, a meta-analysis has shown that the risk of breast cancer is increased for the rs2278415 gene mutation [23]. This phenomenon may be related to the sample size, and this site worth further investigation with enlarged sample sizes.
Polymorphism refers to a DNA sequence polymorphism caused by the substitution, insertion or deletion of a single nucleotide at the genome level. It is a common type of human heritable variation, accounting for more than 90% of known polymorphisms. When the minimum mutation frequency is greater than 1%, it would be called polymorphism. As shown in Table 4, the mutation rate of a single base of the rs138898320 allele was 3/480, and the allele frequency was less than 1%. Therefore, this locus may be a rare mutation rather than a polymorphism. In this study, it is worth noting that, compared with the carriers of CC wild genotype at rs138898320, the risk of breast cancer was reduced by 88.3% in carriers of CT mutant genotype, with statistically significant differences. In the stratification without family history, compared with the carriers of CC wild genotype at rs138898320, the CT mutation genotype carriers had protective effects on breast cancer, with statistically significant differences. However, in the stratification with family history, there was no significant difference in the variation of rs138898320 of ZBRK1/ZNF350 gene polymorphism.
Menstruation and fertility are important components of physiological reproductive factors. It has been shown that the menarche and age of first birth are related to the incidence of breast cancer. Early age of menarche and late age of first birth are important risk factors for breast cancer. In this study, our results showed that there was no statistically significant difference in BMI, age of menarche, age of first birth, or times of pregnancies between the case and control groups, and there was significant differences between the case and control groups with the breast cancer family.