Newly MLH3 gene linked to breast cancer: Genetic and epigenetic investigations

Breast cancer is the most common cancer in women worldwide. Dtermination of the breast cancer susceptibility genes are an important issue. Also, MLH3 is a DNA mismatch repair gene and mutation in this gene is harmful in different cancers. The aim of this study was using exome sequencing to uncover previously undetected breast cancer predisposing variants. we also investigated the MLH3 gene expression and methylation of breast cancer patients which can be a breast cancer susceptibility gene. A total of 80 samples including 40 paired normal and cancer tissue sample were collected at Zheen International Hospital, Erbil, Iraq. Exome sequencing was used to identify mutations. Different insilico tools were used to predict the effect of mutation on the structural features or protein function. Real-time PCR was used for assessing the expression of MLH3 in breast cancer patients. We identified 26 variants in breast cancer patients, 22 inherited variants were found in MLH3, CHECK2, BRCA1, BRCA2, BLM, TP53, MSH6, NBN and PTEN genes and 4 somatic variants were found in PALB2, RAD50 and RBM10 genes. It was found that the expression of MLH3 gene in tumor samples was significantly downregulated compared with normal tissues. Statistically high significance was found. The decrease expression of MLH3 was significant in all range of the ages and all breast cancer types. The expression of MLH3 also decreased significantly in patients with breast cancer grade of II and III. The overall methylation rates in tumor tissue were 3% for MLH3 gene, there was no evidence of MLH3 promoter methylation. In conclusion, MLH3 can be used as a susceptibility gene especially in the grade II and III of breast cancer. Key Words: Breast Cancer, Exome Sequencing, MLH3, qPCR, DNA Repair, Methylation