Haplotypes in Exon 4 of KLK2 Gene as Predictive Markers for Prostate Cancer

Abstract

Prostate cancer is the second highest cause of death due to cancers in men. The risk of developing it increases with age and the highest incidence is observed in men above the age of 50 years. In black men, the estimated lifetime risk of being diagnosed with prostate cancer is 20.6% while the lifetime risk of death due to it is 4.7%.The current standard tests for the diagnosis of prostate cancer are the serum prostate specific antigen (PSA) test, digital rectal examination (DRE) and the histology of prostate biopsy. These diagnostic modalities are limited by their inability to predict which patients are at risk of developing metastatic disease. There is need for research on other biomarkers that may increase diagnostic and prognostic information so that better predictions can be made and treatments may be tailored. Genetic stratification of those at risk of developing prostate cancer will facilitate better and active screening of high risk males thereby reducing mortality due to the disease. The human glandular kallikrein 2 (hK2) gene also known as the KLK2 gene is one of the gene families that have shown strong association with prostate cancer. The aim of this study was to determine the possibility of predicting subjects that are genetically at risk of developing prostate cancer using haplotypes (SNPs) in exon 4 of the kallikrein 2 (KLK2) gene-. Blood samples were collected from one hundred participants who had given their informed consent. Total and free PSA were measured using the enzyme linked immunosorbent assay and % free PSA was calculated. Genomic DNA was extracted from whole blood using Spin column method. Exon 4 of the KLK2 gene was amplified with specific primers. The PCR products were sequenced on ABI 3130 genetic analyzer. The results were aligned and SNPs were identified using the SeqMan alignment program of DNA Star software. The total PSA, free PSA and % free PSA of the subjects ranged between 4.11 -50.63ng/ml, 0.20 – 4.73ng/ml and 1.9% - 25.80% respectively. Out of the 100 subjects studied, 28 had total PSA levels above 4.0 ng/ml which is the conventional cut-off value and an indication for prostate biopsy. Results from direct DNA sequencing showed 11 SNPs. Ten are curated in the SNP database while one is uncurated. Analysis of variance showed a statistically significant difference (p <0.0001) between the PSA levels of subjects who expressed SNPs and that of those who did not express SNPs. Two SNPs: rs6072 and rs74478031 were significantly associated with elevated PSA levels (p<0.05). The presence of SNPs may be used as a genetic tool for stratifying patients who are genetically at risk of developing prostate cancer into high, medium and low risks subjects. It will also shield the low risk subjects who may never develop prostate cancer from the trauma of going through prostate biopsy.