Novel mutations of OGG1 base excision repair pathway gene in laryngeal cancer patients

Abstract

OGG1 (The human 8-oxoguanine glycosylase 1) is the primary enzyme in BER (base excision repair) pathway, responsible for the excision of 7, 8-dihydro-8-oxoguanine (8-oxoG), a mutagenic base byproduct that occurs as a result of exposure to reactive oxygen species. OGG1 gene is highly polymorphic among humans and is mutated in cancer cells. In this case control study, all exons of OGG1 gene and its exon/intron boundaries were amplified in 210 laryngeal cancer cases and 210 matched controls and then analyzed by single stranded conformational polymorphism. Amplified products showing altered mobility patterns were sequenced and analyzed. Two silent (Gln718Gln, His699-700His) and three missense (Ala597, Thr608-610Pro and Glu707Lys) mutations were observed in exon 2. In addition to this one missense mutation (1578G>A) was also observed in 3'UTR region. We found a significant association between OGG1 mutations and laryngeal cancer and observed that His699-His700, silent mutation exhibited an enhanced risk of ~9.0 folds (OR=9.07, 95% CI=4.73-17.39) and 1578G>A, missense mutation ~0.4 folds (OR=0.37, 95% CI=0.15-0.90). Furthermore, a positive association of OGG1 mutations with smoking was observed in laryngeal cancer cases when compared to controls. Heavy smokers have higher incidence of OGG1 mutations when compared to light smokers in present study. Our results demonstrate that OGG1 mutations are associated with an increased risk of laryngeal cancer. OGG1 mutations were found to accumulate more of 8-OHdG in smokers, which may serve as a biomarker for early diagnosis of laryngeal cancer.