OGG1 gene sequence variation in head and neck cancer patients in Pakistan

In Pakistani culture tobacco use is very high and a well known risk factor for developing head and neck cancer (HNC), tobacco smoke containing high quantities of chemical carcinogens such as aromatic amines and reactive oxygen species. OGG1 is the primary enzyme in the base excision repair (BER) pathway, responsible for the excision of 7, 8-dihydro-8-oxoguanine, a mutagenic base byproduct that occurs as a result of exposure to reactive oxygen species. Groups of 300 already diagnosed HNC patients along with normal controls were included in this study. PCR-single-strand conformation polymorphism and DNA sequencing were used to analyze the whole coding region of OGG1 gene. Sequence analysis revealed eight novel mutations (six missense and two frame shift mutations). Frequencies of missense mutations, Asp267Asn, Ser279Gly and Ile253Phe were 0.12, 0.13 and 0.06 respectively. Frequencies of other missense mutations, 1578A> T, 1582C> T and Ala399Glu (1542C> A) were 0.13, 0.13 and 0.16, whereas values for the frame shift mutations 1582insG and 1543-1544delCT were 0.13 and 0.16. In our study, incidence of these mutations was found higher in oral cancers (p<0.002) and in smokers (p<0.002) when compared with other sites of HNC and nonsmokers, respectively. Our finding suggests that these germline mutations in OGG1 gene contribute to risk of developing HNC.