P53 gene mutation spectrum and the relationship between gene mutation and protein levels in pterygium.

PURPOSE To investigate the spectrum of p53 gene mutations and the relationship between gene mutation and p53 protein levels in pterygium. METHODS Pterygial samples were harvested from 51 patients undergoing pterygium surgery. DNA samples for p53 mutation analyses were extracted from epithelial cells and subjected to DNA sequencing for examination of mutations in exons 4, 5, 6, 7, and 8 of the p53 gene. In situ levels of p53 protein were studied by immunohistochemistry (IHC) and the percentage of positively stained cells quantified. Ten normal conjunctiva samples were included in this study as controls. RESULTS Mutations within the p53 gene were detected in 8 pterygial samples (15.7%) with only one mutation found in each sample. All the mutations observed were point mutations, with 6 being substitutions and 2 deletions. Three mutations were identified in exon 6, two in exon 7, and a single mutation found in each of exons 4, 5, and 8. P53 protein levels were scored as 0 (negative) in 31 pterygial specimens (60.8%), +1 in 9 samples (17.6%), +2 in 5 samples (9.8%), and +3 in 6 samples (11.8%) by IHC. The 8 samples found to have p53 gene mutations were equally distributed among the different levels of p53 protein observed using IHC, with 2 samples in each group. The two deletion mutations, which caused a frame shift to occur, were found in samples negative for p53 immunostaining (score 0), while substitution mutations were found in samples positively stained (score +1, +2, and +3). CONCLUSIONS Mutations within p53 gene exons 4-8 were detected in pterygial epithelium and the mutations showed no correlation with p53 protein levels as seen by IHC.