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The p53 gene is a tumour suppressor gene, whose function is mediated by stimulation of p21 (Waf-1) gene, another tumour suppressor gene, to control cell cycle and prevent tumour formation.3 Mutations in either p53 or p21 are detected in many tumour cells,3,4 and polymorphisms of p53 codon 72 or p21 codon 31 were found to be associated with many tumours.5,6
Because of the abnormal expression of the p53 gene in pterygium epithelium1,2 and there is evidence that hereditary factors may have a role in the development of pterygium,7,8 it is logical to suspect the correlation between pterygium formation and p53 and p21 polymorphisms.
In this study, p53 codon 72 and p21 codon 31 polymorphisms were evaluated in order to understand whether these two polymorphisms are associated with increased susceptibility for pterygium.
Patients and methods
A total of 128 pterygium patients (71 men and 57 women) were enrolled in the study with ages ranging from 35 to 90 years (mean 64.6 years). One hundred and three volunteers aged 55 years or more without pterygium were enrolled as the control group. There were 64 men and 39 women in the control group (age range from 50 to 83 years with an average of 64.2 years).
The genomic DNA was prepared from peripheral blood. For p53, the primer Pro 72 was designed for p53 codon 72 in proline form and Arg 72 for arginine form, according to the procedure described by Storey et al.5 For p21, the primer for codon 31 was designed from codon 1 start (5′-GTCAGAACCGGCTGGGGATG-3′) to codon 91 (5′-CTCCTCCCAACTCATCCC GG-3′), according to the procedure described by Li et al.6 The PCR products from the same individual were mixed together and 10 μl of this solution were loaded into 3% agarose gel containing ethidium bromide for electrophoresis.
There were no significant differences between both groups in age and sex.
The frequency of the genotype of p53 codon 72 and p21 codon 31 polymorphisms in the pterygium group and control group is shown in table 1. There were no significant differences between both groups.
The frequency of the alleles for the p53 codon 72 and p21 codon 31 between pterygium and control groups was not statistically different (table 2).
Analysis of combination p53 codon 72 and p21 codon 31 polymorphisms, there was also no significant difference between both groups (table 3).
Weinstein et al suggest the cause of p53 mutation in pterygium may be ultraviolet radiation or be hereditary.2 Detorakis et al proposed a “two hit” model for DNA abnormalities in pterygium.9 The first hit could be either inherited or incurred by ultraviolet radiation, and the second hit could be caused either by solar light or by viral infection. Though the hereditary factor was proposed to have a role in pterygium formation, there were few studies to clarify this proposition. In this study, we try to investigate the hereditary factor of pterygium by single nucleotide polymorphism (SNP) marker. Single nucleotide polymorphisms are the most abundant types of DNA sequence variation in the human genome, and the SNP marker has provided a new method for identification of complex gene associated diseases such as tumour.10
The p53 codon 72 and p21 codon 31 polymorphisms are two of the most important SNP markers for tumour susceptibility. However, there are no significant differences between the pterygium and control group in our study. We suggest the p53 codon 72 and p21 codon 31 polymorphisms maybe cannot become useful genetic markers for pterygium susceptibility. This could be the basis of future surveys.
The authors have no proprietary or financial interest in any material or device mentioned.