MUTYH Association with Esophageal Adenocarcinoma in a Han Chinese Population

Adenocarcinoma of esophagus (AE) is the leading cause of death in industrialized countries, and its prevalence is rapidly increasing in China. Many genes are related with the development of AE. DNA base damage is one of the most significant cause of AE, one of the best characterized oxidative DNA lesion is 7,8-dihydro8-oxoguanine (8-oxo-G), which can give rise to CGgAT transversion mutations, A:8-oxo-G mispairs are proficiently recognized and repaired by MUTYH (Markkanen et al., 2013). As reported earlier loss of MUTYH function in human cells could lead to accumulation of oxidative damage and genetic instability (Ruggieri et al., 2012). Experimental evidence has confirmed that MUTYH plays an important role in many cancers. The MUTYH mutation spectrum in Brazilian polyposis patients showed a high detection rate and was used to identify novel pathogenic mutations (Torrezan et al., 2013). In addition 324 Gln/His (rs3219489) MUTYH genotypes were found to be associated with an increased colorectal cancer (CRC) risk in Polish patients, Moreover, the decrease efficiency of DNA repair were correlated with the genotypes occurrence in CRC patients (Przybylowska et al., 2013). MUTYH-associated polyposis (MAP), caused by biallelic mutations in MUTYH, was characterized by


Introduction
Adenocarcinoma of esophagus (AE) is the leading cause of death in industrialized countries, and its prevalence is rapidly increasing in China.Many genes are related with the development of AE.DNA base damage is one of the most significant cause of AE, one of the best characterized oxidative DNA lesion is 7,8-dihydro-8-oxoguanine (8-oxo-G), which can give rise to CGg AT transversion mutations, A:8-oxo-G mispairs are proficiently recognized and repaired by MUTYH (Markkanen et al., 2013).As reported earlier loss of MUTYH function in human cells could lead to accumulation of oxidative damage and genetic instability (Ruggieri et al., 2012).Experimental evidence has confirmed that MUTYH plays an important role in many cancers.The MUTYH mutation spectrum in Brazilian polyposis patients showed a high detection rate and was used to identify novel pathogenic mutations (Torrezan et al., 2013).In addition 324 Gln/His (rs3219489) MUTYH genotypes were found to be associated with an increased colorectal cancer (CRC) risk in Polish patients, Moreover, the decrease efficiency of DNA repair were correlated with the genotypes occurrence in CRC patients (Przybylowska et al., 2013).MUTYH-associated polyposis (MAP), caused by biallelic mutations in MUTYH, was characterized by

MUTYH Association with Esophageal Adenocarcinoma in a Han Chinese Population
Feng Kong 1 , Xue-Ying Han 2 , Yun Luan 1 , Tong-Gang Qi 1 , Chao Sun 1 , Jue Wang 1 , Hua-Ying Hou 3 , Yu-Hua Jiang 3 , Jing-Jie Zhao 4 *, Guang-Hui Cheng 1 * a greatly increased (43% to nearly 100%) lifetime risk of CRC, in the absence of timely surveillance (Brand et al., 2012).Another research suggested that significantly increased cholangiocarcinoma risk was found in individuals with a homozygous variant genotype for rs3219472.It may be a biomarker for screening individuals at high risk of developing the disease in the Han Chinese population (You et al., 2013).In summary, it was found that MUTYH had been associated with many diseases in various populations.However, convincing evidence of disease association was found in other populations, other than the Han Chinese.The present study aimed to investigate the association between genetic variations in MUTYH and AE in the Han Chinese population.

Study subjects
Subjects with Han Chinese ethnicity (n=456) were included in this case-control study.A total of 207 patients with AE, 133 males and 74 females, were recruited from the Department of oncology in the Second Hospital of Shandong University from September 2011 to march 2013.A total of 249 unrelated subjects, 154 males and 95 females, were randomly selected as controls from a health check-up center in the Second Hospital of Shandong University during the same period.The controls were free of any cancer according to medical history.A structured questionnaire based on interviews and clinical examinations was employed to characterize the subjects and the controls.These included details of medical history, family history of AE and other traditional risk factors (smoking and alcohol drinking) of AE.The clinical and demographic characteristics of the samples are shown in tableⅰ.Genomic DNA was extracted from peripheral blood leukocytes using the QIAamp DNA Blood Mini Kit (Qiagen, Berlin, Germany) (Gu et al., 2012).This study was approved by the Ethics Committee of school of medicine, Shandong University and informed consent was obtained from the participants.

Single-nucleotide polymorphism selection
The single-nucleotide polymorphisms (SNPs) examined here(rs3219472, rs3219489) were the same as previously investigated in the two case-control samples (Przybylowska et al., 2013;You et al., 2013).The other SNP (rs3219463) is located in the 5'-fanking region and may represent potential functional variant.

Statistical analysis
Genotype frequencies of the SNPs detected were tested for Hardy-Weinberg equilibrium.Variations in genotype and allelic frequencies between case and control groups, odds ratios (OR), 95% confdence intervals (CI), and logistic regression analysis were calculated using plink 1.07.Continuous variables were displayed as the mean±standard deviation (SD), and the comparison of continuous variables was carried out using the student's t-test.A p-value <0.05 was considered statiscally signifcant.

Results
Clinical and demographic characteristics of the cases.According to the examination results, the clinical characteristics of the study subjects are shown in Table 1.Age and gender indexs were demonstrated no signifcant variations but smoking and alcohol drinking between the cases and controls.
Association of the polymorphisms with AE.The distributions of three SNPs were in Hardy-Weinberg equilibrium (p>0.05) in both the AE and control groups.The distributions of genotypic and allelic frequencies of these SNPs in each group were shown in Table 2.The genotypes distribution of rs3219472 differed between the case and control groups (OR=1.66,95%CI=1.11-2.48,P=0.012), indicating there might be an association between MUTYH and AE, on the other hand, the allelic frequencies was no signifcant difference, after logistic regression analysis were calculated using plink 1.07, removing the effects of traditional factors such as age, gender, alcohol and cigarettes, the genotypes distribution of rs3219472 still have significant differences (OR=1.48,95%CI=1.07-2.45,P=0.031) between two groups, which further proves that the onset of AE is associated with the MUTYH gene.But the distributions of genotypic and allelic frequencies of the other two SNPs still have no signifcant difference between the two groups.

Discussion
Adenocarcinoma of esophagus (AE) is a complex disorder resulting from the interaction of a number of genetic and environmental factors.Recent researches have demonstrated that many genes play pivotal roles in the pathogenesis of AE.Numerous studies have shown that damage repair genes play critical role in the pathogenesis of some cancers in several populations (Miyaishi et al., 2009;Sliwinski et al., 2009;Picelli et al., 2010;Stanczyk et al., 2011;Santos et al., 2012), indicating the important relationship between the gene MUTYH and AE.The main finding of this study is that the same association dose exist in Han Chinese population.
We first investigated the association of MUTYH and AE using 207 patients and 249 controls.Signifcant difference was found in the genotypic frequency distribution of rs3219472 but allelic frequency between the two groups in Han Chinese population studied.After adjusting for age, gender, smoking and drinking alcohol, the genotypic frequency distribution of rs3219472 still has signifcant difference, but the other two SNPs were not found.Our result demonstrated that the SNPs studied in the MUTYH gene are likely to contribute to the AE risk in Han Chinese population.
In conclution, significant association between SNPrs3219472 and AE were found in our samples.Similiar to the role of MUTYH gene in cancer of other population, our result suggested that the MUTYH gene is likely to be a major susceptibility for AE in Han Chinese population.
Limitation: A number of possibilities may account for the association between the SNPs and AE in this case-control study, including diagnostic heterogeneity, sample size, population stratifcation and various genetic backgrounds in the different populations.Although not likely, these factors may affect our result.