以標誌性基因多型性方式研究麩胺基硫過氧化酶-3與分化性甲狀腺癌症之關係

Tagging single-Nucleotide Polymorphisms in GPX-3 gene and susceptibility to Differentiated Thyroid Cancer

林荏志(Jen-Chih Lin)

指導教授 ： 郭文烈

高雄醫學大學/醫學院/醫學研究所/碩士(2008年)

摘要

目的:分化性甲狀腺癌症的發生機轉至今仍不明瞭。研究顯示放射線的暴露與甲狀腺癌症的發生有關。已知輻射線會造成細胞內單股及雙股DNA斷裂或是增加反應性氧化產物(Reactive oxygen species, ROS)的產生而提高細胞內的氧化壓力(oxidative stress)。氧化壓力的提高會造成細胞內包括DNA、蛋白質或脂質等的損傷，導致細胞發生凋零(apoptosis)、老化和癌症。細胞會藉由抗氧化物質或是抗氧化酵素包括glutathione peroxidase(GPX)的作用分解過量的ROS以降低氧化壓力。反應性氧化產物中的過氧化氫在甲狀腺素的碘化過程中佔有重要的角色。甲狀腺細胞會合成及分泌GPX-3至濾泡腔中分解過氧化氫。已知基因多型性可能會影響酵素的表現能力，並進而與癌症的易感性有關。本研究的目的即在探討GPX-3的基因多型性與分化性甲狀腺癌的相關性。
方法:本案採病例對照研究方法。共收集自高雄醫學大學附設醫院耳鼻喉科及新陳代謝科無血緣關係之268名分化性甲狀腺癌症患者(男性49例，女性219例)為病例組以及285名(男性158例，女性127例)無癌症病史者為對照組。自國際人類基因組單體型圖研究計畫(HapMap)中尋找漢族群有關GPX-3基因的標誌性基因(tagging single nucleotide polymorphism, tSNP)進行研究，共選取6個其最小對偶基因頻率大於10%的tSNP。使用real-time TaqMan PCR基因型定型(genotyping)法來檢測實驗組與對照組的DNA 與所選取的GPX-3基因中的6個tSNPs是否有差異。藉此了解分化性甲狀腺癌症風險與GPX-3標誌性基因多型性的關係。
結果： 本實驗之6個tSNPs基因型定型完成率為98.7至100%。其基因型頻率分佈皆符合Hardy-Weinberg平衡（P>0.05）。整體分析上，病例組及對照組在GPX-3基因出現頻率上雖有所不同，但尚未在統計上達到明顯差異。對45歲以上(含)族群的基因型分析顯示帶有SNP rs3805435少見對偶基因者在分化性甲狀腺癌患者有統計上的意義 (OR=0.46, 95%CI= 0.25-0.87, p=0.016) 。在45歲以上(含)族群的單體型分析發現，病例組Block 1(rs8177412及rs3763013)帶有GC單體的比例高於對照組，且達到統計上的意義( OR=1.75, 95%CI= 1.07-2.91, p=0.028)。
結論：全體分析發現，GPX-3上的六個tSNPs其基因型、表現型或是單體型都與分化性甲狀腺癌症的發生並無統計上有意義的相關。GPX-3上的六個tSNPs與淋巴轉移間之關係，沒有達到統計上的意義。在年齡超過45歲(含)以上的族群具有SNP rs3805435的少見對偶基因的人發生分化性甲狀腺癌症的機會較低。SNP rs8177412的少見對偶基因對分化性甲狀腺癌症來說是一個危險因子。GPX-3基因的單體分析顯示Block 1 (rs8177412及rs3763013)帶有GC單體型的人發生分化性甲狀腺癌症的機會較高。

關鍵字

分化性甲狀腺癌 ； 麩胺基硫過氧化酶標誌性基因多型性

並列摘要

Introduction: Although the exact etiology of differentiated thyroid cancer (DTC) is not well understood, exposure to radiation is considered as a risk factor. Radiation can cause direct DNA damage and the generation of reactive oxygen species (ROS). In the thyroid, ROS and free radicals can participate in physiological and pathological processes. The antioxidant enzymes such as glutathione peroxidase (GPX), especially GPX3, can lower down the oxidative stress in thyrocyte. We want to find the relationship between the genetic variants of GPX3 and differentiated thyroid cancer.
Materials and Methods: This is a case-control study including 268 cases with histologically verified DTC (49 male, 219 female, mean age = 40.0±13.9) and 285 controls (158 male, 127 female, mean age = 45.2±13.3) in Departments of Otolaryngolgy or Endocrinology in Kaohsiung Medical University Hospital between October 2005 and December 2006. Six tSNPs (rs2070593, rs3763013, rs3792796, rs3805435, rs3828599, rs8177412) had been identified with rp2 of 0.8 or greater and MAF > 0.1 in the ethinic group of Chinese Han Beijing in HapMap project. We genotyped all samples for the selected tSNPs using the ABI PRISM 7500 sequence detection system (Applied Biosystems).
Results: Genotyping success rate was ranged from 98.7% to 100%. The distribution of the allele frequency and genotype frequency of our six tSNPs in the case and control groups are in Hardy-Weinberg equilibrium. The overall analysis of the genotype and allele frequencies in each tSNP indicated that there is no significantly associated with differentiated thyroid cancer. The minor allele of SNP rs3805435 shows significant decreased in the group whose age more than 45 year-old. (p=0.016) The analyses of haplotype block 1 including SNP rs8177412 and SNP rs3763013 shows a significant increasing of the GC haplotype in case group whose age more than 45 year-old. (p=0.028)
Conclusion: We found that homozygote AA of rs3805435 significantly increased a risk for differentiated thyroid cancer whose age more than 45 years old. GC haplotype in Block 1 including SNP rs8177412 and SNP rs3763013 has significant increasing in differentiated thyroid cancer.

並列關鍵字

Differentiated thyroid cancer ； Glutathione peroxidase ； Tagging single nucleotide polymorphism

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