搜尋漢人糖化血色素、禁食血糖和第二型糖尿病基因座

Mapping Genes for Hemoglobin A1c, Fasting Plasma Glucose, and Type 2 Diabetes in Han Chinese

張雅茹(Ya-Ju Chang)

指導教授 ： 潘文涵

國立臺灣大學/生命科學院/微生物與生化學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.03424

摘要

糖尿病為全球和臺灣盛行的重大慢性疾病之一，以第二型糖尿病佔最多數。糖尿病成因多元複雜，基因、環境及其交互作用皆參與其中。因此，若從個體與生俱來所帶有的基因多型性著眼，篩選人群中帶有罹患高血糖易感受基因的個體，期望未來將可有效減緩糖尿病發生率。有鑑於以糖化血色素當作糖尿病患者篩檢工具的敏感度和特異度與禁食血糖相似，且糖化血色素檢測值不易受短期或檢測當天生活習慣的突然改變而波動。從遺傳學的角度而言，糖化血色素遺傳度高達75%，且鮮少有漢人族群的糖化血色素計量性狀基因座相關性研究。促使本研究以糖化血色素為主要研究表型、禁食血糖為輔，利用臺灣漢人細胞與基因資料庫和弗明罕心臟研究，從單核苷酸和候選基因兩個層面描繪與糖化血色素相關的遺傳訊息。

本研究採用兩部分且各兩階段的相關性研究設計搜尋糖化血色素之計量性狀基因座。首先，於臺灣漢人資料庫中隨機抽取全基因體相關性研究兩階段的參與者（Nstage1=970; Nstage2=954），確認糖化血色素及單核苷酸基因多型性間的相關性。其次，以臺灣漢人資料庫為主（Nstage1=970），弗明罕心臟研究為輔（NFramingham=1,093），以兩階段候選基因之單核苷酸結合分析相關性研究預測禁食血糖和糖化血色素計量性狀之情形。所有的相關性分析皆校正年齡、性別及身體質量指數。

全基因體相關性研究第一階段中有16個標籤單核苷酸被認為與糖化血色素間有相關性，分別座落/鄰近ALDH1A1、FTO、KCNA4、KCNJ3及TBC1D4；但在第二階段無法重現其顯著性。以座落FTO基因上之rs7200972、rs1125338及rs1345390進行單倍體組合型分析，保護因子組合型（A-T-A/A-T-A）與參考組組合型（G-C-G/G-C-G）之個體相比，可能有顯著較低的「糖化血色素值偏高」之勝算比（全基因體相關性研究第一階段ORA-T-A/A-T-A = 0.57, 95%CI = 0.38-0.84, p-value = 0.005；全基因體相關性研究第二階段ORA-T-A/A-T-A = 0.86, 95%CI = 0.58-1.26, p-value = 0.433；所有全基因體相關性研究參與者ORA-T-A/A-T-A = 0.71, 95%CI = 0.53-0.93, p-value = 0.013）。兩階段候選基因之單核苷酸結合分析相關性研究中，與禁食血糖相關的候選基因ADCY5是唯一在不同族群中，在隱性遺傳模式下，分別和台灣漢人的糖化血色素有顯著的相關性（pRecessive = 5.24×10-4），和弗明罕心臟研究參與者的禁食血糖有接近統計顯著標準之相關性（pRecessive = 1.78×10-3）。

全基因體相關性研究結果無法在第二階段中再次驗證可能是受限於資料庫樣本數不足及糖化血色素數值不易呈常態分佈所致，需要藉由不同的研究設計和更大的樣本族群做進一步的分析和確認。兩階段候選基因之單核苷酸結合分析相關性研究中，台灣漢人與弗明罕心臟研究參與者的分析結果近乎沒有重複性，說明兩族群間存在基因異質性。所篩選出與糖化血色素有相關性的候選基因是否為台灣漢人族群所特有，或者，與禁食血糖有相關性的候選基因是否為弗明罕心臟研究參與者所特有，皆需藉由更多獨立研究結果加以驗證。

關鍵字

全基因體相關性研究 ； 糖化血色素 ； 候選基因 ； 候選基因之單核苷酸結合分析相關性研究 ； 第二型糖尿病 ； FTO基因

並列摘要

Diabetes mellitus is one of chronic diseases affecting people in Taiwan and the world. Type 2 diabetes accounts for the majority of diabetes cases. It is influenced by multiple and complex causes, included genes, environments, and their interactions. Therefore, we focused on screening a number of subjects with hyperglycemia for susceptible variants associated with diabetes. Our findings would be useful in the study of diabetes. The sensitivity and specificity of the measurement for hemoglobin A1c (HbA1c) in diabetes screening are similar to those for fasting plasma glucose (FPG). However, the measurement of HbA1c has less perturbations and greater convenience, compared to the measurement of FPG. Although the highest heritability estimate for HbA1c was 75%, relatively few studies have identified the quantitative trait loci (QTLs) for HbA1c concentrations in Han Chinese population. We performed a genome-wide association study (GWAS) on HbA1c values and a candidate gene-based association study on the values of HbA1c and FPG to identify common genetic variants influencing HbA1c levels in Han Chinese, as well as FPG levels in Framingham subjects.

We conducted a two-stage study design, in both of the GWAS and the candidate gene-based association study. A total of 1,954 individuals were recruited by the Han Chinese Cell and Genome Bank in Taiwan (HCCGBT) study was used in GWAS: 970 in the initial stage and 954 in the confirmatory stage. In candidate gene-based association study, 970 participants derived from the HCCGBT and 1,093 from the Framingham Heart Study were used to reveal the QTs for HbA1c and FPG, separately. We further adjusted for gender, age and body mass index (BMI) in the statistical analysis, in order to control these potential confounding effects.

Although we found that 16 tagSNPs in/near ALDH1A1, FTO, KCNA4, KCNJ3, and TBC1D4 were associated with HbA1c levels at the first-stage GWAS, we were unable to confirm any of them at the second-stage replication sample. We also used haplotype analysis for the three tagSNPs (rs7200972, rs1125338, and rs1345390) at the FTO locus. The estimate of odds ratio (OR) to haplotypes explained the association for all GWAS participants (A-T-A/A-T-A vs. G-C-G/G-C-G: at the stage 1, ORA-T-A/A-T-A = 0.57, 95%CI = 0.38-0.84, p-value = 0.005; at the stage 2, ORA-T-A/A-T-A = 0.86, 95%CI = 0.58-1.26, p-value = 0.433; at the stage1+2, ORA-T-A/A-T-A = 0.71, 95%CI = 0.53-0.93, p-value = 0.013). The results of the candidate gene-based association study showed that ADCY5, the candidate gene of FPG, was associated with HbA1c in the HCCGBT sample (pRecessive=5.24×10-4) and may be associated with FPG in the Framingham sample (pRecessive=1.78×10-3).

Our study was unable to indicate an association between the HbA1c values and five genetic variants, although they are involved in the glucose and/or insulin metabolisms in Han Chinese. The results of the haplotype analysis for the FTO locus were not replicated at the second-stage GWAS. The observed genetic associations between genetic variants of the ALDH1A1, FTO, KCNJ3, KCNA4, and TBC1D4 loci and HbA1c levels may be limited to the small sample size and the abnormal distribution of HbA1c concentration in our study. We need different detected strategies and a large-size sample to examine whether the HbA1c-related tagSNPs are associated with the QTLs for HbA1c. The results of candidate gene-based association study explained the genetic heterogeneity in different populations. To confirm with the candidate genes associated with HbA1c has specificity in Han Chinese, it is necessary to confirm our results in more independent studies.

並列關鍵字

Genome-wide association study ； GWAS ； Hemoglobin A1c ； HbA1c ； candidate genes ； candidate gene-based association study ； type 2 diabetes ； FTO

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