失智症環境與基因危險因子之分子流行病學研究

Abstract

本論文以下列二個子研究探討中年與基因危險因子和主要失智症類型之相關。 研究一：中年危險因子研究 目的 探討可預測老年失智症之中年危險因子。 方法 自1982至1992年所建立的包含40,636名個案的長期追蹤世代研究，選取157名失智症患者與628名比較組個案進行重疊病例對照研究。每一名失智症患者依據進入研究時的年齡、性別、進入研究的時間(相差6個月內)和居住地等變項，以頻率匹配的方式選取四名比較組個案。本研究分析的中年危險因子包括：心血管因子(如身體質量指數、血膽固醇、血三酸甘油酯、血糖、與腦中風、糖尿病和高血壓的過去疾病史)、抽菸、喝酒等變項。失智症患者的確認乃經由與2000至2002年的全民健保資料庫之資料連結以及神經科醫師的臨床確診。統計方法則採用條件式邏輯迴歸分析來估計匹配危險對比值與95%信賴區間。 結果 身體質量指數與失智症之間呈現J型相關。以身體質量指數介於20.5至22.9為參考組(OR=1.0)，在身體質量指數為<20.5、介於23.0至25.4以及>25.5的個案，經多變項調整後罹患失智症的危險對比值(95%信賴區間)分別為1.84 (1.02-3.33)、1.87 (1.08-3.23)和2.44 (1.39-4.28)。再分類為罹患阿滋海默症與血管性失智症的個案也得到類似的結果。肥胖(身體質量指數>25.5)與罹患阿滋海默症和血管性失智症的相關性，僅在有抽菸組發現統計上顯著意義；但無抽菸組卻沒有顯著的結果。另外，腦中風的疾病史對於罹患血管性失智症來說是很重要的危險因子。 結論 本研究顯示在中年，有體重過輕或是過重以及腦中風的人，會增加老年罹患失智症的風險。(已被American Journal of Geriatric Psychiatry雜誌接受刊登) 研究二：基因危險因子研究 目的 探討13個候選基因包括瘦素及其受體基因共18個基因多型性與阿滋海默症和血管性失智症的相關性。 方法 自研究一選取保存有白血球檢體的27名阿滋海默症患者、34名血管性失智症患者，與298名年齡、性別、進入研究時間和居住地等因子匹配的對照個案納入本研究進行分析。18個基因多型性，包括APOE ε2/ε3/ε4, A2M Ile1000Val, LRP C766T, VLDLR 5’UTR CGG-repeat, IDE 5’UTR G/T, TNF T-1031C, BACE C786G, ACE ins/del, MTHFR C677T, PON Arg192Gln, COMT Val158Met, LEP 5’UTR G/T, LEPR Arg109Lys, Arg223Gln Ser343Ser, Lys656Asn, intron 14 A/C and Pro1019Pro以即時定量聚合酶連鎖反應、微衛星方法或是聚合酶連鎖反應結合限制酶切割片段長度多型性分析來進行實驗操作。本研究採用非條件邏輯迴歸來估計經年齡、性別、進入研究時間、居住地和其他干擾因子調整後之危險對比值與95%信賴區間。針對多個瘦素受體基因多型性進行半形分析。另外，更進一步分析基因與基因間的交互作用和基因劑量效應。 結果 發現APOE ε4基因 (多變項調整的OR為3.21；95%信賴區間介於1.09至9.53)、 PON Gln/Gln基因 (多變項調整的OR為6.66；95%信賴區間介於1.98至22.4) 以及由瘦素受體基因上 Lys656Asn G/C, intron 14 A/C 和Pro1019Pro T/C所組成的GCC半形 (多變項調整的OR為6.45；95%信賴區間介於2.07至20.1) 均與罹患阿滋海默症的危險有顯著相關。且帶有越多的APOE、PON和LEPR危險基因，得到阿滋海默症的風險就越高。不過，本研究並未發現與血管性失智症有顯著相關的基因。 結論 本先驅研究證實APOE ε4基因為阿滋海默症的危險基因，更發現了瘦素受體和PON的基因多型性與阿滋海默症有顯著相關存在。

This thesis comprises two component studies to evaluate the associations between midlife and genetic risk factors and subtypes of dementia. PART 1: Midlife Risk Study Objective: To identify the midlife risk factors for subtypes of dementia newly developed later in life. Methods: A nested case-control study was conducted on 157 demented cases and 628 comparison cases selected from 40,636 men and women who were enrolled from 1982 to 1992. Four comparison cases were frequency-matched on age, time at enrollment (within six months), gender, and residential township. Midlife risk factors included vascular risk factors (body mass index (BMI), total cholesterol, total triglycerides, blood sugar, cerebrovascular accident (CVA) history, diabetes mellitus history and hypertension history), cigarette smoking and alcohol consumption. Dementia assessments were ascertained through the computerized data linkage from National Health Insurance Database from 2000 to 2002 and clinically confirmed by neurologists or psychiatrists. Conditional logistic regression analysis was used to estimate the matched odds ratio (OR) and its 95 percent confidence intervals (95% CI) for each risk factor. Results: A J-shaped relationship was observed between BMI (kg/m2) and dementia. The multivariate-adjusted OR (95% CI) of developing dementia was 1.84 (1.02-3.33), 1.87 (1.08-3.23) and 2.44 (1.39-4.28), respectively, for a BMI of <20.5, 23.0-25.4, >25.5 compared with a BMI of 20.5-22.9 as the referent group (OR=1.0). Similar findings were observed for Alzheimer’s disease (AD) and vascular dementia (VaD). The association between obesity (BMI >25.5) and both AD and VaD was statistically significant among cigarette smokers but not among non-smokers. Additionally, history of CVA was a significant risk factor for VaD, but not for AD. Conclusions: Under- and overweight and cerebrovascular accident in midlife may increase the risk of dementia in late life. (This part has been accepted for publication in American Journal of Geriatric Psychiatry) PART 2: Genetic Risk Study Objective: To evaluate the associations of eighteen polymorphisms of thirteen candidate genes including leptin and its receptor genes with Alzheimer’s disease (AD) or vascular dementia (VaD) in Taiwan. Methods: A nested case-control study was conducted within a large population-based cohort, which had buffy coat samples. A total of 28 AD and 34 VaD patients and 298 comparison cases matched with cases on age, gender, entry date and residential area were included in this study. Polymorphisms of APOE ε2/ε3/ε4, A2M Ile1000Val, LRP C766T, VLDLR 5’UTR CGG-repeat, IDE 5’UTR G/T, TNF T-1031C, BACE C786G, ACE ins/del, MTHFR C677T, PON Arg192Gln, COMT Val158Met, LEP 5’UTR G/T, LEPR Arg109Lys, Arg223Gln Ser343Ser, Lys656Asn, intron 14 A/C and Pro1019Pro were examined by real time quantitative PCR, microsatellite or PCR-restriction fragment length polymorphism (RFLP) method. Unconditional logistic regression model was used to estimate multivariate-adjusted odds ratio (ORa) with its 95% confidence interval (CI) of developing AD or VaD for various genotypes after adjustment for age, gender, entry date, residential area and other confounding factors. Haplotype analysis was performed for the leptin receptor gene cluster. Moreover, gene-gene interaction and gene dosage effect were also evaluated. Results: An increased risk of AD was significantly associated with genotypes of APOE ε4 (ORa 3.21; 95% CI 1.09-9.53), PON Gln/Gln (ORa 6.66; 95% CI 1.98-22.4) and LEPR GCC haplotype of Lys656Asn, intron 14 and Pro1019Pro (ORa 6.45; 95% CI 2.07-20.1). The higher the number of putative high-risk genoypes of APOE, PON and LEPR was, the higher the risk of AD was. However, no significant associations were observed between VaD and these gene polymorphisms. Conclusions: This preliminary study confirmed the association between AD and APOE ε4 and found a significant association between AD and polymorphisms of LEPR and PON genes.