早發育年齡與心血管疾病風險之因果中介及全基因體多效性分析

Abstract

背景：近年來，孩童早發育問題日漸突出，已成為小兒科常見的內分泌疾病之一。成長發育時間不只與內分泌系統有關，也可能與心血管代謝疾病風險相關。過去研究證實早發育年齡會增加成人心血管疾病的風險，但還沒有一致的結論，至今還有許多機轉尚未完全了解，像是孩童高血壓、成年時期的代謝中介因子、共同基因位點及蛋白質交互作用的關聯性。因此，本研究旨在（1）確認性早熟與孩童高血壓的關聯性；（2）探討早發育年齡與成年心血管疾病之間可能的代謝中介途徑；（3）探索發育年齡與心血管代謝特徵的共同基因及其分子機轉路徑。 材料與方法：本研究納入臺灣發育長期追蹤研究765位的6－14歲女性，以羅吉斯迴歸分析（Logistic regression）確認性早熟與孩童高血壓（依據年齡與身高定義收縮壓或舒張壓大於95百分位數）的關聯性。透過金山社區心血管疾病世代研究1,589位女性，探討早發育年齡與成年心血管疾病的中介代謝途徑，其中包括身體質量指數、血壓、血脂及血糖。另外，透過臺灣人體生物資料庫71,923位女性的資料，應用觀察性研究及孟德爾隨機定律驗證因果中介效果。由於初經年齡與心血管代謝特徵具有一定的遺傳性，為了避免遺漏遺傳力（missing heritability），我們使用臺灣人體生物資料庫的全基因組關聯分析，篩選出兩個特徵共同常見變異的位點，串聯甲基化數量性狀基因座及表現數量性狀基因座，找出重要的機轉路徑。 結果：孩童研究中，性早熟會增加孩童高血壓的風險（勝算比：2.08，95% 信賴區間：1.14－3.78）。金山社區心血管疾病世代研究中，早初經年齡每提前1個標準差（1.8歲），其成人時期冠狀動脈疾病的風險比為1.75（95%信賴區間：1.12－2.19）。臺灣人體生物資料觀察性研究中，初經年齡每提前1個標準差（1.4歲），其成人時期冠狀動脈疾病的勝算比為1.18（95%信賴區間：1.02－1.21），經過孟德爾隨機化的勝算比為1.02（95% 信賴區間：1.001－1.03）。收縮壓可能是重要的中介因子，其孟德爾隨機化的中介效果比例為29%（95% 信賴區間：26%－32%）。此外，我們透過基因多效性分析，從聯集與交集錯誤發現率（false discovery rate，FDR）的方式，找到27個位點同時與初經年齡和心血管代謝特徵有關，其兩種方法的FDR皆小於0.05。這些位點主要坐落於5個基因序列之內或附近，例如：SEC16B、CSK、CYP1A1、FTO及USB1，這些基因除了影響基因甲基化及表現程度，且彼此之間可能有蛋白質的交互作用。 結論與建議：本研究發現性早熟可能與孩童高血壓有關，而成人研究發現收縮壓是早發育年齡與冠狀動脈疾病的重要中介因子。另外，我們也發現發育年齡與心血管代謝特徵存在著一些共同的基因位點，特別是初經年齡與舒張壓之間有明顯的共同基因網路。建議未來研究除了需要釐清早發育年齡與冠狀動脈疾病是否還有其他分子途徑，也需要透過細胞或動物實驗加以確認這些共同基因位點，以利於性早熟與早期心血管代謝疾病的篩檢與預防。

Background: The prevalence of early puberty has increased in recent decades and has been reported to be associated with endocrine disorders and cardiometabolic diseases. Early puberty leads to the increased risk of cardiovascular diseases in adulthood, but mechanisms in childhood remained unclear. In addition, the risk is suggested to be mediated through intermediate variables and may be caused by early puberty indirectly. Genome-wide association studies have the potential to explain more of the missing heritability of the two complex traits. Objective: We aim (1) to investigate the association between early puberty and early hypertension; (2) to explore the causal mediation pathways between early menarche and adult cardiovascular diseases using the network Mendelian randomization study; (3) to investigate the shared genetic basis for age at menarche and cardiometabolic traits. Methods: From the Taiwan Puberty Longitudinal Study (N=765) in the project 1, we investigated the association between early puberty and childhood cardiovascular risk factors. From Chin-Shan community cardiovascular cohort (N=1,589) in the project 2, we first investigated the risk of incident cardiovascular diseases among those with early menarche. We also investigated whether this association is mediated by body mass index, blood pressure, blood lipid, and fasting plasma glucose. The mediation pathways were validated using a network Mendelian randomization study using the Taiwan biobank dataset (N=71,923). In the project 3, we used a genetic pleiotropy-informed false discovery rate method to identify new loci associated with age at menarche and cardiometabolic traits, two highly heritable disorders with significant missing heritability. We further investigated the biological association between the top loci through changes in methylation and expression levels. Results: Children with early puberty significantly suffered from early hypertension (odds ratio: 2.08; 95% confidence interval: 1.14 to 3.78). Earlier age at menarche was associated with a higher risk of coronary artery disease (hazard ratio: 1.57; 95% CI: 1.12 to 2.19) Chin-Shan community cardiovascular cohort study, a 11% higher risk (odds ratio: 1.11; 95% CI: 1.02 to 1.21) in the Taiwan Biobank study, and a 2% higher risk (odds ratio: 1.02; 95% CI: 1.001 to 1.03) in the Mendelian randomization study. All analysis methods consistently supported the role of systolic blood pressure in mediating this effect. The results indicated that 29% (95% CI: 26% to 32%) of the effect of genetically predicted earlier age at menarche on the risk of coronary artery disease was mediated by genetically predicted systolic blood pressure. In addition, we found 27 novel loci at a false discovery rate of less than 0.05 with overlap between menarcheal timing and cardiometabolic traits, including body fat, blood pressure, cerebrovascular accident, and coronary artery disease. Among the novel genes discovered, SEC16B, CSK, CYP1A1, FTO, and USB1 are within a protein interaction network with known cardiometabolic genes, including traits for obesity and hypertension. The identified novel loci were further proved by significant changes in methylation or expression levels of neighboring genes. Conclusions: We suggested that early puberty was associated with the increased risk of earlt onset hypertension among girls. Adult research studies highlighted systolic blood pressure as the critical mediator in the association of early menarche with the riks of coronary artery diseases. We also highlighted the shared etiology between age at menarche and diastolic blood pressure. Further studies focusing on the molecular pathways of these blood pressure-shared genes are warranted.