台灣布魯蓋達症候群全基因體關聯性研究

Abstract

背景：布魯蓋達症候群為一心臟遺傳罕見疾病，此疾病會造成心臟電流出現異常而導致猝死。布魯蓋達症候群全世界盛行率約0.01-0.05%，其中亞洲地區又高於其他地區國家。目前布魯蓋達症候群被認為是體染色體顯性遺傳疾病，其中SCN5A基因變異為主要的危險因子，但在臨床上僅有20%的病人帶有SCN5A基因突變，這表示了有超過75%的病人，其致病過程仍然未知。過去，有研究針對歐洲族群進行布魯蓋達症候群全基因體關聯性研究，其研究結果顯示，在歐洲族群中有兩個顯著的遺傳變異位點(rs10428132及rs9388451)。然而，由於族群和地域間的布魯蓋達症候群發病機率有所差異，因此，本研究預期針對台灣病患資料找出重要的遺傳多型性位點，並驗證過去所報導的布魯蓋達症候群相關遺傳變異，以提供在布魯蓋達症候群的遺傳機制及致病機轉更進一步的了解。 研究方法：本研究之病例組來自於全台灣各地醫療院所，共190個病人，正常對照組資料來源為台灣人體生物自料庫，共15981人。利用Axiom Genome_Wide TWB Array Plate (Affymetrix)微陣列晶片進行基因型鑑定。使用費雪精確檢定針對相加、顯性及隱性模式進行單一位點分析，接著利用表達數量性狀基因座分析評估遺傳變異在心臟組織間的基因表現，並進行基因組富集分析以探討遺傳變異的傳導途徑及生物功能性，另外，使用SIFT及PolyPhen-2兩種生物資訊演算法針對錯義突變位點進行蛋白質功能預測。多位點分析則使用序列核關聯檢定以評估多個位點同時對疾病的影響。最後，利用基因插補法獲得其中一個過去研究所發現之遺傳變異位點資訊，以供後續驗證。 結果：經質量控管後，共有190病例組及14274正常對照組進行後續分析，其中共有21個位點在三個遺傳模式下皆顯著(病例組及對照組次要等位基因頻率差異> 0.3以上)，rs9875641位點變異與心臟組織中LMCD1-AS1基因表現有顯著相關性，而rs34726907位點變異與RABL2B及AC002055.4基因表現有顯著相關性。四個錯義突變位點rs751074523、rs373144666、rs760608934及rs758378155在兩種演算法預測下，至少有一演算法預測該位點突變可能對蛋白質功能造成有害影響。在多位點分析結果中，共有10個基因對布魯蓋達症候群具有顯著影響。過去歐洲研究所發現的兩個布魯蓋達症候群遺傳變異在台灣族群中亦獲得驗證。 結論：本研究發現了許多在台灣族群中特有的布魯蓋達症候群相關遺傳變異，未來仍需要透過其它外部資料進行驗證。研究結果有助於了解布魯蓋達症候群致病機轉及生物傳導途徑，以協助未來尋找布魯蓋達症候群早期診斷的生物標記及藥物開發上提供參考依據。

Background: Brugada syndrome (BrS) is a rare disease that has a high risk causing sudden cardiac death due to the ventricular fibrillation. The prevalence of BrS is estimated to be 1-5 cases per 10,000 people, and its incidence and prevalence rates are higher in the Asian populations. Currently, BrS is considered as an autosomal dominant disorder, and SCN5A is the major genetic risk factor. However, only 20% of BrS patients can be attributed to SCN5A, which means that the pathogenic process of more than 75% BrS patients remains unclear. Two loci (rs10428132 and rs9388451) were reported in the previous GWAS in the European patients. Therefore, the aim of this study is to identify novel SNP loci associated with BrS in Taiwanese population. Materials and Methods: A total of 190 BrS cases were recruited from hospitals and medical centers in Taiwan, and 15,981 healthy controls were obtained from Taiwan Biobank. The genotyping experiments were performed by using the Axiom Genome_Wide TWB Array Plate (Affymetrix). A Fisher exact test based on the three genetic models (additive, dominant, recessive) were used to evaluate the effect of a SNP locus. We further evaluated the expression quantitative trait loci (eQTL) of selected SNPs in heart tissue. Gene set enrichment analysis was used to characterize enriched biological pathways and molecular functions. Two bioinformatics algorithms (SIFT, Polyphen2) were used to evaluate the functional impact of identified missense variants. Furthermore, the Sequence Kernel Association Test (SKAT) algorithm was used to evaluate the combination effects of multi-markers. Lastly, we performed an imputation study based on the allele frequencies obtained from the East Asian populations in the 1000 genome project in order to obtain the genetic information of one validated SNP locus. Results: There were 190 cases and 14,274 controls passing the quality control steps. A total of 21 SNPs were significant in three genetic models (MAF differences between case and control > 0.3). The SNP, rs9875641 was associated with expression of LMCD1-AS1. The SNP, rs34726907 was associated with expression of RABL2B and AC002055.4 in heart tissue. The 4 SNPs, including rs751074523、rs373144666、rs760608934 and rs758378155 were predicted as possibly damaging variants by at least one bioinformatics algorithm from SIFT and PolyPhen-2. The SKAT approach reported the 10 genes associated with BrS according to their combined effects of multi-markers. Two loci rs10428132(SCN10A) and rs9388451(HEY2) reported in a previous GWAS study in European patients were also significantly associated with BrS in Taiwanese population. Conclusions: We find some common genetic variants in the BrS patients specific to Taiwanese population. However, further replication in different datasets is warranted to validate our findings. The novel DNA loci can provide a better understanding of BrS etiology, and these findings may provide new insights of the diagnosis and treatment in BrS in the future.