利用全外顯子定序探討台灣多重孟德爾遺傳疾病的發生率

Abstract

背景： 在現今醫學遺傳學領域，在臨床上我們依賴全外顯子定序(whole exome sequencing, WES）作為懷疑有遺傳疾病患者基因變異的檢測方式。WES是將NGS次世代技術（Next Generation Sequencing）應用於確定已知基因的所有編碼區域或外顯子的變異。WES的檢測涵蓋了超過95%的外顯子（exome），其中包含了孟德爾遺傳疾病中85%的致病突變。依照過去的研究指出，目前透過WES已能識別出超過150種基因的功能，且仍持續增加中，因此WES成為了極具檢測效益的分子診斷工具之一。 目的： 本研究旨在評估全外顯子定序檢測技術在臨床應用上對多重孟德爾遺傳疾病（Multiple Mendelian disorders）患者的診斷率、具多重孟德爾遺傳疾病個案的疾病類型分布。 方法： 搜集台大醫院基因醫學部於2020年2月至2021年7月進行過WES且已有檢測結果報告的個案，從608位個案中將檢測結果報告中已具一項診斷的個案篩選出。將327位個案執行WES的檢測結果使用MViewer程式進行重新回顧，記錄ClinVar報告為pathogenic、likely pathogenic的基因變異（variant）。將基因變異位點利用ClinVar、ACMG以及HGMD等資料庫做致病性的參考，找出符合孟德爾單基因遺傳的疾病診斷。最終計算所有經過分析的患者其中具有兩種以及三種遺傳疾病個案的比例，同時分析疾病的類型。 結果： 327位個案中具一項WES陽性診斷結果的個案為141位，重新分析的141位個案中，122位僅具有一項孟德爾遺傳疾病（37.31%）有17位（5.2%）具有兩項孟德爾遺傳疾病，有2位（0.61%）具有三項孟德爾遺傳疾病。具有第二及第三個孟德爾遺傳疾病的19位個案中的基因變異共計與15個基因相關，15個基因中導致臨床症狀，其中以神經學和血液方面最多，其次是風濕免疫以及眼科相關。 結論： 透過重新分析進行過WES的基因檢測結果，能檢驗出約6%的個案具有潛在的第二以及第三種遺傳疾病，近一步發現這些多重遺傳疾病的臨床表徵以神經和血液相關為最多，顯示WES能發現多重遺傳疾病在兒科個案中具有一定的發生率。

Background : In the field of medical genetics today, clinical diagnosis of individuals suspected of having genetic disorders relies on Whole Exome Sequencing (WES) as a means of detecting genetic variations. WES applies Next Generation Sequencing (NGS) technology to determine variations in all coding regions or exons of known genes. The testing covers more than 95% of the exome, which includes 85% of the pathogenic mutations found in Mendelian genetic diseases. According to previous studies, WES has identified the functions of over 150 genes and this number continues to increase, making WES one of the highly beneficial molecular diagnostic tools. Aim : This study aims to evaluate the diagnostic rate of whole exome sequencing (WES) technology in clinical applications for patients with multiple Mendelian disorders, the types of diseases in cases with multiple Mendelian conditions, and the rate for diagnosis. Methods : We collected cases from the Department of Medical Genetics at National Taiwan University Hospital who underwent Whole Exome Sequencing (WES) and had test result reports from February, 2020, to July, 2021. From a total of 608 cases, those with category 1 findings in the test result reports were selected. Among the 327 cases that underwent WES, the test results were reviewed using the MViewer program. We applied conditional filtering to identify genetic variants recognized by ClinVar as pathogenic or likely pathogenic, which simultaneously required confirmation of the variant site. Genetic variant sites were referenced for pathogenicity using databases such as ClinVar, ACMG and HGMD to identify diagnoses of Mendelian single-gene inherited diseases. Finally, we calculated the proportion of patients who were reviewed and diagnosed with two or three genetic diseases among all reviewed patients, while also analyzing the types of diseases. Results : Out of the 327 cases, 141 had category 1 diagnostic results. Among the reanalyzed 141 cases, 122 cases (37.31%) had only one Mendelian genetic disease, 17 cases (5.2%) had two Mendelian genetic diseases, and 2 cases (0.61%) had three Mendelian genetic diseases. The genetic variants in the 19 cases with a second or third Mendelian genetic disease were related to a total of 15 genes, Among these 15 genes, the variants potentially led to different clinical symptoms, with the most common being neurological disorders (five types), followed by skin-related and blood-related conditions. Conclusion : By reanalyzing the genetic testing results of cases that underwent WES and referencing updates from genetic databases, we were able to identify approximately 6% of cases with potential genetic diseases. Further research indicates that the primary onset age of multiple genetic diseases ranges from birth to childhood. This demonstrates that WES can identify multiple genetic diseases with a certain incidence in pediatric cases.