以全基因體定序策略探討某一思覺失調症多發性家族的易感受性遺傳變異

Abstract

全基因組關聯分析(Genome-wide association study, GWAS)並無法針對罕見遺傳變異進行探討，近年來發展出來的次世代定序(Next-generation sequencing, NGS)是一種高通量的定序方法，能夠快速地進行全基因體定序，進而探索與思覺失調症(Schizophrenia)相關的罕見遺傳變異。我們假定思覺失調症的多發性家庭有助於找出與思覺失調症相關之罕見遺傳變異，且這些罕見遺傳變異亦能再現於其他多發性家庭。我們從台灣思覺失調症連鎖研究(Taiwan schizophrenia linkage study, TSLS)中挑選出一個多發性家庭作為研究樣本，並針對此多發性家庭中的五位成員(母親與兩位小孩診斷為思覺失調症；父親與另一位小孩並未患病)進行全基因體定序，並建立遺傳模式，試圖找出與思覺失調症相關之罕見易感受性(Susceptibiliy)遺傳變異。結果指出1,147個遺傳變異(6個外顯子單點變異,exonic SNV)符合隱性遺傳模式；39,330個遺傳變異(230個外顯子單點變異,exonic SNV)符合顯性遺傳模式。與千人基因組計畫的變異清單比對之後，有14個非同義外顯子單點變異(non-synonymous exonic SNVs)符合顯性遺傳模式且並未被報告過。其中，有3個非同義外顯子單點變異藉由核酸定序(Sagner sequencing)通過驗證。 本研究展現出次世代定序應用於尋找與多發性思覺失調症家庭相關之罕見遺傳變異的效用。此外，本研究所挑選出之3個非同義外顯子單點變異未來將於TSLS中之其他多發性偵測其再現性。這將有助於找尋與思覺失調症相關之罕見易感受性遺傳變異，進而釐清其病理機轉。

Genome-wide association study (GWAS) has limitations for exploring rare genetic variants. With the advent of next-generation sequencing (NGS), it becomes feasible to search the whole genome for rare genetic variants specific to schizophrenia patients. We hence postulated that high density nuclear families of schizophrenia may help identify certain inherited rare variants that can be used for replication in other multiplex families of schizophrenia. We selected one high density schizophrenia family from Taiwan Schizophrenia Linkage Study (TSLS). NGS was performed to sequence the whole genomes of a 5-member nuclear family, in which the mother and 2 children affected with schizophrenia, and the father and another child unaffected. Both dominant and recessive inheritance models were used to explore schizophrenia related genomic variations. The results showed that total 1,147 variants (6 exonic single nucleotide variants; SNVs) selected under recessive inheritance model. Whereas there were 39,330 variants (230 exonic SNVs) selected under the dominant inheritance model. In addition, 14 non-synonymous exonic SNVs that exhibited inheritance in the family but not seen in 1000 genomes project were identified for those in accordance with dominant inheritance model. Among 14 candidate SNVs, 3 non-synonymous exonic SNVs passed the validation by Sanger sequencing. Our findings demonstrated the utility of NGS in identifying inherited rare genetic variants that are potentially associated with multiplex schizophrenia. In particular, the 3 non-synonymous exonic SNVs warrant future replication in other multiplex families from TSLS. This may lead to discovery if rare but inheritable susceptibility variants for schizophrenia and their underlying pathophysiology.