結節性硬化症:TSC2基因變異與相關表現型研究

Abstract

結節性硬化症(tuberous sclerosis complex, TSC)是一種可影響多數身體器官 的顯性遺傳疾病，包括腦、皮膚、腎臟、 心臟及其它內臟器官或組織均可能發生症 狀(缺陷瘤為主)，常表現出皮膚病變、抽搐 及智障。第二型結節硬化症基因(TSC2)是 一個較大的基因，包含了41 個exons，約 有43kb 的DNA。本研究的目的乃在評估病 人臨床症狀的差異與所帶基因變異的關聯 性。利用Southern blotting，SSCP 及DNA 定序等方法去篩檢較大基因片段異常，較 小的突變並與臨床表現做比較分析。本研 究在大規模TSC2 之exons 篩檢後結果顯示 基因變異有： nonsense (C1531T:1 ； C2269T:1 ； C4393T:3) ， missense (G1850A:1；C4947G:1；C5042T:1)，in-frame deletion (5266 del 18bp:4)，以及多基因缺損 (TSC2-RTS:1)。最後一種情況並由螢光性 原位雜交法(FISH)證實為大片段的基因缺 損。經由基因型及臨床表現型的比較分 析，發現nonsense 者之臨床預後較差即有 較厲害的智障及癲癇症發生，推定乃基因 提早停止功能， 使其最終蛋白質產物 tuberin 嚴重不足所致。另外在18 名TSC 病人當中(包括父或母親3 名)，有15 名呈 現TSC2 基因反應，顯示第二型TSC 較第 一型發生率為高，可能與第一型症狀較緩 和(因此不易早期診斷)有關。另外TSC2 基 因有較多的大片段基因缺損TSC 病人也會 有腎囊腫或罕見的Rubinstein-Taybi 二氏 症，亦顯示在染色體區域16p13.3 處的確存 在一個相鄰基因症候群(contiguous gene syndrome)。

Tuberous sclerosis complex (TSC) is an inherited tumor suppressor syndrome, characterized by a broad phenotypic spectrum that can include seizures, mental retardation, renal dysfunction, and dermatological abnormalities. It is an autosomal dominant neurocutaneous disorder associated with the growth of hamartomas (tumor-like malformations) in many tissues and organs, including brain, skin, heart, and kidney. The TSC2 gene consists of 41 exons, spanning 43kb of genomic DNA. To evaluate the differences in the clinical phenotype of the patients and the underlying mutations, we performed Southern blotting analysis, SSCP analysis and DNA sequencing to screen for large abnormalities, smaller mutations in the TSC2 gene, along with the clinical manifestations. After intensive screening of the exons of TSC2 gene, the results revealed several different mutations: nonsense (C1531T:1; C2269T:1; C4393T:3), missense (G1850A:1; C4947G:1; C5042T:1), in-frame deletion (5266 del 18bp:4), and multigene deletion (TSC2/RTS:1) which is proved by fluorescence in situ hybridization using the probe RT203 and E4F1. The comparison of clinical manifestation and mutational changes showed the patients haboring the nonsense mutation have poor prognsosis, when they are more prone to the occurrence of epilepsy or mental retardation. The result also showed TSC2 (15/18) has higher prevalence than TSC1, possibly due to the milder phenotype in TSC1 patients. Besides, a contiguous gene syndrome does exist in the chromosomal region 16p13.3, because of the more frequent larger abnormalities associated with complicated phenotype (eg, RTS-TSC2- PKD).