體染色體顯性小腦脊髓幹運動失調症候群(autosomal dominant cerebellar ataxias; ADCAs) 是一群遺傳性的神經退化性疾病，其臨床症狀相當的複雜不易區分，而這群疾病有一處共同點，就是其致病基因的轉譯區內皆可發現一段 CAG 重複序列之擴增突變，經由這段擴增重複序列會轉譯出一段較長的多麩胺醯胺序列之蛋白質，而 SCA2就是這群疾病其中之一。SCA2 基因早已先被確認是位在染色體12q24.1 上，本實驗為了觀察 SCA2 基因突變在台灣族群中出現之頻率，所以最近我們從58個帶有遺傳性運動失調症的家族裡確認出 5 個 SCA2 家族，包含 8 個已發病 SCA2 病人與一個未發病個體，而且我們的統計結果得知，在正常的對偶基因其 CAG重複序列的次數為 16-30 ， 但若是在異常的對偶基因則其 CAG 重複序列的次數為 34-49 ，兩者之間並沒有重疊的現象發生。
另外一點是我們特別針對SCA1、SCA2、SCA3/MJD、SCA7 發展了一套非放射性的偵測法，事實上這套快速且精準的檢測方法將對於臨床分析 CAG 重複序列相當有助益 ，而且我們也證實別於傳統的做法，利用非放射性分析法只要數小時內就能得知正確結果。
The autosomal dominant cerebellar ataxias (ADCAs) are a group of genetically diverse neurological conditions linked by progressive deterioration in balance and coordinations. Spinocerebellar ataxia type2 (SCA2) is one of the ADCAs and also belongs to a special group caused by the expansion of an unstable CAG repeat recoding a polyglutamine tract. The gene for SCA2 was mapped to 12q24.1. To investigate the frequency of SCA2 mutation in Taiwan’s population, we have identified eight SCA2 affected patient and one at-risk individual in five unrelated SCA2 families among fifty-eight families with inherent cerebellar ataxias. We also demonstrated here the CAG repeats of normal alleles in Chinese range in size from 16 to 30 repeat units, while those of SCA2 chromosomes are expanded to 34 to 49 repeat units. No overlap in ataxin-2 allele size between normal and expanded chromosomes was observed. 3
We also developed a rapid detection of the expanded SCA1, SCA2, SCA 3/MJD, SCA7 chromosomes by a simple non-radioactive PCR test, allowing direct visualization through ethidium bromide stained agarose gels within hours. This quick and accurate method for the analysis of CAG repeats will be useful in the routine clinical diagnosis. Here we demonstrate a non-radioactive method to detect the CAG repeat region of SCA1, SCA2, SCA 3/MJD, SCA7, allowing direct visualization through ethidium bromide stained agarose gels within hours.
