肌萎縮性脊髓側索硬化症之分子基因研究

Abstract

肌萎縮性脊髓側索硬化症(Amyotrophic lateral sclerosis, ALS) 是最常見一種的運動神經元疾病，疾病特徵是漸進性的上、下運動神經元退化。臨床上，疾病病程進展快速，患者常在發病後的2-5年間發展為呼吸衰竭。家族遺傳型ALS約僅佔ALS中的10%，並且發生年齡較輕 (<55歲)。致病基因以及基因突變率，依序為SOD1基因(20%)，TARDBP基因(2~5%)，FUS基因(4%)，ANG基因則更為罕見。 在本研究中，我們將針對台灣ALS患者(年輕發病及家族型ALS)，進行基因突變率篩檢。總共納入46位患者，其中4位有家族病史，平均發病年齡介於43歲~48歲間。 4個ALS的致病基因被選為進行突變檢測。為鑑別出heteroduplex，將高分辨率熔解曲線分析 (high resolution melting curve, HRM) 應用於本研究中。HRM實驗中的heteroduplex序列變異，被選出進行定序。由於SOD1基因及ANG基因的轉譯範圍較小，則直接進行定序實驗。實驗結果顯示，有2個SOD1 (p.G85R與p.T136R)，1個TARDBP (p.M337V)的missense mutation，以及TARDBP 5’UTR -61C>G和2個FUS (p.G49G與p.T97T)的silence mutation。未發現有ANG基因的突變。帶有基因突變的患者，大約在35歲以及43歲開始出現症狀，症狀進展快速併有早期的呼吸衰竭。在台灣的SOD1突變率，家族型ALS約佔25%，散發型ALS案例約為3%，數據與先前在高加索人所發現數據相似。TARDBP突變率在家族型ALS為25%，與台灣研究團隊的研究資料數據較為相近。 總結本次研究，突變率在散發型ALS並不高，而SOD1仍為家族型ALS最常見的致病基因。 在近期發現的ALS致病基因，如TARDBP、FUS以及ANG的突變並不常見。帶有基因缺損的病患為年輕型發病，快速的漸進性運動神經元退化，及預後不佳。對於此種高損害性的疾病，未來需要再更進一步的釐清其病因機轉。

Amyotrophic lateral sclerosis (ALS), characterizing by progressive upper and lower motor neuron degeneration, is one of the most common forms of motor neuron disease. Clinically, it progressed rapidly and patients usually developed respiratory failure 2 to 5 years post the onset. Familial ALS is only 10% of ALS and it usually occurs at young age (<55 years old). The responsible genes and its associated mutation frequency are as follows, SOD1 (20%), TARDBP (2~5%), FUS (4%) and rare in ANG. In this study, we would screen the mutation frequency in a Taiwanese cohort with ALS (both young-onset and familial ALS). In total, we recruited 46 patients; 4 patients have a positive family history and the average age of onset for these patients are between 43 and 48 years old. The four responsible genes were selected for mutation detection. To identify a heteroduplex, the high resolution melting curve (HRM) analysis has been employed. A sequence variant resulting in a heteroduplex on the HRM, were subjected to sequencing. Because of the small size of transcript, direct sequencing has been used to identify the mutations in SOD1 and ANG genes. The result reveals 2 SOD1 (p.G85R and p.T136R), one TARDBP (p.M337V) missense mutations, one TARDBP 5’UTR -61 C>G mutations, and two FUS (p.G49G and p.T97T) silence mutations. No mutation was observed in ANG genes. Patients with a mutation develop the symptoms at 35 and 43 years of age. The symptoms progressed rapidly with early respiratory failure. The mutation frequency in the Taiwanese cohort is 25% for the SOD1 in familial ALS, 3% for the SOD1 in sporadic ALS. The data is similar to that found in Caucasian people in previous references. The mutation frequency of TARDBP in familial ALS (25%) is similar to previous references at Taiwan. In conclusion, the mutation rate in the sporadic ALS is not high and the SOD1 mutation remains the most common cause for familial ALS. Mutations in the newly identified responsible genes such as TARDBP, FUS and ANG are not common. Patients with a genetic defect developed a young-onset, rapid progressive motor neuron degeneration and a poor outcome. Further investigation is needed to clarify the pathogenic mechanism for this devastating disease.