Department of Clinical Neuroscience, UCL Institute of Neurology, University College London, London, UK.
Department of Academic Haematology, University College London, UK.
Brain. 2018 Aug 1;141(8):2419-2431. doi: 10.1093/brain/awy157.
The α-synuclein protein, encoded by SNCA, has a key role in the pathogenesis of Parkinson's disease and other synucleinopathies. Although usually sporadic, Parkinson's disease can result from inherited copy number variants in SNCA and other genes. We have hypothesized a role of somatic SNCA mutations, leading to mosaicism, in sporadic synucleinopathies. The evidence for mosaicism in healthy and diseased brain is increasing rapidly, with somatic copy number gains of APP reported in Alzheimer's brain. Here we demonstrate somatic SNCA copy number gains in synucleinopathies (Parkinson's disease and multiple system atrophy), focusing on substantia nigra. We selected sporadic cases with relatively young onset or short disease duration, and first excluded high level copy number variant mosaicism by DNA analysis using digital PCR for SNCA, and/or customized array comparative genomic hybridization. To detect low level SNCA copy number variant mosaicism, we used fluorescent in situ hybridization with oligonucleotide custom-designed probes for SNCA, validated on brain and fibroblasts with known copy number variants. We determined SNCA copy number in nigral dopaminergic neurons and other cells in frozen nigra sections from 40 cases with Parkinson's disease and five with multiple system atrophy, and 25 controls, in a blinded fashion. Parkinson's disease cases were significantly more likely than controls to have any SNCA gains in dopaminergic neurons (P = 0.0036), and overall (P = 0.0052). The average proportion of dopaminergic neurons with gains in each nigra was significantly higher in Parkinson's disease than controls (0.78% versus 0.45%; P = 0.017). There was a negative correlation between the proportion of dopaminergic neurons with gains and onset age in Parkinson's disease (P = 0.013), but not with disease duration, or age of death in cases or controls. Cases with tremor at onset were less likely to have gains (P = 0.035). All multiple system atrophy cases had gains, and the highest levels in dopaminergic neurons were in two of these cases (2.76%, 2.48%). We performed selective validation with different probes after dye swapping. All three control probes used showed minimal or no gains (≤0.1% in dopaminergic neurons). We also found occasional SNCA gains in frontal neurons of cases with Parkinson's disease, and the putamen of one multiple system atrophy case. We present evidence of somatic SNCA gains in brain, more commonly in nigral dopaminergic neurons of Parkinson's disease than controls, negatively correlated with onset age, and possibly commonest in some multiple system atrophy cases. Somatic SNCA gains may be a risk factor for sporadic synucleinopathies, or a result of the disease process.10.1093/brain/awy157_video1awy157media15813519976001.
α-突触核蛋白由 SNCA 编码，在帕金森病和其他突触核蛋白病的发病机制中起关键作用。尽管通常是散发性的，但帕金森病可能是由 SNCA 和其他基因的遗传拷贝数变异引起的。我们假设体细胞 SNCA 突变导致镶嵌性在散发性突触核蛋白病中起作用。健康和患病大脑中镶嵌性证据迅速增加，阿尔茨海默病大脑中报道了 APP 的体细胞拷贝数获得。在这里，我们在突触核蛋白病（帕金森病和多系统萎缩）中证明了体细胞 SNCA 拷贝数增加，重点是黑质。我们选择了发病年龄相对较年轻或疾病持续时间较短的散发性病例，并首先通过使用针对 SNCA 的数字 PCR 进行 DNA 分析排除高水平拷贝数变异镶嵌性，和/或定制的阵列比较基因组杂交。为了检测低水平 SNCA 拷贝数变异镶嵌性，我们使用针对 SNCA 的寡核苷酸定制探针进行了荧光原位杂交，该探针已在具有已知拷贝数变异的脑组织和成纤维细胞上进行了验证。我们以盲法方式在 40 例帕金森病和 5 例多系统萎缩患者以及 25 例对照的冷冻黑质切片中测定黑质多巴胺能神经元和其他细胞中的 SNCA 拷贝数。帕金森病病例比对照组更有可能在多巴胺能神经元中出现任何 SNCA 获得（P = 0.0036），并且总体上（P = 0.0052）。帕金森病患者每个黑质中获得多巴胺能神经元的平均比例明显高于对照组（0.78%比 0.45%；P = 0.017）。帕金森病患者中获得多巴胺能神经元的比例与发病年龄呈负相关（P = 0.013），但与疾病持续时间或病例和对照组的死亡年龄无关。发病时出现震颤的病例获得的可能性较小（P = 0.035）。所有多系统萎缩病例均有获得，其中两个病例的多巴胺能神经元水平最高（2.76%，2.48%）。在染料交换后，我们使用不同的探针进行了选择性验证。使用的所有三种对照探针均显示出最小或没有获得（多巴胺能神经元中≤0.1%）。我们还在帕金森病病例的额叶神经元和一个多系统萎缩病例的壳核中偶尔发现 SNCA 获得。我们提供了脑体细胞 SNCA 获得的证据，在帕金森病患者的黑质多巴胺能神经元中比对照组更常见，与发病年龄呈负相关，并且在某些多系统萎缩病例中可能最常见。体细胞 SNCA 获得可能是散发性突触核蛋白病的危险因素，或者是疾病过程的结果。
