以皮膚之小神經病變探討遺傳性腦部小血管病變—CADASIL之認知障礙

Abstract

血管性認知障礙是造成年長者認知退化的第二大病因，僅次於阿茲海默氏症。在針對血管性認知障礙致病機轉的研究中，單基因遺傳的腦部小血管疾病是探討血管性認知障礙的病因機轉重要的疾病模式。體顯性腦動脈血管病變合併皮質下腦梗塞及腦白質病變（CADASIL）是單基因遺傳的腦部小血管疾病中盛行率最高的疾病，其血管的病變肇因於致病性的NOTCH3基因變異。過去針對CADASIL的研究多半著重在其所造成的腦血管病變與相關臨床表徵；然而，CADASIL特有的血管病理變化在全身的血管組織都可以發現，亦可以藉由皮膚切片觀察到。針對CADASIL是否除了中樞神經之外，也會造成周邊神經的病變，過去的文獻探討十分有限，亦沒有一致的結論。本研究探討CADASIL的病患，其周邊小神經的病理變化，進而推演此周邊小神經的病變與病患認知障礙的關聯性。 本研究共招募37位CADASIL病患（包含14位認知功能正常、與23位患有血管性認知障礙的病患）與59位年齡與之相配對的健康受試者，進行皮膚小神經病變的病理檢測。針對小神經病變，我們利用免疫螢光染色定量表皮內神經纖維密度 (intra-epidermal nerve fiber density)、汗腺與真皮層小動脈的神經密度、以及真皮層小動脈上的NOTCH3蛋白沈積量。針對CADASIL的病患，我們進行認知功能測試、腦部影像學檢查、以及神經退化相關的血漿生物標記檢測，並利用多變數迴歸分析，探討上述中樞神經病變相關的臨床表徵與小神經病變嚴重度之間的關聯性。 CADASIL病患的小神經密度，不論在表皮內神經纖維密度（5.22 ± 2.42 vs. 7.88 ± 2.89 fibers/mm, P=0.0001）、汗腺與的神經密度（P<0.0001）、或是小動脈的神經密度（P<0.0001）都顯著低於健康受試者。在校正了年齡之後，CADASIL病患的表皮內神經纖維密度的下降與認知障礙（以簡易心智量表，Mini-Mental State Examination分數為依據）有顯著的相關性（B=1.062, 95% CI=0.370 ~1.753, P=0.004），且此相關性在校正了糖尿病共病之後依然維持顯著（p=0.043）。此外，表皮內神經纖維密度與病患大腦的平均皮質厚度有關（Pearson’s r = 0.565, P=0.0023），然而與白質病變體積、腔隙性腦梗塞（lacune）數量、大腦微出血（cerebral microbleed）數量等腦部小血管病變的特徵性影像標記無顯著之關聯。在32位致病性變異位點位於NOTCH3第11號外顯子的CADASIL病患（其中大部分帶有台灣較常見的NOTCH3 p.R544C變異）當中，表皮內神經纖維密度的下降亦與小動脈上的NOTCH3蛋白沈積量有顯著相關（B= -0.092, 95% CI= -0.175 ~ -0.009, p= 0.031）。相較於認知功能正常的CADASIL病患，患有血管性認知障礙的病患其血漿中的神經纖維絲輕鏈（neurofilament light chain）顯著較高；而同時具有血管性認知障礙與周邊小神經病變的病患，則其血漿中的膠質纖維酸性蛋白（glial fibrillary acidic protein）顯著較高。 在CADASIL病患中，皮膚的小神經病理變化與認知障礙以及神經退化相關的生物標記相關。本研究顯示致病性變異的NOTCH3蛋白，其於周邊神經系統亦有造成神經退化的證據。

Vascular cognitive impairment is the second leading cause of dementia in the elder population, just after Alzheimer’s disease. Monogenetic small vessel disease may provide a unique model to study the pathogenesis and possible treatment strategy for vascular cognitive impairment. Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), the most common monogenetic small vessel disease caused by pathogenic NOTCH3 mutations, is traditionally considered a disease of the cerebrovascular system although the pathologic hallmark is also demonstrated in skin biopsy. Although circumstantial evidence suggests the coexistence of peripheral neurodegeneration, the effect of NOTCH3 mutations on peripheral nerves and its clinical relevance have been sparely investigated. The present study aimed to investigate the patterns of small fiber pathology and its clinical significance in the context of cognitive impairment for CADASIL patients. Thirty-seven genetically confirmed CADASIL patients (14 with normal cognition and 23 with cognitive impairment) and 59 age-matched healthy controls were enrolled to evaluate cutaneous small fiber pathology. Small fiber pathology was assessed by quantitative measures of intraepidermal nerve fiber (IENF) density, sweat gland innervation, and vascular innervation. Cognitive performance of CADASIL patients was evaluated by a comprehensive neuropsychological assessment, and its association with small fiber pathology was tested using multivariable linear regression analysis adjusted for age and diabetes mellitus. We further assessed the relationships of IENF density with cutaneous vascular NOTCH3 ectodomain (NOTCH3ECD) deposition and biomarkers of neurodegeneration including structural brain MRI measures, plasma neurofilament light chain (NfL), glial fibrillary acidic protein (GFAP), tau, and ubiquitin carboxy-terminal hydrolase L1 (UCHL1). CADASIL patients showed reduced IENF density (5.22 ± 2.42 vs. 7.88 ± 2.89 fibers/mm, P=0.0001), as well as reduced sweat gland (P<0.0001) and vascular (P<0.0001) innervations compared to age-matched controls. Reduced IENF density was associated with impaired global cognition measured by Mini-Mental State Examination (B=1.062, 95% CI=0.370 ~1.753, P=0.004), and this association remained after adjustment for age and diabetes mellitus (p=0.043). In addition, IENF density in CADASIL patients was associated with mean cortical thickness (Pearson’s r = 0.565, P=0.0023) but not white matter hyperintensity volume, total lacune count, or total microbleed count. Reduced IENF density was associated with cutaneous vascular NOTCH3ECD deposition amount among patients harboring pathogenic variants in exon 11 (mainly p.R544C) (B= -0.092, 95% CI= -0.175 ~ -0.009, p= 0.031). Compared to those with normal cognition, CADASIL patients with cognitive impairment had an elevated plasma NfL level regardless of concurrent small fiber denervation, while only patients with both cognitive impairment and small fiber denervation showed an elevated plasma GFAP level. Cutaneous small fiber pathology correlates cognitive impairment and CNS neurodegeneration in CADASIL patients, indicating a peripheral neurodegenerative process related to NOTCH3ECD aggregation.