CADASIL: yesterday, today, tomorrow

Distinct neurological phenotypes associated with biallelic loss of NOTCH3 function: evidence for recessive inheritance

BACKGROUND

NOTCH3 variants are known to be linked to cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). However, some null NOTCH3 variants with homozygous inheritance cause neurological symptoms distinct from CADASIL. The aim of this study was to expand the clinical spectrum of this distinct condition and provide further evidence of its autosomal recessive inheritance.

METHODS AND RESULTS

Whole exome sequencing (WES) was performed on a proband who exhibited livedo racemosa, ataxia, cognitive decline, seizures, and MRI white matter abnormalities without anterior temporal pole lesions. Segregation analysis was conducted with Sanger sequencing. WES of the proband identified a novel homozygous NOTCH3 null variant (c.2984delC). The consanguineous parents were confirmed as heterozygous variant carriers. In addition, three heterozygous NOTCH3 null variants were reported as incidental findings in three unrelated cases analyzed in our center.

CONCLUSION

The findings of this study suggest an autosomal recessive inheritance pattern in this early-onset leukoencephalopathy, in contrast to CADASIL's dominant gain-of-function mechanism; which is a clear example of genotype-phenotype correlation. Comprehensive genetic analysis provides valuable insights into disease mechanisms and facilitates diagnosis and family planning for NOTCH3-associated neurological disorders.

Pathophysiology of cerebral small vessel disease: a journey through recent discoveries

Cerebral small vessel disease (cSVD) encompasses a heterogeneous group of age-related small vessel pathologies that affect multiple regions. Disease manifestations range from lesions incidentally detected on neuroimaging (white matter hyperintensities, small deep infarcts, microbleeds, or enlarged perivascular spaces) to severe disability and cognitive impairment. cSVD accounts for approximately 25% of ischemic strokes and the vast majority of spontaneous intracerebral hemorrhage and is also the most important vascular contributor to dementia. Despite its high prevalence and potentially long therapeutic window, there are still no mechanism-based treatments. Here, we provide an overview of the recent advances in this field. We summarize recent data highlighting the remarkable continuum between monogenic and multifactorial cSVDs involving NOTCH3, HTRA1, and COL4A1/A2 genes. Taking a vessel-centric view, we discuss possible cause-and-effect relationships between risk factors, structural and functional vessel changes, and disease manifestations, underscoring some major knowledge gaps. Although endothelial dysfunction is rightly considered a central feature of cSVD, the contributions of smooth muscle cells, pericytes, and other perivascular cells warrant continued investigation.

Progress to Clarify How NOTCH3 Mutations Lead to CADASIL, a Hereditary Cerebral Small Vessel Disease

Notch signaling is conserved in C. elegans, Drosophila, and mammals. Among the four NOTCH genes in humans, NOTCH1, NOTCH2, and NOTCH3 are known to cause monogenic hereditary disorders. Most NOTCH-related disorders are congenital and caused by a gain or loss of Notch signaling activity. In contrast, cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) caused by NOTCH3 is adult-onset and considered to be caused by accumulation of the mutant NOTCH3 extracellular domain (N3ECD) and, possibly, by an impairment in Notch signaling. Pathophysiological processes following mutant N3ECD accumulation have been intensively investigated; however, the process leading to N3ECD accumulation and its association with canonical NOTCH3 signaling remain unknown. We reviewed the progress in clarifying the pathophysiological process involving mutant NOTCH3.

CADASIL: A NOTCH3-associated cerebral small vessel disease

BACKGROUND

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is the most common hereditary cerebral small vessel disease (CSVD), pathologically characterized by a non-atherosclerotic and non-amyloid diffuse angiopathy primarily involving small to medium-sized penetrating arteries and leptomeningeal arteries. In 1996, mutation in the notch receptor 3 gene (NOTCH3) was identified as the cause of CADASIL. However, since that time other genetic CSVDs have been described, including the HtrA serine peptidase 1 gene-associated CSVD and the cathepsin A gene-associated CSVD, that clinically mimic the original phenotype. Though NOTCH3-associated CSVD is now a well-recognized hereditary disorder and the number of studies investigating this disease is increasing, the role of NOTCH3 in the pathogenesis of CADASIL remains elusive.

AIM OF REVIEW

This review aims to provide insights into the pathogenesis and the diagnosis of hereditary CSVDs, as well as personalized therapy, predictive approach, and targeted prevention. In this review, we summarize the current progress in CADASIL, including the clinical, neuroimaging, pathological, genetic, diagnostic, and therapeutic aspects, as well as differential diagnosis, in which the role of NOTCH3 mutations is highlighted.

KEY SCIENTIFIC CONCEPTS OF REVIEW

In this review, CADASIL is revisited as a NOTCH3-associated CSVD along with other hereditary CSVDs.

Epidermal Growth Factor Receptors in Vascular Endothelial Cells Contribute to Functional Hyperemia in the Brain

Functional hyperemia-activity-dependent increases in local blood perfusion-underlies the on-demand delivery of blood to regions of enhanced neuronal activity, a process that is crucial for brain health. Importantly, functional hyperemia deficits have been linked to multiple dementia risk factors, including aging, chronic hypertension, and cerebral small vessel disease (cSVD). We previously reported crippled functional hyperemia in a mouse model of genetic cSVD that was likely caused by depletion of phosphatidylinositol 4,5-bisphosphate (PIP2) in capillary endothelial cells (EC) downstream of impaired epidermal growth factor receptor (EGFR) signaling. Here, using EC-specific EGFR-knockout (KO) mice, we directly examined the role of endothelial EGFR signaling in functional hyperemia, assessed by measuring increases in cerebral blood flow in response to contralateral whisker stimulation using laser Doppler flowmetry. Molecular characterizations showed that EGFR expression was dramatically decreased in freshly isolated capillaries from EC-EGFR-KO mice, as expected. Notably, whisker stimulation-induced functional hyperemia was significantly impaired in these mice, an effect that was rescued by administration of PIP2, but not by the EGFR ligand, HB-EGF. These data suggest that the deletion of the EGFR specifically in ECs attenuates functional hyperemia, likely via depleting PIP2 and subsequently incapacitating Kir2.1 channel functionality in capillary ECs. Thus, our study underscores the role of endothelial EGFR signaling in functional hyperemia of the brain.

Deep learning based on susceptibility-weighted MR sequence for detecting cerebral microbleeds and classifying cerebral small vessel disease

BACKGROUND

Cerebral microbleeds (CMBs) serve as neuroimaging biomarkers to assess risk of intracerebral hemorrhage and diagnose cerebral small vessel disease (CSVD). Therefore, detecting CMBs can evaluate the risk of intracerebral hemorrhage and use its presence to support CSVD classification, both are conducive to optimizing CSVD management. This study aimed to develop and test a deep learning (DL) model based on susceptibility-weighted MR sequence (SWS) to detect CMBs and classify CSVD to assist neurologists in optimizing CSVD management. Patients with arteriolosclerosis (aSVD), cerebral amyloid angiopathy (CAA), and cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) treated at three centers were enrolled between January 2017 and May 2022 in this retrospective study. The SWSs of patients from two centers were used as the development set, and the SWSs of patients from the remaining center were used as the external test set. The DL model contains a Mask R-CNN for detecting CMBs and a multi-instance learning (MIL) network for classifying CSVD. The metrics for model performance included intersection over union (IoU), Dice score, recall, confusion matrices, receiver operating characteristic curve (ROC) analysis, accuracy, precision, and F1-score.

RESULTS

A total of 364 SWS were recruited, including 336 in the development set and 28 in the external test set. IoU for the model was 0.523 ± 0.319, Dice score 0.627 ± 0.296, and recall 0.706 ± 0.365 for CMBs detection in the external test set. For CSVD classification, the model achieved a weighted-average AUC of 0.908 (95% CI 0.895-0.921), accuracy of 0.819 (95% CI 0.768-0.870), weighted-average precision of 0.864 (95% CI 0.831-0.897), and weighted-average F1-score of 0.829 (95% CI 0.782-0.876) in the external set, outperforming the performance of the neurologist group.

CONCLUSION

The DL model based on SWS can detect CMBs and classify CSVD, thereby assisting neurologists in optimizing CSVD management.

Genetic Mechanisms of Migraine: Insights from Monogenic Migraine Mutations

Migraine is a disabling neurological disorder burdening patients globally. Through the increasing development of preclinical and clinical experimental migraine models, advancing appreciation of the extended clinical phenotype, and functional neuroimaging studies, we can further our understanding of the neurobiological basis of this highly disabling condition. Despite increasing understanding of the molecular and chemical architecture of migraine mechanisms, many areas require further investigation. Research over the last three decades has suggested that migraine has a strong genetic basis, based on the positive family history in most patients, and this has steered exploration into possibly implicated genes. In recent times, human genome-wide association studies and rodent genetic migraine models have facilitated our understanding, but most migraine seems polygenic, with the monogenic migraine mutations being considerably rarer, so further large-scale studies are required to elucidate fully the genetic underpinnings of migraine and the translation of these to clinical practice. The monogenic migraine mutations cause severe aura phenotypes, amongst other symptoms, and offer valuable insights into the biology of aura and the relationship between migraine and other conditions, such as vascular disease and sleep disorders. This review will provide an outlook of what is known about some monogenic migraine mutations, including familial hemiplegic migraine, familial advanced sleep-phase syndrome, and cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy.

Neglected Mendelian causes of stroke in adult Chinese patients who had an ischaemic stroke or transient ischaemic attack

BACKGROUND AND PURPOSE

Multiple factors play important roles in the occurrence and prognosis of stroke. However, the roles of monogenic variants in all-cause ischaemic stroke have not been systematically investigated. We aim to identify underdiagnosed monogenic stroke in an adult ischaemic stroke/transient ischaemic attack (TIA) cohort (the Third China National Stroke Registry, CNSR-III).

METHODS

Targeted next-generation sequencing for 181 genes associated with stroke was conducted on DNA samples from 10 428 patients recruited through CNSR-III. The genetic and clinical data from electronic health records (EHRs) were reviewed for completion of the diagnostic process. We assessed the percentages of individuals with pathogenic or likely pathogenic (P/LP) variants, and the diagnostic yield of pathogenic variants in known monogenic disease genes with associated phenotypes.

RESULTS

In total, 1953 individuals harboured at least one P/LP variant out of 10 428 patients. Then, 792 (7.6%) individuals (comprising 759 individuals harbouring one P/LP variant in one gene, 29 individuals harbouring two or more P/LP variants in different genes and 4 individuals with two P/LP variants in ABCC6) were predicted to be at risk for one or more monogenic diseases based on the inheritance pattern. Finally, 230 of 792 individuals manifested a clinical phenotype in the EHR data to support the diagnosis of stroke with a monogenic cause. The most diagnosed Mendelian cause of stroke in the cohort was cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy. There were no relationships between age or family history and the incidence of first symptomatic monogenic stroke in patients.

CONCLUSION

The rate of monogenic cause of stroke was 2.2% after reviewing the clinical phenotype. Possible reasons that Mendelian causes of stroke may be missed in adult patients who had an ischaemic stroke/TIA include a late onset of stroke symptoms, combination with common vascular risks and the absence of a prominent family history.

Induced pluripotent stem cell model revealed impaired neurovascular interaction in genetic small vessel disease Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy

Introduction

Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL) is the most common genetic small vessel disease caused by variants in the NOTCH3 gene. Patients with CADASIL experience recurrent strokes, developing into cognitive defect and vascular dementia. CADASIL is a late-onset vascular condition, but migraine and brain MRI lesions appear in CADASIL patients as early as their teens and twenties, suggesting an abnormal neurovascular interaction at the neurovascular unit (NVU) where microvessels meet the brain parenchyma.

Methods

To understand the molecular mechanisms of CADASIL, we established induced pluripotent stem cell (iPSC) models from CADASIL patients and differentiated the iPSCs into the major NVU cell types including brain microvascular endothelial-like cells (BMECs), vascular mural cells (MCs), astrocytes and cortical projection neurons. We then built an in vitro NVU model by co-culturing different neurovascular cell types in Transwells and evaluated the blood brain barrier (BBB) function by measuring transendothelial electrical resistance (TEER).

Results

Results showed that, while the wild-type MCs, astrocytes and neurons could all independently and significantly enhance TEER of the iPSC-BMECs, such capability of MCs from iPSCs of CADASIL patients was significantly impaired. Additionally, the barrier function of the BMECs from CADASIL iPSCs was significantly decreased, accompanied with disorganized tight junctions in iPSC-BMECs, which could not be rescued by the wild-type MCs or sufficiently rescued by the wild-type astrocytes and neurons.

Discussion

Our findings provide new insight into early disease pathologies on the neurovascular interaction and BBB function at the molecular and cellular levels for CADASIL, which helps inform future therapeutic development.

Advances in Management of the Stroke Etiology One-Percenters

PURPOSE OF REVIEW

Uncommon causes of stroke merit specific attention; when clinicians have less common etiologies of stoke in mind, the diagnosis may come more easily. This is key, as optimal management will in many cases differs significantly from "standard" care.

RECENT FINDINGS

Randomized controlled trials (RCT) on the best medical therapy in the treatment of cervical artery dissection (CeAD) have demonstrated low rates of ischemia with both antiplatelet and vitamin K antagonism. RCT evidence supports the use of anticoagulation with vitamin K antagonism in "high-risk" patients with antiphospholipid antibody syndrome (APLAS), and there is new evidence supporting the utilization of direct oral anticoagulation in malignancy-associated thrombosis. Migraine with aura has been more conclusively linked not only with increased risk of ischemic and hemorrhagic stroke, but also with cardiovascular mortality. Recent literature has surprisingly not provided support the utilization of L-arginine in the treatment of patients with mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS); however, there is evidence at this time that support use of enzyme replacement in patients with Fabry disease. Additional triggers for reversible cerebral vasoconstriction syndrome (RCVS) have been identified, such as capsaicin. Imaging of cerebral blood vessel walls utilizing contrast-enhanced MRA is an emerging modality that may ultimately prove to be very useful in the evaluation of patients with uncommon causes of stroke. A plethora of associations between cerebrovascular disease and COVID-19 have been described. Where pertinent, authors provide additional tips and guidance. Less commonly encountered conditions with updates in diagnosis, and management along with clinical tips are reviewed.

Management of Coronary Artery Disease in CADASIL Patients: Review of Current Literature

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is the most common heritable form of vascular dementia in adults. It is well-established that CADASIL results in neurocognitive dysfunction and mood disturbance. There is also cumulative evidence that CADASIL patients are more susceptible to ischemic heart disease. The aim of this study is to review the current literature regarding the incidence of coronary artery disease in CADASIL patients with a focus on the various management options and the clinical challenges associated with each of these treatment strategies. We conducted a literature search using Cochrane, MEDLINE, and EMBASE for papers that reported the occurrence of coronary artery disease in patients with CADASIL. We supplemented the search with a manual search in Google Scholar. Only case reports, case series, and original articles were included. The search resulted in six reports indicating the association between coronary artery disease and CADASIL and its management. Evidence suggests that extracranial manifestations of CADASIL may include coronary artery disease, presenting as a more extensive burden of disease in younger patients. Surgical and percutaneous revascularization strategies are feasible, but the incidence of peri-procedural stroke remains significant and should be weighed against the potential benefit derived from either of these strategies. A multidisciplinary approach to therapy, with perspectives from neurologists, cardiologists, and cardiac surgeons, is needed to provide the appropriate treatment to the CADASIL patient with severe coronary artery disease. Future studies should be directed toward the development of targeted therapies that may help with the early detection and prevention of disease progress in these patients.

Association between cerebrovasoreactivity and stroke in cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy

Background

Impaired cerebrovasoreactivity is thought to play an important role in the pathophysiology of cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). We aimed to clarify the association between cerebrovascular reactivity and stroke in patients with CADASIL.

Methods

We retrospectively recruited 14 patients with CADASIL, eight of whom had symptomatic stroke. They underwent quantitative single-photon emission computed tomography using an autoradiographic method at rest and after acetazolamide (ACZ) administration. Regional cerebral blood flow (rCBF) in the cerebral cortex, lenticular nucleus, thalamus, and cerebellum was measured. We compared the rCBF parameters between patients with and without stroke.

Results

The baseline characteristics and magnetic resonance imaging findings were similar between the two groups, except for a higher frequency of pyramidal tract sign (75% vs. 0%) and a larger number of old lacunes (15.4 ± 8.8 vs. 2.2 ± 1.8) in the patients with stroke. Of the rCBF parameters measured, significantly lower flow (mL/100 g/min) was observed in ACZ-rCBF in the thalamus (35.6 ± 9.4 vs. 51.1 ± 7.6, p = 0.01) and ΔrCBF in the thalamus (10.6 ± 3.7 vs. 21.0 ± 7.9, p = 0.02) in the patients with stroke.

Conclusion

Cerebrovasoreactivity in the thalamus was significantly associated with stroke in patients with CADASIL.

Segmentation of incident lacunes during the course of ischemic cerebral small vessel diseases

Background

Lacunes represent key imaging markers of cerebral small vessel diseases (cSVDs). During their progression, incident lacunes are related to stroke manifestations and contribute to progressive cognitive and/or motor decline. Assessing new lesions has become crucial but remains time-consuming and error-prone, even for an expert. We, thus, sought to develop and validate an automatic segmentation method of incident lacunes in CADASIL caused by cysteine mutation in the EGFr domains of the NOTCH3 gene, a severe and progressive monogenic form of cSVD.

Methods

Incident lacunes were identified based on difference maps of 3D T1-weighted MRIs obtained at the baseline and 2 years later. These maps were thresholded using clustering analysis and compared with results obtained by expert visual analysis, which is considered the gold standard approach.

Results

The median number of lacunes at the baseline in 30 randomly selected patients was 7 (IQR = [2, 11]). The median number of incident lacunes was 2 (IQR = [0, 3]) using the automatic method (mean time-processing: 25 s/patient) and 0.5 (IQR = [0, 2]) using the standard visual approach (mean time-processing: 8 min/patient). The complementary analysis of segmentation results is enabled to quickly remove false positives detected in specific locations and to identify true incident lesions not previously detected by the standard analysis (2 min/case). A combined approach based on automatic segmentation of incident lacunes followed by quick corrections of false positives allowed to reach high individual sensitivity (median at 0.66, IQR = [0.21, 1.00]) and global specificity scores (0.80).

Conclusion

The automatic segmentation of incident lacunes followed by quick corrections of false positives appears promising for properly and rapidly quantifying incident lacunes in large cohorts of cSVDs.

Association between NOTCH3 gene and Parkinson's disease based on whole-exome sequencing

Objective

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a hereditary cerebral small vessel disease caused by mutations in the NOTCH3 gene. Previous studies have established a link between NOTCH3 variants and Parkinson's disease (PD) in terms of neuropathology and clinical characteristics. In this study, we aimed to explore the role of NOTCH3 gene in PD in a large Chinese cohort.

Methods

A total of 1,917 patients with early-onset or familial PD and 1,652 matched controls were included. All variants were divided into common or rare types by minor allele frequency (MAF) at a threshold of 0.01 (MAF > 0.01 into common variants and others into rare variants). Common variants were subjected to single-variant tests by PLINK, then gene-based analyses were used for rare variants with the optimized sequence kernel association test (SKAT-O). For genotype-phenotype correlation assessment, regression models were conducted to compare clinical features between the studied groups.

Results

Three common variants (rs1044006, rs1043997, and rs1043994) showed a nominal protective effect against PD. However, none of these SNPs survived Bonferroni correction. The results in the validation cohort revealed a significant but opposite association between these variants and PD. The gene-based analyses of rare variants showed no significant associations of NOTCH3 with PD. Although we did not find significant associations in the following genotype-phenotype analysis, the higher clinical scores of motor symptoms in NOTCH3-variant carriers were of interest.

Conclusion

Our results indicated that NOTCH3 gene may not play an important role in the early-onset or familial PD of Chinese population.

Trajectory Pattern of Cognitive Decline in Cerebral Autosomal Dominant Arteriopathy With Subcortical Infarcts and Leukoencephalopathy

BACKGROUND AND OBJECTIVES

The course and pattern of cognitive decline in ischemic cerebral small vessel disease remain poorly characterized. We analyzed the trajectory pattern of cognitive decline from age 25 to 75 years in cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL).

METHODS

We applied latent process mixed models to data obtained from patients with CADASIL who were repeatedly scored during their follow-up using 16 selected clinical scales or cognitive tests.

RESULTS

The modeled evolutions of these scores obtained from 1,243 observations in 265 patients recruited at the French National Referral Centre (50.1 years on average and 45.3% men) showed wide and heterogeneous variations in amplitude along the age-related progression of the disease. Although the Backward Digit Span remained essentially stable, a linear deterioration of scores obtained using the Symbol Digit Numbers or Number of Errors of Trail Making Test B was detected from 25 to 75 years. By contrast, the largest score changes were observed at midlife using the Digit Cancellation Task. All other tests related to executive functions, memory performances, or global cognitive efficiency showed a rate of change accelerating especially at the advanced stage of the disease. Male gender and the presence of gait disorders or of some disability at baseline were found to predict earlier or large changes of 4 scores (Index of Sensitivity to Cueing, Delayed Total Recall, Initiation/Perseveration, and Barthel Index) in a subgroup of individuals distinct from the rest of the sample.

DISCUSSION

Cognitive alterations develop heterogeneously during the progression of CADASIL and vary largely according to the stage of the disease. These results suggest that not only the target population and study duration but also the stage of disease progression should be considered in preparing future clinical trials aimed at reducing cognitive decline in any such condition.

Intracerebral Hemorrhage Genetics

Intracerebral hemorrhage (ICH) is a devastating type of stroke, frequently resulting in unfavorable functional outcomes. Up to 15% of stroke patients experience ICH and approximately half of those have a lethal outcome within a year. Considering the huge burden of ICH, timely prevention and optimized treatment strategies are particularly relevant. Nevertheless, ICH management options are quite limited, despite thorough research. More and more trials highlight the importance of the genetic component in the pathogenesis of ICH. Apart from distinct monogenic disorders of familial character, mostly occurring in younger subjects, there are numerous polygenic risk factors, such as hypertension, neurovascular inflammation, disorders of lipid metabolism and coagulation cascade, and small vessel disease. In this paper we describe gene-related ICH types and underlying mechanisms. We also briefly discuss the emerging treatment options and possible clinical relevance of the genetic findings in ICH management. Although existing data seems of more theoretical and scientific value so far, a growing body of evidence, combined with rapidly evolving experimental research, will probably serve clinicians in the future.

Perspectives on Cognitive Phenotypes and Models of Vascular Disease

Clinical investigations have established that vascular-associated medical conditions are significant risk factors for various kinds of dementia. And yet, we are unable to associate certain types of vascular deficiencies with specific cognitive impairments. The reasons for this are many, not the least of which are that most vascular disorders are multi-factorial and the development of vascular dementia in humans is often a multi-year or multi-decade progression. To better study vascular disease and its underlying causes, the National Heart, Lung, and Blood Institute of the National Institutes of Health has invested considerable resources in the development of animal models that recapitulate various aspects of human vascular disease. Many of these models, mainly in the mouse, are based on genetic mutations, frequently using single-gene mutations to examine the role of specific proteins in vascular function. These models could serve as useful tools for understanding the association of specific vascular signaling pathways with specific neurological and cognitive impairments related to dementia. To advance the state of the vascular dementia field and improve the information sharing between the vascular biology and neurobehavioral research communities, National Heart, Lung, and Blood Institute convened a workshop to bring in scientists from these knowledge domains to discuss the potential utility of establishing a comprehensive phenotypic cognitive assessment of a selected set of existing mouse models, representative of the spectrum of vascular disorders, with particular attention focused on age, sex, and rigor and reproducibility. The workshop highlighted the potential of associating well-characterized vascular disease models, with validated cognitive outcomes, that can be used to link specific vascular signaling pathways with specific cognitive and neurobehavioral deficits.

Early-Onset Vascular Leukoencephalopathy Caused by Bi-Allelic NOTCH3 Variants

OBJECTIVE

Heterozygous NOTCH3 variants are known to cause cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), with patients typically presenting in adulthood. We describe three patients presenting at an early age with a vascular leukoencephalopathy. Genome sequencing revealed bi-allelic variants in the NOTCH3 gene.

METHODS

Clinical records and available MRI and CT scans of three patients from two unrelated families were retrospectively reviewed.

RESULTS

The patients presented at 9 to 14 months of age with developmental delay, seizures, or both. The disease course was characterized by cognitive impairment and variably recurrent strokes, migraine attacks, and seizures. MRI findings pointed at a small vessel disease, with extensive cerebral white matter abnormalities, atrophy, lacunes in the basal ganglia, microbleeds, and microcalcifications. The anterior temporal lobes were spared. Bi-allelic cysteine-sparing NOTCH3 variants in exons 1, 32, and 33 were found.

INTERPRETATION

This study indicates that bi-allelic loss-of-function NOTCH3 variants may cause a vascular leukoencephalopathy, distinct from CADASIL.

CADASIL mutations sensitize the brain to ischemia via spreading depolarizations and abnormal extracellular potassium homeostasis

Cerebral autosomal dominant arteriopathy, subcortical infarcts and leukoencephalopathy (CADASIL) is the most common monogenic form of small vessel disease characterized by migraine with aura, leukoaraiosis, strokes and dementia. CADASIL mutations cause cerebrovascular dysfunction in both animal models and humans. Here, we show that two different human CADASIL mutations (Notch3 R90C or R169C) worsen ischemic stroke outcomes in transgenic mice, explained by a higher blood flow threshold to maintain tissue viability. Both mutants developed larger infarcts and worse neurological deficits compared with wild type regardless of age or sex after filament middle cerebral artery occlusion. However, full-field laser speckle flowmetry during distal middle cerebral artery occlusion showed comparable perfusion deficits in mutants and their respective wild type controls. Circle of Willis anatomy and pial collateralization also did not differ among the genotypes. In contrast, mutants had a higher cerebral blood flow threshold below which infarction ensued, suggesting increased sensitivity of brain tissue to ischemia. Electrophysiological recordings revealed a 1.5- to 2-fold higher frequency of peri-infarct spreading depolarizations in CADASIL mutants. Higher extracellular K+ elevations during spreading depolarizations in the mutants implicated a defect in extracellular K+ clearance. Altogether, these data reveal a novel mechanism of enhanced vulnerability to ischemic injury linked to abnormal extracellular ion homeostasis and susceptibility to ischemic depolarizations in CADASIL.

Specific Abnormalities in White Matter Pathways as Interface to Small Vessels Disease and Cognition in Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy Individuals

Background: Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is characterized by leukoencephalopathy leading to cognitive impairment. Subtle cognitive deficits can be observed early in the course of the disease, before the occurrence of the first stroke. Therefore, markers that can predict disease progression at this early stage, when interventions are likely to alter disease course, are needed. We aimed to examine the biological cascade of microstructural and macrostructural white matter (WM) abnormalities underlying cognitive deficits in CADASIL. Methods: We examined 20 nondemented CADASIL mutation carriers and 23 noncarriers who underwent neuropsychological evaluation and magnetic resonance imaging. Using probabilistic tractography of key WM tracts, we examined group differences in diffusivity measures and WM hyperintensity volume. Successive mediation models examined whether tract-specific WM abnormalities mediated subtle cognitive differences between CADASIL mutation carriers and noncarriers. Results: The largest effect size differentiating the two groups was observed for left superior longitudinal fasciculus-temporal (SLFt) diffusivity (Cohen's f = 0.49). No group differences were observed with a global diffusion measure. These specific microstructural differences in the SLFt were associated with higher WM hyperintensities burden, and subtle executive deficits in CADASIL mutation carriers. Discussion: Worse diffusivity in the left SLFt is related to greater severity of small vessel disease and worse executive functioning in the asymptomatic stage of the disease. Worse diffusivity of the left SLFt may potentially hold promise as an indicator of disease progression. Impact statement Diffusion tensor imaging outperforms conventional imaging of subcortical small vessel disease as a potential marker of future disease progression. Here we identified the left superior longitudinal temporal fasciculus as a critical white matter fiber bundle, of which worse diffusivity can link presence of cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy mutations to greater severity of small vessel disease and worse executive functioning in asymptomatic stages of the disease. This tract may hold promise and deserves further examination as an early indicator of disease progression.

Cognition, mood and behavior in CADASIL

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CADASIL is responsible for cognitive, mood or behavior disturbances.

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Cognitive disturbances range from moderate cognitive slowing to impairment of executive functions and may progress to a global decrease of cognitive efficiency up to severe dementia.

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Mood disturbances are extremely variable in intensity, depression is the most frequent symptom.

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Behavioral changes may occur at all stage of the disease, but are often associated with the onset of cognitive alterations. Apathy is the most prominent behavior alteration.

CADASIL is the most common familial cerebral small vessel disease (cSVD). Stereotyped mutations of the NOTCH3 gene are responsible for this archetypal ischemic cSVD that can lead, at the very end stage, to severe dementia. Variable cognitive alterations, mood, or behavior disturbances are frequently observed during the course of the disease. In this review, these clinical manifestations, their occurrence, severity and duration are analyzed in relation to the disease progression. Also, the potential relationships with cerebral lesions and treatment options are discussed.

Vascular Dementia and Crosstalk Between the Complement and Coagulation Systems

Vascular Dementia (VaD) is a neurocognitive disorder caused by reduced blood flow to the brain tissue, resulting in infarction, and is the second most common type of dementia. The complement and coagulation systems are evolutionary host defence mechanisms activated by acute tissue injury to induce inflammation, clot formation and lysis; recent studies have revealed that these systems are closely interlinked. Overactivation of these systems has been recognised to play a key role in the pathogenesis of neurological disorders such as Alzheimer's disease and multiple sclerosis, however their role in VaD has not yet been extensively reviewed. This review aims to bridge the gap in knowledge by collating current understanding of VaD to enable identification of complement and coagulation components involved in the pathogenesis of this disorder that may have their effects amplified or supressed by crosstalk. Exploration of these mechanisms may unveil novel therapeutic targets or biomarkers that would improve current treatment strategies for VaD.

Heterozygous Cysteine-sparing NOTCH3 Variant p.Val237Met in a Japanese Patient with Suspected Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy

A 64-year-old Japanese man with recurrent cerebral ischemic events and cognitive impairment was suspected of having cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) because of a family history and brain magnetic resonance imaging findings of cerebral white matter hyperintensities. The cysteine-sparing variation p.Val237Met was identified in NOTCH3. An intensive skin biopsy showed negative results (no granular osmiophilic material or positive NOTCH3 immunostaining), suggesting that the patient's definite diagnosis and pathogenicity of p.Val237Met were uncertain. We additionally reviewed previous reports of two Japanese families with p.Val237Met.

Fibrinogen is an Independent Risk Factor for White Matter Hyperintensities in CADASIL but not in Sporadic Cerebral Small Vessel Disease Patients

The relationship between fibrinogen and white matter hyperintensities (WMHs) are inconsistent. Whether there are different relationships between WMHs and fibrinogen in disparate subtypes of cerebral small vessel disease (CSVD) remains unknown. Here, we investigated the roles of plasma fibrinogen in sporadic CSVD (sCSVD) and Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL) patients. We performed a cross-sectional study that included 74 CSVD patients (19 CADASIL and 55 sporadic) and 74 age- and gender-matched healthy controls (HCs). Plasma fibrinogen was determined, and the severity of WMHs in CSVD patients was rated according to Fazekas scales. Univariate analysis and ordinal logistic regression were performed to evaluate the relationship between fibrinogen and the severity of WMHs in CSVD. Both CADASIL and sCSVD patients showed significantly higher plasma fibrinogen levels than HCs. No significant difference in the plasma fibrinogen level was observed between CADASIL and sCSVD. Univariate analysis and ordinal logistic regression indicated that fibrinogen is an independent risk factor for the severity of WMHs in CADASIL patients (odds ratio [OR] =1.064; 95% Confidence interval (CI, 1.004-1.127); p =0.037). However, age (odds ratio [OR] =1.093; 95% CI (1.033-1.156); P = 0.002), but not fibrinogen (odds ratio [OR] =1.004; 95% CI (0.997-1.011); P=0.262), is an independent risk factor for the severity of WMHs in sCSVD patients. Our results suggest that high levels of plasma fibrinogen are associated with the severity of WMHs in CADASIL but not in sCSVD patients, indicating that the role of fibrinogen may be different in disparate subtypes of CSVD. A better understanding of fibrinogen may yield insights into the pathogenesis of CSVD.

Characterisation of early ultrastructural changes in the cerebral white matter of CADASIL small vessel disease using high-pressure freezing/freeze-substitution

AIMS

The objective of this study was to elucidate the early white matter changes in CADASIL small vessel disease.

METHODS

We used high-pressure freezing and freeze substitution (HPF/FS) in combination with high-resolution electron microscopy (EM), immunohistochemistry and confocal microscopy of brain specimens from control and CADASIL (TgNotch3^R169C ) mice aged 4-15 months to study white matter lesions in the corpus callosum.

RESULTS

We first optimised the HPF/FS protocol in which samples were chemically prefixed, frozen in a sample carrier filled with 20% polyvinylpyrrolidone and freeze-substituted in a cocktail of tannic acid, osmium tetroxide and uranyl acetate dissolved in acetone. EM analysis showed that CADASIL mice exhibit significant splitting of myelin layers and enlargement of the inner tongue of small calibre axons from the age of 6 months, then vesiculation of the inner tongue and myelin sheath thinning at 15 months of age. Immunohistochemistry revealed an increased number of oligodendrocyte precursor cells, although only in older mice, but no reduction in the number of mature oligodendrocytes at any age. The number of Iba1 positive microglial cells was increased in older but not in younger CADASIL mice, but the number of activated microglial cells (Iba1 and CD68 positive) was unchanged at any age.

CONCLUSION

We conclude that early WM lesions in CADASIL affect first and foremost the myelin sheath and the inner tongue, suggestive of a primary myelin injury. We propose that those defects are consistent with a hypoxic/ischaemic mechanism.

Two cases of NMOSD with MRI findings mimicking CADASIL

PURPOSE

The purpose of this study is to increase awareness of the importance of considering neuromyelitis optica spectrum disorder (NMOSD) as a differential diagnosis for cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL).

METHODS

We report two NMOSD patients demonstrating magnetic resonance imaging (MRI) abnormalities resembling those of CADASIL.

RESULTS

Brain MRIs of both patients showed symmetrical hyperintense signals in the temporal poles and cerebral hemispheres on T2 weighted images. One case also involved the bilateral external capsule. The chief complaint of both patients was loss of visual acuity, and neurologic examination showed no other apparent neurological signs or symptoms. Anti-aquaporin-4 antibodies were detected on serological examination, and NMOSD was subsequently diagnosed. Visual acuity improved following intravenous methylprednisolone therapy. One patient refused further immunological treatment. Although she remained clinically stable, gradual radiographic deterioration was observed. This deterioration then stabilized after the patient commenced oral prednisolone therapy. The other patient was treated with prednisolone and azathioprine. She is clinically stable, but we have observed gradual radiographic deterioration over the past 5 years.

CONCLUSION

MRI findings in patients with NMOSD may resemble those of CADASIL, namely symmetrical hyperintensities in the temporal poles, external capsules and cerebral hemispheres. NMOSD is a differential diagnosis for CADASIL, and testing for anti-AQP4 antibodies should be considered.