Vascular Contributions in Alzheimer’s Disease-Related Neuropathological Changes: First Autopsy Evidence from a South Asian Aging Population

Abstract

Background: Evidence from various consortia on vascular contributions has been inconsistent in determining the etiology of sporadic Alzheimer’s disease (AD).

Objective: To investigate vascular risk factors and cerebrovascular pathologies associated in manifestation of AD-related neuropathological changes of an elderly population.

Methods: Postmortem brain samples from 76 elderly subjects (≥50 years) were used to study genetic polymorphisms, intracranial atherosclerosis of the circle of Willis (IASCW), and microscopic infarcts in deep white matters. From this cohort, 50 brains (≥60 years) were subjected to neuropathological diagnosis using immunohistopathological techniques.

Results: Besides the association with age, the apolipoprotein E ɛ4 allele was significantly and strongly associated with Thal amyloid-β phases ≥1 [odds ratio (OR) = 6.76, 95% confidence interval (CI) 1.37–33.45] and inversely with Braak neurofibrillary tangle (NFT) stages ≥III (0.02, 0.0–0.47). Illiterates showed a significant positive association for Braak NFT stages ≥IV (14.62, 1.21–176.73) and a significant negative association for microscopic infarcts (0.15, 0.03–0.71) in deep white matters. With respect to cerebrovascular pathologies, cerebral small vessel lesions (white matter hyperintensities and cerebral amyloid angiopathy) showed a higher degree of associations among them and with AD-related neuropathological changes (p < 0.05) compared to large vessel pathology (IASCW), which showed a significant association only with Braak NFT stages ≥I (p = 0.050).

Conclusion: These findings suggest that besides age, education, and genetic factors, other vascular risk factors were not associated with AD-related neuropathological changes and urge prompt actions be taken against cerebral small vessel diseases since evidence for effective prevention is still lacking.

Keywords

Alzheimer’s disease apolipoprotein E atherosclerosis cerebral small vessel diseases neuropathology

INTRODUCTION

Vascular-derived insults might initiate and/or contribute to neuronal degenerations [1]. Of note, midlife hypertension, diabetes mellitus, apolipoprotein E (APOE) ɛ4 isoforms, hypercholesterolemia, homocysteinemia, smoking, obesity, and, of course, age are vascular risk factors that predispose individuals to Alzheimer’s disease (AD) [2 –5]; however, interaction between vascular factors and amyloidosis or tauopathy still remains unresolved [3, 6]. Neuropathological examinations reveal that most cases of AD have mixed vascular pathology and small-vessel disease [6, 7]. In addition, brain hypoperfusion/hypoxia, silent infarcts, the presence of one or more infarcts, stroke episodes, and transient ischemic or hypoxic attacks all increase the risk of AD [8 –10]; however, underlying mechanism in the pathogenetic processes of AD remains unclear. Cerebral hypoperfusion theory is one of the major theories in determining the etiology of sporadic AD and intracranial atherosclerosis of the circle of Willis (IASCW) has been associated with AD via mechanical obstruction and reduction in cerebral arterial inflow; caused by atherosclerotic lesions [11 –14]. However, inconsistencies exist in other investigations [15 –17], and the recent hypoperfusion studies developed via postmortem biochemical methods indicate that the main cause for AD is probably via non-structural vascular dysfunctions influenced strongly by amyloid-β (Aβ) rather than structural pathology [18, 19].

Asians, represent approximately 60% of the total world population [20], are identified as high-risk populations as several modifiable vascular risk factors such as intracranial atherosclerosis [21], hypertension [22], diabetes [23], and metabolic syndrome [24] are being increasingly recognized and may contribute to increased incidence of dementia in addition to their genetic predispositions, i.e., risk and protective effect of APOE ɛ4 and ɛ2 allelic frequencies, respectively [25, 26]. Within Asia, South Asia represents more than 40% of the total Asian and one-fourth (24.8%) of the total world population [20]. To the best of our knowledge, this is the first brain autopsy study undertaken in South Asia that was intended to explore the vascular risk factors and cerebrovascular pathologies associated with AD-related neuropathological changes, since identification of such factors and pathologies may offer new insights into diagnosis and/or early intervention in these populations.

MATERIALS AND METHODS

Sample collection

Consecutive human brain samples were obtained at postmortem examination from 76 older people between May 2009 and March 2010, in the Department of Judicial Medical Office, Colombo South Teaching Hospital. Ethics approval was obtained from the Institutional Scientific Ethics Committee to carry out the study, and informed consent was obtained from the kin to utilize the material for research. The age range was 50–89 years, mean age±S.D was 67.3±10 years, median age was 65.5 years, the male:female ration was 52:24, and the mean postmortem interval±S.D was 17.3±14.2 hours. Recruited cases represented a semi-urban population and the final autopsy diagnosis of these subjects included cardiovascular diseases (45), coronary obstructive airway disease (2), suicide (6), accident (7), pneumonia (3), asphyxia (1), cancer (2), cirrhosis of the liver (1), septicemia/septic shock (3), protracted complicated illness (2), and unknown causes (4). As the samples were collected at postmortem, detailed psychometric evaluation was not available, but the pathomorphological features were noted. An ante-mortem questionnaire was given to kin who were familiar with intellectual and motor functional status of the subjects before death. The purpose of this questionnaire was to obtain information on demographic data, past medical history, family history, health habits, and consumption pattern of the deceased. This information was held strictly confidential. All the recruited cases had incomplete clinical history except three cases that were clinically diagnosed as Parkinson’s disease. Specific neuroanatomical regions were sampled for paraffin embedding and sectioning from both hemispheres: hippocampus along with parahippocampal gyrus, superior frontal gyrus, middle temporal gyrus, superior parietal lobule, midbrain at superior colliculus level, and deep white matters from corpus callosum- major inter-hemispheric white matter tract. Circle of Willis and cadaver blood/clotted blood were also collected at autopsy for the subsequent atherosclerotic and genetic polymorphism studies, respectively.

Screening for neurodegenerative pathologies using histopathological/immunohistochemical techniques

For this purpose, brain samples from 50 out of 76 elderly subjects aged ≥60 years (mean age 72.1 years±7.8, mean±S.D., male:female = 29:21) were used. In the total of 59 cases at the age of ≥60 years, there were 9 cases with incomplete case histories and unavailability of some specific neuroanatomical regions were excluded from this screening. Following routine histological evaluation [hematoxylin and eosin (H&E) staining], brain sections (4μm thick) were immunostained by standard immunoperoxidase technique following antigen retrieval by heat and DAB/H₂O₂ as the chromogen to visualize the immunolabelling (DAKO Envision Detection System). For this screening, following three antibodies namely (i) amyloid-β – monoclonal antibody (1:200 dilution) from Novacastra^TM, (ii) ubiquitin – monoclonal antibody (1:150 dilution) from Novacastra^TM, and (iii) phosphorylated tau–PHF–1 monoclonal antibody (1:50 dilution, a gift) were used. The diagnostic criteria for AD neuropathologic change and Lewy body diseases were based on National Institute on Aging-Alzheimer’s Association guidelines-a practical approach (NIA-AA) [27]. Phosphorylated tau and Aβ positive pathologies were graded semi-quantitatively as given below.

Semi-quantitative 0–3 scale (0–none, +–low, ++–moderate, +++–high) for tau positive neurons (neurons demonstrating tangle and pre-tangle pathology), neuritic plaques (NPs) and neuropil threads.

Semi-quantitative 0–3 scale (0–none, +–sparse, ++–moderate, +++–frequent) for Aβ positive senile plaques (dystrophic neurites and an amyloid core) and diffuse plaques.

Actual burden of AD-related neuropathological changes [neurofibrillary tangles (NFTs) and senile plaques] were counted in specific brain regions such as hippocampus and parahippocampus, superior frontal gyrus, and midbrain based on the methods described by Purohit and colleagues [28].

Due to the high variability of morphological findings and multifactorial pathogenesis of vascular cognitive impairment/vascular dementia (VaD), no generally accepted morphologic scheme for quantitating vascular brain injury and no validated neuropathological criteria for VaD have been established to date [29, 30]. On the whole, the basis of VaD diagnosis is simply the presence of brain lesions related to vascular pathology and it highly depends on neuropathologist’s judgment. IASCW was assessed macroscopically based on degree of stenosis of the each circle of Willis component artery [31] and gross visual inspection, and it was graded semi-quantitatively into four levels: none, mild, moderate, and severe. Cerebral amyloid angiopathy (CAA) in leptomeningeal and cortical arteries of the specific neuroanatomical regions was graded semi-quantitatively based on Greenberg and Vonsattel [32] specifications and the average CAA grade was reported for each case. To assess the microscopic infarcts, deep white matter sections (7μm thick) from both hemispheres were stained with Luxol Fast Blue and Cresyl violet, and graded semi-quantitatively as absent (none or mild) or present (considerable extent at least in one hemisphere). Extent of white matter hyperintensities (WMHs) stained with Luzol fast blue and Eosin, and dilated perivascular spaces stained with H&E were identified in the regions of hippocampus and parahippocampus, middle temporal gyrus, and superior frontal gyrus and reported semi-quantitatively as absent (none/rare) or present (minimum involvement at least in one region). Hippocampal cell loss in cornu ammonis area 1 (CA1) and dentate gyrus (DG) regions were also assessed semi-quantitatively as absent (none/rare) or present.

Finally, all elderly subjects were screened for polymorphisms in genes encoding for APOE, angiotensin converting enzyme (ACE), and methylenetetrahydrofolate reductase (MTHFR C677T) based on standard protocols using polymerized chain reaction based restriction fragment length polymorphism with cadaver blood deoxyribonucleic acids.

Statistical analysis

For this purpose, statistical software SPSS version 16.0 was used. Due to the small number of samples, each dependent variable was individually tested for each independent variable/factor, controlling for age and sex. Binary logistic regression was used to find the odds ratio (OR) for each factor with a 95% confidence interval (CI). For this purpose, dependent variables were dichotomized primarily based on number of cases that have presented it and then by its severity/topographical progression.

CERAD (Consortium to Establish a Registry for Alzheimer’s disease) NP scores were divided into none versus CERAD scores A to C (presence of tau positive NPs) as few number of cases presented it (6/50);

Thal Aβ phases were divided into none versus phases ≥1 (12/50), and phases ≤1 versus phases ≥2 (8/50) as few number of cases presented it (12/50) and the neocortical Aβ plaques are considered as the best correlate for cognitive impairment in AD;

Braak staging was divided into none versus stages I–VI (42/50, presence of tau positive neurofibrillary pathology), stages 0–II (32/50, none to low) versus stages III–VI (18/50, moderate to severe), and stages 0–III (43/50, none to moderate) versus stages IV–VI (7/50, moderate to severe) as it was detected more frequently than tau and Aβ positive plaques, and based on its topographical progression.

Factors including, age, sex, vascular genetic risk factors (APOE, ACE, and MTHFR), physiological factors (diabetes, high blood pressure or hypertension, high cholesterol, ischemic heart disease, and stroke) and lifestyle factors (level of education, smoking and alcohol consumption) were tested in this analysis. Hierarchical multiple regression adjusted for age and sex was used to find the relationship between continuous dependent variables (mean NFTs counts, total senile plaque counts, total CAA score, and total stenosis score) and dichotomized factors (i.e., presence of APOE ɛ4 allele versus APOE ɛ3 and ɛ2 alleles, presence of MTHFR CT/TT genotype versus CC genotype, etc.). Degree of association between AD-related neuropathological stages and cerebrovascular pathologies were assessed using Fisher’s exact test (2×2 contingency table) and Kendall’s tau b correlation coefficient as the sample size is small and the variables are categorical.

RESULTS

Our study consisted of 76 elderly brains aged between 50 and 89 years (mean age 67.3 years±10.0; male:female = 52:24) and out of that, 50 elderly brains aged ≥60 years were used for neuropathological diagnosis. As per NIA-AA [27] guidelines, in the cases with incomplete clinical history (47 cases out of 50), AD neuropathologic change for intermediate level was 4.25% (2/47) and low level was 19.15% (9/47). Parkinsonism associated pathologies were identified in 8.51% (4/47) of the cases: brainstem predominant Lewy bodies, hallmarks of Parkinson’s disease at 6.38% (3/47) and probable progressive supranuclear palsy at 2.13% (1/47). Since the lack of high specificity/high correlation among the studied cerebrovascular pathologies and the non-availability of validated criteria for neuropathological diagnosis of VaD, we could not identify any cases confined to VaD. Within the clinically diagnosed cases (3 cases out of 50), case one presented mixed dementia pathologies including definite progressive supranuclear palsy, intermediate AD neuropathologic change, and brainstem predominant Lewy bodies; case two presented vascular Parkinsonism due to ischemic stroke; and case three presented idiopathic Parkinson’s disease at Braak stage III.

Population demographics including allelic frequency of APOE, ACE, and MTHFR C677T genes, AD-related neuropathological changes and comorbid pathologies are summarized in Table 1. Factors that have demonstrated considerable associations with AD-related neuropathological stages and cerebrovascular pathologies are located in Table 2 (only factors with p values ≤0.2 are presented). Age is the strongest risk factor for dementia whether it results from vascular or neurodegenerative origin or both, and in our study, it demonstrated significant associations with Braak NFT stages, CAA, IASCW. and hippocampal cell loss in CA1 region. Besides age, illiteracy, APOE ɛ4 allele. and MTHFR T allele also showed significant associations with tau and/or Aβ positive pathologies. IASCW was significantly and strongly associated with APOEɛ3/ɛ4 genotype and history of hypertension, and inversely associated with APOE ɛ3/ɛ2 genotype. Increased risk of microscopic infarcts was significantly and strongly associated with history of diabetes and inversely associated with illiteracy. Hierarchical multiple regression analysis did not show any significant associations between factors and mean NFTs counts or total senile plaque counts in specific neuroanatomical region or in all regions except age and mean NFTs counts (p < 0.000). Total stenosis score was significantly and strongly associated (p < 0.000) with history of hypertension, whereas total CAA score was not associated with anyfactors.

Co-morbid cerebrovascular and neurodegenerative pathologies that are commonly detected in the elderly Sri Lankan brains (Fig. 1), and the degree of association between AD-related neuropathological changes and cerebrovascular pathologies are summarized in Table 3. A higher degree of positive association was observed between AD-related neuropathological changes and both the presence of WMHs and CAA. The presence of CAA and WMHs also showed a higher degree of positive association among them. Whereas IASCW was associated only with Braak NFT stages ≥I (p = 0.050). The number of cases that have presented cell loss in the DG and CA1 regions of the hippocampus (Table 1) was almost equal but they did not show any significant associations (Fisher’s exact test, p = 0.77) among them. Hippocampus cell loss in the CA1 region was significantly and strongly related to age (p = 0.001, odds ratio = 1.2, 95% CI 1.07 to 1.33), whereas cell loss in the DG region was not related to any factors.

DISCUSSION

This is the first brain autopsy study from a South Asian aging population that intended to investigatethe vascular risk factors and cerebrovascular pathologies associated with AD-related neuropathological changes. It demonstrates that increasing age, APOE ɛ4 allele, MTHFR T allele, and illiteracy are associated strongly with AD-related tau and/or Aβ positive pathologies. It also demonstrates that presence of WMHs and CAA could be considered as potential coexistent cerebrovascular lesions underlying cerebral hypoperfusion mechanism in sporadic AD rather than large vessel pathology- IASCW. It is also noted in this study that other vascular risk factors such as hypertension and diabetes are associated with degenerative cerebrovascular pathologies rather than degenerative Alzheimer or Lewy body pathology.

To date, only one clinical study has reported dementia prevalence in elderly Sri Lankans [33], and it was 3.98% (age ≥65 years) including AD at 2.85%, VaD at 0.6%, and the remaining due to other causes. In contrast, our neuropathological findings in elderly Sri Lankans showed a higher prevalence of Parkinsonism associated pathologies (8.51%) followed by AD (4.25%). In low and middle income countries (LMICs), dementia prevalence based on clinical diagnosis is often underestimated [34 –36], whereas neuropathological evidences from such populations [28, 37] indicate that actual burden of AD-related pathologies are approximately equivalent between LMICs and high income countries. Therefore, documentation of substantial heterogeneity in dementia prevalence among different counties/ethnicities needs to be investigated on the basis of genetic, environmental, and cultural factors, and the preventive approaches in reducing the burden of dementia [35].

Contribution of vascular risk factors

Genetic factors: APOE, ACE, and MTHFR C677T

The ɛ4 allele of APOE has been found to be the most consistent risk factor in late-onset AD, notably via Aβ protein, whereas associations obtained between APOE ɛ4 allele and NFTs are inconsistent [38 –42]. In our study, decedents with 1 or 2 APOE ɛ4 allele demonstrated a significant positive association with Thal Aβ phases ≥1 and in contrast, a significant negative association with Braak NFT stages ≥III controlling for age and sex. While the former is in line with worldwide evidences, the latter differs from the literature. This finding might be related to APOE ɛ4 allele dispersal among the decedents, which shows an age-associated variation in APOE ɛ4 allele frequency that is presumed to be due to survival effect [43]. The majority of the recruited cases died in their 70 s [52% (26/50)] which reflects the average life expectancy of the Sri Lankans, followed by their 60 s [32% (16/50)] and 80 s [16% (8/50)], and therefore a higher number of APOE ɛ4 alleles was detected in those aged in their 70 s (6/13), followed by ≥60 year olds (5/13) and ≥80 year olds (2/13). In addition to that, our findings also suggest that there is an age associated increase in risk of NFTs, an APOE ɛ4 allele associated increase in risk of Aβ plaques, and the survival probabilities of APOE ɛ4 allele carriers could possibly be a one of the reasons for the discordance between Braak and CERAD scores which have been discussed in population based studies [44, 45]. Frequency of the APOE ɛ4 allele is an important genetic risk factor for explaining ethnic differences [25] and the ɛ4 allele frequency seems to be higher in elderly Sri Lankans compared to the general frequency in Asians (14.6 versus 9.0%) [46]. Therefore, APOE genotypes and their survival probabilities in different ethnic populations could possibly be a one of reasons for the differences observed in AD prevalence and needs to be confirmed through large scale patho-genetic studies, across a large range of ethnicities.

Elderly subjects with the APOE ɛ3/ɛ4 genotype also demonstrate a strong association with severe IASCW as opposed to the APOE ɛ3/ɛ2 genotype, which showed a protective effect against the presence of IASCW [47]. In addition to APOE, we also noted a significant association between MTHFR T allele and sporadic CAA. Plasma total homocysteine has considered as a major vascular risk factor [2] and MTHFR is the central enzyme involved in homocystenine metabolism particularly TT genotype or T allele is associated with high homocysteine levels. Hyperhomocysteinemia is suggested to increase intima-media thickness which in turn damages the micro-vasculature, leading to neuronal damage or death [48]. However, MTHFR polymorphism (C677T) as a risk factor for CAA remains unclear and needs further studies in the future that may offer new therapeutic implications, e.g., folic acid supplementation. Effects obtained with ACE polymorphisms were not statistically significant either for AD-related changes or cerebrovascular pathologies.

Physiological factors: Diabetes and hypertension

We obtained strong associations between history of hypertension and moderate and severe IASCW, and between history of diabetes and microscopic infarcts in deep white matter. However, associations obtained for AD-related neuropathological changes were not statistically significant. Our findings are in line with previous studies [49, 50] and suggest that metabolic dysfunctions (diabetes and hypertension) could contribute to dementia via vascular degenerations rather than AD-related changes.

Lifestyle factors: Education, smoking, and alcohol consumption

Accumulating evidence in population-based studies has emphasized the association between education and reduced risk of dementia, and the real effect is explained via two hypotheses: “brain reserve” and “brain battering” [51, 52]. A previous dementia prevalence study in elderly Sri Lankans [33] has also demonstrated that illiteracy is strongly associated with clinical dementia in addition to greater age and female gender. However, there have been no autopsy verification studies representing LMICs that confirm the association between education and reduced risk of dementia pathology. In this study, we found a strong association between illiteracy and both increased risk of neurofibrillary degenerations and reduced risk of microscopic infarcts. Increased risk of neurofibrillary degenerations in illiterates is consistent with the “brain reserve hypothesis”, whereas reduced risk of microscopic infarcts may be ascribed to their low level of exposure to cerebrovascular risk factors such as smoking, hypertension, diabetes, and obesity [53, 54]. Moreover, effects seen with smoking or alcohol consumption were not found to be statistically important. As far as smoking/alcohol consumption is concerned, it could be that there is a small effect that cannot be detected with statistical significance in a relatively small sample, but it may also be attributable to cultural factors that may attenuate the overall effects given that Sri Lankan women are generally fairly conservative in their smoking/alcohol consumption habits.

Contribution of cerebrovascular pathologies

Apart from vascular risk factors, contribution of cerebrovascular pathology to the burden of sporadic AD has received increasing interest in recent decades. However, autopsy evidence which rely on IASCW, a major cause for cerebral hypoperfusion, are found to be inconsistent [15 –17] and the recent studies indicate a strong relationship between white matter disease (MRI-based) and AD type pathology (Braak score, CERAD score, and a composite AD pathology score) that would explain in part the relationship between cerebral small vessel disease and cognition [55, 56]. There are several studies that have attributed the relationship between white matter disease and cognition to coexisting atherosclerosis [11 –13]; however, it is not the case in all neuropathological studies [55]. Our findings are congruent with those of Moghekar et al. [55] and to a certain extent with both Roher et al. [11] and Luoto et al. [15]. Histopathologically assessed WMHs showed a higher degree of association with all AD-related neuropathological changes (Braak NFT, CERAD NP and Thal Aβ scores), whereas CAA is related only with plaques (CERAD NP and Thal Aβ scores) and IASCW is associated only with tangles (Braak NFT score). Our study also demonstrates a strong association between WMHs and CAA, which supports the previous studies that have suggested WMHs as a feature of sporadic CAA [57 –59]. However, IASCW was not associated with any of the cerebrovascular pathologies studied in contrast to studies that have ascribed white matter disease to coexisting atherosclerosis [11 –13]. Further, as per Luoto et al. [15], it is also arguable that a significant association noted between Braak NFT stage (I-VI) and IASCW (≥mild) grades of our cohort may be attributed to the effect of age and not due to a pathologically direct relationship as other grades of Braak NFT score or IASCW did not show any significant associations.

While this is the first autopsy verification study of an aging population from South Asia, we acknowledge there are limitations to this study such as sample size, incomplete clinical history of the recruited samples lacking objective psychometry and dementia scores, reliability of the case histories obtained through kin, ubiquitin immunohistochemistry for labeling Lewy bodies instead of α-synuclein, histopathological assessments of WMHs instead of radiological examinations, semi-quantitative assessments of certain comorbid pathologies lacking exact quantifications and the non-availability of some brain regions as specified under minimum tissue requirements by NIA-AA guidelines.

Concisely, our findings suggest that besides age, education, and genetic factors (APOE and MTHFR), other vascular risk factors were not associated with AD-related neuropathological changes. It further confirms the strong contribution of cerebral small vessel diseases in AD-related changes, contributes to the uncertainty surrounding the true effect of IASCW/large vessel disease on AD-related changes, and urge prompt action be taken against cerebral small vessel diseases possibly via therapeutic agents that contains both anti-amyloidogenic and anti-atherosclerotic properties as a preventative strategy for subsequent neurodegenerative disease.

Footnotes

ACKNOWLEDGMENTS

This study was supported by Sri Lanka Council for Agricultural Research Policy (CARP Project Grant No–12/684/515), Sri Lanka National Science Foundation (Grant No–RG 2000/M/16), University of Sri Jayewardenepura (Grant No–ASP/06/RE/2010/07), University of New South Wales and the International Brain Research Organization–Asia Pacific Regional Committee (IBRO–APRC). We would like to mention our special thanks to donors and their families for their substantial contribution in this research. We duly acknowledge all the staff of Dept. of Pathology, University of Sri Jayewardenepura and the staff of Judicial Medical Office, Colombo South Teaching Hospital for their kind assistance in this work.

Authors’ disclosures available online ().

References

Zlokovic

(2011) Neurovascular pathways to neurodegeneration in Alzheimer’s disease and other disorders. Nat Rev Neurosci 12, 723–738.

O’Brien

, Markus

(2014) Vascular risk factors and Alzheimer’s disease. BMC Med 12, 218.

Reitz

, Brayne

, Mayeux

(2011) Epidemiology of Alzheimer disease. Nat Rev Neurol 7, 137–152.

Bruijn RF

, Ikram

(2014) Cardiovascular risk factors and future Alzheimer’s disease risk. BMC Med 12, 130.

Gorelick

, Scuteri

, Black

, Decarli

, Greenberg

, Iadecola

, Launer

, Laurent

, Lopez

, Nyenhuis

, Petersen

, Schneider

, Tzourio

, Arnett

, Bennett

, Chui

, Higashida

, Lindquist

, Nilsson

, Roman

, Sellke

, Seshadri

S.; American Heart Association Stroke Council

, Council

on Epidemiology and Prevention

, Council

on Cardiovascular Nursing

, Council

on Cardiovascular Radiology and Intervention

, and

Council on Cardiovascular Surgery and Anesthesia

(2011) Vascular contributions to cognitive impairment and dementia: A statement for healthcare professionals from the American Heart Association/American Stroke Association. Stroke 42, 2672–2713.

Attems

, Jellinger

(2014) The overlap between vascular disease and Alzheimer’s disease – lessons from pathology. BMC Med 12, 206.

Kalaria

, Ballard

(1999) Overlap between pathology of Alzheimer disease and vascular dementia. Alzheimer Dis Assoc Disord 13, S115–S123.

Ruitenberg

, den

Heijer T

, Bakker

, van

Swieten JC

, Koudstaal

, Hofman

, Breteler

(2005) Cerebral hypoperfusion and clinical onset of dementia: The Rotterdam Study. Ann Neurol 57, 789–794.

Vermeer

, Prins

, den

Heijer T

, Hofman

, Koudstaal

, Breteler

(2003) Silent brain infarcts and the risk of dementia and cognitive decline. N Engl J Med 348, 1215–1222.

10.

Snowdon

, Greiner

, Mortimer

, Riley

, Greiner

, Markesbery

(1997) Brain infarction and the clinical expression of Alzheimer’s disease. The Nun Study. JAMA 277, 813–817.

11.

Roher

, Tyas

, Maarouf

, Daugs

, Kokjohn

, Emmerling

, Garami

, Belohlavek

, Sabbagh

, Sue

, Beach

(2011) Intracranial atherosclerosis as a contributing factor to Alzheimer’s disease dementia. Alzheimers Dement 7, 436–444.

12.

Roher

, Esh

, Kokjohn

, Kalback

, Luehrs

, Seward

, Sue

, Beach

(2003) Circle of Willis atherosclerosis is a risk factor for sporadic Alzheimer’s disease. Arterioscler Thromb Vasc Biol 23, 2055–2062.

13.

Beach

, Wilson

, Sue

, Newell

, Poston

, Cisneros

, Pandya

, Esh

, Connor

, Sabbagh

, Walker

, Roher

(2007) Circle of Willis atherosclerosis: Association with Alzheimer’s disease, neuritic plaques and neurofibrillary tangles. Acta Neuropathol 113, 13–21.

14.

Yarchoan

, Xie

, Kling

, Toledo

, Wolk

, Lee

, Van

Deerlin V

, Lee

, Trojanowski

, Arnold

(2012) Cerebrovascular atherosclerosis correlates with Alzheimer pathology in neurodegenerative dementias. Brain 135, 3749–3756.

15.

Luoto

, Haikonen

, Haapasalo

, Goebeler

, Huhtala

, Erkinjuntti

, Karhunen

(2009) Large vessel cerebral atherosclerosis is not in direct association with neuropathological lesions of Alzheimer’s disease. Eur Neurol 62, 93–98.

16.

Dolan

, Troncoso

, Resnick

, Crain

, Zonderman

, O’Brien

(2010) Age, Alzheimer’s disease and dementia in the Baltimore Longitudinal Study of Ageing. Brain 133, 2225–2231.

17.

Bangen

, Nation

, Delano-Wood

, Weissberger

, Hansen

, Galasko

, Salmon

, Bondi

(2015) Aggregate effects of vascular risk factors on cerebrovascular changes in autopsy-confirmed Alzheimer’s disease. Alzheimers Dement 11, 394–403.

18.

Love

, Miners

(2015) White matter hypoperfusion and damage in dementia: Post-mortem assessment. Brain Pathol 25, 99–107.

19.

Barker

, Ashby

, Wellington

, Barrow

, Palmer

, Kehoe

, Esiri

, Love

(2014) Pathophysiology of white matter perfusion in Alzheimer’s disease and vascular dementia. Brain 137, 1524–1532.

20.

Population Division of the Department of Economic and Social Affairs of the United Nations (2015) World Population Prospects: The 2015 Revision, DVD Edition, https://esa.un.org/unpd/wpp/Download/Standard/Population/, Accessed on June 5, 2016.

21.

Lee

, Han

, Yun

, Choi

, Jung

, Cho

, Yu

, Lee

, Hwang

, Song

, Kwon

, Lee

(2006) Posterior circulation ischemic stroke in Korean population. Eur J Neurol 13, 742–748.

22.

Kearney

, Whelton

, Reynolds

, Muntner

, Whelton

, He

(2005) Global burden of hypertension: Analysis of worldwide data. Lancet 365, 217–223.

23.

Chan

, Malik

, Jia

, Kadowaki

, Yajnik

, Yoon

, Hu

(2009) Diabetes in Asia: Epidemiology, risk factors and pathophysiology. JAMA 301, 2129–2140.

24.

Misra

, Khurana

(2009) The metabolic syndrome in South Asians: Epidemiology, determinants and prevention. Metab Syndr Relat Disord 7, 497–514.

25.

Verghese

, Castellano

, Holtzman

(2011) Roles of Apolipoprotein E in Alzheimer’s disease and other neurological disorders. Lancet Neurol 10, 241–252.

26.

Farrer

, Cupples

, Haines

, Hyman

, Kukull

, Mayeux

, Myers

, Pericak-Vance

, Risch

, van

Duijn CM

(1997) Effects of age, sex, and ethnicity on the association between apolipoprotein E genotype and Alzheimer’s disease. A meta-analysis. APOE and Alzheimer’s Disease Meta-Analysis Consortium. JAMA 278, 1349–1356.

27.

Montine

, Phelps

, Beach

, Bigio

, Cairns

, Dickson

, Duyckaerts

, Frosch

, Masliah

, Mirra

, Nelson

, Schneider

, Thal

, Trojanowski

, Vinters

, Hyman

BT; National Institute of Aging; Alzheimer’s Association

(2012) National Institute on Aging-Alzheimer’s Association guidelines for the neuropathological assessment of Alzheimer’s disease: Practical approach. Acta Neuropathol 123, 1–11.

28.

Purohit

, Batheia

, Sano

, Jashnani

, Kalaria

, Karunamurthy

, Kaur

, Shenoy

, Van

Dvk K

, Schmeidler

, Perl

(2011) Profile of Alzheimer’s disease-related pathology in an aging urban population sample in India. J Alzheimers Dis 24, 187–196.

29.

Jellinger

(2013) Pathology and pathogenesis of vascular cognitive impairment - a critical update. Front Aging Neurosci 5, 17.

30.

Alafuzoff

, Gelpi

, Al-Sarraj

, Arzberger

, Attems

, Bodi

, Bogdanovic

, Budka

, Bugiani

, Englund

, Ferrer

, Gentleman

, Giaccone

, Graeber

, Hortobagyi

, Hoftberger

, Ironside

, Jellinger

, Kavantzas

, King

, Korkolopoulou

, Kovacs

, Meyronet

, Monoranu

, Parchi

, Patsouris

, Roggendorf

, Rozemuller

, Seilhean

, Streichenberger

, Thal

, Wharton

, Kretzschmar

(2012) The need to unify neuropathological assessments of vascular alterations in the ageing brain: Multicenter survey by the BrainNet Euroe consortium. Exp Gerontol 47, 825–833

31.

Classification of Atherosclerotic lesions; a report of a study group (1958), World Health Organ Tech Rep Ser 57, 1–20.

32.

Greenberg

, Vonsattel

(1997) Diagnosis of cerebral amyloid angiopathy: Sensitivity and specificity of cortical biopsy. Stroke 28, 1418–1422.

33.

De Silva

, Gunathilake

, Smith

(2003) Prevalence of dementia in a semi-urban population in Sri Lanka: Report from a regional survey. Int J Geriatr Psychiatry 18, 711–715.

34.

Kalaria

, Maestre

, Arizaga

, Friedland

, Galasko

, Hall

, Luchsinger

, Ogunniyi

, Perry

, Potocnik

, Prince

, Stewart

, Wimo

, Zhang

, Antuono

; World Federation of Neurology Demntia Research Group (2008) Alzheimer’s disease and vascular dementia in developing countries: Prevalence, management, and risk factors. Lancet Neurol 7, 812–826.

35.

Venketasubramanian

, Sahadevan

, Kua

, Chen

, Ng

(2010) Interethnic differences in dementia epidemiology: Global and Asia-Pacific perspectives. Dement Geriatr Cogn Disord 30, 492–498.

36.

De Silva

, Disanayaka

, DeZoysa

, Sanjeewanie

, Somaratne

, Foster

, Srikanth

, Kathriarachchi

, Martins

(2009) Norms for the mini-mental state examination from a sample of Sri Lankan older people. Int J Geriatr Psychiatry 24, 666–670.

37.

Wijesinghe

, Shankar

, Yasha

, Gorrie

, Amaratunga

, Hulathduwa

, Sunil Kumara

, Samarasinghe

, Suh

, Steinbusch

, De Silva

KRD

(2016) Cytoskeletal pathologies of age related diseases between elderly Sri Lankan and Indian brain samples. Curr Alzheimer Res 13, 268–280.

38.

Polvikoski

, Sulkava

, Haltia

, Kainulainen

, Vuorio

, Verkkoniemi

, Niinisto

, Halonen

, Kontula

(1995) Apolipoprotein E, dementia, and cortical deposition of beta-amyloid protein. N Engl J Med 333, 1242–1247.

39.

Warzok

, Kessler

, Apel

, Schwarz

, Egensperger

, Schreiber

, Herbst

, Wolf

, Walther

, Walker

(1998) Apolipoprotein E4 promotes incipient Alzheimer pathology in the elderly. Alzheimer Dis AssocDisord 12, 33–39.

40.

Yip

, McKee

, Green

, Wells

, Young

, Cupples

, Farrer

(2005) APOE, vascular pathology, and the AD brain. Neurology 65, 259–265.

41.

Morris

, Roe

, Xiong

, Fagan

, Goate

, Holtzman

, Mintun

(2010) APOE predicts amyloid-beta but not tau Alzheimer pathology in cognitively normal ageing. Ann Neurol 67, 122–131.

42.

Kok

, Haikonen

, Luoto

, Huhtala

, Goebeler

, Haapasalo

, Karhunen

(2009) Apolipoprotein E dependent accumulation of Alzheimer disease-related lesions begins in middle age. Ann Neurol 65, 650–657.

43.

Jicha

, Parisi

, Dickson

, Cha

, Johnson

, Smith

, Boeve

, Petersen

, Knopman

(2008) Age and apoE associations with complex pathologic features in Alzheimer’s disease. J Neurol Sci 273, 34–39.

44.

Geddes

, Tekirian

, Soultanian

, Ashford

, Davis

, Markesbery

(1997) Comparison of neuropathologic criteria for the diagnosis of Alzheimer’s disease. Neurobiol Aging 18, S99–S105.

45.

Kazee

, Johnson

(1998) Alzheimer’s disease pathology in non-demented elderly. J Alzheimers Dis 1, 81–89.

46.

Singh

, Singh

, Mastana

(2006) APOE distribution in world populations with new data from India and the UK. Ann Hum Biol 33, 279–308.

47.

Anuurad

, Rubin

, Lu

, Pearson

, Holleran

, Ramakrishnan

, Berglund

(2006) Protective effect of E2 on coronary artery disease in African Americans is mediated through lipoprotein cholesterol. J Lipid Res 47, 2475–2481.

48.

Gorgone

, Ursini

, Altamura

, Bressi

, Tombini

, Curcio

, Chiovenda

, Squitti

, Silvestrini

, Ientile

, Pisani

, Rossini

, Vernieri

(2009) Hyperhomocysteinemia, intima-media thickness and C677T MTHFR gene polymorphism: A correlation study in patients with cognitive impairment. Atherosclerosis 206, 309–313.

49.

Arvanitakis

, Schneider

, Wilson

, Li

, Arnold

, Wang

, Bennett

(2006) Diabetes is related to cerebral infarction but not to AD pathology in older persons. Neurology 67, 1960–1965.

50.

Chui

, Zheng

, Reed

, Vinters

, Mack

(2012) Vascular risk factors and Alzheimer’s disease: Are these risk factors for plaques and tangles or for concomitant vascular pathology that increases the likelihood of dementia? An evidence-based review. Alzheimers Res Ther 4, 1.

51.

Fratiglioni

, Wang

(2007) Brain reserve hypothesis in dementia. J Alzheimers Dis 12, 11–22.

52.

Del Ser

, Hachinski

, Merskey

, Munoz

(1999) An autopsy-verified study of the effect of education on degenerative dementia. Brain 122, 2309–2319.

53.

Ferri

, Prince

, Brayne

, Brodaty

, Fratiglioni

, Ganguli

, Hall

, Hasegawa

, Hendrie

, Huang

, Jorm

, Mathers

, Menezes

, Rimmer

, Scazufca

, Alzheimer’s Disease International (2005) Global prevalence of dementia: A Delphi consensus study. Lancet 366, 2112–2117.

54.

LlibreRodriguez

, Ferri

, Acosta

, Guerra

, Huang

, Jacob

, Krishnamoorthy

, Salas

, Sosa

, Acosta

, Dewey

, Gaona

, Jotheeswaran

, Li

, Rodriguez

, Rodriquez

, Kumar

, Valhuerdi

, Prince

; 10/66 Dementia Research Group (2008) Prevalence of dementia in Latin America, India and China: A population based cross-sectional slurvey. Lancet 372, 464–474.

55.

Moghekar

, Kraut

, Elkins

, Troncoso

, Zonderman

, Resnick

, O’Brien

(2012) Cerebral white matter disease is associated with Alzheimer pathology. Alzheimers Dement 8, S71–S77.

56.

Prins

, Scheltens

(2015) White matter hyperintensities, cognitive impairment and dementia: An update. Nat Rev Neurol 11, 157–165.

57.

Hancu

, Rasanu

, Butoi

(2009) White matter changes in cerebrovascular disease: Leukoaraiosis. In Advances in Brain Imaging Chaudhar

, ed. InTech, Europe, pp. 249–250.

58.

Gurol

, Viswanathan

, Gidicsin

, Hedden

, Martinez-Ramirez

, Dumas

, Vashkevich

, Ayres

, Auriel

, van Etten

, Becker

, Carmasin

, Schwab

, Rosan

, Johnson

, Greenberg

(2013) Cerebral amyloid angiopathy burden associated with leukoaraiosis: A positron emission tomography/ magnetic resonance imaging study. Ann Neurol 73, 529–536.

59.

Gouw

, Seewann

, van der Filer

, Barkhof

, Rozemuller

, Scheltns

, Geurts

(2011) Heterogeneity of small vessel disease: A systematic review of MRI and histopathological correlations. J Neurol Neurosurg Psychiatry 82, 126–135.