Helena C. Chui

Vascular Contributions to Cognitive Impairment and Dementia A Statement for Healthcare Professionals From the American Heart Association/American Stroke Association

Background and Purpose— This scientific statement provides an overview of the evidence on vascular contributions to cognitive impairment and dementia. Vascular contributions to cognitive impairment and dementia of later life are common. Definitions of vascular cognitive impairment (VCI), neuropathology, basic science and pathophysiological aspects, role of neuroimaging and vascular and other associated risk factors, and potential opportunities for prevention and treatment are reviewed. This statement serves as an overall guide for practitioners to gain a better understanding of VCI and dementia, prevention, and treatment. Methods— Writing group members were nominated by the writing group co-chairs on the basis of their previous work in relevant topic areas and were approved by the American Heart Association Stroke Council Scientific Statement Oversight Committee, the Council on Epidemiology and Prevention, and the Manuscript Oversight Committee. The writing group used systematic literature reviews (primarily covering publications from 1990 to May 1, 2010), previously published guidelines, personal files, and expert opinion to summarize existing evidence, indicate gaps in current knowledge, and, when appropriate, formulate recommendations using standard American Heart Association criteria. All members of the writing group had the opportunity to comment on the recommendations and approved the final version of this document. After peer review by the American Heart Association, as well as review by the Stroke Council leadership, Council on Epidemiology and Prevention Council, and Scientific Statements Oversight Committee, the statement was approved by the American Heart Association Science Advisory and Coordinating Committee. Results— The construct of VCI has been introduced to capture the entire spectrum of cognitive disorders associated with all forms of cerebral vascular brain injury—not solely stroke—ranging from mild cognitive impairment through fully developed dementia. Dysfunction of the neurovascular unit and mechanisms regulating cerebral blood flow are likely to be important components of the pathophysiological processes underlying VCI. Cerebral amyloid angiopathy is emerging as an important marker of risk for Alzheimer disease, microinfarction, microhemorrhage and macrohemorrhage of the brain, and VCI. The neuropathology of cognitive impairment in later life is often a mixture of Alzheimer disease and microvascular brain damage, which may overlap and synergize to heighten the risk of cognitive impairment. In this regard, magnetic resonance imaging and other neuroimaging techniques play an important role in the definition and detection of VCI and provide evidence that subcortical forms of VCI with white matter hyperintensities and small deep infarcts are common. In many cases, risk markers for VCI are the same as traditional risk factors for stroke. These risks may include but are not limited to atrial fibrillation, hypertension, diabetes mellitus, and hypercholesterolemia. Furthermore, these same vascular risk factors may be risk markers for Alzheimer disease. Carotid intimal-medial thickness and arterial stiffness are emerging as markers of arterial aging and may serve as risk markers for VCI. Currently, no specific treatments for VCI have been approved by the US Food and Drug Administration. However, detection and control of the traditional risk factors for stroke and cardiovascular disease may be effective in the prevention of VCI, even in older people. Conclusions— Vascular contributions to cognitive impairment and dementia are important. Understanding of VCI has evolved substantially in recent years, based on preclinical, neuropathologic, neuroimaging, physiological, and epidemiological studies. Transdisciplinary, translational, and transactional approaches are recommended to further our understanding of this entity and to better characterize its neuropsychological profile. There is a need for prospective, quantitative, clinical-pathological-neuroimaging studies to improve knowledge of the pathological basis of neuroimaging change and the complex interplay between vascular and Alzheimer disease pathologies in the evolution of clinical VCI and Alzheimer disease. Long-term vascular risk marker interventional studies beginning as early as midlife may be required to prevent or postpone the onset of VCI and Alzheimer disease. Studies of intensive reduction of vascular risk factors in high-risk groups are another important avenue of research.

Subcortical ischaemic vascular dementia

Vascular dementia is the second most common type of dementia. The subcortical ischaemic form (SIVD) frequently causes cognitive impairment and dementia in elderly people. SIVD results from small-vessel disease, which produces either arteriolar occlusion and lacunes or widespread incomplete infarction of white matter due to critical stenosis of medullary arterioles and hypoperfusion (Binswangers disease). Symptoms include motor and cognitive dysexecutive slowing, forgetfulness, dysarthria, mood changes, urinary symptoms, and short-stepped gait. These manifestations probably result from ischaemic interruption of parallel circuits from the prefrontal cortex to the basal ganglia and corresponding thalamocortical connections. Brain imaging (computed tomography and magnetic resonance imaging) is essential for correct diagnosis. The main risk factors are advanced age, hypertension, diabetes, smoking, hyperhomocysteinaemia, hyperfibrinogenaemia, and other conditions that can cause brain hypoperfusion such as obstructive sleep apnoea, congestive heart failure, cardiac arrhythmias, and orthostatic hypotension. Cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy (CADASIL)and some forms of cerebral amyloid angiopathy have a genetic basis. Treatment is symptomatic and prevention requires control of treatable risk factors.

Magnetic resonance imaging of the entorhinal cortex and hippocampus in mild cognitive impairment and Alzheimer’s disease

OBJECTIVES To explore volume changes of the entorhinal cortex (ERC) and hippocampus in mild cognitive impairment (MCI) and Alzheimers disease (AD) compared with normal cognition (NC); to determine the powers of the ERC and the hippocampus for discrimination between these groups. METHODS This study included 40 subjects with NC, 36 patients with MCI, and 29 patients with AD. Volumes of the ERC and hippocampus were manually measured based on coronal T1 weighted MR images. Global cerebral changes were assessed using semiautomatic image segmentation. RESULTS Both ERC and hippocampal volumes were reduced in MCI (ERC 13%, hippocampus 11%, p<0.05) and AD (ERC 39%, hippocampus 27%, p<0.01) compared with NC. Furthermore, AD showed greater volume losses in the ERC than in the hippocampus (p<0.01). In addition, AD and MCI also had cortical grey matter loss (p< 0.01) and ventricular enlargement (p<0.01) when compared with NC. There was a significant correlation between ERC and hippocampal volumes in MCI and AD (both p<0.001), but not in NC. Using ERC and hippocampus together improved discrimination between AD and CN but did not improve discrimination between MCI and NC. The ERC was better than the hippocampus for distinguishing MCI from AD. In addition, loss of cortical grey matter significantly contributed to the hippocampus for discriminating MCI and AD from NC. CONCLUSIONS Volume reductions in the ERC and hippocampus may be early signs of AD pathology that can be measured using MRI.

The Uniform Data Set (UDS): Clinical and cognitive variables and descriptive data from Alzheimer disease centers

A Clinical Task Force, composed of clinical leaders from Alzheimers Disease Centers (ADC), was convened by the National Institute on Aging to develop a uniform set of assessment procedures to characterize individuals with mild Alzheimer disease and mild cognitive impairment in comparison with nondemented aging. The resulting Uniform Data Set (UDS) defines a common set of clinical observations to be collected longitudinally on ADC participants in accordance with standard methods. The UDS was implemented at all ADCs on September 1, 2005. Data obtained with the UDS are submitted to the National Alzheimers Coordinating Center and represent a unique and valuable source of data to support and stimulate collaborative research.

Blood-brain barrier breakdown in the aging human hippocampus.

UNLABELLED The blood-brain barrier (BBB) limits entry of blood-derived products, pathogens, and cells into the brain that is essential for normal neuronal functioning and information processing. Post-mortem tissue analysis indicates BBB damage in Alzheimers disease (AD). The timing of BBB breakdown remains, however, elusive. Using an advanced dynamic contrast-enhanced MRI protocol with high spatial and temporal resolutions to quantify regional BBB permeability in the living human brain, we show an age-dependent BBB breakdown in the hippocampus, a region critical for learning and memory that is affected early in AD. The BBB breakdown in the hippocampus and its CA1 and dentate gyrus subdivisions worsened with mild cognitive impairment that correlated with injury to BBB-associated pericytes, as shown by the cerebrospinal fluid analysis. Our data suggest that BBB breakdown is an early event in the aging human brain that begins in the hippocampus and may contribute to cognitive impairment. VIDEO ABSTRACT

Head injury and the risk of AD in the MIRAGE study

Objectives: It has been suggested in some studies that head injury is a risk factor for AD, and that this risk is heightened among carriers of the APOE-ε4 allele. We examined the effects of head injury and APOE genotype on AD risk in a large family study. Subjects: A total of 2,233 probands who met criteria for probable or definite AD and their 14,668 first-degree family members (4,465 parents, 7,694 siblings, and 2,509 spouses) were ascertained at 13 centers in the United States, Canada, and Germany participating in the MIRAGE (Multi-Institutional Research in Alzheimer Genetic Epidemiology) project. Information on head injury was collected by interview of multiple informants and review of medical records. Nondemented relatives and spouses served as control subjects for this study. Methods: Odds of AD for head trauma with or without loss of consciousness were computed by comparing probands with unaffected spouses using conditional logistic regression analysis. To account for the unique biologic relationship between probands and their parents and siblings, odds of AD were computed using a generalized estimating equation (GEE) Poisson regression approach. GEE logistic regression was used to examine the joint effects of APOE genotype and head injury on the odds of AD in probands and a control group comprised of unaffected siblings and spouses. Results: Comparison of probands with their unaffected spouses yielded odds ratios for AD of 9.9 (95% CI, 6.5 to 15.1) for head injury with loss of consciousness and 3.1 (2.3 to 4.0) for head injury without loss of consciousness. The corresponding odds derived from the comparison of probands with their parents and sibs were 4.0 (2.9 to 5.5) for head injury with loss of consciousness and 2.0 (1.5 to 2.7) for head injury without loss of consciousness. Head injury without loss of consciousness did not significantly increase the risk of AD in spouses (OR = 1.3; 95% CI, 0.4 to 4.1). The joint effects of head injury and APOE genotype were evaluated in a subsample of 942 probands and 327 controls (spouses and siblings). Head injury increased the odds of AD to a greater extent among those lacking ε4 (OR = 3.3) than among ε4 heterozygotes (OR = 1.8) or homozygotes (OR = 1.3). Conclusion: Head injury is a risk factor for AD. The magnitude of the risk is proportional to severity and heightened among first-degree relatives of AD patients. The influence of head injury on the risk of AD appears to be greater among persons lacking APOE-ε4 compared with those having one or two ε4 alleles, suggesting that these risk factors may have a common biologic underpinning.

The Alzheimer's Disease Centers' Uniform Data Set (UDS): the neuropsychologic test battery.

The neuropsychologic test battery from the Uniform Data Set (UDS) of the Alzheimers Disease Centers (ADC) program of the National Institute on Aging consists of brief measures of attention, processing speed, executive function, episodic memory, and language. This paper describes development of the battery and preliminary data from the initial UDS evaluation of 3268 clinically cognitively normal men and women collected over the first 24 months of utilization. The subjects represent a sample of community-dwelling, individuals who volunteer for studies of cognitive aging. Subjects were considered “clinically cognitively normal” based on clinical assessment, including the Clinical Dementia Rating scale and the Functional Assessment Questionnaire. The results demonstrate performance on tests sensitive to cognitive aging and to the early stages of Alzheimer disease in a relatively well-educated sample. Regression models investigating the impact of age, education, and sex on test scores indicate that these variables will need to be incorporated in subsequent normative studies. Future plans include: (1) determining the psychometric properties of the battery; (2) establishing normative data, including norms for different ethnic minority groups; and (3) conducting longitudinal studies on cognitively normal subjects, individuals with mild cognitive impairment, and individuals with Alzheimer disease and other forms of dementia.

Common variants at 7p21 are associated with frontotemporal lobar degeneration with TDP-43 inclusions

Frontotemporal lobar degeneration (FTLD) is the second most common cause of presenile dementia. The predominant neuropathology is FTLD with TAR DNA-binding protein (TDP-43) inclusions (FTLD-TDP). FTLD-TDP is frequently familial, resulting from mutations in GRN (which encodes progranulin). We assembled an international collaboration to identify susceptibility loci for FTLD-TDP through a genome-wide association study of 515 individuals with FTLD-TDP. We found that FTLD-TDP associates with multiple SNPs mapping to a single linkage disequilibrium block on 7p21 that contains TMEM106B. Three SNPs retained genome-wide significance following Bonferroni correction (top SNP rs1990622, P = 1.08 × 10−11; odds ratio, minor allele (C) 0.61, 95% CI 0.53–0.71). The association replicated in 89 FTLD-TDP cases (rs1990622; P = 2 × 10−4). TMEM106B variants may confer risk of FTLD-TDP by increasing TMEM106B expression. TMEM106B variants also contribute to genetic risk for FTLD-TDP in individuals with mutations in GRN. Our data implicate variants in TMEM106B as a strong risk factor for FTLD-TDP, suggesting an underlying pathogenic mechanism.

MRI predictors of cognition in subcortical ischemic vascular disease and Alzheimer's disease

Background: Causes of cognitive impairment in subcortical ischemic vascular disease (SIVD) are less well understood than in AD, but have been thought to result from direct effects of subcortical lacunes and white matter lesions, perhaps related to disruption of important cortical–subcortical pathways. Objective: To examine the relation between cognitive abilities and quantitative MRI measures of subcortical cerebrovascular disease and cortical and hippocampal atrophy. Methods: Subjects were 157 participants in a multicenter study of SIVD and AD who included cognitively normal, cognitively impaired, and demented individuals with and without subcortical lacunar infarcts. Dependent variables were neuropsychological tests of global cognitive function, memory, language, and executive function. Independent variables were quantitative MRI measures of volume of lacunar infarcts in specific subcortical structures, volume of white matter lesion (WML), volume of cortical gray matter (cGM), and total hippocampal volume (HV). Multiple regression analyses were used to identify MRI predictors of cognition. Results: Subcortical lacunes were not related to cognitive measures independent of effects of other MRI variables. WML was independently related to selected, timed measures. HV and cGM were strong and independent predictors of cognitive variables, with effects that did not differ in subjects with and without subcortical lacunes. Conclusions: Results suggest that cognitive impairment associated with subcortical ischemic vascular disease is primarily a result of associated hippocampal and cortical changes.

Risk of dementia among relatives of Alzheimer's disease patients in the MIRAGE study: What is in store for the oldest old?

Despite recent advances in the molecular genetics of Alzheimers disease (AD), several fundamental questions concerning risk of illness are unresolved, namely, if Mendelian factors account for the incidence of the disease, and if AD is an inevitable consequence of the aging process. This study was designed to address these issues and other aspects of familial aggregation of the disorder. A consecutive sample of 1,694 patients who met criteria for a diagnosis of probable or definite AD were ascertained in 13 centers participating in the Multi-Institutional Research in Alzheimer Genetic Epidemiology (MIRAGE) project. Lifetime risk and age at onset of AD among various strata of 12,971 first-degree relatives was estimated using survival analysis procedures. The lifetime risk of AD in first-degree relatives was 39.0% +/- 2.1% by age 96 years. Age-specific risk of AD declined after age 90 and the data set included 61 apparently unaffected persons who survived to age 96 without becoming demented. Female relatives had a higher risk of AD than male relatives at all ages. By age 80, children of conjugal AD couples had a cumulative risk of 54%, 1.5 times greater than the sum of the risks to children having affected mothers or fathers, and nearly 5 times greater than the risk to children having normal parents. Children of affected fathers had a cumulative risk that was 1.4 times the corresponding risk to children of affected mothers. Risk assessment in early-onset and late-onset families, using various strategies for determining the age cut-off, yielded contradictory results. These data suggest the following: (1) the lifetime risk among relatives does not support a simple autosomal dominant inheritance pattern of disease; (2) women are innately more susceptible to AD than men; (3) the proportion of hereditary cases may be higher in men than women; (4) distinction between early- onset and late-onset forms of AD has little meaning in the absence of a biological marker; (5) the risk of AD decreases after age 90; and (6) AD therefore may not be an inevitable concomitant of the aging process, a conclusion that has profound implications for basic and applied AD research. The age- and sex-specific lifetime risks derived from this study are sufficiently robust to be a reliable source of information for counseling relatives of AD patients.