Research and Alzheimer's disease: an epidemiological perspective

Synergistic Effects of APOE and CLU May Increase the Risk of Alzheimer's Disease: Acceleration of Atrophy in the Volumes and Shapes of the Hippocampus and Amygdala

BACKGROUND

The volume loss of the hippocampus and amygdala in non-demented individuals has been reported to increase the risk of developing Alzheimer's disease (AD). Many neuroimaging genetics studies mainly focused on the individual effects of APOE and CLU on neuroimaging to understand their neural mechanisms, whereas their synergistic effects have been rarely studied.

OBJECTIVE

To assess whether APOE and CLU have synergetic effects, we investigated the epistatic interaction and combined effects of the two genetic variants on morphological degeneration of hippocampus and amygdala in the non-demented elderly at baseline and 2-year follow-up.

METHODS

Besides the widely-used volume indicator, the surface-based morphometry method was also adopted in this study to evaluate shape alterations.

RESULTS

Our results showed a synergistic effect of homozygosity for the CLU risk allele C in rs11136000 and APOEɛ4 on the hippocampal and amygdalar volumes during a 2-year follow-up. Moreover, the combined effects of APOEɛ4 and CLU C were stronger than either of the individual effects in the atrophy progress of the amygdala.

CONCLUSION

These findings indicate that brain morphological changes are caused by more than one gene variant, which may help us to better understand the complex endogenous mechanism of AD.

Limbic-predominant age-related TDP-43 encephalopathy (LATE): consensus working group report

We describe a recently recognized disease entity, limbic-predominant age-related TDP-43 encephalopathy (LATE). LATE neuropathological change (LATE-NC) is defined by a stereotypical TDP-43 proteinopathy in older adults, with or without coexisting hippocampal sclerosis pathology. LATE-NC is a common TDP-43 proteinopathy, associated with an amnestic dementia syndrome that mimicked Alzheimer's-type dementia in retrospective autopsy studies. LATE is distinguished from frontotemporal lobar degeneration with TDP-43 pathology based on its epidemiology (LATE generally affects older subjects), and relatively restricted neuroanatomical distribution of TDP-43 proteinopathy. In community-based autopsy cohorts, ∼25% of brains had sufficient burden of LATE-NC to be associated with discernible cognitive impairment. Many subjects with LATE-NC have comorbid brain pathologies, often including amyloid-β plaques and tauopathy. Given that the 'oldest-old' are at greatest risk for LATE-NC, and subjects of advanced age constitute a rapidly growing demographic group in many countries, LATE has an expanding but under-recognized impact on public health. For these reasons, a working group was convened to develop diagnostic criteria for LATE, aiming both to stimulate research and to promote awareness of this pathway to dementia. We report consensus-based recommendations including guidelines for diagnosis and staging of LATE-NC. For routine autopsy workup of LATE-NC, an anatomically-based preliminary staging scheme is proposed with TDP-43 immunohistochemistry on tissue from three brain areas, reflecting a hierarchical pattern of brain involvement: amygdala, hippocampus, and middle frontal gyrus. LATE-NC appears to affect the medial temporal lobe structures preferentially, but other areas also are impacted. Neuroimaging studies demonstrated that subjects with LATE-NC also had atrophy in the medial temporal lobes, frontal cortex, and other brain regions. Genetic studies have thus far indicated five genes with risk alleles for LATE-NC: GRN, TMEM106B, ABCC9, KCNMB2, and APOE. The discovery of these genetic risk variants indicate that LATE shares pathogenetic mechanisms with both frontotemporal lobar degeneration and Alzheimer's disease, but also suggests disease-specific underlying mechanisms. Large gaps remain in our understanding of LATE. For advances in prevention, diagnosis, and treatment, there is an urgent need for research focused on LATE, including in vitro and animal models. An obstacle to clinical progress is lack of diagnostic tools, such as biofluid or neuroimaging biomarkers, for ante-mortem detection of LATE. Development of a disease biomarker would augment observational studies seeking to further define the risk factors, natural history, and clinical features of LATE, as well as eventual subject recruitment for targeted therapies in clinical trials.

Smoking and Risk for Alzheimer Disease: A Meta-Analysis Based on Both Case-Control and Cohort Study

This study was performed to identify the association between smoking and Alzheimer's disease (AD). To perform this meta-analysis based on case-control and cohort studies, PubMed, Google Scholar, and the CNKI electronic databases were searched through April 30, 2017. Our meta-analysis included 27 studies, including 16 that reported odds ratios (ORs) and 11 that reported hazard ratios (HRs) or ratio risks. No significant association was found between smoking and AD among the studies that reported ORs (1.020, 95% confidence interval [CI] = 0.812-1.281, I = 67.9%, random model, p < 0.001). A subgroup analysis revealed no significant difference between different smoking statuses. The pooled HRs revealed a significant association between smoking and AD (HR = 1.520, 95% CI = 1.194-1.934, I = 83.6%, random model, p < 0.001). Cumulative meta-analysis of the HRs revealed that the effect of smoking on AD tended to be stable over time. Smoking may confer an increased risk of AD, and this effect has tended to be stable over time.

Evolution of social networks: the example of obesity

The present paper deals with the effect of the social transmission of nutrition habits in a social and biological age-dependent context on obesity, and accordingly on type II diabetes and among its complications, the neurodegenerative diseases. The evolution of social networks and inside a network the healthy weight of a person are depending on the context in which this person has contacts and exchanges concerning his alimentation, physical activity and sedentary habits, inside the dominant social network in which the person lives (e.g., scholar for young, professional for adult, home or institution for elderly people). Three successive steps of evolution will be considered for social networks (like for neural one's): initial random connectivity, destruction and consolidation of links following a new transition rule called homophilic until an asymptotic architectural organization and configuration of states. The application of such a network dynamics concerns the sequence overweight/obesity/type II diabetes and neurodegenerative diseases.

The epidemiology of delirium: challenges and opportunities for population studies

Delirium is a serious and common acute neuropsychiatric syndrome that is associated with short- and long-term adverse health outcomes. However, relatively little delirium research has been conducted in unselected populations. Epidemiologic research in such populations has the potential to resolve several questions of clinical significance in delirium. Part 1 of this article explores the importance of population selection, case-ascertainment, attrition, and confounding. Part 2 examines a specific question in delirium epidemiology: What is the relationship between delirium and trajectories of cognitive decline? This section assesses previous work through two systematic reviews and proposes a design for investigating delirium in the context of longitudinal cohort studies. Such a design requires robust links between community and hospital settings. Practical considerations for case-ascertainment in the hospital, as well as the necessary quality control of these programs, are outlined. We argue that attention to these factors is important if delirium research is to benefit fully from a population perspective.

Relationships between the amyloid precursor protein and its various proteolytic fragments and neuronal systems

Alzheimer's disease (AD) is a progressive neurodegenerative disease and in its familial form is associated with mutations in the amyloid precursor protein (APP) and the presenilins (PSs). Much data regarding the interactions of APP, its proteolytic fragments and PS have been generated, expanding our understanding of the roles of these proteins in mechanisms underlying cognitive function and revealing many complex relationships with wide ranging cellular systems. In this review, we examine the multiple interactions of APP and its proteolytic fragments with other neuronal systems in terms of feedback loops and use these relationships to build a map. We highlight the complexity involved in the APP proteolytic system and discuss alternative perspectives on the roles of APP and its proteolytic fragments in dynamic processes associated with disease progression in AD. We highlight areas where data are missing and suggest potential confounding factors. We suggest that a systems biology approach enhances representations of the data and may be more useful in modelling both normal cognition and disease processes.

Aging, Neurodegenerative Disease and the Brain

L'eorganisation anatomique et chimique du cerveau humain subit de nombreux changements au cours du vieillissement. Certains neurons meurent, d'autres s'atrophient et ily a une réduction marquée du nombre de synapses dans des régions spécifiques du cerveau. Des diminutions du métabolisme du glucose et des effets pré- et post-synaptiques des neurotransmetteurs ont aussi été rapportées. À l'exception de certaines structures sous-corticales, il existe cependant une controverse quant à la sévérité des changements dans l'ensemble du cerveau. De plus, les effets du vieillissement sont très variables d'une région du cerveau à l'autre ainsi que d'un individu à l'autre. Certains phénomènes observès dans le vieillissement normal, tels la perte des neurones dopaminergique de la substance noire et celle des neurones cholinergiques du prosencé;phale basal, apparaissent sous une forme grandement exacerbées dans diverses pathologies neurodégénératives comme les maladies de Parkinson et d'Alzeimer. Les faibles altérations qui surviennent au niveau de ces systémes lors du vieillissement normal pourraient étre responsables des troubles d'équilibre, de la pauvreté de mouvement et des pertes de mémoires que l'on observent chez les gens âgés. Cependant, l'inflammation chronique du cerveau semble être une caractéristique typique des individus atteints de maladies neurodégénératives. L'hypothèse voulant que cette inflammation puisse être ralentie par un traitement avec des agents anti-inflammatoires a été supportée par les résultats de 19 études épidémiologiques ainsi que par un essai clinique de moindre envergure. Cependant, d'Autres études cliniques devront ètre réalisées et une attention particulière devra être portée aux effets secondaires de la thérapie anti-inflammatoire conventionnelle afin d'en arriver à une conclusion définitive.

Time for a change in the research paradigm for Alzheimer's disease: the value of a chaotic matrix modeling approach

The amyloid cascade hypothesis, based on the genetic data from early onset, familial forms of the disease, has been the dominant model for many years and involves over production and deposition of the beta amyloid protein as causal in the disease process. However, it does not apply very well to the more common, later onset, sporadic form of the disease, where a wider range of factors appear to be involved in disease progression. Over recent years, data illustrating reciprocal interactions between the amyloid precursor protein (APP) and its various metabolites with many factors involved in normal synaptic plasticity have emerged. These feedback relationships have the potential to affect the complex kinase cascades involved in every aspect of neuronal function. Further, data regarding the multiple roles of the presenilins have the potential to allow the over expression and deposition of the amyloid beta protein to be both a cause and consequence of disease progression, with relevance in both sporadic and familial of Alzheimer's disease (AD). Disease progression might be better explained by a chaotic matrix of factors and raises the question again whether AD should be approached as a single entity or as a syndrome, with important consequences for disease identification and treatment.

The elephant in the room - healthy brains in later life, epidemiology and public health

The increasing age of the population around the world has meant that greater attention is being paid to disorders that mainly affect older people. In particular, work is focusing on ways to preserve the healthy brain and prevent dementia. Preventive studies are complex and must take into account not only simple approaches such as those used in risk and outcome studies, but also stage of life, survival and mortality, and population context before their effect can be assessed. This paper presents questions and areas which must be explored if the potential for prevention of dementia during brain ageing is to be properly understood.

Are tobacco and alcohol use related to Alzheimer's disease? A critical assessment of the evidence and its implications

Elucidation of the association of tobacco and alcohol use with Alzheimer's disease (AD) may advance etiological hypotheses and provide a theoretical basis for treatment. There is currently no cure or effective treatment for AD, and no cause has been established. Pharmacological evidence supports a plausible biological mechanism for the involvement of tobacco use: nicotine compensates for some of the cholinergic deficits observed in AD. Epidemiological evidence, however, is inconsistent, although recent meta-analyses also support a protective effect. Although smoking per se is certainly not advocated, further investigation of a potential protective effect of nicotine on AD is warranted. Pharmacological studies implicate alcohol use as a possible risk factor for AD; the epidemiological studies are again inconclusive. Alcohol consumption is associated with daily smoking and smokers are, in turn, more likely to consume alcohol. Since tobacco use may decrease the risk of developing AD and alcohol use may increase it, it is important to consider these two substances together: the effect of one may negate the other. This literature review critically evaluates the evidence for an association of tobacco and alcohol use with AD and identifies key issues for further research.

Risk factors for Alzheimer's disease: a population-based, longitudinal study in Manitoba, Canada

BACKGROUND

Current knowledge of risk factors for Alzheimer's disease (AD) is limited. Data from a longitudinal, population-based study of dementia in Manitoba, Canada were used to investigate risk factors for AD.

METHODS

Cognitively intact subjects completed a risk factor questionnaire assessing sociodemographic, genetic, environmental, medical and lifestyle exposures. Five years later, 36 subjects had developed AD and 658 remained cognitively intact.

RESULTS

Older subjects or those who had fewer years of education were at greater risk of AD. After adjusting for age, education and sex, occupational exposure to fumigants/ defoliants was a significant risk factor for AD (relative risk [RR] = 4.35; 95% CI : 1.05--17.90). A history of migraines increased the risk of AD (RR = 3.49; 95% CI : 1.39--8.77); an even stronger effect was noted among women. Self-reported memory loss at baseline was associated with subsequent development of AD (RR = 5.15; 95% CI : 2.36--11.27). Vaccinations and occupational exposure to excessive noise reduced the risk of AD.

CONCLUSIONS

Some well-known risk factors for AD were confirmed in this study and potential new risk factors were identified. The association of AD with a history of migraines and occupational exposure to defoliants/fumigants is of particular interest because these are biologically plausible risk factors.

Alzheimer's disease: insights from epidemiology

While a complete understanding of the pathogenesis of Alzheimer's disease (AD) remains elusive, many conclusions can be drawn from the numerous epidemiological studies undertaken to date. Prevalence and incidence estimates show consistency, following a roughly exponential pattern with a doubling of both parameters roughly every five years after age 65. Roughly 7% of the population aged 65 and over has AD. The clinical course of the disease is reasonably well established and mortality rates rise with increasing levels of cognitive deficit. Four risk factors for AD are firmly established: increasing age, the presence of the apolipoproteinE-epsilon4 allele, familial aggregation of cases, and Down's syndrome. Numerous other associations have been shown in some studies, but not in others. For example, women generally appear at higher risk than men, as do people with lower levels of education; depression is probably prodromal; head injury is an established risk factor, and may interact with the apoE gene; several occupational exposures appear hazardous, and exposure to aluminum in the water supply confers excess risk. Hypertension and other vascular symptoms appear to predispose to AD, which is now seen as nosologically closer to vascular dementia than was previously believed. Several apparently protective factors have been identified, although preventive trials based on these have so far shown minimal effectiveness. The use of non-steroidal anti-inflammatory drugs to treat arthritis is associated with a reduced risk of AD, as is estrogen use by post-menopausal women. Physical activity appears beneficial, as does a diet with high levels of vitamins B6, B12 and folate. while red wine in moderate quantities appears protective. This review concludes with a discussion of the strengths and limitations of current epidemiological methods for studying Alzheimer's disease.

Is smoking associated with the risk of developing Alzheimer's disease? Results from three Canadian data sets

PURPOSE

To determine whether smoking is associated with Alzheimer's disease (AD).

METHODS

Analyses were conducted using three Canadian data sets: the University of Western Ontario Dementia Study (200 cases, 163 controls), the Canadian Study of Health and Aging (258 cases, 258 controls), and the patient database from the Clinic for Alzheimer Disease and Related Disorders at the Vancouver Hospital and Health Sciences Centre (566 cases, 277 controls). The association between smoking and AD was investigated using bivariate analyses and multiple logistic regression models adjusted for the potential confounders age, sex, educational level, family history of dementia, head injury, and hypertension.

RESULTS

The results of bivariate analyses were inconsistent across the three data sets, with smoking status a significant protective factor, a significant risk factor, or not associated with AD. The results of multiple logistic regression models, however, were consistent: any association between smoking status and AD disappeared in all three data sets after adjustment for confounders.

CONCLUSIONS

Smoking status was consistently not associated with AD across all three data sets after adjustment for confounders. Failure to adjust for relevant confounders may explain inconsistent reports of the influence of smoking on AD. Any protective effect of smoking may be limited to specific AD subtypes (e.g., early onset AD).

Does an interaction between smoking and drinking influence the risk of Alzheimer's disease? Results from three Canadian data sets

Investigation of the relationship of smoking and drinking to Alzheimer's disease (AD) may advance research on the cause of AD and provide a basis for treatment. Pharmacological mechanisms for an involvement of smoking and drinking are plausible but epidemiologic reports are inconsistent. Evidence of behavioural and physiological interactions suggests that tobacco and alcohol use may not only individually affect AD, but may also modify each other's effects. A modelling strategy was developed to examine the interaction between smoking and drinking on the risk of AD. Three Canadian data sets were analysed: the University of Western Ontario Dementia Study (UWODS) (n=363); the Canadian Study of Health and Aging (CSHA) (n=516), and the database from the Clinic for Alzheimer Disease and Related Disorders at the Vancouver Hospital and Health Sciences Centre, University of British Columbia site (UBC) (n=843). Multiple logistic regression models were adjusted for the potential confounders age, age squared, sex, education, family history of dementia, head injury and hypertension. Analysis of the CSHA provided evidence consistent with the hypothesis that smoking and drinking influence each other's effects on AD, with smoking reducing the risk of AD among drinkers. A similar interaction was marginally significant (p=0.052) in the UWODS data set, but not significant in the UBC data. Extension of these analyses, particularly in longitudinal studies and within genetic risk groups, is needed to determine whether this interaction can be replicated. If so, research on the biological interactions of nicotine and alcohol may provide a basis for the development of therapeutic interventions as well as providing clues to the cause of this disorder.

Effects of literacy and education on measures of word fluency

As part of a cross-national study of dementia epidemiology, two types of verbal fluency tasks were administered to three groups of subjects, varying in level of literacy and education, recruited from the rural district of Ballabgarh in northern India. Subjects were asked to list items in a given semantic category (animals; fruits) or words beginning with a given sound (the phonemes /p/ and /s/) the latter being a minor modification of the more familiar initial letter fluency task in view of the high prevalence of illiteracy in Ballabgarh. Analysis of variance revealed main effects of education and task with a task by education interaction such that education had a greater effect on initial sound fluency than on category fluency. The results are discussed in terms of their implication for the design of cross-cultural studies and the evidence that the ability to segment speech into phonemic units is dependent on literacy.

Dementia in old age: an anthropological perspective

This paper examines the assumption that dementia in old age is a universal phenomenon that will vary in its prevalence and manifestation because of social and cultural factors. It finds that while researchers have been successful in demonstrating the commonality of dementia, they have been less successful in showing whether or not it varies across cultures and between social and ethnic groupings. The inconclusiveness of findings may, in part, be a function of diagnostic differences and the research methodologies employed. New instruments and measures are being devised to overcome these problems. However, the sociocultural context in which dementia occurs and the meaning of the disorder to those involved (as sufferers and caregivers) are often missing dimensions. In particular, there is little knowledge about how the disorders of old age in non-Western settings are experienced and understood. In this respect anthropology has a special contribution to make to research on dementia.

The relationship between clinical dementia and neuropathological staging (Braak) in a very elderly community sample

The neuropathological staging model proposed by Braak and Braak (1991) implies that the evolution of neurofibrillary pathology follows a predictable sequence and can be ordered in a regular regional hierarchy. A total of 42 cases of an elderly population sample, which had been prospectively clinically assessed, were examined. Clinical diagnosis was made according to the CAMDEX criteria, and the sample reported here did not include cases were vascular dementia according to the criteria proposed by Chui et al. (1991). The neuropathological staging procedure was applied as originally proposed by Braak and Braak (1991). In addition, in all cortical laminae and regions which are essential for the staging model neurofibrillary tangles were quantified. Demented cases had significantly more areas involved and more advanced neuropathological stages. Cases with stages 1-3 tended to be non-demented, and cases with stages 4-6 tended to be demented. However, there was a considerable degree of overlap and no clear-cut threshold could be established. This brings into question the diagnostic value of the staging model.

Dementia and age at death

The objective of this paper is to investigate changes in dementia mortality, as recorded on death certificates in Canada. Use is made of data available at Statistics Canada for the period 1990-1991. During this period there have been appreciable changes over time in the ages at death and in the percentage of death certificates that mention dementia. This increase in mortality associated with dementia can be explained, in large part, by an increased tendency for dementia to be listed as an underlying cause of death on the death certificate. Also, the median ages at death of persons in Canada for the period 1990-1991, for whom dementia is recorded as the underlying cause of death, are similar to or greater than the ages at death reported for all other causes of death but excluding dementia. Because those who have dementia are living longer, there is an increase in the number of people with dementia (prevalence of dementia); this has important implications concerning public policy on health and aging. We discuss the significance of these changes with respect to the future prevalence of dementia.

ICD-10 mild cognitive disorder: epidemiological evidence on its validity

Criteria for the diagnosis of ICD-10 Mild Cognitive Disorder (MCD) were applied to a sample of 897 community dwelling elderly participants. Criterion A (the presence of a physical disorder) was met by 44%, Criterion B (report of a cognitive disorder) by 17%, Criterion C (an abnormality in quantified cognitive assessments) by 60%, and Criterion D (exclusion on basis of dementia and other conditions) by 74%. A total of 36 cases (4%) met all four criteria. Correlations between Criteria A and B, and B and C were weak (r = 0.18), and the correlation between Criteria A and C was almost zero (r = 0.02). This suggests that no syndrome exists. Membership of MCD was predicted by a report that memory or intelligence interfered with daily life but not by performance on cognitive tests or by a report of physical illness. Cases of MCD had higher anxiety, depression and neuroticism scores than normal elderly, but did not differ substantially on tests of cognitive functioning. These findings call into question the validity of the ICD-10 diagnosis of MCD.

Studies of the epidemiology of dementia: comparisons between developed and developing countries

By the year 2025, 68% of the world's population aged 65 and above, nearly 277 million people, will be residing in developing countries. The less industrialized nations have been the least studied to date, and may yield significant new information about the etiology and risk factors for Alzheimer's disease (AD) and other dementias. Although it is readily apparent that cross-national and cross-cultural comparisons are desirable, these can be meaningful only if based on comparable methodology. In this work we will discuss some general conceptual and methodological issues regarding epidemiological studies of dementia in developing countries. The topics discussed include community-based screening for dementia, screening instruments and their application in cross-cultural studies, steps in standardization of new or modified neuropsychological tests, and some special considerations in studying uneducated/illiterate populations.

Assessing cognitive abilities and dementia in a predominantly illiterate population of older individuals in Kinmen

A community survey of dementia was conducted on a Chinese islet. A total of 221 men and 234 women in the age range of 50-92 were assessed. The Cognitive Abilities Screening Instrument (CASI), a 100-point cognitive test designed for cross-cultural studies and adapted in Chinese for individuals with little or no formal education, was administered twice by trained field workers with a retest interval of 3 to 4 weeks. In addition, all participants were assessed by physicians who did not know the CASI scores. The physicians' assessment included a complete neurological examination, plus semi-structured tests and interviews covering cognitive abilities, daily activities, depression, cerebrovascular disease, and Parkinson's disease. Dementia was diagnosed by consensus among the physicians according to the DSM-III-R criteria. Among the 455 participants, 16 cases of dementia were identified, including 13 with probable Alzheimer's disease and 1 each with vascular dementia, Parkinson's disease, and alcoholism. The rates of dementia were 0, 3.9 and 11.5% for the age groups of 50-69, 70-79 and 80-92; and 4.4, 2.0 and 0% for the education groups of 0-1, 2-6 and 7-15 years of schooling. No sex difference was found after controlling for education. The Chinese version of the CASI had an intraclass retest reliability of 0.90. Using a cut-off score of < or = 50 for dementia, the sensitivity was 0.88 and the specificity was 0.94. The preliminary study suggests that the CASI can be used in Chinese populations with generally low education levels and that Alzheimer's disease was the most common type of dementia in this population.