Modeling the prevalence and incidence of Alzheimer's disease and mild cognitive impairment

Hearing Loss and Alzheimer Disease

Several studies have been done to investigate the role of hearing loss (HL) in cognitive decline. A co-existence of these two conditions has been identified. Recently, thanks to the use of functional MRI and EEG it has been shown that untreated HL can expose patients with cognitive decline to a higher risk of developing Alzheimer Disease (AD). This chapter will discuss the difference between central and peripheral HL, the link between HL and cognition and the relationship between HL and AD. At the end of the chapter the available technologies to treat HL will be discussed as well as their impact on memory and cognition.

Development and Validation of the Communities Geriatric Mild Cognitive Impairment Risk Calculator (CGMCI-Risk)

Objectives: The aim was to develop and validate the Communities Geriatric Mild Cognitive Impairment Risk Calculator (CGMCI-Risk), aiding community healthcare workers in the early identification of individuals at high risk of mild cognitive impairment (MCI). Methods: Based on nationally representative community survey data, backward stepwise regression was employed to screen the variables, and logistic regression was utilized to construct the CGMCI-Risk. Internal validation was conducted using bootstrap resampling, while external validation was performed using temporal validation. The area under the receiver operating characteristic curve (AUROC), calibration curve, and decision curve analysis (DCA) were employed to evaluate the CGMCI-Risk in terms of discrimination, calibration, and net benefit, respectively. Results: The CGMCI-Risk model included variables such as age, educational level, sex, exercise, garden work, TV watching or radio listening, Instrumental Activity of Daily Living (IADL), hearing, and masticatory function. The AUROC was 0.781 (95% CI = 0.766 to 0.796). The calibration curve showed strong agreement, and the DCA suggested substantial clinical utility. In external validation, the CGMCI-Risk model maintained a similar performance with an AUROC of 0.782 (95% CI = 0.763 to 0.801). Conclusions: CGMCI-Risk is an effective tool for assessing cognitive function risk within the community. It uses readily predictor variables, allowing community healthcare workers to identify the risk of MCI in older adults over a three-year span.

Community Senior Center Intervention to Address Factors Related to Memory Screening Engagement

There are many individual and societal benefits to screen older adults for memory problems. Four theoretically derived psychosocial factors are predictive of dementia screening intention: perceived benefits, perceived susceptibility, self-efficacy, and knowledge about memory. The current study tested whether these factors could be modified with an educational memory screening intervention given in community senior centers. An educational presentation was designed to address these factors by increasing knowledge about memory and aging, discussing the benefits of screening and older adults' susceptibility to memory issues, and increasing self-efficacy by teaching about the memory screening process, discussing a vignette, and fielding participants' questions. The educational presentation was offered four times at three community senior centers. Quantitative data on the psychosocial factors were collected before and after the presentation from 44 older adult participants (age M = 78.70, SD = 7.21). Narrative data on satisfaction and feedback about the intervention were collected. Hierarchical linear modeling analyses were performed to measure change from pre- to post-presentation and follow-up 1 to 2 weeks after the intervention. The educational presentation effectively increased knowledge about aging memory, perceived benefits of screenings, and self-efficacy to seek screening. The presentation intervention was well received by community participants. Results provide guidance about how an intervention based in community senior centers can be refined to address factors predictive of memory screening intention in older adults.

Mitigating effects and mechanisms of Tai Chi on mild cognitive impairment in the elderly

Mild cognitive impairment (MCI) is a major public health concern that endangers health and decreases the quality of life of the elderly around the world. A recent clinical guideline has recommended regular exercise (twice per week) for patients with MCI as part of an overall approach to management. Tai Chi, a form of light-to-moderate-intensity mind-body exercise, is particularly suitable for seniors. This review aims to summarize epidemiological studies related to the effects of Tai Chi on symptom remission in older adults with MCI and reveal the potential mechanisms. Evidence suggested that Tai Chi can improve cognitive functions and alleviate the accompanying symptoms of MCI in the elderly potentially by activating the expression of signals in different brain regions, altering their connectivity, increasing the brain volume, and modulating brain-derived neurotropic and inflammation factors. Studies comparing various types of Tai Chi may contribute to the identification of paradigms that have appropriate intensities and difficulty and exert good effects on older people with MCI. In addition, studies are warranted to determine the frequency and duration of training that can optimize the beneficial effects of Tai Chi on MCI.

THE EFFICACY OF PHYSICAL EXERCISE ON CORTICAL ACTIVITY MODULATION IN MILD COGNITIVE IMPAIRMENT: A SYSTEMATIC REVIEW

OBJECTIVE

To investigate the effects of physical exercise on cortical activity measured via EEG in individuals with Mild Cognitive Impairment (MCI).

DATA SOURCES

Pubmed, Web of Science, PsycINFO, Scielo databases were searched, using: "physical exercise"; "physical activity"; "physical therapy"; "exercise"; "training"; "electroencephalogram"; "electroencephalography"; "EEG"; "mild cognitive impairment"; "cognitive dysfunction"; "MCI". PRISMA statement was followed and the PEDro scale was used to assess the risk of bias of each study.

STUDY SELECTION

Original articles, sample including individuals with MCI, physical exercise intervention, use of EEG to measure cortical activity.

DATA EXTRACTION

Sample characteristics, physical exercise protocol characteristics, results related to effects of physical exercise on parameters derived from EEG signals and on other cognitive assessments, strengths, limitations and conclusions of the studies were selected by two investigators.

DATA SYNTHESIS

365 articles were identified in electronic databases. After the selection stage, seven studies were included. Although there was a large spectrum of type of exercise (aerobic, resistance, multimodal, exergames and combined exercise with cognitive training), all exercise protocols altered cortical activity in MCI patients. An exercise session (acute response) causes power reduction of delta band and increases complexity and P300 amplitude in resting-state EEG. After an intervention with an exercise program (chronic response), there was a reduction in the power of delta and theta bands and an increase in beta and alpha bands, as well an increase in complexity in resting-state EEG.

CONCLUSIONS

Physical exercise seems to play a role in cortical activity in MCI patients, suggesting neural plasticity in such individuals.

Is Korea Prepared for an Alzheimer's Disease-Modifying Therapy? Assessing the Korean Healthcare System Infrastructure and the Effect of Blood-Based Biomarker Tests

Background

With the rapid demographic change in Korea, Alzheimer’s disease has become a primary concern. Recent developments in disease-modifying therapies provide hope that therapy may become available soon. The high disease prevalence and complex evaluation process will create challenges for the healthcare system already burdened by the current pandemic. This study examined the preparedness of the South Korean healthcare system to identify and treat patients when such a therapy becomes available.

Methods

We used a Markov model to simulate a stylized patient’s journey. Based on national data and expert input, we presented projections of the diagnosis and treatment wait times and respective queues of patients under treatment and no-treatment scenarios and further simulated the possible option of adopting a blood-based biomarker test.

Results

Under the current system, we estimated a peak waiting time of 14 months when a treatment became available, largely because of the limited number of dementia specialists. Adopting a blood-based biomarker test dramatically reduced the initial wait times by more than half. A disease-modifying therapy was estimated to avert 575,000 incident cases in the first 10 years after the treatment entered the market, and a blood-based test further avoided 86,000 additional cases.

Conclusion

South Korea’s healthcare infrastructure requires more preparation for the introduction of a disease-modifying therapy, with the primary capacity limitation being the low number of dementia specialists. The utilization of a blood-based test for Alzheimer’s disease biomarkers may be an effective solution.

Water Loss in Aging Erythrocytes Provides a Clue to a General Mechanism of Cellular Senescence

Experimental evidence for age-dependent loss of intracellular water content as a widespread concomitant of cellular senescence is reviewed. Quantitative models are presented, indicating that an age-dependent increase in macromolecular crowding resulting from water loss may be responsible for three observed phenomena: a general age-dependent loss of intracellular protein solubility, a delayed and rapid appearance of high molecular weight aggregates, and an age-dependent transfer of intracellular protein from dilute to concentrated or condensed phases.

Study Protocol - Insight 46 Cardiovascular: A Sub-study of the MRC National Survey of Health and Development

The commonest causes of dementia are Alzheimer's disease and vascular cognitive impairment. Although these conditions have been viewed as distinct entities, there is increasing evidence that neurodegenerative and vascular pathologies interact or overlap to cause cognitive decline, and that at least in some cases individuals at risk of cognitive decline exhibit abnormal cardiovascular physiology long before emergence of disease. However, the mechanisms linking haemodynamic disturbances with cognitive impairment and the various pathologies that cause dementia are poorly understood. A sub-sample of 502 participants from the Medical Research Council National Survey of Health and Development (NSHD) have participated in the first visit of a neuroscience sub-study referred to as Insight 46, where clinical, cognitive, imaging, and lifestyle data have been collected for the purpose of elucidating the pathological changes preceding dementia. This paper outlines the cardiovascular phenotyping performed in the follow-up visit of Insight 46, with the study participants now aged 74. In addition to standard cardiovascular assessments such as blood pressure measurements, echocardiography, and electrocardiography (ECG), functional Near Infrared Spectroscopy (fNIRS) has been included to provide an assessment of cerebrovascular function. A detailed description of the fNIRS protocol along with preliminary results from pilot data is presented. The combination of lifestyle data, brain structure/function, cognitive performance, and cardiovascular health obtained not only from Insight 46, but also from the whole NSHD provides an exciting opportunity to advance our understanding of the cardiovascular mechanisms underlying dementia and cognitive decline, and identify novel targets for intervention.

Targeted Metabolic Profiling of Urine Highlights a Potential Biomarker Panel for the Diagnosis of Alzheimer's Disease and Mild Cognitive Impairment: A Pilot Study

The lack of sensitive and specific biomarkers for the early detection of mild cognitive impairment (MCI) and Alzheimer’s disease (AD) is a major hurdle to improving patient management. A targeted, quantitative metabolomics approach using both ¹H NMR and mass spectrometry was employed to investigate the performance of urine metabolites as potential biomarkers for MCI and AD. Correlation-based feature selection (CFS) and least absolute shrinkage and selection operator (LASSO) methods were used to develop biomarker panels tested using support vector machine (SVM) and logistic regression models for diagnosis of each disease state. Metabolic changes were investigated to identify which biochemical pathways were perturbed as a direct result of MCI and AD in urine. Using SVM, we developed a model with 94% sensitivity, 78% specificity, and 78% AUC to distinguish healthy controls from AD sufferers. Using logistic regression, we developed a model with 85% sensitivity, 86% specificity, and an AUC of 82% for AD diagnosis as compared to cognitively healthy controls. Further, we identified 11 urinary metabolites that were significantly altered to include glucose, guanidinoacetate, urocanate, hippuric acid, cytosine, 2- and 3-hydroxyisovalerate, 2-ketoisovalerate, tryptophan, trimethylamine N oxide, and malonate in AD patients, which are also capable of diagnosing MCI, with a sensitivity value of 76%, specificity of 75%, and accuracy of 81% as compared to healthy controls. This pilot study suggests that urine metabolomics may be useful for developing a test capable of diagnosing and distinguishing MCI and AD from cognitively healthy controls.

Blood-based biomarkers for Alzheimer's pathology and the diagnostic process for a disease-modifying treatment: Projecting the impact on the cost and wait times

INTRODUCTION

Concerns have been raised about the limited health system capacity for identification of patients who are eligible for a disease-modifying Alzheimer's treatment (DMT). Blood-based biomarker (BBBM) tests are a promising tool to improve triaging at the primary care level. We projected their impact on cost of and wait times during the diagnostic process.

METHODS

We compare four scenarios for triaging patients at the primary care level from the perspective of the U.S. health care system: (1) cognitive test only (Mini Mental State Examination [MMSE]), (2) BBBM test only, (3) MMSE followed by BBBM if positive, and (4) BBBM followed by MMSE if positive.

RESULTS

Referring patients to dementa specialists based on MMSE or BBBM results alone would continuously require more specialist appointments than projected to be available until 2050. Combining MMSE and BBBM would eliminate wait lists after the first 3 years and reduce average annual cost by $400 to 700 million, while increasing correctly identified cases by about 120,000 per year.

DISCUSSION

The combination BBBM with MMSE is projected to increase the efficiency and value of the triage process for DMT eligibility.

Distribution and clinical impact of apolipoprotein E4 in subjective memory impairment and early mild cognitive impairment

The apolipoprotein E (APOE) e4 allele is the most common genetic variant associated with Alzheimer’s disease (AD). We sought to investigate the distribution of APOE genotypes across the full clinical AD spectrum including AD, late-stage amnestic mild cognitive impairment (L-aMCI), early-stage aMCI (E-aMCI), subjective memory impairment (SMI), and controls. We prospectively recruited 713 AD patients, 735 aMCI patients, 575 SMI patients, and 8,260 individuals as controls. The frequency of the APOE e4 allele revealed an ordered fashion in the AD (30.8%), L-aMCI (24.0%), E-aMCI (15.1%), SMI (11.7%), and control (9.1%) groups. APOE e3/e4 and e4/e4 genotype frequencies also appeared in an ordered fashion in the AD group (39.1% of e3/e4 and 10.9% of e4/e4), as well as the L-aMCI (28.3% and 9.4%), E-aMCI (22.3% and 3.7%), SMI (18.3% and 1.9%), and control (15.1% and 0.8%) groups. In the comparisons of APOE e3/e3 vs. e3/e4 genotypes, all patient groups had a higher frequency of APOE e3/e4 relative to the control group. Relative to the SMI and E-aMCI groups, the AD and L-aMCI groups had higher frequency of the APOE e3/e4 genotype, and the AD group had a higher frequency relative to the L-aMCI group. However, there was no significant difference between the E-aMCI and SMI groups. In our longitudinal data, APOE e4 carrier showed a steeper incline slope in a clinical dementia rating sum of boxes (CDR-SB) score than APOE e4 non-carrier in SMI (B = 0.0066, p = 0.0104), E-aMCI (B = 0.0313, p < 0.0001), and L-aMCI (B = 0.0178, p = 0.0007). APOE e4 carrier showed a steeper decline slope in the CDR-SB than APOE e4 non-carrier in AD (B = − 0.0309, p = 0.0003). These findings suggest that E-aMCI and SMI are associated with a similarly increased frequency of the APOE e4 allele compared to controls, suggesting a greater genetic risk for AD and the importance of monitoring the allele more closely.

Flemish Normative Data for the Buschke Selective Reminding Test

The purpose of this study was to provide normative data for a Flemish version of the Buschke Selective Reminding Test (SRT). The SRT allows for the simultaneous analysis of several components of verbal memory, such as short and long term retrieval. The Flemish SRT was administered to 3257 neurologically healthy adults (1627 men and 1630 women, age range = 18-94 years). Effects of age, sex and education on SRT performance were assessed. Results indicate that SRT performance decreased with age and that this decline accelerated in men compared to women. Furthermore, an effect of education was found favoring participants who completed a higher education. Normative data quantified through percentile ranks and stratified by age, sex and education level are provided.

Can cochlear implantation improve neurocognition in the aging population?

Introduction

The relationship between cognition and the ability to hear is well known. Due to changes in demographics, the number of people with sensorineural hearing loss and cognitive impairment is increasing. The aim of this study was to identify the impact of hearing rehabilitation via cochlear implantation on cognitive decline among the aging population.

Patients and methods

This prospective study included 60 subjects aged between 50 and 84 years (mean 65.8 years, SD=8.9) with a severe to profound bilateral hearing impairment. A computer-based evaluation of short- and long-term memory, processing speed, attention, working memory and inhibition was performed prior to surgery as well as 6 and 12 months after cochlear implantation. Additionally, speech perception at 65 and 80 dB (Freiburger monosyllabic speech test) as well as disease-related (Nijmegen Cochlear Implant Questionnaire) and general (WHOQOL-OLD) quality of life were assessed.

Results

Six months postimplantation, speech perception, quality of life and also neurocognitive abilities significantly increased. The most remarkable improvement after 6 months was detected in executive functions such as attention (p<0.001), inhibition (p=0.025) and working memory (n-back: p=0.002; operation span task: p=0.008), followed by delayed recall (p=0.03). In contrast, long-term memory showed a significant change of performance only after 12 months (p=0.021). After 6 months, most cognitive domains remained stable, except working memory assessed by the operation span task, which significantly improved between 6 and 12 months (p<0.001). No correlation was found between cognitive results and duration of deafness, speech perception or quality of life.

Conclusion

Cochlear implantation does not only lead to better speech perception and quality of life, but has also been shown to improve cognitive skills in hearing impaired adults aged 50 years or more. These effects seem to be independent of each other.

The development of a stochastic mathematical model of Alzheimer's disease to help improve the design of clinical trials of potential treatments

Alzheimer's disease (AD) is a neurodegenerative disorder characterised by a slow progressive deterioration of cognitive capacity. Drugs are urgently needed for the treatment of AD and unfortunately almost all clinical trials of AD drug candidates have failed or been discontinued to date. Mathematical, computational and statistical tools can be employed in the construction of clinical trial simulators to assist in the improvement of trial design and enhance the chances of success of potential new therapies. Based on the analysis of a set of clinical data provided by the Alzheimer's Disease Neuroimaging Initiative (ADNI) we developed a simple stochastic mathematical model to simulate the development and progression of Alzheimer's in a longitudinal cohort study. We show how this modelling framework could be used to assess the effect and the chances of success of hypothetical treatments that are administered at different stages and delay disease development. We demonstrate that the detection of the true efficacy of an AD treatment can be very challenging, even if the treatment is highly effective. An important reason behind the inability to detect signals of efficacy in a clinical trial in this therapy area could be the high between- and within-individual variability in the measurement of diagnostic markers and endpoints, which consequently results in the misdiagnosis of an individual's disease state.

A review of new insights on the association between hearing loss and cognitive decline in ageing

Age-related hearing loss (ARHL) has a multifactorial pathogenesis and it is an inevitable hearing impairment associated with reduction of communicative skills related to ageing. Increasing evidence has linked ARHL to more rapid progression of cognitive decline and incidental dementia. Many aspects of daily living of elderly people have been associated to hearing abilities, showing that hearing loss (HL) affects the quality of life, social relationships, motor skills, psychological aspects and function and morphology in specific brain areas. Epidemiological and clinical studies confirm the assumption of a relationship between these conditions. However, the mechanisms are still unclear and are reviewed herein. Long-term hearing deprivation of auditory inputs can impact cognitive performance by decreasing the quality of communication leading to social isolation and depression and facilitate dementia. On the contrary, the limited cognitive skills may reduce the cognitive resources available for auditory perception, increasing the effects of HL. In addition, hearing loss and cognitive decline may reflect a 'common cause' on the auditory pathway and brain. In fact, some pathogenetic factors are recongised in common microvascular disease factors such as diabetes, atherosclerosis and hypertension. Interdisciplinary efforts to investigate and address HL in the context of brain and cognitive ageing are needed. Surprisingly, few studies have been adressed on the effectiveness of hearing aids in changing the natural history of cognitive decline. Effective interventions with hearing aids or cochlear implant may improve social and emotional function, communication, cognitive function and positively impact quality of life. The aim of this review is to overview new insights on this challenging topic and provide new ideas for future research.

Cognitive and imaging markers in non-demented subjects attending a memory clinic: study design and baseline findings of the MEMENTO cohort

Background

The natural history and disease mechanisms of Alzheimer’s disease and related disorders (ADRD) are still poorly understood. Very few resources are available to scrutinise patients as early as needed and to use integrative approaches combining standardised, repeated clinical investigations and cutting-edge biomarker measurements.

Methods

In the nationwide French MEMENTO cohort study, participants were recruited in memory clinics and screened for either isolated subjective cognitive complaints (SCCs) or mild cognitive impairment (MCI; defined as test performance 1.5 SD below age, sex and education-level norms) while not demented (Clinical Dementia Rating [CDR] <1). Baseline data collection included neurological and physical examinations as well as extensive neuropsychological testing. To be included in the MEMENTO cohort, participants had to agree to undergo both brain magnetic resonance imaging (MRI) and blood sampling. Cerebral ¹⁸F-fluorodeoxyglucose positon emission tomography and lumbar puncture were optional. Automated analyses of cerebral MRI included assessments of volumes of whole-brain, hippocampal and white matter lesions.

Results

The 2323 participants, recruited from April 2011 to June 2014, were aged 71 years, on average (SD 8.7), and 62% were women. CDR was 0 in 40% of participants, and 30% carried at least one apolipoprotein E ε4 allele. We observed that more than half (52%) of participants had amnestic mild cognitive impairment (17% single-domain aMCI), 32% had non-amnestic mild cognitive impairment (16.9% single-domain naMCI) and 16% had isolated SCCs. Multivariable analyses of neuroimaging markers associations with cognitive categories showed that participants with aMCI had worse levels of imaging biomarkers than the others, whereas participants with naMCI had markers at intermediate levels between SCC and aMCI. The burden of white matter lesions tended to be larger in participants with aMCI. Independently of CDR, all neuroimaging and neuropsychological markers worsened with age, whereas differences were not consistent according to sex.

Conclusions

MEMENTO is a large cohort with extensive clinical, neuropsychological and neuroimaging data and represents a platform for studying the natural history of ADRD in a large group of participants with different subtypes of MCI (amnestic or not amnestic) or isolated SCCs.

Trial registration

Clinicaltrials.gov, NCT01926249. Registered on 16 August 2013.

Electronic supplementary material

The online version of this article (doi:10.1186/s13195-017-0288-0) contains supplementary material, which is available to authorized users.

Anxiety and depression symptoms among caregivers of care-recipients with subjective cognitive decline and cognitive impairment

Background

Caregivers of care-recipients with mild cognitive impairment (MCI) or dementia experience high caregiver burden; however, the psychiatric burden of caregivers of care-recipients with subjective cognitive decline (SCD) has not been investigated. We aimed to explore the prevalence of and risk factors for anxiety and depression symptoms among the caregivers of care-recipients with SCD and cognitive impairment.

Methods

The Hospital Anxiety and Depression Scale (HADS) was used to examine the anxiety and depression symptoms among the caregivers of 343 care-recipients (84 with SCD, 120 with MCI and 139 with dementia) treated at the Memory Clinic of Huashan Hospital in Shanghai, China from May 2012 to October 2014. A logistic regression was used to explore the factors associated with caregiver’s anxiety and depression symptoms.

Results

In total, 26.5 % of caregivers had anxiety symptoms, and 22.4 % had depression symptoms. Totals of 17.9, 30.0 and 28.8 % of caregivers of care-recipients with SCD, MCI or dementia, respectively, had anxiety symptoms (P = 0.1140), whereas 22.6, 24.2 and 20.9 %, respectively, had depression symptoms (P = 0.8165). The risk factors for caregiver’s anxiety symptoms were increased caregiver age as well as having care-recipients who were male, had higher Cohen Mansfield Agitation Inventory (CMAI) scores, and higher Geriatric Depression Scale (GDS) scores. The risk factors for caregiver’s depression symptoms were increased caregiver age as well as caring for care-recipients with MCI or SCD, those with lower Toronto Empathy Questionnaire (TEQ) scores, and those with higher GDS scores.

Conclusions

Caregivers of care-recipients with SCD showed the same level of depression symptoms as those of care-recipients with MCI. Caregiver’s depression and anxiety symptoms were associated with their care-recipients’ psychiatric and behavioral syndromes.

Aging Affects Neural Synchronization to Speech-Related Acoustic Modulations

As people age, speech perception problems become highly prevalent, especially in noisy situations. In addition to peripheral hearing and cognition, temporal processing plays a key role in speech perception. Temporal processing of speech features is mediated by synchronized activity of neural oscillations in the central auditory system. Previous studies indicate that both the degree and hemispheric lateralization of synchronized neural activity relate to speech perception performance. Based on these results, we hypothesize that impaired speech perception in older persons may, in part, originate from deviances in neural synchronization. In this study, auditory steady-state responses that reflect synchronized activity of theta, beta, low and high gamma oscillations (i.e., 4, 20, 40, and 80 Hz ASSR, respectively) were recorded in young, middle-aged, and older persons. As all participants had normal audiometric thresholds and were screened for (mild) cognitive impairment, differences in synchronized neural activity across the three age groups were likely to be attributed to age. Our data yield novel findings regarding theta and high gamma oscillations in the aging auditory system. At an older age, synchronized activity of theta oscillations is increased, whereas high gamma synchronization is decreased. In contrast to young persons who exhibit a right hemispheric dominance for processing of high gamma range modulations, older adults show a symmetrical processing pattern. These age-related changes in neural synchronization may very well underlie the speech perception problems in aging persons.

Mild cognitive impairment affects motor control and skill learning

Mild cognitive impairment (MCI) is a transitional phase between normal cognitive aging and dementia. As the world population is aging rapidly, more MCI patients will be identified, posing significant problems to society. Normal aging is associated with cognitive and motor decline, and MCI brings additional impairments. Compared to healthy older adults, MCI patients show poorer motor control in a variety of tasks. Efficient motor control and skill learning are essential for occupational and leisure purposes; degradation of motor behaviors in MCI patients often adversely affects their health and quality of life. In this article, we first define MCI and describe its pathology and neural correlates. After this, we review cognitive changes and motor control and skill learning in normal aging. This section is followed by a discussion of MCI-related degradation of motor behaviors. Finally, we propose that multicomponent interventions targeting both cognitive and motor domains can improve MCI patients’ motor functions. Future research directions are also raised.

Prediabetes and Alzheimer's Disease

Aging patients with diabetes are at higher risk of developing Alzheimer's disease. Emerging evidences demonstrate the role of brain insulin resistance, which is a key mediator in prediabetes and diabetes mellitus that may lead to Alzheimer's disease. Insulin and insulin-like growth factors regulate many biological processes such as axonal growth, protein synthesis, cell growth, gene expression, proliferation, differentiation, and development. Among these, the energy metabolism and synaptic plasticity are the major transduction processes regulated by insulin, which are the core objectives for learning and memory. It was also proposed that hyper insulinemia induced insulin resistance results in injury to the central nervous system by the activation of glycogen synthase kinase 3β which is the key ailment in the cognitive decline. Hence, the endogenous brain specific insulin impairments and signaling account for the majority of Alzheimer's abnormalities.

Risk Factors of Cognitive Impairment and Brief Cognitive Tests to Predict Cognitive Performance Determined by a Formal Neuropsychological Evaluation of Primary Health Care Patients

BACKGROUND

Case finding for cognitive impairment (CI) is recommended for all persons older than 70 years.

OBJECTIVE

The present study identified additional risk factors of CI so as to operationalize a composite total risk score (TRS) for case finding. We then examined the additive effect of the TRS and brief cognitive tests to improve the diagnosis of CI.

METHODS

The study was conducted in 2 primary health care centers in Singapore. A total of 1082 individuals (≥60 years old) were assessed for sociodemographic risk factors and their informants were administered the AD8; 309 individuals who agreed for further cognitive assessments completed the Mini-mental state examination (MMSE) and Montreal Cognitive Assessment (MoCA), and a neuropsychological battery at a research center. Primary health care medical records were accessed for data on vascular risk factors.

RESULTS

Of the 309 individuals who underwent neuropsychological evaluation, 4 were excluded due to missing medical data; 167 (54.8%) individuals had CI and 138 (45.2%) had No Cognitive Impairment (NCI). The β coefficients were standardized to calculate risk scores. CI was significantly predicted by age >70 years (odds ratio [OR] 5.99; score = 3), diabetes (OR 3.36; score = 2), stroke (OR 2.70; score = 1), female gender (OR 2.02; score = 1) and individual cognitive complaints (SCC) (OR 1.95; score = 1). The TRS had an optimal cutoff of ≥3 and explained considerable variance in global cognitive composite Z-scores (R(2) = 0.41, P < .001). The MoCA explained substantial variance compared with the MMSE and AD8 (R(2) changes of 0.474, 0.422, and 0.157, P < .001, respectively).

CONCLUSION

The TRS is a reasonable measure to predict individuals at risk of CI. The addition of the MoCA, in persons with positive TRS scores, is a useful approach to improve the diagnosis of CI for at-risk patients attending primary health care.

Tooth loss is associated with severe cognitive impairment among older people: findings from a population-based study in Brazil

BACKGROUND

A consistent and low-to-moderate association between markers of oral infection and loss of cognitive function has been demonstrated in the literature. However, such evidence comes from population studies carried out mainly in the USA.

OBJECTIVES

To assess the association between tooth loss and loss of cognitive function in older people from Southern Brazil, with particular interest on how age may modify such association. In addition, we also test the association between loss of cognition (exposure) and tooth loss (outcome).

METHODS

Data from a baseline population-based cohort study were cross-sectionally analyzed, including tooth loss, cognitive impairment, sex, income, educational attainment, color/race, smoking status and a range of self-reported chronic diseases. Participants (n = 1705) were 60 years of age and over, from a midsized Southern Brazilian city. Odds ratios (OR) and 95% confidence intervals (95%CI) were estimated using multivariable logistic and partial ordinal logistic analyses.

RESULTS

Edentate status was associated (OR 3.3; 95%CI 1.2-9.3) with severe cognitive impairment in the fully adjusted model. Moreover, there was an interaction between number of teeth and age on severe cognitive impairment. A weak association between severe cognitive impairment (exposure) and tooth loss (outcome) was identified after the adjustment for potential covariates.

CONCLUSIONS

This study lends support to hypothesized association between tooth loss and severe cognitive impairment. Older adults seem to be particularly vulnerable to such effects. However, the bidirectional association between tooth loss and severe cognitive impairment cannot be ruled out.

Common polygenic variation enhances risk prediction for Alzheimer's disease

The identification of subjects at high risk for Alzheimer's disease is important for prognosis and early intervention. We investigated the polygenic architecture of Alzheimer's disease and the accuracy of Alzheimer's disease prediction models, including and excluding the polygenic component in the model. This study used genotype data from the powerful dataset comprising 17 008 cases and 37 154 controls obtained from the International Genomics of Alzheimer's Project (IGAP). Polygenic score analysis tested whether the alleles identified to associate with disease in one sample set were significantly enriched in the cases relative to the controls in an independent sample. The disease prediction accuracy was investigated in a subset of the IGAP data, a sample of 3049 cases and 1554 controls (for whom APOE genotype data were available) by means of sensitivity, specificity, area under the receiver operating characteristic curve (AUC) and positive and negative predictive values. We observed significant evidence for a polygenic component enriched in Alzheimer's disease (P = 4.9 × 10(-26)). This enrichment remained significant after APOE and other genome-wide associated regions were excluded (P = 3.4 × 10(-19)). The best prediction accuracy AUC = 78.2% (95% confidence interval 77-80%) was achieved by a logistic regression model with APOE, the polygenic score, sex and age as predictors. In conclusion, Alzheimer's disease has a significant polygenic component, which has predictive utility for Alzheimer's disease risk and could be a valuable research tool complementing experimental designs, including preventative clinical trials, stem cell selection and high/low risk clinical studies. In modelling a range of sample disease prevalences, we found that polygenic scores almost doubles case prediction from chance with increased prediction at polygenic extremes.

Mild Cognitive Impairment Subtypes in Older People With Depressive Symptoms: Relationship With Clinical Variables and Hippocampal Change

AIMS

To examine the rates and clinical characteristics of mild cognitive impairment (MCI) in older people with depressive symptoms and to determine the relative contribution of hippocampal volume and MCI to memory change.

METHOD

One hundred and fifty-two participants with lifetime Major Depression and remitted or mild symptoms and 28 healthy controls underwent psychiatric and neuropsychological assessments. Magnetic resonance imaging was also conducted in a subset of the patients (n = 81) and healthy controls (n = 18).

RESULTS

MCI was diagnosed in 75.7% of the patients and was associated with increasing age, medical burden, vascular risk factors, later age of depression onset and smaller hippocampi. Multiple regression showed that both hippocampal volume and MCI diagnosis mediate memory performance in depression.

CONCLUSIONS

MCI occurs in older adults with a history of depression and is not simply due to symptom severity. Memory change is linked to underlying hippocampal atrophy in this patient group.

Cognitive Decline and Hearing Health Care for Older Adults

PURPOSE

The purpose of this article is to consider the implications of age-related cognitive decline for hearing health care.

METHOD

Recent research and current thinking about age-related declines in cognition and the links between auditory and cognitive aging are reviewed briefly. Implications of this research for improving prevention, assessment, and intervention in audiologic practice and for enhancing interprofessional teamwork are highlighted.

CONCLUSIONS

Given the important connection between auditory and cognitive aging and given the high prevalence of both hearing and cognitive impairments in the oldest older adults, health care services could be improved by taking into account how both the ear and the brain change over the life span. By incorporating cognitive factors into audiologic prevention, assessment, and intervention, hearing health care can contribute to better hearing and communication as well as to healthy aging.

Oxidative stress, redox signalling and endothelial dysfunction in ageing-related neurodegenerative diseases: a role of NADPH oxidase 2

Chronic oxidative stress and oxidative damage of the cerebral microvasculature and brain cells has become one of the most convincing theories in neurodegenerative pathology. Controlled oxidative metabolism and redox signalling in the central nervous system are crucial for maintaining brain function; however, excessive production of reactive oxygen species and enhanced redox signalling damage neurons. While several enzymes and metabolic processes can generate intracellular reactive oxygen species in the brain, recently an O2−-generating enzyme, NADPH oxidase 2 (Nox2), has emerged as a major source of oxidative stress in ageing-related vascular endothelial dysfunction and neurodegenerative diseases. The currently available inhibitors of Nox2 are not specific, and general antioxidant therapy is not effective in the clinic; therefore, insights into the mechanism of Nox2 activation and its signalling pathways are needed for the discovery of novel drug targets to prevent or treat these neurodegenerative diseases. This review summarizes the recent developments in understanding the mechanisms of Nox2 activation and redox-sensitive signalling pathways and biomarkers involved in the pathophysiology of the most common neurodegenerative diseases, such as ageing-related mild cognitive impairment, Alzheimer's disease and Parkinson's disease.

Increased brain amyloid deposition in patients with a lifetime history of major depression: evidenced on 18F-florbetapir (AV-45/Amyvid) positron emission tomography

PURPOSE

The literature suggests that a history of depression is associated with an increased risk of developing Alzheimer's disease (AD). The aim of this study was to examine brain amyloid accumulation in patients with lifetime major depression using (18)F-florbetapir (AV-45/Amyvid) PET imaging in comparison with that in nondepressed subjects.

METHODS

The study groups comprised 25 depressed patients and 11 comparison subjects who did not meet the diagnostic criteria for AD or amnestic mild cognitive impairment. Vascular risk factors, homocysteine and apolipoprotein E (ApoE) genotype were also examined. The standard uptake value ratio (SUVR) of each volume of interest was analysed using whole the cerebellum as the reference region.

RESULTS

Patients with a lifetime history of major depression had higher (18)F-florbetapir SUVRs in the precuneus (1.06 ± 0.08 vs. 1.00 ± 0.06, p = 0.045) and parietal region (1.05 ± 0.08 vs. 0.98 ± 0.07, p = 0.038) than the comparison subjects. Voxel-wise analysis revealed a significantly increased SUVR in depressed patients in the frontal, parietal, temporal and occipital areas (p < 0.01). There were no significant associations between global (18)F-florbetapir SUVRs and prior depression episodes, age at onset of depression, or time since onset of first depression.

CONCLUSION

Increased (18)F-florbetapir binding values were found in patients with late-life major depression relative to comparison subjects in specific brain regions, despite no differences in age, sex, education, Mini Mental Status Examination score, vascular risk factor score, homocysteine and ApoE ε4 genotype between the two groups. A longitudinal follow-up study with a large sample size would be worthwhile.

Care planning in dementia: tips for clinicians

Care planning in dementia is made more complicated by the increasing prevalence of multiple chronic comorbidities, also termed 'frailty'. Consideration of the reciprocal impact of dementia and other health issues is critical to appropriate care planning. This may be best achieved through an ordered process whereby the clinician first considers medical evidence and its limitations to the medical, physical and social determinants of the patient's health trajectory and quality of life. The next step is to provide information and recommendations to the patient and a second decision maker (who will become increasingly involved as dementia progresses). The end point of care planning is an informed and empowered decision maker who is able to dynamically apply skills to measure any treatment option that may be proposed, while having access to the decisional support of a health professional familiar with the patient's health status.

Heavy metals and neurodegenerative diseases: an observational study

In this study, we evaluated the levels of some of the most investigated metals (Cu, Se, Zn, Pb, and Hg) in the blood of patients affected by the most common chronic neurodegenerative diseases like Alzheimer's disease (AD) and multiple sclerosis (MS), in order to better clarify their involvement. For the first time, we investigated a Sicilian population living in an area exposed to a potentially contaminated environment from dust and fumes of volcano Etna and consumer of a considerable quantity of fish in their diet, so that this represents a good cohort to demonstrate a possible link between metals levels and development of neurodegenerative disorders. More specifically, 15 patients affected by AD, 41 patients affected by MS, 23 healthy controls, and 10 healthy elderly controls were recruited and subjected to a venous blood sampling. Quantification of heavy metals was performed by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). This technique has allowed us to establish that there is a concomitance of heavy metal unbalance associated with AD more than in other neurodegenerative pathologies, such as MS. Also, we can assess that the concentration of these elements is independent from the diet, especially from occasional or habitual consumption of fruits and vegetables, prevalence in the diet of meat or fish, possible exposure to contaminated environment due both to the occupation and place of residence.

Characterization of metal profiles in serum during the progression of Alzheimer's disease

Metal dyshomeostasis is closely related to Alzheimer's disease, so the characterization of the metal profiles in these patients is of special interest for studying associated neurodegenerative processes and to discover potential markers of disease. An analytical approach, based on non-denaturing precipitation of proteins, has been optimized for the fractionation of high molecular mass (HMM) and low molecular mass (LMM) metal-species from serum, which were subjected to multielemental analysis by inductively coupled plasma mass spectrometry (ICP-MS). This methodology was applied to healthy controls, Alzheimer's disease (AD) and mild cognitive impairment (MCI) patients in order to study the progression of dementia. Thus, it was found that some metals, such as iron, copper, zinc and aluminium, suffer progressive changes along the advance of neurodegeneration, suggesting that these imbalances could be related to the decline of cognitive functions. On the other hand, elements such as manganese, lithium or vanadium allow discriminating between controls and diseased subjects, both AD and MCI, but no differences were found between these two clinical stages, so they could be considered as precursors in the early development of neurodegenerative failures. In addition, it should be noted the important role that low molecular mass fractions of iron, copper, aluminium and cobalt appear to play in pathogenesis of Alzheimer. Finally, correlation analysis indicated that these metal abnormalities can be interrelated, participating in common processes such as oxidative stress, altered homeostasis and uptake into brain, as well as impaired glucose metabolism.

Effects of problem solving therapy on mental health outcomes in family caregivers of persons with a new diagnosis of mild cognitive impairment or early dementia: a randomized controlled trial

OBJECTIVE

Interventions directed at the mental health of family dementia caregivers may have limited impact when focused on caregivers who have provided care for years and report high burden levels. We sought to evaluate the mental health effects of problem-solving therapy (PST), designed for caregivers of individuals with a recent diagnosis of Mild Cognitive Impairment (MCI) or early dementia.

METHOD

Seventy-three (43 MCI and 30 early dementia) family caregivers were randomly assigned to receive PST or a comparison condition (nutritional education). Depression, anxiety, and problem-solving orientation were assessed at baseline and at 1, 3, 6, and 12 months post intervention.

RESULTS

In general, the PST caregiver intervention was feasible and acceptable to family caregivers of older adults with a new cognitive diagnosis. Relative to nutritional education, PST led to significantly reduced depression symptoms, particularly among early dementia caregivers. PST also lowered caregivers' anxiety levels, and led to lessening of negative problem orientation.

DISCUSSION

Enhanced problem-solving skills, learned early after a loved one's cognitive diagnosis (especially dementia), results in positive mental health outcomes among new family caregivers.

Impaired generation of new subcategories and switching in a semantic verbal fluency test in older adults with mild cognitive impairment

The semantic verbal fluency task is broadly used in the neuropsychological assessment of elderly subjects. Even some studies have identified differences in verbal fluency clustering and switching measures between subjects with normal aging and a clinical condition such as mild cognitive impairment (MCI) and Alzheimer's disease, the results are not always consistent. This study aimed to compare clustering and switching measures of an animal's semantic verbal fluency task among normal controls (NC, n = 25), amnestic mild cognitive impairment (aMCI; n = 25), amnestic multiple domain Mild Cognitive Impairment (a+mdMCI; n = 25) and Alzheimer's disease (AD; n = 25) Brazilian subjects. The analyses were executed considering three (unifying the MCI subtypes) and four groups. As the data were not normally distributed, we carried out non-parametric tests (Kruskal-Wallis and Mann-Whitney tests) to evaluate the differences in performance in the measures of the verbal fluency test among the groups. The comparison demonstrated that the groups differed in the total of correct words produced, number of clusters and switching but the measure of new subcategories was the only with significant difference among the NC and all the clinical groups. The measure of new subcategories is the number of original subcategories inside the higher category of animals that the subject produced, such as farm, domestic, African animals. Our results indicate that semantic memory impairment is a visible and recent deficit that occurs even in non-demented subjects with very MCI and the implications of these findings are discussed.

Ecological validity of virtual reality daily living activities screening for early dementia: longitudinal study

Background

Dementia is a multifaceted disorder that impairs cognitive functions, such as memory, language, and executive functions necessary to plan, organize, and prioritize tasks required for goal-directed behaviors. In most cases, individuals with dementia experience difficulties interacting with physical and social environments. The purpose of this study was to establish ecological validity and initial construct validity of a fire evacuation Virtual Reality Day-Out Task (VR-DOT) environment based on performance profiles as a screening tool for early dementia.

Objective

The objectives were (1) to examine the relationships among the performances of 3 groups of participants in the VR-DOT and traditional neuropsychological tests employed to assess executive functions, and (2) to compare the performance of participants with mild Alzheimer’s-type dementia (AD) to those with amnestic single-domain mild cognitive impairment (MCI) and healthy controls in the VR-DOT and traditional neuropsychological tests used to assess executive functions. We hypothesized that the 2 cognitively impaired groups would have distinct performance profiles and show significantly impaired independent functioning in ADL compared to the healthy controls.

Methods

The study population included 3 groups: 72 healthy control elderly participants, 65 amnestic MCI participants, and 68 mild AD participants. A natural user interface framework based on a fire evacuation VR-DOT environment was used for assessing physical and cognitive abilities of seniors over 3 years. VR-DOT focuses on the subtle errors and patterns in performing everyday activities and has the advantage of not depending on a subjective rating of an individual person. We further assessed functional capacity by both neuropsychological tests (including measures of attention, memory, working memory, executive functions, language, and depression). We also evaluated performance in finger tapping, grip strength, stride length, gait speed, and chair stands separately and while performing VR-DOTs in order to correlate performance in these measures with VR-DOTs because performance while navigating a virtual environment is a valid and reliable indicator of cognitive decline in elderly persons.

Results

The mild AD group was more impaired than the amnestic MCI group, and both were more impaired than healthy controls. The novel VR-DOT functional index correlated strongly with standard cognitive and functional measurements, such as mini-mental state examination (MMSE; rho=0.26, P=.01) and Bristol Activities of Daily Living (ADL) scale scores (rho=0.32, P=.001).

Conclusions

Functional impairment is a defining characteristic of predementia and is partly dependent on the degree of cognitive impairment. The novel virtual reality measures of functional ability seem more sensitive to functional impairment than qualitative measures in predementia, thus accurately differentiating from healthy controls. We conclude that VR-DOT is an effective tool for discriminating predementia and mild AD from controls by detecting differences in terms of errors, omissions, and perseverations while measuring ADL functional ability.

Familiarity, knowledge, and preferences of family physicians regarding mild cognitive impairment

BACKGROUND

Mild cognitive impairment (MCI) is a common condition among elderly persons. Its early identification is important because MCI can be a precursor of dementia. Since physicians' knowledge and preferences regarding MCI can be critical in its identification, this study assessed family physicians' familiarity, knowledge, and preferences regarding help-seeking, diagnosis, and treatment options for MCI.

METHOD

A convenience sample of 197 family physicians working in one of the largest Health Maintenance Organizations (HMOs) in Israel completed a structured questionnaire. Familiarity, knowledge, and preferences regarding diagnosis, help-seeking, and treatment of MCI were assessed.

RESULTS

The majority of the participants had heard about MCI but a third of those familiar with the term reported knowing almost nothing about it. Participants' objective knowledge was good regarding several causes of MCI, but 70% reported it to be caused by normal aging. Help-seeking and treatment preferences corresponded with the literature on MCI.

CONCLUSION

Our findings stress the need to broaden the understanding of primary care physicians' knowledge and preferences regarding MCI. This research can guide in developing continuous education programs to strengthen areas and groups of physicians reporting low knowledge.

Evaluating research for clinical significance: using critically appraised topics to enhance evidence-based neuropsychology

Meehl's (1973, Psychodiagnosis: Selected papers. Minneapolis: University of Minnesota Press) distinction between statistical and clinical significance holds special relevance for evidence-based neuropsychological practice. Meehl argued that despite attaining statistical significance, many published findings have limited practical value since they do not inform clinical care. In the context of an ever expanding clinical research literature, accessible methods to evaluate clinical impact are needed. The method of Critically Appraised Topics (Straus, Richardson, Glasziou, & Haynes, 2011, Evidence-based medicine: How to practice and teach EBM (4th ed.). Edinburgh: Elsevier Churchill-Livingstone) was developed to provide clinicians with a "toolkit" to facilitate implementation of evidence-based practice. We illustrate the Critically Appraised Topics method using a dementia screening example. We argue that the skills practiced through critical appraisal provide clinicians with methods to: (1) evaluate the clinical relevance of new or unfamiliar research findings with a focus on patient benefit, (2) help focus of research quality, and (3) incorporate evaluation of clinical impact into educational and professional development activities.

Type 2 diabetes and cognitive impairment: linking mechanisms

This manuscript provides a brief review of current concepts in the mechanisms potentially linking type-2-diabetes (T2D) with cognitive impairment. Existing epidemiologic studies, imaging studies, autopsy studies, and clinical trials provide insights into the mechanisms linking T2D and cognitive impairment. There seems to be little dispute that T2D can cause cerebrovascular disease and thus cause vascular cognitive impairment (VCI). Whether T2D can cause late onset Alzheimer's disease (LOAD) remains to be elucidated. Many epidemiologic studies show an association between T2D and cognitive impairment, but the association with VCI seems to be stronger compared to LOAD, suggesting that cerebrovascular disease may be the main mechanism linking T2D and cognitive impairment. Imaging studies show an association between T2D and imaging markers of LOAD, but these observations could still be explained by cerebrovascular mechanisms. Autopsy studies are few and conflicting, with some suggesting a predominantly cerebrovascular mechanism, and others providing support for a neurodegenerative mechanism. Thus far, the evidence from clinical trials is mixed in supporting a causal association between T2D and cognitive impairment, and most clinical trials that can answer this question are yet to be reported or finished. Given the epidemic of T2D in the world, it is important to elucidate whether the association between T2D and cognitive impairment, particularly LOAD, is causal, and if so, what the mechanisms are.

Mild cognitive impairment: historical development and summary of research

This review article broadly traces the historical development, diagnostic criteria, clinical and neuropathological characteristics, and treatment strategies related to mild cognitive impairment (MCI), The concept of MCI is considered in the context of other terms that have been developed to characterize the elderly with varying degrees of cognitive impairment Criteria based on clinical global scale ratings, cognitive test performance, and performance on other domains of functioning are discussed. Approaches employing clinical, neuropsychological, neuroimaging, biological, and molecular genetic methodology used in the validation of MCI are considered, including results from cross-sectional, longitudinal, and postmortem investigations. Results of recent drug treatment studies of MCI and related methodological issues are also addressed.

Mild cognitive impairment: an epidemiological perspective

Mild cognitive impairment (MCI) refers to cognitive impairment that is assumed to be due to pathological central nervous system processes, but which interacts with normal aging-related changes. Epidemiological studies conducted in the general population have been able to examine more heterogeneous forms of this disorder than clinical studies, and have also been able to provide early estimations of population incidence and prevalence. Large differences in case identification procedures and sampling methods have led to considerable divergence in the rates of prevalence reported, which ranged from 1% to 29%. Suggested improvements in the definition of MCI have led to an upward adjustment of prevalence rates in most studies, giving between 5% and 29%. Incidence is estimated as 8 to 58 new cases per thousand persons per year, and the probability of conversion from MCI to dementia is estimated at around 15%. The principal risk factors that have been identified so far for MCI using regression models applied to general population data are age, education, race, medicated hypertension, infarcts, white matter lesions, depression, and apolipoprotein E4 (AP0E-4J allele. An etiological model derived from these studies indicates possible intervention points for future therapeutic strategies at the level of both clinical intervention and environmental exposure. There is, however, a clear need for epidemiological studies that take into account a broader range of risk factors than those studied to date, which have focused principally on known risk factors for dementia.

Structural imaging in early pre-states of dementia

In this review focus is on structural imaging in the Alzheimer's disease (AD) pre-states, particularly cognitively normal (CN) persons at future dementia risk. Findings in mild cognitive impairment (MCI) are described here only for comparison with CN. Cited literature evidence and commentary address issues of structural imaging alterations in CN that precede MCI and AD, regional patterns of such alterations, and the time relationship between structural imaging alterations and the appearance of symptoms of AD, issues relevant to the conduct of future AD prevention trials. This article is part of a Special Issue entitled: Imaging Brain Aging and Neurodegenerative disease.

Prevalence of dementia and mild cognitive impairment in a Bulgarian urban population

BACKGROUND

Prevalence of cognitive impairment and dementia has not been studied in Bulgaria up to date. A 2-phase cross-sectional study was designed in order to determine the prevalence of dementia, its subtypes, and mild cognitive impairment in a Bulgarian population.

METHODS

The study sample consisted of 605 participants over the age of 65, residents of the city of Varna. A total of 540 participants (89%) completed the screening phase of the study. All positive screens and a control group were included in the diagnostic phase of the study, where comprehensive neuropsychological, clinical, and imaging assessments were performed.

RESULTS

Dementia was diagnosed in 39 persons (7.2%) and 36 had mild cognitive impairment (6.7%). Alzheimer's disease was the most frequent type of dementia (3.1%), followed by vascular dementia (2.0%).

DISCUSSION

Our results support the hypothesis that prevalence of vascular cognitive impairment may be higher in Bulgaria than in most European countries.

A comparison of non-homogeneous Markov regression models with application to Alzheimer's disease progression

Markov regression models are useful tools for estimating the impact of risk factors on rates of transition between multiple disease states. Alzheimer's disease (AD) is an example of a multi-state disease process in which great interest lies in identifying risk factors for transition. In this context, non-homogeneous models are required because transition rates change as subjects age. In this report we propose a non-homogeneous Markov regression model that allows for reversible and recurrent disease states, transitions among multiple states between observations, and unequally spaced observation times. We conducted simulation studies to demonstrate performance of estimators for covariate effects from this model and compare performance with alternative models when the underlying non-homogeneous process was correctly specified and under model misspecification. In simulation studies, we found that covariate effects were biased if non-homogeneity of the disease process was not accounted for. However, estimates from non-homogeneous models were robust to misspecification of the form of the non-homogeneity. We used our model to estimate risk factors for transition to mild cognitive impairment (MCI) and AD in a longitudinal study of subjects included in the National Alzheimer's Coordinating Center's Uniform Data Set. Using our model, we found that subjects with MCI affecting multiple cognitive domains were significantly less likely to revert to normal cognition.

The regulation of mitochondrial morphology: intricate mechanisms and dynamic machinery

Mitochondria typically form a reticular network radiating from the nucleus, creating an interconnected system that supplies the cell with essential energy and metabolites. These mitochondrial networks are regulated through the complex coordination of fission, fusion and distribution events. While a number of key mitochondrial morphology proteins have been identified, the precise mechanisms which govern their activity remain elusive. Moreover, post translational modifications including ubiquitination, phosphorylation and sumoylation of the core machinery are thought to regulate both fusion and division of the network. These proteins can undergo several different modifications depending on cellular signals, environment and energetic demands of the cell. Proteins involved in mitochondrial morphology may also have dual roles in both dynamics and apoptosis, with regulation of these proteins under tight control of the cell to ensure correct function. The absolute reliance of the cell on a functional mitochondrial network is highlighted in neurons, which are particularly vulnerable to any changes in organelle dynamics due to their unique biochemical requirements. Recent evidence suggests that defects in the shape or distribution of mitochondria correlate with the progression of neurodegenerative diseases such as Alzheimer's, Huntington's and Parkinson's disease. This review focuses on our current understanding of the mitochondrial morphology machinery in cell homeostasis, apoptosis and neurodegeneration, and the post translational modifications that regulate these processes.

Non-homogeneous Markov process models with informative observations with an application to Alzheimer's disease

Identifying risk factors for transition rates among normal cognition, mildly cognitive impairment, dementia and death in an Alzheimer's disease study is very important. It is known that transition rates among these states are strongly time dependent. While Markov process models are often used to describe these disease progressions, the literature mainly focuses on time homogeneous processes, and limited tools are available for dealing with non-homogeneity. Further, patients may choose when they want to visit the clinics, which creates informative observations. In this paper, we develop methods to deal with non-homogeneous Markov processes through time scale transformation when observation times are pre-planned with some observations missing. Maximum likelihood estimation via the EM algorithm is derived for parameter estimation. Simulation studies demonstrate that the proposed method works well under a variety of situations. An application to the Alzheimer's disease study identifies that there is a significant increase in transition rates as a function of time. Furthermore, our models reveal that the non-ignorable missing mechanism is perhaps reasonable.

Advanced glycation endproducts as gerontotoxins and biomarkers for carbonyl-based degenerative processes in Alzheimer's disease

Alzheimer's disease (AD) is the most common dementia disorder of later life. Although there might be various different triggering events in the early stages of the disease, they appear to converge on a few characteristic final pathways in the late stages, characterized by inflammation and neurodegeneration. Here, we review the hypothesis that advanced glycation end products (AGEs), which reflect carbonyl stress, an imbalance between the production of reactive carbonyl compounds and their detoxification, can serve as biomarkers for the progression of disorder. AGE modification may explain many of the neuropathological and biochemical features of AD, such as extensive protein cross-linking shown as amyloid plaques and neurofibrillary tangles, inflammation, oxidative stress and neuronal cell death. Although accumulation of AGEs is a normal feature of aging, it appears to be significantly accelerated in AD. We suggest that higher AGE concentrations in brain tissue and in cerebrospinal fluid might be able to distinguish between normal aging and AD.