Clinical and epidemiologic investigations are paying increasing attention to the critical constructs of "representativeness" of study samples and "generalizability" of study results. This is a ...laudable trend and yet, these key concepts are often misconstrued and conflated, masking the central issues of internal and external validity. The authors define these issues and demonstrate how they are related to one another and to generalizability. Providing examples, they identify threats to validity from different forms of bias and confounding. They also lay out relevant practical issues in study design, from sample selection to assessment of exposures, in both clinic-based and population-based settings.
Context Some evidence suggests that treating vascular risk factors and performing mentally stimulating activities may delay cognitive impairment onset in older adults. Exposure to a complex ...neighborhood environment may be one mechanism to help delay cognitive decline. Evidence acquisition PubMed, Web of Science, and ProQuest Dissertation and Theses Global database were systematically reviewed, identifying 25 studies published from February 1, 1989 to March 5, 2016 (data synthesized, May 3, 2015 to October 7, 2016). The review was restricted to quantitative studies focused on: (1) neighborhood social and built environment and cognition; and (2) community-dwelling adults aged ≥45 years. Evidence synthesis The majority of studies were cross-sectional, U.S.-based, and found at least one significant association. The diversity of measures and neighborhood definitions limited the synthesis of findings in many instances. Evidence was moderately strong for an association between neighborhood SES and cognition, and modest for associations between neighborhood demographics, design, and destination accessibility and cognition. Most studies examining effect modification found significant associations, with some evidence for effect modification of the neighborhood SES−cognition association by individual-level SES. No studies had low risk of bias and many tested multiple associations that increased the chance of a statistically significant finding. Considering the studies to date, the evidence for an association between neighborhood characteristics and cognition is modest. Conclusions Future studies should include longitudinal measures of neighborhood characteristics and cognition; examine potential effect modifiers, such as sex and disability; and study mediators that may help elucidate the biological mechanisms linking neighborhood environment and cognition.
Background
Seizures are an important comorbidity in Alzheimer’s disease (AD). Conflicting results regarding clinical parameters associated with seizures in AD were previously reported. Data on ...seizure recurrence risk, a crucial parameter for treatment decisions, are lacking.
Methods
National Alzheimer’s Coordinating Center data were analyzed. Seizure prevalence in AD and an association with disease duration were investigated. Associations of seizures with age of AD onset and with cognitive and functional performance, and seizure recurrence risk were studied.
Results
20,745 individuals were investigated. In AD dementia, seizure recurrence risk was 70.4% within 7.5 months. Seizure history was associated with an earlier age of onset of cognitive symptoms (seizures vs. no seizures: 64.7 vs. 70.4 years;
p
< 0.0001) and worse cognitive and functional performance (mean MMSE score: 16.6 vs. 19.6; mean CDR-sum of boxes score: 9.3 vs. 6.8;
p
< 0.0001; adjusted for disease duration and age). Seizure prevalence increased with duration of AD dementia (standardized OR = 1.55, 95% CI = 1.39–1.73,
p
< 0.0001), rising from 1.51% at 4.8 years to 5.43% at 11 years disease duration. Seizures were more frequent in AD dementia compared to normal controls (active seizures: 1.51% vs. 0.35%,
p
< 0.0001, OR = 4.34, 95% CI = 3.01–6.27; seizure history: 3.14% vs. 1.57%,
p
< 0.0001, OR = 2.03, 95% CI = 1.67–2.46).
Conclusion
Seizures in AD dementia feature an exceptionally high recurrence risk and are associated with a poor course of cognitive symptoms. AD patients are at an increased risk for seizures, particularly in later disease stages. Our findings emphasize a need for seizure history assessment in AD, inform individual therapeutic decisions and underline the necessity of systematic treatment studies of AD-associated epilepsy.
ABSTRACTThe neuropathologic examination is considered to provide the gold standard for Alzheimer disease (AD). To determine the accuracy of currently used clinical diagnostic methods, clinical and ...neuropathologic data from the National Alzheimer’s Coordinating Center, which gathers information from the network of National Institute on Aging (NIA)-sponsored Alzheimer Disease Centers (ADCs), were collected as part of the National Alzheimer’s Coordinating Center Uniform Data Set (UDS) between 2005 and 2010. A database search initially included all 1198 subjects with at least one UDS clinical assessment and who had died and been autopsied; 279 were excluded as being not demented or because critical data fields were missing. The final subject number was 919. Sensitivity and specificity were determined based on “probable” and “possible” AD levels of clinical confidence and 4 levels of neuropathologic confidence based on varying neuritic plaque densities and Braak neurofibrillary stages. Sensitivity ranged from 70.9% to 87.3%; specificity ranged from 44.3% to 70.8%. Sensitivity was generally increased with more permissive clinical criteria and specificity was increased with more restrictive criteria, whereas the opposite was true for neuropathologic criteria. When a clinical diagnosis was not confirmed by minimum levels of AD histopathology, the most frequent primary neuropathologic diagnoses were tangle-only dementia or argyrophilic grain disease, frontotemporal lobar degeneration, cerebrovascular disease, Lewy body disease and hippocampal sclerosis. When dementia was not clinically diagnosed as AD, 39% of these cases met or exceeded minimum threshold levels of AD histopathology. Neurologists of the NIA-ADCs had higher predictive accuracy when they diagnosed AD in subjects with dementia than when they diagnosed dementing diseases other than AD. The misdiagnosis rate should be considered when estimating subject numbers for AD studies, including clinical trials and epidemiologic studies.
The neuropsychological battery of the Uniform Data Set (UDSNB) was implemented in 2005 by the National Institute on Aging (NIA) Alzheimer Disease Centers program to measure cognitive performance in ...dementia and mild cognitive impairment due to Alzheimer Disease. This paper describes a revision, the UDSNB 3.0.
The Neuropsychology Work Group of the NIA Clinical Task Force recommended revisions through a process of due diligence to address shortcomings of the original battery. The UDSNB 3.0 covers episodic memory, processing speed, executive function, language, and constructional ability. Data from 3602 cognitively normal participants in the National Alzheimer Coordinating Center database were analyzed.
Descriptive statistics are presented. Multivariable linear regression analyses demonstrated score differences by age, sex, and education and were also used to create a normative calculator available online.
The UDSNB 3.0 neuropsychological battery provides a valuable non proprietary resource for conducting research on cognitive aging and dementia.
Identifying individuals at risk for developing Alzheimer disease (AD) is of utmost importance. Although genetic studies have identified AD-associated SNPs in APOE and other genes, genetic information ...has not been integrated into an epidemiological framework for risk prediction.
Using genotype data from 17,008 AD cases and 37,154 controls from the International Genomics of Alzheimer's Project (IGAP Stage 1), we identified AD-associated SNPs (at p < 10-5). We then integrated these AD-associated SNPs into a Cox proportional hazard model using genotype data from a subset of 6,409 AD patients and 9,386 older controls from Phase 1 of the Alzheimer's Disease Genetics Consortium (ADGC), providing a polygenic hazard score (PHS) for each participant. By combining population-based incidence rates and the genotype-derived PHS for each individual, we derived estimates of instantaneous risk for developing AD, based on genotype and age, and tested replication in multiple independent cohorts (ADGC Phase 2, National Institute on Aging Alzheimer's Disease Center NIA ADC, and Alzheimer's Disease Neuroimaging Initiative ADNI, total n = 20,680). Within the ADGC Phase 1 cohort, individuals in the highest PHS quartile developed AD at a considerably lower age and had the highest yearly AD incidence rate. Among APOE ε3/3 individuals, the PHS modified expected age of AD onset by more than 10 y between the lowest and highest deciles (hazard ratio 3.34, 95% CI 2.62-4.24, p = 1.0 × 10-22). In independent cohorts, the PHS strongly predicted empirical age of AD onset (ADGC Phase 2, r = 0.90, p = 1.1 × 10-26) and longitudinal progression from normal aging to AD (NIA ADC, Cochran-Armitage trend test, p = 1.5 × 10-10), and was associated with neuropathology (NIA ADC, Braak stage of neurofibrillary tangles, p = 3.9 × 10-6, and Consortium to Establish a Registry for Alzheimer's Disease score for neuritic plaques, p = 6.8 × 10-6) and in vivo markers of AD neurodegeneration (ADNI, volume loss within the entorhinal cortex, p = 6.3 × 10-6, and hippocampus, p = 7.9 × 10-5). Additional prospective validation of these results in non-US, non-white, and prospective community-based cohorts is necessary before clinical use.
We have developed a PHS for quantifying individual differences in age-specific genetic risk for AD. Within the cohorts studied here, polygenic architecture plays an important role in modifying AD risk beyond APOE. With thorough validation, quantification of inherited genetic variation may prove useful for stratifying AD risk and as an enrichment strategy in therapeutic trials.
Cerebrovascular disease and vascular risk factors are associated with Alzheimer's disease, but the evidence for their association with other neurodegenerative disorders is limited. Therefore, we ...compared the prevalence of cerebrovascular disease, vascular pathology and vascular risk factors in a wide range of neurodegenerative diseases and correlate them with dementia severity. Presence of cerebrovascular disease, vascular pathology and vascular risk factors was studied in 5715 cases of the National Alzheimer's Coordinating Centre database with a single neurodegenerative disease diagnosis (Alzheimer's disease, frontotemporal lobar degeneration due to tau, and TAR DNA-binding protein 43 immunoreactive deposits, α-synucleinopathies, hippocampal sclerosis and prion disease) based on a neuropathological examination with or without cerebrovascular disease, defined neuropathologically. In addition, 210 'unremarkable brain' cases without cognitive impairment, and 280 cases with pure cerebrovascular disease were included for comparison. Cases with cerebrovascular disease were older than those without cerebrovascular disease in all the groups except for those with hippocampal sclerosis. After controlling for age and gender as fixed effects and centre as a random effect, we observed that α-synucleinopathies, frontotemporal lobar degeneration due to tau and TAR DNA-binding protein 43, and prion disease showed a lower prevalence of coincident cerebrovascular disease than patients with Alzheimer's disease, and this was more significant in younger subjects. When cerebrovascular disease was also present, patients with Alzheimer's disease and patients with α-synucleinopathy showed relatively lower burdens of their respective lesions than those without cerebrovascular disease in the context of comparable severity of dementia at time of death. Concurrent cerebrovascular disease is a common neuropathological finding in aged subjects with dementia, is more common in Alzheimer's disease than in other neurodegenerative disorders, especially in younger subjects, and lowers the threshold for dementia due to Alzheimer's disease and α-synucleinopathies, which suggests that these disorders should be targeted by treatments for cerebrovascular disease.
Primary age-related tauopathy is increasingly recognized as a separate neuropathological entity different from Alzheimer's disease. Both share the neuropathological features of tau aggregates and ...neuronal loss in the temporal lobe, but primary age-related tauopathy lacks the requisite amyloid plaques central to Alzheimer's disease. While both have similar clinical presentations, individuals with symptomatic primary age-related tauopathy are commonly of more advanced ages with milder cognitive dysfunction. Direct comparison of the neuropsychological trajectories of primary age-related tauopathy and Alzheimer's disease has not been thoroughly evaluated and thus, our objective was to determine how cognitive decline differs longitudinally between these two conditions after the onset of clinical symptoms. Data were obtained from the National Alzheimer's Coordinating Center on participants with mild cognitive impairment at baseline and either no neuritic plaques (i.e. primary age-related tauopathy) or moderate to frequent neuritic plaques (i.e. Alzheimer neuropathological change) at subsequent autopsy. For patients with Alzheimer's disease and primary age-related tauopathy, we compared rates of decline in the sum of boxes score from the CDR® Dementia Staging Instrument and in five cognitive domains (episodic memory, attention/working memory, executive function, language/semantic memory, and global composite) using z-scores for neuropsychological tests that were calculated based on scores for participants with normal cognition. The differences in rates of change were tested using linear mixed-effects models accounting for clinical centre clustering and repeated measures by individual. Models were adjusted for sex, age, education, baseline test score, Braak stage, apolipoprotein ε4 (APOE ε4) carrier status, family history of cognitive impairment, and history of stroke, hypertension, or diabetes. We identified 578 participants with a global CDR of 0.5 (i.e. mild cognitive impairment) at baseline, 126 with primary age-related tauopathy and 452 with Alzheimer's disease. Examining the difference in rates of change in CDR sum of boxes and in all domain scores, participants with Alzheimer's disease had a significantly steeper decline after becoming clinically symptomatic than those with primary age-related tauopathy. This remained true after adjusting for covariates. The results of this analysis corroborate previous studies showing that primary age-related tauopathy has slower cognitive decline than Alzheimer's disease across multiple neuropsychological domains, thus adding to the understanding of the neuropsychological burden in primary age-related tauopathy. The study provides further evidence to support the hypothesis that primary age-related tauopathy has distinct neuropathological and clinical features compared to Alzheimer's disease.
To conduct a clinicopathologic study to characterize clinical and neuropathologic features associated with cognitive impairment in participants with no neuritic amyloid plaques (primary age-related ...tauopathy PART definite) and sparse neuritic plaques (amyloid sparse).
Using the National Alzheimer's Coordinating Center database, we identified 377 individuals who were PART definite (n = 170) or amyloid sparse (n = 207), clinically examined within 1 year of death, and autopsied at 1 of 26 National Institute on Aging-funded Alzheimer's Disease Centers. Factors associated with the odds of being symptomatic (global Clinical Dementia Rating CDR score >0) were identified with multivariable logistic regression.
PART-definite participants less often had a high Braak neurofibrillary tangle stage V or VI (4%) compared to amyloid sparse participants (28%,
< 0.001). Of the PART-definite participants, 98 were symptomatic and 72 asymptomatic according to their global CDR scores. PART-definite participants were less often symptomatic (58%) compared with amyloid sparse participants (80%,
< 0.001). Within the PART-definite group, independent predictors of symptomatic status included depression (adjusted odds ratio aOR 4.20, 95% confidence interval CI 2.15-8.19), Braak stage (aOR 1.42, 95% CI 1.04-1.95), and history of stroke (aOR 8.09, 95% CI 2.63-24.82). Within the amyloid sparse group, independent predictors of symptomatic status included education (aOR 0.80, 95% CI 0.65-0.99), Braak stage (aOR 1.91, 95% CI 1.07-3.43), and amyloid angiopathy (aOR 2.75, 95% CI 1.14-6.64).
These findings support the hypothesis that participants with PART have an amyloid-independent dementing Alzheimer disease-like temporal lobe tauopathy.
We aimed to prospectively assess the change in neuropsychiatric symptoms among people who develop cognitive impairment and have a history of post-traumatic stress disorder (PTSD). We analyzed ...longitudinal data from the National Alzheimer's Coordinating Center Unified Data Set (March 2015 to December 2021). Analyses included individuals who were cognitively normal and who had nonmissing assessment of PTSD at the initial visit and had at least 1 follow-up visit with cognitive impairment. We compared the difference in the mean neuropsychiatric symptom score at the first Unified Data Set visit versus the first visit with a Clinical Dementia Rating of 0.5 between those with and without a history of PTSD. The mean neuropsychiatric symptom score change did not differ between those with and without a history of PTSD (1.06 vs. 0.77, respectively; P =0.79). The null results found in this study warrant future research. Several methodological limitations might explain these results.
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