We aimed to determine whether network-level functional connectivity differs in two clinical variants of Alzheimer’s disease: logopenic primary progressive aphasia (lvPPA) and dementia of the Alzheimer’s type (DAT). Twenty-four lvPPA subjects with amyloid deposition on PET and task-free fMRI were matched to 24 amyloid-positive DAT subjects and 24 amyloid-negative controls. Independent-component analysis and spatial-temporal dual-regression were used to assess functional connectivity within the language network, left and right working memory networks and ventral default mode network. lvPPA showed reduced connectivity in left temporal language network and inferior parietal and prefrontal regions of the left working memory network compared to controls and DAT. Both groups showed reduced connectivity in parietal regions of the right working memory network compared to controls. Only DAT showed reduced ventral default mode network connectivity compared to controls. Aphasia severity correlated with connectivity in left working memory network within lvPPA. Patterns of network dysfunction differ across these two clinical variants of Alzheimer’s disease, with lvPPA particularly associated with disruptions in the language and left working memory networks.
Alzheimer’s disease; primary progressive aphasia; language; MRI; functional imaging
Classifying primary progressive aphasia (PPA) into variants that may predict the underlying pathology is important. However, some PPA patients cannot be classified. A 78-year-old woman had unclassifiable PPA characterized by anomia, dysarthria and apraxia of speech without agrammatism. MRI revealed left mesial temporal atrophy and 18-flourodeoxy-glucose PET showed left anterior temporal and posterior frontal (premotor) hypometabolism. Autopsy revealed a mixed tauopathy (argyrophilic grain disease) and TAR-DNA-binding-protein-43 proteinopathy. Dual pathologies may explain the difficulty classifying some PPA patients and recognizing this will be important as new imaging techniques (particularly tau-PET) are introduced and patients begin enrollment in clinical trials targeting the underlying proteinopathy.
frontotemporal lobar degeneration; primary progressive aphasia; argyrophilic grain disease; tau; TDP 43
Subsystems within the default mode network are differentially affected in Alzheimer’s disease. Jones et al. present an in-depth analysis of changes within these subsystems and relate them to biomarker profiles across the Alzheimer’s disease spectrum. Results support a cascading network failure model of Alzheimer’s disease.
Subsystems within the default mode network are differentially affected in Alzheimer’s disease. Jones et al. present an in-depth analysis of changes within these subsystems and relate them to biomarker profiles across the Alzheimer’s disease spectrum. Results support a cascading network failure model of Alzheimer’s disease.
Complex biological systems are organized across various spatiotemporal scales with particular scientific disciplines dedicated to the study of each scale (e.g. genetics, molecular biology and cognitive neuroscience). When considering disease pathophysiology, one must contemplate the scale at which the disease process is being observed and how these processes impact other levels of organization. Historically Alzheimer’s disease has been viewed as a disease of abnormally aggregated proteins by pathologists and molecular biologists and a disease of clinical symptoms by neurologists and psychologists. Bridging the divide between these scales has been elusive, but the study of brain networks appears to be a pivotal inroad to accomplish this task. In this study, we were guided by an emerging systems-based conceptualization of Alzheimer’s disease and investigated changes in brain networks across the disease spectrum. The default mode network has distinct subsystems with unique functional-anatomic connectivity, cognitive associations, and responses to Alzheimer’s pathophysiology. These distinctions provide a window into the systems-level pathophysiology of Alzheimer’s disease. Using clinical phenotyping, metadata, and multimodal neuroimaging data from the Alzheimer’s Disease Neuroimaging Initiative, we characterized the pattern of default mode network subsystem connectivity changes across the entire disease spectrum (n = 128). The two main findings of this paper are (i) the posterior default mode network fails before measurable amyloid plaques and appears to initiate a connectivity cascade that continues throughout the disease spectrum; and (ii) high connectivity between the posterior default mode network and hubs of high connectivity (many located in the frontal lobe) is associated with amyloid accumulation. These findings support a system model best characterized by a cascading network failure—analogous to cascading failures seen in power grids triggered by local overloads proliferating to downstream nodes eventually leading to widespread power outages, or systems failures. The failure begins in the posterior default mode network, which then shifts processing burden to other systems containing prominent connectivity hubs. This model predicts a connectivity ‘overload’ that precedes structural and functional declines and recasts the interpretation of high connectivity from that of a positive compensatory phenomenon to that of a load-shifting process transiently serving a compensatory role. It is unknown whether this systems-level pathophysiology is the inciting event driving downstream molecular events related to synaptic activity embedded in these systems. Possible interpretations include that the molecular-level events drive the network failure, a pathological interaction between the network-level and the molecular-level, or other upstream factors are driving both.
Alzheimer’s disease; pathophysiology; cascading failure; complex systems; default mode network
Inexpensive, non-invasive tools for assessing Alzheimer-type pathophysiologies are needed. Computerized cognitive assessments are prime candidates.
Cognitively normal participants, aged 51-71, with MRI, FDG-PET, amyloid PET, CogState computerized cognitive assessment, and standard neuropsychological tests were included. We first examined the association between the CogState battery and neuroimaging measures. We then compared that association to the one between standard neuropsychological z-scores and neuroimaging.
Slower reaction times for CogState Identification and One Back, and lower memory and attention z-scores, were associated (P<.05) with FDG-PET hypometabolism. Slower time on the Groton Maze Learning Task and worse One Card Learning accuracy were associated (P<.05) with smaller hippocampal volumes. There were no associations with amyloid PET. Associations of CogState and neuropsychological z-scores with neuroimaging were small and of a similar magnitude.
CogState subtests were cross-sectionally comparable to standard neuropsychological tests in their relatively weak associations with neurodegeneration imaging markers.
Preclinical Alzheimer's disease; Neuropsychology; Computerized cognitive battery; Neuroimaging; Amyloid-beta; Hippocampal volume
This is a narrative review of new ideas and concepts related to differences between men and women in their risk of developing dementia or Alzheimer's disease (AD). We introduce the concept of dimorphic neurology and the distinction between sex and gender. We then provide three examples of risk factors related to sex and gender from the literature. Apolipoprotein E genotype is equally common in men and women but has a stronger effect in women. Apolipoprotein E genotype is a biological factor that cannot be modified but interacts with sex or gender related factors that can be modified. Low education has a similar harmful effect in men and women but has been historically more common in women. Education is a social factor related to gender that can be modified. Finally, bilateral oophorectomy is a factor restricted to women. Bilateral oophorectomy is a surgical practice related to sex that can be modified. Consideration of risk and protective factors in men and women separately may accelerate etiologic research for neurological diseases in general, and for dementia and AD in particular. Similarly, future preventive interventions for dementia should be tailored to men and women separately.
Dementia; sex; gender; APOE genotype; education; oophorectomy
Our objective was to examine associations between glucose metabolism, as measured by 18F-fluorodeoxyglucose positron emission tomography (FDG PET), and age and to evaluate the impact of carriage of an apolipoprotein E (APOE) ε4 allele on glucose metabolism and on the associations between glucose metabolism and age. We studied 806 cognitively normal (CN) and 70 amyloid-imaging-positive cognitively impaired participants (35 with mild cognitive impairment and 35 with Alzheimer’s disease [AD] dementia) from the Mayo Clinic Study of Aging, Mayo Alzheimer’s Disease Research Center and an ancillary study who had undergone structural MRI, FDG PET, and 11C-Pittsburgh compound B (PiB) PET. Using partial volume corrected and uncorrected FDG PET glucose uptake ratios, we evaluated associations of regional FDG ratios with age and carriage of an APOE ε4 allele in CN participants between the ages of 30 and 95 years, and compared those findings with the cognitively impaired participants. In region-of-interest (ROI) analyses, we found modest but statistically significant declines in FDG ratio in most cortical and subcortical regions as a function of age. We also found a main effect of APOE ε4 genotype on FDG ratio, with greater uptake in ε4 noncarriers compared with carriers but only in the posterior cingulate and/or precuneus, lateral parietal, and AD-signature meta-ROI. The latter consisted of voxels from posterior cingulate and/or precuneus, lateral parietal, and inferior temporal. In age- and sex-matched CN participants the magnitude of the difference in partial volume corrected FDG ratio in the AD-signature meta-ROI for APOE ε4 carriers compared with noncarriers was about 4 times smaller than the magnitude of the difference between age- and sex-matched elderly APOE ε4 carrier CN compared with AD dementia participants. In an analysis in participants older than 70 years (31.3% of whom had elevated PiB), there was no interaction between PiB status and APOE ε4 genotype with respect to glucose metabolism. Glucose metabolism declines with age in many brain regions. Carriage of an APOE ε4 allele was associated with reductions in FDG ratio in the posterior cingulate and/or precuneus, lateral parietal, and AD-signature ROIs, and there was no interaction between age and APOE ε4 status. The posterior cingulate and/or precuneus and lateral parietal regions have a unique vulnerability to reductions in glucose metabolic rate as a function both of age and carriage of an APOE ε4 allele.
Aging; Alzheimer’s disease; FDG positron emission tomography; Apolipoprotein E
As treatment of pre-clinical Alzheimer's disease (AD) becomes a focus of therapeutic intervention, observational research studies should recognize the overlap between imaging abnormalities associated with typical aging vs those associated with AD. Our objective was to characterize how typical aging and pre-clinical AD blend together with advancing age in terms of neurodegeneration and b-amyloidosis.
We measured age-specific frequencies of amyloidosis and neurodegeneration in 985 cognitively normal subjects age 50 to 89 from a population-based study of cognitive aging. Potential participants were randomly selected from the Olmsted County, Minnesota population by age- and sex-stratification and invited to participate in cognitive evaluations and undergo multimodality imaging. To be eligible for inclusion, subjects must have been judged clinically to have no cognitive impairment and have undergone amyloid PET, FDG PET and MRI. Imaging studies were obtained from March 2006 to December 2013. Amyloid positive/negative status (A+/A−) was determined by amyloid PET using Pittsburgh Compound B. Neurodegeneration positive/negative status (N+/N−) was determined by an AD-signature FDG PET measure and/or hippocampal volume on MRI. We labeled subjects positive or negative for neurodegeneration (FDG PET or MRI) or amyloidosis by using cutpoints defined such that 90% of 75 clinically diagnosed AD dementia subjects were categorized as abnormal. APOE genotype was assessed using DNA extracted from blood. Every individual was assigned to one of four groups: A−N−, A+N−, A−N+, or A+N+. Age specific frequencies of the 4 A/N groups were determined cross-sectionally using multinomial regression models. Associations with APOE ε4 and sex effects were evaluated by including these covariates in the multinomial models.
The population frequency of A−N− was 100% (n=985) at age 50 and declined thereafter. The frequency of A+N− increased to a maximum of 28% (95% CI, 24%-32%) at age 74 then decreased to 17% (95% CI, 11%-25%) by age 89. A−N+ increased from age 60 onward reaching a frequency of 24% (95% CI, 16%-34%) by age 89. A+N+ increased from age 65 onward reaching a frequency of 42% (95% CI, 31%-52%) by age 89. A+N− and A+N+ were more frequent in APOE ε4 carriers. A+N+ was more, and A+N− less frequent in men.
Accumulation of A/N imaging abnormalities is nearly inevitable by old age yet people are able to remain cognitively normal despite these abnormalities. . The multinomial models suggest the A/N frequency trends by age are modified by APOE ε4 , which increases risk for amyloidosis, and male sex, which increases risk for neurodegeneration. Changing A/N frequencies with age suggest that individuals may follow different pathophysiological sequences.
National Institute on Aging; Alexander Family Professorship of Alzheimer's Disease Research.
Cognitive aging; Brain aging; Amyloid imaging; Alzheimer disease; Brain atrophy and Alzheimer disease; FDG PET and Alzheimer disease
Our primary objective was to compare the performance of unaccelerated vs. accelerated structural MRI for measuring disease progression using serial scans in Alzheimer’s disease (AD).
We identified cognitively normal (CN), early mild cognitive impairment (EMCI), late mild cognitive impairment (LMCI) and AD subjects from all available Alzheimer’s Disease Neuroimaging Initiative (ADNI) subjects with usable pairs of accelerated and unaccelerated scans. There were a total of 696 subjects with baseline and 3 month scans, 628 subjects with baseline and 6 month scans and 464 subjects with baseline and 12 month scans available. We employed the Symmetric Diffeomorphic Image Normalization method (SyN) for normalization of the serial scans to obtain Tensor Based Morphometry (TBM) maps which indicate the structural changes between pairs of scans. We computed a TBM-SyN summary score of annualized structural changes over 31 regions of interest (ROIs) that are characteristically affected in AD. TBM-SyN scores were computed using accelerated and unaccelerated scan pairs and compared in terms of agreement, group-wise discrimination, and sample size estimates for a hypothetical therapeutic trial.
We observed a number of systematic differences between TBM-SyN scores computed from accelerated and unaccelerated pairs of scans. TBM-SyN scores computed from accelerated scans tended to have overall higher estimated values than those from unaccelerated scans. However, the performance of accelerated scans was comparable to unaccelerated scans in terms of discrimination between clinical groups and sample sizes required in each clinical group for a therapeutic trial. We also found that the quality of both accelerated vs. unaccelerated scans were similar.
Accelerated scanning protocols reduce scan time considerably. Their group-wise discrimination and sample size estimates were comparable to those obtained with unaccelerated scans. The two protocols did not produce interchangeable TBM-SyN estimates, so it is arguably important to use either accelerated pairs of scans or unaccelerated pairs of scans throughout the study duration.
To determine antemortem MRI findings associated with microinfarcts at autopsy.
Patients with microinfarcts (n = 22) and patients without microinfarcts (n = 44) who underwent antemortem MRI were identified from a dementia clinic–based, population–based, and community clinic–based autopsy cohort. The microinfarct and no-microinfarct groups were matched on age at MRI, age at death, sex, APOE status, Mini-Mental State Examination score, and pathologic diagnosis of Alzheimer disease. Brain infarcts were assessed on fluid-attenuated inversion recovery (FLAIR) MRI. White matter hyperintensities on FLAIR MRI and hippocampal volumes on T1-weighted MRI were quantified using automated methods. A subset of subjects with microinfarcts (n = 15) and a matched group of subjects without microinfarcts (n = 15) had serial T1-weighted MRIs and were included in an analysis of global and regional brain atrophy rates using automated methods.
The presence of cortical (p = 0.03) and subcortical (p = 0.02) infarcts on antemortem MRI was associated with presence of microinfarcts at autopsy. Higher numbers of cortical (p = 0.05) and subcortical (p = 0.03) infarcts on antemortem MRI were also associated with presence of microinfarcts. Presence of microinfarcts was not associated with white matter hyperintensities and cross-sectional hippocampal volume on antemortem MRI. Whole-brain and regional precuneus, motor, and somatosensory atrophy rates were higher in subjects with microinfarcts compared to subjects without microinfarcts.
Microinfarcts increase brain atrophy rates independent of Alzheimer disease pathology. Association between microinfarct pathology and macroinfarcts on MRI suggests either common risk factors or a shared pathophysiology and potentially common preventive targets.
We evaluated the relationship of amyloid, seen on Pittsburgh compound B (PiB)-PET, and metabolism, seen on [18F]-fluorodeoxyglucose (FDG)-PET, in normal subjects to better understand pathogenesis and biomarker selection in presymptomatic subjects.
Normal participants (aged 70–95 years; 600 with PiB-PET, FDG-PET, and MRI) were included. We performed a cross-sectional evaluation and subcategorized participants into amyloid-negative (<1.4), high-normal (1.4–1.5), positive (1.5–2.0), and markedly positive (>2.0) PiB standardized uptake value ratio groups representing different levels of amyloid brain load. Associations with metabolism were assessed in each group. Relationships with APOE ε4 carriage were evaluated.
Hypometabolism in “Alzheimer disease (AD)-signature” regions was strongly associated with PiB load. Hypometabolism was greater with more positive PiB levels. Additional, more-diffuse cortical hypometabolism was also found to be associated with PiB, although less so. No hypermetabolism was seen in any subset. No significant incremental hypometabolism was seen in APOE-positive vs -negative subjects.
Hypometabolism in PiB-positive, cognitively normal subjects in a population-based cohort occurs in AD-signature cortical regions and to a lesser extent in other cortical regions. It is more pronounced with higher amyloid load and supports a dose-dependent association. The effect of APOE ε4 carriage in this group of subjects does not appear to modify their hypometabolic “AD-like” neurodegeneration. Consideration of hypometabolism associated with amyloid load may aid trials of AD drug therapy.
The logopenic variant of primary progressive aphasia (lvPPA) strongly associates with Alzheimer’s disease, but can also associate with frontotemporal lobar degeneration. We aimed to assess the frequency of lvPPA in patients with speech and language disorders without β-amyloid deposition, and to perform detailed neuroimaging and genetic testing in such lvPPA patients. Seventy-six patients with a neurodegenerative speech and language disorder and Pittsburgh compound B (PiB) PET imaging demonstrating no β-amyloid deposition were analyzed. Six lvPPA patients (8 %) were identified. All six underwent progranulin (GRN) gene testing. Structural abnormality index maps and Cortex ID analysis were utilized to assess individual patterns of grey matter atrophy on MRI and hypometabolism on 18-F fluorodeoxyglucose (FDG) PET. Statistical parametric mapping was used to perform MRI and FDG-PET group comparisons between those with (GRN-positive) and without (GRN-negative) progranulin mutations. All six lvPPA patients showed left temporoparietal atrophy and hypometabolism. Three patients (50 %) were GRN-positive. Speech, language, and neurological and neuropsychological profiles did not differ between GRN-positive and negative patients, although GRN-positive patients had family histories, were on average 8 years younger, and had lower PiB-PET ratios. All six patients showed similar patterns of atrophy and hypometabolism, although, as a group, GRN-positive patients had more severe abnormalities, particularly in anteromedial temporal lobes. Logopenic PPA accounts for a small minority of neurodegenerative speech and language disorders not associated with β-amyloid deposition. Identification of such patients, however, should prompt testing for GRN mutations, since GRN-positive patients do not have distinctive features, yet account for 50 % of this patient population.
Progranulin; Logopenic; Primary progressive aphasia; β-amyloid; MRI; FDG-PET
Vemuri et al. show that amyloid and vascular pathologies are independent processes, and that both are major drivers of cognitive decline in the elderly. Cognitive reserve as measured by educational/occupational level and mid/late-life cognitive activity seems to offset the deleterious effects of both pathologies on cognitive trajectories.
Our primary objective was to investigate a biomarker driven model for the interrelationships between vascular disease pathology, amyloid pathology, and longitudinal cognitive decline in cognitively normal elderly subjects between 70 and 90 years of age. Our secondary objective was to investigate the beneficial effect of cognitive reserve on these interrelationships. We used brain amyloid-β load measured using Pittsburgh compound B positron emission tomography as a marker for amyloid pathology. White matter hyperintensities and brain infarcts were measured using fluid-attenuated inversion recovery magnetic resonance imaging as a marker for vascular pathology. We studied 393 cognitively normal elderly participants in the population-based Mayo Clinic Study of Aging who had a baseline 3 T fluid-attenuated inversion recovery magnetic resonance imaging assessment, Pittsburgh compound B positron emission tomography scan, baseline cognitive assessment, lifestyle measures, and at least one additional clinical follow-up. We classified subjects as being on the amyloid pathway if they had a global cortical amyloid-β load of ≥1.5 standard uptake value ratio and those on the vascular pathway if they had a brain infarct and/or white matter hyperintensities load ≥1.11% of total intracranial volume (which corresponds to the top 25% of white matter hyperintensities in an independent non-demented sample). We used a global cognitive z-score as a measure of cognition. We found no evidence that the presence or absence of vascular pathology influenced the presence or absence of amyloid pathology and vice versa, suggesting that the two processes seem to be independent. Baseline cognitive performance was lower in older individuals, in males, those with lower education/occupation, and those on the amyloid pathway. The rate of cognitive decline was higher in older individuals (P < 0.001) and those with amyloid (P = 0.0003) or vascular (P = 0.0037) pathologies. In those subjects with both vascular and amyloid pathologies, the effect of both pathologies on cognition was additive and not synergistic. For a 79-year-old subject, the predicted annual rate of global z-score decline was −0.02 if on neither pathway, −0.07 if on the vascular pathway, −0.08 if on the amyloid pathway and −0.13 if on both pathways. The main conclusions of this study were: (i) amyloid and vascular pathologies seem to be at least partly independent processes that both affect longitudinal cognitive trajectories adversely and are major drivers of cognitive decline in the elderly; and (ii) cognitive reserve seems to offset the deleterious effect of both pathologies on the cognitive trajectories.
ageing; cognitive neurology; neuroimaging; neuro protective strategies
We determined whether head trauma was associated with amyloid deposition and neurodegeneration among individuals who were cognitively normal (CN) or had mild cognitive impairment (MCI).
Participants included 448 CN individuals and 141 individuals with MCI from the Mayo Clinic Study of Aging who underwent Pittsburgh compound B (PiB)-PET, fluorodeoxyglucose-PET, and MRI. Head trauma was defined as a self-reported brain injury with at least momentary loss of consciousness or memory. Regression models examined whether head trauma was associated with each neuroimaging variable (assessed as continuous and dichotomous measures) in both CN and MCI participants, controlling for age and sex.
Among 448 CN individuals, 74 (17%) self-reported a head trauma. There was no difference in any neuroimaging measure between CN subjects with and without head trauma. Of 141 participants with MCI, 25 (18%) self-reported a head trauma. MCI participants with a head trauma had higher amyloid levels (by an average 0.36 standardized uptake value ratio units, p = 0.002).
Among individuals with MCI, but not CN individuals, self-reported head trauma with at least momentary loss of consciousness or memory was associated with greater amyloid deposition, suggesting that head trauma may be associated with Alzheimer disease–related neuropathology. Differences between CN individuals and individuals with MCI raise questions about the relevance of head injury–PET abnormality findings in those with MCI.
Microtubule-associated protein tau encoded by the MAPT gene binds to microtubules and is important for maintaining neuronal morphology and function. Alternative splicing of MAPT pre-mRNA generates six major tau isoforms in the adult central nervous system resulting in tau proteins with three or four microtubule-binding repeat domains. In a group of neurodegenerative disorders called tauopathies, tau becomes aberrantly hyperphosphorylated and dissociates from microtubules, resulting in a progressive accumulation of intracellular tau aggregates. The spectrum of sporadic frontotemporal lobar degeneration associated with tau pathology includes progressive supranuclear palsy, corticobasal degeneration, and Pick’s disease. Alzheimer’s disease is considered the most prevalent tauopathy. This review is divided into two broad sections. In the first section we discuss the molecular classification of sporadic tauopathies, with a focus on describing clinicopathologic relationships. In the second section we discuss the neuroimaging methodologies that are available for measuring tau pathology (directly using tau positron emission tomography ligands) and tau-mediated neuronal injury (magnetic resonance imaging and fluorodeoxyglucose positron emission tomography). Both sections have detailed descriptions of the following neurodegenerative dementias – Alzheimer’s disease, progressive supranuclear palsy, corticobasal degeneration and Pick’s disease.
Intellectual lifestyle enrichment throughout life is increasingly viewed as a protective strategy against commonly observed cognitive decline in the elderly.
To investigate the association of lifetime intellectual enrichment with baseline cognitive performance and rate of cognitive decline in a non-demented elderly population and to estimate difference (in years) associated with lifetime intellectual enrichment to the onset of cognitive impairment.
DESIGN, SETTING, PARTICIPANTS
Prospective analysis of subjects enrolled in the Mayo Clinic Study of Aging (MCSA), a longitudinal population-based study of cognitive aging in Olmsted County, Minnesota. We studied 1995 non-demented (1718 cognitively normal, 277 MCI) participants in MCSA who completed intellectual lifestyle measures at baseline and underwent at least one follow-up visit.
MAIN OUTCOMES AND MEASURES
We studied the effect of lifetime intellectual enrichment by separating the variables into two non-overlapping principal components: education/occupation-score and mid/late-life cognitive activity measure based on self-report questionnaires. A global cognitive Z-score served as our summary cognition measure. We used linear mixed-effects models to investigate the associations of demographic and intellectual enrichment measures with global cognitive Z-score trajectories.
Baseline cognitive performance was lower in older subjects and in those with lower education/occupation, lower mid/late-life cognitive activity, apolipoprotein E4 (APOE) genotype, and in men. The interaction between the two intellectual enrichment measures was significant such that the beneficial effect of mid/late-life cognitive activity on baseline cognitive performance was reduced with increasing education/occupation. Only baseline age, mid/late-life cognitive activity, and APOE4 genotype were significantly associated with longitudinal change in cognitive performance from baseline. For APOE4 carriers with high lifetime intellectual enrichment (75th percentile of both education/occupation and mid/late-life cognitive activity), the onset of cognitive impairment was about 8.7 years later compared with low lifetime intellectual enrichment (25th percentile of both education/occupation and mid/late-life cognitive activity) in an 80 year old subject.
CONCLUSIONS AND RELEVANCE
Higher levels of education/occupation were associated with higher levels of cognition. Higher levels of mid/late-life leisure activity were also associated with higher levels of cognition, but the slope of this relationship slightly increased over time. Lifetime intellectual enrichment might delay the onset of cognitive impairment and be used as a successful preventive intervention to reduce the impending dementia epidemic.
To determine structural MRI and digital microscopic characteristics of REM sleep behavior disorder in individuals with low-, intermediate-, and high-likelihood dementia with Lewy bodies (DLB) at autopsy.
Patients with autopsy-confirmed low-, intermediate-, and high-likelihood DLB, according to the probability statement recommended by the third report of the DLB Consortium, and antemortem MRI, were identified (n = 75). The clinical history was assessed for presence (n = 35) and absence (n = 40) of probable REM sleep behavior disorder (pRBD), and patients' antemortem MRIs were compared using voxel-based morphometry. Pathologic burdens of phospho-tau, β-amyloid, and α-synuclein were measured in regions associated with early neuropathologic involvement, the hippocampus and amygdala.
pRBD was present in 21 patients (60%) with high-likelihood, 12 patients (34%) with intermediate-likelihood, and 2 patients (6%) with low-likelihood DLB. Patients with pRBD were younger, more likely to be male (p ≤ 0.001), and had a more frequent neuropathologic diagnosis of diffuse (neocortical) Lewy body disease. In the hippocampus and amygdala, phospho-tau and β-amyloid burden were lower in patients with pRBD compared with those without pRBD (p < 0.01). α-Synuclein burden did not differ in the hippocampus, but trended in the amygdala. Patients without pRBD had greater atrophy of temporoparietal cortices, hippocampus, and amygdala (p < 0.001) than those with pRBD; atrophy of the hippocampus (p = 0.005) and amygdala (p = 0.02) were associated with greater phospho-tau burdens in these regions.
Presence of pRBD is associated with a higher likelihood of DLB and less severe Alzheimer-related pathology in the medial temporal lobes, whereas absence of pRBD is characterized by Alzheimer-like atrophy patterns on MRI and increased phospho-tau burden.
Tract-Based Spatial Statistics (TBSS) is a popular software pipeline to coregister sets of diffusion tensor Fractional Anisotropy (FA) images for performing voxel-wise comparisons. It is primarily defined by its skeleton projection step intended to reduce effects of local misregistration. A white matter “skeleton” is computed by morphological thinning of the inter-subject mean FA, and then all voxels are projected to the nearest location on this skeleton. Here we investigate several enhancements to the TBSS pipeline based on recent advances in registration for other modalities, principally based on groupwise registration with the ANTS-SyN algorithm. We validate these enhancements using simulation experiments with synthetically-modified images. When used with these enhancements, we discover that TBSS's skeleton projection step actually reduces algorithm accuracy, as the improved registration leaves fewer errors to warrant correction, and the effects of this projection's compromises become stronger than those of its benefits. In our experiments, our proposed pipeline without skeleton projection is more sensitive for detecting true changes and has greater specificity in resisting false positives from misregistration. We also present comparative results of the proposed and traditional methods, both with and without the skeleton projection step, on three real-life datasets: two comparing differing populations of Alzheimer's disease patients to matched controls, and one comparing progressive supranuclear palsy patients to matched controls. The proposed pipeline produces more plausible results according to each disease's pathophysiology.
DTI; Fractional Anisotropy; Voxel-based analysis; VBM; TBSS; Registration
To investigate MRI and proton magnetic resonance spectroscopy (MRS) predictors of mild cognitive impairment (MCI) in cognitively normal older adults.
Subjects were cognitively normal older adults (n = 1,156) who participated in the population-based Mayo Clinic Study of Aging MRI/MRS study from August 2005 to December 2010 and had at least one annual clinical follow-up. Single-voxel MRS was performed from the posterior cingulate gyri, and hippocampal volumes and white matter hyperintensity volumes were quantified using automated methods. Brain infarcts were assessed on MRI. Cox proportional hazards regression, with age as the time scale, was used to assess the effect of MRI and MRS markers on the risk of progression from cognitively normal to MCI. Linear mixed-effects models were used to assess the effect of MRI and MRS markers on cognitive decline.
After a median follow-up of 2.8 years, 214 participants had progressed to MCI or dementia (estimated incidence rate = 6.1% per year; 95% confidence interval = 5.3%–7.0%). In univariable modeling, hippocampal volume, white matter hyperintensity volume, and N-acetylaspartate/myo-inositol were significant predictors of MCI in cognitively normal older adults. In multivariable modeling, only decreased hippocampal volume and N-acetylaspartate/myo-inositol were independent predictors of MCI. These MRI/MRS predictors of MCI as well as infarcts were associated with cognitive decline (p < 0.05).
Quantitative MRI and MRS markers predict progression to MCI and cognitive decline in cognitively normal older adults. MRS may contribute to the assessment of preclinical dementia pathologies by capturing neurodegenerative changes that are not detected by hippocampal volumetry.
We describe the operationalization of the National Institute on Aging–Alzheimer’s Association (NIA-AA) workgroup diagnostic guidelines pertaining to Alzheimer disease (AD) dementia in a large multicenter group of subjects with AD dementia.
Subjects with AD dementia from the Alzheimer’s Disease Neuroimaging Initiative (ADNI) with at least 1 amyloid biomarker (n = 211) were included in this report. Biomarker data from CSF Aβ42, amyloid PET, fluorodeoxyglucose-PET, and MRI were examined. The biomarker results were assessed on a per-patient basis and the subject categorization as defined in the NIA-AA workgroup guidelines was determined.
When using a requirement that subjects have a positive amyloid biomarker and single neuronal injury marker having an AD pattern, 87% (48% for both neuronal injury biomarkers) of the subjects could be categorized as “high probability” for AD. Amyloid status of the combined Pittsburgh compound B–PET and CSF results showed an amyloid-negative rate of 10% in the AD group. In the ADNI AD group, 5 of 92 subjects fit the category “dementia unlikely due to AD” when at least one neuronal injury marker was negative.
A large proportion of subjects with AD dementia in ADNI may be categorized more definitively as high-probability AD using the proposed biomarker scheme in the NIA-AA criteria. A minority of subjects may be excluded from the diagnosis of AD by using biomarkers in clinically categorized AD subjects. In a well-defined AD dementia population, significant biomarker inconsistency can be seen on a per-patient basis.
To test the hypotheses predicted in a hypothetical model of Alzheimer disease (AD) biomarkers that rates of β-amyloid (Aβ) accumulation on PET imaging are not related to hippocampal neurodegeneration whereas rates of neurodegenerative brain atrophy depend on the presence of both amyloid and neurodegeneration in a population-based sample.
A total of 252 cognitively normal (CN) participants from the Mayo Clinic Study of Aging had 2 or more serial visits with both amyloid PET and MRI. Subjects were classified into 4 groups based on baseline positive/negative amyloid PET (A+ or A−) and baseline hippocampal volume (N+ or N−). We compared rates of amyloid accumulation and rates of brain atrophy among the 4 groups.
At baseline, 148 (59%) were amyloid negative and neurodegeneration negative (A−N−), 29 (12%) amyloid negative and neurodegeneration positive (A−N+), 56 (22%) amyloid positive and neurodegeneration negative (A+N−), and 19 (8%) amyloid positive and neurodegeneration positive (A+N+). High rates of Aβ accumulation were found in those with abnormal amyloid at baseline and were not influenced by hippocampal neurodegeneration at baseline. In contrast, rates of brain atrophy were greatest in A+N+.
We describe a 2-feature biomarker approach to classifying elderly CN subjects that is complementary to the National Institute on Aging–Alzheimer's Association preclinical staging criteria. Our results support 2 key concepts in a model of the temporal evolution of AD biomarkers. First, the rate of Aβ accumulation is not influenced by neurodegeneration and thus may be a biologically independent process. Second, Aβ pathophysiology increases or catalyzes neurodegeneration.
The new criteria for preclinical Alzheimer’s Disease (AD) proposed 3 stages: abnormal levels of β-amyloid (stage 1); stage 1 plus evidence of brain injury (stage 2); and stage 2 plus subtle cognitive changes (stage 3). However, a large group of subjects with normal β-amyloid biomarkers have evidence of brain injury; we labeled them as “suspected non-Alzheimer pathway” (sNAP) group. The characteristics of the sNAP group are poorly understood.
Using the preclinical AD classification, 430 cognitively normal subjects from the Mayo Clinic Study of Aging who underwent brain MR, 18fluorodeoxyglucose (FDG) and Pittsburgh compound B (PiB) positron emission tomography (PET) were evaluated with FDG PET regional volumetrics, MR regional brain volumetrics, white matter hyperintensity (WMH) volume and number of infarcts. We examined cross-sectional associations across AD preclinical stages, those with all biomarkers normal, and the sNAP group.
The sNAP group had a lower proportion (14%) with APOE ε4 genotype than the preclinical AD stages 2 + 3. The sNAP group did not show any group differences compared to stages 2 + 3 of the preclinical AD group on measures of FDG PET regional hypometabolism, MR regional brain volume loss, cerebrovascular imaging lesions, vascular risk factors, imaging changes associated with α-synucleinopathy or physical findings of parkinsonism.
Cognitively normal persons with brain injury biomarker abnormalities, with or without abnormal levels of β-amyloid, were indistinguishable on a variety of imaging markers, clinical features and risk factors. The initial appearance of brain injury biomarkers that occurs in cognitively normal persons with preclinical AD may not depend on β-amyloidosis.
Alzheimer’s disease; PET imaging; MR imaging; Epidemiology
To determine the association of conventional cardiovascular risk factors, markers of platelet activation, and thrombogenic blood-borne microvesicles with white matter hyperintensity (WMH) load and progression in recently menopausal women.
Women (n = 95) enrolled in the Mayo Clinic Kronos Early Estrogen Prevention Study underwent MRI at baseline and at 18, 36, and 48 months after randomization to hormone treatments. Conventional cardiovascular risk factors, carotid intima-medial thickness, coronary arterial calcification, plasma lipids, markers of platelet activation, and thrombogenic microvesicles were measured at baseline. WMH volumes were calculated using a semiautomated segmentation algorithm based on fluid-attenuated inversion recovery MRI. Correlations of those parameters with baseline WMH and longitudinal change in WMH were adjusted for age, months past menopause, and APOE ε4 status in linear regression analysis.
At baseline, WMH were present in all women. The WMH to white matter volume fraction at baseline was 0.88% (0.69%, 1.16%). WMH volume increased by 122.1 mm3 (95% confidence interval: −164.3, 539.5) at 36 months (p = 0.003) and 155.4 mm3 (95% confidence interval: −92.13, 599.4) at 48 months (p < 0.001). These increases correlated with numbers of platelet-derived and total thrombogenic microvesicles at baseline (p = 0.03).
Associations of platelet-derived, thrombogenic microvesicles at baseline and increases in WMH suggest that in vivo platelet activation may contribute to a cascade of events leading to development of WMH in recently menopausal women.
To model the temporal trajectory of β-amyloid accumulation using serial amyloid PET imaging.
Participants, aged 70–92 years, were enrolled in either the Mayo Clinic Study of Aging (n = 246) or the Mayo Alzheimer's Disease Research Center (n = 14). All underwent 2 or more serial amyloid PET examinations. There were 205 participants classified as cognitively normal and 55 as cognitively impaired (47 mild cognitive impairment and 8 Alzheimer dementia). We measured baseline amyloid PET-relative standardized uptake values (SUVR) and, for each participant, estimated a slope representing their annual amyloid accumulation rate. We then fit regression models to predict the rate of amyloid accumulation given baseline amyloid SUVR, and evaluated age, sex, clinical group, and APOE as covariates. Finally, we integrated the amyloid accumulation rate vs baseline amyloid PET SUVR association to an amyloid PET SUVR vs time association.
Rates of amyloid accumulation were low at low baseline SUVR. Rates increased to a maximum at baseline SUVR around 2.0, above which rates declined—reaching zero at baseline SUVR above 2.7. The rate of amyloid accumulation as a function of baseline SUVR had an inverted U shape. Integration produced a sigmoid curve relating amyloid PET SUVR to time. The average estimated time required to travel from an SUVR of 1.5–2.5 is approximately 15 years.
This roughly 15-year interval where the slope of the amyloid SUVR vs time curve is greatest and roughly linear represents a large therapeutic window for secondary preventive interventions.
In 2010, the authors published a hypothetical model of the major biomarkers of Alzheimer’s disease (AD). The model was received with interest because we described the temporal evolution of AD biomarkers in relation to each other and to the onset and progression of clinical symptoms. In the interim, evidence has accumulated that supports the major assumptions of this model. Evidence has also appeared that challenges some of the assumptions underlying our original model. Recent evidence has allowed us to modify our original model. Refinements include indexing subjects by time rather than clinical symptom severity; incorporating inter-subject variability in cognitive response to the progression of AD pathophysiology; modifications of the specific temporal ordering of some biomarkers; and, recognition that the two major proteinopathies underlying AD biomarker changes, Aβ and tau, may be initiated independently in late onset AD where we hypothesize that an incident Aβopathy can accelerate an antecedent tauopathy.
The appearance of β-amyloidosis and brain injury biomarkers in cognitively normal (CN) persons is thought to define risk for the future development of cognitive impairment due to Alzheimer’s disease (AD), but their interaction is poorly understood.
To test the hypothesis that the joint presence of β-amyloidosis and brain injury biomarkers would lead to more rapid neurodegeneration.
Longitudinal Cohort Study
Population-based Mayo Clinic Study of Aging.
191 CN persons (median age 77, range 71–93) in the Mayo Clinic Study of Aging who underwent MR, FDG PET and PiB PET imaging at least twice 15 months apart. Subjects were grouped according to the recommendations of the NIA-AA Preclinical AD criteria, based on the presence of β-amyloidosis, defined as a PiB PET SUVr >1.5, alone (Stage 1) or with brain injury (stage 2+3), defined as hippocampal atrophy or FDG hypometabolism. We also studied a group of MCI (n=17) and dementia (n=9) patients from the Mayo Clinic Study of Aging or the Mayo Alzheimer Center with similar follow-up times who had had comparable imaging and who all had PiB PET SUVr >1.5.
Main Outcome Measures
Rate of change of cortical volume on volumetric MR scans and rate of change of glucose metabolism on FDG PET scans.
There were 25 CN subjects with both high PiB retention and low hippocampal volume or FDG hypometabolism at baseline (Preclinical AD stages 2+3). On follow-up scans, the Preclinical AD stages 2+3 subjects had greater loss of medial temporal lobe volume and greater glucose hypometabolism in the medial temporal lobe compared to other CN groups. The changes were similar to the cognitively impaired participants. Extra-temporal regions did not show similar changes.
Higher rates of medial temporal neurodegeneration occurred in CN individuals who, on their initial scans, had abnormal levels of both β-amyloid and brain injury biomarkers.
Alzheimer’s disease; PET imaging; MR imaging; Epidemiology