Unrecognized preclinical Alzheimer disease confounds rs-fcMRI studies of normal aging.
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ABSTRACT:
SUBMITTER: Brier MR
PROVIDER: S-EPMC4223085 | biostudies-literature | 2014 Oct
REPOSITORIES: biostudies-literature
Publications
Unrecognized preclinical Alzheimer disease confounds rs-fcMRI studies of normal aging.
Brier Matthew R MR Thomas Jewell B JB Snyder Abraham Z AZ Wang Liang L Fagan Anne M AM Benzinger Tammie T Morris John C JC Ances Beau M BM
Neurology 20140926 18
<h4>Objective</h4>To determine whether, and to what degree, preclinical Alzheimer disease (AD) confounds studies of healthy aging where "healthy" is based on cognitive normality alone.<h4>Methods</h4>We examined the effects of preclinical AD in cognitively normal older individuals using resting-state functional connectivity MRI. We investigated 2 groups of cognitively normal participants: one group with evidence of preclinical AD as assessed by CSF markers of AD and the other group with normal C ...[more]
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Project description:Background"Brain-predicted age" estimates biological age from complex, nonlinear features in neuroimaging scans. The brain age gap (BAG) between predicted and chronological age is elevated in sporadic Alzheimer disease (AD), but is underexplored in autosomal dominant AD (ADAD), in which AD progression is highly predictable with minimal confounding age-related co-pathology.MethodsWe modeled BAG in 257 deeply-phenotyped ADAD mutation-carriers and 179 non-carriers from the Dominantly Inherited Alzheimer Network using minimally-processed structural MRI scans. We then tested whether BAG differed as a function of mutation and cognitive status, or estimated years until symptom onset, and whether it was associated with established markers of amyloid (PiB PET, CSF amyloid-β-42/40), phosphorylated tau (CSF and plasma pTau-181), neurodegeneration (CSF and plasma neurofilament-light-chain [NfL]), and cognition (global neuropsychological composite and CDR-sum of boxes). We compared BAG to other MRI measures, and examined heterogeneity in BAG as a function of ADAD mutation variants, APOE ε4 carrier status, sex, and education.ResultsAdvanced brain aging was observed in mutation-carriers approximately 7 years before expected symptom onset, in line with other established structural indicators of atrophy. BAG was moderately associated with amyloid PET and strongly associated with pTau-181, NfL, and cognition in mutation-carriers. Mutation variants, sex, and years of education contributed to variability in BAG.ConclusionsWe extend prior work using BAG from sporadic AD to ADAD, noting consistent results. BAG associates well with markers of pTau, neurodegeneration, and cognition, but to a lesser extent, amyloid, in ADAD. BAG may capture similar signal to established MRI measures. However, BAG offers unique benefits in simplicity of data processing and interpretation. Thus, results in this unique ADAD cohort with few age-related confounds suggest that brain aging attributable to AD neuropathology can be accurately quantified from minimally-processed MRI.
| S-EPMC10729487 | biostudies-literature
Project description:Importance:Circadian rhythm disturbances occur in symptomatic Alzheimer disease (AD) and have been hypothesized to contribute to disease pathogenesis. However, it is unknown whether circadian changes occur during the presymptomatic phase of the disease. Objective:To examine the associations between circadian function, aging, and preclinical AD pathology in cognitively normal adults. Design, Setting, and Participants:This cross-sectional study was conducted using community volunteers from the Knight Alzheimer's Disease Research Center at Washington University in St Louis. Cognitively normal participants (n?=?205) underwent 7 to 14 days of actigraphy in their home environment between 2010 and 2012, in addition to clinical assessment, amyloid imaging with Pittsburgh Compound B (PiB), and cerebrospinal fluid biomarker collection. Data collected from 3 years before to 6 months after actigraphy were included. Sixteen participants were excluded owing to incomplete data collection. Main Outcomes and Measures:Circadian rhythm analysis was performed on actigraphy data using 3 methods: cosinor, nonparametric, and empirical mode decomposition. Preclinical AD was assessed by longitudinal clinical assessment, amyloid imaging with PiB, and cerebrospinal fluid biomarker collection. Results:Data from 189 participants were included in the analyses. The mean (SD) age was 66.6 (8.3) years, and 121 participants (64%) were women. Older age (??=?.247; P?=?.003) and male sex (??=?.170; P?=?.04), in the absence of amyloid pathology, were associated with a significant increase in intradaily variability, a nonparametric measure of rest-activity rhythm fragmentation, as well as decreased amplitude by several measures. After correction for age and sex, the presence of preclinical amyloid plaque pathology, assessed by positive PiB imaging (mean [SD], 0.804 [0.187] for PiB negative vs 0.875 [0.178] for PiB positive; P?=?.05) or increasing cerebrospinal fluid phosphorylated-tau to amyloid ? 42 ratio (??=?.231; P?=?.008), was associated with increased intradaily variability, indicating rest-activity rhythm fragmentation. Conclusions and Relevance:Preclinical AD is associated with rest-activity rhythm fragmentation, independent of age or sex. Aging was also associated with circadian dysfunction independently of preclinical AD pathology, particularly in men. The presence of circadian rhythm abnormalities in the preclinical phase of AD suggests that circadian dysfunction could contribute to early disease pathogenesis or serve as a biomarker of preclinical disease.
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Project description:ObjectiveA National Institute on Aging-sponsored work group on preclinical Alzheimer's disease (AD) articulated the need to characterize cognitive differences between normal aging and preclinical AD.MethodsSeventy-one apolipoprotein E (APOE) ε4 homozygotes, 194 ε3/ε4 heterozygotes, and 356 ε4 noncarriers age 21 to 87 years who were cognitively healthy underwent neuropsychological testing every 2 years. Longitudinal trajectories of test scores were compared between APOE subgroups.ResultsThere was a significant effect of age on all cognitive domains in both APOE ε4 carriers and noncarriers. A significant effect of APOE ε4 gene dose was confined to the memory domain and the Dementia Rating Scale. Cross-sectional comparisons did not discriminate the groups.ConclusionsAlthough cognitive aging patterns are similar in APOE ε4 carriers and noncarriers, preclinical AD is characterized by a significant ε4 gene dose effect that impacts memory and is detectable longitudinally. Preclinical neuropsychological testing strategies should emphasize memory-sensitive measures and longitudinal design.
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Project description:ObjectiveTo evaluate the spatial pattern and regional rates of neocortical atrophy from normal aging to early Alzheimer disease (AD).MethodsLongitudinal MRI data were analyzed using high-throughput image analysis procedures for 472 individuals diagnosed as normal, mild cognitive impairment (MCI), or AD. Participants were divided into 4 groups based on Clinical Dementia Rating Sum of Boxes score (CDR-SB). Annual atrophy rates were derived by calculating percent cortical volume loss between baseline and 12-month scans. Repeated-measures analyses of covariance were used to evaluate group differences in atrophy rates across regions as a function of impairment. Planned comparisons were used to evaluate the change in atrophy rates across levels of disease severity.ResultsIn patients with MCI-CDR-SB 0.5-1, annual atrophy rates were greatest in medial temporal, middle and inferior lateral temporal, inferior parietal, and posterior cingulate. With increased impairment (MCI-CDR-SB 1.5-2.5), atrophy spread to parietal, frontal, and lateral occipital cortex, followed by anterior cingulate cortex. Analysis of regional trajectories revealed increasing rates of atrophy across all neocortical regions with clinical impairment. However, increases in atrophy rates were greater in early disease within medial temporal cortex, whereas increases in atrophy rates were greater at later stages in prefrontal, parietal, posterior temporal, parietal, and cingulate cortex.ConclusionsAtrophy is not uniform across regions, nor does it follow a linear trajectory. Knowledge of the spatial pattern and rate of decline across the spectrum from normal aging to Alzheimer disease can provide valuable information for detecting early disease and monitoring treatment effects at different stages of disease progression.
| S-EPMC2727145 | biostudies-literature
Project description:ObjectiveRecent studies suggest that white matter hyperintensities (WMH) on MRI, which primarily reflect small vessel cerebrovascular disease, may play a role in the evolution of Alzheimer disease (AD). In a longitudinal study, we investigated whether WMH promote the progression of AD pathology, or alter the association between AD pathology and risk of progression from normal cognition to mild cognitive impairment (MCI).MethodsTwo sets of analyses were conducted. The relationship between whole brain WMH load, based on fluid-attenuated inversion recovery MRI, obtained in initially cognitively normal participants (n = 274) and time to onset of symptoms of MCI (n = 60) was examined using Cox regression models. In a subset of the participants with both MRI and CSF data (n = 204), the interaction of WMH load and CSF AD biomarkers was also evaluated.ResultsBaseline WMH load interacted with CSF total tau (t-tau) with respect to symptom onset, but not with CSF β-amyloid 1-42 or phosphorylated tau (p-tau) 181. WMH volume was associated with time to symptom onset of MCI among individuals with low t-tau (hazard ratio [HR] 1.35, confidence interval [CI] 1.06-1.73, p = 0.013), but not those with high t-tau (HR 0.86, CI 0.56-1.32, p = 0.47). The rate of change in the CSF biomarkers over time was not associated with the rate of change in WMH volumes.ConclusionThese results suggest that WMH primarily affect the risk of progression when CSF measures of neurodegeneration or neuronal injury (as reflected by t-tau) are low. However, CSF biomarkers of amyloid and p-tau and WMH appear to have largely independent and nonsynergistic effects on the risk of progression to MCI.
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Project description:Identifying asymptomatic older individuals at elevated risk for developing Alzheimer disease (AD) is of clinical importance. Among 1,081 asymptomatic older adults, a recently validated polygenic hazard score (PHS) significantly predicted time to AD dementia and steeper longitudinal cognitive decline, even after controlling for APOE ɛ4 carrier status. Older individuals in the highest PHS percentiles showed the highest AD incidence rates. PHS predicted longitudinal clinical decline among older individuals with moderate to high Consortium to Establish a Registry for Alzheimer's Disease (amyloid) and Braak (tau) scores at autopsy, even among APOE ɛ4 noncarriers. Beyond APOE, PHS may help identify asymptomatic individuals at highest risk for developing Alzheimer neurodegeneration. Ann Neurol 2017;82:484-488.
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Project description:A neuropathological hallmark of Alzheimer disease (AD) is a widespread amyloid deposition. We analyzed the entire amino acid sequences in an amyloid preparation and found, in addition to the major beta/A4-protein (A beta) fragment, two unknown peptides. We raised antibodies against synthetic peptides using subsequences of these peptides. These antibodies immunostained amyloid in neuritic and diffuse plaques as well as vascular amyloid. Electron microscopic analysis demonstrated that the immunostaining was localized on amyloid fibrils. We have isolated an apparently full-length cDNA encoding a 140-amino-acid protein within which two previously unreported amyloid sequences are encoded in tandem in the most hydrophobic domain. We tentatively named this 35-amino acid peptide NAC (non-A beta component of AD amyloid) and its precursor NACP. NAC is the second component, after A beta, identified chemically in the purified AD amyloid preparation. Secondary structure predictions indicate that the NAC peptide sequence has a strong tendency to form beta-structures consistent with its association with amyloid. NACP is detected as a M(r) 19,000 protein in the cytosolic fraction of brain homogenates and comigrates on immunoblots with NACP synthesized in Escherichia coli from NACP cDNA. NACP mRNA is expressed principally in brain but is also expressed in low concentrations in all tissues examined except in liver, suggesting its ubiquitous and brain-specific functions. The availability of the cDNA encoding full-length NACP should help to elucidate the mechanisms of amyloidosis in AD.
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Project description:The enigma that is Alzheimer's disease (AD) continues to present daunting challenges for effective therapeutic intervention. The lack of disease-modifying therapies may, in part, be attributable to the narrow research focus employed to understand this complex disease. Most studies into disease pathogenesis are based on a priori assumptions about the role of AD lesion-associated proteins such as amyloid-β and tau. However, the complex disease processes at work may not be amenable to single-target therapeutic approaches. Genome-wide expression studies provide an unbiased approach for investigating the pathogenesis of complex diseases like AD. A growing literature suggests a role for cerebrovascular contributions to the pathogenesis of AD. The objective of the current study is to examine human brain microvessels isolated from AD patients and controls by microarray analysis. Differentially expressed genes with more than 2-fold change are used for further data analysis. Gene ontology analysis and pathway analysis algorithms within GeneSpringGX are employed to understand the regulatory networks of differentially expressed genes. Twelve matched pairs of AD and control brain microvessel samples are hybridized to Agilent Human 4 × 44 K arrays in replication. We document that more than 2,000 genes are differentially altered in AD microvessels and that a large number of these genes map to pathways associated with immune and inflammatory response, signal transduction, and nervous system development and function categories. These data may help elucidate heretofore unknown molecular alterations in the AD cerebromicrovasculature.
2013-03-29 | GSE45596 | GEO
Project description:The enigma that is Alzheimer's disease (AD) continues to present daunting challenges for effective therapeutic intervention. The lack of disease-modifying therapies may, in part, be attributable to the narrow research focus employed to understand this complex disease. Most studies into disease pathogenesis are based on a priori assumptions about the role of AD lesion-associated proteins such as amyloid-? and tau. However, the complex disease processes at work may not be amenable to single-target therapeutic approaches. Genome-wide expression studies provide an unbiased approach for investigating the pathogenesis of complex diseases like AD. A growing literature suggests a role for cerebrovascular contributions to the pathogenesis of AD. The objective of the current study is to examine human brain microvessels isolated from AD patients and controls by microarray analysis. Differentially expressed genes with more than 2-fold change are used for further data analysis. Gene ontology analysis and pathway analysis algorithms within GeneSpringGX are employed to understand the regulatory networks of differentially expressed genes. Twelve matched pairs of AD and control brain microvessel samples are hybridized to Agilent Human 4 × 44 K arrays in replication. We document that more than 2,000 genes are differentially altered in AD microvessels and that a large number of these genes map to pathways associated with immune and inflammatory response, signal transduction, and nervous system development and function categories. These data may help elucidate heretofore unknown molecular alterations in the AD cerebromicrovasculature. Two condition experiment, diseased vs normal, our study included 12 pairs of biological replicates and each pair was repeated with dye swap making total of 24 double channel hybridizations. we excluded 4 samples for not passing QC. So 20 samples were included in the data analysis.
2013-03-29 | E-GEOD-45596 | biostudies-arrayexpress
Project description:ObjectiveThe present work was undertaken to study the genetic contribution to the start of Alzheimer's disease (AD) with amyloid and tau biomarkers in cognitively intact older identical twins.MethodsWe studied in 96 monozygotic twin-pairs relationships between amyloid-beta (Aβ) aggregation as measured by the Aβ1-42/1-40 ratio in cerebrospinal fluid (CSF; n = 126) and positron emission tomography (PET, n = 194), and CSF markers for Aβ production (beta-secretase 1, Aβ1-40, and Aβ1-38) and CSF tau. Associations among markers were tested with generalized estimating equations including a random effect for twin status, adjusted for age, gender, and apolipoprotein E ε4 genotype. We used twin analyses to determine relative contributions of genetic and/or environmental factors to AD pathophysiological processes.ResultsTwenty-seven individuals (14%) had an abnormal amyloid PET, and 14 twin-pairs (15%) showed discordant amyloid PET scans. Within twin-pairs, Aβ production markers and total-tau (t-tau) levels strongly correlated (r range = 0.73-0.86, all p < 0.0001), and Aβ aggregation markers and 181-phosphorylated-tau (p-tau) levels correlated moderately strongly (r range = 0.50-0.64, all p < 0.0001). Cross-twin cross-trait analysis showed that Aβ1-38 in one twin correlated with Aβ1-42/1-40 ratios, and t-tau and p-tau levels in their cotwins (r range = -0.28 to 0.58, all p < .007). Within-pair differences in Aβ production markers related to differences in tau levels (r range = 0.49-0.61, all p < 0.0001). Twin discordance analyses suggest that Aβ production and tau levels show coordinated increases in very early AD.InterpretationOur results suggest a substantial genetic/shared environmental background contributes to both Aβ and tau increases, suggesting that modulation of environmental risk factors may aid in delaying the onset of AD pathophysiological processes. ANN NEUROL 2021;89:987-1000.
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