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Do white matter hyperintensities mediate the association between brain iron deposition and cognitive abilities in older people?

ABSTRACT: Several studies have reported associations between brain iron deposits (IDs), white matter hyperintensities (WMHs) and cognitive ability in older individuals. Whether the association between brain IDs and cognitive abilities in older people is mediated by or independent of total brain tissue damage represented by WMHs visible on structural magnetic resonance imaging (MRI) was examined.Data from 676 community-dwelling individuals from the Lothian Birth Cohort 1936, with Mini-Mental State Examination scores >24, who underwent detailed cognitive testing and multimodal brain MRI at mean age 72.7 years were analysed. Brain IDs were assessed automatically following manual editing. WMHs were assessed semi-automatically. Brain microbleeds were visually counted. Structural equation modelling was used to test for mediation.Overall, 72.8% of the sample had IDs with a median total volume of 0.040 ml (i.e. 0.004% of the total brain volume). The total volume of IDs, significantly and negatively associated with general cognitive function (standardized ? = -0.17, P < 0.01), was significantly and positively associated with WMH volume (std ? = 0.13, P = 0.03). WMH volume had a significant negative association with general cognitive function, independent of IDs (std ? = -0.13, P < 0.01). The association between cognition and IDs in the brain stem (and minimally the total brain iron load) was partially and significantly mediated by WMH volume (P = 0.03).The negative association between brain IDs and cognitive ability in the elderly is partially mediated by WMHs, with this mediation mainly arising from the iron deposition load in the brain stem. IDs might be an indicator of small vessel disease that predisposes to white matter damage, affecting the neuronal networks underlying higher cognitive functioning.

SUBMITTER: Valdes Hernandez M

PROVIDER: S-EPMC4950475 | biostudies-literature | 2016 Jul

REPOSITORIES: biostudies-literature

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Do white matter hyperintensities mediate the association between brain iron deposition and cognitive abilities in older people?

Valdés Hernández M M Allerhand M M Glatz A A Clayson L L Muñoz Maniega S S Gow A A Royle N N Bastin M M Starr J J Deary I I Wardlaw J J

European journal of neurology 20160420 7

<h4>Background and purpose</h4>Several studies have reported associations between brain iron deposits (IDs), white matter hyperintensities (WMHs) and cognitive ability in older individuals. Whether the association between brain IDs and cognitive abilities in older people is mediated by or independent of total brain tissue damage represented by WMHs visible on structural magnetic resonance imaging (MRI) was examined.<h4>Methods</h4>Data from 676 community-dwelling individuals from the Lothian Bir ...[more]

PMID: 27094820

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Project description:BackgroundAlbuminuria, a kidney marker of microvascular disease, may herald microvascular disease elsewhere, including in the brain.Study designCross sectional.Setting & participantsBoston, MA, elders receiving home health services to maintain independent living who consented to brain magnetic resonance imaging.PredictorUrine albumin-creatinine ratio (ACR).OutcomePerformance on a cognitive battery assessing executive function and memory by using principal components analysis and white matter hyperintensity volume on brain imaging, evaluated in logistic and linear regression models.ResultsIn 335 participants, mean age was 73.4 +/- 8.1 years and 123 participants had microalbuminuria or macroalbuminuria. Each doubling of ACR was associated with worse executive function (beta = -0.05; P = 0.005 in univariate and beta = -0.07; P = 0.004 in multivariable analyses controlling for age, sex, race, education, diabetes, cardiovascular disease, hypertension, medications, and estimated glomerular filtration rate [eGFR]), but not with worse memory or working memory. Individuals with microalbuminuria or macroalbuminuria were more likely to be in the lower versus the highest tertile of executive functioning (odds ratio, 1.18; 95% confidence interval, 1.06 to 1.32; odds ratio, 1.19; 95% confidence interval, 1.05 to 1.35 per doubling of ACR in univariate and multivariable analyses, respectively). Albuminuria was associated with qualitative white matter hyperintensity grade (odds ratio, 1.13; 95% confidence interval, 1.02 to 1.25; odds ratio, 1.15; 95% confidence interval, 1.02 to 1.29 per doubling of ACR) in univariate and multivariable analyses and with quantitative white matter hyperintensity volume (beta = 0.11; P = 0.007; beta = 0.10; P = 0.01) in univariate and multivariable analyses of log-transformed data. Results were similar when excluding individuals with macroalbuminuria.LimitationsSingle measurement of ACR, indirect creatinine calibration, and reliance on participant recall for elements of medical history.ConclusionsAlbuminuria is associated with worse cognitive performance, particularly in executive functioning, as well as increased white matter hyperintensity volume. Albuminuria likely identifies greater brain microvascular disease burden.

Project description:BackgroundPatients with Parkinson's disease (PD) present with a broad spectrum of nonmotor features including autonomic disorders. More severe autonomic dysfunction in PD is associated with increased cognitive deficits. The presence of cerebral small-vessel disease, measured by T2-weighted magnetic resonance imaging white matter hyperintensity (WMH) burden, is also observed in patients with PD with faster cognitive decline.ObjectiveTo investigate whether baseline orthostatic hypotension and autonomic dysfunction in early-stage PD affect later cognitive decline via mediation through cerebral small-vessel disease.MethodsDe novo PD patients (N = 365) and age-matched controls (N = 174) with baseline T2-weighted/ fluid-attenuated inversion recovery scans were selected from the Parkinson's Progression Markers Initiative. WMHs were automatically segmented. Mediation analysis was used to assess whether WMH load mediates the effect of orthostatic hypotension and autonomic dysfunction (measured by Scales for Outcomes in Parkinson's Disease-Autonomic) on future cognitive decline (measured by Montreal Cognitive Assessment) in an average of 4 years of follow-up.ResultsMediation analysis supported the existence of a full mediation of WMHs on the effect of diastolic orthostatic hypotension in patients with PD and future cognitive decline (average causal mediation effect: ab = -0.032, 95% confidence interval = -0.064 to -0.01, P = 0.01). There was also a partial mediation for overall autonomic dysfunction (ab = -0.027, 95% confidence interval = -0.054 to 0.00, P = 0.02).ConclusionsWMHs fully mediate the effect of diastolic orthostatic hypotension and partially mediate the effect of autonomic dysregulation on future cognitive decline in patients with PD. Our findings support the hypothesis that autonomic dysfunction in early clinical stages predisposes the brain to WMHs through dysregulation of the blood flow in the small vessels. This in turn increases the risk of future cognitive impairment in early PD.

Project description:Frontal lobe structures decline faster than most other brain regions in older adults. Age-related change in the frontal lobe is associated with poorer executive function (e.g., working memory, switching/set-shifting, and inhibitory control). The effects and presence of frontal lobe white matter hyperintensities (WMH) on executive function in normal aging is relatively unknown. The current study assessed relationships between region-specific frontal WMH load and cognitive performance in healthy older adults using three executive function tasks from the NIH Toolbox (NIHTB) Cognition Battery. A cohort of 279 healthy older adults ages 65-88 completed NIHTB and 3T T1-weighted and FLAIR MRI. Lesion Segmentation Toolbox quantified WMH volume and generated lesion probability maps. Individual lesion maps were registered to the Desikan-Killiany atlas in FreeSurfer 6.0 to define regions of interest (ROI). Independent linear regressions assessed relationships between executive function performance and region-specific WMH in frontal lobe ROIs. All models included age, sex, education, estimated total intracranial volume, multi-site scanner differences, and cardiovascular disease risk using Framingham criteria as covariates. Poorer set-shifting performance was associated with greater WMH load in three frontal ROIs including bilateral superior frontal (left β = -0.18, FDR-p = 0.02; right β = -0.20, FDR-p = 0.01) and right medial orbitofrontal (β = -0.17, FDR-p = 0.02). Poorer inhibitory performance associated with higher WMH load in one frontal ROI, the right superior frontal (right β = -0.21, FDR-p = 0.01). There were no significant associations between working memory and WMH in frontal ROIs. Our study demonstrates that location and pattern of frontal WMH may be important to assess when examining age-related differences in cognitive functions involving switching/set-shifting and inhibition. On the other hand, working memory performance was not related to presence of frontal WMH in this sample. These data suggest that WMH may contribute selectively to age-related declines in executive function. Findings emerged beyond predictors known to be associated with WMH presence, including age and cardiovascular disease risk. The spread of WMH within the frontal lobes may play a key role in the neuropsychological profile of cognitive aging. Further research should explore whether early intervention on modifiable vascular factors or cognitive interventions targeted for executive abilities may help mitigate the effect of frontal WMH on executive function.

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Do white matter hyperintensities mediate the association between brain iron deposition and cognitive abilities in older people?

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Do white matter hyperintensities mediate the association between brain iron deposition and cognitive abilities in older people?

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