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Amyloid-?, Tau, and Cognition in Cognitively Normal Older Individuals: Examining the Necessity to Adjust for Biomarker Status in Normative Data.

ABSTRACT: We investigated whether amyloid-? (A?) and tau affected cognition in cognitively normal (CN) individuals, and whether norms for neuropsychological tests based on biomarker-negative individuals would improve early detection of dementia. We included 907 CN individuals from 8 European cohorts and from the Alzheimer's disease Neuroimaging Initiative. All individuals were aged above 40, had A? status and neuropsychological data available. Linear mixed models were used to assess the associations of A? and tau with five neuropsychological tests assessing memory (immediate and delayed recall of Auditory Verbal Learning Test, AVLT), verbal fluency (Verbal Fluency Test, VFT), attention and executive functioning (Trail Making Test, TMT, part A and B). All test except the VFT were associated with A? status and this influence was augmented by age. We found no influence of tau on any of the cognitive tests. For the AVLT Immediate and Delayed recall and the TMT part A and B, we calculated norms in individuals without A? pathology (A?- norms), which we validated in an independent memory-clinic cohort by comparing their predictive accuracy to published norms. For memory tests, the A?- norms rightfully identified an additional group of individuals at risk of dementia. For non-memory test we found no difference. We confirmed the relationship between A? and cognition in cognitively normal individuals. The A?- norms for memory tests in combination with published norms improve prognostic accuracy of dementia.

SUBMITTER: Bos I

PROVIDER: S-EPMC6027060 | biostudies-literature | 2018

REPOSITORIES: biostudies-literature

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Amyloid-β, Tau, and Cognition in Cognitively Normal Older Individuals: Examining the Necessity to Adjust for Biomarker Status in Normative Data.

Bos Isabelle I Vos Stephanie J B SJB Jansen Willemijn J WJ Vandenberghe Rik R Gabel Silvy S Estanga Ainara A Ecay-Torres Mirian M Tomassen Jori J den Braber Anouk A Lleó Alberto A Sala Isabel I Wallin Anders A Kettunen Petronella P Molinuevo José L JL Rami Lorena L Chetelat Gaël G de la Sayette Vincent V Tsolaki Magda M Freund-Levi Yvonne Y Johannsen Peter P Novak Gerald P GP Ramakers Inez I Verhey Frans R FR Visser Pieter Jelle PJ

Frontiers in aging neuroscience 20180625

We investigated whether amyloid-β (Aβ) and tau affected cognition in cognitively normal (CN) individuals, and whether norms for neuropsychological tests based on biomarker-negative individuals would improve early detection of dementia. We included 907 CN individuals from 8 European cohorts and from the Alzheimer's disease Neuroimaging Initiative. All individuals were aged above 40, had Aβ status and neuropsychological data available. Linear mixed models were used to assess the associations of Aβ ...[more]

PMID: 29988624

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Project description:BackgroundIndividuals on the preclinical Alzheimer's continuum, particularly those with both amyloid and tau positivity (A + T +), display a rapid cognitive decline and elevated disease progression risk. However, limited studies exist on brain atrophy trajectories within this continuum over extended periods.MethodsThis study involved 367 ADNI participants grouped based on combinations of amyloid and tau statuses determined through cerebrospinal fluid tests. Using longitudinal MRI scans, brain atrophy was determined according to the whole brain, lateral ventricle, and hippocampal volumes and cortical thickness in AD-signature regions. Cognitive performance was evaluated with the Preclinical Alzheimer's Cognitive Composite (PACC). A generalized linear mixed-effects model was used to examine group × time interactions for these measures. In addition, progression risks to mild cognitive impairment (MCI) or dementia were compared among the groups using Cox proportional hazards models.ResultsA total of 367 participants (48 A + T + , 86 A + T - , 63 A - T + , and 170 A - T - ; mean age 73.8 years, mean follow-up 5.1 years, and 47.4% men) were included. For the lateral ventricle and PACC score, the A + T - and A + T + groups demonstrated statistically significantly greater volume expansion and cognitive decline over time than the A - T - group (lateral ventricle: β = 0.757 cm3/year [95% confidence interval 0.463 to 1.050], P < .001 for A + T - , and β = 0.889 cm3/year [0.523 to 1.255], P < .001 for A + T + ; PACC: β = - 0.19 /year [- 0.36 to - 0.02], P = .029 for A + T - , and β = - 0.59 /year [- 0.80 to - 0.37], P < .001 for A + T +). Notably, the A + T + group exhibited additional brain atrophy including the whole brain (β = - 2.782 cm3/year [- 4.060 to - 1.504], P < .001), hippocampus (β = - 0.057 cm3/year [- 0.085 to - 0.029], P < .001), and AD-signature regions (β = - 0.02 mm/year [- 0.03 to - 0.01], P < .001). Cox proportional hazards models suggested an increased risk of progressing to MCI or dementia in the A + T + group versus the A - T - group (adjusted hazard ratio = 3.35 [1.76 to 6.39]).ConclusionsIn cognitively normal individuals, A + T + compounds brain atrophy and cognitive deterioration, amplifying the likelihood of disease progression. Therapeutic interventions targeting A + T + individuals could be pivotal in curbing brain atrophy, cognitive decline, and disease progression.

Project description:To improve the ability to develop treatments that prevent incipient Alzheimer disease (AD) from progressing to overt AD, it is important to understand the molecular basis of the earliest pathophysiological abnormalities and to determine how amyloid-? (A?) is involved very early in its pathogenesis.To investigate 2 specific A? oligomers, A? trimers and A?*56, in human cerebrospinal fluid (CSF); evaluate the effects of aging and AD; and obtain support for the hypothesis that they may be pathogenic by determining their relationships to CSF tau.A CSF sampling study.The University of Minnesota Medical School in Minneapolis, Minnesota, and the Salhgrenska University Hospital, Sweden.Forty-eight older adults with mild cognitive impairment or AD (impaired group); 49 age-matched cognitively intact control subjects (unimpaired group); and 10 younger, normal control subjects.Measurements of CSF A? trimers, A?*56, the 42-amino acid A? isoform (A?1-42), total tau (T-tau), and phospho-tau 181 (p-tau(181)). The hypothesis being tested was formulated after data collection. RESULTS We observed that A? trimers and A?*56 levels increased with age; within the unimpaired group, they were elevated in subjects with T-tau/A?1-42 ratios greater than a cutoff that distinguished the unimpaired group from subjects with AD. In the unimpaired group, T-tau and p-tau(181) were found to correlate strongly with A? trimers and A?*56 (r > 0.63), but not with A?1-42 (-0.10 < r < -0.01). The strong correlations were found to be attenuated in the impaired group.In cognitively intact older adults, CSF A? trimers and A?*56 were elevated in individuals at risk for AD, and they showed stronger relationships with tau than did A?1-42, a surrogate for A? fibril deposition. These findings suggest that prior to overt symptoms, 1 or both of the A? oligomers, but not fibrillar A?, is coupled to tau; however, this coupling is weakened or broken when AD advances to symptomatic stages. The uncoupling is interesting in light of the failure of experimental A? therapies to improve mild cognitive impairment/AD, which has prompted a shift in the timing of A? therapies to asymptomatic subjects. Knowing which A? species to target in asymptomatic subjects may enhance the success of future treatments for AD.

Project description:ImportanceThe role of amyloid in the progression of Alzheimer disease (AD) pathophysiology is of central interest to the design of randomized clinical trials. The presence of amyloid has become a prerequisite for enrollment in several secondary prevention trials for AD, yet the precise effect of elevated amyloid levels on subsequent clinical and biomarker events is less certain.ObjectiveTo explore the effect of elevated amyloid levels on subsequent changes in cognition and biomarkers.Design, setting, and participantsA total of 564 cognitively normal individuals (median age, 78 years) from the Mayo Clinic Study of Aging, a population-based longitudinal study in Olmsted County, Minnesota, with serial cognitive data were selected for this study. The data used in this study were collected from January 12, 2006, to January 9, 2014. Individuals included in this study had undergone magnetic resonance imaging, fluorodeoxyglucose positron emission tomography (FDG-PET), and Pittsburgh Compound B (PiB) PET at baseline were not cognitively impaired at baseline and had at least 1 clinical follow-up. A subset of 286 individuals also underwent serial imaging. Elevated amyloid level was defined as a standardized uptake value ratio of greater than 1.5 on PiB PET. Associations with baseline amyloid status and baseline and longitudinal change in clinical and imaging measures were evaluated after adjusting for age and hippocampal volume. APOE4 effects were also evaluated.Main outcomes and measuresCognitive measures of memory, language, attention/executive function, visuospatial skills, PiB levels, hippocampal and ventricular volumes, and FDG-PET measures.ResultsAt baseline, 179 (31.7%) individuals with elevated amyloid levels had poorer cognition in all domains measured, reduced hippocampal volume, and greater FDG-PET hypometabolism. Elevated amyloid levels at baseline were associated with a greater rate of cognitive decline in all domains (0.04 to 0.09 z score units per year) except language and a greater rate of amyloid accumulation (1.6% per year), hippocampal atrophy (30 mm3 per year), and ventricular enlargement (565 mm3 per year). Elevated amyloid levels were also associated with an increased risk of mild cognitive impairment (hazard ratio, 2.9; 95% CI, 1.7-5.0, and hazard ratio, 1.6; 95% CI, 0.9-2.8, for PiB+ APOE4 carriers and PiB+ noncarriers, respectively, compared with PiB- noncarriers). These associations were largely independent of APOE4.Conclusions and relevanceIn persons selected from a population-based study, elevated amyloid levels at baseline were associated with worse cognition and imaging biomarkers at baseline and with greater clinical decline and neurodegeneration. These results have implications for the design of randomized clinical trials for AD.

Project description:Importance:The goal of Alzheimer disease (AD) prevention together with advances in understanding the pathophysiology of AD have led to clinical trials testing drugs in cognitively unimpaired persons who show evidence of AD biomarkers. Data are needed to inform the processes of describing AD biomarkers to cognitively normal adults and assessing their understanding of this knowledge. Objective:To determine the comprehension of an elevated amyloid positron emission tomographic (PET) biomarker result by cognitively unimpaired adults. Design, Setting, and Participants:The Study of Knowledge and Reactions to Amyloid Testing, a substudy of an AD prevention trial, involved 2 semistructured telephone interviews with 80 participants recruited from 9 study sites: 50 received elevated and 30 received not elevated amyloid PET scan results. Interviews were conducted 4 to 12 weeks after result disclosure and again 1 year later. Data presented here were collected from November 5, 2014, through December 10, 2015. The 50 participants included in this study were cognitively normal, aged 65 to 85 years, evenly distributed by gender, and had elevated amyloid PET results. Subsequent reports will examine persons with "not elevated" results and compare the influence of the different results. Main Outcomes and Measures:Participant comprehension of an elevated amyloid result was assessed by analyzing their responses to the following questions: "What was the result of your amyloid PET scan?" (followed by "Can you tell me in your own words what that means?" or "How would you explain it to a friend?"), "Was it the result you expected?" and "Did the result teach you anything or clarify anything for you?" Results:Of the 50 participants aged 65 to 85 years, 49 (98%) were white, 40 (80%) reported a family history of AD, and 30 (60%) had a postgraduate educational level. Most participants (31 [62%]) understood that elevated amyloid conferred an increased but uncertain risk of developing AD. Some desired understanding of the term elevated other than its being a categorical result enabling trial entry eligibility; they wanted information regarding how elevated their amyloid was, how close to the study threshold they were, or percentages, numbers, or a scale to help them make sense of the result. Conclusions and Relevance:Including an explanation of how and why a dimensional biomarker is converted to a categorical classification would enhance future AD biomarker clinical trials and educational materials.

Dataset Information

Amyloid-?, Tau, and Cognition in Cognitively Normal Older Individuals: Examining the Necessity to Adjust for Biomarker Status in Normative Data.

Publications

Amyloid-β, Tau, and Cognition in Cognitively Normal Older Individuals: Examining the Necessity to Adjust for Biomarker Status in Normative Data.

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