Alzheimer’s disease (AD) affects more than twenty-five million people worldwide and is the most common form of dementia. Symptomatic treatments have been developed, but effective intervention to alter disease progression is needed. Targets have been identified for disease-modifying drugs, but the results of clinical trials have been disappointing. Peripheral biomarkers of disease state may improve clinical trial design and analysis, increasing the likelihood of successful drug development. Amyloid-related measures, presumably reflecting principal pathology of AD, are among the leading cerebrospinal fluid and neuroimaging biomarkers, and measurement of plasma levels of amyloid peptides has been the focus of much investigation. In this review, we discuss recent data on plasma β-amyloid (Aβ) and examine the issues that have arisen in establishing it as a reliable biomarker of AD.
Alzheimer’s disease; Protein biomarker; Plasma amyloid
Among the major impediments to the design of clinical trials for the prevention of Alzheimer's disease (AD), the most critical is the lack of validated biomarkers, assessment tools, and algorithms that would facilitate identification of asymptomatic individuals with elevated risk who might be recruited as study volunteers. Thus, the Leon Thal Symposium 2009 (LTS'09), on October 27–28, 2009 in Las Vegas, Nevada, was convened to explore strategies to surmount the barriers in designing a multisite, comparative study to evaluate and validate various approaches for detecting and selecting asymptomatic people at risk for cognitive disorders/dementia. The deliberations of LTS'09 included presentations and reviews of different approaches (algorithms, biomarkers, or measures) for identifying asymptomatic individuals at elevated risk for AD who would be candidates for longitudinal or prevention studies. The key nested recommendations of LTS'09 included: (1) establishment of a National Database for Longitudinal Studies as a shared research core resource; (2) launch of a large collaborative study that will compare multiple screening approaches and biomarkers to determine the best method for identifying asymptomatic people at risk for AD; (3) initiation of a Global Database that extends the concept of the National Database for Longitudinal Studies for longitudinal studies beyond the United States; and (4) development of an educational campaign that will address public misconceptions about AD and promote healthy brain aging.
Alzheimer's disease; Dementia; Mild cognitive impairment; Prevention; Biomarkers; Diagnosis; Screening; Clinical trials; MCI; Asymptomatic; Risk factors; Registry; Longitudinal studies; Database; PAD2020; Leon Thal Symposium; Treatment; Drug development; Health policy
To identify factors influencing age at symptom onset and disease course in autosomal dominant Alzheimer disease (ADAD), and develop evidence-based criteria for predicting symptom onset in ADAD.
We have collected individual-level data on ages at symptom onset and death from 387 ADAD pedigrees, compiled from 137 peer-reviewed publications, the Dominantly Inherited Alzheimer Network (DIAN) database, and 2 large kindreds of Colombian (PSEN1 E280A) and Volga German (PSEN2 N141I) ancestry. Our combined dataset includes 3,275 individuals, of whom 1,307 were affected by ADAD with known age at symptom onset. We assessed the relative contributions of several factors in influencing age at onset, including parental age at onset, age at onset by mutation type and family, and APOE genotype and sex. We additionally performed survival analysis using data on symptom onset collected from 183 ADAD mutation carriers followed longitudinally in the DIAN Study.
We report summary statistics on age at onset and disease course for 174 ADAD mutations, and discover strong and highly significant (p < 10−16, r2 > 0.38) correlations between individual age at symptom onset and predicted values based on parental age at onset and mean ages at onset by mutation type and family, which persist after controlling for APOE genotype and sex.
Significant proportions of the observed variance in age at symptom onset in ADAD can be explained by family history and mutation type, providing empirical support for use of these data to estimate onset in clinical research.
APOE ε4’s role as a modulator of the relationship between soluble plasma beta-amyloid (Aβ) and fibrillar brain Aβ measured by Pittsburgh Compound-B positron emission tomography ([11C]PiB PET) has not been assessed.
Ninety-six Alzheimer’s Disease Neuroimaging Initiative participants with [11C]PiB scans and plasma Aβ1-40 and Aβ1-42 measurements at time of scan were included. Regional and voxel-wise analyses of [11C]PiB data were used to determine the influence of APOE ε4 on association of plasma Aβ1-40, Aβ1-42, and Aβ1-40/Aβ1-42 with [11C]PiB uptake.
In APOE ε4− but not ε4+ participants, positive relationships between plasma Aβ1-40/Aβ1-42 and [11C]PiB uptake were observed. Modeling the interaction of APOE and plasma Aβ1-40/Aβ1-42 improved the explained variance in [11C]PiB binding compared to using APOE and plasma Aβ1-40/Aβ1-42 as separate terms.
The results suggest that plasma Aβ is a potential Alzheimer’s disease biomarker and highlight the importance of genetic variation in interpretation of plasma Aβ levels.
Alzheimer’s disease (AD); mild cognitive impairment (MCI); Alzheimer’s Disease Neuroimaging Initiative (ADNI); beta-amyloid (Aβ); plasma beta-amyloid; positron emission tomography (PET); Pittsburgh Compound-B ([11C]PiB); Apolipoprotein E (APOE)
The Alzheimer's Disease Cooperative Study Prevention Instrument Project is a longitudinal study that recruited 644 cognitively healthy older subjects (aged between 75 and 93 years, 58% women) at baseline and evaluated their cognitive change over 4 years. The study was structured like a clinical trial to anticipate a prevention trial and to determine the performance of novel trial instruments in a longitudinal non-interventional trial framework. Behavioral symptoms were assessed at baseline.
The existence of participant-reported behavioral symptoms at baseline predicted conversion to Clinical Dementia Rating scale score ≥0.5 over the 4-year period.
The results imply that early anxiety and depression may be harbingers of future cognitive decline, and that patients exhibiting such symptoms, even in the absence of co-occurring cognitive symptoms, should be closely followed over time.
Aging; Depression; Anxiety; Mild cognitive impairment; Alzheimer's disease
Prevalence and risk factors for focal hemosiderin deposits are important considerations when planning amyloid–modifying trials for treatment and prevention of Alzheimer’s disease (AD).
Subjects were cognitively normal (n=171), early-mild cognitive impairment (MCI) (n=240), late-MCI (n=111) and AD (n=40) from the Alzheimer’s Disease Neuroimaging Initiative (ADNI). Microhemorrhages and superficial siderosis were assessed at baseline and on all available MRIs at 3, 6 and 12 months. β-amyloid load was assessed with 18F-florbetapir PET.
Prevalence of superficial siderosis was 1% and prevalence of microhemorrhages was 25% increasing with age (p<0.001) and β-amyloid load (p<0.001). Topographic densities of microhemorrhages were highest in the occipital lobes and lowest in the deep/infratentorial regions. A greater number of microhemorrhages at baseline was associated with a greater annualized rate of additional microhemorrhages by last follow-up (rank correlation=0.49;P<0.001).
Focal hemosiderin deposits are relatively common in the ADNI cohort and are associated with β-amyloid load.
ADNI; microhemorrhage; superficial siderosis; MRI; Amyloid; PET; Florbetapir; Alzheimer’s disease; mild cognitive impairment; early mild cognitive impairment
This report describes the baseline experience of the multi-center, Home Based Assessment (HBA) study, designed to develop methods for dementia prevention trials using novel technologies for test administration and data collection. Non-demented individuals ≥ 75 years old were recruited and evaluated in-person using established clinical trial outcomes of cognition and function, and randomized to one of 3 assessment methodologies: 1) mail-in questionnaire/live telephone interviews (MIP); 2) automated telephone with interactive voice recognition (IVR); and 3) internet-based computer Kiosk (KIO). Brief versions of cognitive and non-cognitive outcomes, were adapted to each methodology and administered at baseline and repeatedly over a 4-year period. “Efficiency” measures assessed the time from screening to baseline, and staff time required for each methodology. 713 individuals signed consent and were screened; 640 met eligibility and were randomized to one of 3 assessment arms and 581 completed baseline. Drop out, time from screening to baseline and total staff time were highest among those assigned to KIO. However efficiency measures were driven by non-recurring start-up activities suggesting that differences may be mitigated over a long trial. Performance among HBA instruments collected via different technologies will be compared to established outcomes over this 4 year study.
Alzheimer’s disease; clinical trials; in-home assessment; prevention studies
Deposition of amyloid-β (Aβ) in the cerebral cortex is thought to be a pivotal event in Alzheimer’s disease (AD) pathogenesis with a significant genetic contribution. Molecular imaging can provide an early noninvasive phenotype but small samples have prohibited genome-wide association studies (GWAS) of cortical Aβ load until now. We employed florbetapir (18F) positron emission tomography (PET) imaging to assess brain Aβ levels in vivo for 555 participants from the Alzheimer’s Disease Neuroimaging Initiative (ADNI). More than six million common genetic variants were tested for association to quantitative global cortical Aβ load controlling for age, gender, and diagnosis. Independent genome-wide significant associations were identified on chromosome 19 within APOE (rs429358, p = 5.5 × 10−14) and on chromosome 3 upstream of BCHE (rs509208, p = 2.7 × 10−8) in a region previously associated with serum butyrylcholinesterase activity. Together, these loci explained 15% of the variance in cortical Aβ levels in this sample (APOE 10.7%, BCHE 4.3%). Suggestive associations were identified within ITGA6, near EFNA5, EDIL3, ITGA1, PIK3R1, NFIB, and ARID1B, and between NUAK1 and C12orf75. These results confirm the association of APOE with Aβ deposition and represent the largest known effect of BCHE on an AD-related phenotype. Butyrylcholinesterase has been found in senile plaques and this new association of genetic variation at the BCHE locus with Aβ burden in humans may have implications for potential disease-modifying effects of butyrylcholinesterase-modulating agents in the AD spectrum.
Alzheimer’s disease (AD); amyloid; apolipoprotein E (APOE); butyrylcholinesterase (BCHE); florbetapir (AV-45); genome-wide association study (GWAS)
The Alzheimer's Disease Neuroimaging Initiative (ADNI) is an ongoing, longitudinal, multicenter study designed to develop clinical, imaging, genetic, and biochemical biomarkers for the early detection and tracking of Alzheimer's disease (AD). The study aimed to enroll 400 subjects with early mild cognitive impairment (MCI), 200 subjects with early AD, and 200 normal control subjects; $67 million funding was provided by both the public and private sectors, including the National Institute on Aging, 13 pharmaceutical companies, and 2 foundations that provided support through the Foundation for the National Institutes of Health. This article reviews all papers published since the inception of the initiative and summarizes the results as of February 2011. The major accomplishments of ADNI have been as follows: (1) the development of standardized methods for clinical tests, magnetic resonance imaging (MRI), positron emission tomography (PET), and cerebrospinal fluid (CSF) biomarkers in a multicenter setting; (2) elucidation of the patterns and rates of change of imaging and CSF biomarker measurements in control subjects, MCI patients, and AD patients. CSF biomarkers are consistent with disease trajectories predicted by β-amyloid cascade (Hardy, J Alzheimers Dis 2006;9(Suppl 3):151–3) and tau-mediated neurodegeneration hypotheses for AD, whereas brain atrophy and hypometabolism levels show predicted patterns but exhibit differing rates of change depending on region and disease severity; (3) the assessment of alternative methods of diagnostic categorization. Currently, the best classifiers combine optimum features from multiple modalities, including MRI, [18F]-fluorodeoxyglucose-PET, CSF biomarkers, and clinical tests; (4) the development of methods for the early detection of AD. CSF biomarkers, β-amyloid 42 and tau, as well as amyloid PET may reflect the earliest steps in AD pathology in mildly symptomatic or even nonsymptomatic subjects, and are leading candidates for the detection of AD in its preclinical stages; (5) the improvement of clinical trial efficiency through the identification of subjects most likely to undergo imminent future clinical decline and the use of more sensitive outcome measures to reduce sample sizes. Baseline cognitive and/or MRI measures generally predicted future decline better than other modalities, whereas MRI measures of change were shown to be the most efficient outcome measures; (6) the confirmation of the AD risk loci CLU, CR1, and PICALM and the identification of novel candidate risk loci; (7) worldwide impact through the establishment of ADNI-like programs in Europe, Asia, and Australia; (8) understanding the biology and pathobiology of normal aging, MCI, and AD through integration of ADNI biomarker data with clinical data from ADNI to stimulate research that will resolve controversies about competing hypotheses on the etiopathogenesis of AD, thereby advancing efforts to find disease-modifying drugs for AD; and (9) the establishment of infrastructure to allow sharing of all raw and processed data without embargo to interested scientific investigators throughout the world. The ADNI study was extended by a 2-year Grand Opportunities grant in 2009 and a renewal of ADNI (ADNI-2) in October 2010 through to 2016, with enrollment of an additional 550 participants.
Alzheimer's disease; Mild cognitive impairment; Amyloid; Tau; Biomarker
The newly proposed National Institute on Aging-Alzheimer’s Association (NIA-AA) criteria for mild cognitive impairment (MCI) due to Alzheimer’s disease (AD) suggest a combination of clinical features and biomarker measures, but their performance in the community is not known.
The Mayo Clinic Study of Aging (MCSA) is a population-based longitudinal study of non-demented subjects in Olmsted County, Minnesota. A sample of 154 MCI subjects from the MCSA was compared to a sample of 58 amnestic MCI subjects from the Alzheimer’s Disease Neuroimaging Initiative 1 (ADNI 1) to assess the applicability of the criteria in both settings and to assess their outcomes.
In the MCSA, 14% and in ADNI 1 16% of subjects were biomarker negative. In addition, 14% of the MCSA and 12% of ADNI 1 subjects had evidence for amyloid deposition only, while 43% of MCSA and 55% of ADNI 1 subjects had evidence for amyloid deposition plus neurodegeneration (MRI atrophy, FDG PET hypometabolism or both). However, a considerable number of subjects had biomarkers inconsistent with the proposed AD model, e.g., 29% of MCSA subjects and 17% of the ADNI 1 subjects had evidence for neurodegeneration without amyloid deposition. These subjects may not be on an AD pathway. Neurodegeneration appears to be a key factor in predicting progression relative to amyloid deposition alone.
The NIA-AA criteria apply to most MCI subjects in both the community and clinical trials settings however, a sizeable proportion of subjects had conflicting biomarkers which may be very important and need to be explored.
This study examined the impact of age and apolipoprotein E (APOE) genotype on the rate of cognitive decline in non-demented elderly participants in a simulated Alzheimer’s disease (AD) primary prevention treatment trial carried out by the Alzheimer’s Disease Cooperative Study.
Cognitive tests were administered at baseline and at four subsequent annual evaluations to 417 non-demented participants (172 men, 245 women) between the ages of 74 and 93 (mean=79.13 ± 3.34). APOE genotyping was available for 286 of the participants.
Four-year decline was evident on measures of orientation, memory, executive function and language. Faster decline was evident in APOE ε4+ (a genetic risk factor for AD; n=73) than ε4− participants (n=213), even after controlling for education, gender, ethnicity, and baseline functional and cognitive abilities. This discrepancy increased with increasing age indicating an age X genotype interaction.
These results are consistent with population-based studies, and extend the findings to a carefully-screened sample that meets inclusion and exclusion criteria for an AD primary prevention trial. The interaction between age and APOE genotype on rate of decline suggests that preclinical disease may be over represented in olderε4+ individuals. Thus, APOE genotype and age should be considered in the design of AD primary prevention treatment trials.
Cognitive decline; Apolipoprotein E; Aging
A secondary prevention trial in older people with amyloid accumulation at high risk for Alzheimer’s disease dementia should provide insights into whether anti-amyloid therapy can delay cognitive decline.
Background and Purpose
Among cognitively normal older individuals, the relationship between the two hallmark proteins of Alzheimer’s disease (AD), amyloid-β (Aβ) and tau, the ε4 allele of apolipoprotein E (APOE ε4), and neurodegeneration is not well understood.
Materials and Methods
We examined 107 cognitively healthy older adults who underwent longitudinal MR imaging and baseline lumbar puncture. Within the same linear mixed effects model, we concurrently investigated main and interactive effects between APOE ε4 genotype and CSF Aβ1-42, CSF phospo-tau (p-tau181p) and CSF Aβ1-42, and APOE ε4 genotype and CSF p-tau181p on entorhinal cortex atrophy rate. We also examined the relationship between APOE ε4, CSF p-tau181p, and CSF Aβ1-42 on atrophy rate of other AD-vulnerable neuroanatomic regions.
The full model with main and interactive effects demonstrated a significant interaction only between CSF p-tau181p and CSF Aβ1-42 on entorhinal cortex atrophy rate indicating elevated atrophy over time in individuals with increased CSF p-tau181p and decreased CSF Aβ1-42. APOE ε4 genotype was significantly and specifically associated with CSF Aβ1-42. However, the interaction between APOE ε4 genotype and either CSF Aβ1-42 or CSF p-tau181p on entorhinal cortex atrophy rate was not significant. We found similar results in other AD-vulnerable regions.
Based upon our findings and building upon prior experimental evidence, we propose a model of the pathogenic cascade underlying preclinical AD where APOE ε4 primarily influences Alzheimer’s pathology via Aβ-related mechanisms and in turn, Aβ-associated neurodegeneration occurs only in the presence of phospho-tau.
preclinical AD; neurodegeneration; p-tau; amyloid-β; APOE
We analyzed the baseline and 3-year T1-weighted magnetic resonance imaging data of 110 amnestic mild cognitive impairment (MCI) participants with minimal hippocampal atrophy at baseline from the Alzheimer’s Disease Cooperative Study group (ADCS) MCI Donepezil/Vitamin E trial. 46 subjects converted to AD (MCIc) while 64 remained stable (MCInc). We used the radial distance technique to examine the differences in lateral ventricle shape and size between MCIc and MCInc and the associations between ventricular enlargement and cognitive decline.
MCIc group had significantly larger frontal and right body/occipital horns relative to MCInc at baseline and significantly larger bilateral frontal, body/occipital and left temporal horns at follow-up. Global cognitive decline measured with ADAScog and MMSE and decline in activities of daily living (ADL) were associated with posterior lateral ventricle enlargement. Decline in ADAScog and ADL were associated with left temporal and decline in MMSE with right temporal horn enlargement. After correction for baseline hippocampal volume decline in ADL showed a significant association with right frontal horn enlargement. Executive decline was associated with right frontal and left temporal horn enlargement.
Alzheimer’s disease; AD; mild cognitive impairment; MCI; imaging; MRI; brain atrophy; ventricular enlargement
To assess differences in resource use and cost between older adults with and without mild cognitive impairment (MCI) over time.
Multicenter, longitudinal study.
Sixty-eight Alzheimer’s Disease Cooperative Study (ADCS) sites in the United States.
Two hundred fifty-nine individuals diagnosed with MCI and 107 cognitively normal elderly adults followed annually for 3 years.
The Resource Use Instrument (RUI) was used to capture medical and nonmedical care use. Generalized linear latent and mixed models were used to estimate differences in resource use and costs in older adults with and without MCI after controlling for clinical and demographic characteristics.
At baseline, average annual direct medical cost per person was substantially higher for participants with MCI ($6,499) than for those without ($2,969) P < .001). Informal care use was also substantially higher (33% vs 8.4%, P < .001). Results from multivariate analyses of longitudinal data show that, after controlling for participant and informant characteristics, direct medical costs were 44% higher for participants with MCI than for those without. Participants with MCI were almost five times as likely to use informal care as those without. Number of medical conditions and older age were associated with higher medical cost. Worse functional and cognitive status, older age, being married, and being female were associated with higher likelihood of informal care use. Having an adult child informant was associated with higher likelihood of using informal care.
The RUI captured differences in resource use and costs between individuals with and without MCI. Clinicians who care for individuals with MCI should address informal care needs early in the disease course.
mild cognitive impairment; case–control study; medical care; resource use; cost; informal care
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.
Alzheimer disease (AD) dementia clinical trials require 2 participants: a patient and a study partner. We assessed the prevalence of study partner types and how these types associate with patient-related outcome measures.
Retrospective analyses of 6 Alzheimer’s Disease Cooperative Study (ADCS) randomized clinical trials were conducted. Study partners were categorized as spouse, adult child, or other. Prevalence of study partner type and associations between study partner type and trial outcomes including study completion and placebo decline on the Mini-Mental State Examination, the Alzheimer’s Disease Assessment Scale–cognitive subscale, the Clinical Dementia Rating scale Sum of the Boxes score, and the ADCS–Activities of Daily Living were examined.
More participants (67%) enrolled with spouses than adult children (26%) or other study partners (7%). Participants with spouse partners had a lower dropout rate (25%) than those with adult child (32%) or other study partners (34%); only the difference vs others was statistically significant. Participants with adult child and other partners randomized to placebo performed worse at baseline than those with spouse partners on the ADCS–Activities of Daily Living (p = 0.04), but were not different at 18 months. There were no differences at baseline for the Mini-Mental State Examination, Clinical Dementia Rating scale Sum of the Boxes score, or Alzheimer’s Disease Assessment Scale–cognitive subscale. In multivariate models of the rates of change over time among placebo participants, no differences among study partner groups reached statistical significance.
Patients with nonspouse caregivers less frequently participate in AD dementia trials. Increased enrollment of AD patients with nonspouse caregivers may require additional recruitment and retention strategies.
TTP488, an antagonist at the Receptor for Advanced Glycation End products, was evaluated as a potential treatment for patients with mild-to-moderate Alzheimer’s disease (AD). A previous report describes decreased decline in ADAS-cog (delta = 3.1, p = 0.008 at 18 months, ANCOVA with multiple imputation), relative to placebo, following a 5 mg/day dose of TTP488. Acute, reversible cognitive worsening was seen with a 20 mg/day dose. The present study further evaluates the efficacy of TTP488 by subgroup analyses based on disease severity and concentration effect analysis.
399 patients were randomized to one of two oral TTP488 doses (60 mg for 6 days followed by 20 mg/day; 15 mg for 6 days followed by 5 mg/day) or placebo for 18 months. Pre-specified primary analysis, using an ITT population, was on the ADAS-cog11. Secondary analyses included as a key secondary variable the Clinical Dementia Rating-Sum of Boxes (CDR-SB), and another secondary variable of the ADCS-ADL.
On-treatment analysis demonstrated numerical differences favoring 5 mg/day over placebo, with nominal significance at Month 18 (delta = 2.7, p = 0.03). Patients with mild AD, whether defined by MMSE or ADAS-cog, demonstrated significant differences favoring 5 mg/day on ADAS-cog and trends on CDR-sb and ADCS-ADL at Month 18. TTP488 plasma concentrations of 7.6-16.8 ng/mL were associated with a decreased decline in ADAS-cog over time compared to placebo. Worsening on the ADAS-cog relative to placebo was evident at 46.8-167.0 ng/mL.
Results of these analyses support further investigation of 5 mg/day in future Phase 3 trials in patients with mild AD.
This article reviews measures of Alzheimer’s disease (AD) progression in relation to patient dependence and offers a unifying conceptual framework for dependence in AD. Clinicians typically characterize AD by symptomatic impairments in three domains: cognition, function, and behavior. From a patient’s perspective, changes in these domains, individually and in concert, ultimately lead to increased dependence and loss of autonomy. Examples of dependence in AD range from a need for reminders (early AD) to requiring safety supervision and assistance with basic functions (late AD). Published literature has focused on the clinical domains as somewhat separate constructs and has given limited attention to the concept of patient dependence as a descriptor of AD progression. This article presents the concept of dependence on others for care needs as a potential method for translating the effect of changes in cognition, function, and behavior into a more holistic, transparent description of AD progression.
Alzheimer’s disease; Dementia; Functional impairment; Dependence; Disease progression
Memory deficits are prominent features of mild cognitive impairment (MCI) and Alzheimer’s disease (AD). The genetic architecture underlying these memory deficits likely involves the combined effects of multiple genetic variants operative within numerous biological pathways. In order to identify functional pathways associated with memory impairment, we performed a pathway enrichment analysis on genome-wide association data from 742 Alzheimer’s Disease Neuroimaging Initiative (ADNI) participants. A composite measure of memory was generated as the phenotype for this analysis by applying modern psychometric theory to item-level data from the ADNI neuropsychological test battery. Using the GSA-SNP software tool, we identified 27 canonical, expertly-curated pathways with enrichment (FDR-corrected p-value < 0.05) against this composite memory score. Processes classically understood to be involved in memory consolidation, such as neurotransmitter receptor-mediated calcium signaling and long-term potentiation, were highly represented among the enriched pathways. In addition, pathways related to cell adhesion, neuronal differentiation and guided outgrowth, and glucose- and inflammation-related signaling were also enriched. Among genes that were highly-represented in these enriched pathways, we found indications of coordinated relationships, including one large gene set that is subject to regulation by the SP1 transcription factor, and another set that displays co-localized expression in normal brain tissue along with known AD risk genes. These results 1) demonstrate that psychometrically-derived composite memory scores are an effective phenotype for genetic investigations of memory impairment and 2) highlight the promise of pathway analysis in elucidating key mechanistic targets for future studies and for therapeutic interventions.
memory; psychometrics; Alzheimer’s disease; mild cognitive impairment; pathway analysis; genome-wide association study
The Dominantly Inherited Alzheimer Network (DIAN) is a collaborative effort of international Alzheimer disease (AD) centers that are conducting a multifaceted prospective biomarker study in individuals at-risk for autosomal dominant AD (ADAD). DIAN collects comprehensive information and tissue in accordance with standard protocols from asymptomatic and symptomatic ADAD mutation carriers and their non-carrier family members to determine the pathochronology of clinical, cognitive, neuroimaging, and fluid biomarkers of AD. This article describes the structure, implementation, and underlying principles of DIAN, as well as the demographic features of the initial DIAN cohort.
Alzheimer disease; autosomal dominant; biomarkers of Alzheimer disease; PSEN1; PSEN2; APP; amyloid-beta; preclinical Alzheimer disease
Using data from the Alzheimer’s Disease Neuroimaging Initiative (ADNI) population, we examined (1) cross-sectional relationships between amyloid deposition, hypometabolism, and cognition, and (2) associations between amyloid and hypometabolism measurements and longitudinal cognitive measurements.
We examined associations between mean cortical florbetapir uptake, mean 18F-fluorodeoxyglucose–positron emission tomography (FDG-PET) within a set of predefined regions, and Alzhiemer’s Disease Assessment Scale (ADAS-cog) performance in 426 ADNI participants (126 normal, 162 early mild cognitive impairment [EMCI], 85 late MCI [LMCI], 53 Alzheimer disease [AD] patients). For a subset of these (76 normal, 81 LMCI) we determined whether florbetapir and FDG-PET were associated with retrospective decline in longitudinal ADAS-cog measurements.
Twenty-nine percent of normal subjects, 43% of EMCI patients, 62% of LMCI patients, and 77% of AD patients were categorized as florbetapir positive. Florbetapir was negatively associated with concurrent FDG and ADAS-cog in both MCI groups. In longitudinal analyses, florbetapir-positive subjects in both normal and LMCI groups had greater ongoing ADAS-cog decline than those who were florbetapir negative. However, in normal subjects, florbetapir positivity was associated with greater ADAS-cog decline than FDG, whereas in LMCI, FDG positivity was associated with greater decline than florbetapir.
Although both hypometabolism and β-amyloid (Aβ) deposition are detectable in normal subjects and all diagnostic groups, Aβ showed greater associations with cognitive decline in normal participants. In view of the minimal cognitive deterioration overall in this group, this suggests that amyloid deposition has an early and subclinical impact on cognition that precedes metabolic changes. At moderate and later stages of disease (LMCI/AD), hypometabolism becomes more pronounced and more closely linked to ongoing cognitive decline.
This study aimed to identify baseline features of normal subjects that are associated with subsequent cognitive decline. Publicly available data from the Alzheimer’s Disease Neuroimaging Initiative was used to find differences in baseline clinical assessments (ADAScog, AVLT, FAQ) between cognitively healthy individuals who will suffer cognitive decline within 48 months and those who will remain stable for that period. Linear regression models indicated an individual’s conversion status was significantly associated with certain baseline neuroimaging measures, including posterior cingulate glucose metabolism. Linear Discriminant Analysis models built with baseline features derived from MRI and FDG-PET measures were capable of successfully predicting whether an individual will convert to MCI within 48 months or remain cognitively stable. The findings from this study support the idea that there exist informative differences between normal people who will later develop cognitive impairments and those who will remain cognitively stable for up to four years. Further, the feasibility of developing predictive models that can detect early states of cognitive decline in seemingly normal individuals was demonstrated.
Beta-amyloid (Aβ) is a histopathological hallmark of Alzheimer’s disease dementia, but high levels of Aβ in the brain can also be found in a substantial proportion of nondemented subjects. Here we investigated which 2-year rate of brain and cognitive changes are present in nondemented subjects with high and low Aβ levels, as assessed with cerebrospinal fluid and molecular positron emission tomography (PET)–based biomarkers of Aβ. In subjects with mild cognitive impairment, increased brain Aβ levels were associated with significantly faster cognitive decline, progression of gray matter atrophy within temporal and parietal brain regions, and a trend for a faster decline in parietal Fludeoxyglucose (FDG)-PET metabolism. Changes in gray matter and FDG-PET mediated the association between Aβ and cognitive decline. In contrast, elderly cognitively healthy controls (HC) with high Aβ levels showed only a faster medial temporal lobe and precuneus volume decline compared with HC with low Aβ. In conclusion, the current results suggest not only that both functional and volumetric brain changes are associated with high Aβ years before the onset of dementia but also that HC with substantial Aβ levels show higher Aβ pathology resistance, lack other pathologies that condition neurotoxic effects of Aβ, or accumulated Aβ for a shorter time period.
Aβ; FDG-PET; MCI; PIB-PET
Alzheimer’s disease (AD) is the only leading cause of death for which no disease-modifying therapy is currently available. Recent disappointing trial results at the dementia stage of AD have raised multiple questions about our current approaches to the development of disease-modifying agents. Converging evidence suggests that the pathophysiological process of AD begins many years before the onset of dementia. So why do we keep testing drugs aimed at the initial stages of the disease process in patients at the end-stage of the illness?
Alzheimer’s disease (AD) remains one of the most feared consequences of aging, affecting more than one out of every ten individuals over the age of 65. With more than 10,000 baby boomers turning 65 every day in the United States alone, we are truly facing an AD epidemic. Over the past decade, a string of disappointing clinical trial results have raised concerns about our current strategy for development of AD-modifying therapies. Three hypotheses can explain these recent AD trial failures: (i) We are targeting the wrong pathophysiological mechanisms; (ii) The drugs do not engage the intended targets in patients; and (iii) The drugs are hitting the right targets, but are doing so at the wrong stage of the disease. Here, we address the third supposition and suggest that specific amyloid-based therapies be directed at much earlier stages of ADperhaps even prior to the emergence of clinical symptoms. Furthermore, we argue that the field has sufficient tools to begin “secondary prevention” trials in asymptomatic individuals whoare at high risk for progression to cognitive impairment and AD dementia.