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1.  Cerebrospinal fluid amyloid β42, phosphorylated tau181, and resting state functional connectivity 
JAMA neurology  2013;70(10):1242-1248.
Resting state functional connectivity magnetic resonance imaging (rs-fcMRI) has great potential for characterizing pathophysiological changes during the preclinical phase of Alzheimer’s disease (AD).
To assess the relationship between default mode network (DMN) integrity and cerebrospinal fluid (CSF) biomarkers of AD pathology in cognitively normal older individuals
Cross-sectional cohort study
Knight Alzheimer’s Disease Research Center at Washington University in St Louis, Missouri.
207 older adults with normal cognition (Clinical Dementia Rating of 0).
Main Outcome measures
rs-fcMRI measures of DMN integrity.
Decreased CSF Aβ42 or increased CSF phosphorylated tau181 (ptau181) were independently associated with reduced DMN integrity, with the most prominent decreases in functional connectivity observed between the posterior cingulate and medial temporal regions. Observed reductions in functional connectivity were not attributable to age or structural atrophy in the posterior cingulate and medial temporal areas. Similar rs-fcMRI findings in relation to CSF biomarkers were obtained using region-of-interest analyses and voxel-wise correlation mapping.
Both Aβ and tau pathology affect DMN integrity prior to clinical onset of AD.
PMCID: PMC3836828  PMID: 23959173
2.  Cerebrospinal fluid APOE levels: an endophenotype for genetic studies for Alzheimer's disease 
Human Molecular Genetics  2012;21(20):4558-4571.
The apolipoprotein E (APOE) genotype is the major genetic risk factor for Alzheimer's disease (AD). We have access to cerebrospinal fluid (CSF) and plasma APOE protein levels from 641 individuals and genome-wide genotyped data from 570 of these samples. The aim of this study was to test whether CSF or plasma APOE levels could be a useful endophenotype for AD and to identify genetic variants associated with APOE levels. We found that CSF (P = 8.15 × 10−4) but not plasma (P = 0.071) APOE protein levels are significantly associated with CSF Aβ42 levels. We used Mendelian randomization and genetic variants as instrumental variables to confirm that the association of CSF APOE with CSF Aβ42 levels and clinical dementia rating (CDR) is not because of a reverse causation or confounding effect. In addition the association of CSF APOE with Aβ42 levels was independent of the APOE ɛ4 genotype, suggesting that APOE levels in CSF may be a useful endophenotype for AD. We performed a genome-wide association study to identify genetic variants associated with CSF APOE levels: the APOE ɛ4 genotype was the strongest single-genetic factor associated with CSF APOE protein levels (P = 6.9 × 10−13). In aggregate, the Illumina chip single nucleotide polymorphisms explain 72% of the variability in CSF APOE protein levels, whereas the APOE ɛ4 genotype alone explains 8% of the variability. No other genetic variant reached the genome-wide significance threshold, but nine additional variants exhibited a P-value <10−6. Pathway mining analysis indicated that these nine additional loci are involved in lipid metabolism (P = 4.49 × 10−9).
PMCID: PMC3459471  PMID: 22821396
3.  CSF Proteins Predict Longitudinal Hippocampal Degeneration in Early Stage Dementia of the Alzheimer Type 
Biomarkers are needed to improve the sensitivity and accuracy of diagnosis as well as prognosis in individuals with early Alzheimer disease (AD). Measures of brain structure and disease-related proteins in the cerebrospinal fluid (CSF) have been proposed as biomarkers, yet relatively little is known about the relationships between such measures. The present study was conducted to assess the relationship between CSF Aβ and tau protein levels and longitudinal measures of hippocampal structure in individuals with and without very mild dementia of the Alzheimer type.
A single CSF sample and longitudinal MR scans were collected. The CSF samples were assayed for tau, p-tau181, Aβ1–42 and Aβ1–40 by ELISA. Large-deformation diffeomorphic metric mapping was used to generate hippocampal surfaces, and a composite hippocampal surface (previously constructed from 86 healthy participants) was used as a structural reference.
Patients or Other Participants
13 participants with very mild AD (Clinical Dementia Rating, CDR 0.5) and 11 cognitively normal participants (CDR 0).
Main Outcome Measures
Initial and rate-of-change measures of total hippocampal volume and displacement of the hippocampal surface within zones overlying the CA1, subiculum and CA2-4+DG cellular subfields. Their correlations with initial CSF measures.
Lower CSF Aβ1–42 levels and higher tau/Aβ1–42 and p-tau181/Aβ1–42 ratios were strongly correlated with decreases in hippocampal volume and measure of progressive inward deformations of the CA1 subfield in participants with early AD, but not cognitively normal participants.
Despite small sample size, we found that Aβ1–42 and tau-related CSF measures were related to hippocampal degeneration in individuals with clinically diagnosed early AD, and may reflect an association with a common underlying disease mechanism.
PMCID: PMC3309103  PMID: 22156755
Magnetic Resonance Imaging (MRI); Hippocampal subfields; β-Amyloid; Tau; P-Tau; biomarkers
4.  Toward a multifactorial model of Alzheimer disease 
Neurobiology of aging  2012;33(10):2262-2271.
Relations among antecedant biomarkers of AD were evaluated using causal modeling; although correlation cannot be equated to causation, causation does require correlation. Individuals aged 43 to 89 years (N = 220) enrolled as cognitively normal controls in longitudinal studies had clinical and psychometric assessment, structural magnetic resonance imaging (MRI), cerebrospinal fluid (CSF) biomarkers, and brain amyloid imaging via positron emission tomography with Pittsburgh Compound B (PIB) obtained within 1 year. CSF levels of Aβ42 and tau were minimally correlated, indicating they represent independent processes. Aβ42, tau, and their interaction explained 60% of the variance in PIB. Effects of APOE genotype and age on PIB were indirect, operating through CSF markers. Only spurious relations via their common relation with age were found between the biomarkers and regional brain volumes or cognition. Hence, at least two independent hypothesized processes, one reflected by CSF Aβ42 and one by CSF tau, contribute to the development of fibrillar amyloid plaques preclinically. The lack of correlation between these two processes and brain volume in the regions most often affected in AD suggests the operation of a third process related to brain atrophy.
PMCID: PMC3334456  PMID: 22261556
preclinical Alzheimer disease; amyloid-β; tau; PIB; amyloid plaque; APOE; brain volumetry; memory; biomarkers; cerebrospinal fluid
5.  Developing an international network for Alzheimer research: The Dominantly Inherited Alzheimer Network 
Clinical investigation  2012;2(10):975-984.
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.
PMCID: PMC3489185  PMID: 23139856
Alzheimer disease; autosomal dominant; biomarkers of Alzheimer disease; PSEN1; PSEN2; APP; amyloid-beta; preclinical Alzheimer disease
6.  The Alzheimer’s Association external quality control program for cerebrospinal fluid biomarkers 
Mattsson, Niklas | Andreasson, Ulf | Persson, Staffan | Arai, Hiroyuki | Batish, Sat Dev | Bernardini, Sergio | Bocchio-Chiavetto, Luisella | Blankenstein, Marinus A. | Carrillo, Maria C. | Chalbot, Sonia | Coart, Els | Chiasserini, Davide | Cutler, Neal | Dahlfors, Gunilla | Duller, Stefan | Fagan, Anne M. | Forlenza, Orestes | Frisoni, Giovanni B. | Galasko, Douglas | Galimberti, Daniela | Hampel, Harald | Handberg, Aase | Heneka, Michael T. | Herskovits, Adrianna Z. | Herukka, Sanna-Kaisa | Holtzman, David M. | Humpel, Christian | Hyman, Bradley T. | Iqbal, Khalid | Jucker, Mathias | Kaeser, Stephan A. | Kaiser, Elmar | Kapaki, Elisabeth | Kidd, Daniel | Klivenyi, Peter | Knudsen, Cindy S. | Kummer, Markus P. | Lui, James | Lladó, Albert | Lewczuk, Piotr | Li, Qiao-Xin | Martins, Ralph | Masters, Colin | McAuliffe, John | Mercken, Marc | Moghekar, Abhay | Molinuevo, José Luis | Montine, Thomas J. | Nowatzke, William | O’Brien, Richard | Otto, Markus | Paraskevas, George P. | Parnetti, Lucilla | Petersen, Ronald C. | Prvulovic, David | de Reus, Herman P. M. | Rissman, Robert A. | Scarpini, Elio | Stefani, Alessandro | Soininen, Hilkka | Schröder, Johannes | Shaw, Leslie M. | Skinningsrud, Anders | Skrogstad, Brith | Spreer, Annette | Talib, Leda | Teunissen, Charlotte | Trojanowski, John Q. | Tumani, Hayrettin | Umek, Robert M. | Van Broeck, Bianca | Vanderstichele, Hugo | Vecsei, Laszlo | Verbeek, Marcel M. | Windisch, Manfred | Zhang, Jing | Zetterberg, Henrik | Blennow, Kaj
The cerebrospinal fluid (CSF) biomarkers amyloid β (Aβ)-42, total-tau (T-tau), and phosphorylated-tau (P-tau) demonstrate good diagnostic accuracy for Alzheimer’s disease (AD). However, there are large variations in biomarker measurements between studies, and between and within laboratories. The Alzheimer’s Association has initiated a global quality control program to estimate and monitor variability of measurements, quantify batch-to-batch assay variations, and identify sources of variability. In this article, we present the results from the first two rounds of the program.
The program is open for laboratories using commercially available kits for Aβ, T-tau, or P-tau. CSF samples (aliquots of pooled CSF) are sent for analysis several times a year from the Clinical Neurochemistry Laboratory at the Molndal campus of the University of Gothenburg, Sweden. Each round consists of three quality control samples.
Forty laboratories participated. Twenty-six used INNOTESTenzyme-linked immunosorbent assay kits, 14 used Luminex xMAP with the INNO-BIA AlzBio3 kit (both measure Aβ-(1-42), P-tau(181P), and T-tau), and 5 used Meso Scale Discovery with the Aβ triplex (AβN-42, AβN-40, and AβN-38) or T-tau kits. The total coefficients of variation between the laboratories were 13% to 36%. Five laboratories analyzed the samples six times on different occasions. Within-laboratory precisions differed considerably between biomarkers within individual laboratories.
Measurements of CSF AD biomarkers show large between-laboratory variability, likely caused by factors related to analytical procedures and the analytical kits. Standardization of laboratory procedures and efforts by kit vendors to increase kit performance might lower variability, and will likely increase the usefulness of CSF AD biomarkers.
PMCID: PMC3710290  PMID: 21784349
Alzheimer’s disease; Cerebrospinal fluid; Biomarkers; External assurance; External control; Proficiency testing
7.  Upcoming candidate cerebrospinal fluid biomarkers of Alzheimer’s disease 
Biomarkers in medicine  2012;6(4):455-476.
Dementia due to Alzheimer’s disease (AD) is estimated to reach epidemic proportions by the year 2030. Given the limited accuracy of current AD clinical diagnosis, biomarkers of AD pathologies are currently being sought. Reductions in cerebrospinal fluid levels of β-amyloid 42 (a marker of amyloid plaques) and elevations in tau species (markers of neurofibrillary tangles and/or neurodegeneration) are well-established as biomarkers useful for AD diagnosis and prognosis. However, novel markers for other features of AD pathophysiology (e.g., β-amyloid processing, neuroinflammation and neuronal stress/dysfunction) and for other non-AD dementias are required to improve the accuracy of AD disease diagnosis, prognosis, staging and therapeutic monitoring (theragnosis). This article discusses the potential of several promising novel cerebrospinal fluid analytes, highlights the next steps critical for advancement in the field, and provides a prediction on how the field may evolve in 5–10 years.
PMCID: PMC3477809  PMID: 22917147
Alzheimer’s disease; amyloid; biomarker; cerebrospinal fluid; diagnostic accuracy; neurodegeneration; neurofibrillary tangles; neuroinflammation; prognosis; theragnosis
8.  Clinical and Biomarker Changes in Dominantly Inherited Alzheimer’s Disease 
The New England journal of medicine  2012;367(9):795-804.
The order and magnitude of pathologic processes in Alzheimer’s disease are not well understood, partly because the disease develops over many years. Autosomal dominant Alzheimer’s disease has a predictable age at onset and provides an opportunity to determine the sequence and magnitude of pathologic changes that culminate in symptomatic disease.
In this prospective, longitudinal study, we analyzed data from 128 participants who underwent baseline clinical and cognitive assessments, brain imaging, and cerebrospinal fluid (CSF) and blood tests. We used the participant’s age at baseline assessment and the parent’s age at the onset of symptoms of Alzheimer’s disease to calculate the estimated years from expected symptom onset (age of the participant minus parent’s age at symptom onset). We conducted cross-sectional analyses of baseline data in relation to estimated years from expected symptom onset in order to determine the relative order and magnitude of pathophysiological changes.
Concentrations of amyloid-beta (Aβ)42 in the CSF appeared to decline 25 years before expected symptom onset. Aβ deposition, as measured by positron-emission tomography with the use of Pittsburgh compound B, was detected 15 years before expected symptom onset. Increased concentrations of tau protein in the CSF and an increase in brain atrophy were detected 15 years before expected symptom onset. Cerebral hypometabolism and impaired episodic memory were observed 10 years before expected symptom onset. Global cognitive impairment, as measured by the Mini–Mental State Examination and the Clinical Dementia Rating scale, was detected 5 years before expected symptom onset, and patients met diagnostic criteria for dementia at an average of 3 years after expected symptom onset.
We found that autosomal dominant Alzheimer’s disease was associated with a series of pathophysiological changes over decades in CSF biochemical markers of Alzheimer’s disease, brain amyloid deposition, and brain metabolism as well as progressive cognitive impairment. Our results require confirmation with the use of longitudinal data and may not apply to patients with sporadic Alzheimer’s disease. (Funded by the National Institute on Aging and others; DIAN number, NCT00869817.)
PMCID: PMC3474597  PMID: 22784036
9.  Exercise engagement as a moderator of APOE effects on amyloid deposition 
Archives of neurology  2012;69(5):636-643.
APOE ε4 status has been associated with greater cortical amyloid deposition whereas exercise has been associated with less in cognitively normal adults. The primary objective here was to examine whether physical exercise moderates the association between APOE genotype and amyloid deposition in cognitively normal adults.
APOE genotyping and a questionnaire on physical exercise engagement over the last decade were obtained in conjunction with cerebrospinal fluid (CSF) samples and amyloid imaging with PET-PIB. Participants were classified as either low or high exercisers based on exercise guidelines of the American Heart Association.
201 cognitively normal adults (135 females) aged 45–88 were recruited from the Knight Alzheimer Disease Research Center at Washington University. CSF samples were collected from 165 participants. Amyloid imaging was performed on 163 participants.
APOE ε4 carriers evidenced higher PIB binding (p<.001) and lower CSF Aβ42 levels (p<.001) than non-carriers. Our previous findings of higher PIB binding (p=.005) and lower CSF Aβ42 levels (p=.009) in more sedentary individuals were replicated. Most importantly, we observed a novel interaction between APOE status and exercise engagement for PIB binding (p=.008) such that a more sedentary lifestyle was significantly associated with higher PIB binding for ε4 carriers (p=.013) but not for ε4 non-carriers (p=.208). All findings remained significant after controlling for age, gender, education, hypertension, body mass index, diabetes, heart problems, history of depression and interval between assessments.
Collectively, these results suggest that cognitively normal sedentary APOE ε4+ individuals may be at augmented risk for cerebral amyloid deposition.
PMCID: PMC3583203  PMID: 22232206
10.  HIV Associated Neurocognitive Disorder (HAND) is Not Associated with Increased Fibrillar Amyloid Deposits Using 11C-PiB in Middle-Aged HIV+ Participants 
Archives of neurology  2012;69(1):72-77.
Diagnostic challenges exist for differentiating HIV associated neurocognitive disorders (HAND) from symptomatic Alzheimer’s disease (AD) in HIV+ participants. Both disorders have cerebral amyloid containing plaques associated with abnormalities in amyloid beta protein 1–42 (Aβ42) metabolism. We evaluated if the amyloid-binding agent 11C-Pittsburgh compound B (11C-PiB) could discriminate AD from HAND in middle-aged HIV+ participants.
11C-PiB scanning, clinical assessment, and cerebrospinal fluid (CSF) analysis were performed. χ2 and t-tests assessed differences in clinical and demographic variables between HIV+ participants and community-living individuals followed by Alzheimer Disease Research Center (ADRC). An analysis of variance (ANOVA) assessed for regional differences in Aβ42 using 11C-PiB.
ADRC and HIV clinic
16 HIV+ participants (11 cognitively normal, 5 with HAND) and 19 ADRC participants (8 cognitively normal, 11 with symptomatic AD).
Main Outcome Measure(s)
Mean and regional 11C-PiB binding potentials
Symptomatic AD were older (p < 0.001), had lower CSF Aβ42 (p < 0.001), and had higher CSF tau levels (p < 0.001) than other groups. Regardless of degree of impairment, HIV+ participants did not have increased 11C-PiB. Mean and regional binding potentials were elevated for symptomatic AD participants (p <0.0001).
Middle-aged HIV+ participants, even with HAND, do not exhibit increased 11C-PiB while symptomatic AD individuals have increased fibrillar Aβ42 deposition in cortical and subcortical regions. Observed dissimilarities between HAND and AD may reflect differences in Aβ42 metabolism. 11C-PiB may provide a diagnostic biomarker for distinguishing symptomatic AD from HAND in middle-aged HIV+ participants. Future cross sectional and longitudinal studies are required to assess utility of 11C-PiB in older HAND individuals.
PMCID: PMC3536500  PMID: 22232345
HIV; Pittsburgh compound B (PIB); amyloid; HIV associated neurocognitive disorders; Alzheimer’s disease
11.  Impaired default network functional connectivity in autosomal dominant Alzheimer disease 
Neurology  2013;81(8):736-744.
To investigate default mode network (DMN) functional connectivity MRI (fcMRI) in a large cross-sectional cohort of subjects from families harboring pathogenic presenilin-1 (PSEN1), presenilin-2 (PSEN2), and amyloid precursor protein (APP) mutations participating in the Dominantly Inherited Alzheimer Network.
Eighty-three mutation carriers and 37 asymptomatic noncarriers from the same families underwent fMRI during resting state at 8 centers in the United States, United Kingdom, and Australia. Using group-independent component analysis, fcMRI was compared using mutation status and Clinical Dementia Rating to stratify groups, and related to each participant's estimated years from expected symptom onset (eYO).
We observed significantly decreased DMN fcMRI in mutation carriers with increasing Clinical Dementia Rating, most evident in the precuneus/posterior cingulate and parietal cortices (p < 0.001). Comparison of asymptomatic mutation carriers with noncarriers demonstrated decreased fcMRI in the precuneus/posterior cingulate (p = 0.014) and right parietal cortex (p = 0.0016). We observed a significant interaction between mutation carrier status and eYO, with decreases in DMN fcMRI observed as mutation carriers approached and surpassed their eYO.
Functional disruption of the DMN occurs early in the course of autosomal dominant Alzheimer disease, beginning before clinically evident symptoms, and worsening with increased impairment. These findings suggest that DMN fcMRI may prove useful as a biomarker across a wide spectrum of disease, and support the feasibility of DMN fcMRI as a secondary endpoint in upcoming multicenter clinical trials in Alzheimer disease.
PMCID: PMC3776464  PMID: 23884042
12.  Cerebrospinal Fluid Biomarkers, Education, Brain Volume and Future Cognition 
Archives of neurology  2011;68(9):1145-1151.
To evaluate the combination of cerebrospinal fluid biomarkers of Aβ42, tau, and phosphorylated tau (ptau181) with education and normalized whole brain volume (nWBV) to predict incident cognitive impairment and test the cognitive/brain reserve hypothesis.
Longitudinal cohort study.
Charles F. and Joanne Knight Alzheimer’s Disease Research Center of Washington University, St. Louis, Missouri.
Convenience sample of 197 participants aged 50 years and above, with normal cognition (Clinical Dementia Rating [CDR] of 0) at baseline, followed for a mean of 3.3 years.
Main outcome measure
Time to cognitive impairment (CDR ≥ 0.5).
Three-factor interactions between the baseline biomarker values, education, and nWBV were found for Cox proportional hazards models testing tau (p=.03) and ptau (p=.008). Among those with lower tau values, nWBV (hazard ratio [HR]=.54, 95% confidence interval [CI]=.31–.91; p=.02), but not education, was related to time to cognitive impairment. For participants with higher tau values, education interacted with nWBV to predict incident impairment (p=.01). For individuals with lower ptau values, there was no effect of education or nWBV. Education interacted with nWBV to predict incident cognitive impairment among those with higher ptau values (p=.02). In models testing Aβ42, larger nWBV was associated with a slower time to cognitive impairment (HR=.84, 95%CI=.71–.99, p=.0348), but there was no effect of Aβ42 or education.
Among individuals with higher levels of CSF tau and ptau, but normal cognition at baseline, time to incident cognitive impairment is moderated by education and brain volume as predicted by the cognitive/brain reserve hypothesis.
PMCID: PMC3203689  PMID: 21911695
Annals of neurology  2011;70(2):274-285.
There is a growing need to identify cerebrospinal fluid (CSF) markers that can detect Alzheimer’s disease (AD) pathology in cognitively normal individuals since it is in this population that disease-modifying therapies may have the greatest chance of success. While AD pathology is estimated to begin ~10–15 years prior to the onset of cognitive decline, substantial neuronal loss is present by the time the earliest signs of cognitive impairment appear. Visinin-like protein −1 (VILIP-1) has demonstrated potential utility as a marker of neuronal injury. We here investigate CSF VILIP-1 and VILIP-1/amyloid-β42 (Aβ42) ratio as diagnostic and prognostic markers in early AD.
We assessed CSF levels of VILIP-1, tau, phosphorylated-tau181 (p-tau181), and Aβ42 in cognitively normal controls [CNC] (n=211), individuals with early symptomatic AD (n=98), and individuals with other dementias (n=19). Structural magnetic resonance imaging (n=192) and amyloid imaging with Pittsburgh Compound-B (n=156) were obtained in subsets of this cohort. Among the CNC cohort, 164 individuals had follow-up annual cognitive assessments for 2–3 years.
CSF VILIP-1 levels differentiated individuals with AD from CNC and individuals with other dementias. CSF VILIP-1 levels correlated with CSF tau, p-tau181, and brain volumes in AD. VILIP-1 and VILIP-1/Aβ42 predicted future cognitive impairment in CNC over the follow-up period. Importantly, CSF VILIP-1/Aβ42 predicted future cognitive impairment at least as well as tau/Aβ42 and p-tau181/Aβ42.
These findings suggest that CSF VILIP-1 and VILIP-1/Aβ42 offer diagnostic utility for early AD, and can predict future cognitive impairment in cognitively normal individuals similarly to tau and tau/Aβ42, respectively.
PMCID: PMC3154071  PMID: 21823155
Visinin-like protein-1; Alzheimer’s disease; biomarkers; cerebrospinal fluid; neuronal injury
14.  Association and Expression analyses with SNPs in TOMM40 in Alzheimer’s Disease 
Archives of neurology  2011;68(8):1013-1019.
Apolipoprotein E (APOE) is the most statistically significant genetic risk factor for late-onset Alzheimer’s disease (LOAD). The linkage disequilibrium pattern around the APOE gene has made it difficult to determine whether all of the association signal is derived from APOE or if there is an independent signal from a nearby gene. In this study we attempted to replicate a recently reported association of APOE 3-TOMM40 haplotypes with risk and age at onset.
We used standard techniques to genotype several polymorphisms in the APOE-TOMM40 region in a large case-control series, in a series with cerebrospinal fluid biomarker data and in brain tissue.
We failed to replicate the previously reported association of the polyT polymorphism (rs10524523) with risk and age at onset. We found a significant association between rs10524523 and risk for LOAD among APOE 33 homozygotes but in the opposite direction to the previously reported association (the very-long allele was underrepresented in cases compared to controls in our study (allele frequency: 0.41 vs. 0.48 respectively; p=0.004)). We found no association between rs10524523 and CSF tau or Aβ42 levels or TOMM40 or APOE gene expression.
Although we were not able to replicate the earlier association between the APOE 3-TOMM40 haplotypes and age at onset, we did observe that the polyT polymorphism is associated with risk for LOAD among APOE 33 homozygotes in a large case-control series, but in the opposite direction to the previous report. Additional studies in very large samples will be needed to confirm this association.
PMCID: PMC3204798  PMID: 21825236
15.  Human apoE isoforms differentially regulate brain amyloid-β peptide clearance 
Science translational medicine  2011;3(89):89ra57.
The apolipoprotein E (APOE) ε4 allele is the strongest genetic risk factor for late-onset, sporadic Alzheimer’s disease (AD). The APOE ε4 allele dramatically increases AD risk and decreases age of onset, likely through its strong effect on the accumulation of amyloid-β (Aβ) peptide. In contrast, the APOE ε2 allele appears to decrease AD risk. Most rare, early-onset forms of familial AD are caused by autosomal dominant mutations that often lead to overproduction of Aβ42 peptide. However, the mechanism by which APOE alleles differentially modulate Aβ accumulation in sporadic, late-onset AD is less clear. In a cohort of cognitively normal individuals, we report that reliable molecular and neuroimaging biomarkers of cerebral Aβ deposition vary in an apoE isoform-dependent manner. We hypothesized that human apoE isoforms differentially affect Aβ clearance or synthesis in vivo, resulting in an apoE isoform-dependent pattern of Aβ accumulation later in life. Performing in vivo microdialysis in a mouse model of β-amyloidosis expressing human apoE isoforms (PDAPP/TRE), we find that the concentration and clearance of soluble Aβ in the brain interstitial fluid depends on the isoform of apoE expressed. This pattern parallels the extent of Aβ deposition observed in aged PDAPP/TRE mice. Importantly, apoE isoform-dependent differences in soluble Aβ metabolism are observed not only in aged PDAPP/TRE mice but also in young PDAPP/TRE mice, well before the onset of Aβ deposition in amyloid plaques. Additionally, amyloidogenic processing of amyloid precursor protein and Aβ synthesis, as assessed by in vivo stable isotopic labeling kinetics, do not vary according to apoE isoform in young PDAPP/TRE mice. Our results suggest that APOE alleles contribute to AD risk by differentially regulating clearance of Aβ from the brain, suggesting that Aβ clearance pathways may be useful therapeutic targets for AD prevention.
PMCID: PMC3192364  PMID: 21715678
16.  Toward defining the preclinical stages of Alzheimer's disease: Recommendations from the National Institute on Aging-Alzheimer's Association workgroups on diagnostic guidelines for Alzheimer's disease 
The pathophysiological process of Alzheimer's disease (AD) is thought to begin many years before the diagnosis of AD dementia. This long “preclinical” phase of AD would provide a critical opportunity for therapeutic intervention; however, we need to further elucidate the link between the pathological cascade of AD and the emergence of clinical symptoms. The National Institute on Aging and the Alzheimer's Association convened an international workgroup to review the biomarker, epidemiological, and neuropsychological evidence, and to develop recommendations to determine the factors which best predict the risk of progression from “normal” cognition to mild cognitive impairment and AD dementia. We propose a conceptual framework and operational research criteria, based on the prevailing scientific evidence to date, to test and refine these models with longitudinal clinical research studies. These recommendations are solely intended for research purposes and do not have any clinical implications at this time. It is hoped that these recommendations will provide a common rubric to advance the study of preclinical AD, and ultimately, aid the field in moving toward earlier intervention at a stage of AD when some disease-modifying therapies may be most efficacious.
PMCID: PMC3220946  PMID: 21514248
Preclinical Alzheimer's disease; Biomarker; Amyloid; Neurodegeneration; Prevention
17.  Multiple γ-secretase product peptides are coordinately increased in concentration in the cerebrospinal fluid of a subpopulation of sporadic Alzheimer’s disease subjects 
Alcadeinα (Alcα) is a neuronal membrane protein that colocalizes with the Alzheimer's amyloid-β precursor protein (APP). Successive cleavage of APP by β- and γ-secretases generates the aggregatable amyloid-β peptide (Aβ), while cleavage of APP or Alcα by α- and γ-secretases generates non-aggregatable p3 or p3-Alcα peptides. Aβ and p3-Alcα can be recovered from human cerebrospinal fluid (CSF). We have previously reported alternative processing of APP and Alcα in the CSF of some patients with sporadic mild cognitive impairment (MCI) and AD (SAD).
Using the sandwich enzyme-linked immunosorbent assay (ELISA) system that detects total p3-Alcα, we determined levels of total p3-Alcα in CSF from subjects in one of four diagnostic categories (elderly controls, MCI, SAD, or other neurological disease) derived from three independent cohorts. Levels of Aβ40 correlated with levels of total p3-Alcα in all cohorts.
We confirm that Aβ40 is the most abundant Aβ species, and we propose a model in which CSF p3-Alcα can serve as a either (1) a nonaggregatable surrogate marker for γ-secretase activity; (2) as a marker for clearance of transmembrane domain peptides derived from integral protein catabolism; or (3) both. We propose the specification of an MCI/SAD endophenotype characterized by co-elevation of levels of both CSF p3-Alcα and Aβ40, and we propose that subjects in this category might be especially responsive to therapeutics aimed at modulation of γ-secretase function and/or transmembrane domain peptide clearance. These peptides may also be used to monitor the efficacy of therapeutics that target these steps in Aβ metabolism
PMCID: PMC3422204  PMID: 22534039
Alzheimer's disease; Cerebrospinal fluid; γ-secretase; Alcadein; β-amyloid
18.  Relationship of dementia screening tests with biomarkers of Alzheimer’s disease 
Brain  2010;133(11):3290-3300.
Screening tests for Alzheimer’s disease lack sensitivity and specificity. We developed the AD8, a brief dementia screening interview validated against clinical and cognitive evaluations, as an improvement over current screening methods. Because insufficient follow-up has occurred to validate the AD8 against the neuropathologic findings of Alzheimer’s disease, we investigated whether AD8 scores correspond to impairment in episodic memory testing and changes in biomarkers of Alzheimer’s disease (cerebrospinal fluid and amyloid imaging with Pittsburgh compound B) characteristic of symptomatic Alzheimer’s disease. We also compared informant-based assessments with brief performance-based dementia screening measurements such as the Mini Mental State Exam. The sample (n = 257) had a mean age of 75.4 years with 15.1 years of education; 88.7% were Caucasian and 45.5% were male. The sample was divided into two groups based on their AD8 scores: those with a negative dementia screening test (AD8 score 0 or 1, n = 137) and those with a positive dementia screening test (AD8 score ≥2, n = 120). Individuals with positive AD8 scores had abnormal Pittsburgh compound B binding (P < 0.001) and cerebrospinal fluid biomarkers (P < 0.001) compared with individuals with negative AD8 scores. Individuals with positive AD8 tests and positive biomarkers scored in the impaired range on the Wechsler Logical Memory Story A (mean score 7.0 ± 4.5 for Pittsburgh compound B; mean score 7.6 ± 5.3 for cerebrospinal fluid amyloid beta protein 1–42). The AD8 area under the curve for Pittsburgh compound B was 0.737 (95% confidence interval: 0.64–0.83) and for cerebrospinal fluid amyloid beta protein 1–42 was 0.685 (95% confidence interval: 0.60–0.77) suggesting good discrimination. The AD8 had superior sensitivity in detecting early stages of dementia compared with the Mini Mental State Examination. The AD8 had a likelihood ratio of a positive test of 5.8 (95% confidence interval: 5.4–6.3) and likelihood ratio of a negative test of 0.04 (95% confidence interval: 0.03–0.06), increasing the pre-test probability of an individual having symptomatic Alzheimer’s disease. Individuals with AD8 scores of ≥2 had a biomarker phenotype consistent with Alzheimer’s disease and lower performance on episodic memory tests, supporting a diagnosis of Alzheimer’s disease. Informant-based assessments may be superior to performance-based screening measures such as the Mini Mental State Examination in corresponding to underlying Alzheimer’s disease pathology, particularly at the earliest stages of decline. The use of a brief test such as the AD8 may improve strategies for detecting dementia in community settings where biomarkers may not be readily available, and may enrich clinical trial recruitment by increasing the likelihood that participants have underlying biomarker abnormalities.
PMCID: PMC2965421  PMID: 20823087
AD8; Alzheimer’s disease; screening; biomarkers; preclinical; cognition
19.  Comparison of analytical platforms for cerebrospinal fluid measures of Aβ1-42, total tau and p-tau181 for identifying Alzheimer’s disease amyloid plaque pathology 
Archives of neurology  2011;68(9):1137-1144.
Cerebrospinal fluid (CSF) biomarkers of Alzheimer’s disease (AD) are currently being considered for inclusion in revised diagnostic criteria for research and/or clinical purposes to increase the certainty of ante-mortem diagnosis. Establishing biomarker validity requires demonstration that the assays are true markers of underlying disease pathology (e.g., amyloid plaques and/or neurofibrillary tangles) in living individuals.
We compared the performances of the two most commonly used platforms, INNOTEST® ELISA and INNO-BIA AlzBio3 for measurement of CSF amyloid-beta (Aβ) and tau(s), for identifying the presence of amyloid plaques in a research cohort (n=103). Values obtained for CSF Aβ1-42, total tau and phosphorylated tau181 (p-tau181) using the two assay platforms were compared to brain amyloid load as assessed by positron emission tomography using the amyloid imaging agent, Pittsburgh Compound B (PIB).
Research volunteers who are cognitively normal or have very mild to moderate AD dementia.
The two assay platforms yielded different (~2–6-fold) absolute values for the various analytes, but relative values were highly correlated. CSF Aβ1-42 correlated inversely, and tau and p-tau181 correlated positively, with the amount of cortical PIB binding, albeit to differing degrees. Both assays yielded similar patterns of CSF biomarker correlations with amyloid load. The ratios of total tau/Aβ1-42 and p-tau181/Aβ1-42 outperformed any single analyte, including Aβ1-2, in discriminating individuals with versus without cortical amyloid.
The INNOTEST® and INNO-BIA CSF platforms performed equally well in identifying individuals with underlying amyloid plaque pathology. Differences in absolute values, however, point to the need for assay-specific diagnostic cut-point values.
PMCID: PMC3154969  PMID: 21555603
Alzheimer’s disease; amyloid; biomarkers; cerebrospinal fluid; imaging (PET, MRI) in dementias; Pittsburgh Compound B
20.  Exercise and Alzheimer's Disease Biomarkers in Cognitively Normal Older Adults 
Annals of neurology  2010;68(3):311-318.
In addition to the increasingly recognized role of physical exercise in maintaining cognition, exercise may influence Alzheimer's disease (AD) pathology as transgenic mouse studies show lowered levels of AD pathology in exercise groups. The objective of this study was to elucidate the association between exercise and AD pathology in humans using Pittsburgh Compound B (PIB), amyloid-β (Aβ)42, tau, and phosphorylated tau (ptau)181 biomarkers.
Sixty-nine older adults (17 males, 52 females) aged 55–88 were recruited and confirmed to be cognitively normal. A questionnaire on physical exercise levels over the last decade was administered to all. Cerebrospinal fluid (CSF) samples were collected from 56 participants, and amyloid imaging with PIB was performed on 54 participants.
Participants were classified based on biomarker levels. Those with elevated PIB (p=.030), tau (p=.040) and ptau181 ((p=.044) had significantly lower exercise with a non-significant trend for lower Aβ42 (p=.135) to be associated with less exercise. Results were similar for PIB after controlling for covariates; tau (p=.115) and ptau181 (p=.123) differences were reduced to non-significant trends. Additional analyses also demonstrated that active individuals who met the exercise guidelines set by the American Heart Association (AHA) had significantly lower PIB binding and higher Aβ42 levels with and without controlling for covariates (PIB: p=.006 and p=.001; Aβ42: p=.042 and p=.046). Lastly, the associations between exercise engagement and PIB levels were more prominent in APOE epsilon 4 non-carriers.
Collectively, these results are supportive of an association between exercise engagement and AD biomarkers in cognitively normal older adults.
PMCID: PMC2936720  PMID: 20818789
21.  Cortical binding of Pittsburgh compound B, an endophenotype for genetic studies of Alzheimer's disease 
Biological psychiatry  2009;67(6):581-583.
To date, all known Alzheimer's disease genes influence amyloid beta (Aβ). The development of in vivo imaging of Aβ deposition in the human brain using Pittsburgh compound B (PIB) offers the possibility of using cortical PIB binding as a quantitative endophenotype for genetic studies of late-onset Alzheimer's disease (LOAD).
Heritability of Aβ deposition was determined using 82 elderly siblings from 35 families. Correlation with other Aβ related traits was determined using an unrelated sample of 112 individuals. For both samples, APOE ε4 was genotyped and PET imaging was performed using the PIB ligand. Mean cortical binding potential (MCBP) was computed from several regions-of-interest.
MCBP has a high heritability (0.61, p=0.043). Furthermore, most of the heritable component (74%) cannot be explained by APOE ε4 genotype. Analysis of the unrelated sample reveals that a third of the variance of MCBP cannot be predicted by other biological traits, including CSF Aβ42 levels.
These findings demonstrate that MCBP is a genetic trait and that other more easily measured Aβ related traits such as CSF Aβ42 do not fully explain the variance in MCBP. Thus, mean cortical PIB binding is a useful trait for large-scale genetic studies of LOAD.
PMCID: PMC2866645  PMID: 19892322
22.  Validating predicted biological effects of Alzheimer’s disease associated SNPs using CSF biomarker levels 
Recent large-scale genetic studies of late-onset Alzheimer’s disease (LOAD) have identified risk variants in CALHM1, GAB2 and SORL1. The mechanisms by which these genes might modulate risk are not definitively known. CALHM1 and SORL1 may alter amyloid-beta (Aβ) levels and GAB2 may influence phosphorylation of the tau protein. In this study we have analyzed disease associated genetic variants in each of these genes for association with cerebrospinal fluid (CSF) Aβ or tau levels in 602 samples from two independent CSF series. We failed to detect association between CSF Aβ42 levels and SNPs in SORL1 despite substantial statistical power to detect association. While we also failed to detect association between variants in GAB2 and CSF tau levels, power to detect this association was limited. Finally, our data suggest that the minor allele of rs2986017, in CALHM1, is marginally associated with CSF Aβ42 levels. This association is consistent with previous reports that this non-synonymous coding substitution results in increased Aβ levels in vitro and provides support for an Aβ-related mechanism for modulating risk for AD.
PMCID: PMC3032214  PMID: 20634593
Alzheimer’s disease; genetics; association; endophenotypes; amyloid; tau; CALHM1; SORL1; GAB2
23.  APOE Predicts Aβ but not Tau Alzheimer’s Pathology in Cognitively Normal Aging 
Annals of neurology  2010;67(1):122-131.
To examine interactions of Apolipoprotein E (APOE) genotype with age and with in vivo measures of preclinical Alzheimer’s disease (AD) in cognitively normal aging.
Two hundred and 41 cognitively normal individuals, age 45 to 88 years, had cerebral amyloid imaging studies with Pittsburgh Compound-B (PIB). Of the 241 individuals, 168 (70%) also had cerebrospinal fluid (CSF) assays of amyloid-beta42 (Aβ42), tau, and phosphorylated tau (ptau181). All individuals were genotyped for APOE.
The frequency of individuals with elevated mean cortical binding potential (MCBP) for PIB rose in an age-dependent manner from 0% at ages 45-49 years to 30.3% at 80-88 years. Reduced levels of CSF Aβ42 appear to begin earlier (18.2% of those age 45-49 years) and increase with age in higher frequencies (50% at age 80-88 years) than elevations of MCBP. There is a gene dose effect for the APOE4 genotype, with greater MCBP increases and greater reductions in CSF Aβ42 with increased numbers of APOE4 alleles. Individuals with an APOE2 have no increase in MCBP with age and have higher CSF Aβ42 levels than individuals without an APOE2 allele. There is no APOE4 or APOE2 effect on CSF tau or ptau181.
Increasing cerebral Aβ deposition with age is the pathobiological phenotype of APOE4. The biomarker sequence that detects Aβ deposition may first be lowered CSF Aβ42, followed by elevated MCBP for PIB. A substantial proportion of cognitively normal individuals have presumptive preclinical AD.
PMCID: PMC2830375  PMID: 20186853
preclinical Alzheimer’s disease; Alzheimer’s biomarkers; Aβ; amyloid imaging (PIB); APOE
24.  PIB Imaging Predicts Progression from Cognitively Normal to Symptomatic Alzheimer’s Disease 
Archives of neurology  2009;66(12):1469-1475.
To determine whether preclinical Alzheimer’s disease (AD), as detected by the amyloid imaging agent Pittsburgh Compound B (PIB) in cognitively normal older adults, is associated with risk of symptomatic AD.
A longitudinal cohort study of cognitively normal older adults assessed with positron emission tomography (PET) to determine the mean cortical binding potential for PIB and followed with annual clinical and cognitive assessments for progression to very mild dementia of the Alzheimer type (DAT).
Alzheimer’s Disease Research Center
One hundred and fifty-nine participants with mean age of 71.5 y in a longitudinal study of memory and aging had a PET PIB scan when cognitively normal with Clinical Dementia Rating (CDR) of 0.
Outcome Measure
Progression from CDR 0 status to CDR 0.5 (very mild dementia).
Twenty-three participants progressed to CDR 0.5 at follow-up assessment (range: 1–5 assessments after PET PIB). Of these, 9 also were diagnosed with DAT. Higher MCBP values for PIB (hazard ratio 4.85, 95% CI, 1.22–19.01, p = .02) and age (hazard ratio 1.14, 95% CI 1.02–1.28, p = .03) predicted progression to CDR 0.5 DAT. The CDR 0.5 DAT group showed decline in three cognitive domains (episodic memory, semantic memory, and visuospatial performance) and had volume loss in the parahippocampal gyrus (includes entorhinal cortex) compared with individuals who remained CDR 0.
Preclinical AD, as detected by PET PIB, is not benign as it is associated with progression to symptomatic AD.
PMCID: PMC2798814  PMID: 20008650
25.  Cerebrospinal fluid biomarkers of Alzheimer’s disease 
Biomarkers in medicine  2010;4(1):51-63.
Alzheimer’s disease will reach epidemic proportions within the next 20–30 years if left unchecked. Currently, there are no treatments that prevent or slow Alzheimer’s disease but many are being developed. Parallel efforts to develop biomarkers to aid in disease diagnosis and prognosis, and assess disease risk are currently underway. Clinicopathological and biomarker studies have demonstrated that Alzheimer’s disease pathology can be detected preclinically. Using biomarkers to identify affected individuals prior to the onset of clinical symptoms and associated synaptic/neuronal loss should enable novel clinical trial design and early mechanism-based therapeutic intervention. This article summarizes the most promising cerebrospinal fluid biomarkers, highlights novel applications and current challenges, and provides a prediction on how the field may evolve in 5–10 years.
PMCID: PMC2846664  PMID: 20361010
Alzheimer’s disease; amyloid-β; biomarkers; cerebrospinal fluid; preclinical Alzheimer’s disease; tau

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