Substances produced throughout the body are detectable in the blood, which is the most common biological fluid used in clinical testing. Biomarkers for Alzheimer's disease (AD) have long been sought in the blood, but none has become an established or validated diagnostic test. Companion reviews in Alzheimer's Research & Therapy will review specific types of biomarkers or applications; in this overview, we cover key concepts related to AD blood biomarker studies in general. Reasons for the difficulty of detecting markers of a brain-specific disorder, such as AD, in the blood are outlined; these pose conceptual challenges for blood biomarker discovery and development. Applications of blood tests in AD go beyond screening and diagnostic testing; other potential uses are risk assessment, prognostication, and evaluation of treatment target engagement, toxicity, and outcome. Opportunities and questions that may surround these different uses are discussed. A systematic approach to biomarker discovery, detection, assay development and quality control, sample collection, handling and storage, and design and analysis of clinical studies needs to be implemented at every step of discovery and translation to identify an interpretable and useful biomarker.
The current study explored the value of visuospatial findings for predicting the occurrence of visual hallucinations (VH) in a sample of patients with Dementia with Lewy bodies (DLB) compared to patients with Alzheimer’s disease (AD).
Retrospective analysis of 55 autopsy-confirmed DLB and 55 demographically-similar, autopsy-confirmed AD cases determined whether severe initial visuospatial deficits on the WISC-R Block Design subtest predicted the development of VH. Visuospatial deficits were considered severe if Block Design z-scores were 2.5 or more standard deviations below the mean of a well-characterized normal control group (Severe-VIS; DLB: n=35, AD: n=26) and otherwise were considered mild (Mild-VIS; DLB: n=20, AD: n=29).
Forty percent of the Severe-VIS DLB group had baseline VH compared to 0% of Mild-VIS DLB patients. Only 8% of the Severe-VIS and 3% Mild-VIS AD patients had baseline VH. During the follow-up period (mean=5.0 years), an additional 61% of the Severe-VIS but only 11% of the Mild-VIS DLB patients developed VH. In that period, 38% of the Severe-VIS and 20% of the Mild-VIS AD patients developed VH. After considering initial MMSE score and rate of decline, logistic regression analyses found that performance on Block Design significantly predicted the presence of VH in the DLB group but not the AD group.
The presence of early, severe deficits on neuropsychological tests of visuospatial skill increases the likelihood that patients with suspected DLB will develop the prototypical DLB syndrome. The presence of such deficits may identify those DLB patients whose syndrome is driven by alpha-synuclein pathology rather than AD pathology and may inform treatment plans as well as future research.
Lewy body disease; Hallucinations, visual; Alzheimer’s disease; Visuospatial cognition
Although significant progress has occurred in the past 20 years regarding our understanding of Alzheimer disease pathogenesis, we have yet to identify disease-modifying therapeutics capable of substantially altering the clinical course of this prevalent neurodegenerative disease. In this short review, we discuss 2 approaches that are currently being tested clinically (γ-secretase inhibition and γ-secretase modulation) and emphasize the significant differences between these 2 therapeutic approaches. We also discuss certain genetic- and biomarker-based translational and clinical trial paradigms that may assist in developing a useful therapeutic agent.
Temporal sequence learning is a critical aspect of episodic memory that may be dependent on the temporal and frontal lobes. Since amnestic mild cognitive impairment (aMCI) and normal aging may result in changes within the temporal and frontal lobes, the present study investigated temporal sequence learning in patients with aMCI, cognitively normal older adults, and young adults.
On each trial of a temporal sequence task, circles appeared one at a time at the end of each arm of a computerized radial 8-arm maze. Participants were asked to reproduce the temporal sequence by placing numbered circles (1-8) on the arms of the 8-arm maze. Participants were presented with the same fixed sequence on each trial until the sequence was replicated without any errors, or until 15 trials were presented.
Individuals with aMCI required significantly more trials to learn the temporal sequence compared to older adults (p <. 05). Older adults required significantly more trials to learn the sequence than young adults (p <. 05). Older adults and individuals with aMCI committed significantly more Trial 1 errors (p <. 05) than young adults; however, there were no significant differences between the aMCI and older adult groups on Trial 1.
The results suggest that temporal sequence learning deficits are detectable in aMCI. These deficits may disrupt a number of cognitive processes, such as episodic memory, that are important for the execution of daily activities. The results suggest that although temporal sequence learning declines with normal aging, this decline is greater in individuals who have a diagnosis of aMCI and are at higher risk for developing AD.
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.
Alzheimer’s disease; Cerebrospinal fluid; Biomarkers; External assurance; External control; Proficiency testing
Increased susceptibility of the aging brain to both chronic stress and incipient dementia-related neuropathology may accelerate cognitive decline. We investigated associations between chronic stress and diagnostic change in 62 individuals (mean age=78.7) participating in an Alzheimer’s disease research center longitudinal study. Subjects, diagnosed at baseline as cognitively normal (CN) or Mild Cognitive Impairment (MCI) were followed an average of 2.5 years. Senior neurologists, blind to detailed measures of stress and cognition, assigned diagnoses annually. Logistic regression analyses assessed accuracy with which measures of stress (event-based ratings, cortisol levels) predicted conversion to MCI and dementia. Eleven individuals with MCI at baseline received a dementia diagnosis during follow-up. Sixteen converted from CN to MCI. Prolonged, highly stressful experiences were associated with conversion from MCI to dementia. The cortisol awakening response, with age and education, was associated with diagnostic change to MCI. Cortisol measures were not associated with progression from MCI to dementia, and there was no association between stressful experiences and change to MCI. Mechanisms associated with the transition from normal cognition to MCI may differ from those associated with diagnostic change to dementia. These findings could facilitate identification of interventional strategies to reduce risk of decline at different stages of susceptibility.
chronic stress; aging; Alzheimer’s disease; mild cognitive impairment; dementia; diurnal rhythm; cortisol awakening response
To evaluate whether antioxidant supplements presumed to target specific cellular compartments affected cerebrospinal fluid (CSF) biomarkers.
Double-blind, placebo-controlled clinical trial.
Academic medical centers.
Subjects with mild to moderate Alzheimer disease.
Random assignment to treatment for 16 weeks with 800 IU/d of vitamin E (α-tocopherol) plus 500 mg/d of vitamin C plus 900 mg/d of α-lipoic acid (E/C/ALA); 400 mg of coenzyme Q 3 times/d; or placebo.
Main Outcome Measures
Changes from baseline to 16 weeks in CSF biomarkers related to Alzheimer disease and oxidative stress, cognition (Mini-Mental State Examination), and function (Alzheimer’s Disease Cooperative Study Activities of Daily Living Scale).
Seventy-eight subjects were randomized; 66 provided serial CSF specimens adequate for biochemical analyses. Study drugs were well tolerated, but accelerated decline in Mini-Mental State Examination scores occurred in the E/C/ALA group, a potential safety concern. Changes in CSF Aβ42, tau, and P-tau181 levels did not differ between the 3 groups. Cerebrospinal fluid F2-isoprostane levels, an oxidative stress biomarker, decreased on average by 19% from baseline to week 16 in the E/C/ALA group but were unchanged in the other groups.
Antioxidants did not influence CSF biomarkers related to amyloid or tau pathology. Lowering of CSF F2-isoprostane levels in the E/C/ALA group suggests reduction of oxidative stress in the brain. However, this treatment raised the caution of faster cognitive decline, which would need careful assessment if longer-term clinical trials are conducted.
clinicaltrials.gov Identifier: NCT00117403
To estimate the incidence rate and predictors of seizures in patients with mild to moderate Alzheimer disease (AD).
Cohort study of patients with mild to moderate AD in clinical trials. Risk factors for potential seizures were evaluated by stratified descriptive statistics and univariable and multivariable Cox proportional hazards regressions.
Pooled patient-level data from 10 Alzheimer Disease Cooperative Study clinical trials in mild to moderate AD from 1995 to 2010.
Three thousand seventy-eight subjects randomized to the treatment or placebo arms of 10 AD clinical trials. Screening Mini-Mental State Examination scores ranged between 10 and 28.
Eighteen seizures were reported in 3078 randomized subjects, with an incidence rate of 484 per 100 000 person-years (95% CI, 287–764). Statistically significant independent risk factors for seizure were younger age (adjusted hazard ratio, 0.80; 95% CI, 0.69–0.93 per every 5 years of age), greater cognitive impairment at baseline (adjusted hazard ratio, 2.79; 95% CI, 1.06–7.33 for Mini-Mental State Examination scores <18 compared with Mini-Mental State Examination scores ≥18), and antipsychotic use at baseline (adjusted hazard ratio, 3.47; 95% CI, 1.33–9.08).
Seizure rates in patients with mild to moderate AD in clinical trials are similar to rates observed in longer observational cohort studies, but they are greater than expected in the general elderly population. Younger age, greater degree of cognitive impairment, and history of antipsychotic use were independent risk factors for new-onset seizures in AD.
The Mild Cognitive Impairment Screen (MCIS) is a computer-based cognitive assessment designed for clinical and research use in detecting amnestic mild cognitive impairment (aMCI). Performance on the MCIS is reported as the Memory Performance Index (MPI). However, the comparability between the MPI and traditional neuropsychological tests in detecting aMCI, and in differentiating it from Alzheimer’s disease (AD) and normal aging has not been examined. A cross-sectional study was conducted to assess the validity of the MPI relative to standard neuropsychological measures. Participants included 12 individuals diagnosed with aMCI, 49 with mild AD, and 25 healthy elderly. The MCIS significantly discriminated among aMCI, AD, and healthy elderly controls. The MCIS is effective in detecting aMCI, and in discriminating it from cognitive changes observed in AD and normal aging. The MCIS may be a valuable tool in the identification of elderly at high risk for dementia due to its ease-of-use and brief administration time.
Mild Cognitive Impairment; Dementia; Alzheimer’s Disease; Screening; Memory
TDP-43 is a major component of the ubiquitinated inclusions that characterise amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) with ubiquitin inclusions (FTLD-U). TDP-43 is an RNA-binding and DNA-binding protein that has many functions and is encoded by the TAR DNA-binding protein gene (TARDBP) on chromosome 1. Our aim was to investigate whether TARDBP is a candidate disease gene for familial ALS that is not associated with mutations in superoxide dismutase 1 (SOD1).
TARDBP was sequenced in 259 patients with ALS, FTLD, or both. We used TaqMan-based SNP genotyping to screen for the identifi ed variants in control groups matched to two kindreds of patients for age and ethnic origin. Additional clinical, genetic, and pathological assessments were made in these two families.
We identified two variants, p.Gly290Ala and p.Gly298Ser, in TARDBP in two familial ALS kindreds and we observed TDP-43 neuropathology in the CNS tissue available from one family. The variants are considered pathogenic mutations because they co-segregate with disease in both families, are absent in ethnically-matched controls, and are associated with TDP-43 neuropathology in several family members.
The p.Gly290Ala and p.Gly298Ser mutations are located in the glycine-rich domain that regulates gene expression and mediates protein-protein interactions; in particular TDP-43 binds to heterogeneous ribonucleoproteins (hnRNPs) via this domain. We postulate that due to the varied and important cellular functions of TDP-43, these mutations may cause neurodegeneration through both gains and losses of function. The finding of TARDBP mutations implicates TDP-43 as an active mediator of neurodegeneration in a novel class of disorders, TDP-43 proteinopathies, a class of disorder that includes ALS and FTLD-U.
The current study investigated the relationship between bilingual language proficiency and onset of probable Alzheimer’s disease (AD) in 44 Spanish-English bilinguals at the UCSD Alzheimer’s Disease Research Center. Degree of bilingualism along a continuum was measured using Boston Naming Test (BNT) scores in each language. Higher degrees of bilingualism were associated with increasingly later age-of-diagnosis (and age of onset of symptoms), but this effect was driven by participants with low education level (a significant interaction between years of education and bilingualism) most of whom (73%) were also Spanish-dominant. Additionally, only objective measures (i.e., BNT scores), not self-reported degree of bilingualism, predicted age-of-diagnosis even though objective and self-reported measures were significantly correlated. These findings establish a specific connection between knowledge of two languages and delay of AD onset, and demonstrate that bilingual effects can be obscured by interactions between education and bilingualism, and by failure to obtain objective measures of bilingualism. More generally, these data support analogies between the effects of bilingualism and “cognitive reserve” and suggest an upper limit on the extent to which reserve can function to delay dementia.
Based on the recent literature and collective experience, an international consortium developed revised guidelines for the diagnosis of behavioural variant frontotemporal dementia. The validation process retrospectively reviewed clinical records and compared the sensitivity of proposed and earlier criteria in a multi-site sample of patients with pathologically verified frontotemporal lobar degeneration. According to the revised criteria, ‘possible’ behavioural variant frontotemporal dementia requires three of six clinically discriminating features (disinhibition, apathy/inertia, loss of sympathy/empathy, perseverative/compulsive behaviours, hyperorality and dysexecutive neuropsychological profile). ‘Probable’ behavioural variant frontotemporal dementia adds functional disability and characteristic neuroimaging, while behavioural variant frontotemporal dementia ‘with definite frontotemporal lobar degeneration’ requires histopathological confirmation or a pathogenic mutation. Sixteen brain banks contributed cases meeting histopathological criteria for frontotemporal lobar degeneration and a clinical diagnosis of behavioural variant frontotemporal dementia, Alzheimer’s disease, dementia with Lewy bodies or vascular dementia at presentation. Cases with predominant primary progressive aphasia or extra-pyramidal syndromes were excluded. In these autopsy-confirmed cases, an experienced neurologist or psychiatrist ascertained clinical features necessary for making a diagnosis according to previous and proposed criteria at presentation. Of 137 cases where features were available for both proposed and previously established criteria, 118 (86%) met ‘possible’ criteria, and 104 (76%) met criteria for ‘probable’ behavioural variant frontotemporal dementia. In contrast, 72 cases (53%) met previously established criteria for the syndrome (P < 0.001 for comparison with ‘possible’ and ‘probable’ criteria). Patients who failed to meet revised criteria were significantly older and most had atypical presentations with marked memory impairment. In conclusion, the revised criteria for behavioural variant frontotemporal dementia improve diagnostic accuracy compared with previously established criteria in a sample with known frontotemporal lobar degeneration. Greater sensitivity of the proposed criteria may reflect the optimized diagnostic features, less restrictive exclusion features and a flexible structure that accommodates different initial clinical presentations. Future studies will be needed to establish the reliability and specificity of these revised diagnostic guidelines.
behavioural variant frontotemporal dementia; diagnostic criteria; frontotemporal lobar degeneration; FTD; pathology
Phosphorylated α-synuclein (PS-129), a protein implicated in the pathogenesis of Parkinson’s disease (PD), was identified by mass spectrometry in human cerebrospinal fluid (CSF). A highly sensitive and specific assay was established and used to measure PS-129, along withtotal α-synuclein, in the CSF of patients with PD, other parkinsonian disorders such as multiple system atrophy (MSA) and progressive supranuclear palsy (PSP), and healthy individuals (a total of ~600 samples). PS-129 CSF concentrations correlated weakly with PD severity and, when combined with total α-synuclein CSF concentrations, contributed to distinguishing PD from MSA and PSP. Further rigorous validation in independent cohorts of patients, especially those where samples have been collected longitudinally, will determine whether PS-129 CSF concentrations will be useful for diagnosing PD and for monitoring PD severity and progression.
To evaluate the safety and tolerability of PF-04494700, an oral Inhibitor of receptor for advanced glycation end products (RAGE), in subjects with mild-to-moderate dementia of the Alzheimer’s type.
Subjects 50 years and older who met NINCDS-ADRDA criteria for AD with an MMSE score between 12–26 (inclusive) were randomized to 10-weeks of double-blind treatment with either a 10 mg “low dose” of PF-04494700 (after a 6-day loading dose of 30 mg/d to); or a 20 mg “high dose” of PF-04494700 (after a loading dose of 60 mg/d); or placebo. Safety measures included adverse events, laboratory tests, vital signs, and 12-lead ECG.
27 subjects received PF-04494700 30/10 mg (female, 63%; mean age, 74.6 years; mean MMSE, 21.1), 28 subjects received PF-04494700 60/20 mg (female, 57%; mean age, 76.6 years; mean MMSE, 21.6), and 12 subjects received placebo (female, 67%; mean age, 74.1 years; mean MMSE, 19.2). A higher proportion of subjects completed 10 weeks of double-blind treatment on both the “low dose” regimen of PF-04494700 (88.9%) and the “high dose” regimen (85.7%) than completed on placebo (66.7%). Discontinuation due to adverse events, and incidence of severe adverse events, respectively, were lower on the “low dose” regimen (7.4%,11.1%) and the “high dose” regimen (3.6%,10.7%) compared to placebo (25.0%,16.7%). There were no clinically meaningful differences in vital signs, laboratory test results, or mean ECG parameters in subjects treated with PF-04494700. PF-04494700 had no consistent effect on plasma levels of Aβ, inflammatory biomarkers, or secondary cognitive outcomes.
Ten weeks of treatment with PF-04494700 was safe and well-tolerated in subjects with mild-to-moderate AD, indicating the feasibility of a larger long-term efficacy trial.
Alzheimer’s disease; randomized clinical trial; RAGE
Elevated pulse pressure (PP) is associated with cognitive decline and increased risk of Alzheimer’s disease (AD) in older adults, although the mechanisms behind these associations remain unclear. To address this question, we examined whether antemortem late-life PP elevation predicted vascular or AD pathology in autopsy-confirmed AD patients. Sixty-five elderly patients (mean age 74.2 years) clinically diagnosed with possible or probable AD underwent neuropsychological testing and blood pressure examinations. Postmortem histopathological measures of cerebrovascular disease (CVD) and AD neuropathology were later obtained on these same patients. We expected that antemortem PP elevation, but not standard blood pressure measures such as systolic or diastolic blood pressure, would predict the autopsy-based presence of CVD, and possibly AD pathology, in elderly AD patients. Results demonstrated that antemortem PP elevation was associated with the presence and severity of CVD at autopsy. For every 5 mmHg increase in antemortem PP there was an estimated 36% increase in the odds of having CVD at autopsy. Additionally, PP accounted for 12% of variance in CVD severity. No significant associations were present for cerebral amyloid angiopathy or Braak and Braak staging of the severity of AD pathology. Other standard blood pressure measures also did not significantly predict neuropathology. The association between antemortem PP and CVD at autopsy suggests that in older adults with AD, PP elevation may increase the risk of CVD. These findings may have treatment implications since some antihypertensive medications specifically address the pulsatile component of blood pressure (e.g., renin-angiotensin system inhibitors, calcium channel blockers).
Alzheimer’s disease; blood pressure; cerebrovascular disease; pulse pressure
There is a clear need to develop biomarkers for Parkinson disease (PD) diagnosis, differential diagnosis of parkinsonian disorders, and monitoring disease progression. We and others have demonstrated that a decrease in DJ-1 and/or α-synuclein in the cerebrospinal fluid (CSF) is a potential index for PD diagnosis, but not for PD severity.
Using highly sensitive and quantitative Luminex assays, we measured total tau, phosphorylated tau, amyloid beta peptide 1-42 (Aβ1-42), Flt3 ligand and fractalkine levels in CSF in a large cohort of PD patients at different stages as well as healthy and diseased controls. The utility of these five markers was evaluated for disease diagnosis and severity/progression correlation alone, as well as in combination with DJ-1 and α-synuclein. The major results were further validated in an independent cohort of cross-sectional PD patients as well as in PD cases with CSF samples collected longitudinally.
The results demonstrated that combinations of these biomarkers could differentiate PD patients not only from normal controls but also from patients with Alzheimer disease and multiple system atrophy. Particularly, with CSF Flt3 ligand, PD could be clearly differentiated from multiple system atrophy, a disease that overlaps with PD clinically, with excellent sensitivity (99%) and specificity (95%). In addition, we identified CSF fractalkine/Aβ1-42 that positively correlated with PD severity in cross-sectional samples as well as with PD progression in longitudinal samples.
We have demonstrated that this panel of seven CSF proteins could aid in PD diagnosis, differential diagnosis, and correlation with disease severity and progression.
Alzheimer’s disease (AD) is a common age-related chronic illness with latent, prodrome, and fully symptomatic dementia stages. Increased free radical injury to regions of brain is one feature of prodrome and dementia stages of AD; however, it also is associated with advancing age. This raises the possibility that age-related free radical injury to brain might be caused in part or in full by latent AD. We quantified free radical injury in the central nervous system with cerebrospinal fluid (CSF) F2-isoprostanes (IsoPs) in 421 clinically normal individuals and observed a significant increase over the adult human lifespan (P < 0.001). Using CSF amyloid (A) β42 and tau, we defined normality using results from 28 clinically normal individuals < 50 years old, and then stratified 74 clinically normal subjects ≥ 60 years into those with CSF that had normal CSF Aβ42 and tau (n=37); abnormal CSF Aβ42 and tau, the biomarker signature of AD (n=24); decreased Aβ42 only (n=4); or increased tau only (n=9). Increased CSF F2-IsoPs were present in clinically normal subjects with the biomarker signature of AD (P < 0.05) and those subjects with increased CSF tau (P < 0.001). Finally, we analyzed the relationship between age and CSF F2-IsoPs for those clinically normal adults with normal CSF (n=37) and those with abnormal CSF Aβ42 and/or tau (n=37); only those with normal CSF demonstrated a significant increase with age (P < 0.01). These results show that CSF F2-IsoPs increased across the human lifespan and that this age-related increase in free radical injury to brain persisted after culling those with laboratory evidence of latent AD.
Alzheimer’s disease; cerebrospinal fluid; biomarkers; Aβ42; tau; F2-isoprostanes
In the central nervous system (CNS), aging results in a precipitous decline in adult neural stem/progenitor cells (NPCs) and neurogenesis, with concomitant impairments in cognitive functions1. Interestingly, such impairments can be ameliorated through systemic perturbations such as exercise1. Here, using heterochronic parabiosis we show that blood-borne factors present in the systemic milieu can inhibit or promote adult neurogenesis in an age dependent fashion in mice. Accordingly, exposing a young animal to an old systemic environment, or to plasma from old mice, decreased synaptic plasticity and impaired contextual fear conditioning and spatial learning and memory. We identify chemokines - including CCL11/Eotaxin – whose plasma levels correlate with reduced neurogenesis in heterochronic parabionts and aged mice, and whose levels are increased in plasma and cerebral spinal fluid of healthy aging humans. Finally, increasing peripheral CCL11 chemokine levels in vivo in young mice decreased adult neurogenesis and impaired learning and memory. Together our data indicate that the decline in neurogenesis, and cognitive impairments, observed during aging can be in part attributed to changes in blood-borne factors.
Dementia with Lewy Bodies (DLB) is a common neurodegenerative disorder of the aging population characterized by α–synuclein accumulation in cortical and subcortical regions. Although neuropathology in advanced age has been investigated in dementias such as Alzheimer Disease (AD), severity of the neuropathology in the oldest old with DLB remains uncharacterized. For this purpose we compared characteristics of DLB cases divided into three age groups 70–79, 80–89 and ≥90 years (oldest old). Neuropathological indicators and levels of synaptophysin were assessed and correlated with clinical measurements of cognition and dementia severity. These studies showed that frequency and severity of DLB was lower in 80–89 and ≥90 year cases compared to 70–79 year old group but cognitive impairment did not vary with age. The extent of AD neuropathology correlated with dementia severity only in the 70–79 year group, while synaptophysin immunoreactivity more strongly associated with dementia severity in the older age group in both DLB and AD. Taken together these results suggest that the oldest old with DLB might represent a distinct group.
Cognition; Neuropsychological assessment
We tested the hypothesis that the CSF biomarker signature associated with Alzheimer’s disease (AD) is present in a subset of individuals with Parkinson’s disease and Dementia (PD-D) or with PD and Cognitive Impairment, Not Dementia (PD-CIND). We quantified CSF Aβ42, total tau (T-tau), and phospho-tau (P181-Tau) using commercially available kits. Samples were from 345 individuals in seven groups (n): Controls ≤ 50 years (35), Controls > 50 years (115), amnestic Mild Cognitive Impairment (aMCI) (24), AD (49), PD (49), PD-CIND (62), and PD-D (11). We observed expected changes in AD or aMCI compared with age-matched or younger controls. CSF Aβ42 was reduced in PD-CIND (P < 0.05) and PD-D (P < 0.01) while average CSF T-Tau and P181-Tau were unchanged or decreased. One-third of PD-CIND and one-half of PD-D patients had the biomarker signature of AD. Abnormal metabolism of Aβ42 may be a common feature of PD-CIND and PD-D.
Parkinson’s disease; cognitive impairment; CSF biomarkers; Aβ42; tau
Disease-modifying therapies for Alzheimer’s disease (AD) would be most beneficial if applied during the ‘preclinical’ stage (pathology present with cognition intact) before significant neuronal loss occurs. Therefore, biomarkers that can detect AD pathology in its early stages and predict dementia onset and progression will be invaluable for patient care and efficient clinical trial design.
2D–difference gel electrophoresis and liquid chromatography tandem mass spectrometry were used to measure AD-associated changes in cerebrospinal fluid (CSF). Concentrations of CSF YKL-40 were further evaluated by enzyme-linked immunosorbent assay in the discovery cohort (N=47), an independent sample set (N=292) with paired plasma samples (N=237), frontotemporal lobar degeneration (N=9), and progressive supranuclear palsy (PSP, N=6). Human AD brain was studied immunohistochemically to identify potential source(s) of YKL-40.
In the discovery and validation cohorts, mean CSF YKL-40 was higher in very mild and mild AD-type dementia (Clinical Dementia Rating [CDR] 0.5 and 1) vs. controls (CDR 0) and PSP. Importantly, CSF YKL-40/Aβ42 ratio predicted risk of developing cognitive impairment (CDR 0 to CDR>0 conversion) as well as the best CSF biomarkers identified to date, tau/Aβ42 and p-tau181/Aβ42. Mean plasma YKL-40 was higher in CDR 0.5 and 1 vs. CDR 0 groups, and correlated with CSF levels. YKL-40 immunoreactivity was observed within astrocytes near a subset of amyloid plaques, implicating YKL-40 in the neuroinflammatory response to Aβ deposition.
These data demonstrate that YKL-40, a putative indicator of neuroinflammation, is elevated in AD, and that, together with Aβ42, has potential prognostic utility as a biomarker for preclinical AD.
YKL-40; Alzheimer’s disease; biomarkers; cerebrospinal fluid; chitinase-3 like-1; inflammation
A functional repeat polymorphism in the SNCA promoter (REP1) conveys susceptibility for Parkinson’s disease (PD). There is also increasing evidence that SNPs elsewhere in the gene associate with risk. We sought to further explore the disease association, determine whether evidence of allelic heterogeneity exists, and examine the correlation between PD-associated variants and plasma α-synuclein levels.
We performed a two-tiered analysis of 1,956 PD patients and 2,112 controls from the NeuroGenetics Research Consortium using a comprehensive tagSNP approach. Previously published REP1 genotypes were also included. Plasma α-synuclein was assayed in 86 cases and 78 controls using a highly sensitive Luminex assay.
Five of the 15 SNPs genotyped were associated with PD under an additive model in Tier 1 (α=0.05). Of these, four were successfully replicated in Tier 2. In the combined sample, the most significant marker was rs356219 (OR, 1.41; CI, 1.28–1.55; p = 1.6 × 10−12) located ~ 9 kb downstream from the gene. A regression model containing rs356219 alone best fit the data. The linkage disequilibrium correlation coefficient between this SNP and REP1 was low (r2=0.09). The risk-associated C allele of rs356219 was also correlated with higher transformed plasma α-synuclein levels in cases under an adjusted additive model (p = 0.005).
Our data suggest that one or more unidentified functional SNCA variants modify risk for PD, and that the effect is larger than, and independent of, REP1. This variant(s), tagged by rs356219, might act by upregulating SNCA expression in a dose-dependent manner.
The ε4 allele of the apolipoprotein E gene (APOE) is associated with increased risk and earlier age at onset in late onset Alzheimer’s disease (AD). Other factors, such as expression level of apolipoprotein E protein (apoE), have been postulated to modify the APOE related risk of developing AD. Multiple loci in and outside of APOE are associated with a high risk of AD. The aim of this exploratory hypothesis generating investigation was to determine if some of these loci predict cerebrospinal fluid (CSF) apoE levels in healthy non-demented subjects. CSF apoE levels were measured from healthy non-demented subjects 21–87 years of age (n = 134). Backward regression models were used to evaluate the influence of 21 SNPs, within and surrounding APOE, on CSF apoE levels while taking into account age, gender, APOE ε4 and correlation between SNPs (linkage disequilibrium). APOE ε4 genotype does not predict CSF apoE levels. Three SNPs within the TOMM40 gene, one APOE promoter SNP and two SNPs within distal APOE enhancer elements (ME1 and BCR) predict CSF apoE levels. Further investigation of the genetic influence of these loci on apoE expression levels in the central nervous system is likely to provide new insight into apoE regulation as well as AD pathogenesis.
Apolipoprotein E gene; apolipoprotein E protein; cerebroshinal fluid; enhancer; promoter; SNP