Improving CSF biomarker accuracy in predicting prevalent and incident Alzheimer disease

Four Distinct Subtypes of Alzheimer's Disease Based on Resting-State Connectivity Biomarkers

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disorder with significant heterogeneity. Different AD phenotypes may be associated with specific brain network changes. Uncovering disease heterogeneity by using functional networks could provide insights into precise diagnoses.

METHODS

We investigated the subtypes of AD using nonnegative matrix factorization clustering on the previously identified 216 resting-state functional connectivities that differed between AD and normal control subjects. We conducted the analysis using a discovery dataset (n = 809) and a validated dataset (n = 291). Next, we grouped individuals with mild cognitive impairment according to the model obtained in the AD groups. Finally, the clinical measures and brain structural characteristics were compared among the subtypes to assess their relationship with differences in the functional network.

RESULTS

Individuals with AD were clustered into 4 subtypes reproducibly, which included those with 1) diffuse and mild functional connectivity disruption (subtype 1), 2) predominantly decreased connectivity in the default mode network accompanied by an increase in the prefrontal circuit (subtype 2), 3) predominantly decreased connectivity in the anterior cingulate cortex accompanied by an increase in prefrontal cortex connectivity (subtype 3), and 4) predominantly decreased connectivity in the basal ganglia accompanied by an increase in prefrontal cortex connectivity (subtype 4). In addition to these differences in functional connectivity, differences between the AD subtypes were found in cognition, structural measures, and cognitive decline patterns.

CONCLUSIONS

These comprehensive results offer new insights that may advance precision medicine for AD and facilitate strategies for future clinical trials.

Antimicrobial Peptides (AMPs) in the Pathogenesis of Alzheimer’s Disease: Implications for Diagnosis and Treatment

Alzheimer’s disease (AD) represents the most frequent type of dementia in elderly people. There are two major forms of the disease: sporadic (SAD)—whose causes are not completely understood—and familial (FAD)—with clear autosomal dominant inheritance. The two main hallmarks of AD are extracellular deposits of amyloid-beta (Aβ) peptide and intracellular deposits of the hyperphosphorylated form of the tau protein (P-tau). An ever-growing body of research supports the infectious hypothesis of sporadic forms of AD. Indeed, it has been documented that some pathogens, such as herpesviruses and certain bacterial species, are commonly present in AD patients, prompting recent clinical research to focus on the characterization of antimicrobial peptides (AMPs) in this pathology. The literature also demonstrates that Aβ can be considered itself as an AMP; thus, representing a type of innate immune defense peptide that protects the host against a variety of pathogens. Beyond Aβ, other proteins with antimicrobial activity, such as lactoferrin, defensins, cystatins, thymosin β4, LL37, histatin 1, and statherin have been shown to be involved in AD. Here, we summarized and discussed these findings and explored the diagnostic and therapeutic potential of AMPs in AD.

Cognitive Reserve, Brain Reserve, APOEɛ4, and Cognition in Individuals with Subjective Cognitive Decline in the SILCODE Study

BACKGROUND

Cognitive reserve (CR) and brain reserve (BR) could offer protective effects on cognition in the early stage of Alzheimer's disease (AD). However, the effects of CR or BR on cognition in individuals with subjective cognitive decline (SCD) are not clear.

OBJECTIVE

To explore the effects of CR and BR on cognition in subjects with SCD.

METHODS

We included 149 subjects from the Sino Longitudinal Study on Cognitive Decline (SILCODE) study. Education was used as a proxy for CR, and head circumference was used as a proxy for BR. Multiple linear regression models were conducted to examine the effects of CR and BR on cognitive scores. Furthermore, we assessed differences in effects between APOEɛ4 carriers with SCD (n = 35) and APOEɛ4 non-carriers with SCD (n = 114) and linear trends among 4 reserve levels (low BR/CR, high BR/low CR, low BR/high CR, and high BR/high CR).

RESULTS

Both CR and BR had independent positive effects on multiple cognitive measures in SCD participants, and the effects of CR were greater than those of BR. CR has positive effects on cognitive measures in both APOEɛ4 carriers and non-carriers with SCD. However, the positive effects of BR on cognitive measures were observed in APOEɛ4 non-carriers with SCD but not in APOEɛ4 carriers with SCD. Furthermore, there was a linear trend toward better cognitive performance on all cognitive measures in the BR+/CR+ group, followed by the BR-/CR+, BR+/CR-, and BR-/CR-groups.

CONCLUSION

This study suggests that both CR and BR have the potential to delay or slow cognitive decline in individuals with SCD.

Cognitive Reserve, Alzheimer's Neuropathology, and Risk of Dementia: A Systematic Review and Meta-Analysis

Cognitive reserve (CR) may reduce the risk of dementia. We summarized the effect of CR on progression to mild cognitive impairment (MCI) or dementia in studies accounting for Alzheimer's disease (AD)-related structural pathology and biomarkers. Literature search was conducted in Web of Science, PubMed, Embase, and PsycINFO. Relevant articles were longitudinal, in English, and investigating MCI or dementia incidence. Meta-analysis was conducted on nine articles, four measuring CR as cognitive residual of neuropathology and five as composite psychosocial proxies (e.g., education). High CR was related to a 47% reduced relative risk of MCI or dementia (pooled-hazard ratio: 0.53 [0.35, 0.81]), with residual-based CR reducing risk by 62% and proxy-based CR by 48%. CR protects against MCI and dementia progression above and beyond the effect of AD-related structural pathology and biomarkers. The finding that proxy-based measures of CR rivaled residual-based measures in terms of effect on dementia incidence underscores the importance of early- and mid-life factors in preventing dementia later.

Cognitive Reserve from the Perspective of Preclinical Alzheimer Disease: 2020 Update

The concept of cognitive reserve (CR) was proposed to account for the discrepancy between levels of brain pathologic process or damage and clinical and cognitive function. We provide a detailed review of prospective longitudinal studies that have investigated the interaction between CR and Alzheimer disease (AD) biomarkers on clinical and cognitive outcomes among individuals with normal cognition at baseline. Current evidence is consistent with the view that higher levels of CR are associated with a delay in the onset of symptoms of mild cognitive impairment and that there may be multiple pathways by which CR exerts its protective effects.

Defining Cognitive Reserve and Implications for Cognitive Aging

PURPOSE OF REVIEW

The aim of this review is to summarize current conceptual models of cognitive reserve (CR) and related concepts and to discuss evidence for these concepts within the context of aging and Alzheimer's disease.

RECENT FINDINGS

Evidence to date supports the notion that higher levels of CR, as measured by proxy variables reflective of lifetime experiences, are associated with better cognitive performance, and with a reduced risk of incident mild cognitive impairment/dementia. However, the impact of CR on longitudinal cognitive trajectories is unclear and may be influenced by a number of factors. Although there is promising evidence that some proxy measures of CR may influence structural brain measures, more research is needed. The protective effects of CR may provide an important mechanism for preserving cognitive function and cognitive well-being with age, in part because it can be enhanced throughout the lifespan. However, more research on the mechanisms by which CR is protective is needed.

Hypertension and obesity moderate the relationship between β-amyloid and cognitive decline in midlife

BACKGROUND

This study tested if central obesity, hypertension, or depressive symptoms moderated the relationship between β-amyloid (Aβ) and longitudinal cognitive performance in late middle-aged adults enriched for Alzheimer's disease (AD) risk.

METHODS

Participants (n = 207; ages = 40-70 years; 73% parental AD) in the Wisconsin Registry for Alzheimer's Prevention study completed 3+ neuropsychological evaluations and a [¹¹C]PiB positron emission tomography scan or lumbar puncture. Linear mixed-effects regression models tested interactions of risk factor × Aβ × visit age on longitudinal Verbal Learning & Memory and Speed & Flexibility factor scores.

RESULTS

The relationship between Aβ and Verbal Learning & Memory decline was moderated by hypertension (χ²₍₁₎ = 3.85, P = .04) and obesity (χ²₍₁₎ = 6.12, P = .01); those with both elevated Aβ and the risk factor declined at faster rates than those with only elevated Aβ or elevated risk factors.

CONCLUSION

In this cohort, hypertension and obesity moderated the relationship between Aβ and cognitive decline.

Evaluating Cognitive Reserve Through the Prism of Preclinical Alzheimer Disease

The concept of cognitive reserve (CR) was proposed to account for the discrepancy between levels of brain pathologic features or damage and clinical and cognitive function. This article provides a detailed review of prospective longitudinal studies that have investigated the interaction between CR and Alzheimer's disease (AD) biomarkers on clinical and cognitive outcomes among individuals with preclinical AD. Current evidence shows that higher levels of CR are associated with a delay in the onset of symptoms of mild cognitive impairment and that there may be multiple pathways by which CR exerts its protective effects.

Cerebrospinal Fluid Biomarkers and Reserve Variables as Predictors of Future "Non-Cognitive" Outcomes of Alzheimer's Disease

BACKGROUND

The influence of reserve variables and Alzheimer's disease (AD) biomarkers on cognitive test performance has been fairly well-characterized. However, less is known about the influence of these factors on "non-cognitive" outcomes, including functional abilities and mood.

OBJECTIVE

We examined whether cognitive and brain reserve variables mediate how AD biomarker levels in cognitively normal persons predict future changes in function, mood, and neuropsychiatric behavior.

METHODS

Non-cognitive outcomes were examined in 328 individuals 50 years and older enrolled in ongoing studies of aging and dementia at the Knight Alzheimer Disease Research Center (ADRC). All participants were cognitively normal at baseline (Clinical Dementia Rating [CDR] 0), completed cerebrospinal fluid (CSF) and structural neuroimaging studies within one year of baseline, and were followed for an average of 4.6 annual visits. Linear mixed effects models explored how cognitive reserve and brain reserve variables mediate the relationships between AD biomarker levels and changes in function, mood, and neuropsychiatric behavior in cognitively normal participants.

RESULTS

Education levels did not have a significant effect on predicting non-cognitive decline. However, participants with smaller brain volumes exhibited the worst outcomes on measures of mood, functional abilities, and behavioral disturbance. This effect was most pronounced in individuals who also had abnormal CSF biomarkers.

CONCLUSIONS

The findings suggest that brain reserve plays a stronger, or earlier, role than cognitive reserve in protecting against non-cognitive impairment in AD.

Early diagnosis of mild cognitive impairment and Alzheimer's disease based on salivary lactoferrin

Introduction

The Alzheimer's disease (AD) process is likely initiated many years before clinical onset. Biomarkers of preclinical disease are critical for the development of disease-modifying or even preventative therapies. Current biomarkers for early disease, including cerebrospinal fluid tau and amyloid β (Aβ) levels, structural and functional magnetic resonance imaging, and the use of brain amyloid imaging, are limited because they are very invasive or expensive. Noninvasive biomarkers may be a more accessible alternative, but none can currently detect preclinical AD with the required sensitivity and specificity.

Methods

Here, we show a novel, straight-forward, and noninvasive approach for assessment of early stages of cognitive decline. Salivary samples from cases of amnestic mild cognitive impairment (aMCI) and AD, and neurology controls were analyzed.

Results

We have discovered and validated a new single saliva biomarker, lactoferrin, which in our cross-sectional investigation perfectly discriminates clinically diagnosed aMCI and AD patients from a cognitively healthy control group. The accuracy for AD diagnosis shown by salivary lactoferrin was greater than that obtained from core cerebrospinal fluid (CSF) biomarkers, including total tau and CSF Aβ₄₂. Furthermore, salivary lactoferrin can be used for population screening and for identifying those underdiagnosed subjects with very early stages of mild cognitive impairment and AD.

Conclusion

This biomarker may offer new insights in the early diagnostics for AD.

Biomarkers for the Early Detection and Progression of Alzheimer's Disease

The recent failures of potential disease-modifying drugs for Alzheimer's disease (AD) may reflect the fact that the enrolled participants in clinical trials are already too advanced to derive a clinical benefit. Thus, well-validated biomarkers for the early detection and accurate diagnosis of the preclinical stages of AD will be crucial for therapeutic advancement. The combinatorial use of biomarkers derived from biological fluids, such as cerebrospinal fluid (CSF), with advanced molecular imaging and neuropsychological testing may eventually achieve the diagnostic sensitivity and specificity necessary to identify people in the earliest stages of the disease when drug modification is most likely possible. In this regard, positive amyloid or tau tracer retention on positron emission tomography imaging, low CSF concentrations of the amyloid-β 1-42 peptide, high CSF concentrations in total tau and phospho-tau, mesial temporal lobe atrophy on magnetic resonance imaging, and temporoparietal/precuneus hypometabolism or hypoperfusion on 18F-fluorodeoxyglucose positron emission tomography have all emerged as biomarkers for the progression to AD. However, the ultimate AD biomarker panel will likely involve the inclusion of novel CSF and blood biomarkers more precisely associated with confirmed pathophysiologic mechanisms to improve its reliability for detecting preclinical AD. This review highlights advancements in biological fluid and imaging biomarkers that are moving the field towards achieving the goal of a preclinical detection of AD.

Early diagnosis of Alzheimer's disease from elevated olfactory mucosal miR-206 level

MicroRNA-206, which suppresses the expression of brain-derived neurotrophic factor, is known to be elevated in the brains of Alzheimer's disease (AD) patients. We performed intranasal biopsy of the olfactory epithelia of early dementia patients (n = 24) and cognitively healthy controls (n = 9). Patients with significant depression (n = 8) were analyzed separately, as their cognitive impairments were thought to be caused by their depression. Real-time PCR was performed on the biopsied tissues. The relative microRNA-206 level exhibited a 7.8-fold increase (P = 0.004) in the mild cognitive impairment group (CDR 0.5; n = 13) and a 41.5-fold increase (P < 0.001) in the CDR 1 group (n = 11). However, this level was not increased in the depression group, even in those with cognitive decline. Using the optimal cutoff value, the sensitivity/specificity for diagnosing CDR 0.5 and CDR 1 dementia were 87.5%/94.1% and 90.9%/93.3%, respectively. In ROC analysis, the AUCs were 0.942 and 0.976 in the CDR 0.5 and CDR 1 groups, respectively. The olfactory mucosal microRNA-206 level and cognitive assessment scores were significantly correlated in the non-depressed subjects with cognitive impairment. In conclusion, the olfactory mucosal microRNA-206 level can be easily measured, and it can be utilized as an excellent biomarker for the diagnosis of early AD, including mild cognitive impairment.

Cerebrospinal Fluid Biomarkers in Spinocerebellar Ataxia: A Pilot Study

Neurodegenerative diseases, including the spinocerebellar ataxias (SCA), would benefit from the identification of reliable biomarkers that could serve as disease subtype-specific and stage-specific indicators for the development and monitoring of treatments. We analyzed the cerebrospinal fluid (CSF) level of tau, α-synuclein, DJ-1, and glial fibrillary acidic protein (GFAP), proteins previously associated with neurodegenerative processes, in patients with the autosomal dominant SCA1, SCA2, and SCA6, and the sporadic disease multiple system atrophy, cerebellar type (MSA-C), compared with age-matched controls. We estimated disease severity using the Scale for the Assessment and Rating of Ataxia (SARA). Most proteins measured trended higher in disease versus control group yet did not reach statistical significance. We found the levels of tau in both SCA2 and MSA-C patients were significantly higher than control. We found that α-synuclein levels were lower with higher SARA scores in SCA1 and tau levels were higher with greater SARA in MSA-C, although this final correlation did not reach statistical significance after post hoc correction. Additional studies with larger sample sizes are needed to improve the power of these studies and validate the use of CSF biomarkers in SCA and MSA-C.

Network Diffusion Model of Progression Predicts Longitudinal Patterns of Atrophy and Metabolism in Alzheimer's Disease

Alzheimer's disease pathology (AD) originates in the hippocampus and subsequently spreads to temporal, parietal, and prefrontal association cortices in a relatively stereotyped progression. Current evidence attributes this orderly progression to transneuronal transmission of misfolded proteins along the projection pathways of affected neurons. A network diffusion model was recently proposed to mathematically predict disease topography resulting from transneuronal transmission on the brain's connectivity network. Here, we use this model to predict future patterns of regional atrophy and metabolism from baseline regional patterns of 418 subjects. The model accurately predicts end-of-study regional atrophy and metabolism starting from baseline data, with significantly higher correlation strength than given by the baseline statistics directly. The model's rate parameter encapsulates overall atrophy progression rate; group analysis revealed this rate to depend on diagnosis as well as baseline cerebrospinal fluid (CSF) biomarker levels. This work helps validate the model as a prognostic tool for Alzheimer's disease assessment.

Cognitive reserve and Aβ1-42 in mild cognitive impairment (Argentina-Alzheimer's Disease Neuroimaging Initiative)

BACKGROUND

The purpose of this study was to investigate the relationship between cognitive reserve and concentration of Aβ1-42 in the cerebrospinal fluid (CSF) of patients with mild cognitive impairment, those with Alzheimer's disease, and in control subjects.

METHODS

Thirty-three participants from the Argentina-Alzheimer's Disease Neuroimaging Initiative database completed a cognitive battery, the Cognitive Reserve Questionnaire (CRQ), and an Argentinian accentuation reading test (TAP-BA) as a measure of premorbid intelligence, and underwent lumbar puncture for CSF biomarker quantification.

RESULTS

The CRQ significantly correlated with TAP-BA, education, and Aβ1-42. When considering Aβ1-42 levels, significant differences were found in CRQ scores; higher levels of CSF Aβ1-42 were associated with higher CRQ scores.

CONCLUSION

Reduced Aβ1-42 in CSF is considered as evidence of amyloid deposition in the brain. Previous results suggest that individuals with higher education, higher occupational attainment, and participation in leisure activities (cognitive reserve) have a reduced risk of developing Alzheimer's disease. Our results support the notion that enhanced neural activity has a protective role in mild cognitive impairment, as evidenced by higher CSF Aβ1-42 levels in individuals with more cognitive reserve.

Plasma phospholipids identify antecedent memory impairment in older adults

Alzheimer's disease causes a progressive dementia that currently affects over 35 million individuals worldwide and is expected to affect 115 million by 2050 (ref. 1). There are no cures or disease-modifying therapies, and this may be due to our inability to detect the disease before it has progressed to produce evident memory loss and functional decline. Biomarkers of preclinical disease will be critical to the development of disease-modifying or even preventative therapies. Unfortunately, current biomarkers for early disease, including cerebrospinal fluid tau and amyloid-β levels, structural and functional magnetic resonance imaging and the recent use of brain amyloid imaging or inflammaging, are limited because they are either invasive, time-consuming or expensive. Blood-based biomarkers may be a more attractive option, but none can currently detect preclinical Alzheimer's disease with the required sensitivity and specificity. Herein, we describe our lipidomic approach to detecting preclinical Alzheimer's disease in a group of cognitively normal older adults. We discovered and validated a set of ten lipids from peripheral blood that predicted phenoconversion to either amnestic mild cognitive impairment or Alzheimer's disease within a 2-3 year timeframe with over 90% accuracy. This biomarker panel, reflecting cell membrane integrity, may be sensitive to early neurodegeneration of preclinical Alzheimer's disease.

Regional variability of imaging biomarkers in autosomal dominant Alzheimer's disease

Major imaging biomarkers of Alzheimer's disease include amyloid deposition [imaged with [(11)C]Pittsburgh compound B (PiB) PET], altered glucose metabolism (imaged with [(18)F]fluro-deoxyglucose PET), and structural atrophy (imaged by MRI). Recently we published the initial subset of imaging findings for specific regions in a cohort of individuals with autosomal dominant Alzheimer's disease. We now extend this work to include a larger cohort, whole-brain analyses integrating all three imaging modalities, and longitudinal data to examine regional differences in imaging biomarker dynamics. The anatomical distribution of imaging biomarkers is described in relation to estimated years from symptom onset. Autosomal dominant Alzheimer's disease mutation carrier individuals have elevated PiB levels in nearly every cortical region 15 y before the estimated age of onset. Reduced cortical glucose metabolism and cortical thinning in the medial and lateral parietal lobe appeared 10 and 5 y, respectively, before estimated age of onset. Importantly, however, a divergent pattern was observed subcortically. All subcortical gray-matter regions exhibited elevated PiB uptake, but despite this, only the hippocampus showed reduced glucose metabolism. Similarly, atrophy was not observed in the caudate and pallidum despite marked amyloid accumulation. Finally, before hypometabolism, a hypermetabolic phase was identified for some cortical regions, including the precuneus and posterior cingulate. Additional analyses of individuals in which longitudinal data were available suggested that an accelerated appearance of volumetric declines approximately coincides with the onset of the symptomatic phase of the disease.

Relationship of cognitive reserve and cerebrospinal fluid biomarkers to the emergence of clinical symptoms in preclinical Alzheimer's disease

The levels of β-amyloid (Aβ) and phosphorylated tau (p-tau), as measured in cerebrospinal fluid, have been associated with the risk of progressing from normal cognition to onset of clinical symptoms during preclinical Alzheimer's disease. We examined whether cognitive reserve (CR) modifies this association. Cerebrospinal fluid was obtained at baseline from 239 participants (mean age, 57.2 years) who had been followed for up to 17 years with clinical and cognitive assessments (mean follow-up, 8 years). A composite score based on the National Adult Reading Test, vocabulary, and years of education at baseline was used as an index of CR. Cox regression models showed that the increased risk of progressing from normal cognition to symptom onset was associated with lower CR, lower baseline Aβ, and higher baseline p-tau. There was no interaction between CR and Aβ, suggesting that the protective effects of higher CR are equivalent across the observed range of amyloid levels. In contrast, both tau and p-tau interacted with CR, indicating that CR was more protective at lower levels of tau and p-tau.

Amyloid imaging and CSF biomarkers in predicting cognitive impairment up to 7.5 years later

OBJECTIVES

We compared the ability of molecular biomarkers for Alzheimer disease (AD), including amyloid imaging and CSF biomarkers (Aβ42, tau, ptau181, tau/Aβ42, ptau181/Aβ42), to predict time to incident cognitive impairment among cognitively normal adults aged 45 to 88 years and followed for up to 7.5 years.

METHODS

Longitudinal data from Knight Alzheimer's Disease Research Center participants (N = 201) followed for a mean of 3.70 years (SD = 1.46 years) were used. Participants with amyloid imaging and CSF collection within 1 year of a clinical assessment indicating normal cognition were eligible. Cox proportional hazards models tested whether the individual biomarkers were related to time to incident cognitive impairment. "Expanded" models were developed using the biomarkers and participant demographic variables. The predictive values of the models were compared.

RESULTS

Abnormal levels of all biomarkers were associated with faster time to cognitive impairment, and some participants with abnormal biomarker levels remained cognitively normal for up to 6.6 years. No differences in predictive value were found between the individual biomarkers (p > 0.074), nor did we find differences between the expanded biomarker models (p > 0.312). Each expanded model better predicted incident cognitive impairment than the model containing the biomarker alone (p < 0.005).

CONCLUSIONS

Our results indicate that all AD biomarkers studied here predicted incident cognitive impairment, and support the hypothesis that biomarkers signal underlying AD pathology at least several years before the appearance of dementia symptoms.

Cognitive reserve associated with FDG-PET in preclinical Alzheimer disease

OBJECTIVE

To examine the effect of education (a surrogate measure of cognitive reserve) on FDG-PET brain metabolism in elderly cognitively healthy (HC) subjects with preclinical Alzheimer disease (AD).

METHODS

Fifty-two HC subjects (mean age 75 years) with FDG-PET and CSF measurement of Aβ1-42 were included from the prospective Alzheimer's Disease Neuroimaging Initiative biomarker study. HC subjects received a research classification of preclinical AD if CSF Aβ1-42 was <192 pg/mL (Aβ1-42 [+]) vs HC with normal Aβ (Aβ1-42 [-]). In regression analyses, we tested the interaction effect between education and CSF Aβ1-42 status (Aβ1-42 [+] vs Aβ1-42 [-]) on FDG-PET metabolism in regions of interest (ROIs) (posterior cingulate, angular gyrus, inferior/middle temporal gyrus) and the whole brain (voxel-based).

RESULTS

An interaction between education and CSF Aβ1-42 status was observed for FDG-PET in the posterior cingulate (p < 0.001) and angular gyrus ROIs (p = 0.03), but was not significant for the inferior/middle temporal gyrus ROI (p = 0.06), controlled for age, sex, and global cognitive ability (Alzheimer's Disease Assessment Scale-cognitive subscale). The interaction effect was such that higher education was associated with lower FDG-PET in the Aβ1-42 (+) group, but with higher FDG-PET in the Aβ1-42 (-) group. Voxel-based analysis showed that this interaction effect was primarily restricted to temporo-parietal and ventral prefrontal brain areas.

CONCLUSIONS

Higher education was associated with lower FDG-PET in preclinical AD (Aβ1-42 [+]), suggesting that cognitive reserve had a compensatory function to sustain cognitive ability in presence of early AD pathology that alters FDG-PET metabolism.

Clinical, imaging, and pathological heterogeneity of the Alzheimer's disease syndrome

With increasing knowledge of clinical in vivo biomarkers and the pathological intricacies of Alzheimer's disease (AD), nosology is evolving. Harmonized consensus criteria that emphasize prototypic illness continue to develop to achieve diagnostic clarity for treatment decisions and clinical trials. However, it is clear that AD is clinically heterogeneous in presentation and progression, demonstrating variable topographic distributions of atrophy and hypometabolism/hypoperfusion. AD furthermore often keeps company with other conditions that may further nuance clinical expression, such as synucleinopathy exacerbating executive and visuospatial dysfunction and vascular pathologies (particularly small vessel disease that is increasingly ubiquitous with human aging) accentuating frontal-dysexecutive symptomatology. That some of these atypical clinical patterns recur may imply the existence of distinct AD variants. For example, focal temporal lobe dysfunction is associated with a pure amnestic syndrome, very slow decline, with atrophy and neurofibrillary tangles limited largely to the medial temporal region including the entorhinal cortex. Left parietal atrophy and/or hypometabolism/hypoperfusion are associated with language symptoms, younger age of onset, and faster rate of decline - a potential 'language variant' of AD. Conversely, the same pattern but predominantly affecting the right parietal lobe is associated with a similar syndrome but with visuospatial symptoms replacing impaired language function. Finally, the extremely rare frontal variant is associated with executive dysfunction out of keeping with degree of memory decline and may have prominent behavioural symptoms. Genotypic differences may underlie some of these subtypes; for example, absence of apolipoprotein E e4 is often associated with atypicality in younger onset AD. Understanding the mechanisms behind this variability merits further investigation, informed by recent advances in imaging techniques, biomarker assays, and quantitative pathological methods, in conjunction with standardized clinical, functional, neuropsychological and neurobehavioral evaluations. Such an understanding is needed to facilitate 'personalized AD medicine', and eventually allow for clinical trials targeting specific AD subtypes. Although the focus legitimately remains on prototypic illness, continuing efforts to develop disease-modifying therapies should not exclude the rarer AD subtypes and common comorbid presentations, as is currently often the case. Only by treating them as well can we address the full burden of this devastating dementia syndrome.

Clinical, methodological and theoretical issues in the assessment of cognition after anaesthesia and surgery: a review

As people live longer, the burden of cognitive impairment to elderly patients, their families and society becomes increasingly common and important. The loss of independence, a reduction in the quality of life and increased mortality are possible correlates to the mental disintegration. Cognitive dysfunction following major surgery on the elderly is a significant problem which adds to other cognitive impairments caused by neurodegeneration, cerebrovascular impairments and other causes. There are challenges in reviewing the literature because of many methodological concerns. There is no standard definition; the diagnosis is made only by the results of neuropsychological tests which are not standardised for this purpose; test results are analysed by different statistical methods (some of them inappropriate); controls are often absent or poorly matched; and pre-existing mild cognitive impairment, which affects 10 to 20% of people older than 65 years and is similar to the subtle cognitive impairment following surgery, is not sought for and recognised. Reviews of the subject have varied from descriptions such as 'a well recognised and significant problem' to 'a hypothetical phenomenon for which there is no International Statistical Classification of Disease (ICD-9) code, and no Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) code'. This article examines both sides of the spectrum in a detailed review which explains the necessary psychological 'jargon', discusses the methods used and points to areas of future research.

Comparing ROC curves derived from regression models

In constructing predictive models, investigators frequently assess the incremental value of a predictive marker by comparing the ROC curve generated from the predictive model including the new marker with the ROC curve from the model excluding the new marker. Many commentators have noticed empirically that a test of the two ROC areas often produces a non-significant result when a corresponding Wald test from the underlying regression model is significant. A recent article showed using simulations that the widely used ROC area test produces exceptionally conservative test size and extremely low power. In this article, we demonstrate that both the test statistic and its estimated variance are seriously biased when predictions from nested regression models are used as data inputs for the test, and we examine in detail the reasons for these problems. Although it is possible to create a test reference distribution by resampling that removes these biases, Wald or likelihood ratio tests remain the preferred approach for testing the incremental contribution of a new marker.

Blood-based protein biomarkers for diagnosis of Alzheimer disease

OBJECTIVE

To identify plasma biomarkers for the diagnosis of Alzheimer disease (AD).

DESIGN

Baseline plasma screening of 151 multiplexed analytes combined with targeted biomarker and clinical pathology data.

SETTING

General community-based, prospective, longitudinal study of aging.

PARTICIPANTS

A total of 754 healthy individuals serving as controls and 207 participants with AD from the Australian Imaging Biomarker and Lifestyle study (AIBL) cohort with identified biomarkers that were validated in 58 healthy controls and 112 individuals with AD from the Alzheimer Disease Neuroimaging Initiative (ADNI) cohort.

RESULTS

A biomarker panel was identified that included markers significantly increased (cortisol, pancreatic polypeptide, insulinlike growth factor binding protein 2, β(2) microglobulin, vascular cell adhesion molecule 1, carcinoembryonic antigen, matrix metalloprotein 2, CD40, macrophage inflammatory protein 1α, superoxide dismutase, and homocysteine) and decreased (apolipoprotein E, epidermal growth factor receptor, hemoglobin, calcium, zinc, interleukin 17, and albumin) in AD. Cross-validated accuracy measures from the AIBL cohort reached a mean (SD) of 85% (3.0%) for sensitivity and specificity and 93% (3.0) for the area under the receiver operating characteristic curve. A second validation using the ADNI cohort attained accuracy measures of 80% (3.0%) for sensitivity and specificity and 85% (3.0) for area under the receiver operating characteristic curve.

CONCLUSIONS

This study identified a panel of plasma biomarkers that distinguish individuals with AD from cognitively healthy control subjects with high sensitivity and specificity. Cross-validation within the AIBL cohort and further validation within the ADNI cohort provides strong evidence that the identified biomarkers are important for AD diagnosis.

Feed-forward hierarchical model of the ventral visual stream applied to functional brain image classification

Functional brain imaging is a common tool in monitoring the progression of neurodegenerative and neurological disorders. Identifying functional brain imaging derived features that can accurately detect neurological disease is of primary importance to the medical community. Research in computer vision techniques to identify objects in photographs have reported high accuracies in that domain, but their direct applicability to identifying disease in functional imaging is still under investigation in the medical community. In particular, Serre et al. (: In: IEEE Conference on Computer Vision and Pattern Recognition (CVPR-05). pp 994-1000) introduced a biophysically inspired filtering method emulating visual processing in striate cortex which they applied to perform object recognition in photographs. In this work, the model described by Serre et al. [2005] is extended to three-dimensional volumetric images to perform signal detection in functional brain imaging (PET, SPECT). The filter outputs are used to train both neural network and logistic regression classifiers and tested on two distinct datasets: ADNI Alzheimer's disease 2-deoxy-D-glucose (FDG) PET and National Football League players Tc99m HMPAO SPECT. The filtering pipeline is analyzed to identify which steps are most important for classification accuracy. Our results compare favorably with other published classification results and outperform those of a blinded expert human rater, suggesting the utility of this approach.

Short-term clinical outcomes for stages of NIA-AA preclinical Alzheimer disease

OBJECTIVE

Recommendations for the diagnosis of preclinical Alzheimer disease (AD) have been formulated by a workgroup of the National Institute on Aging and Alzheimer's Association. Three stages of preclinical AD were described. Stage 1 is characterized by abnormal levels of β-amyloid. Stage 2 represents abnormal levels of β-amyloid and evidence of brain neurodegeneration. Stage 3 includes the features of stage 2 plus subtle cognitive changes. Stage 0, not explicitly defined in the criteria, represents subjects with normal biomarkers and normal cognition. The ability of the recommended criteria to predict progression to cognitive impairment is the crux of their validity.

METHODS

Using previously developed operational definitions of the 3 stages of preclinical AD, we examined the outcomes of subjects from the Mayo Clinic Study of Aging diagnosed as cognitively normal who underwent brain MRI or [(18)F]fluorodeoxyglucose and Pittsburgh compound B PET, had global cognitive test scores, and were followed for at least 1 year.

RESULTS

Of the 296 initially normal subjects, 31 (10%) progressed to a diagnosis of mild cognitive impairment (MCI) or dementia (27 amnestic MCI, 2 nonamnestic MCI, and 2 non-AD dementias) within 1 year. The proportion of subjects who progressed to MCI or dementia increased with advancing stage (stage 0, 5%; stage 1, 11%; stage 2, 21%; stage 3, 43%; test for trend, p < 0.001).

CONCLUSIONS

Despite the short follow-up period, our operationalization of the new preclinical AD recommendations confirmed that advancing preclinical stage led to higher proportions of subjects who progressed to MCI or dementia.

Cerebrospinal fluid biomarkers, education, brain volume, and future cognition

BACKGROUND

Cross-sectional studies suggest that the cognitive impact of Alzheimer disease pathology varies depending on education and brain size.

OBJECTIVE

To evaluate the combination of cerebrospinal fluid biomarkers of β-amyloid(42) (Aβ(42)), tau, and phosphorylated tau (ptau(181)) with education and normalized whole-brain volume (nWBV) to predict incident cognitive impairment.

DESIGN

Longitudinal cohort study.

SETTING

Charles F. and Joanne Knight Alzheimer's Disease Research Center, Washington University, St Louis, Missouri.

PARTICIPANTS

A convenience sample of 197 individuals 50 years and older with normal cognition (Clinical Dementia Rating of 0) at baseline observed for a mean of 3.3 years.

MAIN OUTCOME MEASURE

Time to Clinical Dementia Rating ≥ 0.5.

RESULTS

Three-factor interactions among the baseline biomarker values, education, and nWBV were found for Cox proportional hazards regression models testing tau (P = .02) and ptau (P = .008). In those with lower tau values, nWBV (hazard ratio [HR], 0.54; 95% confidence interval [CI], 0.31-0.91; 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 in those with higher ptau values (P = .02).

CONCLUSION

In individuals with normal cognition and higher levels of cerebrospinal fluid tau and ptau at baseline, time to incident cognitive impairment is moderated by education and brain volume as predicted by the cognitive/brain reserve hypothesis.

Diagnosis of Alzheimer's disease in Brazil: Supplementary exams

This article presents a review of the recommendations on supplementary exams employed for the clinical diagnosis of Alzheimer’s disease (AD) in Brazil published in 2005. A systematic assessment of the consensus reached in other countries, and of articles on AD diagnosis in Brazil available on the PUBMED and LILACS medical databases, was carried out. Recommended laboratory exams included complete blood count, serum creatinine, thyroid stimulating hormone (TSH), albumin, hepatic enzymes, Vitamin B12, folic acid, calcium, serological reactions for syphilis and serology for HIV in patients aged younger than 60 years with atypical clinical signs or suggestive symptoms. Structural neuroimaging, computed tomography or – preferably – magnetic resonance exams, are indicated for diagnostic investigation of dementia syndrome to rule out secondary etiologies. Functional neuroimaging exams (SPECT and PET), when available, increase diagnostic reliability and assist in the differential diagnosis of other types of dementia. The cerebrospinal fluid exam is indicated in cases of pre-senile onset dementia with atypical clinical presentation or course, for communicant hydrocephaly, and suspected inflammatory, infectious or prion disease of the central nervous system. Routine electroencephalograms aid the differential diagnosis of dementia syndrome with other conditions which impair cognitive functioning. Genotyping of apolipoprotein E or other susceptibility polymorphisms is not recommended for diagnostic purposes or for assessing the risk of developing the disease. Biomarkers related to the molecular alterations in AD are largely limited to use exclusively in research protocols, but when available can contribute to improving the accuracy of diagnosis of the disease.

A window into the heterogeneity of human cerebrospinal fluid Aβ peptides

The initiating event in Alzheimer's disease (AD) is an imbalance in the production and clearance of amyloid beta (Aβ) peptides leading to the formation of neurotoxic brain Aβ assemblies. Cerebrospinal Fluid (CSF), which is a continuum of the brain, is an obvious source of markers reflecting central neuropathologic features of brain diseases. In this review, we provide an overview and update on our current understanding of the pathobiology of human CSF Aβ peptides. Specifically, we focused our attention on the heterogeneity of the CSF Aβ world discussing (1) basic research studies and what has been translated to clinical practice, (2) monomers and other soluble circulating Aβ assemblies, and (3) communication modes for Aβ peptides and their microenvironment targets. Finally, we suggest that Aβ peptides as well as other key signals in the central nervous system (CNS), mainly involved in learning and hence plasticity, may have a double-edged sword action on neuron survival and function.

Can Functional Magnetic Resonance Imaging Improve Success Rates in CNS Drug Discovery?

INTRODUCTION: The bar for developing new treatments for CNS disease is getting progressively higher and fewer novel mechanisms are being discovered, validated and developed. The high costs of drug discovery necessitate early decisions to ensure the best molecules and hypotheses are tested in expensive late stage clinical trials. The discovery of brain imaging biomarkers that can bridge preclinical to clinical CNS drug discovery and provide a 'language of translation' affords the opportunity to improve the objectivity of decision-making. AREAS COVERED: This review discusses the benefits, challenges and potential issues of using a science based biomarker strategy to change the paradigm of CNS drug development and increase success rates in the discovery of new medicines. The authors have summarized PubMed and Google Scholar based publication searches to identify recent advances in functional, structural and chemical brain imaging and have discussed how these techniques may be useful in defining CNS disease state and drug effects during drug development. EXPERT OPINION: The use of novel brain imaging biomarkers holds the bold promise of making neuroscience drug discovery smarter by increasing the objectivity of decision making thereby improving the probability of success of identifying useful drugs to treat CNS diseases. Functional imaging holds the promise to: (1) define pharmacodynamic markers as an index of target engagement (2) improve translational medicine paradigms to predict efficacy; (3) evaluate CNS efficacy and safety based on brain activation; (4) determine brain activity drug dose-response relationships and (5) provide an objective evaluation of symptom response and disease modification.