Differential CSF biomarker levels in APOE-epsilon4-positive and -negative patients with memory impairment

β-amyloid: The known unknowns

Alzheimer's disease (AD) stands out as a major disease without any form of preventative or disease modifying therapy. This is not for lack of trying. 33 phase 3 clinical trials of drugs targeting amyloid beta (Aβ) have failed to slow cognitive decline in AD. The field is at a cross-roads about whether to continue anti-Aβ therapy or more actively pursue alternative targets. With the burden of this disease to patients, families, and healthcare budgets growing yearly, the need for disease modifying AD therapies has become one of the highest priorities in all of medicine. While pathology, genetic and biochemical data offer a popular narrative for the causative role of Aβ, there are alternative explanations, and dissenting findings that, now more than ever, warrant thorough reanalysis. This review questions the major assumptions about Aβ on which therapies for AD were premised, and invites renewed interrogation into AD pathogenesis.

Impact of cerebrospinal fluid matrix on the detection of Alzheimer's disease with Aβ42 and influence of disease on the total-Aβ42/Aβ40 ratio

The 42-amino acid fragment of amyloid β (Aβ1-42) in cerebrospinal fluid has continued to be important for detecting cerebral β-amyloidosis in Alzheimer's disease (AD). However, there are impediments to our ability to fully understand this measurement, including matrix interference and changes linked to apolipoprotein E (APOE) ε4 genotype. This study investigated matrix interference as a contributing factor for detecting AD in APOE ε4-negative patients by comparing total extractable Aβ1-42 to free Aβ1-42. It also examined the ratio of total Aβ1-42 to Aβ1-40, since changes relative to other Aβ peptides may provide a measurement of cerebral β-amyloidosis that is neutral to changes in APP metabolism. Total Aβ1-42 lost the diagnostic power for detecting AD, confirming a role for matrix in the diagnostic. However, when total Aβ1-42/Aβ1-40 was examined, the separation between groups was reestablished. This result was confirmed in a second sample set of unknown APOE status. These results confirmed that matrix interference in some cerebrospinal fluid samples appears to contribute to identifying AD patients and this can be compensated by using a total extracted Aβ1-42/Aβ1-40 ratio when matrix interference is small. It may be preferable to employ a total Aβ1-42/Aβ1-40 measurement, since this could minimize variability because of matrix and compensate for across patient differences. Aβ1-42 measurement in CSF has provided an important tool for early detection of AD. However, it appears that most assays measure a free fraction of Aβ1-42. This study examined total extracted Aβ1-42, since this would provide a more accurate assessment of Aβ1-42 in AD CSF. Total Aβ1-42 measurements alone were not good for detecting AD but total Aβ1-42/Aβ1-40 performed well.

Plasma and cerebrospinal fluid amyloid beta for the diagnosis of Alzheimer's disease dementia and other dementias in people with mild cognitive impairment (MCI)

BACKGROUND

According to the latest revised National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association (now known as the Alzheimer's Association) (NINCDS-ADRDA) diagnostic criteria for Alzheimer's disease dementia of the National Institute on Aging and Alzheimer Association, the confidence in diagnosing mild cognitive impairment (MCI) due to Alzheimer's disease dementia is raised with the application of biomarkers based on measures in the cerebrospinal fluid (CSF) or imaging. These tests, added to core clinical criteria, might increase the sensitivity or specificity of a testing strategy. However, the accuracy of biomarkers in the diagnosis of Alzheimer's disease dementia and other dementias has not yet been systematically evaluated. A formal systematic evaluation of sensitivity, specificity, and other properties of plasma and CSF amyloid beta (Aß) biomarkers was performed.

OBJECTIVES

To determine the accuracy of plasma and CSF Aß levels for detecting those patients with MCI who would convert to Alzheimer's disease dementia or other forms of dementia over time.

SEARCH METHODS

The most recent search for this review was performed on 3 December 2012. We searched MEDLINE (OvidSP), EMBASE (OvidSP), BIOSIS Previews (ISI Web of Knowledge), Web of Science and Conference Proceedings (ISI Web of Knowledge), PsycINFO (OvidSP), and LILACS (BIREME). We also requested a search of the Cochrane Register of Diagnostic Test Accuracy Studies (managed by the Cochrane Renal Group).No language or date restrictions were applied to the electronic searches and methodological filters were not used so as to maximise sensitivity.

SELECTION CRITERIA

We selected those studies that had prospectively well defined cohorts with any accepted definition of cognitive decline, but no dementia, with baseline CSF or plasma Aß levels, or both, documented at or around the time the above diagnoses were made. We also included studies which looked at data from those cohorts retrospectively, and which contained sufficient data to construct two by two tables expressing plasma and CSF Aß biomarker results by disease status. Moreover, studies were only selected if they applied a reference standard for Alzheimer's dementia diagnosis, for example the NINCDS-ADRDA or Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) criteria.

DATA COLLECTION AND ANALYSIS

We screened all titles generated by the electronic database searches. Two review authors independently assessed the abstracts of all potentially relevant studies. We assessed the identified full papers for eligibility and extracted data to create standard two by two tables. Two independent assessors performed quality assessment using the QUADAS-2 tool. Where data allowed, we derived estimates of sensitivity at fixed values of specificity from the model we fitted to produce the summary receiver operating characteristic (ROC) curve.

MAIN RESULTS

Alzheimer's disease dementia was evaluated in 14 studies using CSF Aß42. Of the 1349 participants included in the meta-analysis, 436 developed Alzheimer's dementia. Individual study estimates of sensitivity were between 36% and 100% while the specificities were between 29% and 91%. Because of the variation in assay thresholds, we did not estimate summary sensitivity and specificity. However, we derived estimates of sensitivity at fixed values of specificity from the model we fitted to produce the summary ROC curve. At the median specificity of 64%, the sensitivity was 81% (95% CI 72 to 87). This equated to a positive likelihood ratio (LR+) of 2.22 (95% CI 2.00 to 2.47) and a negative likelihood ratio (LR-) of 0.31 (95% CI 0.21 to 0.48).The accuracy of CSF Aß42 for all forms of dementia was evaluated in four studies. Of the 464 participants examined, 188 developed a form of dementia (Alzheimer's disease and other forms of dementia).The thresholds used were between 209 mg/ml and 512 ng/ml. The sensitivities were between 56% and 75% while the specificities were between 47% and 76%. At the median specificity of 75%, the sensitivity was estimated to be 63% (95% CI 22 to 91) from the meta-analytic model. This equated to a LR+ of 2.51 (95% CI 1.30 to 4.86) and a LR- of 0.50 (95% CI 0.16 to 1.51).The accuracy of CSF Aß42 for non-Alzheimer's disease dementia was evaluated in three studies. Of the 385 participants examined, 61 developed non-Alzheimer's disease dementia. Since there were very few studies and considerable variation between studies, the results were not meta-analysed. The sensitivities were between 8% and 63% while the specificities were between 35% and 67%.Only one study examined the accuracy of plasma Aß42 and the plasma Aß42/Aß40 ratio for Alzheimer's disease dementia. The sensitivity of 86% (95% CI 81 to 90) was the same for both tests while the specificities were 50% (95% CI 44 to 55) and 70% (95% CI 64 to 75) for plasma Aß42 and the plasma Aß42/Aß40 ratio respectively. Of the 565 participants examined, 245 developed Alzheimer's dementia and 87 non-Alzheimer's disease dementia.There was substantial heterogeneity between studies. The accuracy of Aß42 for the diagnosis of Alzheimer's disease dementia did not differ significantly (P = 0.8) between studies that pre-specified the threshold for determining test positivity (n = 6) and those that only determined the threshold at follow-up (n = 8). One study excluded a sample of MCI non-Alzheimer's disease dementia converters from their analysis. In sensitivity analyses, the exclusion of this study had no impact on our findings. The exclusion of eight studies (950 patients) that were considered at high (n = 3) or unclear (n = 5) risk of bias for the patient selection domain also made no difference to our findings.

AUTHORS' CONCLUSIONS

The proposed diagnostic criteria for prodromal dementia and MCI due to Alzheimer's disease, although still being debated, would be fulfilled where there is both core clinical and cognitive criteria and a single biomarker abnormality. From our review, the measure of abnormally low CSF Aß levels has very little diagnostic benefit with likelihood ratios suggesting only marginal clinical utility. The quality of reports was also poor, and thresholds and length of follow-up were inconsistent. We conclude that when applied to a population of patients with MCI, CSF Aß levels cannot be recommended as an accurate test for Alzheimer's disease.

Vitamin D in relation to cognitive impairment, cerebrospinal fluid biomarkers, and brain volumes

BACKGROUND

Low vitamin D status is associated with poorer cognitive function in older adults, but little is known about the potential impact on cerebrospinal fluid (CSF) biomarkers and brain volumes. The objective of this study was to examine the relations between plasma 25-hydroxyvitamin D (25(OH)D) and cognitive impairment, CSF biomarkers of Alzheimer's disease (AD), and structural brain tissue volumes.

METHODS

A total of 75 patients (29 with subjective cognitive impairment, 28 with mild cognitive impairment, 18 with AD) referred to the Memory Clinic at Karolinska University Hospital, Huddinge, Sweden were recruited. Plasma 25(OH)D, CSF levels of amyloid β (Aβ(1-42)), total-tau, and phosphorylated tau, and brain tissue volumes have been measured.

RESULTS

After adjustment for several potential confounders, the odds ratios (95% confidence interval) for cognitive impairment were as follows: 0.969 (0.948-0.990) per increase of 1 nmol/L of 25(OH)D and 4.19 (1.30-13.52) for 24(OH)D values less than 50 nmol/L compared with values greater than or equal to 50 nmol/L. Adjusting for CSF Aβ(1-42) attenuated the 25(OH)D-cognition link. In a multiple linear regression analysis, higher 25(OH)D levels were related to higher concentrations of CSF Aβ(1-42) and greater brain volumes (eg, white matter, structures belonging to medial temporal lobe). The associations between 25(OH)D and tau variables were not significant.

CONCLUSIONS

This study suggests that vitamin D may be associated with cognitive status, CSF Aβ(1-42) levels, and brain tissue volumes.

CSF T-Tau/Aβ42 predicts white matter microstructure in healthy adults at risk for Alzheimer's disease

Cerebrospinal fluid (CSF) biomarkers T-Tau and Aβ(42) are linked with Alzheimer's disease (AD), yet little is known about the relationship between CSF biomarkers and structural brain alteration in healthy adults. In this study we examined the extent to which AD biomarkers measured in CSF predict brain microstructure indexed by diffusion tensor imaging (DTI) and volume indexed by T1-weighted imaging. Forty-three middle-aged adults with parental family history of AD received baseline lumbar puncture and MRI approximately 3.5 years later. Voxel-wise image analysis methods were used to test whether baseline CSF Aβ(42), total tau (T-Tau), phosphorylated tau (P-Tau) and neurofilament light protein predicted brain microstructure as indexed by DTI and gray matter volume indexed by T1-weighted imaging. T-Tau and T-Tau/Aβ(42) were widely correlated with indices of brain microstructure (mean, axial, and radial diffusivity), notably in white matter regions adjacent to gray matter structures affected in the earliest stages of AD. None of the CSF biomarkers were related to gray matter volume. Elevated P-Tau and P-Tau/Aβ(42) levels were associated with lower recognition performance on the Rey Auditory Verbal Learning Test. Overall, the results suggest that CSF biomarkers are related to brain microstructure in healthy adults with elevated risk of developing AD. Furthermore, the results clearly suggest that early pathological changes in AD can be detected with DTI and occur not only in cortex, but also in white matter.

Relationship between CSF biomarkers of Alzheimer's disease and rates of regional cortical thinning in ADNI data

Previously it was reported that Alzheimer's disease (AD) patients have reduced amyloid (Aβ 1-42) and elevated total tau (t-tau) and phosphorylated tau (p-tau 181p) in the cerebro-spinal fluid (CSF), suggesting that these same measures could be used to detect early AD pathology in healthy elderly (CN) and mild cognitive impairment (MCI). In this study, we tested the hypothesis that there would be an association among rates of regional brain atrophy, the CSF biomarkers Aβ 1-42, t-tau, and p-tau 181p and ApoE ε4 status, and that the pattern of this association would be diagnosis specific. Our findings primarily showed that lower CSF Aβ 1-42 and higher tau concentrations were associated with increased rates of regional brain tissue loss and the patterns varied across the clinical groups. Taken together, these findings demonstrate that CSF biomarker concentrations are associated with the characteristic patterns of structural brain changes in CN and MCI that resemble to a large extent the pathology seen in AD. Therefore, the finding of faster progression of brain atrophy in the presence of lower Aβ 1-42 levels and higher p-tau levels supports the hypothesis that CSF Aβ 1-42 and tau are measures of early AD pathology. Moreover, the relationship among CSF biomarkers, ApoE ε4 status, and brain atrophy rates are regionally varying, supporting the view that the genetic predisposition of the brain to amyloid and tau mediated pathology is regional and disease stage specific.

Measurement of Aβ1-42 in cerebrospinal fluid is influenced by matrix effects

Aβ1-42 measurement in CSF is an important biochemical marker for Alzheimer disease (AD). However, our understanding of why this biomarker is predictive and why it is often difficult to measure in a reproducible fashion is still lacking. To study these questions, the concentration of Aβ1-42 in CSF was compared before and after denaturation with 6M guanidine and reverse-phase HPLC. Measurement of the Aβ1-42 after denaturation and reverse-phase HPLC demonstrated that considerably more Aβ1-42 was present in CSF than revealed when assaying non-denatured CSF. A comparison of Aβ1-42 concentrations before and after HPLC in AD CSF with that in normal controls suggested that matrix interference may affect the differentiation between the diagnostic groups. A similar effect was observed with dilutions of crude CSF. Together, these results suggested that at least part of the mechanism by which low Aβ1-42 concentrations in CSF function as a biomarker of AD is related to matrix components which preferentially hide a portion of the Aβ1-42 from detection in AD CSF. In contrast, we show that the association of the APOEε4 allele with lower Aβ1-42 concentrations in CSF is preserved even after denaturation and HPLC. A similar relationship between the presence of the APOEε4 allele and lower concentrations of Aβ1-40 was also apparent, thereby generating similar ratios of Aβ1-42/ Aβ1-40 across the APOE genotypes. The results from the present study suggested that Aβ1-42 in CSF functions as a biomarker of AD in tandem with other CSF matrix components that are increased in AD CSF. Further studies are needed to identify which matrix factors (e.g. binding of Aβ to proteins) underlie the increased detection of Aβ1-42 concentrations after denaturation and HPLC. The data also suggested that denaturation and HPLC of CSF may be a useful approach for studies using Aβ1-42 as a pharmacodynamic marker or in other paradigms where measurement of total non-covalently bound Aβ1-42 is required.

Impact of early intervention and disease modification in patients with predementia Alzheimer's disease: a Markov model simulation

Background:

Early screenings involving biomarkers and use of potential disease-modifying therapies (DMTs) may have significant humanistic implications for treatment strategies in Alzheimer’s disease.

Methods:

Markov models simulated transitions of patient cohorts beginning in predementia, a hypothetical early stage of Alzheimer’s disease marked by objective cognitive impairment/memory complaints without functional impairment, and followed for 10 years. Hypothetical cohorts of 10,000 patients included those who were treated with standard of care (donepezil) upon reaching mild–moderate Alzheimer’s disease, a DMT in predementia, and a DMT in mild-moderate Alzheimer’s disease. Transition probabilities were based on data from the Alzheimer’s Disease Neuroimaging Initiative and published clinical data, and estimated for the hypothetical DMT. In each disease stage (predementia, mild, moderate, or severe), time was computed and costs were estimated using literature review and published data, and published data provided mortality rates. The impact of screening was evaluated using positive predictive value (patients identified as predementia truly at risk for transition to dementia).

Results:

Earlier treatment yielded modest gains in total life-years; however, the distribution was skewed towards milder disease. Assuming a 25% reduction in the annual risk of progression, treating predementia patients with DMT increased life-years in predementia to mild states on average from 3.2 to 4.2, while life-years spent in moderate-to-severe Alzheimer’s disease decreased from 2.6 to 2.2. Average time in the community increased from 4.4 to 5.4 years, while time in long-term care declined from 1.3 to 0.9 years. This impact grows as the advantage of the novel agent increases. Screening accuracy had significant implications for cost-effectiveness.

Conclusion:

If screening can accurately identify predementia patients at risk for progression, earlier treatment with DMTs has the potential benefit to patients of prolonging time in milder disease, reducing time spent with more severe disease, increasing time in the community, and reducing time in long-term care.

Epidemiology of Alzheimer disease

The global prevalence of dementia is estimated to be as high as 24 million, and is predicted to double every 20 years through to 2040, leading to a costly burden of disease. Alzheimer disease (AD) is the leading cause of dementia and is characterized by a progressive decline in cognitive function, which typically begins with deterioration in memory. Before death, individuals with this disorder have usually become dependent on caregivers. The neuropathological hallmarks of the AD brain are diffuse and neuritic extracellular amyloid plaques-which are frequently surrounded by dystrophic neurites-and intracellular neurofibrillary tangles. These hallmark pathologies are often accompanied by the presence of reactive microgliosis and the loss of neurons, white matter and synapses. The etiological mechanisms underlying the neuropathological changes in AD remain unclear, but are probably affected by both environmental and genetic factors. Here, we provide an overview of the criteria used in the diagnosis of AD, highlighting how this disease is related to, but distinct from, normal aging. We also summarize current information relating to AD prevalence, incidence and risk factors, and review the biomarkers that may be used for risk assessment and in diagnosis.

Structural brain changes in aging: courses, causes and cognitive consequences

The structure of the brain is constantly changing from birth throughout the lifetime, meaning that normal aging, free from dementia, is associated with structural brain changes. This paper reviews recent evidence from magnetic resonance imaging (MRI) studies about age-related changes in the brain. The main conclusions are that (1) the brain shrinks in volume and the ventricular system expands in healthy aging. However, the pattern of changes is highly heterogeneous, with the largest changes seen in the frontal and temporal cortex, and in the putamen, thalamus, and accumbens. With modern approaches to analysis of MRI data, changes in cortical thickness and subcortical volume can be tracked over periods as short as one year, with annual reductions of between 0.5% and 1.0% in most brain areas. (2) The volumetric brain reductions in healthy aging are likely only to a minor extent related to neuronal loss. Rather, shrinkage of neurons, reductions of synaptic spines, and lower numbers of synapses probably account for the reductions in grey matter. In addition, the length of myelinated axons is greatly reduced, up to almost 50%. (3) Reductions in specific cognitive abilities--for instance processing speed, executive functions, and episodic memory--are seen in healthy aging. Such reductions are to a substantial degree mediated by neuroanatomical changes, meaning that between 25% and 100% of the differences between young and old participants in selected cognitive functions can be explained by group differences in structural brain characteristics.

Relations between brain tissue loss, CSF biomarkers, and the ApoE genetic profile: a longitudinal MRI study

Previously it was reported that Alzheimer's disease (AD) patients have reduced beta amyloid (Abeta(1-42)) and elevated total tau (t-tau) and phosphorylated tau (p-tau(181p)) in the cerebrospinal fluid (CSF), suggesting that these same measures could be used to detect early AD pathology in healthy elderly individuals and those with mild cognitive impairment (MCI). In this study, we tested the hypothesis that there would be an association among rates of regional brain atrophy, the CSF biomarkers Abeta(1-42), t-tau, and p-tau(181p) and apolipoprotein E (ApoE) epsilon4 status, and that the pattern of this association would be diagnosis-specific. Our findings primarily showed that lower CSF Abeta(1-42) and higher tau concentrations were associated with increased rates of regional brain tissue loss and the patterns varied across the clinical groups. Taken together, these findings demonstrate that CSF biomarker concentrations are associated with the characteristic patterns of structural brain changes in healthy elderly and mild cognitive impairment subjects that resemble to a large extent the pathology seen in AD. Therefore, the finding of faster progression of brain atrophy in the presence of lower Abeta(1-42) levels and higher tau levels supports the hypothesis that CSF Abeta(1-42) and tau are measures of early AD pathology. Moreover, the relationship among CSF biomarkers, ApoE epsilon4 status, and brain atrophy rates are regionally varying, supporting the view that the genetic predisposition of the brain to beta amyloid and tau mediated pathology is regional and disease stage specific.

Brain atrophy in healthy aging is related to CSF levels of Aβ1-42

Reduced levels of beta-amyloid(1-42) (Abeta1-42) and increased levels of tau proteins in the cerebrospinal fluid (CSF) are found in Alzheimer's disease (AD), likely reflecting Abeta deposition in plaques and neuronal and axonal damage. It is not known whether these biomarkers are associated with brain atrophy also in healthy aging. We tested the relationship between CSF levels of Abeta1-42 and tau (total tau and tau phosphorylated at threonine 181) proteins and 1-year brain atrophy in 71 cognitively normal elderly individuals. Results showed that under a certain threshold value, levels of Abeta1-42 correlated highly with 1-year change in a wide range of brain areas. The strongest relationships were not found in the regions most vulnerable early in AD. Above the threshold level, Abeta1-42 was not related to brain changes, but significant volume reductions as well as ventricular expansion were still seen. It is concluded that Abeta1-42 correlates with brain atrophy and ventricular expansion in a subgroup of cognitively normal elderly individuals but that reductions independent of CSF levels of Abeta1-42 is common. Further research and follow-up examinations over several years are needed to test whether degenerative pathology will eventually develop in the group of cognitively normal elderly individuals with low levels of Abeta1-42.

Biomarkers of HIV-1-associated neurocognitive disorders: challenges of proteomic approaches

HIV-1 enters the brain shortly after infection, which may lead to neurological complications and in the most severe cases to encephalitis, dementia and death. The introduction of antiretroviral therapy reduced the incidence of the most severe conditions, nevertheless, approximately half of those infected with this virus will suffer to various degrees from HIV-1-associated neurocognitive disorders. Despite many years of research, there are no biomarkers that can objectively measure and, more importantly, predict the onset and the tempo of HIV-1-associated neurocognitive disorders. Here we review biomarker candidates of neurocognitive impairment due to HIV infection of the brain that have been proposed during the last two decades, and discuss perspectives and limitations of proteomic approaches in the search for new, more sensitive and specific biomarkers.

Challenges in phenotype definition in the whole-genome era: multivariate models of memory and intelligence

Refining phenotypes for the study of neuropsychiatric disorders is of paramount importance in neuroscience. Poor phenotype definition provides the greatest obstacle for making progress in disorders like schizophrenia, bipolar disorder, Attention Deficit/Hyperactivity Disorder (ADHD), and autism. Using freely available informatics tools developed by the Consortium for Neuropsychiatric Phenomics (CNP), we provide a framework for defining and refining latent constructs used in neuroscience research and then apply this strategy to review known genetic contributions to memory and intelligence in healthy individuals. This approach can help us begin to build multi-level phenotype models that express the interactions between constructs necessary to understand complex neuropsychiatric diseases. These results are available online through the http://www.phenowiki.org database. Further work needs to be done in order to provide consensus-building applications for the broadly defined constructs used in neuroscience research.

Increasing CSF phospho-tau levels during cognitive decline and progression to dementia

BACKGROUND

Little is known about longitudinal changes of cerebrospinal fluid (CSF) biomarkers during cognitive decline in neurodegenerative disease progression.

OBJECTIVE

To investigate longitudinal changes in CSF biomarkers--total-tau (T-tau), phospho-tau (P-tau) and beta-amyloid (Abeta42)--during cognitive decline.

METHODS

Forty memory clinic patients (47.5% females), aged 61.3+/-7.6 (S.D.) years, non-demented at baseline, underwent lumbar puncture and neuropsychological testing at two occasions. Baseline mean MMSE-score was 28.3+/-1.8. Patients were divided into three groups based on baseline memory functioning; severely impaired (SIM), moderately impaired (MIM) and no impairment (NIM).

RESULTS

There was a significant increase in P-tau in the SIM-group during follow-up, while P-tau in MIM and NIM did not change. Eighty-three percent of the SIM-patients converted to dementia (80% AD), while most MIM- and NIM-patients remained non-demented. T-tau- and Abeta42-levels did not change in any of the memory groups during follow-up.

CONCLUSION

Increasing P-tau levels during cognitive decline and conversion to dementia suggest that P-tau may be useful as a longitudinal marker of the neurodegenerative process.

Morphometric changes in the episodic memory network and tau pathologic features correlate with memory performance in patients with mild cognitive impairment

BACKGROUND AND PURPOSE

Mild cognitive impairment (MCI) may affect several cognitive domains, including attention and reasoning, but is often first characterized by memory deficits. The purpose of this study was to ask these 2 questions: 1) Can levels of CSF tau proteins and amyloid beta 42 peptide explain thinning of the cerebral cortex in patients with MCI? 2) How are brain morphometry, CSF biomarkers, and apolipoprotein E (APOE) allelic variation related to episodic memory function in MCI?

MATERIALS AND METHODS

Hippocampal volume and cortical thickness were estimated by MR imaging and compared for patients with MCI (n = 18) and healthy controls (n = 18). In addition, regions of interest (ROIs) were selected in areas where the MCI group had atrophy and which overlapped with the episodic memory network (temporal, entorhinal, inferior parietal, precuneus/posterior cingulate, and frontal). Relationships among morphometry, CSF biomarkers, APOE, and memory were tested. The analyses were repeated with an independent sample of patients with MCI (n = 19).

RESULTS

Patients with MCI and pathologic CSF values had hippocampal atrophy. However, both patients with pathologic and patients with nonpathologic CSF had a thinner cortex outside the hippocampal area. CSF pathology was related to hippocampal volume, whereas relationships with cortical thickness were found mainly in one of the samples. Morphometry correlated robustly with memory performance across MCI samples, whereas less stable results were found for tau protein.

CONCLUSION

The differences in hippocampal volume between the MCI and the healthy control groups were only found in patients with pathologic CSF biomarkers, whereas differences in cortical thickness were also found for patients without such pathologic features. Morphometry in areas in the episodic memory network was robustly correlated with memory performance. It is speculated that atrophy in these areas may be associated with the memory problems seen in MCI.