Altered resting state networks in mild cognitive impairment and mild Alzheimer's disease: an fMRI study

Activity and reactivity of the default mode network in the brain was studied using functional magnetic resonance imaging (fMRI) in 28 nondemented individuals with mild cognitive impairment (MCI), 18 patients with mild Alzheimer's disease (AD), and 41 healthy elderly controls (HC). The default mode network was interrogated by means of decreases in brain activity, termed deactivations, during a visual encoding task and during a nonspatial working memory task. Deactivation was found in the default mode network involving the anterior frontal, precuneus, and posterior cingulate cortex. MCI patients showed less deactivation than HC, but more than AD. The most pronounced differences between MCI, HC, and AD occurred in the very early phase of deactivation, reflecting the reactivity and adaptation of the network. The default mode network response in the anterior frontal cortex significantly distinguished MCI from both HC (in the medial frontal) and AD (in the anterior cingulate cortex). The response in the precuneus could only distinguish between patients and HC, not between MCI and AD. These findings may be consistent with the notion that MCI is a transitional state between healthy aging and dementia and with the proposed early changes in MCI in the posterior cingulate cortex and precuneus. These findings suggest that altered activity in the default mode network may act as an early marker for AD pathology.     

Brain structure and allelic associations in Alzheimer's disease

Background

Alzheimer's disease (AD), the most prevalent form of dementia, affects 6.5 million Americans and over 50 million people globally. Clinical, genetic, and phenotypic studies of dementia provide some insights of the observed progressive neurodegenerative processes, however, the mechanisms underlying AD onset remain enigmatic.

Aims

This paper examines late-onset dementia-related cognitive impairment utilizing neuroimaging-genetics biomarker associations.

Materials and Methods

The participants, ages 65–85, included 266 healthy controls (HC), 572 volunteers with mild cognitive impairment (MCI), and 188 Alzheimer's disease (AD) patients. Genotype dosage data for AD-associated single nucleotide polymorphisms (SNPs) were extracted from the imputed ADNI genetics archive using sample-major additive coding. Such 29 SNPs were selected, representing a subset of independent SNPs reported to be highly associated with AD in a recent AD meta-GWAS study by Jansen and colleagues.

Results

We identified the significant correlations between the 29 genomic markers (GMs) and the 200 neuroimaging markers (NIMs). The odds ratios and relative risks for AD and MCI (relative to HC) were predicted using multinomial linear models.

Discussion

In the HC and MCI cohorts, mainly cortical thickness measures were associated with GMs, whereas the AD cohort exhibited different GM-NIM relations. Network patterns within the HC and AD groups were distinct in cortical thickness, volume, and proportion of White to Gray Matter (pct), but not in the MCI cohort. Multinomial linear models of clinical diagnosis showed precisely the specific NIMs and GMs that were most impactful in discriminating between AD and HC, and between MCI and HC.

Conclusion

This study suggests that advanced analytics provide mechanisms for exploring the interrelations between morphometric indicators and GMs. The findings may facilitate further clinical investigations of phenotypic associations that support deep systematic understanding of AD pathogenesis.     

Mild cognitive impairment in Parkinson's disease versus Alzheimer's disease

IntroductionNo known studies have compared longitudinal characteristics between individuals with incident mild cognitive impairment due to Parkinson's disease (PD-MCI) versus Alzheimer's Disease (AD-MCI).MethodsWe used longitudinal data from the National Alzheimer's Coordinating Center's Uniform Data Set to compare 41 PD-MCI and 191 AD-MCI participants according to their demographics, presence of ≥1 APOE e4 allele, and baseline and change over time in clinical characteristics, neuropsychological test scores, and Clinical Dementia Rating sum of boxes (CDR-SB). Multivariable linear regression models with generalized estimating equations were used to account for clustered data and to test for baseline and longitudinal differences in neuropsychological test scores.ResultsPD-MCI and AD-MCI participants differed by many demographic and clinical characteristics. Significantly fewer PD-MCI participants developed dementia over one year. Compared to AD-MCI participants, PD-MCI participants performed better at baseline and over time on a global measure of cognition (Mini Mental State Exam), memory measures (immediate and delayed Logical Memory), and a language measure (Boston Naming Test), and additionally performed better over time on an attention measure (Digit Span Forward), a language measure (Vegetable List), a processing speed measure (Digit Symbol), and an overall measure of memory and functional impairment (CDR-SB).ConclusionOur study provides further evidence that PD-MCI is clinically distinct from AD-MCI and requires different tools for diagnosis and monitoring clinical progression. More importantly, this study suggests that PD-MCI takes longer to convert into dementia than AD-MCI, findings that require replication by other studies.     

Subjective memory complaints in Chinese subjects with mild cognitive impairment and early Alzheimer's disease

BACKGROUND: Mild cognitive impairment (MCI) represents a transitional state between normal aging and dementia. However, there is inconsistent opinion as to the validity of subjective memory complaints as a criterion for diagnosis. OBJECTIVE: This study aimed to examine the potential significance of applying a short memory questionnaire in the assessment of Chinese subjects with MCI and early dementia. METHODS: Three hundred and six ambulatory Chinese subjects were recruited. Each participant completed a short memory questionnaire. They were also assessed with the Chinese versions of the mini-mental state examination (CMMSE), Alzheimer's disease assessment scale-cognitive subscale (ADAS-Cog), category verbal fluency test (CVFT) and span tests. Severity of cognitive impairment was evaluated using the Clinical Dementia Rating (CDR); subjects with CDR 0.5 were further classified into MCI not demented (MCIND) and MCI possible incipient dementia (MCIID) depending on the subscale scores of CDR. RESULTS: An increasing frequency of memory complaints with increasing CDR was observed (Kruskal Wallis test, chi square = 21.29, df 3, p < 0.001). With a cutoff of 3 or more memory complaints, the memory questionnaire demonstrated a sensitivity of 65.3% and 70.4% in identifying subjects with incipient and early dementia respectively. Significant associations between memory complaints and most cognitive test performance were found (Spearman's correlations, p < 0.01). Logistic regression analysis revealed that educational level, the memory questionnaire, ADAS-Cog total and delayed recall scores were significant predictors of MCIID status. CONCLUSIONS: The findings suggested that a short memory questionnaire is useful in the screening of MCI, particularly in subjects who already present with subtle functioning disturbances. Subjective memory complaints were significant correlated with objective performance of memory functions, reflecting the usefulness of memory complaints in the assessment of MCI.     

Making sense of self in Alzheimer's disease: reflective function and memory

Objective: The current investigation examined the relationship between cognitive impairment and sense of self in Alzheimer's disease (AD).

Method: Forty-nine participants with dementia associated with AD were recruited through memory clinics in Victoria, Australia. The 26 participants of the healthy control sample were recruited from a retirement village. Self was measured via the Reflective Self-Function Scale – a theory of mind indicator that provides personal and social self-reflection scores. Cognitive assessment included measures of new learning, executive function, and speed of information processing.

Results: A reduction in sense of self in mild AD was demonstrated in both personal and social domains, as compared to healthy adults of a similar age. With a focus on specific cognitive impairment relationships, new learning was found to predict personal self-reflection, whereas speed of information processing predicted social self-reflection capacity.

Conclusion: Findings suggest that deficits in new learning ability contribute to a reduced ability of people with early AD to understand their mental world and interpret thoughts, feelings, and beliefs about themselves. This impaired capacity to self-reflect will be intrusive in daily activities that require monitoring of current self-performance. Furthermore, with reduced speed of information processing found to impact on ability to reflect on social relations, individuals with AD are placed at risk of reduced ability to understand their social world, including communicating and interacting with others. Notwithstanding the overall group findings, individual variability was evident which reinforces the need for person-centred care in dementia.     

Coalition Against Major Diseases/European Medicines Agency biomarker qualification of hippocampal volume for enrichment of clinical trials in predementia stages of Alzheimer's disease

BackgroundRegulatory qualification of a biomarker for a defined context of use provides scientifically robust assurances to sponsors and regulators that accelerate appropriate adoption of biomarkers into drug development.MethodsThe Coalition Against Major Diseases submitted a dossier to the Scientific Advice Working Party of the European Medicines Agency requesting a qualification opinion on the use of hippocampal volume as a biomarker for enriching clinical trials in subjects with mild cognitive impairment, incorporating a scientific rationale, a literature review and a de novo analysis of Alzheimer's Disease Neuroimaging Initiative data.ResultsThe literature review and de novo analysis were consistent with the proposed context of use, and the Committee for Medicinal Products for Human Use released an opinion in November 2011.ConclusionsWe summarize the scientific rationale and the data that supported the first qualification of an imaging biomarker by the European Medicines Agency.     

A conceptual framework for research on subjective cognitive decline in preclinical Alzheimer's disease

There is increasing evidence that subjective cognitive decline (SCD) in individuals with unimpaired performance on cognitive tests may represent the first symptomatic manifestation of Alzheimer's disease (AD). The research on SCD in early AD, however, is limited by the absence of common standards. The working group of the Subjective Cognitive Decline Initiative (SCD-I) addressed this deficiency by reaching consensus on terminology and on a conceptual framework for research on SCD in AD. In this publication, research criteria for SCD in pre-mild cognitive impairment (MCI) are presented. In addition, a list of core features proposed for reporting in SCD studies is provided, which will enable comparability of research across different settings. Finally, a set of features is presented, which in accordance with current knowledge, increases the likelihood of the presence of preclinical AD in individuals with SCD. This list is referred to as SCD plus.     

Structural MRI biomarkers for preclinical and mild Alzheimer's disease

Noninvasive MRI biomarkers for Alzheimer's disease (AD) may enable earlier clinical diagnosis and the monitoring of therapeutic effectiveness. To assess potential neuroimaging biomarkers, the Alzheimer's Disease Neuroimaging Initiative is following normal controls (NC) and individuals with mild cognitive impairment (MCI) or AD. We applied high‐throughput image analyses procedures to these data to demonstrate the feasibility of detecting subtle structural changes in prodromal AD. Raw DICOM scans (139 NC, 175 MCI, and 84 AD) were downloaded for analysis. Volumetric segmentation and cortical surface reconstruction produced continuous cortical surface maps and region‐of‐interest (ROI) measures. The MCI cohort was subdivided into single‐ (SMCI) and multiple‐domain MCI (MMCI) based on neuropsychological performance. Repeated measures analyses of covariance were used to examine group and hemispheric effects while controlling for age, sex, and, for volumetric measures, intracranial vault. ROI analyses showed group differences for ventricular, temporal, posterior and rostral anterior cingulate, posterior parietal, and frontal regions. SMCI and NC differed within temporal, rostral posterior cingulate, inferior parietal, precuneus, and caudal midfrontal regions. With MMCI and AD, greater differences were evident in these regions and additional frontal and retrosplenial cortices; evidence for non‐AD pathology in MMCI also was suggested. Mesial temporal right‐dominant asymmetries were evident and did not interact with diagnosis. Our findings demonstrate that high‐throughput methods provide numerous measures to detect subtle effects of prodromal AD, suggesting early and later stages of the preclinical state in this cross‐sectional sample. These methods will enable a more complete longitudinal characterization and allow us to identify changes that are predictive of conversion to AD. Hum Brain Mapp 2009. © 2009 Wiley‐Liss, Inc.     

Patterns of Word-List Generation in Mild Cognitive Impairment and Alzheimer's Disease

Patients with amnestic mild cognitive impairment (aMCI) have been described as exhibiting greater impairment on tests of category fluency than letter fluency. This has been offered as evidence that this condition represents pre-clinical Alzheimer's disease (AD). We hypothesized that this pattern of differential impairment is dependent on the specific semantic categories and initial letters selected, and is not specific to AD and aMCI. A total of 40 cognitively normal older adults, 74 MCI patients—25 “amnestic single domain” (aMCI), 27 “amnestic multiple domain”, and 22 non-amnestic—and 29 AD patients were tested with multiple forms of semantic-category and initial-letter fluency tasks. The pattern of deficits within and across groups was highly dependent on the specific categories and letters chosen. Overall, aMCI patients did not demonstrate greater impairment in category than letter fluency. In fact, the level and pattern of their performance resembled that of cognitively normal older adults much more than AD patients. MCI patients with deficits in multiple cognitive domains performed most like AD patients. These findings indicate that verbal fluency performance is highly influenced by the specific tasks used, and impairment on semantic fluency is not characteristic of pure amnestic MCI.