Plasma and cerebrospinal fluid ABeta42 for the differential diagnosis of Alzheimer's disease dementia in participants diagnosed with any dementia subtype in a specialist care setting.

BACKGROUND: Dementia is a syndrome that comprises many differing pathologies, including Alzheimer's disease dementia (ADD), vascular dementia (VaD) and frontotemporal dementia (FTD). People may benefit from knowing the type of dementia they live with, as this could inform prognosis and may allow for tailored treatment. Beta-amyloid (1-42) (ABeta42) is a protein which decreases in both the plasma and cerebrospinal fluid (CSF) of people living with ADD, when compared to people with no dementia. However, it is not clear if changes in ABeta42 are specific to ADD or if they are also seen in other types of dementia. It is possible that ABeta42 could help differentiate ADD from other dementia subtypes. OBJECTIVES: To determine the accuracy of plasma and CSF ABeta42 for distinguishing ADD from other dementia subtypes in people who meet the criteria for a dementia syndrome. SEARCH METHODS: We searched MEDLINE, and nine other databases up to 18 February 2020. We checked reference lists of any relevant systematic reviews to identify additional studies. SELECTION CRITERIA: We considered cross-sectional studies that differentiated people with ADD from other dementia subtypes. Eligible studies required measurement of participant plasma or CSF ABeta42 levels and clinical assessment for dementia subtype. DATA COLLECTION AND ANALYSIS: Seven review authors working independently screened the titles and abstracts generated by the searches. We collected data on study characteristics and test accuracy. We used the second version of the 'Quality Assessment of Diagnostic Accuracy Studies' (QUADAS-2) tool to assess internal and external validity of results. We extracted data into 2 x 2 tables, cross-tabulating index test results (ABeta42) with the reference standard (diagnostic criteria for each dementia subtype). We performed meta-analyses using bivariate, random-effects models. We calculated pooled estimates of sensitivity, specificity, positive predictive values, positive and negative likelihood ratios, and corresponding 95% confidence intervals (CIs). In the primary analysis, we assessed accuracy of plasma or CSF ABeta42 for distinguishing ADD from other mixed dementia types (non-ADD). We then assessed accuracy of ABeta42 for differentiating ADD from specific dementia types: VaD, FTD, dementia with Lewy bodies (DLB), alcohol-related cognitive disorder (ARCD), Creutzfeldt-Jakob disease (CJD) and normal pressure hydrocephalus (NPH). To determine test-positive cases, we used the ABeta42 thresholds employed in the respective primary studies. We then performed sensitivity analyses restricted to those studies that used common thresholds for ABeta42. MAIN RESULTS: We identified 39 studies (5000 participants) that used CSF ABeta42 levels to differentiate ADD from other subtypes of dementia. No studies of plasma ABeta42 met the inclusion criteria. No studies were rated as low risk of bias across all QUADAS-2 domains. High risk of bias was found predominantly in the domains of patient selection (28 studies) and index test (25 studies). The pooled estimates for differentiating ADD from other dementia subtypes were as follows: ADD from non-ADD: sensitivity 79% (95% CI 0.73 to 0.85), specificity 60% (95% CI 0.52 to 0.67), 13 studies, 1704 participants, 880 participants with ADD; ADD from VaD: sensitivity 79% (95% CI 0.75 to 0.83), specificity 69% (95% CI 0.55 to 0.81), 11 studies, 1151 participants, 941 participants with ADD; ADD from FTD: sensitivity 85% (95% CI 0.79 to 0.89), specificity 72% (95% CI 0.55 to 0.84), 17 studies, 1948 participants, 1371 participants with ADD; ADD from DLB: sensitivity 76% (95% CI 0.69 to 0.82), specificity 67% (95% CI 0.52 to 0.79), nine studies, 1929 participants, 1521 participants with ADD. Across all dementia subtypes, sensitivity was greater than specificity, and the balance of sensitivity and specificity was dependent on the threshold used to define test positivity. AUTHORS' CONCLUSIONS: Our review indicates that measuring ABeta42 levels in CSF may help differentiate ADD from other dementia subtypes, but the test is imperfect and tends to misdiagnose those with non-ADD as having ADD. We would caution against the use of CSF ABeta42 alone for dementia classification. However, ABeta42 may have value as an adjunct to a full clinical assessment, to aid dementia diagnosis.

Additive toxicity of ß-amyloid by a novel bioactive peptide in vitro: possible implications for Alzheimer's disease.

BACKGROUND: ß-amyloid is regarded as a significant factor in Alzheimer's disease: but inefficient therapies based on this rationale suggests that additional signalling molecules or intermediary mechanisms must be involved in the actual initiation of the characteristic degeneration of neurons. One clue could be that acetylcholinesterase, also present in amyloid plaques, is aberrant in peripheral tissues such as blood and adrenal medulla that can be implicated in Alzheimer's disease. The aim of this study was to assess the bioactivity of a fragment of acetylcholinesterase responsible for its non-enzymatic functions, a thirty amino acid peptide ("T30") which has homologies with ß-amyloid. METHODS: Cell viability was measured by sulforhodamine B assay and also lactate dehydrogenase assay: meanwhile, changes in the status of living cells was monitored by measuring release of acetylcholinesterase in cell perfusates using the Ellman reagent. FINDINGS: T30 peptide and ß-amyloid each have toxic effects on PC12 cells, comparable to hydrogen peroxide(.) However only the two peptides selectively then evoke a subsequent, enhanced release in acetylcholinesterase that could only be derived from the extant cells. Moreover, unlike hydrogen peroxide, the T30 peptide selectively shifted a sub-threshold dose of ß-amyloid to a toxic effect, which also resulted in a comparable enhanced release of acetylcholinesterase. INTERPRETATION: This is the first study comparing directly the bioactivity of ß-amyloid with a peptide derived from acetylcholinesterase: the similarity in action suggests that the sequence homology between the two compounds might have a functional and/or pathological relevance. The subsequent enhanced release of acetylcholinesterase from the extant cells could reflect a primary 'compensatory' response of cells prone to degeneration, paradoxically providing further availability of the toxic C-terminal peptide to modulate the potency of ß-amyloid. Such a cycle of events may provide new insights into the mechanism of continuing selective cell loss in Alzheimer's disease and related degenerative disorders.

Systematic review of the body of evidence for the use of biomarkers in the diagnosis of dementia.

BACKGROUND: Although recent diagnostic criteria for Alzheimer's disease propose the use of biomarkers, validation of these biomarkers by diagnostic test accuracy studies is a necessary first step, followed by the synthesis of the evidence from these studies in systematic reviews and meta-analyses. The quality of the resulting evidence depends on the number and size of the primary studies, their quality, and the adequacy of their reporting. This systematic review assesses the weight and quality of the evidence available from primary diagnostic test accuracy studies. METHODS: A MEDLINE search was performed in August 2011 to identify all potentially relevant publications relating to the biomarkers ß-amyloid, tau, positron emission tomography ((18)F-fluorodeoxyglucose or ligands for amyloid), or magnetic resonance imaging (MRI). The reporting and methodology were assessed using the Standards for Reporting of Diagnostic Accuracy and Quality Assessment of Diagnostic Accuracy Studies assessment tools, respectively. Because clinical progression to dementia is the most commonly used reference standard, this review focuses on participants with objective cognitive impairment but no dementia at baseline. RESULTS: Of the 19,104 published references identified by the search, 142 longitudinal studies relating to the biomarkers of interest were identified, which included subjects who had objective cognitive impairment but no dementia at baseline. The highest number of studies (n = 70) and of participants (n = 4722) related to structural MRI. MRI also yielded the highest number of studies with extractable data for meta-analysis (n = 32 [46% of all structural MRI studies]), followed by cerebrospinal fluid tau (n = 24 [73%]). There were few studies on positron emission tomography ligands for amyloid having suitable data for meta-analysis (n = 4). There was considerable variation across studies in reporting outcomes, methods of blinding and selection, means of accounting for indeterminate or missing values, the interval between the test and assessments, and the determination of test thresholds. CONCLUSIONS: The body of evidence for biomarkers is not large and is variable across the different types of biomarkers. Important information is missing from many study reports, highlighting the need for standardization of methodology and reporting to improve the rigor of biomarker validation.