ObjectiveThe objectives of this study were to investigate whether the plasma levels of oligomeric amyloid-β (OAβ) were affected in Alzheimer’s disease (AD) and to examine the associations (or possible correlations) between plasma OAβ levels and memory performance.MethodThirty subjects with AD and 28 cognitively normal controls were recruited in the study. The multimer detection system (MDS) was used to measure the levels of OAβ in the plasma. In addition to assessing the general cognitive function with the Mini-Mental State Examination (MMSE), Cognitive Abilities Screening Instrument (CASI), and Alzheimer’s Disease Assessment Scale–cognitive portion (ADAS-Cog), the common objects memory test (COMT) was used to examine the episodic memory performance. Pearson’s and partial correlation analyses were conducted to explore the associations between cognitive performance and OAβ levels in the plasma. A receiving operating curve (ROC) analysis was used to discriminate between the AD and control groups.ResultsThe plasma OAβ levels in the AD group were significantly higher than those in the control group [1.88 (0.38) ng/ml vs 1.20 (0.40) ng/ml, p < 0.001]. The elevated levels of plasma OAβ showed a strong correlation with cognitive performance in patients with AD, including an inverse correlation with scores on the MMSE (r = − 0.43, p = 0.02), CASI (r = − 0.56, p < 0.01), and the immediate recall (r = − 0.45, p = 0.01), 5-min delayed recall (r = − 0.56, p < 0.01), and 30-min delayed recall (r = − 0.71, p < 0.001) tests of the COMT, and a positive correlation with the ADAS-Cog scores (r = 0.59, p < 0.001). The EDTA plasma Aβ oligomer optical density (OD) value measured using the MDS could discriminate between the AD and control groups with an area under the curve (AUC) of 0.89. The optimal sensitivity and specificity were 82.1% and 90.0%, respectively.ConclusionThe elevated levels of OAβ in the plasma distinguished the AD and control groups and were associated with the severity of symptoms, especially memory performance, in patients with AD. Our results suggested that plasma OAβ could potentially be a simple and non-invasive blood-based biomarker for AD diagnosis. Furthermore, longitudinal studies are warranted to explore the application of plasma OAβ levels as a valid diagnostic biomarker in patients with AD.Electronic supplementary materialThe online version of this article (10.1186/s13195-019-0535-7) contains supplementary material, which is available to authorized users.

Background: Mild behavioral impairment (MBI) has been proposed as an early manifestation of dementia. The Mild Behavioral Impairment Checklist (MBI-C) may help identify MBI in prodromal and preclinical dementia. Objective: The study aimed to evaluate the reliability and validity of the Chinese version of MBI-C in mild cognitive impairment (MCI) and mild Alzheimer’s disease (AD), and to explore the structure of the five factors of the MBI-C in Chinese culture. Methods: Sixty dyads of MCI and mild AD (MCI, n = 33; mild AD, n = 35) were recruited. The informants completed the MBI-C and Neuropsychiatric Inventory Questionnaire (NPI-Q) and were interviewed for clinician rating of the NPI. The Cronbach’s coefficient was used to measure the structural reliability of the MBI-C. The criterion-validity was evaluated with the correlation coefficient between the MBI-C and the total scores of NPI-Q and NPI. Exploratory factor analysis was conducted to investigate the structure of the MBI-C. Results: The Cronbach’s α coefficient was 0.895. The MBI-C total score was positively correlated with all five domains (r = 0.577∼0.840). The total score of MBI-C was significantly correlated with the total scores of NPI-Q (r = 0.714) and NPI (r = 0.749). Similarly, the five domain scores of MBI-C were significantly correlated with the factor and total scores of NPI-Q (r = 0.312∼0.673) and NPI (r = 0.389∼0.673). The components of each factor in Chinese version of MBI-C were slightly different from those of the a priori defined domains (χ2 = 1818.202, df = 496, p < 0.001). Conclusion: The Chinese version of MBI-C has good reliability and validity, and can be used to evaluate the psychological and behavioral changes in MCI and mild AD.

It is widely recognized that depression may precipitate the incidence of dementia in the elderly individuals and individuals with amnestic mild cognitive impairment (aMCI) in particular. However, the association between subthreshold depression (SD) and cognitive deficits in patients with aMCI remains unclear. To address this, we collected demographic information and conducted a battery of neuropsychological cognitive assessments in 33 aMCI participants with SD (aMCI/SD+), 33 nondepressed aMCI participants (aMCI/SD−), and 53 normal controls (NC). Both aMCI groups showed significantly poorer performance in most cognitive domains relative to the NC group (ie, memory, language, processing speed, and executive function). Notably, the aMCI/SD+ group showed significantly poorer attention/working memory compared with the aMCI/SD− group. Multiple linear regression analyses revealed a significant negative association between the severity of depressive symptoms and attention/working memory capacity (β = − .024, P = .024), accounting for 8.28% of the variations in this cognitive domain. All statistical analyses were adjusted by age, sex, and years of education. A logistic regression model had an accuracy of 72.4% in discriminating between the aMCI/SD+ and aMCI/SD− groups based on individual cognitive profiles over 6 domains. Our findings indicate that patients with aMCI with and without SD have distinct patterns of cognitive impairment. This finding may facilitate the diagnosis and treatment of SD in patients with aMCI.