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Background: Age is the strongest risk factor for dementia, including Alzheimer's disease (AD). However, across individuals of the same chronological age there is considerable heterogeneity in rates of cognitive decline. These differences have been attributed to individual differences in age‐related biological processes, including brain protein expression. To capture these differences, we developed a measure of protein brain age from cerebrospinal fluid (CSF)‐proteins, and validated its predictive utility. Methods: In older adults across the dementia continuum enrolled in DELCODE (training cohort; N = 488, 5‐year follow‐up) and patients with subjective cognitive decline and mild cognitive impairment (MCI) from the memory‐clinic based Fundació ACE (FACE) cohort (test cohort; N = 509, 3‐year follow‐up), 1063 CSF‐proteins were measured using OLINK‐technology. Proteins optimally predicting chronological age in A/T/N‐negative individuals without dementia from DELCODE (N = 196) were selected based on a LASSO‐regression and summarized into a BrainProteinAge‐score for all participants. A harmonized, age‐sensitive cognitive composite was created and the association between BrainProteinAge and cognitive decline assessed using structural equation modeling. Further, the predictive utility of ProteinBrainAge for incident all‐cause‐dementia was examined using time‐dependent ROC analysis in MCI patients from the test cohort. Results: 118 CSF‐proteins were selected and used to calculate BrainProteinAge. In the training (Est[SE] = 0.06[0.02],p<0.001) and test (Est[SE] = 0.04[0.02],p = 0.013) cohorts, BrainProteinAge predicted cognitive decline beyond demographic characteristics (chronological age, sex, education) and A/T/N profiles. ProteinBrainAge captured 40% of the processes linking chronological age and cognitive decline, and improved prediction to all‐cause dementia beyond demographic characteristics and A/T/N profiles in MCI‐patients (1‐year AUC: 0.78 versus 0.82, p(difference) = 0.006). Specifically, within the AD‐continuum, BrainProteinAge (HR[CI] = 1.056[1.004‐1.110]), compared to chronological age (HR[CI] = 1.022[0.990‐1.054]), has greater predictive utility. Whilst an 8.6‐year ProteinBrainAge difference corresponded to the same risk increase observed between A+/T+ and A+/T‐ MCI patients, a difference of 24.6‐years was required for chronological age. All results remained substantively unchanged when using an optimized BrainProteinAge based on 10 proteins most strongly linked to cognitive decline. Conclusions: A new measure of biological age improves individualized prediction of cognitive decline and conversion to dementia in memory clinic patients. This provides an opportunity for precision medicine and a better understanding of age‐related biological processes contributing to dementia. [ABSTRACT FROM AUTHOR]

Introduction: Increased plasma levels of C‐reactive protein (CRP) in midlife are associated with increased risk of Alzheimer's disease (AD), whereas in older age the opposite association is observed. Whether genetically determined CRP is associated with AD remains unclear. Methods: A total of 111,242 White individuals from the Copenhagen General Population Study and the Copenhagen City Heart Study were included. Plasma levels of CRP and four regulatory genetic variants in the CRP gene were determined. Results: For CRP percentile group 1 to 5 (lowest plasma CRP) versus the 50 to 75 group (reference), the hazard ratio for AD was 1.69 (95% confidence interval 1.29–2.16). Genetically low CRP was associated with increased risk of AD in individuals with body mass index ≤25 kg/m2 (P = 4 × 10−6). Discussion: Low plasma levels of CRP at baseline were associated with high risk of AD in individuals from the general population. These observational findings were supported by genetic studies. [ABSTRACT FROM AUTHOR]

Background: High‐throughput proteomic platforms are an useful strategy to detect novel biomarkers and pathways involved in Alzheimer's disease (AD) development. Due to the novelty of these techniques, an extensive quality control assessment is needed to ensure the reliability of those protein measurements. In this study, we aimed to assess the reproducibility and reliability of SomaScan and Olink proteomic platforms and select top‐performing proteins for further analysis. Method: To assess CSF proteomic measurements, we used the SomaScan 7k platform (an aptamer‐based technique) measuring 7335 human proteins, and Olink proteomics platform (Explore panel, an antibody‐based technique), measuring 3072 proteins in a subset of 509 individuals from ACE Alzheimer Center Barcelona (Spain). To assess intra‐ and inter‐platform reproducibility and reliability, we evaluated 1) the correlations of aptamers of two studies carried out in the same samples with SomaScan platform and 2) the correlation between SomaScan vs Olink proteomics, respectively. Then, we created a metric of 6 categories of reproducibility combining both intra and inter‐ correlation analysis, considering good (r > 0.5), modest (0.2 > r ≥ 0.5), poor (r ≤ 0.2) correlation. We considered proteins in the top 3 categories as potential candidates to further analysis. Result: From the intra‐platform analysis, only 2402 proteins (35.45%) showed a Pearson's correlation higher than 0.5. Regarding inter‐platform assessment, 2160 proteins were overlapping between both platforms. From these overlapping proteins, 712 proteins exhibited a Pearson's r > 0.5 (26.67%). We considered potential candidate proteins those with good intra‐ and inter‐platform correlation (n = 687, 9.02%), only good intra‐platform correlation (n = 2015, 26.45%) and modest intra‐ and inter‐platform correlation (n = 5, 0.06%) for analysis. Conclusion: The validation of the reproducibility and reliability of the new proteomics platforms is essential for the correct analysis of the results. The classification of measured proteins in different categories could be useful to increase the confidence in these highly multiplexed proteomic panels. [ABSTRACT FROM AUTHOR]

Introduction: The mechanism behind the strong association between the ɛ2/ɛ3/ɛ4 apolipoprotein E gene (APOE) polymorphism and Alzheimer's disease is not well‐characterized. Because low plasma levels of apoE associate with risk of dementia, genetic variants altering apoE levels in general may also associate with dementia. Methods: The APOE gene was sequenced in 10,369 individuals, and nine amino acid–changing variants with frequencies ≥2/10,000 were further genotyped in 95,228 individuals. Plasma apoE levels were measured directly. Results: Risk of all dementia and Alzheimer's disease (AD) increased with decreasing genetically determined apoE levels (P = 5 × 10−4 and P = 1 × 10−4 after APOE ɛ2/ɛ3/ɛ4 adjustment). Hazard ratios (95% confidence intervals) for all dementia and AD were 2.76 (1.39 to 5.47) and 4.92 (2.36 to 10.29) for the group with the genetically lowest apoE versus ɛ33. Discussion: We found that genetically low apoE levels increase and genetically high levels decrease risk, beyond ɛ2/ɛ3/ɛ4. This underscores that dementia risk more likely relates to variants affecting levels of apoE. [ABSTRACT FROM AUTHOR]

Introduction The adenosine triphosphate-binding cassette transporter A1 ( ABCA1 ) is a major cholesterol transporter highly expressed in the liver and brain. In the brain, ABCA1 lipidates apolipoprotein E (apoE), facilitates clearance of amyloid-β, and may be involved in maintenance of the blood-brain barrier via apoE-mediated pathways. Methods We tested whether a loss-of-function mutation in ABCA1 , N1800H, is associated with plasma levels of apoE and with risk of Alzheimer's disease (AD) in 92,726 individuals and with risk of cerebrovascular disease in 64,181 individuals. Results N1800H AC (0.2%) versus AA (99.8%) was associated with a 13% lower plasma level of apoE ( P = 1 × 10 −11 ). Multifactorially adjusted hazard ratios for N1800H AC versus AA were 4.13 (95% confidence interval, 1.32–12.9) for AD, 2.46 (1.10–5.50) for cerebrovascular disease, and 8.28 (2.03–33.7) for the hemorrhagic stroke subtype. Discussion A loss-of-function mutation in ABCA1 , present in 1:500 individuals, was associated with low plasma levels of apoE and with high risk of AD and cerebrovascular disease in the general population. [ABSTRACT FROM AUTHOR]