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Objective Expression of glial fibrillary acidic protein (GFAP), a marker of reactive astrocytosis, colocalizes with neuropathology in the brain. Blood levels of GFAP have been associated with cognitive decline and dementia status. However, further examinations at a population‐based level are necessary to broaden generalizability to community settings. Methods Circulating GFAP levels were assayed using a Simoa HD‐1 analyzer in 4338 adults without prevalent dementia from four longitudinal community‐based cohort studies. The associations between GFAP levels with general cognition, total brain volume, and hippocampal volume were evaluated with separate linear regression models in each cohort with adjustment for age, sex, education, race, diabetes, systolic blood pressure, antihypertensive medication, body mass index, apolipoprotein E ε4 status, site, and time between GFAP blood draw and the outcome. Associations with incident all‐cause and Alzheimer's disease dementia were evaluated with adjusted Cox proportional hazard models. Meta‐analysis was performed on the estimates derived from each cohort using random‐effects models. Results Meta‐analyses indicated that higher circulating GFAP associated with lower general cognition (ß = −0.09, [95% confidence interval [CI]: −0.15 to −0.03], p = 0.005), but not with total brain or hippocampal volume (p > 0.05). However, each standard deviation unit increase in log‐transformed GFAP levels was significantly associated with a 2.5‐fold higher risk of incident all‐cause dementia (Hazard Ratio [HR]: 2.47 (95% CI: 1.52–4.01)) and Alzheimer's disease dementia (HR: 2.54 [95% CI: 1.42–4.53]) over up to 15‐years of follow‐up. Interpretation Results support the potential role of circulating GFAP levels for aiding dementia risk prediction and improving clinical trial stratification in community settings.

BACKGROUND Peak‐width of skeletonized mean diffusivity (PSMD), a neuroimaging marker of cerebral small vessel disease (SVD), has shown excellent instrumental properties. Here, we extend our work to perform a biological validation of PSMD. METHODS We included 396 participants from the Biomarkers for Vascular Contributions to Cognitive Impairment and Dementia (MarkVCID‐1) Consortium and three replication samples (Cohorts for Heart and Aging Research in Genomic Epidemiology = 6172, Rush University Medical Center = 287, University of California Davis Alzheimer's Disease Research Center = 567). PSMD was derived from diffusion tensor imaging using an automated algorithm. We related PSMD to a composite measure of general cognitive function using linear regression models adjusting for confounders. RESULTS Higher PSMD was associated with lower general cognition in MarkVCID‐1 independent of age, sex, education, and intracranial volume (Beta [95% confidence interval], −0.8 [−1.2, −0.4], P < 0.001). These findings were replicated in independent samples. Furthermore, PSMD explained cognitive status above and beyond white matter hyperintensities. DISCUSSION Our biological validation work supports the pursuit of larger clinical validation studies evaluating PSMD as a susceptibility/risk biomarker of small vessel disease contributing to cognitive impairment and dementia. Highlights Peak‐width of skeletonized mean diffusivity (PSMD) is a novel small vessel disease neuroimaging biomarker. A prior instrumental validation study demonstrated that PSMD is a robust biomarker. This biological validation study shows that high PSMD relates to worse cognition. PSMD explains cognitive function above and beyond white matter hyperintensities. Future clinical validation will assess PSMD as a vascular contribution to cognitive impairment and dementia biomarker in clinical trials.

INTRODUCTION Dementia prevalence is associated with modifiable factors. We quantified the contribution of dementia risk factors in midlife (45–64 years) and late life (≥ 65 years) in the United States. METHODS Data from six community‐based cohorts in the Dementia Risk Prediction Project (DRPP) were used. We estimated risk factor prevalence using nationally representative data. Cohort‐specific Cox regression models were used to estimate the association between modifiable risk factors and incident dementia in midlife and late life. Hazard ratios were pooled using meta‐analysis then used to calculate population attributable fractions (PAFs) and potential impact fractions. RESULTS Midlife and late‐life risk factors contributed to 22.7% and 16.5% of total dementia cases, respectively. Midlife obesity (PAF: 7.7%; 95% confidence interval [CI]: 4.9%–10.5%), lower education (PAF: 8.1%; 95% CI: 5.2%–11.1%), and late‐life physical inactivity (PAF: 10.4%; 95% CI: 6.2%–14.5%) were the greatest contributors. DISCUSSION Midlife and late‐life modifiable risk factors contribute to dementia risk, highlighting a need for interventions across the life course. Highlights Our sample included 37,931 participants across six pooled, longitudinal US cohorts. We observed midlife and late‐life risk factors contributed to 22.7% and 16.5% of dementia cases, respectively. Midlife obesity, late‐life physical inactivity, and lower education appear to be the greatest contributors to dementia risk.

Background The MarkVCID consortium was established to address the paucity of biomarkers for vascular contributions to cognitive impairment and dementia (VCID), a leading cause of dementia. Plasma neurofilament light (NfL), a neuroaxonal injury marker elevated in several neurological and neurodegenerative diseases, was selected as one of the first biomarkers to be examined. We performed comprehensive instrumental and clinical validation of the Quanterix Simoa NfL assay using the first MarkVCID cohort. Method Plasma NfL was measured using HD‐X and HD‐1 Simoa instruments. Samples from the MarkVCID consortium were used to evaluate intra‐ and inter‐plate reliability, test‐retest repeatability, and inter‐site reproducibility. We used linear regression models to assess the association of NfL in MarkVCID with general cognitive function (GCF) as the primary outcome (n=331). In secondary analyses we assessed NfL associations with white matter hyperintensities (WMH). Models were adjusted for potential confounders, including eGFR as renal function influences NfL clearance. We replicated our findings using cohorts from the CHARGE consortium (CARDIA, ARIC, FHS, AGES; n=4,772), the UKY ADRC (n=350), and the UCD ADRC (n=196). Result We found the Quanterix Simoa platform to be reliable with low coefficients of variation (average CV<12%), high inter‐site reproducibility (overall ICC = 0.93) and high repeatability in test‐retest samples drawn within 30 days (ICC=0.968). There was strong consistency across Quanterix instruments (HD‐X and HD‐1; R2≥0.98) and kits (N4PA and single molecule NfL; ICC≥0.81). We observed consistent significant associations between higher NfL concentrations and worse GCF in MarkVCID (β=‐0.23; [95% CI ‐0.41; ‐0.01), CHARGE cohorts (meta‐analysis β=‐0.11; [95% CI ‐0.17; ‐0.06]), the UKY ADRC (β=‐0.16; [95% CI ‐0.27; ‐0.05]) and the UCD ADRC (UCD: β=‐0.28; [95% CI ‐0.48; ‐0.08). Secondary analyses revealed significant associations between elevated NfL concentrations and higher WMH burden in MarkVCID (when controlled for eGFR), CHARGE, and the UCD ADRC. Conclusion We have found that NfL can be reliably measured using the Quanterix platform, making this marker ideal for multi‐site clinical trials. We observed consistent associations for plasma NfL concentrations with cognition and WMH in MarkVCID and across independent samples, providing evidence that it can be a useful biomarker for stratification in VCID trials.

Background Peak‐width of skeletonized mean diffusivity (PSMD) is an emerging biomarker of cerebral small vessel disease (cSVD)‐related vascular contributions to cognitive impairment and dementia (VCID). Higher PSMD values reflect greater white matter microstructural damage, and prior research has related PSMD to sporadic and monogenic forms of cSVD and worse cognitive function. Therefore, we proposed PSMD as a risk stratification biomarker for VCID. This study aimed to perform a rigorous instrumental and biological validation for PSMD in the MarkVCID‐1 consortium. Method Methods to derive PSMD were packaged in a kit containing a protocol, scripts, and instructions. The instrumental validation included a pre‐specified plan to assess inter‐rater reliability, test‐retest repeatability, and inter‐scanner reproducibility among MarkVCID‐1 participants aged 53‐78 years across the spectrum of cSVD. We used intra‐class correlations for absolute agreement (ICCAA) and consistency (ICCC) to evaluate results, with ICC>0.07 as the pre‐specified goal. The biological validation was performed on 7,289 participants of diverse ages and racial/ethnic backgrounds from MarkVCID‐1 and population‐based cohorts from CHARGE, RUSH, and UCD‐ADRC. All sites derived a composite measure of general cognitive function using neuropsychological tests assessing distinct cognitive domains. Finally, we used linear regression models to assess the association between log‐PSMD and general cognition adjusting for age, age2, sex, and education. Result Our instrumental validation results (Figure 1) showed excellent reliability between raters from seven sites (overall ICCAA=0.945, P<0.001), agreement between test and retest measurements obtained within two weeks (ICCAA=0.986, P<0.001), and reproducibility across Philips Achieva, Siemens Prisma, and Siemens Trio scanners (ICCC= 0.954, P<0.001). In the biological validation, higher PSMD values were associated with lower general cognitive function in MarkVCID‐1 (Beta=‐0.82, P<0.001), and these findings were replicated across the CHARGE, RUSH, and UCD‐ADRC cohorts (Table 1). Conclusion Our rigorous instrumental validation study showed excellent inter‐rater reliability, test‐retest repeatability, and inter‐scanner reproducibility for the PSMD kit. We further observed strong associations between higher PSMD values and poorer cognitive function across diverse samples in the biological validation. Taken together, our findings support using PSMD as a robust risk stratification biomarker in multi‐site clinical trials of VCID. Additional longitudinal validation studies for PSMD are underway in MarkVCID‐2.