Measurement batch differences and between-batch conversion of Alzheimer's disease cerebrospinal fluid biomarker values

INTRODUCTION

Batch differences in cerebrospinal fluid (CSF) biomarker measurement can introduce bias into analyses for Alzheimer's disease studies. We evaluated and adjusted for batch differences using statistical methods.

METHODS

A total of 792 CSF samples from 528 participants were assayed in three batches for 12 biomarkers and 3 biomarker ratios. Batch differences were assessed using Bland-Altman plot, paired t test, Pitman-Morgan test, and linear regression. Generalized linear models were applied to convert CSF values between batches.

RESULTS

We found statistically significant batch differences for all biomarkers and ratios, except that neurofilament light was comparable between batches 1 and 2. The conversion models generally had high R 2 except for converting P-tau between batches 1 and 3.

DISCUSSION

Between-batch conversion allows harmonized CSF values to be used in the same analysis. Such method may be applied to adjust for other sources of variability in measuring CSF or other types of biomarkers.

Association of Cardiovascular Risk Factors with Cerebral Perfusion in Whites and African Americans

BACKGROUND

Midlife cardiovascular risk factors increase risk for Alzheimer's disease (AD). Despite disproportionately high cardiovascular disease and dementia rates, African Americans are under-represented in studies of AD risk and research-based guidance on targeting vascular risk factors is lacking.

OBJECTIVE

This study investigated relationships between specific cardiovascular risk factors and cerebral perfusion in White and African American adults enriched for AD risk.

METHODS

Participants included 397 cognitively unimpaired White (n = 330) and African American (n = 67) adults enrolled in the Wisconsin Alzheimer's Disease Research Center who underwent pseudo-continuous arterial spin labeling MRI. Multiple linear regression models examined independent relationships between cardiovascular risk factors and mean cerebral perfusion. Subsequent interaction and stratified models assessed the role for APOE genotype and race.

RESULTS

When risk factor p-values were FDR-adjusted, diastolic blood pressure was significantly associated with mean perfusion. Tobacco use, triglycerides, waist-to-hip ratio, and a composite risk score were not associated with perfusion. Without FDR adjustment, a relationship was also observed between perfusion and obesity, cholesterol, and fasting glucose. Neither APOE genotype nor race moderated relationships between risk factors and perfusion.

CONCLUSION

Higher diastolic blood pressure predicted lower perfusion more strongly than other cardiovascular risk factors. This relationship did not vary by racial group or genetic risk for AD, although the African American sample had greater vascular risk burden and lower perfusion rates. Our findings highlight the need to prioritize inclusion of underrepresented groups in neuroimaging studies and to continue exploring the link between modifiable risk factors, cerebrovascular health, and AD risk in underrepresented populations.

Latent Factor Structure and Measurement Invariance of the NIH Toolbox Cognition Battery in an Alzheimer's Disease Research Sample

OBJECTIVE

This study investigated the latent factor structure of the NIH Toolbox Cognition Battery (NIHTB-CB) and its measurement invariance across clinical diagnosis and key demographic variables including sex, race/ethnicity, age, and education for a typical Alzheimer's disease (AD) research sample.

METHOD

The NIHTB-CB iPad English version, consisting of 7 tests, was administered to 411 participants aged 45-94 with clinical diagnosis of cognitively unimpaired, dementia, mild cognitive impairment (MCI), or impaired not MCI. The factor structure of the whole sample was first examined with exploratory factor analysis (EFA) and further refined using confirmatory factor analysis (CFA). Two groups were classified for each variable (diagnosis or demographic factors). The confirmed factor model was next tested for each group with CFA. If the factor structure was the same between the groups, measurement invariance was then tested using a hierarchical series of nested two-group CFA models.

RESULTS

A two-factor model capturing fluid cognition (executive function, processing speed, and memory) versus crystalized cognition (language) fit well for the whole sample and each group except for those with age < 65. This model generally had measurement invariance across sex, race/ethnicity, and education, and partial invariance across diagnosis. For individuals with age < 65, the language factor remained intact while the fluid cognition was separated into two factors: (1) executive function/processing speed and (2) memory.

CONCLUSIONS

The findings mostly supported the utility of the battery in AD research, yet revealed challenges in measuring memory for AD participants and longitudinal change in fluid cognition.

Association of Neighborhood Context, Cognitive Decline, and Cortical Change in an Unimpaired Cohort

OBJECTIVE

To test the hypothesis that neighborhood-level disadvantage is associated with longitudinal measures of neurodegeneration and cognitive decline in an unimpaired cohort.

METHODS

Longitudinal MRI and cognitive testing data were collected from 601 cognitively unimpaired participants in the Wisconsin Registry for Alzheimer's Prevention Study and the Wisconsin Alzheimer's Disease Research Center clinical cohort. Area Deprivation Index was geospatially determined based on participant residence geocode and ranked relative to state of residence. Linear regression models were fitted to test associations between neighborhood-level disadvantage and longitudinal change in cortical thickness and cognitive test performance. Mediation tests were used to assess whether neurodegeneration and cognitive decline were associated with neighborhood-level disadvantage along the same theoretical causal path.

RESULTS

In our middle- to older-aged study population (mean baseline age 59 years), living in the 20% most disadvantaged neighborhoods (n = 19) relative to state of residence was associated with cortical thinning in Alzheimer signature regions (p = 0.002) and decline in the Preclinical Alzheimer's Disease Cognitive Composite (p = 0.04), particularly the Trail-Making Test, part B (p < 0.001), but not Rey Auditory Verbal Learning Test (p = 0.77) or Story Memory Delayed Recall (p = 0.49) subtests. Associations were attenuated but remained significant after controlling for racial and demographic differences between neighborhood-level disadvantage groups. Cortical thinning partially mediated the association between neighborhood-level disadvantage and cognitive decline.

CONCLUSIONS

In this longitudinal study of cognitively unimpaired adults, living in the most highly disadvantaged neighborhoods was associated with accelerated degeneration in Alzheimer signature regions and cognitive decline. This study provides further evidence for neighborhood-level disadvantage as a risk factor for preclinical neurodegeneration and cognitive decline in certain populations. Limitations of the present study, including a small number of participants from highly disadvantaged neighborhoods and a circumscribed geographic setting, should be explored in larger and more diverse study cohorts.

Sleep quality and cortical amyloid-β deposition in postmenopausal women of the Kronos early estrogen prevention study

Hormone therapy improves sleep in menopausal women and recent data suggest that transdermal 17β-estradiol may reduce the accumulation of cortical amyloid-β. However, how menopausal hormone therapies modify the associations of amyloid-β accumulation with sleep quality is not known. In this study, associations of sleep quality with cortical amyloid-β deposition and cognitive function were assessed in a subset of women who had participated in the Kronos early estrogen prevention study. It was a randomized, placebo-controlled trial in which recently menopausal women (age, 42-58; 5-36 months past menopause) were randomized to (1) oral conjugated equine estrogen (n = 19); (2) transdermal 17β-estradiol (tE2, n = 21); (3) placebo pills and patch (n = 32) for 4 years. Global sleep quality score was calculated using Pittsburgh sleep quality index, cortical amyloid-β deposition was measured with Pittsburgh compound-B positron emission tomography standard uptake value ratio and cognitive function was assessed in four cognitive domains 3 years after completion of trial treatments. Lower global sleep quality score (i.e., better sleep quality) correlated with lower cortical Pittsburgh compound-B standard uptake value ratio only in the tE2 group (r = 0.45, P = 0.047). Better global sleep quality also correlated with higher visual attention and executive function scores in the tE2 group (r = -0.54, P = 0.02) and in the oral conjugated equine estrogen group (r = -0.65, P = 0.005). Menopausal hormone therapies may influence the effects of sleep on cognitive function, specifically, visual attention and executive function. There also appears to be a complex relationship between sleep, menopausal hormone therapies, cortical amyloid-β accumulation and cognitive function, and tE2 formulation may modify the relationship between sleep and amyloid-β accumulation.

Disclosure of preclinical Alzheimer's disease biomarker results in research and clinical settings: Why, how, and what we still need to know

Disclosure of personal disease-related information to asymptomatic adults has been debated over the last century in medicine and research. Recently, Alzheimer's disease (AD) has been conceptualized as a continuum that begins with a "preclinical" stage in which biomarkers are present in the absence of cognitive impairment. Studies have begun assessing the safety, psychological, and behavioral effects of disclosing both AD-related genetic and biomarker information to cognitively unimpaired older adults. Yet, debate continues over the appropriate circumstances and methods for returning such information. This article outlines concerns with and rationale for AD biomarker disclosure and summarizes findings from prior studies. Overall, this article aims to describe and respond to key questions concerning disclosure of amyloid positron emission tomography scan results to asymptomatic adults in a research setting. Moving forward, such conditions are important to consider as interventions target the preclinical phase of AD and normalize disclosing biomarker information to cognitively unimpaired persons.

Cigarette Smoking Status, Cigarette Exposure, and Duration of Abstinence Predicting Incident Dementia and Death: A Multistate Model Approach

BACKGROUND

To fully characterize the risk for dementia associated with cigarette smoking, studies must consider competing risks that hinder the observation of dementia or modify the chance that dementia occurs (i.e., death). Extant research examining the competing risks fails to account for the occurrence of death following dementia, limiting our understanding of the relation between smoking and dementia.

OBJECTIVE

Examine the impact of smoking status, lifetime smoking exposure, and duration of abstinence on incident dementia, death following dementia, and death without dementia.

METHODS

Multi-state models estimated hazard ratios (HR) for 95% confidence interval (CI) of 10,681 cognitively healthy adults for transition from baseline to dementia, baseline to death, and dementia to death based on smoking status, lifetime cigarette exposure, and abstinence duration.

RESULTS

Compared to never smokers, current smokers had increased risk of dementia (HR = 1.66; 95% CI 1.18- 2.32; p = 0.004), and death from baseline (HR = 2.98; 95% CI 2.24- 3.98; p < 0.001) and incident dementia (HR = 1.88; 95% CI 1.08- 3.27; p = 0.03). Pack years increased risk of death from baseline (HR = 1.01; 95% CI 1.00- 1.01; p < 0.001), but not dementia risk (HR = 1.00; 95% CI 1.00- 1.00; p = 0.78) or death following dementia (HR = 1.01; 95% CI 1.00- 1.01; p = 0.05). Recent quitters (quit < 10 years), compared to never smokers, had increased risk of death after baseline (HR = 2.31; 95% CI 1.55- 3.43; p < 0.001), but not dementia (HR = 1.17; 95% CI 0.73- 1.88; p = 0.52) or death following dementia (HR = 1.01; 95% CI 0.42- 2.41; p = 0.99).

CONCLUSION

Current smoking increases the risk for dementia and death, but dementia is better attributed to smoking recency than lifetime exposure. Smoking cessation at any age might reduce these risks for cognitively healthy individuals.

Perspectives of Veterans Affairs mental health providers on working with older adults with dementia and their caregivers

Continuing education directed at building providers' skills and knowledge in geriatrics represents a practical approach to addressing the geriatric mental health (MH) care workforce shortage. To inform the development of professional training curricula, we surveyed MH providers (N = 65) at a Veterans Affairs medical center on working with older persons with dementia (PwD) and informal caregivers. Providers rated service provision to PwD and caregivers as highly important but endorsed modest self-efficacy. Half of respondents were minimally confident in managing risk of harm to self or others in a PwD. Respondents believed PwD can benefit from MH treatments, yet identified several barriers to providing care, including inadequate time and staffing resources. Interest in geriatric training topics was high. Findings demonstrate that MH providers at this site value care provision to PwD and caregivers, and desire additional training to serve this population. System-level barriers to MH care for PwD should also be identified and addressed.

Association of Cardiovascular and Alzheimer's Disease Risk Factors with Intracranial Arterial Blood Flow in Whites and African Americans

BACKGROUND

Alzheimer's disease (AD) has a higher prevalence among African Americans. Targeting cardiovascular and metabolic risk factors may be potential mechanisms to modify AD risk and address racial/ethnic disparities in AD dementia.

OBJECTIVE

This study investigated relationships among cardiovascular and metabolic risk factors, APOE genotype, AD biomarkers, and intracranial arterial blood flow in Whites and African Americans enriched for AD risk.

METHODS

399 cognitively unimpaired adults from the Wisconsin Alzheimer's Disease Research Center completed physical and neuroimaging examinations. A 4D Flow MRI sequence (phase-contrast vastly under sampled isotropic projection imaging) measured intracranial arterial flow in the Circle of Willis. Linear mixed-effects regression models estimated relationships between risk factors and intracranial arterial flow and tested interactions with racial group, APOE genotype, and AD biomarkers, with separate models per risk factor.

RESULTS

Higher fasting glucose was associated with lower intracranial arterial flow; no additional relationships between flow and risk factors were observed. Main effects of racial group were observed, without an interaction, indicating lower flow in African Americans compared to Whites. In race-stratified analyses, higher glucose and triglycerides were associated with lower flow for African Americans, but not for Whites. No main effects or interactions among risk factors, APOE, or AD biomarkers, and flow were observed.

CONCLUSION

Elevated fasting glucose and triglycerides were associated with lower intracranial arterial flow; these relationships were more prominent in African Americans. Targeting metabolic risk factors may impact intracranial arterial health. Additional research is needed to determine if this will impact disparities in dementia prevalence.

Stressful Life Events and Racial Disparities in Cognition Among Middle-Aged and Older Adults

BACKGROUND

It is well-documented that African Americans have elevated risk for cognitive impairment and dementia in late life, but reasons for the racial disparities remain unknown. Stress processes have been linked to premature age-related morbidity, including Alzheimer's and related dementias (ADRD), and plausibly contribute to social disparities in cognitive aging.

OBJECTIVE

We examined the relationship between stressful life events and cognitive decline among African American and White participants enrolled in the Wisconsin Registry for Alzheimer's Prevention (WRAP).

METHODS

Linear mixed models including demographic, literacy, and health-related covariates were used to estimate (1) relationships between a life event index score and decline in cognitive test performance in two domains of executive function (Speed & Flexibility, Working Memory) and one domain of episodic memory (Verbal Learning & Memory) among 1,241 WRAP enrollees, stratified by race, and (2) contributions of stressful life events to racial differences in cognition within the full sample.

RESULTS

African Americans (N = 50) reported more stressful life events than Whites (N = 1,191). Higher stress scores associated with poorer Speed & Flexibility performance in both groups, though not with declines across time, and partially explained racial differentials in this domain. Among African Americans only, stressor exposure also associated with age-related decline in Verbal Learning & Memory. Stressor-cognition relationships were independent of literacy and health-related variables.

CONCLUSIONS

Greater lifetime stress predicted poorer later-life cognition, and, in a small sample of African Americans, faster declines in a key domain of episodic memory. These preliminary findings suggest that future work in large minority aging cohorts should explore stress as an important source of modifiable, socially-rooted risk for impairment and ADRD in African Americans, who are disproportionately exposed to adverse experiences across the life course.

Lessons from KEEPS: the Kronos Early Estrogen Prevention Study

The Kronos Early Estrogen Prevention Study (KEEPS) was a randomized, double-blind, placebo-controlled trial designed to determine the effects of hormone treatments (menopausal hormone treatments [MHTs]) on the progression of carotid intima-medial thickness (CIMT) in recently menopausal women. Participants less than 3 years from menopause and without a history of overt cardiovascular disease (CVD), defined as no clinical CVD events and coronary artery calcium < 50 Agatston units, received either oral conjugated equine estrogens (0.45 mg/day) or transdermal 17β-estradiol (50 µg/day), both with progesterone (200 mg/day for 12 days/month), or placebo pills and patches for 4 years. Although MHT did not decrease the age-related increase in CIMT, KEEPS provided other important insights about MHT effects. Both MHTs versus placebo reduced the severity of menopausal symptoms and maintained bone density, but differed in efficacy regarding mood/anxiety, sleep, sexual function, and deposition of β-amyloid in the brain. Additionally, genetic variants in enzymes for metabolism and uptake of estrogen affected the efficacy of MHT for some aspects of symptom relief. KEEPS provides important information for use of MHT in clinical practice, including type, dose, and mode of delivery of MHT recently after menopause, and how genetic variants in hormone metabolism may affect MHT efficacy on specific outcomes.