Maternal dementia age at onset in relation to amyloid burden in non-demented elderly offspring

Increased Functional Connectivity of the Precuneus in Individuals with a Family History of Alzheimer's Disease

BACKGROUND

First-degree relatives of individuals with late-onset Alzheimer's disease (AD) have increased risk for AD, with children of affected parents at an especially high risk.

OBJECTIVE

We aimed to investigate default mode network connectivity, medial temporal cortex volume, and cognition in cognitively healthy (CH) individuals with (FH+) and without (FH-) a family history of AD, alongside amnestic mild cognitive impairment (aMCI) and AD individuals, to determine the context and directionality of dysfunction in at-risk individuals. Our primary hypothesis was that there would be a linear decline (CH FH- > CH FH+ > aMCI > AD) within the risk groups on all measures of AD risk.

METHODS

We used MRI and fMRI to study cognitively healthy individuals (n = 28) with and without AD family history (FH+ and FH-, respectively), those with aMCI (n = 31) and early-stage AD (n = 25). We tested connectivity within the default mode network, as well as measures of volume and thickness within the medial temporal cortex and selected seed regions.

RESULTS

As expected, we identified decreased medial temporal cortex volumes in the aMCI and AD groups compared to cognitively healthy groups. We also observed patterns of connectivity across risk groups that suggest a nonlinear relationship of change, such that the FH+ group showed increased connectivity compared to the FH- and AD groups (CH FH+ > CH FH- > aMCI > AD). This pattern emerged primarily in connectivity between the precuneus and frontal regions.

CONCLUSION

These results add to a growing literature that suggests compensatory brain function in otherwise cognitively healthy individuals with a family history of AD.

Parental History of Dementia Is Associated with Increased Small Vessel Cerebrovascular Disease

BACKGROUND

Small vessel cerebrovascular dysfunction that manifests on magnetic resonance imaging (MRI) as white matter hyperintensities (WMH) is linked to increased risk and progression of Alzheimer's disease (AD), but there is considerable debate about whether it represents a core feature of the disease. Parental history of dementia is a risk factor for AD, suggesting a strong heritable component; the examination of the extent to which parental history of dementia is associated with cerebrovascular disease could provide insight into the aggregation of AD and cerebrovascular disease.

METHODS

This study included 481 community-dwelling older adults (mean age = 74.07 ± 5.81; 56% women) with available MRI scans. Participants were classified as having a parental history of dementia or having no parental history based on self-report. Total WMH values were calculated and compared between the two groups with general linear models, adjusting for relevant covariates. We also compared WMH volume between those with a reported sibling history of dementia and those without.

RESULTS

One hundred twelve participants reported having a parental history of dementia and 369 reported no parental history. Those with parental history had greater total WMH volume than those without (F = 4.17, p = .042, partial η 2 = 0.009). Results were strongest for those with maternal versus paternal history (F = 2.43, p = .089, partial η 2 = 0.010 vs <0.001) and among Hispanic (F = 5.57, p = .020, partial η 2 = 0.038) and non-Hispanic White participants (F = 4.17, p = .042, partial η 2 = 0.009). Those with reported sibling history of dementia did not differ from those without.

CONCLUSIONS

Older adults with parental, particularly maternal, history of dementia have increased WMH. The results highlight the possibility that cerebrovascular changes are a core feature of AD, as WMH severity and parental history aggregate together.

The effect of physical activity on cognition relative to APOE genotype (PAAD-2): study protocol for a phase II randomized control trial

BACKGROUND

By 2050, the prevalence of Alzheimer's disease (AD) in the United States is predicted to reach 13.8 million. Despite worldwide research efforts, a cure for AD has not been identified. Thus, it is critical to identify preventive strategies that can reduce the risk of or delay the onset of AD. Physical activity (PA) has potential in this regard. This randomized clinical trial aims to (a) test the causal relationship between PA and AD-associated cognitive function for persons with a family history of AD (FH+), (b) determine the moderating role of apolipoprotein epsilon 4 (APOE4) carrier status on cognition, and (c) assess cerebral structure, cerebral function, and putative biomarkers as mediators of the effects of PA on cognition.

METHODS

We are recruiting cognitively normal, middle aged (40-65 years) sedentary adults with FH+. Participants are randomly assigned to a 12-month PA intervention for 3 days/week or to a control group maintaining their normal lifestyle. Saliva samples are taken at pre-test to determine APOE genotype. At pre-, mid-, and post-tests, participants complete a series of cognitive tests to assess information-processing speed, verbal and visual episodic memory, constructional praxis, mnemonic discrimination, and higher-order executive functions. At pre- and post-tests, brain imaging and blood biomarkers are assessed.

DISCUSSION

We hypothesize that 1) the PA group will demonstrate improved cognition compared with controls; 2) PA-derived cognitive changes will be moderated by APOE4 status; and 3) PA-induced changes in neural and blood biomarkers will contribute to cognitive changes and differ as a function of APOE4 status. Our results may provide important insights into the potential of PA to preserve neurocognitive function in people with a heightened risk of AD due to FH+ and as moderated by APOE4 status. By using sophisticated analytic techniques to assess APOE as a moderator and neurobiological mechanisms as mediators across trajectories of cognitive change in response to PA, we will advance our understanding of the potential of PA in protecting against AD.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03876314. Registered March 15, 2019.

Sex, amyloid, and APOE ε4 and risk of cognitive decline in preclinical Alzheimer's disease: Findings from three well-characterized cohorts

INTRODUCTION

Our objective was to investigate the effect of sex on cognitive decline within the context of amyloid β (Aβ) burden and apolipoprotein E genotype.

METHODS

We analyzed sex-specific effects on Aβ-positron emission tomography, apolipoprotein, and rates of change on the Preclinical Alzheimer Cognitive Composite-5 across three cohorts, such as the Alzheimer's Disease Neuroimaging Initiative, Australian Imaging, Biomarker and Lifestyle, and Harvard Aging Brain Study (n = 755; clinical dementia rating = 0; age (standard deviation) = 73.6 (6.5); female = 55%). Mixed-effects models of cognitive change by sex, Aβ-positron emission tomography, and apolipoprotein ε4 were examined with quadratic time effects over a median of 4 years of follow-up.

RESULTS

Apolipoprotein ε4 prevalence and Aβ burden did not differ by sex. Sex did not directly influence cognitive decline. Females with higher Aβ exhibited faster decline than males. Post hoc contrasts suggested that females who were Aβ and apolipoprotein ε4 positive declined faster than their male counterparts.

DISCUSSION

Although Aβ did not differ by sex, cognitive decline was greater in females with higher Aβ. Our findings suggest that sex may play a modifying role on risk of Alzheimer's disease-related cognitive decline.

Threshold regression to accommodate a censored covariate

In several common study designs, regression modeling is complicated by the presence of censored covariates. Examples of such covariates include maternal age of onset of dementia that may be right censored in an Alzheimer's amyloid imaging study of healthy subjects, metabolite measurements that are subject to limit of detection censoring in a case-control study of cardiovascular disease, and progressive biomarkers whose baseline values are of interest, but are measured post-baseline in longitudinal neuropsychological studies of Alzheimer's disease. We propose threshold regression approaches for linear regression models with a covariate that is subject to random censoring. Threshold regression methods allow for immediate testing of the significance of the effect of a censored covariate. In addition, they provide for unbiased estimation of the regression coefficient of the censored covariate. We derive the asymptotic properties of the resulting estimators under mild regularity conditions. Simulations demonstrate that the proposed estimators have good finite-sample performance, and often offer improved efficiency over existing methods. We also derive a principled method for selection of the threshold. We illustrate the approach in application to an Alzheimer's disease study that investigated brain amyloid levels in older individuals, as measured through positron emission tomography scans, as a function of maternal age of dementia onset, with adjustment for other covariates. We have developed an R package, censCov, for implementation of our method, available at CRAN.

Parental family history of dementia in relation to subclinical brain disease and dementia risk

Objective:

To determine the association of parental family history with risk of dementia by age at onset and sex of affected parent in a population-based cohort.

Methods:

From 2000 to 2002, we assessed parental history of dementia in participants without dementia of the Rotterdam Study. We investigated associations of parental history with risk of dementia until 2015, adjusting for demographics, cardiovascular risk factors, and known genetic risk variants. Furthermore, we determined the association between parental history and markers of neurodegeneration and vascular disease on MRI.

Results:

Of 2,087 participants (mean age 64 years, 55% female), 407 (19.6%) reported a history of dementia in either parent (mean age at diagnosis 79 years). During a mean follow-up of 12.2 years, 142 participants developed dementia. Parental history was associated with risk of dementia independently of known genetic risk factors (hazard ratio [HR] 1.67, 95% confidence interval [CI] 1.12–2.48), in particular when parents were diagnosed at younger age (<80 years: HR 2.58, 95% CI 1.61–4.15; ≥80 years: HR 1.01, 95% CI 0.58–1.77). Accordingly, age at diagnosis in probands was highly correlated with age at diagnosis in their parents <80 years (r = 0.57, p = 0.001) but not thereafter (r = 0.17, p = 0.55). Among 1,161 participants without dementia with brain MRI, parental history was related to lower cerebral perfusion and higher burden of white matter lesions and microbleeds. Dementia risk and MRI markers were similar for paternal and maternal history.

Conclusions:

Parental history of dementia increases risk of dementia, primarily when age at parental diagnosis is <80 years. Unexplained heredity may be attributed in part to cerebral hypoperfusion and small vessel disease. We found no evidence of preferential maternal compared to paternal transmission.

Linear Regression with a Randomly Censored Covariate: Application to an Alzheimer's Study

The association between maternal age of onset of dementia and amyloid deposition (measured by in vivo positron emission tomography (PET) imaging) in cognitively normal older offspring is of interest. In a regression model for amyloid, special methods are required due to the random right censoring of the covariate of maternal age of onset of dementia. Prior literature has proposed methods to address the problem of censoring due to assay limit of detection, but not random censoring. We propose imputation methods and a survival regression method that do not require parametric assumptions about the distribution of the censored covariate. Existing imputation methods address missing covariates, but not right censored covariates. In simulation studies, we compare these methods to the simple, but inefficient complete case analysis, and to thresholding approaches. We apply the methods to the Alzheimer's study.