A pathway linking pulse pressure to dementia in adults with Down syndrome.

Adults with Down syndrome are less likely to have hypertension than neurotypical adults. However, whether blood pressure measures are associated with brain health and clinical outcomes in this population has not been studied in detail. Here, we assessed whether pulse pressure is associated with markers of cerebrovascular disease and is linked to a diagnosis of dementia in adults with Down syndrome via structural imaging markers of cerebrovascular disease and atrophy. The study included participants with Down syndrome from the Alzheimer's Disease - Down Syndrome study (n = 195, age = 50.6 ± 7.2 years, 44% women, 18% diagnosed with dementia). Higher pulse pressure was associated with greater global, parietal and occipital white matter hyperintensity volume but not with enlarged perivascular spaces, microbleeds or infarcts. Using a structural equation model, we found that pulse pressure was associated with greater white matter hyperintensity volume, which in turn was related to increased neurodegeneration, and subsequent dementia diagnosis. Pulse pressure is an important determinant of brain health and clinical outcomes in individuals with Down syndrome despite the low likelihood of frank hypertension.

Cerebrovascular disease emerges with age and Alzheimer's disease in adults with Down syndrome.

Adults with Down syndrome have a genetic form of Alzheimer's disease (AD) and evidence of cerebrovascular disease across the AD continuum, despite few systemic vascular risk factors. The onset and progression of AD in Down syndrome is highly age-dependent, but it is unknown at what age cerebrovascular disease emerges and what factors influence its severity. In the Alzheimer's Biomarker Consortium-Down Syndrome study (ABC-DS; n = 242; age = 25-72), we estimated the age inflection point at which MRI-based white matter hyperintensities (WMH), enlarged perivascular spaces (PVS), microbleeds, and infarcts emerge in relation to demographic data, risk factors, amyloid and tau, and AD diagnosis. Enlarged PVS and infarcts appear to develop in the early 30s, while microbleeds, WMH, amyloid, and tau emerge in the mid to late 30s. Age-residualized WMH were higher in women, in individuals with dementia, and with lower body mass index. Participants with hypertension and APOE-ε4 had higher age-residualized PVS and microbleeds, respectively. Lifespan trajectories demonstrate a dramatic cerebrovascular profile in adults with Down syndrome that appears to evolve developmentally in parallel with AD pathophysiology approximately two decades prior to dementia symptoms.

ANTsX neuroimaging-derived structural phenotypes of UK Biobank.

UK Biobank is a large-scale epidemiological resource for investigating prospective correlations between various lifestyle, environmental, and genetic factors with health and disease progression. In addition to individual subject information obtained through surveys and physical examinations, a comprehensive neuroimaging battery consisting of multiple modalities provides imaging-derived phenotypes (IDPs) that can serve as biomarkers in neuroscience research. In this study, we augment the existing set of UK Biobank neuroimaging structural IDPs, obtained from well-established software libraries such as FSL and FreeSurfer, with related measurements acquired through the Advanced Normalization Tools Ecosystem. This includes previously established cortical and subcortical measurements defined, in part, based on the Desikan-Killiany-Tourville atlas. Also included are morphological measurements from two recent developments: medial temporal lobe parcellation of hippocampal and extra-hippocampal regions in addition to cerebellum parcellation and thickness based on the Schmahmann anatomical labeling. Through predictive modeling, we assess the clinical utility of these IDP measurements, individually and in combination, using commonly studied phenotypic correlates including age, fluid intelligence, numeric memory, and several other sociodemographic variables. The predictive accuracy of these IDP-based models, in terms of root-mean-squared-error or area-under-the-curve for continuous and categorical variables, respectively, provides comparative insights between software libraries as well as potential clinical interpretability. Results demonstrate varied performance between package-based IDP sets and their combination, emphasizing the need for careful consideration in their selection and utilization.

Cerebrovascular pathology mediates associations between hypoxemia during rapid eye movement sleep and medial temporal lobe structure and function in older adults.

Obstructive sleep apnea (OSA) is common in older adults and is associated with medial temporal lobe (MTL) degeneration and memory decline in aging and Alzheimer's disease (AD). However, the underlying mechanisms linking OSA to MTL degeneration and impaired memory remains unclear. By combining magnetic resonance imaging (MRI) assessments of cerebrovascular pathology and MTL structure with clinical polysomnography and assessment of overnight emotional memory retention in older adults at risk for AD, cerebrovascular pathology in fronto-parietal brain regions was shown to statistically mediate the relationship between OSA-related hypoxemia, particularly during rapid eye movement (REM) sleep, and entorhinal cortical thickness. Reduced entorhinal cortical thickness was, in turn, associated with impaired overnight retention in mnemonic discrimination ability across emotional valences for high similarity lures. These findings identify cerebrovascular pathology as a contributing mechanism linking hypoxemia to MTL degeneration and impaired sleep-dependent memory in older adults.

Cerebrovascular disease drives Alzheimer plasma biomarker concentrations in adults with Down syndrome.

Importance: By age 40 years over 90% of adults with Down syndrome (DS) have Alzheimer's disease (AD) pathology and most progress to dementia. Despite having few systemic vascular risk factors, individuals with DS have elevated cerebrovascular disease (CVD) markers that track with the clinical progression of AD, suggesting a role for CVD that is hypothesized to be mediated by inflammatory factors. Objective: To examine the pathways through which small vessel CVD contributes to AD-related pathophysiology and neurodegeneration in adults with DS. Design: Cross sectional analysis of neuroimaging, plasma, and clinical data. Setting: Participants were enrolled in Alzheimer's Biomarker Consortium - Down Syndrome (ABC-DS), a multisite study of AD in adults with DS. Participants: One hundred eighty-five participants (mean [SD] age=45.2 [9.3] years) with available MRI and plasma biomarker data were included. White matter hyperintensity (WMH) volumes were derived from T2-weighted FLAIR MRI scans and plasma biomarker concentrations of amyloid beta (Aß42/Aß40), phosphorylated tau (p-tau217), astrocytosis (glial fibrillary acidic protein, GFAP), and neurodegeneration (neurofilament light chain, NfL) were measured with ultrasensitive immunoassays. Main Outcomes and Measures: We examined the bivariate relationships of WMH, Aß42/Aß40, p-tau217, and GFAP with age-residualized NfL across AD diagnostic groups. A series of mediation and path analyses examined causal pathways linking WMH and AD pathophysiology to promote neurodegeneration in the total sample and groups stratified by clinical diagnosis. Results: There was a direct and indirect bidirectional effect through GFAP of WMH on p-tau217 concentration, which was associated with NfL concentration in the entire sample. Among cognitively stable participants, WMH was directly and indirectly, through GFAP, associated with p-tau217 concentration, and in those with MCI, there was a direct effect of WMH on p-tau217 and NfL concentrations. There were no associations of WMH with biomarker concentrations among those diagnosed with dementia. Conclusions and Relevance: The findings suggest that among individuals with DS, CVD promotes neurodegeneration by increasing astrocytosis and tau pathophysiology in the presymptomatic phases of AD. This work joins an emerging literature that implicates CVD and its interface with neuroinflammation as a core pathological feature of AD in adults with DS.

ANTsX neuroimaging-derived structural phenotypes of UK Biobank.

UK Biobank is a large-scale epidemiological resource for investigating prospective correlations between various lifestyle, environmental, and genetic factors with health and disease progression. In addition to individual subject information obtained through surveys and physical examinations, a comprehensive neuroimaging battery consisting of multiple modalities provides imaging-derived phenotypes (IDPs) that can serve as biomarkers in neuroscience research. In this study, we augment the existing set of UK Biobank neuroimaging structural IDPs, obtained from well-established software libraries such as FSL and FreeSurfer, with related measurements acquired through the Advanced Normalization Tools Ecosystem. This includes previously established cortical and subcortical measurements defined, in part, based on the Desikan-Killiany-Tourville atlas. Also included are morphological measurements from two recent developments: medial temporal lobe parcellation of hippocampal and extra-hippocampal regions in addition to cerebellum parcellation and thickness based on the Schmahmann anatomical labeling. Through predictive modeling, we assess the clinical utility of these IDP measurements, individually and in combination, using commonly studied phenotypic correlates including age, fluid intelligence, numeric memory, and several other sociodemographic variables. The predictive accuracy of these IDP-based models, in terms of root-mean-squared-error or area-under-the-curve for continuous and categorical variables, respectively, provides comparative insights between software libraries as well as potential clinical interpretability. Results demonstrate varied performance between package-based IDP sets and their combination, emphasizing the need for careful consideration in their selection and utilization.

Pathways linking pulse pressure to dementia in adults with Down syndrome.

Individuals with Down syndrome (DS) are less likely to have hypertension than neurotypical adults. However, whether blood pressure measures are associated with brain health and clinical outcomes in this population has not been studied in detail. Here, we assessed whether pulse pressure is associated with markers of cerebrovascular disease, entorhinal cortical atrophy, and diagnosis of dementia in adults with DS. Participants with DS from the Biomarkers of Alzheimer's Disease in Adults with Down Syndrome study (ADDS; n=195, age=50.6±7.2 years, 44% women, 18% diagnosed with dementia) were included. Higher pulse pressure was associated with greater global, parietal, and occipital WMH volume. Pulse pressure was not related to enlarged PVS, microbleeds, infarcts, entorhinal cortical thickness, or dementia diagnosis. However, in a serial mediation model, we found that pulse pressure was indirectly related to dementia diagnosis through parieto-occipital WMH and, subsequently through entorhinal cortical thickness. Higher pulse pressure may be a risk factor for dementia in people with DS by promoting cerebrovascular disease, which in turn affects neurodegeneration. Pulse pressure is an important determinant of brain health and clinical outcomes in individuals with Down syndrome despite the low likelihood of frank hypertension.

Posterior white matter hyperintensities are associated with reduced medial temporal lobe subregional integrity and long-term memory in older adults.

White matter hyperintensities are a marker of small vessel cerebrovascular disease that are strongly related to cognition in older adults. Similarly, medial temporal lobe atrophy is well-documented in aging and Alzheimer's disease and is associated with memory decline. Here, we assessed the relationship between lobar white matter hyperintensities, medial temporal lobe subregional volumes, and hippocampal memory in older adults. We collected MRI scans in a sample of 139 older adults without dementia (88 females, mean age (SD) = 76.95 (10.61)). Participants were administered the Rey Auditory Verbal Learning Test (RAVLT). Regression analyses tested for associations among medial temporal lobe subregional volumes, regional white matter hyperintensities and memory, while adjusting for age, sex, and education and correcting for multiple comparisons. Increased occipital white matter hyperintensities were related to worse RAVLT delayed recall performance, and to reduced CA1, dentate gyrus, perirhinal cortex (Brodmann area 36), and parahippocampal cortex volumes. These medial temporal lobe subregional volumes were related to delayed recall performance. The association of occipital white matter hyperintensities with delayed recall performance was fully mediated statistically only by perirhinal cortex volume. These results suggest that white matter hyperintensities may be associated with memory decline through their impact on medial temporal lobe atrophy. These findings provide new insights into the role of vascular pathologies in memory loss in older adults and suggest that future studies should further examine the neural mechanisms of these relationships in longitudinal samples.

Brain Aging Among Racially and Ethnically Diverse Middle-Aged and Older Adults.

Importance: Neuroimaging studies have documented racial and ethnic disparities in brain health in old age. It remains unclear whether these disparities are apparent in midlife. Objective: To assess racial and ethnic disparities in magnetic resonance imaging (MRI) markers of cerebrovascular disease and neurodegeneration in midlife and late life. Design, Setting, and Participants: Data from 2 community-based cohort studies, Washington Heights-Inwood Columbia Aging Project (WHICAP) and the Offspring Study of Racial and Ethnic Disparities in Alzheimer Disease (Offspring), were used. Enrollment took place from March 2011 and June 2017, in WHICAP and Offspring, respectively, to January 2021. Of the 822 Offspring and 1254 WHICAP participants approached for MRI scanning, 285 and 176 refused participation in MRI scanning, 36 and 76 were excluded for contraindications/ineligibility, and 4 and 32 were excluded for missing key variables, respectively. Main Outcomes and Measures: Cortical thickness in Alzheimer disease-related regions, white matter hyperintensity (WMH) volume. Results: The final sample included 1467 participants. Offspring participants (497 [33.9%]) had a mean (SD) age of 55 (10.7) years, had a mean (SD) of 13 (3.5) years of education, and included 117 Black individuals (23.5%), 348 Latinx individuals (70%), 32 White individuals (6.4%), and 324 women (65.2%). WHICAP participants (970 [66.1%]) had a mean (SD) age of 75 (6.5) years, had a mean (SD) of 12 (4.7) years of education, and included 338 Black individuals (34.8%), 389 Latinx individuals (40.1%), 243 White individuals (25.1%), and 589 women (65.2%). Racial and ethnic disparities in cerebrovascular disease were observed in both midlife (Black-White: B = 0.357; 95% CI, 0.708-0.007; P = .046) and late life (Black-Latinx: B = 0.149, 95% CI, 0.068-0.231; P < .001; Black-White: B = 0.166; 95% CI, 0.254-0.077; P < .001), while disparities in cortical thickness were evident in late life only (Black-Latinx: B = -0.037; 95% CI, -0.055 to -0.019; P < .001; Black-White: B = -0.064; 95% CI -0.044 to -0.084; P < .001). Overall, Black-White disparities were larger than Latinx-White disparities for cortical thickness and WMH volume. Brain aging, or the association of age with MRI measures, was greater in late life compared with midlife for Latinx (cortical thickness: B = 0.006; 95% CI, 0.004-0.008; P < .001; WMH volume: B = -0.010; 95% CI, -0.018 to -0.001; P = .03) and White (cortical thickness: B = 0.005; 95% CI, 0.002-0.008; P = .001; WMH volume: B = -0.021; 95% CI -0.043 to 0.002; P = .07) participants but not Black participants (cortical thickness: B = 0.001; 95% CI, -0.002 to 0.004; P =.64; WMH volume: B = 0.003; 95% CI, -0.010 to 0.017; P = .61), who evidenced a similarly strong association between age and MRI measures in midlife and late life. Conclusions and Relevance: In this study, racial and ethnic disparities in small vessel cerebrovascular disease were apparent in midlife. In Latinx and White adults, brain aging was more pronounced in late life than midlife, whereas Black adults showed accelerated pattern of brain aging beginning in midlife.

Entorhinal-Hippocampal Circuit Integrity Is Related to Mnemonic Discrimination and Amyloid-ß Pathology in Older Adults.

Mnemonic discrimination, a cognitive process that relies on hippocampal pattern separation, is one of the first memory domains to decline in aging and preclinical Alzheimer's disease. We tested whether functional connectivity (FC) within the entorhinal-hippocampal circuit, measured with high-resolution resting state fMRI, is associated with mnemonic discrimination and amyloid-ß (Aß) pathology in a sample of 64 cognitively normal human older adults (mean age, 71.3 ± 6.4 years; 67% female). FC was measured between entorhinal-hippocampal circuit nodes with known anatomical connectivity, as well as within cortical memory networks. Aß pathology was measured with 18F-florbetapir-PET, and neurodegeneration was assessed with subregional volume from structural MRI. Participants performed both object and spatial versions of a mnemonic discrimination task outside of the scanner and were classified into low-performing and high-performing groups on each task using a median split. Low object mnemonic discrimination performance was specifically associated with increased FC between anterolateral entorhinal cortex (alEC) and dentate gyrus (DG)/CA3, supporting the importance of this connection to object memory. This hyperconnectivity between alEC and DG/CA3 was related to Aß pathology and decreased entorhinal cortex volume. In contrast, spatial mnemonic discrimination was not associated with altered FC. Aß was further associated with dysfunction within hippocampal subfields, particularly with decreased FC between CA1 and subiculum as well as reduced volume in these regions. Our findings suggest that Aß may indirectly lead to memory impairment through entorhinal-hippocampal circuit dysfunction and neurodegeneration and provide a mechanism for increased vulnerability of object mnemonic discrimination.SIGNIFICANCE STATEMENT Mnemonic discrimination is a critical episodic memory process that is performed in the dentate gyrus (DG) and CA3 subfield of the hippocampus, relying on input from entorhinal cortex. Mnemonic discrimination is particularly vulnerable to decline in older adults; however, the mechanisms behind this vulnerability are still unknown. We demonstrate that object mnemonic discrimination impairment is related to hyperconnectivity between the anterolateral entorhinal cortex and DG/CA3. This hyperconnectivity was associated with amyloid-ß pathology and neurodegeneration in entorhinal cortex, suggesting aberrantly increased network activity is a pathological process. Our findings provide a mechanistic explanation of the vulnerability of object compared to spatial mnemonic discrimination in older adults and has translational implications for choice of outcome measures in clinical trials for Alzheimer's disease.

Probing the proteome to explore potential correlates of increased Alzheimer's-related cerebrovascular disease in adults with Down syndrome.

Cerebrovascular disease is associated with symptoms and pathogenesis of Alzheimer's disease (AD) among adults with Down syndrome (DS). The cause of increased dementia-related cerebrovascular disease in DS is unknown. We explored whether protein markers of neuroinflammation are associated with markers of cerebrovascular disease among adults with DS. Participants from the Alzheimer's disease in Down syndrome (ADDS) study with magnetic resonance imaging (MRI) scans and blood biomarker data were included. Support vector machine (SVM) analyses examined the relationship of blood-based proteomic biomarkers with MRI-defined cerebrovascular disease among participants characterized as having cognitive decline (n = 36, mean age ± SD = 53 ± 6.2) and as being cognitively stable (n = 78, mean age = 49 ± 6.4). Inflammatory and AD markers were associated with cerebrovascular disease, particularly among symptomatic individuals. The pattern suggested relatively greater inflammatory involvement among cognitively stable individuals and greater AD involvement among those with cognitively decline. The findings help to generate hypotheses that both inflammatory and AD markers are implicated in cerebrovascular disease among those with DS and point to potential mechanistic pathways for further examination.

Association of Regional White Matter Hyperintensities With Longitudinal Alzheimer-Like Pattern of Neurodegeneration in Older Adults.

Importance: Small vessel cerebrovascular disease, visualized as white matter hyperintensities (WMH), is associated with cognitive decline and risk of clinical Alzheimer disease (AD). One way in which small vessel cerebrovascular disease could contribute to AD is through the promotion of neurodegeneration; the effect of small vessel cerebrovascular disease on neurodegeneration may differ across racial and ethnic groups. Objective: To examine whether WMH volume is associated with cortical thinning over time and subsequent memory functioning and whether the association between WMH volume and cortical thinning differs among racial and ethnic groups. Design, Setting, and Participants: This longitudinal community-based cohort study included older adults from northern Manhattan who were participants in the Washington Heights-Inwood Columbia Aging Project. Participants underwent two 3T magnetic resonance imaging (MRI) scans a mean of 4 years apart. Data were collected from March 2011 to January 2020. Exposures: Total and regional WMH volumes. Main Outcomes and Measures: The association of total and regional WMH volumes with cortical thinning over time was tested using general linear models in a vertexwise analysis. Cortical thinning was measured vertexwise by symmetrized percent change between 2 time points. The association of changes in cortical thickness with memory and whether this association differed by race and ethnicity was also analyzed. Delayed memory was a secondary outcome. Results: In 303 participants (mean [SD] age, 73.16 [5.19] years, 181 [60%] women, 96 [32%] non-Hispanic White, 113 [37%] Non-Hispanic Black, 94 [31%] Hispanic), baseline WMH volumes were associated with cortical thinning in medial temporal and frontal/parietal regions. Specifically, total WMH volume was associated with cortical thinning in the right caudal middle frontal cortex (P = .001) and paracentral cortex (P = .04), whereas parietal WMH volume was associated with atrophy in the left entorhinal cortex (P = .03) and right rostral middle frontal (P < .001), paracentral (P < .001), and pars triangularis (P = .02) cortices. Thinning of the right caudal middle frontal and left entorhinal cortices was related to lower scores on a memory test administered closest to the second MRI visit (right caudal middle frontal cortex: standardized ß = 0.129; unstandardized b = 0.335; 95% CI, 0.055 to 0.616; P = .01; left entorhinal cortex: ß = 0.119; b = 0.290; 95% CI, 0.018 to 0.563; P = .03). The association of total WMH with thinning in the right caudal middle frontal and right paracentral cortex was greater in non-Hispanic Black participants compared with White participants (right caudal middle frontal cortex: ß = -0.222; b = -0.059; 95% CI, -0.114 to -0.004; P = .03; right paracentral cortex: ß = -0.346; b = -0.155; 95% CI, -0.244 to -0.066; P = .001). The association of parietal WMH with cortical thinning of the right rostral middle frontal, right pars triangularis, and right paracentral cortices was also stronger among non-Hispanic Black participants compared with White participants (right rostral middle frontal cortex: ß = -0.252; b = -0.202; 95% CI, -0.349 to -0.055; P = .007; right pars triangularis cortex: ß = -0.327; b = -0.253; 95% CI, -0.393 to -0.113; P < .001; right paracentral cortex: ß = -0.263; b = -0.337; 95% CI, -0.567 to -0.107; P = .004). Conclusions and Relevance: In this study, small vessel cerebrovascular disease, operationalized as WMH, was associated with subsequent cortical atrophy in regions that overlap with typical AD neurodegeneration patterns, particularly among non-Hispanic Black older adults. Cerebrovascular disease may affect risk and progression of AD by promoting neurodegeneration and subsequent memory decline.

Anterolateral entorhinal cortex volume is associated with memory retention in clinically unimpaired older adults.

The entorhinal cortex is subdivided into anterolateral entorhinal cortex (alERC) and posteromedial entorhinal cortex (pmERC) subregions, which are theorized to support distinct cognitive roles. This distinction is particularly important as the alERC is one of the earliest cortical regions affected by Alzheimer's pathology and related neurodegeneration. The relative associations of alERC/pmERC with neuropsychological test performance have not been examined. We examined how alERC/pmERC volumes differentially relate to performance on 1) the Modified Rey Auditory Learning Test (ModRey), a verbal memory test designed to assess normal/preclinical populations, 2) the Montreal Cognitive Assessment (MoCA), and 3) the National Alzheimer's Coordinating Center neuropsychological battery. We also examined whether alERC/pmERC volumes correlate with Alzheimer's disease cerebrospinal fluid (CSF) biomarkers. In 65 cognitively healthy (CDR = 0) older adults, alERC, but not pmERC, volume was associated with ModRey memory retention. Only alERC volume differentiated between participants who scored above and below the MoCA cutoff score for impairment. Evaluating the MoCA subdomains revealed that alERC was particularly associated with verbal recall. On the National Alzheimer's Coordinating Center battery, both alERC and pmERC volumes were associated with Craft story recall and Benson figure copy, but only alERC volume was associated with Craft story retention and semantic fluency. Neither alERC nor pmERC volume correlated with CSF levels of amyloid or tau, and regression analyses showed that alERC volume and CSF amyloid levels were independently associated with ModRey retention performance. Taken together, these results suggest that the alERC is important for memory performance and that alERC volume differences are related to a pattern of neuropsychological test performance (i.e., impairments in episodic memory and semantic fluency) typically seen in clinical Alzheimer's disease.

Alzheimer-Related Cerebrovascular Disease in Down Syndrome.

OBJECTIVE: Adults with Down syndrome (DS) develop Alzheimer disease (AD) pathology by their 5th decade. Compared with the general population, traditional vascular risks in adults with DS are rare, allowing examination of cerebrovascular disease in this population and insight into its role in AD without the confound of vascular risk factors. We examined in vivo magnetic resonance imaging (MRI)-based biomarkers of cerebrovascular pathology in adults with DS, and determined their cross-sectional relationship with age, beta-amyloid pathology, and mild cognitive impairment or clinical AD diagnostic status. METHODS: Participants from the Biomarkers of Alzheimer's Disease in Down Syndrome study (n = 138, 50 ± 7 years, 39% women) with MRI data and a subset (n = 90) with amyloid positron emission tomography (PET) were included. We derived MRI-based biomarkers of cerebrovascular pathology, including white matter hyperintensities (WMH), infarcts, cerebral microbleeds, and enlarged perivascular spaces (PVS), as well as PET-based biomarkers of amyloid burden. Participants were characterized as cognitively stable (CS), mild cognitive impairment-DS (MCI-DS), possible AD dementia, or definite AD dementia based on in-depth assessments of cognition, function, and health status. RESULTS: There were detectable WMH, enlarged PVS, infarcts, and microbleeds as early as the 5th decade of life. There was a monotonic increase in WMH volume, enlarged PVS, and presence of infarcts across diagnostic groups (CS < MCI-DS < possible AD dementia < definite AD dementia). Higher amyloid burden was associated with a higher likelihood of an infarct. INTERPRETATION: The findings highlight the prevalence of cerebrovascular disease in adults with DS and add to a growing body of evidence that implicates cerebrovascular disease as a core feature of AD and not simply a comorbidity. ANN NEUROL 2020;88:1165-1177.

White matter hyperintensities mediate the association of nocturnal blood pressure with cognition.

OBJECTIVE: To test the hypotheses that hypertension and nocturnal blood pressure are related to white matter hyperintensity (WMH) volume, an MRI marker of small vessel cerebrovascular disease, and that WMH burden statistically mediates the association of hypertension and dipping status with memory functioning, we examined the relationship of hypertension and dipping status on WMH volume and neuropsychological test scores in middle-aged and older adults. METHODS: Participants from the community-based Maracaibo Aging Study received ambulatory 24-hour blood pressure monitoring, structural MRI, and neuropsychological assessment. Four hundred thirty-five participants (mean ± SD age 59 ± 13 years, 71% women) with available ambulatory blood pressure, MRI, and neuropsychological data were included in the analyses. Ambulatory blood pressure was used to define hypertension and dipping status (i.e., dipper, nondipper, and reverse dipper based on night/day blood pressure ratio <0.9, 0.9-1, and >1, respectively). Outcome measures included regional WMH and memory functioning derived from a neuropsychological test battery. RESULTS: The majority of the participants (59%) were hypertensive. Ten percent were reverse dippers, and 40% were nondippers. Reverse dipping in the presence of hypertension was associated with particularly elevated periventricular WMH volume (F 2,423 = 3.78, p = 0.024) and with lowered memory scores (F 2,423 = 3.911, p = 0.021). Periventricular WMH volume mediated the effect of dipping status and hypertension on memory (ß = -4.1, 95% confidence interval -8.7 to -0.2, p < 0.05). CONCLUSION: Reverse dipping in the presence of hypertension is associated with small vessel cerebrovascular disease, which, in turn, mediates memory functioning. These results point toward reverse dipping as a marker of poor nocturnal blood pressure control, particularly among hypertensive individuals, with potentially pernicious effects on cerebrovascular health and associated cognitive function.

Structural Brain Changes in Pre-Clinical FTD MAPT Mutation Carriers.

BACKGROUND: Frontotemporal dementia (FTD) is the second most common cause of early-onset neurodegenerative dementia. Several studies have focused on early imaging changes in FTD patients, but once subjects meet full criteria for FTD diagnosis, structural changes are generally widespread. OBJECTIVE: This study aims to determine the earliest structural brain changes in asymptomatic MAPT MUTATION carriers. METHODS: This is a cross-sectional multicenter study comparing global and regional brain volume and white matter integrity in a group of MAPT mutation preclinical carriers and controls. Participants belong to multiple generations of six families with five MAPT mutations. All participants underwent a medical examination, neuropsychological tests, genetic analysis, and a magnetic resonance scan (3T, scout, T1-weighted image followed by EPI (BOLD), MPRAGE, DTI, FLAIR, and ASL sequences). RESULTS: Volumes of five cortical and subcortical areas were strongly correlated with mutation status: temporal lobe (left amygdala, left temporal pole), cingulate cortex (left rostral anterior cingulate gyrus, right posterior cingulate), and the lingual gyrus in the occipital lobe. We did not find significant differences in whole brain volume, white matter hyperintensities volume, and white matter integrity using DTI analysis. CONCLUSION: Temporal lobe, cingulate cortex and the lingual gyrus seem to be early targets of the disease and may serve as biomarkers for FTD prior to overt symptom onset.

Tract-defined regional white matter hyperintensities and memory.

White matter hyperintensities (WMH) are common radiological findings among older adults and strong predictors of age-related cognitive decline. Recent work has implicated WMH in the pathogenesis and symptom presentation of Alzheimer's disease (AD), which is characterized clinically primarily by a deficit in memory. The severity of WMH volume is typically quantified globally or by lobe, whereas white matter itself is organized by tracts and fiber classes. We derived WMH volumes within white matter tract classes, including association, projection, and commissural tracts, in 519 older adults and tested whether WMH volume within specific fiber classes is related to memory performance. We found that increased association and projection tract defined WMH volumes were related to worse memory function but not to a global cognition summary score that excluded memory. We conclude that macrostructural damage to association and projection tracts, manifesting as WMH, may result in memory decline among older adults.

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.