Plasma trimethylamine N-oxide (TMAO): associations with cognition, neuroimaging, and dementia.

BACKGROUND: The gut-derived metabolite Trimethylamine N-oxide (TMAO) and its precursors - betaine, carnitine, choline, and deoxycarnitine - have been associated with an increased risk of cardiovascular disease, but their relation to cognition, neuroimaging markers, and dementia remains uncertain. METHODS: In the population-based Rotterdam Study, we used multivariable regression models to study the associations between plasma TMAO, its precursors, and cognition in 3,143 participants. Subsequently, we examined their link to structural brain MRI markers in 2,047 participants, with a partial validation in the Leiden Longevity Study (n = 318). Among 2,517 participants, we assessed the risk of incident dementia using multivariable Cox proportional hazard models. Following this, we stratified the longitudinal associations by medication use and sex, after which we conducted a sensitivity analysis for individuals with impaired renal function. RESULTS: Overall, plasma TMAO was not associated with cognition, neuroimaging markers or incident dementia. Instead, higher plasma choline was significantly associated with poor cognition (adjusted mean difference: -0.170 [95% confidence interval (CI) -0.297;-0.043]), brain atrophy and more markers of cerebral small vessel disease, such as white matter hyperintensity volume (0.237 [95% CI: 0.076;0.397]). By contrast, higher carnitine concurred with lower white matter hyperintensity volume (-0.177 [95% CI: -0.343;-0.010]). Only among individuals with impaired renal function, TMAO appeared to increase risk of dementia (hazard ratio (HR): 1.73 [95% CI: 1.16;2.60]). No notable differences were observed in stratified analyses. CONCLUSIONS: Plasma choline, as opposed to TMAO, was found to be associated with cognitive decline, brain atrophy, and markers of cerebral small vessel disease. These findings illustrate the complexity of relationships between TMAO and its precursors, and emphasize the need for concurrent study to elucidate gut-brain mechanisms.

Sex-differences in the association of social health and marital status with blood-based immune and neurodegeneration markers in a cohort of community-dwelling older adults.

BACKGROUND: The immune system has been proposed to play a role in the link between social health and all-cause dementia risk. We explored cross-sectional and longitudinal associations between social health, immune system balance and plasma neurodegeneration markers in community-dwelling older adults, and explored whether the balance between innate and adaptive immunity mediates associations between social health and both cognition and total brain volume. METHODS: Social health markers (social support, marital status, loneliness) were measured in the Rotterdam Study between 2002-2008. Immune system cell counts and balance were assessed repeatedly from 2002 to 2016 using white blood-cell-based indices and individual counts (granulocyte-to-lymphocyte ratio (GLR), platelet-to-lymphocyte ratio (PLR), and systemic immune-inflammation index (SII)). Plasma neurodegeneration biomarkers (amyloid-ß40, amyloid-ß42, total tau and neurofilament light chain) were measured once from blood samples collected between 2002-2008. Global cognitive function and total brain volume (MRI) were measured at the follow-up visit between 2009-2014. We used linear mixed models to study longitudinal associations and performed causal mediation analyses. RESULTS: In 8374 adults (mean age 65.7, 57 % female), never married participants (n = 394) had higher GLR, PLR and SII compared to married peers at baseline and during follow-up, indicating imbalance towards innate immunity. Being never married was associated with higher plasma amyloid-ß40, and being widowed or divorced with higher plasma total tau levels at baseline. Widowed or divorced males, but not females, had higher GLR, PLR and SII at baseline. Higher social support was associated with lower PLR in females, but higher PLR in males. Loneliness was not associated with any of the immune system balance ratios. Never married males had higher levels of all plasma neurodegeneration markers at baseline. Immune system balance did not mediate associations between social health and cognition or total brain volume, but does interact with marital status. CONCLUSION: This study indicates that marital status is associated with blood-based immune system markers toward innate immunity and higher levels of plasma neurodegeneration markers. This is particularly evident for never married or previously married male older adults compared to married or female peers.

Nonalcoholic fatty liver disease, liver fibrosis, and structural brain imaging: The Cross-Cohort Collaboration.

BACKGROUND AND PURPOSE: Prior studies reported conflicting findings regarding the association of nonalcoholic fatty liver disease (NAFLD) and liver fibrosis with measures of brain health. We examined whether NAFLD and liver fibrosis are associated with structural brain imaging measures in middle- and old-age adults. METHODS: In this cross-sectional study among dementia- and stroke-free individuals, data were pooled from the Offspring and Third Generation cohorts of the Framingham Heart Study (FHS), the Rotterdam Study (RS), and the Study of Health in Pomerania. NAFLD was assessed through abdominal imaging. Transient hepatic elastography (FibroScan) was used to assess liver fibrosis in FHS and RS. Linear regression models were used to explore the relation of NAFLD and liver fibrosis with brain volumes, including total brain, gray matter, hippocampus, and white matter hyperintensities, adjusting for potential confounders. Results were combined using fixed effects meta-analysis. RESULTS: In total, 5660 and 3022 individuals were included for NAFLD and liver fibrosis analyses, respectively. NAFLD was associated with smaller volumes of total brain (ß = -3.5, 95% confidence interval [CI] = -5.4 to -1.7), total gray matter (ß = -1.9, 95% CI = -3.4 to -0.3), and total cortical gray matter (ß = -1.9, 95% CI = -3.7 to -0.01). In addition, liver fibrosis (defined as liver stiffness measure ≥8.2 kPa) was related to smaller total brain volumes (ß = -7.3, 95% CI = -11.1 to -3.5). Heterogeneity between studies was low. CONCLUSIONS: NAFLD and liver fibrosis may be directly related to brain aging. Larger and prospective studies are warranted to validate these findings and identify liver-related preventive strategies for neurodegeneration.

Serum immunoglobulins and biomarkers of dementia: a population-based study.

BACKGROUND: Inflammation plays a key role in the development of dementia, but its link to early biomarkers, particularly those in plasma or neuroimaging, remains elusive. This study aimed to investigate the association between serum immunoglobulins and biomarkers of dementia. METHODS: Between 1997 and 2009, serum immunoglobulins (IgA, IgG and IgM) were measured in dementia-free participants of the population-based Rotterdam Study. A random subset of participants had assessment of biomarkers in plasma (total tau (t-tau), neurofilament light chain (NfL), amyloid-ß40 (Aß-40), amyloid-ß42 (Aß-42), while another subset of participants underwent neuroimaging to quantify brain volume, white matter structural integrity and markers of cerebral small vessel disease. Linear regression models were constructed to determine cross-sectional associations between IgA, IgG, IgM and biomarkers of dementia, with adjustment for potential confounders. Multiple testing correction was applied using the false discovery rate. As a sensitivity analysis, we re-ran the models for participants within the reference range of immunoglobulins, excluding those using immunomodulating drugs, and conducted a stratified analysis by APOE-ε4 carriership and sex. RESULTS: Of 8,768 participants with serum immunoglobulins, 3,455 participants (65.8 years [interquartile range (IQR): 61.5-72.0], 57.2% female) had plasma biomarkers available and 3,139 participants (57.4 years [IQR: 52.7-60.7], 54.4% female) had neuroimaging data. Overall, no associations between serum immunoglobulins and biomarkers of dementia remained significant after correction for multiple testing. However, several suggestive associations were noted: higher serum IgA levels concurred with lower plasma levels of Aß-42 (standardized adjusted mean difference: -0.015 [95% confidence interval (CI): -0.029--0.002], p = 2.8 × 10-2), and a lower total brain volume, mainly driven by less gray matter (-0.027 [-0.046--0.008], p = 6.0 × 10-3) and more white matter hyperintensities (0.047 [0.016 - 0.077], p = 3.0 × 10-3). In sensitivity analyses, higher IgM was linked to lower t-tau, Aß-40, and Aß-42, but also a loss of white matter microstructural integrity. Stratified analyses indicate that these associations potentially differ between carriers and non-carriers of the APOE-ε4 allele and men and women. CONCLUSIONS: While associations between serum immunoglobulins and early markers of dementia could not be established in this population-based sample, it may be valuable to consider factors such as APOE-ε4 allele carriership and sex in future investigations.

Diagnostic challenge of Creutzfeldt-Jakob disease in a patient with multimorbidity: a case-report.

BACKGROUND: Creutzfeldt-Jakob disease (CJD) is a rapidly progressive and ultimately fatal neurodegenerative condition caused by prions. The clinical symptoms of CJD vary with its subtype, and may include dementia, visual hallucinations, myoclonus, ataxia, (extra)pyramidal signs and akinetic mutism. In the early course of disease however, several clinical symptoms of CJD may mimic those of co-existing morbidities. CASE PRESENTATION: We report a male in his 60s with a history of situs inversus totalis and Churg Strauss syndrome, who presented with speech fluency disturbances, neuropsychiatric symptoms and allodynia, a few months after becoming a widower. Initially presumed a bereavement disorder along with a flare-up of Churg Strauss, his symptoms gradually worsened with apraxia, myoclonic jerks and eventually, akinetic mutism. MRI revealed hyperintensities at the caudate nucleus and thalami, while the cerebrospinal fluid was positive for the 14-3-3 protein and the real-time quick test, making the diagnosis of CJD highly probable. This case illustrates the complexities that may arise in diagnosing CJD when pre-existing multimorbidity may cloud the clinical presentation. We also discuss the potential mechanisms underlying the co-occurrence of three rare conditions (situs inversus totalis, Churg Strauss syndrome, CJD) in one patient, taking into consideration the possibility of coincidence as well as common underlying factors. CONCLUSIONS: The diagnosis of CJD may be easily missed when its clinical symptoms are obscured by those of pre-existing (rare) multimorbidity. This case highlights that when the multimorbidity has neurological manifestations, an extensive evaluation remains crucial to establish the diagnosis, minimize the risk of prion-transmission and provide appropriate guidance to patients and their caregivers.

Genome-wide profiling of circulatory microRNAs associated with cognition and dementia.

INTRODUCTION: MicroRNAs (miRNAs) are post-transcriptional regulators of gene expression. Their role in the pathophysiology of dementia and potential as biomarkers remains undetermined. METHODS: We conducted a single- (one-by-one) and multi-marker (joint) analysis to identify well-expressed circulating miRNAs in plasma (total = 591) associated with general cognition and incident dementia, for 1615 participants of the population-based Rotterdam Study. RESULTS: During single-marker analysis, 47 miRNAs were nominally (P ≤ .05) associated with cognition and 18 miRNAs were nominally associated with incident dementia, after adjustment for potential confounders. Three miRNAs were common between cognition and dementia (miR-4539, miR-372-3p, and miR-566), with multi-marker analysis revealing another common miRNA (miR-7106-5p). In silico analysis of these four common miRNAs led to several putative target genes expressed in the brain, highlighting the mitogen-activated protein kinase signaling pathway. DISCUSSION: We provide population-based evidence on the relationship between circulatory miRNAs with cognition and dementia, including four common miRNAs that may elucidate downstream mechanisms. HIGHLIGHTS: MicroRNAs (miRNAs) are involved in the (dys)function of the central nervous system. Four circulating miRNAs in plasma are associated with cognition and incident dementia. Several predicted target genes of these four miRNAs are expressed in the brain. These four miRNAs may be linked to pathways underlying dementia. Although miRNAs are promising biomarkers, experimental validation remains essential.

Plasma Amyloid-ß in Relation to Cardiac Function and Risk of Heart Failure in General Population.

BACKGROUND: Amyloid-ß (Aß) may be related to cardiac function. However, there are limited data on the association of plasma Aß with cardiac function and risk of heart failure (HF) in the general population. OBJECTIVES: This study sought to determine the associations of plasma amyloid-ß40 (Aß40) and amyloid-ß42 (Aß42) with echocardiographic measurements of cardiac dysfunction and with incident HF in the general population. METHODS: The study included 4,156 participants of the population-based Rotterdam Study (mean age: 71.4 years; 57.1% women), who had plasma Aß samples collected between 2002 and 2005 and had no established dementia and HF at baseline. Multivariable linear regression models were used to explore the cross-sectional association of plasma Aß with echocardiographic measures. Participants were followed up until December 2016. Cox proportional hazards models were used to assess the association of Aß levels with incident HF. Models were adjusted for cardiovascular risk factors. RESULTS: A per 1-SD increase in log-transformed plasma Aß40 was associated with a 0.39% (95% CI: -0.68 to -0.10) lower left ventricular ejection fraction and a 0.70 g/m2 (95% CI: 0.06-1.34) larger left ventricular mass indexed by body surface area. Aß42 was not significantly associated with echocardiographic measures cross-sectionally. During follow-up (median: 10.2 years), 472 incident HF cases were identified. A per 1-SD increase in log-transformed Aß40 was associated with a 32% greater risk of HF (HR: 1.32; 95% CI: 1.15-1.51), and the association was significant in men, but not in women. Higher plasma Aß42 levels were associated with an increased risk of HF (HR: 1.12; 95% CI: 1.02-1.24), although the association was attenuated after further adjustment for concomitant Aß40 (HR: 1.03; 95% CI: 0.92-1.16). CONCLUSIONS: Higher levels of Aß40 were associated with worse cardiac function and higher risk of new onset HF in the general population, in particular among men.

The association of serum immunoglobulins with cognition and dementia: the Rotterdam Study.

BACKGROUND: Chronic inflammation is involved in the pathophysiology of dementia, but the association of serum immunoglobulins with dementia has been understudied and longitudinal data are currently lacking. We investigated the association of serum immunoglobulin (Ig) A, G, and M with cognition and dementia in a population-based cohort. METHODS: This study was embedded in the Rotterdam Study. Participants with information on serum immunoglobulin levels, measured between 1997 and 2009, were followed for incident dementia until 2016. Assessment of cognitive function and dementia was performed according to validated tests and clinical criteria respectively. We studied the association between serum immunoglobulins with prevalent and incident dementia using logistic regression and Cox proportional hazards regression analyses respectively. We performed linear regression analyses to quantify the cross-sectional association of serum immunoglobulins with global cognition as well as separate cognitive tests. Analyses were adjusted for age, sex, lifestyle, and cardiovascular factors. RESULTS: We included 8768 participants (median age of 62.2 years, 57% women, median follow-up 10.7 years). Overall, none of the immunoglobulins was associated with prevalent or incident dementia. Higher IgG levels were associated with lower scores of global cognition (adjusted standardized mean difference - 0.04; 95% confidence interval:- 0.06; - 0.02) and separate cognitive tests. CONCLUSION: In middle-aged and older individuals from the general population, serum Igs were not associated with prevalent or incident dementia, which may imply that serum Igs are not involved in the pathophysiology of dementia. Although higher IgG levels were associated with worse cognitive function, studies with longitudinal data should exclude reverse causation.

Associations of Pulmonary Function with MRI Brain Volumes: A Coordinated Multi-Study Analysis.

BACKGROUND: Previous studies suggest poor pulmonary function is associated with increased burden of cerebral white matter hyperintensities and brain atrophy among elderly individuals, but the results are inconsistent. OBJECTIVE: To study the cross-sectional associations of pulmonary function with structural brain variables. METHODS: Data from six large community-based samples (N = 11,091) were analyzed. Spirometric measurements were standardized with respect to age, sex, height, and ethnicity using reference equations of the Global Lung Function Initiative. Associations of forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), and their ratio FEV1/FVC with brain volume, gray matter volume, hippocampal volume, and volume of white matter hyperintensities were investigated using multivariable linear regressions for each study separately and then combined using random-effect meta-analyses. RESULTS: FEV1 and FVC were positively associated with brain volume, gray matter volume, and hippocampal volume, and negatively associated with white matter hyperintensities volume after multiple testing correction, with little heterogeneity present between the studies. For instance, an increase of FVC by one unit was associated with 3.5 ml higher brain volume (95% CI: [2.2, 4.9]). In contrast, results for FEV1/FVC were more heterogeneous across studies, with significant positive associations with brain volume, gray matter volume, and hippocampal volume, but not white matter hyperintensities volume. Associations of brain variables with both FEV1 and FVC were consistently stronger than with FEV1/FVC, specifically with brain volume and white matter hyperintensities volume. CONCLUSION: In cross-sectional analyses, worse pulmonary function is associated with smaller brain volumes and higher white matter hyperintensities burden.

[Population attributable fraction: a guideline for disease prevention]. / Populatie-attributieve fractie.

The improvement of public health relies on effective strategies for disease prevention, but the optimal preventive strategy is often difficult to determine. The population attributable fraction is a tool that allows policy makers to prioritise among different interventions by quantifying the share of disease in the population that is due to one specific risk factor. In this article, we discuss the computation of the population attributable fraction, as well as its advantages, limitations, and challenges for proper interpretation. We further compare the population attributable fraction to the etiologic fraction, which concerns the impact of a risk factor of disease at the individual level. We illustrate the importance of either measure, as well as differences between them, on the basis of scenarios in which community medicine and patient-centred care might not always be in agreement.

New insights into the genetic etiology of Alzheimer's disease and related dementias.

Characterization of the genetic landscape of Alzheimer's disease (AD) and related dementias (ADD) provides a unique opportunity for a better understanding of the associated pathophysiological processes. We performed a two-stage genome-wide association study totaling 111,326 clinically diagnosed/'proxy' AD cases and 677,663 controls. We found 75 risk loci, of which 42 were new at the time of analysis. Pathway enrichment analyses confirmed the involvement of amyloid/tau pathways and highlighted microglia implication. Gene prioritization in the new loci identified 31 genes that were suggestive of new genetically associated processes, including the tumor necrosis factor alpha pathway through the linear ubiquitin chain assembly complex. We also built a new genetic risk score associated with the risk of future AD/dementia or progression from mild cognitive impairment to AD/dementia. The improvement in prediction led to a 1.6- to 1.9-fold increase in AD risk from the lowest to the highest decile, in addition to effects of age and the APOE ε4 allele.

Meta-analysis of genome-wide association studies identifies ancestry-specific associations underlying circulating total tau levels.

Circulating total-tau levels can be used as an endophenotype to identify genetic risk factors for tauopathies and related neurological disorders. Here, we confirmed and better characterized the association of the 17q21 MAPT locus with circulating total-tau in 14,721 European participants and identified three novel loci in 953 African American participants (4q31, 5p13, and 6q25) at P < 5 × 10-8. We additionally detected 14 novel loci at P < 5 × 10-7, specific to either Europeans or African Americans. Using whole-exome sequence data in 2,279 European participants, we identified ten genes associated with circulating total-tau when aggregating rare variants. Our genetic study sheds light on genes reported to be associated with neurological diseases including stroke, Alzheimer's, and Parkinson's (F5, MAP1B, and BCAS3), with Alzheimer's pathological hallmarks (ADAMTS12, IL15, and FHIT), or with an important function in the brain (PARD3, ELFN2, UBASH3B, SLIT3, and NSD3), and suggests that the genetic architecture of circulating total-tau may differ according to ancestry.

Risk factors, neuroimaging correlates and prognosis of the motoric cognitive risk syndrome: A population-based comparison with mild cognitive impairment.

BACKGROUND AND PURPOSE: This study was undertaken to compare risk factors, neuroimaging characteristics and prognosis between two clinical prodromes of dementia, namely, the motoric cognitive risk syndrome (MCRS) and mild cognitive impairment (MCI). METHODS: Between 2009 and 2015, dementia-free participants of the population-based Rotterdam Study were classified with a dementia prodrome if they had subjective cognitive complaints and scored >1 SD below the population mean of gait speed (MCRS) or >1.5 SD below the population mean of cognitive test scores (MCI). Using multinomial logistic regression models, we determined cross-sectional associations of risk factors and structural neuroimaging markers with MCRS and MCI, followed by subdistribution hazard models, to determine risk of incident dementia until 2016. RESULTS: Of 3025 included participants (mean age = 70.4 years, 54.7% women), 231 had MCRS (7.6%), 132 had MCI (4.4%), and 62 (2.0%) fulfilled criteria for both. Although many risk factors were shared, a higher body mass index predisposed to MCRS, whereas male sex and hypercholesterolemia were associated with MCI only. Gray matter volumes, hippocampal volumes, white matter hyperintensities, and structural white matter integrity were worse in both MCRS and MCI. During a mean follow-up of 3.9 years, 71 individuals developed dementia and 200 died. Five-year cumulative risk of dementia was 7.0% (2.5%-11.5%) for individuals with MCRS, versus 13.3% (5.8%-20.8%) with MCI and only 2.3% (1.5%-3.1%) in unaffected individuals. CONCLUSIONS: MCRS is associated with imaging markers of neurodegeneration and risk of dementia, even in the absence of MCI, highlighting the potential of motor function assessment in early risk stratification for dementia.

Life expectancy with and without dementia in persons with mild cognitive impairment in the community.

BACKGROUND: Various clinical studies have provided estimates of life expectancy of patients with mild cognitive impairment (MCI) from outpatient clinics, but whether these apply to community-dwelling individuals at home or in primary care is uncertain. METHODS: Within the population-based Rotterdam Study, we studied life expectancy with and without dementia in 648 community-dwelling persons with MCI and 6410 without MCI. Participants aged 60 years and older were assessed for MCI at baseline (2002-2014) and subsequently followed for the onset of dementia and death. We used multistate life tables to determine age-specific life expectancy with and without dementia by sex, educational attainment, and MCI subtype. RESULTS: Total life expectancy for MCI ranged from 21.4 years (95% CI: 19.0-23.6) at age 60 to 2.6 years (1.6-3.6) at age 95. With advancing age, an increasing proportion of these years was lived with dementia (2.9 years [1.8-4.0] at age 60; 1.2 [0.2-2.2] at age 95). Women and higher educated individuals lived longer and lived more years with dementia. No differences in total life expectancy were observed by MCI subtype, although individuals with amnestic MCI lived a larger proportion of those years with dementia. CONCLUSIONS: Prognosis of MCI, in terms of life years lived with and without dementia, is more favorable in the general population than described in prior clinical observations, due likely to a substantial proportion of individuals with MCI in the clinic not seeking medical attention in an earlier stage.

Biological age in healthy elderly predicts aging-related diseases including dementia.

Application of biological age as a measure of an individual´s health status offers new perspectives into extension of both lifespan and healthspan. While algorithms predicting mortality and most aging-related morbidities have been reported, the major shortcoming has been an inability to predict dementia. We present a community-based cohort study of 1930 participants with a mean age of 72 years and a follow-up period of over 7 years, using two variants of a phenotypic blood-based algorithm that either excludes (BioAge1) or includes (BioAge2) neurofilament light chain (NfL) as a neurodegenerative marker. BioAge1 and BioAge2 predict dementia equally well, as well as lifespan and healthspan. Each one-year increase in BioAge1/2 was associated with 11% elevated risk (HR 1.11; 95%CI 1.08-1.14) of mortality and 7% elevated risk (HR 1.07; 95%CI 1.05-1.09) of first morbidities. We additionally tested the association of microRNAs with age and identified 263 microRNAs significantly associated with biological and chronological age alike. Top differentially expressed microRNAs based on biological age had a higher significance level than those based on chronological age, suggesting that biological age captures aspects of aging signals at the epigenetic level. We conclude that accelerated biological age for a given age is a predictor of major age-related morbidity, including dementia, among healthy elderly.