Inflammation in the Alzheimer's disease cascade: culprit or innocent bystander?

The strongest known risk factors for late-onset Alzheimer disease (LOAD) remain a positive family history and the APOE ε4 allele. van Exel and colleagues used these known risk factors to identify high- and low-risk samples of middle-aged persons in whom they compared levels of inflammatory and vascular risk factors. They observed that, compared with controls, middle-aged offspring of families with a parental history of LOAD had higher blood pressures, lower ankle-brachial indices (measure of peripheral atherosclerosis), and increased production of proinflammatory cytokines in lipopolysaccharide-stimulated whole blood samples, associations that were independent of APOE genotype. This study adds to the growing body of evidence linking inflammatory mechanisms to Alzheimer disease risk and, especially when considered in light of the recently described association of genetic variation in the complement receptor 1 (CR1) gene with LOAD, suggests that inflammatory biomarkers (whether causal or incidental) could be measured and perhaps used to risk-stratify middle-aged persons for early preventive and therapeutic interventions

Association of metabolic dysregulation with volumetric brain magnetic resonance imaging and cognitive markers of subclinical brain aging in middle-aged adults: the Framingham Offspring Study.

ObjectiveDiabetic and prediabtic states, including insulin resistance, fasting hyperglycemia, and hyperinsulinemia, are associated with metabolic dysregulation. These components have been individually linked to increased risks of cognitive decline and Alzheimer's disease. We aimed to comprehensively relate all of the components of metabolic dysregulation to cognitive function and brain magnetic resonance imaging (MRI) in middle-aged adults.Research design and methodsFramingham Offspring participants who underwent volumetric MRI and detailed cognitive testing and were free of clinical stroke and dementia during examination 7 (1998-2001) constituted our study sample (n = 2,439; 1,311 women; age 61 ± 9 years). We related diabetes, homeostasis model assessment of insulin resistance (HOMA-IR), fasting insulin, and glycohemoglobin levels to cross-sectional MRI measures of total cerebral brain volume (TCBV) and hippocampal volume and to verbal and visuospatial memory and executive function. We serially adjusted for age, sex, and education alone (model A), additionally for other vascular risk factors (model B), and finally, with the inclusion of apolipoprotein E-ε4, plasma homocysteine, C-reactive protein, and interleukin-6 (model C).ResultsWe observed an inverse association between all indices of metabolic dysfunction and TCBV in all models (P < 0.030). The observed difference in TCBV between participants with and without diabetes was equivalent to approximately 6 years of chronologic aging. Diabetes and elevated glycohemoglobin, HOMA-IR, and fasting insulin were related to poorer executive function scores (P < 0.038), whereas only HOMA-IR and fasting insulin were inversely related to visuospatial memory (P < 0.007).ConclusionsMetabolic dysregulation, especially insulin resistance, was associated with lower brain volumes and executive function in a large, relatively healthy, middle-aged, community-based cohort

Elevated Amyloid-β and Tau Levels in the Brain are Associated with a Reduced Abundance of Neuroprotective Gut Bacteria

Background: Recent research suggests that differences in the gut microbiome composition may contribute to the pathogenesis of neurological disorders, including Alzheimer\u27s disease (AD). Animal studies have shown that fecal microbiota transplantation reduces amyloid plaques in mouse AD models. However, whether the buildup of Aβ and tau deposits in the brain are associated with shifts in the human gut microbiota composition is understudied. Method: We used stool specimens and neuropathological measures from 140 middle-aged individuals (Table 1: mean age 56, 54% Female) from the Framingham Heart Study (FHS) to assess the link between the gut microbiome composition and Aβ Positron Emission Tomography (Aβ-PET) in a global composite brain measure, and tau-PET deposits in the rhinal cortex and the inferior temporal cortex. We quantified gut microbiome composition using 16S rRNA sequencing. We performed multivariable association and differential abundance analyses, adjusting for age, sex, body mass index, and other confounders. Result: Multivariable association results (Figure 1) indicated significant associations (adjusted p-value \u3c 0.001) between both Aβ-PET and tau-PET levels with abundance of genera Butyricicoccus and Ruminococcus. Moreover, differential abundance analysis (Figure 2) showed that these bacteria have lower than expected abundance in individuals with elevated Aβ-PET and tau-PET measures (Aβ-PET, Ruminococcus: OR = 0.89, [0.88, 0.91]; Butyricicoccus: OR = 0.77, [0.72, 0.81]); (tau-PET in the rhinal cortex: Ruminococcus: OR = 0.82, [0.8, 0.83]; Butyricicoccus: OR = 0.91 [0.88, 0.94]); (tau-PET in the inferotemporal cortex:, Ruminococcus: OR = 0.79 [0.78, 0.81]; Butyricicoccus: OR = 0.83 [0.81, 0.86]). Conversely, we observed an increased abundance of genera Cytophaga (tau-PET in the rhinal cortex, OR = 1.78, [1.15, 2.75]) and Alistipes (tau-PET in the rhinal cortex, OR = 1.19, [1.17, 1.22]) in individuals with high Aβ-PET and tau-PET levels. Finally, functional analysis showed that Butyricicoccus and Ruminococcus are butyrate-producing bacteria harboring neuroprotective effects. Conclusion: We showed that elevated measures of Aβ-PET and tau-PET in the rhinal and the inferior temporal cortex are associated with a reduced abundance of butyrate-producing Butyricicoccus and Ruminococcus in the gut of middle-aged individuals from the FHS. As these bacteria harbor neuroprotective effects, further studies are needed to elucidate underlying mechanisms and assess their therapeutic potential

Genetic Correlates of Brain Aging on MRI and Cognitive Test Measures: A Genome-Wide Association and Linkage Analysis in the Framingham Study

BACKGROUND: Brain magnetic resonance imaging (MRI) and cognitive tests can identify heritable endophenotypes associated with an increased risk of developing stroke, dementia and Alzheimer's disease (AD). We conducted a genome-wide association (GWA) and linkage analysis exploring the genetic basis of these endophenotypes in a community-based sample. METHODS: A total of 705 stroke- and dementia-free Framingham participants (age 62 +9 yrs, 50% male) who underwent volumetric brain MRI and cognitive testing (1999–2002) were genotyped. We used linear models adjusting for first degree relationships via generalized estimating equations (GEE) and family based association tests (FBAT) in additive models to relate qualifying single nucleotide polymorphisms (SNPs, 70,987 autosomal on Affymetrix 100K Human Gene Chip with minor allele frequency ≥ 0.10, genotypic call rate ≥ 0.80, and Hardy-Weinberg equilibrium p-value ≥ 0.001) to multivariable-adjusted residuals of 9 MRI measures including total cerebral brain (TCBV), lobar, ventricular and white matter hyperintensity (WMH) volumes, and 6 cognitive factors/tests assessing verbal and visuospatial memory, visual scanning and motor speed, reading, abstract reasoning and naming. We determined multipoint identity-by-descent utilizing 10,592 informative SNPs and 613 short tandem repeats and used variance component analyses to compute LOD scores. RESULTS: The strongest gene-phenotype association in FBAT analyses was between SORL1 (rs1131497; p = 3.2 × 10-6) and abstract reasoning, and in GEE analyses between CDH4 (rs1970546; p = 3.7 × 10-8) and TCBV. SORL1 plays a role in amyloid precursor protein processing and has been associated with the risk of AD. Among the 50 strongest associations (25 each by GEE and FBAT) were other biologically interesting genes. Polymorphisms within 28 of 163 candidate genes for stroke, AD and memory impairment were associated with the endophenotypes studied at p < 0.001. We confirmed our previously reported linkage of WMH on chromosome 4 and describe linkage of reading performance to a marker on chromosome 18 (GATA11A06), previously linked to dyslexia (LOD scores = 2.2 and 5.1). CONCLUSION: Our results suggest that genes associated with clinical neurological disease also have detectable effects on subclinical phenotypes. These hypothesis generating data illustrate the use of an unbiased approach to discover novel pathways that may be involved in brain aging, and could be used to replicate observations made in other studies.National Institutes of Health National Center for Research Resources Shared Instrumentation grant (ISI0RR163736-01A1); National Heart, Lung, and Blood Institute's Framingham Heart Study (N01-HC-25195); National Institute of Aging (5R01-AG08122, 5R01-AG16495); National Institute of Neurological Disorders and Stroke (5R01-NS17950

Genetic correlates of longevity and selected age-related phenotypes: a genome-wide association study in the Framingham Study

BACKGROUND: Family studies and heritability estimates provide evidence for a genetic contribution to variation in the human life span. METHODS:We conducted a genome wide association study (Affymetrix 100K SNP GeneChip) for longevity-related traits in a community-based sample. We report on 5 longevity and aging traits in up to 1345 Framingham Study participants from 330 families. Multivariable-adjusted residuals were computed using appropriate models (Cox proportional hazards, logistic, or linear regression) and the residuals from these models were used to test for association with qualifying SNPs (70, 987 autosomal SNPs with genotypic call rate [greater than or equal to]80%, minor allele frequency [greater than or equal to]10%, Hardy-Weinberg test p [greater than or equal to] 0.001).RESULTS:In family-based association test (FBAT) models, 8 SNPs in two regions approximately 500 kb apart on chromosome 1 (physical positions 73,091,610 and 73, 527,652) were associated with age at death (p-value < 10-5). The two sets of SNPs were in high linkage disequilibrium (minimum r2 = 0.58). The top 30 SNPs for generalized estimating equation (GEE) tests of association with age at death included rs10507486 (p = 0.0001) and rs4943794 (p = 0.0002), SNPs intronic to FOXO1A, a gene implicated in lifespan extension in animal models. FBAT models identified 7 SNPs and GEE models identified 9 SNPs associated with both age at death and morbidity-free survival at age 65 including rs2374983 near PON1. In the analysis of selected candidate genes, SNP associations (FBAT or GEE p-value < 0.01) were identified for age at death in or near the following genes: FOXO1A, GAPDH, KL, LEPR, PON1, PSEN1, SOD2, and WRN. Top ranked SNP associations in the GEE model for age at natural menopause included rs6910534 (p = 0.00003) near FOXO3a and rs3751591 (p = 0.00006) in CYP19A1. Results of all longevity phenotype-genotype associations for all autosomal SNPs are web posted at http://www.ncbi.nlm.nih.gov/projects/gap/cgi-bin/study.cgi?id=phs000007. CONCLUSION: Longevity and aging traits are associated with SNPs on the Affymetrix 100K GeneChip. None of the associations achieved genome-wide significance. These data generate hypotheses and serve as a resource for replication as more genes and biologic pathways are proposed as contributing to longevity and healthy aging

Poor cognition is associated with increased abundance of Alistipes and decreased abundance of Clostridium genera in the gut

Background: Brain and gut health are intricately connected via the gut-microbiota-brain axis. Studies have shown that gut dysbiosis is associated with neurodegenerative diseases, including Alzheimer’s disease. However, how cognitive changes affects the gut microbiome structure is currently understudied. We aimed to assess the association between the gut microbiome and global cognitive scores in the Framingham Heart Study (FHS). Method: Our sample included 1,014 participants (mean age 52, 55% female) of the third generation FHS cohort with available stool samples, cognitive assessments, and no history of dementia or stroke (Table 1).We quantified the gut microbiome composition using 16S rRNA sequencing and performed multivariable association and differential abundance analyses, adjusting for age, sex, education, BMI, and other confounders. The global cognitive score (GCS) was built using neuropsychological assessments of four cognitive domains: Executive function (trails-making B); Processing speed (visual reproduction immediate and delayed); Language (similarity test); and Memory (logical memory immediate and delayed). Participants were additionally stratified by GCS with lower and higher scores indicating poor and normal cognition, respectively. Result: Our results (Figure 1) showed that individuals with poor cognition have a decreased abundance of genera Clostridium (OR = 0.69, 95% CI [0.55, 0.86]) and Ruminococcus (0.93, [0.93, 0.94]). Meanwhile, the genus Alistipes, previously connected to anxiety, chronic fatigue syndrome, depression, and hypertension, was more abundant (1.06, [1.05, 1.06]) in the poor cognition group. Moreover, the genus Pseudobutyrivibrio, a butyrate-producing bacteria from the rumen, was also found to be highly abundant (1.12, [1.11, 1.14]) in the poor cognition compared to normal. Finally, there was no difference in alpha and beta diversity between cognitive groups (Figure 2). Conclusion: Our study suggests that the abundance of several genera, including Pseudobutyrivibrio, Alistipes, Ruminococcus, and Clostridium is associated with cognition in middle-age. Clostridium was previously proposed as novel probiotics for human health, and increasing its abundance was viewed as an effective strategy to regulate and maintain the homeostasis of the gut microbiota. As all these bacteria have neuroprotective effects, manipulating their abundance through diet and pre/pro-biotics could be a research path for preserving global cognitive function in the future

New Norms for a New Generation: Cognitive Performance in the Framingham Offspring Cohort

A previous publication presented normative data on neuropsychological tests stratified by age, gender, and education based on the Original Cohort of the Framingham Heart Study. Many contemporary investigations include subject samples with higher levels of education, a factor known to affect cognitive performance. Secular change in education prompted the reexamination of norms in the children of the Original Cohort. The study population consisted of 853 men and 988 women from the Offspring Study, free of clinical neurological disease, who underwent a neuropsychological examination, which included tests given to their parents in 1974 to 1976 as well as additional newer tests to provide a more comprehensive battery. The Offspring population overall was more evenly distributed by gender and better educated. Their performance on cognitive tests was superior to that of the Original Cohort. Multivariable analyses revealed that more years of education explained only a part of the cohort differences. These findings suggest that continued surveillance of each generation is necessary to document the impact that unique social and economic variables have on cognitive function. Here, the authors provide updated normative data

Using Family-Based Imputation in Genome-Wide Association Studies with Large Complex Pedigrees: The Framingham Heart Study

Imputation has been widely used in genome-wide association studies (GWAS) to infer genotypes of un-genotyped variants based on the linkage disequilibrium in external reference panels such as the HapMap and 1000 Genomes. However, imputation has only rarely been performed based on family relationships to infer genotypes of un-genotyped individuals. Using 8998 Framingham Heart Study (FHS) participants genotyped with Affymetrix 550K SNPs, we imputed genotypes of same set of SNPs for additional 3121 participants, most of whom were never genotyped due to lack of DNA sample. Prior to imputation, 122 pedigrees were too large to be handled by the imputation software Merlin. Therefore, we developed a novel pedigree splitting algorithm that can maximize the number of genotyped relatives for imputing each un-genotyped individual, while keeping new sub-pedigrees under a pre-specified size. In GWAS of four phenotypes available in FHS (Alzheimer disease, circulating levels of fibrinogen, high-density lipoprotein cholesterol, and uric acid), we compared results using genotyped individuals only with results using both genotyped and imputed individuals. We studied the impact of applying different imputation quality filtering thresholds on the association results and did not found a universal threshold that always resulted in a more significant p-value for previously identified loci. However most of these loci had a lower p-value when we only included imputed genotypes with with ≥60% SNP- and ≥50% person-specific imputation certainty. In summary, we developed a novel algorithm for splitting large pedigrees for imputation and found a plausible imputation quality filtering threshold based on FHS. Further examination may be required to generalize this threshold to other studies

Incidence of seizures following initial ischemic stroke in a community-based cohort: The Framingham Heart Study

Purpose We examined the incidence of seizures following ischemic stroke in a community-based sample. Methods All subjects with incident ischemic strokes in the Framingham Original and Offspring cohorts between 1982 and 2003 were identified and followed for up to 20 years to determine incidence of seizures. Seizure-type was based on the 2010 International League Against Epilepsy (ILAE) classification. Disability was stratified into mild/none, moderate and severe, based on post-stroke neurological deficit documentation according to the Framingham Heart Study (FHS) protocol and functional status was determined using the Barthel Index. Results An initial ischemic stroke occurred in 469 subjects in the cohort and seizures occurred in 25 (5.3%) of these subjects. Seizure incidence was similar in both large artery atherosclerosis (LAA) (6.8%) and cardio-embolic (CE) (6.2%) strokes. No seizures occurred following lacunar strokes. The predominant seizure type was focal seizure with or without evolution to bilateral convulsive seizure. One third of participants had seizures within the first 24 h from stroke onset and half of all seizures occurred within the first 30 days. On multivariate analysis, moderate and severe disability following stroke was associated with increased risk of incident seizure. Conclusions Seizures occurred in approximately 5% of subjects after an ischemic stroke. One third of these seizures occurred in the first 24 h after stroke and none followed lacunar strokes. Focal seizures with or without evolution in bilateral convulsive seizures were the most common seizure type. Moderate and severe disability was predictive of incident seizures