INFLAMMATION's cognitive impact revealed by a novel "Line of Identity" approach

IMPORTANCE

Dementia is an "overdetermined" syndrome. Few individuals are demented by any single biomarker, while several may independently explain small fractions of dementia severity. It may be advantageous to identify individuals afflicted by a specific biomarker to guide individualized treatment.

OBJECTIVE

We aim to validate a psychometric classifier to identify persons adversely impacted by inflammation and replicate it in a second cohort.

DESIGN

Secondary analyses of data collected by the Texas Alzheimer's Research and Care Consortium (TARCC) (N = 3497) and the Alzheimer's Disease Neuroimaging Initiative (ADNI) (N = 1737).

SETTING

Two large, well-characterized multi-center convenience samples.

PARTICIPANTS

Volunteers with normal cognition (NC), Mild Cognitive Impairment (MCI) or clinical "Alzheimer's Disease (AD)".

EXPOSURE

Participants were assigned to "Afflicted" or "Resilient" classes on the basis of a psychometric classifier derived by confirmatory factor analysis.

MAIN OUTCOME(S) AND MEASURE(S)

The groups were contrasted on multiple assessments and biomarkers. The groups were also contrasted regarding 4-year prospective conversions to "AD" from non-demented baseline diagnoses (controls and MCI). The Afflicted groups were predicted to have adverse levels of inflammation-related blood-based biomarkers, greater dementia severity and greater risk of prospective conversion.

RESULTS

In ADNI /plasma, 47.1% of subjects were assigned to the Afflicted class. 44.6% of TARCC's subjects were afflicted, 49.5% of non-Hispanic Whites (NHW) and 37.2% of Mexican Americans (MA). There was greater dementia severity in the Afflicted class [by ANOVA: ADNI /F(1) = 686.99, p <0.001; TARCC /F(1) = 1544.01, p <0.001]. "INFLAMMATION" factor composite scores were significantly higher (adverse) in Afflicted subjects [by ANOVA in ADNI /plasma F(1) = 1642.64, p <0.001 and in TARCC /serum F(1) = 3059.96, p <0.001]. Afflicted cases were more likely to convert to AD in the next four years [by Cox's F, ADNI /plasma: F (252, 268) = 3.74 p < 0.001; TARCC /serum: F (160, 134) = 3.03, p < 0.001 (in TARCC's entire sample), F (110, 90) = 4.92, p <0.001 in NHW, and F(50, 44) = 2.13, p = 0.006 in MA]. The proportions converting were similar among afflicted NHW in both cohorts /biofluids but MA exhibited a lower risk (7% in TARCC /serum at 48 months).

CONCLUSIONS AND RELEVANCE

Our inflammation-specific psychometric classifier selects individuals with pre-specified biomarker profiles and predicts conversion to "AD" across cohorts, biofluids, and ethnicities. This algorithm might be applied to any dementia-related biomarker making the psychometric estimation of individual biomarker effects feasible without biomarker assessment. Our approach also distinguishes individuals resilient to individual biomarker effects allowing for more accurate prediction and precision intervention.

Statin use moderates APOE's and CRP's associations with dementia and is associated with lesser dementia severity in ε4 carriers

INTRODUCTION

We tested the effect of statins on C-reactive protein (CRP) and apolipoprotein E (APOE)'s associations with dementia severity.

METHODS

A total of 1725 participants of the Alzheimer's Disease Neuroimaging Initiative (ADNI) were assigned from 12-month follow-up data into the following groups: (1) ε4 (-)/statin (-), (2) ε4 (-)/statin (+), (3) ε4 (+)/statin (-), and (4) ε4 (+)/statin (+). Dementia severity was assessed by a δ homolog: "dHABS." A mediation model was stratified on statin use and moderation effects tested by a chi-square difference.

RESULTS

Plasma CRP level decreased with ε4 allelic dose. Statins had no effect on the dHABS d-score in non-carriers but were associated with better scores in carriers. Treated carriers did not have more severe dementia than non-carriers. Statin use moderated the mutual adjusted effects of APOE and CRP. CRP was not a mediator of APOE's effect.

DISCUSSION

Statins may provide a protective effect on the dementia severity of ε4 carriers.

HIGHLIGHTS

δ is a dementia-specific phenotype related to general intelligence "g" and is assessed via a "d-score." Apolipoprotein E (APOE) and plasma C-reactive protein (CRP) are independently associated with δ. Plasma CRP decreases with ε4 allelic dose. Statins were associated with better (less demented) d-scores in ε4 carriers but had no effect in non-ε4 carriers. Treated ε4 carriers did not have more severe dementia than non-carriers. Statin use moderated the effects of APOE and CRP on δ. CRP was not a mediator of APOE's effect on δ.

The effects of CNS atrophy and ICVD on tests of executive function and functional status are mediated by intelligence

Background

Impairments in executive function (EF) are often attributed to ischemic cerebrovascular disease (ICVD) and frontal circuit pathology. However, EF can be distinguished from general intelligence and the latter is likely to manifest in "executive" measures. We aimed to distinguish the effects of imaging biomarkers on these constructs.

Methods

We tested neuroimaging biomarkers as independent predictors of observed 12 month-prospective cognitive performance by a Multiple Indicators Multiple Causes (MIMIC) model in the Alzheimer's Disease Neuroimaging Initiative (ADNI) (N ≅ 1750).

Results

ICVD was associated with ''Organization" (ORG) and "Planning" (PLAN) domain scores from the test of Every Day Cognition. Left anterior cingulate (LAC) atrophy was independently associated with Trail-Making part B and Animal Naming. The MIMIC model had excellent fit and tests additional latent variables i.e., EF and dEF (a latent δ homolog derived from Spearman's general intelligence factor, g). Only dEF was associated with instrumental activities of daily living (IADL). ICVD and LAC were both associated with observed executive measures through dEF. ICVD was independently associated with those same measures through EF.

Conclusions

Observed EF is independently determined by multiple factors. The effects of EF-associated MRI biomarkers can be related to disability and dementia only via their effects on g. Because g /δ are unlikely to be located within the frontal lobes, the dementia-specific variance in executive measures may have little to do with either frontal structure or function. Conversely, domain-specific variance in EF may have little to do with either IADL-impairment or dementia.

Multi-ancestry genome-wide meta-analysis of 56,241 individuals identifies LRRC4C, LHX5-AS1 and nominates ancestry-specific loci PTPRK , GRB14 , and KIAA0825 as novel risk loci for Alzheimer's disease: the Alzheimer's Disease Genetics Consortium

Limited ancestral diversity has impaired our ability to detect risk variants more prevalent in non-European ancestry groups in genome-wide association studies (GWAS). We constructed and analyzed a multi-ancestry GWAS dataset in the Alzheimer's Disease (AD) Genetics Consortium (ADGC) to test for novel shared and ancestry-specific AD susceptibility loci and evaluate underlying genetic architecture in 37,382 non-Hispanic White (NHW), 6,728 African American, 8,899 Hispanic (HIS), and 3,232 East Asian individuals, performing within-ancestry fixed-effects meta-analysis followed by a cross-ancestry random-effects meta-analysis. We identified 13 loci with cross-ancestry associations including known loci at/near CR1 , BIN1 , TREM2 , CD2AP , PTK2B , CLU , SHARPIN , MS4A6A , PICALM , ABCA7 , APOE and two novel loci not previously reported at 11p12 ( LRRC4C ) and 12q24.13 ( LHX5-AS1 ). Reflecting the power of diverse ancestry in GWAS, we observed the SHARPIN locus using 7.1% the sample size of the original discovering single-ancestry GWAS (n=788,989). We additionally identified three GWS ancestry-specific loci at/near ( PTPRK ( P =2.4×10 -8 ) and GRB14 ( P =1.7×10 -8 ) in HIS), and KIAA0825 ( P =2.9×10 -8 in NHW). Pathway analysis implicated multiple amyloid regulation pathways (strongest with P adjusted =1.6×10 -4 ) and the classical complement pathway ( P adjusted =1.3×10 -3 ). Genes at/near our novel loci have known roles in neuronal development ( LRRC4C, LHX5-AS1 , and PTPRK ) and insulin receptor activity regulation ( GRB14 ). These findings provide compelling support for using traditionally-underrepresented populations for gene discovery, even with smaller sample sizes.

Multiple Adipokines Predict Dementia Severity as Measured by δ: Replication Across Biofluids and Cohorts

BACKGROUND

We have explored dementia's blood-based protein biomarkers in the Texas Alzheimer's Research and Care Consortium (TARCC) study. Among them are adipokines, i.e., proteins secreted by adipose tissue some of which have been associated with cognitive impairment.

OBJECTIVE

To associate adipokines with dementia severity and replicate their association across cohorts and biofluids (serum /plasma).

METHODS

We used eight rationally chosen blood-based protein biomarkers as indicators of a latent variable, i.e., "Adipokines". We then associated that construct with dementia severity as measured by the latent dementia-specific phenotype "δ" in structural equation models (SEM). Significant factor loadings and Adipokines' association with δ were replicated across biofluids in the Alzheimer's Disease Neuroimaging Initiative (ADNI).

RESULTS

Eight adipokine proteins loaded significantly on the Adipokines construct. Adipokines measured in plasma (ADNI) or serum (TARCC) explained 24 and 70% of δ's variance, respectively. An Adipokine composite score, derived from the latent variables, rose significantly across clinical diagnoses and achieved high areas under the receiver operating characteristic curve (ROC/AUC) for discrimination of Alzheimer's disease from normal controls (NC) or cases of mild cognitive impairment (MCI) and between NC and MCI.

CONCLUSION

These results again suggest that SEM can be used to create latent biomarker classifiers that replicate across samples and biofluids, and that a substantial fraction of dementia's variance is attributable to peripheral blood-based protein levels via the patterns codified in those latent constructs.

Cognitive intraindividual variability as a potential biomarker for early detection of cognitive and functional decline

OBJECTIVE

Intraindividual variability (IIV) in cognitive performance has been associated with cognitive decline and reductions in white matter integrity, but the predictive utility of IIV-between versus IIV-within domains is unknown. The present study aimed to determine if IIV-within a "frontal-subcortical" domain may be a more robust predictor of changes in general cognitive status and functional independence over time than IIV-between cognitive domains.

METHOD

Mixed linear modeling was used to analyze the relationship between cognitive IIV and cognitive and functional status in 651 controls, 211 people with mild cognitive impairment, and 218 people with Alzheimer's disease over a 5-year period.

RESULTS

Both IIV-between and IIV-within a frontal-subcortical domain improved prediction of cognitive and functional declines beyond demographic characteristics, genetic risk, and vascular integrity. IIV-between showed the greatest effect over time and was driven primarily by increases in IIV-within.

CONCLUSIONS

Cognitive IIV, especially between cognitive domains, may be useful for identifying individuals at risk for cognitive and functional decline. Findings may facilitate investigations into mechanisms underlying declines in global cerebral integrity and aid clinical trials aimed at early detection and treatment. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Blood biomarkers for cognitive decline and clinical progression in a Mexican American cohort

Introduction: The clinical translation of biofluid markers for dementia requires validation in diverse cohorts. The study goal was to evaluate if blood biomarkers reflecting diverse pathophysiological processes predict disease progression in Mexican American adults. Methods: Mexican American adults (n = 745), 50 years of age and older, completed annual assessments over a mean of 4 years. Serum collected at baseline was assayed for total tau, neurofilament light (NFL), ubiquitin carboxyl-terminal hydrolase LI, glial fibrillary acidic protein (GFAP), soluble cluster of differentiation 14 (sCD14), and chitinase-3-like protein 1 (YKL-40). Results: Higher GFAP and NFL were associated with global cognitive decline. Only GFAP was associated with increased incident dementia risk (hazard ratio: 1.611 (95% confidence interval: 1.204-2.155)) and inclusion of additional biomarkers did not improve model fit. Discussion: Among a panel of six blood biomarkers previously associated with neurodegenerative disease, only GFAP predicted incident dementia in our cohort. The findings suggest that blood GFAP levels may aid dementia-risk prediction among Mexican American adults.

A-49 Construct Validity and Predictive Utility of Cognitive Intraindividual Variability Varies Based on Ethnic Group

Objective

Compare the construct validity and predictive utility of cognitive intraindividual variability (IIV) in a sample of community dwelling Hispanic and non-Hispanic older adults.

Methods

The present study included annual data from 651 older adult control participants (Hispanic = 293; Non-Hispanic = 358) enrolled in the Texas Alzheimer’s Research and Care Consortium for at least 5 years. Mean composite z-scores were calculated for attention, language, memory and executive function domains. IIV-across domains was calculated as the standard deviation between these composite scores, while IIV-within domain scores were computed as the absolute difference between tests in each domain.

Results

At baseline, Non-Hispanic individuals obtained significantly higher composite scores in each domain than their Hispanic counterparts. They also showed significantly greater variability across and within domains, with the exception of IIV-within the language domain which was significantly larger in the Hispanic group. IIV-across domains was driven primarily by IIV-within the executive function domain in the non-Hispanic cohort and by IIV-within the language domain in the Hispanic cohort. In both groups, the addition of IIV-within and -across cognitive domains at baseline significantly improved prediction of cognitive status (MMSE) after 5 years above and beyond demographic characteristics, genetic risk and vascular integrity. However, IIV-across domains was the strongest predictor in the non-Hispanic group, while IIV-within the attention domain was the strongest predictor in the Hispanic group.

Conclusions

Findings suggest that, while IIV-across domains is a promising preclinical biomarker of subsequent cognitive decline, its construct validity and predictive utility varies based on ethnic group.

δ scores predict multiple neuropsychiatric symptoms

OBJECTIVES

Dementia severity is strongly related to Spearman's general intelligence factor "g", via the latent dementia phenotype "δ" and is distinct from domain-specific cognitive impairments arising from disease-specific regional pathologies. It is an empiric question whether behavioral and psychological symptoms of dementia (BPSD) are associated with δ or with domain-specific constructs.

METHODS

A recently developed δ homolog ("dDx") was tested as a predictor of 1 year prospective BPSD in n = 723 Mexican-American and non-Hispanic White participants in the Texas Alzheimer's Research and Care Consortium (TARCC). The informant-rated frequencies of 12 BPSD were rated by the neuropsychiatric inventory (NPI-Q). Baseline BPSD, demographic features, selected biomarkers, and treatment exposure to acetylcholinesterase inhibitors were used as covariates. Composite scores derived from orthogonal latent measures of domain-specific memory (MEM) and executive function (EF) were also tested as predictors.

RESULTS

"Functionally salient cognitive impairment (FSCI)" that is, categorical "dementia" as diagnosed by dDx was associated with increased prospective frequency of 11/12 BPSD, independently of baseline behavior and covariates. Age, depressive symptoms, and EF were associated with individual BPSD. MEM was not associated with any. Dementia severity, as measured by dDx, was also associated with a prospective increase in total NPI-Q scores.

CONCLUSION

δ is associated non-specifically with multiple BPSD. This suggests the existence of a dementia-specific behavioral profile, arising from insults to general intelligence, and unrelated to disease-specific regional pathology(ies).

δ-Related Biomarkers Attenuate Multiple Alzheimer's Disease Conversion Risks and Offer Targets for Intervention

BACKGROUND

We tested certain serum proteins' ability to mediate the effects of demographic variables on prospective 5-year conversion to clinical "Alzheimer's disease" from non-demented states (i.e. normal control and mild cognitive impairment). The proteins were rationally selected from previously published mediators of those same variables' (plural posessive) association with the latent variable "δ," a novel omnibus dementia severity metric.

METHODS

Each protein's attenuation of its risk factor's independent association with conversion was performed using logistic regression, adjusted for education, ethnicity, self-reported diabetes mellitus, and hypertension, among initially non-demented Mexican American and non-Hispanic white (N = 772) participants in the Texas Alzheimer's Research and Care Consortium.

RESULTS

A total of 70 (9.1%) non-demented participants at baseline converted to "Alzheimer's disease", with a mean follow-up of 5.4 years. Age >80 years (odds ratio = 3.1), 30-item Geriatric Depression Scale >10/30 (odds ratio = 2.3), female gender (odds ratio = 2.2), and the presence of an apolipoprotein E ε4 allele (odds ratio = 2.4) were independently associated with prospective conversion. These effects were fully attenuated by five serum proteins: age: insulin-like growth factor-binding protein 2 and epidermal growth factor receptor 1; depression: resistin; gender: thrombopoietin; and apolipoprotein E: C-reactive protein.

CONCLUSION

Clinical dementia arises from the sum of independent δ-related processes. This analysis provides proof of concept for the rational selection of antidementia targets and offers a foundation for precision antidementia therapy.

Serum Adiponectin is Related to Dementia

BACKGROUND

The adipokine adiponectin (APN)'s role in Alzheimer's disease (AD) is controversial. Some studies suggest APN is neuroprotective while others propose it has harmful effects. We have used Multiple Indicators Multiple Causes (MIMIC) models to evaluate the effects of serum protein biomarkers on cognitive performance in the Texas Alzheimer's Research and Care Consortium (TARCC) (Royall DR, Bishnoi RJ, Palmer RF. Serum IGF-BP2 strongly moderates age's effect on cognition: a MIMIC analysis. Neurobiol Aging. 2015;36:2232-2240; Bishnoi RJ, Palmer RF, Royall DR. Vitamin D binding protein as a serum biomarker of Alzheimer's disease. J Alzheimers Dis. 2015;43:37-45; Bishnoi RJ, Palmer RF, Royall DR. Serum interleukin (IL)-15 as a biomarker of Alzheimer's disease. PLoS One. 2015;10:e0117282).

METHODS

MIMIC models were constructed and replicated in randomly selected 50% splits of TARCC's data (Group 1 N = 1,691; Group 2 N = 1,690) and used to evaluate the relationship between serum APN levels and cognition. Our approach has been to divide general intelligence (Spearman's g) (Spearman C. The Abilities of Man: Their Nature and Measurement. 1932) into two latent variables, δ (ie, a dementia-specific phenotype representing the disabling fraction of cognitive variance) and g prime (g') (ie, the residual non-disabling fraction). Only effects on δ are likely to be dementing.

RESULTS

Serum APN was significantly related to δ scores (r = .10, p = .015). APN had no significant effect on g' (r = -.25, p = .66), nor did it have any independent direct effects on cognitive performance. These results were replicated across random subsets (ΔCHISQ = 2.8(7), p > .90).

CONCLUSIONS

APN's effect on cognition is mediated through intelligence (ie, δ), likely to be disabling, and therefore to mediate one or more dementing processes. We have previously shown APN to partially mediate age's-specific effect on δ (Royall DR, Al-Rubaye S, Bishnoi R, Palmer RF. Serum protein mediators of dementia and aging proper. Aging (Albany NY). 2016;8:3241-3254). However, because the current model is age adjusted, APN must mediate one or more additional age-independent dementing process(es), possibly AD.

Blood-based protein predictors of dementia severity as measured by δ: Replication across biofluids and cohorts

INTRODUCTION

Dementia severity can be empirically described by the latent dementia phenotype "δ" and its various composite "homologs". We have explored δ's blood-based protein biomarkers in the Texas Alzheimer's Research and Care Consortium (TARCC) study. However, it would be convenient to replicate those associations in the Alzheimer's Disease Neuroimaging Initiative (ADNI). To this end, we recently engineered a δ homolog from observed cognitive performance measures common to both projects (i.e., "dT2A").

METHODS

We used nine rationally chosen peripheral blood-based protein biomarkers as indicators of a latent variable "INFLAMMATION". We then associated that construct with dT2A in structural equation models adjusted for age, gender, depressive symptoms, and apolipoprotein E (APOE) ε4 allelic burden. Significant factor loadings and INFLAMMATION's association with dT2A were confirmed in random splits of TARCC's relatively large sample, and across biofluids in the ADNI.

RESULTS

Nine proteins measured in serum (TARCC) or plasma (ADNI) explained ≅10% of dT2A's variance in both samples, independently of age, APOE, education, and gender. All loaded significantly on INFLAMMATION, and positively or negatively, depending on their known roles are PRO- or ANTI-inflammatory proteins, respectively. The parameters of interest were confirmed across random 50% splits of the TARCC's sample, and replicated across biofluids in the ADNI.

DISCUSSION

These results suggest that SEM can be used to replicate biomarker findings across samples and biofluids, and that a substantial fraction of dementia's variance is attributable to peripheral blood-based protein levels.

Blood-based protein mediators of senility with replications across biofluids and cohorts

Dementia severity can be quantitatively described by the latent dementia phenotype 'δ' and its various composite 'homologues'. We have explored δ's blood-based protein biomarkers in the Texas Alzheimer's Research and Care Consortium. However, it would be convenient to replicate them in the Alzheimer's Disease Neuroimaging Initiative. To that end, we have engineered a δ homologue from the observed cognitive performance measures common to both projects [i.e. 'd:Texas Alzheimer's Research and Care Consortium to Alzheimer's Disease Neuroimaging Initiative' (dT2A)]. In this analysis, we confirm 13/22 serum proteins as partial mediators of age's effect on dementia severity as measured by dT2A in the Texas Alzheimer's Research and Care Consortium and then replicate 4/13 in the Alzheimer's Disease Neuroimaging Initiative's plasma data. The replicated mediators of age-specific effects on dementia severity are adiponectin, follicle-stimulating hormone, pancreatic polypeptide and resistin. In their aggregate, the 13 confirmed age-specific mediators suggest that 'cognitive frailty' pays a role in dementia severity as measured by δ. We provide both discriminant and concordant support for that hypothesis. Weight, calculated low-density lipoprotein and body mass index are partial mediators of age's effect in the Texas Alzheimer's Research and Care Consortium. Biomarkers related to other disease processes (e.g. cerebrospinal fluid Alzheimer's disease-specific biomarkers in the Alzheimer's Disease Neuroimaging Initiative) are not. It now appears that dementia severity is the sum of multiple independent processes impacting δ. Each may have a unique set of mediating biomarkers. Age's unique effect appears to be at least partially mediated through proteins related to frailty. Age-specific mediation effects can be replicated across cohorts and biofluids. These proteins may offer targets for the remediation of age-specific cognitive decline (aka 'senility'), help distinguish it from other determinants of dementia severity and/or provide clues to the biology of Aging Proper.

δ PREDICTS GENERAL PSYCHOPATHOLOGY

“δ” is a transdiagnostic omnibus dementia severity measure derived from general intelligence (i.e., Spearman’s “g”). It can be estimated in any cognitive battery that contains a measure of Instrumental Activities of Daily Living (IADL). As dementia’s essential cognitive impairment, δ may also explain the appearance of Behavioral and Psychological Symptoms of Dementia (BPSD). Alternatively, the latter may be associated with orthogonal domain-specific cognitive impairments, unrelated to δ and therefore to dementia. The δ homolog ”dDx” was tested as a predictor of one year prospective BPSD among n = 723 participants in the Texas Alzheimer’s Research and Care Consortium (TARCC). Twelve Neuropsychiatric Inventory (NPI-Q)-rated BPSD were themselves submitted to confirmatory factor analysis resulting in a well-fit bifactor model rating general psychopathology (p), positive (+) and negative (-) symptoms. dDx and orthogonal cognitive factors rating memory (MEM) and executive function (EF) were regressed onto prospective p, (+) and (-). dDx was strongly associated with p (r = -0.59, p <0.001). MEM was associated only with (+) (r = 0.14, p <0.001). EF was associated only with (-) (r = -0.23, p <0.001). This is the first demonstration of p in the geriatric literature. p’s strong association with δ suggests that general psychopathology arises from dementia itself. In contrast, (+) and (-) symptoms may arise from regional insults, e.g., to temporo-limbic and frontal circuits (respectively). No such regional pathology is likely to impact δ or p, as they are “indifferent” to their indicators and must derive from global Central Nervous System (CNS) features.

FRAILTY MEDIATES SENILITY IN MEXICAN AMERICANS

The latent construct “d” (for “dementia”) offers a continuously distributed transdiagnostic dementia severity metric. Age is significantly associated with “d”. We test whether frailty mediates age’s effect on 6 year prospective change in dementia severity in Mexican-Americans (MA), using data from the Hispanic Established Population for Epidemiological Studies in the Elderly (HEPESE). Age was regressed onto the 6yr prospective slope of change in “d” in N = 880 [mean age = 77.4 (6.1) at wave 3]. Change in “d” was estimated by a latent growth curve (LGC) indicated by latent cognitive measures across three HEPESE waves (i.e., 3, 5 and 6). “Frailty” was assessed by a modified version of Fried et al.’s construct observed at wave 5, and was tested as a mediator of age’s association with change in “d”. The mediation effect was estimated by MacKinnon’s method. “d” at each wave, and the LGC of change in “d” all had acceptable model fit (e.g. RMSEA <.05). Age was significantly associated with change in “d”. 51% of their association was explained by frailty. Frailty mediates the majority of age’s association with dementia severity. Not only does this support the existence of a cognitive “frailty” syndrome in MA, it also implicates an effect of frailty on intelligence (as “d” is derived from Spearman’s general intelligence factor “g”). Their association may be mediated by blood-based serum biomarkers, including somatomedins, which may offer targets for the treatment and /or prevention of senility in frail elderly persons.

Selection for depression-specific dementia cases with replication in two cohorts

The latent variable "δ" (for "dementia") provides an etiologically "agnostic" omnibus dementia severity metric capable of recognizing the dementing potential of any condition. Depressive symptoms are independent predictors of δ and are thereby implicated as "dementing". Serum resistin levels partially mediate the association between depressive symptoms and δ. We use a novel "off-diagonal" CHI SQ algorithm to demonstrate our ability to select individuals demented solely by depression's effect in both the Texas Alzheimer's Research and Care Consortium (TARCC) (N ≌ 3,500), and the Alzheimer's Disease Neuroimaging Initiative (ADNI (N ≌ 1,750), and demonstrate the higher resistin levels of such cases in TARCC. This approach can be adapted to any δ-related dementia risk factor or biomarker and used identify individuals who might revert back to non-demented states after its successful treatment.

Genetic meta-analysis of diagnosed Alzheimer's disease identifies new risk loci and implicates Aβ, tau, immunity and lipid processing

Risk for late-onset Alzheimer's disease (LOAD), the most prevalent dementia, is partially driven by genetics. To identify LOAD risk loci, we performed a large genome-wide association meta-analysis of clinically diagnosed LOAD (94,437 individuals). We confirm 20 previous LOAD risk loci and identify five new genome-wide loci (IQCK, ACE, ADAM10, ADAMTS1, and WWOX), two of which (ADAM10, ACE) were identified in a recent genome-wide association (GWAS)-by-familial-proxy of Alzheimer's or dementia. Fine-mapping of the human leukocyte antigen (HLA) region confirms the neurological and immune-mediated disease haplotype HLA-DR15 as a risk factor for LOAD. Pathway analysis implicates immunity, lipid metabolism, tau binding proteins, and amyloid precursor protein (APP) metabolism, showing that genetic variants affecting APP and Aβ processing are associated not only with early-onset autosomal dominant Alzheimer's disease but also with LOAD. Analyses of risk genes and pathways show enrichment for rare variants (P = 1.32 × 10-7), indicating that additional rare variants remain to be identified. We also identify important genetic correlations between LOAD and traits such as family history of dementia and education.

A δ Homolog for Dementia Case Finding with Replication in the Alzheimer's Disease Neuroimaging Initiative

Dementia can be empirically described by the latent dementia phenotype "δ" and its various composite "homologs". We have explored δ's blood-based protein biomarkers in the Texas Alzheimer's Research and Care Consortium (TARCC) study. However, it would be convenient to replicate those associations in the Alzheimer's Disease Neuroimaging Initiative (ADNI). To this end, we have engineered a δ homolog from observed cognitive performance measures common to both projects. Our findings were replicated in randomly selected 50% splits of TARCC data (Group 1, N = 1,747; Group 2, N = 1,755), and then independently in ADNI (N = 1,737). The new δ homolog, i.e., "dT2A" (d-TARCC to ADNI), fit the data of both studies well, and was strongly correlated with dementia severity, as rated by the Clinical Dementia Rating Scale "sum of boxes" (TARCC: r = 0.99, p < 0.001; ADNI: r = 0.96, p < 0.001). dT2A achieved an area under the receiver operating characteristic curve of 0.981 (0.976-0.985) for the discrimination of Alzheimer's disease from normal controls in TARCC, and 0.988 (0.983-0.993) in ADNI. dT2A is the 12th δ homolog published to date, and opens the door to independent replications across these and similar studies.

Construction of a Potential Telephone Assessment of Dementia Prevalence and Severity

The "δ" (for "dementia") is a latent dementia phenotype that can be constructed by a unique confirmatory bifactor model in a structural equation model framework. Because it is derived from Spearman's general intelligence factor, "g," δ can be constructed from any cognitive battery. This may allow for accurate dementia case-finding by telephone and in the absence of expert clinical evaluation or review. The authors constructed a new δ homolog in a large ethnically diverse convenience sample: the Texas Alzheimer's Research and Care Consortium, comprising 2,016 participants (Alzheimer's disease [AD], N=920; mild cognitive impairment, N=277; normal controls, N=819). A δ composite ("dTEL") was extracted from informant-rated Instrumental Activities of Daily Living and a brief battery of verbal cognitive measures. The entire battery was engineered to be administered over the telephone. dTEL's model had excellent fit. dTEL correlated strongly with dementia severity, as measured by the Clinical Dementia Rating "sum of boxes" scale (r=0.78, p<0.001). The dTEL composite's area under the receiver operating characteristic curve for the discrimination between control subjects and AD patients was 0.97 (95% CI=0.964-0.975). This was superior to all dTEL indicators. Therefore, the authors have demonstrated that a δ homolog composite constructed entirely from verbal measures is strongly associated with dementia severity, can accurately diagnose dementia, and outperforms all observed measures from which it is constructed. Future studies are required to assess dTEL's performance relative to evaluation by expert clinicians when obtained by lay psychometricians over the telephone.

Exportation and Validation of Latent Constructs for Dementia Case Finding in a Mexican American Population-based Cohort

BACKGROUND

The latent variable "δ" has been validated as a dementia phenotype. δ can be extracted from Spearman's general intelligence factor "g" in any data set that contains measures of cognition and instrumental activities of daily living (IADL). We used δ composites ("d-scores") to estimate the prevalence of dementia in the Hispanic Established Population for Epidemiological Studies in the Elderly (H-EPESE).

METHOD

δ was constructed from Mini-Mental State Examination, a clock-drawing task (CLOX), and IADL. δ's H-EPESE factor weights were validated in the well-characterized Texas Alzheimer's Research and Care Consortium (TARCC). Optimal thresholds for the discrimination between "Alzheimer's disease" (AD) versus normal controls (NCs) were determined by receiver operating characteristic curve. Those thresholds were used to estimate the prevalence of dementia in H-EPESE.

RESULTS

Each δ homolog fits its source's data well. d-scores were strongly associated with Clinical Dementia Rating scale Sum of Boxes (r = .74-.85, all p < .001], and accurately distinguished AD cases from NCs, in both Mexican Americans (MAs) and non-Hispanic Whites (NHWs) [c = 0.94-0.96]. The TARCC MA threshold estimated the prevalence of dementia at 21.4% in H-EPESE. The NHW threshold estimated the prevalence of dementia at 21.0%.

CONCLUSIONS

It is possible to export δ composites from populations to well-characterized cohorts for validation.

Rare coding variants in PLCG2, ABI3, and TREM2 implicate microglial-mediated innate immunity in Alzheimer's disease

We identified rare coding variants associated with Alzheimer's disease in a three-stage case-control study of 85,133 subjects. In stage 1, we genotyped 34,174 samples using a whole-exome microarray. In stage 2, we tested associated variants (P < 1 × 10-4) in 35,962 independent samples using de novo genotyping and imputed genotypes. In stage 3, we used an additional 14,997 samples to test the most significant stage 2 associations (P < 5 × 10-8) using imputed genotypes. We observed three new genome-wide significant nonsynonymous variants associated with Alzheimer's disease: a protective variant in PLCG2 (rs72824905: p.Pro522Arg, P = 5.38 × 10-10, odds ratio (OR) = 0.68, minor allele frequency (MAF)cases = 0.0059, MAFcontrols = 0.0093), a risk variant in ABI3 (rs616338: p.Ser209Phe, P = 4.56 × 10-10, OR = 1.43, MAFcases = 0.011, MAFcontrols = 0.008), and a new genome-wide significant variant in TREM2 (rs143332484: p.Arg62His, P = 1.55 × 10-14, OR = 1.67, MAFcases = 0.0143, MAFcontrols = 0.0089), a known susceptibility gene for Alzheimer's disease. These protein-altering changes are in genes highly expressed in microglia and highlight an immune-related protein-protein interaction network enriched for previously identified risk genes in Alzheimer's disease. These genetic findings provide additional evidence that the microglia-mediated innate immune response contributes directly to the development of Alzheimer's disease.

Clock Copying Predicts Mortality in Adult Protective Services Clients

OBJECTIVE

The objective of this study was to determine if a clock copying task predicts 18-month mortality in an Adult Protective Services (APS) sample referred for a decision-making capacity assessment.

METHODS

The authors performed a retrospective medical record review of clients (N = 233) referred by APS for a decision-making capacity assessment during a 3-year time period. Information extracted included demographic data and neuropsychological performance on a battery sensitive to executive function, visuospatial ability, depression, memory, and general cognition. A Cox proportional hazards models was constructed to determine the relationship between Executive Clock Drawing Task Part 2 (CLOX2) performance and survival.

RESULTS

Poor clock copying, as measured by CLOX2, predicted 18-month mortality when covaried for age, education, sex, rural dwelling status, depression, and general cognition.

CONCLUSIONS

Clock copying is an easily administered visuospatial task that may inform survival in this vulnerable population.

Serum proteins mediate depression's association with dementia

The latent variable "δ" (for "dementia") uniquely explains dementia severity. Depressive symptoms are independent predictors of δ. We explored 115 serum proteins as potential causal mediators of the effect of depressive symptoms on δ in a large, ethnically diverse, longitudinal cohort. All models were adjusted for age, apolipoprotein E, education, ethnicity, gender, hemoglobin A1c, and homocysteine, and replicated in randomly selected 50% subsets. Alpha1-antitrypsin (A1AT), FAS, Heparin-binding EGF-like Growth Factor (HB-EGF), Insulin-like Growth Factor-1 (IGF-1), Luteinizing Hormone (LH), Macrophage Inflammatory Protein type 1 alpha (MIP-1α), Resitin, S100b, Tissue Inhibitor of Metalloproteinase type 1 (TIMP-1), and Vascular Cell Adhesion Molecule type 1 (VCAM-1) each were partial mediators of depression's association with δ. These proteins may offer targets for the treatment of depression's specific effect on dementia severity and Alzheimer's Disease (AD) conversion risk.

Cross-Ethnic Differences in the Severity of Neuropsychiatric Symptoms in Persons With Mild Cognitive Impairment and Alzheimer's Disease

In this cross-sectional study, we examined the neuropsychiatric profile of mild cognitive impairment (MCI) and Alzheimer's disease (AD) using the Neuropsychiatric Inventory Questionnaire (NPI-Q). Data were available on 875 controls, 339 MCI cases, and 975 AD participants. Surprisingly, differences in neuropsychiatric symptom (NPS) severity by ethnicity in subjects with AD, but not with MCI, were found. More so, in Hispanics with AD, a higher frequency in most of the individual NPI-Q symptom items of the scale was observed, except for apathy. After adjustment for clinical features, some individual NPI-Q symptoms also showed an association with Hispanic ethnicity in the control group that nearly reached statistical significance. There may be cross-ethnic differences in the neuropsychiatric presentation of AD in Hispanics versus non-Hispanic whites. Future studies are needed to clarify the etiology of these differences, and to assess the need for ethnicity-specific treatment and care-giving interventions.

Few serum proteins mediate APOE's association with dementia

The latent variable "δ" (for "dementia") appears to be uniquely responsible for the dementing aspects of cognitive impairment. Age, depression, gender and the apolipoprotein E (APOE) e4 allele are independently associated with δ. In this analysis, we explore serum proteins as potential mediators of APOE's specific association with δ in a large, ethnically diverse longitudinal cohort, the Texas Alzheimer's Research and Care Consortium (TARCC). APOE was associated only with C-Reactive Protein (CRP), Adiponectin (APN) and Amphiregulin (AREG), although the latter two's associations did not survive Bonferroni correction for multiple comparisons. All three proteins were associated with δ and had weak potential mediation effects on APOE's association with that construct. Our findings suggest that APOE's association with cognitive performance is specific to δ and partially mediated by serum inflammatory proteins. The majority of APOE's significant unadjusted effect on δ is unexplained. It may instead arise from direct central nervous system effects, possibly on native intelligence. If so, then APOE may exert a life-long influence over δ and therefore all-cause dementia risk.

δ scores predict mild cognitive impairment and Alzheimer's disease conversions from nondemented states

INTRODUCTION

We tested the latent variable "δ" (for "dementia")'s ability to predict conversion to "mild cognitive impairment" (MCI) and Alzheimer's disease (AD).

METHODS

An ethnicity equivalent d homolog ("dEQ") was constructed in n = 1113 Mexican- American (MA) and n = 1958 non-Hispanic white (NHW) participants in the Texas Alzheimer's Research and Care Consortium. "Normal Controls" (NC) (n = 1276) and MCI cases (n = 611) were followed annually for up to 6 years [m = 4.7(0.6)].

RESULTS

22.0% (n = 281) of NC converted to "MCI" or "AD". 17.3%( n = 106) of MCI converted to "AD." Independently of covariates, each quintile increase in the dEQ scores of NC increased the odds of conversion by 52%. Each quintile increase in the dEQ scores of MCI cases increased the odds of conversion to AD almost three-fold.

DISCUSSION

Baseline δ scores predict MCI and AD conversions from nondemented states in MA and NHW.

Serum protein mediators of dementia and aging proper

The latent variable "δ" (for "dementia") appears to be uniquely responsible for the dementing aspects of cognitive impairment. Age, depressive symptoms, gender and the apolipoprotein E (APOE) ε4 allele are independently associated with δ. In this analysis, we explore serum proteins as potential mediators of age's specific association with δ in a large, ethnically diverse longitudinal cohort, the Texas Alzheimer's Research and Care Consortium (TARCC). 22 serum proteins were recognized as partial mediators of age's association with δ. These include Insulin-like Growth Factor-Binding Protein 2 (IGF-BP2), which we had previously associated with age-specific cognitive change, and both Pancreatic Polypeptide (PP) and von Willebrand Factor (vWF), previously associated with δ. Nine other δ-related proteins were not confirmed by this ethnicity adjusted analysis. Our findings suggest that age's association with the disabling fraction of cognitive performance is partially mediated by serum proteins, somatomedins and hormones. Those proteins may offer targets for the specific treatment of age-related effects on dementia severity and conversion risk.

Welcome Back to Your Future: The Assessment of Dementia by the Latent Variable "δ"

The latent variable "δ" (for "dementia") has been proposed as a phenotype for all cause dementia. δ is extracted from cognitive batteries by a specific confirmatory factor analysis in a structural equation modeling framework. δ appears to be uniquely responsible for cognition's association with functional status. Because it is extracted from Spearman's general intelligence factor "g", this has broad implications for dementia's assessment and pathophysiology. This issue of the Journal of Alzheimer's Disease brings together several demonstrations of δ's psychometric properties by investigative groups from three continents. In their aggregate, they suggest that δ homologs may have far ranging applications in dementia's clinical assessment and biomarker selection.

Aging is a weak but relentless determinant of dementia severity

Structural Equation Models (SEM) can explicitly distinguish "dementia-relevant" variance in cognitive task performance (i.e., "δ" for dementia). In prior work, δ appears to uniquely account for dementia severity regardless of the cognitive measures used to construct it. In this study, we test δ as a mediator of age's prospective association with future cognitive performance and dementia severity in a large, ethnically diverse longitudinal cohort, the Texas Alzheimer's Research and Care Consortium (TARCC). Age had adverse effects on future cognition, and these were largely mediated through δ, independently of education, ethnicity, gender, depression ratings, serum homo-cysteine levels, hemoglobin A1c, and apolipoprotein e4 status. Age explained 4% of variance in δ, and through it, 11-18% of variance in future cognitive performance. Our findings suggest that normative aging is a dementing condition (i.e., a "senility"). While the majority of variance in dementia severity must be independent of age, age's specific effect is likely to accumulate over the lifespan. Our findings also constrain age's dementing effects on cognition to the age-related fraction of "general intelligence" (Spearman's "g"). That has broad biological and pathophysiological implications.

Thrombopoietin is associated with δ's intercept, and only in Non-Hispanic Whites

Introduction

Serum thrombopoietin (THPO) is a biomarker of Alzheimer's disease (AD) and the latent dementia phenotype, “δ”. Both associations may be specific to non-Hispanic whites (NHW), not Mexican-Americans (MA). In this analysis, we examine ethnicity's effect on THPO's association with change in δ scores, in the Texas Alzheimer's Research and Care Consortium (TARCC).

Methods

We constructed an ethnicity equivalent δ homolog (“dEQ”) among n = 1113 MA and n = 1958 NHW. dEQ was output as a composite “dEQ-score” for each of five annual TARCC waves. Those composites were used as indicators of a latent growth curve (LGC). The mean dEQ intercept (idEQ) and slope (ΔdEQ) were estimated in a random subset of N = 1528 participants and replicated in the remainder (n = 1544). THPO was regressed onto idEQ and ΔdEQ. Those associations were tested separately in MA and NHW.

Results

dEQ correlated strongly with CDR-SB (r = 0.99, P < .001) and achieved high AUCs for AD diagnosis at each wave (range = 0.95–0.99). THPO was significantly associated with idEQ but not ΔdEQ. That effect was observed in NHW only. In MA, THPO had no associations with either idEQ or ΔdEQ.

Discussion

We confirm THPO's ethnicity-specific association with δ in NHW. It is further clarified that this association is specific to δ's intercept and not its slope. This analysis provides a model for how dementia's specific serum biomarkers can be characterized.

Vitamin D binding protein as a serum biomarker of Alzheimer's disease

Vitamin D binding protein (VDBP), a multifunctional protein, has been found to be elevated in the cerebrospinal fluid (CSF) of neurodegenerative disorder cases, implicating it in the pathogenesis of Alzheimer's disease (AD). However, the contribution of VDBP to AD has not been fully explored. We used a Multiple Indicators Multiple Causes (MIMIC) approach to examine the relationship between serum VDBP levels and cognitive performance in a well characterized AD cohort, the Texas Alzheimer's Research and Care Consortium (TARCC). Instead of categorical diagnoses, we used a latent dementia phenotype (d), which has been validated in several prior studies using this dataset. We found that serum VDBP levels are significantly positively associated with d scores, which in turn are inversely related to cognitive performance. This suggests that d mediates the adverse effects of serum VDB on cognition and therefore that its effects are specifically dementing. d scores are also specifically related to default mode network (DMN) structure. VDBP acts as an amyloid-β (Aβ) scavenger, and Aβ deposition in the DMN is seen in the pre-clinical stages of AD. We speculate then that serum effects of VDBP are mediated through changes in DMN structure or function, most probably via Aβ. Aβ affects the DMN early in the course of AD. Therefore, raised serum VDBP levels may be a useful indicator of future dementia and/or dementia conversion. This might be confirmed through longitudinal analysis of TARCC data.

Serum IGF-BP2 strongly moderates age's effect on cognition: a MIMIC analysis

We have used structural equation models to explicitly distinguish functional status and therefore "dementia-relevant" variance in cognitive task performance (i.e., "δ" for dementia). Our approach is modular and can be directed to other targets. In this analysis, we construct a δ ortholog representing the "cognitive correlates of age" (cAGE). cAGE largely mediates age's effects on dementia severity, as rated by the Clinical Dementia Rating Scale Sum of boxes and has an area under the receiver operating curve = 0.96 for the diagnosis of Alzheimer's Disease versus controls. We then test cAGE's association with serum insulin-like growth factor binding protein 2 (IGF-BP2), which has previously been associated with age-related cognitive changes in animals, and with cortical atrophy in older humans. IGF-BP2's adverse effects on cognition are largely mediated through cAGE, independent of education, ethnicity, gender, depression ratings, serum homocysteine levels, hemoglobin A1c, and apolipoprotein e4 status. This suggests that age-specific cognitive decline may be moderated by IGF-BP2 and that modulation of that protein's function(s) might ameliorate age-specific cognitive impairments.

Neuropsychiatric symptoms in community-dwelling Mexican-Americans: results from the Hispanic Established Population for Epidemiological Study of the Elderly (HEPESE) study

OBJECTIVE

The Neuropsychiatric Inventory (NPI) is a well-established measure of psychopathology and frequently used in dementia studies. Little is known about its psychometric characteristics at a population level, particularly among Hispanics. We report the frequency of NPI symptoms in a community-dwelling older Mexican-American (MA) population cohort and the degree of symptom-related distress experienced by participant informants.

METHODS

Participants were 1079 MA age 80 years and over residing in five southwestern states who were administered the NPI as part of wave-7 of the Hispanic Established Population for Epidemiological Study of the Elderly (HEPESE) conducted from 2010 to 2011.

RESULTS

Nine hundred twenty-five informants rated NPI domains. Prevalence of neuropsychiatric symptoms (NPS) varied by symptom domain and ranged from agitation/aggression (32%) to euphoria/elation (5%). The overall rate of behavioral disturbances was 62.7%. On the other hand, 37.3% of informants reported no NPS. A significant fraction of the informants reported distress from the mood disorder cluster of the scale.

CONCLUSIONS

A large percentage (>60%) of community-dwelling older MA have one or more informant-reported NPS. These symptoms have diagnostic, prognostic, and therapeutic implications. Although neuropsychiatric disorders may be the initial clinical manifestation of dementia and often appear before cognitive alterations, the high frequency of these symptoms in the HEPESE cohort may reflect a high prevalence of these disorders among community-dwelling MA. The pattern we observed also suggests relatively advanced stages of dementia.

Serum interleukin (IL)-15 as a biomarker of Alzheimer's disease

Interleukin (IL-15), a pro-inflammatory cytokine has been studied as a possible marker of Alzheimer’s disease (AD); however its exact role in neuro-inflammation or the pathogenesis AD is not well understood yet. A Multiple Indicators Multiple Causes (MIMIC) approach was used to examine the relationship between serum IL-15 levels and AD in a well characterized AD cohort, the Texas Alzheimer's Research and Care Consortium (TARCC). Instead of categorical diagnoses, we used two latent construct d (for dementia) and g’ (for cognitive impairments not contributing to functional impairments) in our analysis. The results showed that the serum IL-15 level has significant effects on cognition, exclusively mediated by latent construct d and g’. Contrasting directions of association lead us to speculate that IL-15’s effects in AD are mediated through functional networks as d scores have been previously found to be specifically related to default mode network (DMN). Our finding warrants the need for further research to determine the changes in structural and functional networks corresponding to serum based biomarkers levels.

The temporospatial evolution of neuritic plaque-related and independent tauopathies: implications for dementia staging

Neuritic plaque (NP) formation can be dated in vivo. This analysis attempts to "date" the progression of neurofibrillary tangles (NFT) using the spatial distribution of NP as a reference. Autopsy data from 471 participants in the Honolulu-Asia Aging Study (HAAS) were combined into latent factor measures of NFT and NP counts. The variance in "early" and "late" NP pathology was used to estimate the spatial distribution of "early" and "late" NFT formation. A third latent factor representing "non-NP-related NFT" was also constructed. "Early" NP and "late" NP correlated significantly with objectively early and later cognitive performance, respectively. In contrast to our expectations, neocortical NFT correlated best with "early" NP pathology, while NFT in allocortical structures correlated best with "late" NP pathology. Therefore, the NP-related fraction of NFT appears to be co-localized spatially with NP. However, since the latter evolve corticofugally in time, this suggests that NP-related NFT do so as well. Corticotropic NFT formation must therefore be either unrelated to NP formation, a temporally distinct process, or both.