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.

Future Dementia Severity is Almost Entirely Explained by the Latent Variable δ's Intercept and Slope

BACKGROUND

Structural equation models (SEM) can explicitly distinguish dementia-relevant variance in cognitive task performance. The resulting latent construct "δ" (for dementia) provides a relatively "error free" continuously varying dementia-specific phenotype.

OBJECTIVE

To estimate δ's change over time (Δδ) and determine Δδ's predictive validity using future dementia status as an outcome.

METHODS

Data from n = 2,191 participants of the Texas Alzheimer's Research and Care Consortium (TARCC) were used to construct a latent growth curve model of longitudinal change over four years using five cognitive measures and one measure of Instrumental Activities of Daily Living. Four final latent factors, including baseline δ and Δδ, were simultaneously entered as predictors of wave 4 dementia severity, as estimated by the Clinical Dementia Rating Scale "sum of boxes" (CDR).

RESULTS

All observed measures exhibited significant change [χ2 = 1,152 (df = 229); CFI = 0.968; RMSEA = 0.043]. The final model demonstrated excellent fit to the data [χ2 = 543 (df = 245); CFI = 0.991; RMSEA = 0.023]. All latent indicator loadings were significant, yielding four distinct factors. After adjustment for demographic covariates and baseline CDR scores, d and Δd were significantly independently associated with CDR4, explaining 25% and 49% of its variance, respectively. The latent variable g' significantly explained 3% of CDR4 variance independently of d and Δd. Δg' was not significantly associated with CDR4. Baseline CDR explained 16% of CDR4 variance.

CONCLUSIONS

Future dementia severity is almost entirely explained by the latent construct δ's intercept and slope.

Greater than the sum of its parts: δ Improves upon a battery's diagnostic performance

OBJECTIVE

"δ", a latent variable constructed from batteries that contain both cognitive and functional status measures, can accurately diagnose dementia relative to expert clinicians. The minimal assessment needed is unknown.

METHODS

We validated 2 δ homologs in a convenience sample of elderly Japanese persons with normal cognition (NC), mild cognitive impairment (MCI), and dementia (n = 176). The latent δ homolog "d" (for dementia) was constructed from Instrumental Activities of Daily Living (IADL) and Japanese translations of the Executive Clock-Drawing Task (CLOX), Frontal Assessment Battery (FAB), and Executive Interview (EXIT25). The latent delta homolog "d3" was constructed from a restricted set of d's factor loadings.

RESULTS

d and d3 were highly intercorrelated (r = .97) and strongly related to both IADL and dementia severity, as rated blindly by the Clinical Dementia Rating Scale (CDR). d was more strongly related to IADL and CDR than any of its indicators. In multivariate regression, d explained more variance in CDR scores than all of its indicators combined. d's areas under the receiver operating characteristic curve (AUC) were 0.95 for the discrimination between Alzheimer's disease (AD) vs. NC, 0.84 for AD vs. MCI and 0.81 for NC vs. MCI. d3's AUC's were statistically indiscriminable. These AUC's are higher than any of d's indicators, as reported recently by Matsuoka et al. (2014), as well as the Mini-Mental State Examination (MMSE), which had been made available by Matsuoka et al. to the CDR raters.

CONCLUSIONS

Latent variables can improve upon a battery's diagnostic performance and offer the potential for accurate dementia case-finding after a minimal bedside assessment.

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.

Ethnicity moderates dementia's biomarkers

We have employed structural equation models to explicitly distinguish functional status, and therefore "dementia-relevant" variance in cognitive task performance (i.e., "δ"). We previously associated δ with cytokines and other serum biomarkers in a well characterized Alzheimer's disease cohort, the Texas Alzheimer's Research and Care Consortium. However, that δ homolog did not exhibit factor equivalence across ethnicity. In this study, we construct a δ homolog that exhibits mean and factor equivalence across ethnicity [i.e., "d(=)"]. d(=) is associated significantly with ten of the twelve previously selected biomarkers. Most of these associations are again specific to Non-Hispanic White participants. These findings have yet to be validated in other cohorts, but may suggest cross-ethnic differences in dementia's pathobiological mechanisms between Hispanic Mexican-Americans and Non-Hispanic Whites.