Total Brain and Hippocampal Volumes and Cognition in Older American Indians: The Strong Heart Study

Alzheimer disease blood biomarkers: considerations for population-level use

In the past 5 years, we have witnessed the first approved Alzheimer disease (AD) disease-modifying therapy and the development of blood-based biomarkers (BBMs) to aid the diagnosis of AD. For many reasons, including accessibility, invasiveness and cost, BBMs are more acceptable and feasible for patients than a lumbar puncture (for cerebrospinal fluid collection) or neuroimaging. However, many questions remain regarding how best to utilize BBMs at the population level. In this Review, we outline the factors that warrant consideration for the widespread implementation and interpretation of AD BBMs. To set the scene, we review the current use of biomarkers, including BBMs, in AD. We go on to describe the characteristics of typical patients with cognitive impairment in primary care, who often differ from the patient populations used in AD BBM research studies. We also consider factors that might affect the interpretation of BBM tests, such as comorbidities, sex and race or ethnicity. We conclude by discussing broader issues such as ethics, patient and provider preference, incidental findings and dealing with indeterminate results and imperfect accuracy in implementing BBMs at the population level.

Multimodal imaging of the aging brain: Baseline findings of the LoCARPoN study

We quantified and investigated multimodal brain MRI measures in the LoCARPoN Study due to lack of normative data among Indians. A total of 401 participants (aged 50-88 years) without stroke or dementia completed MRI investigation. We assessed 31 brain measures in total using four brain MRI modalities, including macrostructural (global & lobar volumes, white matter hyperintensities [WMHs]), microstructural (global and tract-specific white matter fractional anisotropy [WM-FA] and mean diffusivity [MD]) and perfusion measures (global and lobar cerebral blood flow [CBF]). The absolute brain volumes of males were significantly larger than those of females, but such differences were relatively small (<1.2% of intracranial volume). With increasing age, lower macrostructural brain volumes, lower WM-FA, greater WMHs, higher WM-MD were found (P = 0.00018, Bonferroni threshold). Perfusion measures did not show significant differences with increasing age. Hippocampal volume showed the greatest association with age, with a reduction of approximately 0.48%/year. This preliminary study augments and provides insight into multimodal brain measures during the nascent stages of aging among the Indian population (South Asian ethnicity). Our findings establish the groundwork for future hypothetical testing studies.

Intraindividual Cognitive Variability and Magnetic Resonance Imaging in Aging American Indians: Data from the Strong Heart Study

BACKGROUND

American Indians have high prevalence of risk factors for Alzheimer's disease and related dementias (ADRD) compared to the general population, yet dementia onset and frequency in this population are understudied. Intraindividual cognitive variability (IICV), a measure of variability in neuropsychological test performance within a person at a single timepoint, may be a novel, noninvasive biomarker of neurodegeneration and early dementia.

OBJECTIVE

To characterize the cross-sectional associations between IICV and hippocampal, total brain volume, and white matter disease measured by magnetic resonance imaging (MRI) among older American Indians.

METHODS

IICV measures for memory, executive function, and processing speed, and multidomain cognition were calculated for 746 American Indians (aged 64-95) who underwent MRI. Regression models were used to examine the associations of IICV score with hippocampal volume, total brain volume, and graded white matter disease, adjusting for age, sex, education, body mass index, intracranial volume, diabetes, stroke, hypertension, hypercholesterolemia, alcohol use, and smoking.

RESULTS

Higher memory IICV measure was associated with lower hippocampal volume (Beta = -0.076; 95% CI -0.499, -0.023; p = 0.031). After adjustment for Bonferroni or IICV mean scores in the same tests, the associations were no longer significant. No IICV measures were associated with white matter disease or total brain volume.

CONCLUSION

These findings suggest that the IICV measures used in this research cannot be robustly associated with cross-sectional neuroimaging features; nonetheless, the results encourage future studies investigating the associations between IICV and other brain regions, as well as its utility in the prediction of neurodegeneration and dementia in American Indians.

APOE genotype, hippocampus, and cognitive markers of Alzheimer's disease in American Indians: Data from the Strong Heart Study

BACKGROUND

The apolipoprotein E (APOE) ε4 allele confers higher risk of neurodegeneration and Alzheimer's disease (AD), but differs by race/ethnicity. We examined this association in American Indians.

METHODS

The Strong Heart Study is a population-based cohort of American Indians who were 64 to 95 years of age in 2010 to 2013. APOE ε4 status, brain imaging, and neuropsychological testing was collected in N = 811 individuals. Summary statistics, graphics, and generalized linear regressions-adjusted for sociodemographics, clinical features, and intracranial volume with bootstrap variance estimator-compared APOE ε4 carriers with non-carriers.

RESULTS

APOE ε4 carriers comprised 22% of the population (0.7% homozygotes). Participants were mean 73 years, 67% female, and 54% had some college education. The majority were obese (>50%), hypertensive (>80%), and diabetic (>50%). Neither imaging findings nor multidomain cognitive testing showed any substantive differences between APOE ε4 carriers and non-carriers.

CONCLUSION

We found no evidence of neurodegenerative risk from APOE ε4 in American Indians. Additional studies are needed to examine potential protective features.

Combining Visual Rating Scales for Medial Temporal Lobe Atrophy and Posterior Atrophy to Identify Amnestic Mild Cognitive Impairment from Cognitively Normal Older Adults: Evidence Based on Two Cohorts

BACKGROUND

Visual rating scales for medial temporal lobe atrophy (MTA) and posterior atrophy (PA) have been reported to be useful for Alzheimer's disease diagnosis in routine clinical practice.

OBJECTIVE

To investigate the efficacy of combined MTA and PA visual rating scales to discriminate amnestic mild cognitive impairment (aMCI) patients from healthy controls.

METHODS

This study included T1-weighted MRI images from two different cohorts. In the first cohort, we recruited 73 patients with aMCI and 48 group-matched cognitively normal controls for training and validation. Visual assessments of MTA and PA were carried out for each participant. Global gray matter volume and density were estimated using voxel-based morphometry analysis as the objective reference. We investigated the discriminative power of a single visual rating scale and the combination of the MTA and PA rating scales for identifying aMCI. The second cohort, consisting of 33 aMCI patients and 45 controls, was used to verify the reliability of the visual assessments.

RESULTS

Compared with the single visual rating scale, the combination of the MTA and PA exhibited the best discriminative power, with an AUC of 0.818±0.041, which was similar to the diagnostic accuracy of the gray matter volumetric measures. The discriminative power of the combined MTA and PA was verified in the second cohort (AUC 0.824±0.058).

CONCLUSION

The combined MTA and PA rating scales demonstrated practical diagnostic value for distinguishing aMCI patients from controls, suggesting its potential to serve as a convenient and reproducible method to assess the degree of atrophy in clinical settings.

Comparing Vascular Brain Injury and Stroke by Cranial Magnetic Resonance Imaging, Physician-Adjudication, and Self-Report: Data from the Strong Heart Study

BACKGROUND

Epidemiologic studies often use self-report as proxy for clinical history. However, whether self-report correctly identifies prevalence in minority populations with health disparities and poor health-care access is unknown. Furthermore, overlap of clinical vascular events with covert vascular brain injury (VBI), detected by imaging, is largely unexamined.

METHODS

The Strong Heart Study recruited American Indians from 3 regions, with surveillance and adjudication of stroke events from 1989 to 2013. In 2010-2013, all 817 survivors, aged 65-95 years, underwent brain imaging, neurological history interview, and cognitive testing. VBI was defined as imaged infarct or hemorrhage.

RESULTS

Adjudicated stroke was prevalent in 4% of participants and separately collected, self-reported stroke in 8%. Imaging-defined VBI was detected in 51% and not associated with any stroke event in 47%. Compared with adjudication, self-report had 76% sensitivity and 95% specificity. Participants with adjudicated or self-reported stroke had the poorest performance on cognitive testing; those with imaging-only (covert) VBI had intermediate performance.

CONCLUSION

In this community-based cohort, self-report for prior stroke had good performance metrics. A majority of participants with VBI did not have overt, clinically recognized events but did have neurological or cognitive symptoms. Data collection methodology for studies in a resource-limited setting must balance practical limitations in costs, accuracy, feasibility, and research goals.

The Prevalence of Cardiovascular Disease and Other Comorbidities Among American Indian and Alaska Native Adults with Diabetes

AIMS

American Indians and Alaska Native (AI/ANs) peoples experience significant health disparities compared to the U.S. general population. We report comorbidities among AI/ANs with diabetes to guide efforts to improve their health status.

METHODS

Drawing upon data for over 640,000 AI/ANs who used services funded by the Indian Health Service, we identified 43,518 adults with diabetes in fiscal year 2010. We reported the prevalence of comorbidities by age and cardiovascular disease (CVD) status. Generalized linear models were estimated to describe associations between CVD and other comorbidities.

RESULTS

Nearly 15% of AI/AN adults had diabetes. Hypertension, CVD and kidney disease were comorbid in 77.9%, 31.6%, and 13.3%, respectively. Nearly 25% exhibited a mental health disorder; 5.7%, an alcohol or drug use disorder. Among AI/ANs with diabetes absent CVD, 46.9% had 2 or more other chronic conditions; the percentage among adults with diabetes and CVD was 75.5%. Hypertension and tobacco use disorders were associated with a 71% (95% CI for prevalence ratio: 1.63 - 1.80) and 33% (1.28 - 1.37) higher prevalence of CVD, respectively, compared to adults without these conditions.

CONCLUSION

Detailed information on the morbidity burden of AI/ANs with diabetes may inform enhancements to strategies implemented to prevent and treat CVD and other comorbidities.

Urinary Arsenic and Cadmium Associations with Findings from Cranial MRI in American Indians: Data from the Strong Heart Study

BACKGROUND

Arsenic and cadmium are known cardiovascular toxicants that pose disproportionate risk to rural communities where environmental exposures are high. American Indians have high vascular risk, which may be attributable in part to these exposures.

OBJECTIVE

We examined urine metal concentrations in association with magnetic resonance imaging findings of vascular brain injury or cerebral atrophy in adult American Indians.

METHODS

We measured arsenic and cadmium in American Indian participants from the Strong Heart Study (1989-1991) and evaluated these associations with later (2010-2013) measures of infarct, hemorrhage, white matter hyperintensity (WMH) grade, brain and hippocampal volume, and sulcal and ventricle atrophy using nested multivariate regression analyses.

RESULTS

Among participants with available data (N=687), the median urine arsenic:creatinine ratio was 7.54μg/g [interquartile range (IQR): 4.90-11.93] and the cadmium:creatinine ratio was 0.96μg/g (IQR: 0.61-1.51). Median time between metal measurement and brain imaging was 21 y (range: 18-25 y). Statistical models detected significant associations between arsenic and higher burden of WMH [grade increase=0.014 (95% CI: 0.000, 0.028) per 10% increase in arsenic]; and between cadmium and presence of lacunar infarcts [relative risk (RR)=1.024 (95% CI: 1.004, 1.045) per 10% increase in cadmium].

DISCUSSION

This population-based cohort of American Indian elders had measured values of urine arsenic and cadmium several times higher than previous population- and clinic-based studies in the United States and Mexico, and comparable values with European industrial workers. Our findings of associations for arsenic and cadmium exposures with vascular brain injury are consistent with established literature. Environmental toxicant accumulation is modifiable; public health policy may benefit from focusing on reductions in environmental metals. https://doi.org/10.1289/EHP6930.

Cognitive Correlates of MRI-defined Cerebral Vascular Injury and Atrophy in Elderly American Indians: The Strong Heart Study

OBJECTIVE

American Indians experience substantial health disparities relative to the US population, including vascular brain aging. Poorer cognitive test performance has been associated with cranial magnetic resonance imaging findings in aging community populations, but no study has investigated these associations in elderly American Indians.

METHODS

We examined 786 American Indians aged 64 years and older from the Cerebrovascular Disease and its Consequences in American Indians study (2010-2013). Cranial magnetic resonance images were scored for cortical and subcortical infarcts, hemorrhages, severity of white matter disease, sulcal widening, ventricle enlargement, and volumetric estimates for white matter hyperintensities (WMHs), hippocampus, and brain. Participants completed demographic, medical history, and neuropsychological assessments including testing for general cognitive functioning, verbal learning and memory, processing speed, phonemic fluency, and executive function.

RESULTS

Processing speed was independently associated with the presence of any infarcts, white matter disease, and hippocampal and brain volumes, independent of socioeconomic, language, education, and clinical factors. Other significant associations included general cognitive functioning with hippocampal volume. Nonsignificant, marginal associations included general cognition with WMH and brain volume; verbal memory with hippocampal volume; verbal fluency and executive function with brain volume; and processing speed with ventricle enlargement.

CONCLUSIONS

Brain-cognition associations found in this study of elderly American Indians are similar to those found in other racial/ethnic populations, with processing speed comprising an especially strong correlate of cerebrovascular disease. These findings may assist future efforts to define opportunities for disease prevention, to conduct research on diagnostic and normative standards, and to guide clinical evaluation of this underserved and overburdened population.