Staging the cognitive continuum in prodromal Alzheimer's disease with episodic memory

Chronic memantine disrupts spatial memory and up-regulates Htr1a gene expression in the hippocampus of GPR39 (zinc-sensing receptor) KO male mice

GPR39 is a receptor involved in zincergic neurotransmission, and its role in regulating psychological functions is an active area of research. The purported roles of GPR39 at the cellular level include regulation of inflammatory and oxidative stress response, and modulation of GABAergic and endocannabinoid neurotransmission. GPR39 knock-out (KO) mice exhibit episodic-like and spatial memory (ELM and SM, respectively) deficits throughout their lifetime, and are similar in that respect to senescent wild-type (WT) conspecifics. Since a role for zinc has been postulated in neurodegenerative disorders, in this study we investigated the possibility of a pharmacological rescue of both types of declarative memory with memantine - a noncompetitive NMDAR antagonist used for slowing down dementia; or, a putative GPR39 agonist - TC-G 1008. First, we tested adult WT and GPR39KO male mice under acute 5 mg/kg memantine or vehicle treatment in an object recognition task designed to simultaneously probe the "what?", "where?" and "when?" components of ELM. Next, we investigated the impact of chronic memantine or TC-G 1008 on ELM and SM (Morris water maze, MWM) in both WT and GPR39KO mice. Following chronic experiments, we assessed with qRT-PCR hippocampal gene expression of targets previously associated with GPR39. We report: no effects of acute memantine on ELM; a tendency to improve the "where?" component of ELM in both WT and GPR39 KO mice following 12 days of memantine; and, a disruption of SM in GPR39KO mice after 24 days of memantine treatment. The latter result was associated with upregulation of Htr1a hippocampal expression.

Multi-domain cognition dysfunction accompanies frontoparietal and temporal amyloid accumulation in the elderly

It is helpful to understand the pathology of Alzheimer's disease by exploring the relationship between amyloid-β accumulation and cognition. The study explored the relationship between regional amyloid-β accumulation and multiple cognitions and study their application value in the Alzheimer's disease diagnosis. 135 participants completed 18F-florbetapir Positron Emission Tomography (PET), structural MRI, and a cognitive battery. Partial correlation was used to examine the relationship between global and regional amyloid-β accumulation and cognitions. Then, a support vector machine was applied to determine whether cognition-related accumulation regions can adequately distinguish the cognitively normal controls (76 participants) and mild cognitive impairment (30 participants) groups or mild cognitive impairment and Alzheimer's disease (29 participants) groups. The result showed that amyloid-β accumulation regions were mainly located in the frontoparietal cortex, calcarine fissure, and surrounding cortex and temporal pole regions. Episodic memory-related regions included the frontoparietal cortices; executive function-related regions included the frontoparietal, temporal, and occipital cortices; and processing speed-related regions included the frontal and occipital cortices. Support vector machine analysis showed that only episodic memory-related amyloid-β accumulation regions had better classification performance during the progression of Alzheimer's disease. Assessing regional changes in amyloid, particularly in frontoparietal regions, can aid in the early detection of amyloid-related decline in cognitive function.

Olfactory function reflects episodic memory performance and atrophy in the medial temporal lobe in individuals at risk for Alzheimer's disease

We examined cognitive domains and brain regions associated with olfactory performance in cognitively unimpaired older adults (CU-OAs) and individuals with or at risk for Alzheimer's Disease (AD). We compared CU-OAs (N = 55), individuals with subjective cognitive decline (SCD, N = 55), mild cognitive impairment (MCI, N = 101), and AD (N = 45) on measures of olfactory function (Brief Smell Identification Test), cognition (episodic and semantic memory), and medial temporal lobe thickness and volume. Analyses controlled for age, sex, education, and total intracranial volume. Olfactory function decreased from SCD to MCI to AD. CU-OAs outperformed all groups except SCDs on tests of cognition and olfaction. Although these measures did not differ between the CU-OAs and SCDs, olfactory function correlated with episodic memory tests and with entorhinal cortex atrophy only in the SCD group. Olfactory function also correlated with hippocampal volume and right-hemisphere entorhinal cortex thickness in the MCI group. Olfactory dysfunction reflects medial temporal lobe integrity and memory performance in a group at risk for AD with normal cognition and olfaction.

Effect of acupuncture on episodic memory for amnesia-type mild cognitive impairment: study protocol of a multicenter, randomized, controlled trial

BACKGROUND

Amnesic mild cognitive impairment (aMCI) is the main subtype of mild cognitive impairment (MCI) and has the highest risk of conversion to Alzheimer's disease (AD) among all MCI subtypes. Episodic memory impairment is the early cognitive impairment of aMCI, which has become an important target for AD prevention. Previous clinical evidence has shown that acupuncture can improve the cognitive ability of MCI patients. This experiment aimed to observe the efficacy and neural mechanism of TiaoshenYizhi acupuncture on the episodic memory of patients with aMCI.

METHODS

In this multicenter, parallel-group, double-blind, randomized controlled trial, 360 aMCI participants will be recruited from six subcenters and randomly assigned to the acupuncture group, sham acupuncture group, and control group. The acupuncture group will receive TiaoshenYizhi (TSYZ) acupuncture, the sham acupuncture group will use streitberger sham acupuncture, and the control group will only receive free health education. Participants in the two acupuncture groups will receive real acupuncture treatment or placebo acupuncture three times per week, 24 sessions over 8 consecutive weeks. The primary outcome will be global cognitive ability. Secondary outcomes will be a specific cognitive domain, including episodic memory and execution ability, electroencephalogram, and functional magnetic resonance imaging data. Outcomes will be measured at baseline and the fourth and eighth weeks after randomization. Repeated measurement analysis of variance and a mixed linear model will be used to observe the intervention effect.

DISCUSSION

The protocol will give a detailed procedure to the multicenter clinical trial to further evaluate the efficacy and neural mechanism of TiaoshenYizhi acupuncture on episodic memory in patients with aMCI. From this research, we expect to provide clinical evidence for early aMCI management.

TRIAL REGISTRATION

http://www.chictr.org.cn/edit.aspx?pid=142612&htm=4 , identifier: ChiCTR2100054009.

Imaging glucose metabolism to reveal tumor progression

Purpose: To analyze and review the progress of glucose metabolism-based molecular imaging in detecting tumors to guide clinicians for new management strategies. Summary: When metabolic abnormalities occur, termed the Warburg effect, it simultaneously enables excessive cell proliferation and inhibits cell apoptosis. Molecular imaging technology combines molecular biology and cell probe technology to visualize, characterize, and quantify processes at cellular and subcellular levels in vivo. Modern instruments, including molecular biochemistry, data processing, nanotechnology, and image processing, use molecular probes to perform real-time, non-invasive imaging of molecular and cellular events in living organisms. Conclusion: Molecular imaging is a non-invasive method for live detection, dynamic observation, and quantitative assessment of tumor glucose metabolism. It enables in-depth examination of the connection between the tumor microenvironment and tumor growth, providing a reliable assessment technique for scientific and clinical research. This new technique will facilitate the translation of fundamental research into clinical practice.

NEURONORMA Cognitive Battery Associations with Cerebrospinal Fluid Amyloid-β and Tau Levels in the Continuum of Alzheimer's Disease

BACKGROUND

Neuropsychological assessments are essential to define the cognitive profile and contribute to the diagnosis of Alzheimer's disease (AD). The progress in knowledge about the pathophysiological process of the disease has allowed conceptualizing AD through biomarkers as a biological continuum that encompasses different clinical stages.

OBJECTIVE

To explore the association between cerebrospinal fluid (CSF) biomarkers of AD and cognition using the NEURONORMA battery, in a sample of cognitively unimpaired (CU), mild cognitive impaired (MCI), and mild dementia of the Alzheimer type (DAT) subjects, and to characterize the cognitive profiles in MCI subjects classified by A/T/N system.

METHODS

42 CU, 35 MCI, and 35 mild DAT were assessed using the NEURONORMA battery. Core AD biomarkers [amyloid-β42 (Aβ42) peptide, total tau (t-tau), and phosphorylated tau 181 (p-tau181)] proteins were measured in CSF. Correlation coefficients, multivariate regression, and effect sizes were calculated. We explored the age- and education-adjusted cognitive profiles by A/T/N variants within the MCI group.

RESULTS

Cognitive outcomes were directly associated with CSF Aβ42 and inversely with CSF tau measures. We found differences in both biomarkers and cognitive outcomes comparing all pairs except for CSF measures between cognitively impaired groups. The highest effect size was in memory tasks and biomarkers ratios. Lower performances were in memory and executive domains in MCI subjects with AD pathology (A+T+N±) compared to those with normal levels of AD biomarkers (A- T- N).

CONCLUSION

This study provides further evidence of the validity of Spanish NEURONORMA cognitive battery to characterize cognitive impairment in the AD pathological continuum.

Spread of pathological human Tau from neurons to oligodendrocytes and loss of high-firing pyramidal neurons in aging mice

Intracellular aggregation of hyperphosphorylated Tau (pTau) in the brain is associated with cognitive and motor impairments, and ultimately neurodegeneration. We investigate how human pTau affects cells and network activity in the hippocampal formation of the THY-Tau22 tauopathy model mice in vivo. We find that pTau preferentially accumulates in deep-layer pyramidal neurons, leading to neurodegeneration, and we establish that pTau spreads to oligodendrocytes. During goal-directed virtual navigation in aged transgenic mice, we detect fewer high-firing prosubicular pyramidal cells, but the firing population retains its coupling to theta oscillations. Analysis of network oscillations and firing patterns of pyramidal and GABAergic neurons recorded in head-fixed and freely moving mice suggests preserved neuronal coordination. In spatial memory tests, transgenic mice have reduced short-term familiarity, but spatial working and reference memory are surprisingly normal. We hypothesize that unimpaired subcortical network mechanisms maintain cortical neuronal coordination, counteracting the widespread pTau aggregation, loss of high-firing cells, and neurodegeneration.

Applying ACE-III, M-ACE and MMSE to Diagnostic Screening Assessment of Cognitive Functions within the Polish Population

The research aims to compare the accuracy of the mini-mental state examination (MMSE), the Addenbrooke's cognitive examination III (ACE-III) and the mini-Addenbrooke's cognitive examination (M-ACE) within the Polish population. The model comprised several stages: the features of each test were compared; the shifts in result categorisations between the norm and below the norm were analysed; a third category-mild cognitive impairment (MCI)-was included. Additionally, particular ACE-III domains that scored below domain-specific norm thresholds were analysed to establish the potential early predictors of dementia. All tests correlated to a high and very high degree-cf. MMSE and ACE-III (r = 0.817; p < 0.001), MMSE and M-ACE (r = 0.753; p < 0.001), ACE-III and M-ACE (r = 0.942; p < 0.001). The area under the ROC curve for the ACE-III diagnostic variable had a high value (AUC = 0.920 ± 0.014). A cut-off point of 81 points was suggested for ACE-III; the M-ACE diagnostic variable had an equally high value (AUC = 0.891 ± 0.017). A cut-off point of 20 points was suggested. A significant decrease in the mean score values for people who scored norm or below the norm under ACE-III, as compared to the MMSE results for norm (p < 0.0001), occurred for speech fluency (which decreased by 26.4%). The tests in question are characterised by high sensitivity and specificity. Targeted ACE-III seems best recommended for use in specialised diagnostic centres, whereas M-ACE appears to be a better suited diagnostic alternative for primary health care centres in comparison to MMSE.

The Zinc-sensing Receptor (GPR39) Modulates Declarative Memory and Age-related Hippocampal Gene Expression in Male Mice

As a neuromodulator, zinc regulates synaptic plasticity, learning and memory. Synaptic zinc is also a crucial factor in the development of toxic forms of amyloid beta protein and, subsequently, of Alzheimer's dementia (AD). Therefore, efforts to pinpoint mechanisms underlying zinc-dependent cognitive functions might aid AD research, by providing potential novel targets for drugs. One of the most understudied proteins in this regard is a zinc-sensing metabotropic receptor: GPR39. In this study we investigated the impact of GPR39 knock-out (KO) on age-related memory decline in mice of both sexes, by comparing them to age-matched wild-type (WT) littermates. We also tested the effects of a GPR39 agonist (TC-G 1008) on declarative memory of old animals, and its disruption in adult mice. We observed episodic-like memory (ELM) and spatial memory (SM) deficits in male GPR39 KO mice, as well as intact procedural memory in GPR39 KO mice regardless of age and sex. ELM was also absent in old WT male mice, and all female mice regardless of their genotype. Acute application of TC-G 1008 (10 mg/kg) reversed a deficit in two of three ELM components in old WT male mice, and had no promnesic effect on consolidation interference of ELM in adult WT mice. We discuss the possible neurobiological mechanisms and the translational value of these results for potential add-on pharmacotherapy of AD aimed at the zinc-sensing receptor.

The CORCOBIA study: Cut-off points of Alzheimer's disease CSF biomarkers in a clinical cohort

INTRODUCTION

The analysis of the core biomarkers of Alzheimer's Disease (AD) in the cerebrospinal fluid (CSF) is recommended in the clinical units where it is available. Because of the absence of universal validated values, the determination of specific cut-off points for each center and its population is recommended. The main objective of the CORCOBIA study was to determine the cut-off points of core AD CSF biomarkers for several centers (Parc de Salut Mar, Barcelona and Hospital General de Granollers), which work with the same reference laboratory (Laboratori de Referència de Catalunya).

METHODS

Prospective study including cognitively unimpaired individuals (CU, n = 42), subjects with amnestic mild cognitive impairment (aMCI, n = 35) and patients with dementia due to Alzheimer's Disease (AD, n = 48), in whom clinical and neuropsychological assessment, neuroimaging, APOE genotyping and lumbar puncture to analyse amyloid beta peptides (Aβ42, Aβ40), total tau (tTau) and phosphorylated Tau (pTau181) using the Lumipulse G600II (Fujirebio) was performed. The values of sensitivity (SE), specificity (SP), predictive values and area under the curve (AUC) were calculated, determining the cut-off point according to the Youden index by comparing the CU and AD groups.

RESULTS

The resulting cut-offs and their AUC were the following: Aβ42 750 pg/mL (AUC 0.809); Aβ42/Aβ40 0.062 (AUC 0.78); pTau181 69.85 pg/mL (AUC 0.81); tTau 522.0 pg/mL (AUC 0.79); Aβ42/tTau 1.76 (AUC 0.86); Aβ42/pTau181 10.25 (AUC 0.86).

CONCLUSIONS

The determination of cut-off points of core AD CSF biomarkers for the participating centers allows a better diagnostic accuracy. The ratio CSF Aβ42/pTau181 shows the highest AUC and better balance between sensitivity and specificity.

Episodic Memory in Amnestic Mild Cognitive Impairment (aMCI) and Alzheimer’s Disease Dementia (ADD): Using the “Doors and People” Tool to Differentiate between Early aMCI—Late aMCI—Mild ADD Diagnostic Groups

Episodic memory is the type of memory that allows the recollection of personal experiences containing information on what has happened and, also, where and when it happened. Because of its sensitivity to neurodegenerative diseases and the aging of the brain, it is considered a hallmark of Alzheimer’s disease dementia (ADD). The objective of the present study was to examine episodic memory in amnestic mild cognitive impairment (aMCI) and ADD. Patients with the diagnosis of early aMCI, late aMCI, and mild ADD were evaluated using the Doors and People tool which consists of four subtests examining different aspects of episodic memory. The statistical analysis with receiver operating characteristic curves (ROC) showed the discriminant potential and the cutoffs of every subtest. Overall, the evaluation of episodic memory with the Doors and People tool can discriminate with great sensitivity between the different groups of people with AD and, especially, early aMCI, late aMCI, and mild ADD patients.

A Validation Study of the Hong Kong Brief Cognitive Test for Screening Patients with Mild Cognitive Impairment and Alzheimer’s Disease

Background: The Hong Kong Brief Cognitive Test (HKBC), a brief instrument designed to screen for cognitive impairment in older adults, has been validated in Cantonese-speaking populations and has shown better performance than the Mini-Mental State Examination (MMSE) in detecting both mild and major neurocognitive disorder (NCD). Objective: This study aimed to validate the HKBC for detecting patients with amnestic mild cognitive impairment (aMCI) and Alzheimer’s disease (AD) in a Mandarin-speaking Chinese population. Methods: Two hundred forty-eight patients with aMCI, 67 patients with mild AD and 306 healthy controls (HCs) were recruited for this study and completed both the HKBC and the MMSE. The performance of the HKBC and MMSE in distinguishing patients with aMCI from HCs and distinguishing patients with AD from patients with aMCI was compared in the whole population and in age- and education-stratified subgroups. Results: The optimal HKBC cutoff score for distinguishing patients with aMCI from HCs was 23, and the optimal cutoff for distinguishing patients with AD from patients with aMCI was 17. The HKBC significantly outperformed the MMSE at differentiating patients with aMCI from HCs in the whole population (z = 12.38, p <  0.01) and all subgroups stratified by age or education. Regarding the discrimination of patients with AD from patients with aMCI, the HKBC showed better performance than the MMSE in the oldest subgroup (z = 2.18, p = 0.03). Conclusion: The HKBC is a sensitive and specific screening tool for detecting aMCI and AD in the Chinese population across age groups and educational levels.

Using the ATN system as a guide for the neuropsychological assessment of Alzheimer's disease

INTRODUCTION

Many studies have attempted to determine whether Alzheimer's disease (AD) in-vivo biomarkers can predict neuropsychological performance since pathophysiological changes precede cognitive changes by several years. Nonetheless, neuropsychological measures can also detect cognitive deterioration in cognitively normal individuals with AD-positive biomarkers. Recent studies have investigated whether cognitive measures can be used as a proxy for biomarkers. This is a crucial issue since biomarker analysis is expensive, invasive, and not yet widespread in clinical practice. However, these studies have so far considered only one or two classes of AD biomarkers. Here, we aim at preliminarily evaluating whether and which neuropsychological measures can discriminate individuals that have been classified according to the full scheme of biomarkers known as ATN system. This scheme groups biomarkers as a function of the three main AD-related pathologic processes they measure (i.e., β-amyloidosis, tauopathy, and neurodegeneration) to provide an unbiased and descriptive definition of the Alzheimer's continuum.

METHOD

Biomarkers and neuropsychological data from 78 patients (70.01 ± 9.15 years; 38 females) with suspected cognitive decline were extracted from a medical database. Participants' biomarker profiles were classified into the following ATN categories: normal AD biomarkers; Alzheimer's continuum; non-AD pathologic change. Data were analyzed using a Bayesian approach, to guarantee reliable result interpretation of data stemming from small samples.

RESULTS

The discrimination ability of each neuropsychological measure varied depending on the pairs of ATN categories compared. The best-discriminating predictor in the Alzheimer's continuum vs. normal biomarkers comparison was the figure naming ability. In contrast, in the Alzheimer's continuum vs. non-AD pathologic change comparison the best predictor was the wordlist forgetting rate.

CONCLUSIONS

Although the study was exploratory in nature, the proposed methodological approach may have the potential to identify the best neuropsychological measures for estimating AD neuropathological changes, leading to a more biologically informed use of neuropsychological assessment.

18F-florbetapir PET as a marker of myelin integrity across the Alzheimer's disease spectrum

Purpose

Recent evidence suggests that PET imaging with amyloid-β (Aβ) tracers can be used to assess myelin integrity in cerebral white matter (WM). Alzheimer’s disease (AD) is characterized by myelin changes that are believed to occur early in the disease course. Nevertheless, the extent to which demyelination, as measured with Aβ PET, contributes to AD progression remains unexplored.

Methods

Participants with concurrent ¹⁸F-florbetapir (FBP) PET, MRI, and cerebrospinal fluid (CSF) examinations were included (241 cognitively normal, 347 Aβ-positive cognitively impaired, and 207 Aβ-negative cognitively impaired subjects). A subset of these participants had also available diffusion tensor imaging (DTI) images (n = 195). We investigated cross-sectional associations of FBP retention in the white matter (WM) with MRI-based markers of WM degeneration, AD clinical progression, and fluid biomarkers. In longitudinal analyses, we used linear mixed models to assess whether FBP retention in normal-appearing WM (NAWM) predicted progression of WM hyperintensity (WMH) burden and clinical decline.

Results

In AD-continuum individuals, FBP retention in NAWM was (1) higher compared with WMH regions, (2) associated with DTI-based measures of WM integrity, and (3) associated with longitudinal progression of WMH burden. FBP uptake in WM decreased across the AD continuum and with increasingly abnormal CSF biomarkers of AD. Furthermore, FBP retention in the WM was associated with large-calibre axon degeneration as reflected by abnormal plasma neurofilament light chain levels. Low FBP uptake in NAWM predicted clinical decline in preclinical and prodromal AD, independent of demographics, global cortical Aβ, and WMH burden. Most of these associations were also observed in Aβ-negative cognitively impaired individuals.

Conclusion

These results support the hypothesis that FBP retention in the WM is myelin-related. Demyelination levels progressed across the AD continuum and were associated with clinical progression at early stages, suggesting that this pathologic process might be a relevant degenerative feature in the disease course.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-021-05493-y.

Robust Discovery of Mild Cognitive Impairment Subtypes and Their Risk of Alzheimer's Disease Conversion Using Unsupervised Machine Learning and Gaussian Mixture Modeling

BACKGROUND

Alzheimer's Disease (AD) is an irreversible, progressive brain disorder that slowly destroys memory and thinking skills. The ability to correctly predict the diagnosis of Alzheimer's disease in its earliest stages can help physicians make more informed clinical decisions on therapy plans.

OBJECTIVE

This study aimed to determine whether the unsupervised discovering of latent classes of subjects with Mild Cognitive Impairment (MCI) may be useful in finding different prodromal AD stages and/or subjects with a low MCI to AD conversion risk.

METHODS

Total 18 features relevant to the MCI to AD conversion process led to the identification of 681 subjects with early MCI. Subjects were divided into training (70%) and validation (30%) sets. Subjects from the training set were analyzed using consensus clustering, and Gaussian Mixture Models (GMM) were used to describe the latent classes. The discovered GMM predicted the latent class of the validation set. Finally, descriptive statistics, rates of conversion, and Odds Ratios (OR) were computed for each discovered class.

RESULTS

Through consensus clustering, we discovered three different clusters among MCI subjects. The three clusters were associated with low-risk (OR = 0.12, 95%CI = 0.04 to 0.3|), medium-risk (OR = 1.33, 95%CI = 0.75 to 2.37), and high-risk (OR = 3.02, 95%CI = 1.64 to 5.57) of converting from MCI to AD, with the high-risk and low-risk groups highly contrasting. Hence, prodromal AD subjects were present in only two clusters.

CONCLUSION

We successfully discovered three different latent classes among MCI subjects with varied risks of MCI-to-AD conversion through consensus clustering. Two of the discovered classes may represent two different prodromal presentations of Alzheimer´s disease.

A Study of the Brain Network Connectivity in Visual-Word Pairing Associative Learning and Episodic Memory Reactivating Task

Episodic memory allows a person to recall and mentally reexperience specific episodes from one's personal past. Studies of episodic memory are of great significance for the diagnosis and the exploration of the mechanism of memory generation. Most of the current studies focus on certain brain regions and pay less attention to the interrelationship between multiple brain regions. To explore the interrelationship in the brain network, we use an open fMRI dataset to construct the brain functional connectivity and effective connectivity network. We establish a binary directed network of the memory when it is reactivated. The binary directed network shows that the occipital lobe and parietal lobe have the most causal connections. The number of edges starting from the superior parietal lobule is the highest, with 49 edges, and 31 of which are connected to the occipital cortex. This means that the interaction between the superior parietal lobule and the occipital lobe plays the most important role in episodic memory, and the superior parietal lobule plays a more causal role in causality. In addition, memory regions such as the precuneus and fusiform also have some edges. The results show that the posterior parietal cortex plays an important role of hub node in the episodic memory network. From the brain network model, more information can be obtained, which is conducive to exploring the brain's changing pattern in the whole memory process.

Degree of cognitive impairment does not signify early versus late mild cognitive impairment: confirmation based on Alzheimer's disease polygenic risk

Degree of memory impairment is often used to infer early versus late amnestic mild cognitive impairment (aMCI). Previously, 318 Alzheimer's Disease Neuroimaging Initiative participants with aMCI-determined by a single memory test-were divided based on Rey Auditory Verbal Learning Task (AVLT) delayed recall: AVLT-impaired (n = 225) and AVLT-normal (n = 93). Equally consistent with differential progression or differential diagnosis, the AVLT-impaired group had more abnormal Alzheimer's disease (AD) biomarkers, more neurodegeneration over time, and was more likely to develop AD. In the present study, higher AD polygenic risk scores were associated with increased odds of being AVLT-impaired (odds ratio 1.8, p < 0.001). Thus, impairment severity does not necessarily reflect early versus late aMCI because disease progression cannot alter polygenic risk. Presumed early MCI is likely a heterogeneous category that includes excess false-positives. The additional cognitive test improved diagnostic precision by reducing false positives. Impairment severity may reflect differences in underlying disease risk but cannot be used to infer early versus late MCI based on cross-sectional data alone.