Comparison of amyloid burden in individuals with Down syndrome versus autosomal dominant Alzheimer's disease: a cross-sectional study

Clinical and research application of fluid biomarkers in autosomal dominant Alzheimer's disease and Down syndrome

Autosomal dominant Alzheimer's disease (ADAD) and Down syndrome (DS) constitute genetic forms of Alzheimer's disease (AD). The study of these forms has been crucial in understanding the biomarker changes and disease progression, notably in advancing our knowledge of the natural history of AD. However, some specific characteristics of biomarkers in genetically determined forms and, most importantly, the near full penetrance and predictability of disease onset lead to a very different context of use for biomarkers in these populations. This article delves into the similarities and differences in biomarker profiles between genetically determined AD and sporadic cases, discussing the implications for research and clinical practice. It also emphasizes the need to account for factors that may affect biomarker reliability differently in genetically determined AD. Enhancing our understanding of the disease will pave the way for more personalized therapeutic approaches for affected individuals.

The immunoreactive signature of monocyte-derived dendritic cells from patients with Down syndrome

The clinical spectrum of Down syndrome (DS) ranges from congenital malformations to premature aging and early-onset senescence. Excessive immunoreactivity and oxidative stress are thought to accelerate the pace of aging in DS patients; however, the immunological profile remains elusive. We investigated whether peripheral blood monocyte-derived dendritic cells (MoDCs) in DS patients respond to lipopolysaccharide (LPS) distinctly from non-DS control MoDCs. Eighteen DS patients (age 2-47 years, 12 males) and 22 controls (age 4-40 years, 15 males) were enrolled. CD14-positive monocytes were immunopurified and cultured for 7 days in the presence of granulocyte-macrophage colony-stimulating factor and IL-4, yielding MoDCs in vitro. After the LPS-stimulation for 48 hours from days 7 to 9, culture supernatant cytokines were measured by multiplex cytokine bead assays, and bulk-prepared RNA from the cells was used for transcriptomic analyses. MoDCs from DS patients produced cytokines/chemokines (IL-6, IL-8, TNF-α, MCP-1, and IP-10) at significantly higher levels than those from controls in response to LPS. RNA sequencing revealed that DS-derived MoDCs differentially expressed 137 genes (74 upregulated and 63 downregulated) compared with controls. A gene enrichment analysis identified 5 genes associated with Toll-like receptor signaling (KEGG: hsa04620, P = 0.00731) and oxidative phosphorylation (hsa00190, P = 0.0173) pathways. MoDCs obtained from DS patients showed higher cytokine or chemokine responses to LPS than did control MoDCs. Gene expression profiles suggest that hyperactive Toll-like receptor and mitochondrial oxidative phosphorylation pathways configure the immunoreactive signature of MoDCs in DS patients.

Amyloid age and tau PET timeline to symptomatic Alzheimer's disease in Down syndrome

Background

Adults with Down syndrome (DS) are at risk for Alzheimer's disease (AD). Recent natural history cohort studies have characterized AD biomarkers, with a focus on PET amyloid-beta (Aβ) and PET tau. Leveraging these well-characterized biomarkers, the present study examined the timeline to symptomatic AD based on estimated years since reaching Aβ+, referred to as "amyloid age", and in relation to tau in a large cohort of individuals with DS.

Methods

In this multicenter cohort study, 25 - 57-year-old adults with DS (n = 167) were assessed twice from 2017 to 2022, with approximately 32 months between visits as part of the Alzheimer Biomarker Consortium - Down Syndrome. Adults with DS completed amyloid and tau PET scans, and were administered the modified Cued Recall Test and the Down Syndrome Mental Status Examination. Study partners completed the National Task Group-Early Detection Screen for Dementia.

Findings

Mixed linear regressions showed significant quadratic associations between amyloid age and cognitive performance and cubic associations between amyloid age and tau, both at baseline and across 32 months. Using broken stick regression models, differences in mCRT scores were detected beginning 2.7 years following Aβ+ in cross-sectional models, with an estimated decline of 1.3 points per year. Increases in tau began, on average, 2.7 - 6.1 years following Aβ+. On average, participants with mild cognitive impairment were 7.4 years post Aβ+ and those with dementia were 12.7 years post Aβ+.

Interpretation

There is a short timeline to initial cognitive decline and dementia from Aβ+ (Centiloid = 18) and tau deposition in DS relative to late onset AD. The established timeline based on amyloid age (or equivalent Centiloid values) is important for clinical practice and informing AD clinical trials, and avoids limitations of timelines based on chronological age. Funding. National Institute on Aging and the National Institute for Child Health and Human Development.

Research in Context

Evidence before this study: We searched PubMed for articles published involving the progression of Aβ and tau deposition in adults with Down syndrome from database inception to March 1, 2024. Terms included "amyloid", "Down syndrome", "tau", "Alzheimer's disease", "cognitive decline", and "amyloid chronicity," with no language restrictions. One previous study outlined the progression of tau in adults with Down syndrome without consideration of cognitive decline or clinical status. Other studies reported cognitive decline associated with Aβ burden and estimated years to AD symptom onset in Down syndrome. Amyloid age estimates have also been created for older neurotypical adults and compared to cognitive performance, but this has not been investigated in Down syndrome.Added value of this study: The timeline to symptomatic Alzheimer's disease in relation to amyloid, expressed as duration of Aβ+, and tau has yet to be described in adults with Down syndrome. Our longitudinal study is the first to provide a timeline of cognitive decline and transition to mild cognitive impairment and dementia in relation to Aβ+.Implications of all the available evidence: In a cohort study of 167 adults with Down syndrome, cognitive decline began 2.7 - 5.4 years and tau deposition began 2.7 - 6.1 years following Aβ+ (Centiloid = 18). Adults with Down syndrome converted to MCI after ~7 years and dementia after ~12-13 years of Aβ+. This shortened timeline to AD symptomology from Aβ+ and tau deposition in DS based on amyloid age (or corresponding Centiloid values) can inform clinical AD intervention trials and is of use in clinical settings.

Assessing amyloid PET positivity and cognitive function in Down syndrome to guide clinical trials targeting amyloid

INTRODUCTION

Trisomy 21, or Down syndrome (DS), predisposes individuals to early-onset Alzheimer's disease (AD). While monoclonal antibodies (mAbs) targeting amyloid are approved for older AD patients, their efficacy in DS remains unexplored. This study examines amyloid positron emission tomography (PET) positivity (A+), memory function, and clinical status across ages in DS to guide mAb trial designs.

METHODS

Cross-sectional data from the Alzheimer Biomarker Consortium-Down Syndrome (ABC-DS) was analyzed. PET amyloid beta in Centiloids classified amyloid status using various cutoffs. Episodic memory was assessed using the modified Cued Recall Test, and clinical status was determined through consensus processes.

RESULTS

Four hundred nine DS adults (mean age = 44.83 years) were evaluated. A+ rates increased with age, with mean amyloid load rising significantly. Memory decline and cognitive impairment are also correlated with age.

DISCUSSION

These findings emphasize the necessity of tailoring mAb trials for DS, considering age-related AD characteristics.

HIGHLIGHTS

There is rapid increase in prevalence of amyloid beta (Aβ) positron emission tomography (PET) positivity in Down syndrome (DS) after the age of 40 years. Aβ PET positivity thresholds have significant impact on prevalence rates in DS. There is a significant lag between Aβ PET positivity and clinical symptom onset in DS.

SIL1 improves cognitive impairment in APP23/PS45 mice by regulating amyloid precursor protein processing and Aβ generation

SIL1, an endoplasmic reticulum (ER)-resident protein, is reported to play a protective role in Alzheimer's disease (AD). However, the effect of SIL1 on amyloid precursor protein (APP) processing remains unclear. In this study, the role of SIL1 in APP processing was explored both in vitro and in vivo. In the in vitro experiment, SIL1 was either overexpressed or knocked down in cells stably expressing the human Swedish mutant APP695. In the in vivo experiment, AAV-SIL1-EGFP or AAV-EGFP was microinjected into APP23/PS45 mice and their wild-type littermates. Western blotting (WB), immunohistochemistry, RNA sequencing (RNA-seq), and behavioral experiments were performed to evaluate the relevant parameters. Results indicated that SIL1 expression decreased in APP23/PS45 mice. Overexpression of SIL1 significantly decreased the protein levels of APP, presenilin-1 (PS1), and C-terminal fragments (CTFs) of APP in vivo and in vitro. Conversely, knockdown of SIL1 increased the protein levels of APP, β-site APP cleavage enzyme 1 (BACE1), PS1, and CTFs, as well as APP mRNA expression in 2EB2 cells. Furthermore, SIL1 overexpression reduced the number of senile plaques in APP23/PS45 mice. Importantly, Y-maze and Morris Water maze tests demonstrated that SIL1 overexpression improved cognitive impairment in APP23/PS45 mice. These findings indicate that SIL1 improves cognitive impairment in APP23/PS45 mice by inhibiting APP amyloidogenic processing and suggest that SIL1 is a potential therapeutic target for AD by modulating APP processing.

Comparison of tau spread in people with Down syndrome versus autosomal-dominant Alzheimer's disease: a cross-sectional study

BACKGROUND

In people with genetic forms of Alzheimer's disease, such as in Down syndrome and autosomal-dominant Alzheimer's disease, pathological changes specific to Alzheimer's disease (ie, accumulation of amyloid and tau) occur in the brain at a young age, when comorbidities related to ageing are not present. Studies including these cohorts could, therefore, improve our understanding of the early pathogenesis of Alzheimer's disease and be useful when designing preventive interventions targeted at disease pathology or when planning clinical trials. We compared the magnitude, spatial extent, and temporal ordering of tau spread in people with Down syndrome and autosomal-dominant Alzheimer's disease.

METHODS

In this cross-sectional observational study, we included participants (aged ≥25 years) from two cohort studies. First, we collected data from the Dominantly Inherited Alzheimer's Network studies (DIAN-OBS and DIAN-TU), which include carriers of autosomal-dominant Alzheimer's disease genetic mutations and non-carrier familial controls recruited in Australia, Europe, and the USA between 2008 and 2022. Second, we collected data from the Alzheimer Biomarkers Consortium-Down Syndrome study, which includes people with Down syndrome and sibling controls recruited from the UK and USA between 2015 and 2021. Controls from the two studies were combined into a single group of familial controls. All participants had completed structural MRI and tau PET (18F-flortaucipir) imaging. We applied Gaussian mixture modelling to identify regions of high tau PET burden and regions with the earliest changes in tau binding for each cohort separately. We estimated regional tau PET burden as a function of cortical amyloid burden for both cohorts. Finally, we compared the temporal pattern of tau PET burden relative to that of amyloid.

FINDINGS

We included 137 people with Down syndrome (mean age 38·5 years [SD 8·2], 74 [54%] male, and 63 [46%] female), 49 individuals with autosomal-dominant Alzheimer's disease (mean age 43·9 years [11·2], 22 [45%] male, and 27 [55%] female), and 85 familial controls, pooled from across both studies (mean age 41·5 years [12·1], 28 [33%] male, and 57 [67%] female), who satisfied the PET quality-control procedure for tau-PET imaging processing. 134 (98%) people with Down syndrome, 44 (90%) with autosomal-dominant Alzheimer's disease, and 77 (91%) controls also completed an amyloid PET scan within 3 years of tau PET imaging. Spatially, tau PET burden was observed most frequently in subcortical and medial temporal regions in people with Down syndrome, and within the medial temporal lobe in people with autosomal-dominant Alzheimer's disease. Across the brain, people with Down syndrome had greater concentrations of tau for a given level of amyloid compared with people with autosomal-dominant Alzheimer's disease. Temporally, increases in tau were more strongly associated with increases in amyloid for people with Down syndrome compared with autosomal-dominant Alzheimer's disease.

INTERPRETATION

Although the general progression of amyloid followed by tau is similar for people Down syndrome and people with autosomal-dominant Alzheimer's disease, we found subtle differences in the spatial distribution, timing, and magnitude of the tau burden between these two cohorts. These differences might have important implications; differences in the temporal pattern of tau accumulation might influence the timing of drug administration in clinical trials, whereas differences in the spatial pattern and magnitude of tau burden might affect disease progression.

FUNDING

None.

Cognitive and functional performance and plasma biomarkers of early Alzheimer's disease in Down syndrome

INTRODUCTION

People with Down syndrome (DS) have a 75% to 90% lifetime risk of Alzheimer's disease (AD). AD pathology begins a decade or more prior to onset of clinical AD dementia in people with DS. It is not clear if plasma biomarkers of AD pathology are correlated with early cognitive and functional impairments in DS, and if these biomarkers could be used to track the early stages of AD in DS or to inform inclusion criteria for clinical AD treatment trials.

METHODS

This large cross-sectional cohort study investigated the associations between plasma biomarkers of amyloid beta (Aβ)42/40, total tau, and neurofilament light chain (NfL) and cognitive (episodic memory, visual-motor integration, and visuospatial abilities) and functional (adaptive behavior) impairments in 260 adults with DS without dementia (aged 25-81 years).

RESULTS

In general linear models lower plasma Aβ42/40 was related to lower visuospatial ability, higher total tau was related to lower episodic memory, and higher NfL was related to lower visuospatial ability and lower episodic memory.

DISCUSSION

Plasma biomarkers may have utility in tracking AD pathology associated with early stages of cognitive decline in adults with DS, although associations were modest.

Highlights

Plasma Alzheimer's disease (AD) biomarkers correlate with cognition prior to dementia in Down syndrome.Lower plasma amyloid beta 42/40 was related to lower visuospatial abilities.Higher plasma total tau and neurofilament light chain were associated with lower cognitive performance.Plasma biomarkers show potential for tracking early stages of AD symptomology.

Advanced structural brain aging in preclinical autosomal dominant Alzheimer disease

BACKGROUND

"Brain-predicted age" estimates biological age from complex, nonlinear features in neuroimaging scans. The brain age gap (BAG) between predicted and chronological age is elevated in sporadic Alzheimer disease (AD), but is underexplored in autosomal dominant AD (ADAD), in which AD progression is highly predictable with minimal confounding age-related co-pathology.

METHODS

We modeled BAG in 257 deeply-phenotyped ADAD mutation-carriers and 179 non-carriers from the Dominantly Inherited Alzheimer Network using minimally-processed structural MRI scans. We then tested whether BAG differed as a function of mutation and cognitive status, or estimated years until symptom onset, and whether it was associated with established markers of amyloid (PiB PET, CSF amyloid-β-42/40), phosphorylated tau (CSF and plasma pTau-181), neurodegeneration (CSF and plasma neurofilament-light-chain [NfL]), and cognition (global neuropsychological composite and CDR-sum of boxes). We compared BAG to other MRI measures, and examined heterogeneity in BAG as a function of ADAD mutation variants, APOE ε4 carrier status, sex, and education.

RESULTS

Advanced brain aging was observed in mutation-carriers approximately 7 years before expected symptom onset, in line with other established structural indicators of atrophy. BAG was moderately associated with amyloid PET and strongly associated with pTau-181, NfL, and cognition in mutation-carriers. Mutation variants, sex, and years of education contributed to variability in BAG.

CONCLUSIONS

We extend prior work using BAG from sporadic AD to ADAD, noting consistent results. BAG associates well with markers of pTau, neurodegeneration, and cognition, but to a lesser extent, amyloid, in ADAD. BAG may capture similar signal to established MRI measures. However, BAG offers unique benefits in simplicity of data processing and interpretation. Thus, results in this unique ADAD cohort with few age-related confounds suggest that brain aging attributable to AD neuropathology can be accurately quantified from minimally-processed MRI.

Down Syndrome in a New Era for Alzheimer Disease

This Viewpoint explains the genetic association between Alzheimer disease and Down syndrome and the negative impact of excluding people with Down syndrome from clinical trials on treatment for Alzheimer disease.

Integration of ATAC-seq and RNA-seq identifies MX1-mediated AP-1 transcriptional regulation as a therapeutic target for Down syndrome

BACKGROUND

Growing evidence has suggested that Type I Interferon (I-IFN) plays a potential role in the pathogenesis of Down Syndrome (DS). This work investigates the underlying function of MX1, an effector gene of I-IFN, in DS-associated transcriptional regulation and phenotypic modulation.

METHODS

We performed assay for transposase-accessible chromatin with high-throughout sequencing (ATAC-seq) to explore the difference of chromatin accessibility between DS derived amniocytes (DSACs) and controls. We then combined the annotated differentially expressed genes (DEGs) and enriched transcriptional factors (TFs) targeting the promoter region from ATAC-seq results with the DEGs in RNA-seq, to identify key genes and pathways involved in alterations of biological processes and pathways in DS.

RESULTS

Binding motif analysis showed a significant increase in chromatin accessibility of genes related to neural cell function, among others, in DSACs, which is primarily regulated by members of the activator protein-1 (AP-1) transcriptional factor family. Further studies indicated that MX Dynamin Like GTPase 1 (MX1), defined as one of the key effector genes of I-IFN, is a critical upstream regulator. Its overexpression induced expression of AP-1 TFs and mediated inflammatory response, thus leading to decreased cellular viability of DS cells. Moreover, treatment with specific AP-1 inhibitor T-5224 improved DS-associated phenotypes in DSACs.

CONCLUSIONS

This study demonstrates that MX1-mediated AP-1 activation is partially responsible for cellular dysfunction of DS. T-5224 effectively ameliorated DS-associated phenotypes in DSACs, suggesting it as a potential treatment option for DS patients.

Emerging diagnostics and therapeutics for Alzheimer disease

Alzheimer disease (AD) is the most common contributor to dementia in the world, but strategies that slow or prevent its clinical progression have largely remained elusive, until recently. This Review highlights the latest advances in biomarker technologies and therapeutic development to improve AD diagnosis and treatment. We review recent results that enable pathological staging of AD with neuroimaging and fluid-based biomarkers, with a particular emphasis on the role of amyloid, tau and neuroinflammation in disease pathogenesis. We discuss the lessons learned from randomized controlled trials, including some supporting the proposal that certain anti-amyloid antibodies slow cognitive decline during the mildly symptomatic phase of AD. In addition, we highlight evidence for newly identified therapeutic targets that may be able to modify AD pathogenesis and progression. Collectively, these recent discoveries-and the research directions that they open-have the potential to move AD clinical care toward disease-modifying treatment strategies with maximal benefits for patients.

Positron emission tomography and magnetic resonance imaging methods and datasets within the Dominantly Inherited Alzheimer Network (DIAN)

The Dominantly Inherited Alzheimer Network (DIAN) is an international collaboration studying autosomal dominant Alzheimer disease (ADAD). ADAD arises from mutations occurring in three genes. Offspring from ADAD families have a 50% chance of inheriting their familial mutation, so non-carrier siblings can be recruited for comparisons in case-control studies. The age of onset in ADAD is highly predictable within families, allowing researchers to estimate an individual's point in the disease trajectory. These characteristics allow candidate AD biomarker measurements to be reliably mapped during the preclinical phase. Although ADAD represents a small proportion of AD cases, understanding neuroimaging-based changes that occur during the preclinical period may provide insight into early disease stages of 'sporadic' AD also. Additionally, this study provides rich data for research in healthy aging through inclusion of the non-carrier controls. Here we introduce the neuroimaging dataset collected and describe how this resource can be used by a range of researchers.

Detection and treatment of Alzheimer's disease in its preclinical stage

Longitudinal multimodal biomarker studies reveal that the continuum of Alzheimer's disease (AD) includes a long latent phase, referred to as preclinical AD, which precedes the onset of symptoms by decades. Treatment during the preclinical AD phase offers an optimal opportunity for slowing the progression of disease. However, trial design in this population is complex. In this Review, we discuss the recent advances in accurate plasma measurements, new recruitment approaches, sensitive cognitive instruments and self-reported outcomes that have facilitated the successful launch of multiple phase 3 trials for preclinical AD. The recent success of anti-amyloid immunotherapy trials in symptomatic AD has increased the enthusiasm for testing this strategy at the earliest feasible stage. We provide an outlook for standard screening of amyloid accumulation at the preclinical stage in clinically normal individuals, during which effective therapy to delay or prevent cognitive decline can be initiated.

A Brief Overview of Neutrophils in Neurological Diseases

Neutrophils are the most abundant leukocyte in circulation and are the first line of defense after an infection or injury. Neutrophils have a broad spectrum of functions, including phagocytosis of microorganisms, the release of pro-inflammatory cytokines and chemokines, oxidative burst, and the formation of neutrophil extracellular traps. Traditionally, neutrophils were thought to be most important for acute inflammatory responses, with a short half-life and a more static response to infections and injury. However, this view has changed in recent years showing neutrophil heterogeneity and dynamics, indicating a much more regulated and flexible response. Here we will discuss the role of neutrophils in aging and neurological disorders; specifically, we focus on recent data indicating the impact of neutrophils in chronic inflammatory processes and their contribution to neurological diseases. Lastly, we aim to conclude that reactive neutrophils directly contribute to increased vascular inflammation and age-related diseases.