Cognitive markers of preclinical and prodromal Alzheimer's disease in Down syndrome

Maternal choline supplementation rescues early endosome pathology in basal forebrain cholinergic neurons in the Ts65Dn mouse model of Down syndrome and Alzheimer's disease

Individuals with DS develop Alzheimer's disease (AD) neuropathology, including endosomal-lysosomal system abnormalities and degeneration of basal forebrain cholinergic neurons (BFCNs). We investigated whether maternal choline supplementation (MCS) affects early endosome pathology within BFCNs using the Ts65Dn mouse model of DS/AD. Ts65Dn and disomic (2N) offspring from dams administered MCS were analyzed for endosomal pathology at 3-4 months or 10-12 months. Morphometric analysis of early endosome phenotype was performed on individual BFCNs using Imaris. The effects of MCS on the endosomal interactome were interrogated by relative co-expression (RCE) analysis. MCS effectively reduced age- and genotype-associated increases in early endosome number in Ts65Dn and 2N offspring, and prevented increases in early endosome size in Ts65Dn offspring. RCE revealed a loss of interactome cooperativity among endosome genes in Ts65Dn offspring that was restored by MCS. These findings demonstrate MCS rescues early endosome pathology, a driver of septohippocampal circuit dysfunction. The genotype-independent benefits of MCS on endosomal phenotype indicate translational applicability as an early-life therapy for DS as well as other neurodevelopmental/neurodegenerative disorders involving endosomal pathology.

Symptoms and age of prodromal Alzheimer's disease in Down syndrome: a systematic review and meta-analysis

The diagnostic criteria for adult-onset Alzheimer's disease (AD) in patients with Down syndrome (DS) have not been standardised. This study investigated the specific symptoms of AD in the prodromal stage of DS, the mean age at diagnosis at each stage of dementia, and the relationship between intellectual disability (ID) and dementia. PubMed, Web of Science, and Embase were searched for studies on DS, AD, early-stage disease, initial symptoms, and prodromal dementia registered between January 2012 and January 2022. We also performed a meta-analysis of the differences between the mean age at prodromal symptoms and AD diagnosis and the proportion of mild cognitive impairment in patients with mild and moderately abnormal ID. We selected 14 articles reporting the behavioural and psychological symptoms of dementia (BPSD) and memory- and language-related impairments as early symptoms of AD in patients with DS. The specific symptoms of BPSD were classified into five categories: irritability (agitation), apathy, abnormal behaviour, adaptive functioning, and sleep disturbance. The mean age at the diagnosis of prodromal symptoms and AD dementia was 52.7 and 56.2 years, respectively (mean difference, + 3.11 years; 95% CI 1.82-4.40) in the meta-analysis. The diagnosis of mild dementia tended to correlate with ID severity (odds ratio [OR], 1.38; 95% CI 0.87-2.18). The features of behaviour-variant frontotemporal dementia may be clinically confirmed in diagnosing early symptoms of DS-associated AD (DSAD). Moreover, age-appropriate cognitive assessment is important. Further studies are required to evaluate DSAD using a combination of biomarkers and ID-related data.

Characterizing the emergence of amyloid and tau burden in Down syndrome

INTRODUCTION

Almost all individuals with Down syndrome (DS) will develop neuropathological features of Alzheimer's disease (AD). Understanding AD biomarker trajectories is necessary for DS-specific clinical interventions and interpretation of drug-related changes in the disease trajectory.

METHODS

A total of 177 adults with DS from the Alzheimer's Biomarker Consortium-Down Syndrome (ABC-DS) underwent positron emission tomography (PET) and MR imaging. Amyloid-beta (Aβ) trajectories were modeled to provide individual-level estimates of Aβ-positive (A+) chronicity, which were compared against longitudinal tau change.

RESULTS

Elevated tau was observed in all NFT regions following A+ and longitudinal tau increased with respect to A+ chronicity. Tau increases in NFT regions I-III was observed 0-2.5 years following A+. Nearly all A+ individuals had tau increases in the medial temporal lobe.

DISCUSSION

These findings highlight the rapid accumulation of amyloid and early onset of tau relative to amyloid in DS and provide a strategy for temporally characterizing AD neuropathology progression that is specific to the DS population and independent of chronological age.

HIGHLIGHTS

Longitudinal amyloid trajectories reveal rapid Aβ accumulation in Down syndrome NFT stage tau was strongly associated with A+ chronicity Early longitudinal tau increases were observed 2.5-5 years after reaching A.

Hippocampal CA1 Pyramidal Neurons Display Sublayer and Circuitry Dependent Degenerative Expression Profiles in Aged Female Down Syndrome Mice

Background

Individuals with Down syndrome (DS) have intellectual disability and develop Alzheimer's disease (AD) pathology during midlife, particularly in the hippocampal component of the medial temporal lobe memory circuit. However, molecular and cellular mechanisms underlying selective vulnerability of hippocampal CA1 neurons remains a major knowledge gap during DS/AD onset. This is compounded by evidence showing spatial (e.g., deep versus superficial) localization of pyramidal neurons (PNs) has profound effects on activity and innervation within the CA1 region.

Objective

We investigated whether there is a spatial profiling difference in CA1 PNs in an aged female DS/AD mouse model. We posit dysfunction may be dependent on spatial localization and innervation patterns within discrete CA1 subfields.

Methods

Laser capture microdissection was performed on trisomic CA1 PNs in an established mouse model of DS/AD compared to disomic controls, isolating the entire CA1 pyramidal neuron layer and sublayer microisolations of deep and superficial PNs from the distal CA1 (CA1a) region.

Results

RNA sequencing and bioinformatic inquiry revealed dysregulation of CA1 PNs based on spatial location and innervation patterns. The entire CA1 region displayed the most differentially expressed genes (DEGs) in trisomic mice reflecting innate DS vulnerability, while trisomic CA1a deep PNs exhibited fewer but more physiologically relevant DEGs, as evidenced by bioinformatic inquiry.

Conclusions

CA1a deep neurons displayed numerous DEGs linked to cognitive functions whereas CA1a superficial neurons, with approximately equal numbers of DEGs, were not linked to pathways of dysregulation, suggesting the spatial location of vulnerable CA1 PNs plays an important role in circuit dissolution.

Prodromal Alzheimer's disease can affect activities of daily living for adults with Down syndrome

INTRODUCTION

Alzheimer's disease (AD) affecting adults with Down syndrome (DS-AD), like late-onset AD (LOAD) in the neurotypical population, has preclinical, prodromal, and more advanced stages. Only tasks placing high demands on cognition are expected to be affected during the prodromal stage, with activities of daily living (ADLs) typically being spared. However, cognitive demands of ADLs could be high for adults with DS and may be affected during prodromal DS-AD.

METHODS

Cognitively stable cases that subsequently developed prodromal DS-AD were identified within a set of archived data from a previous longitudinal study. Measures of ADLs and multiple cognitive domains were examined over time.

RESULTS

Clear declines in ADLs accompanied cognitive declines with prodromal DS-AD while stability in all measures was verified during preclinical DS-AD.

DISCUSSION

Operationally defining prodromal DS-AD is essential to disease staging in this high-risk population and for informing treatment options and timing as new disease-modifying drugs become available.

Highlights

Cognitive and functional stability were demonstrated prior to the onset of prodromal DS-AD.ADL declines accompanied cognitive declines as adults with DS transitioned to prodromal AD.Declines in ADLs should be a defining feature of prodromal AD for adults with DS.Better characterization of prodromal DS-AD can improve AD diagnosis and disease staging.Improvements in DS-AD diagnosis and staging could also inform the timing of interventions.

Exploring semantic verbal fluency patterns and their relationship to age and Alzheimer's disease in adults with Down syndrome

INTRODUCTION

Adults with Down syndrome (DS) are at ultra-high risk of developing Alzheimer's disease (AD), characterized by poor episodic memory and semantic fluency in the preclinical phase in the general population. We explored semantic fluency performance in DS and its relationship to age, AD, and blood biomarkers.

METHODS

A total of 302 adults with DS at baseline and 87 at follow-up from the London Down Syndrome Consortium cohort completed neuropsychological assessments. Blood biomarkers were measured with the single molecule array technique in a subset of 94 participants.

RESULTS

Poorer verbal fluency performance was observed as age increases. Number of correct words declined in those with AD compared to those without over 2 years and was negatively correlated with neurofilament light (r = -0.37, P = .001) and glial fibrillary acidic protein (r = -0.31, P = .012).

DISCUSSION

Semantic fluency may be useful as an early indicator of cognitive decline and provide additional information on AD-related change, showing associations with biomarkers in DS.

Maternal choline supplementation protects against age-associated cholinergic and GABAergic basal forebrain neuron degeneration in the Ts65Dn mouse model of Down syndrome and Alzheimer's disease

Down syndrome (DS) is a genetic disorder caused by triplication of human chromosome 21. In addition to intellectual disability, DS is defined by a premature aging phenotype and Alzheimer's disease (AD) neuropathology, including septohippocampal circuit vulnerability and degeneration of basal forebrain cholinergic neurons (BFCNs). The Ts65Dn mouse model recapitulates key aspects of DS/AD pathology, namely age-associated atrophy of BFCNs and cognitive decline in septohippocampal-dependent behavioral tasks. We investigated whether maternal choline supplementation (MCS), a well-tolerated treatment modality, protects vulnerable BFCNs from age- and genotype-associated degeneration in trisomic offspring. We also examined the effect of trisomy, and MCS, on GABAergic basal forebrain parvalbumin neurons (BFPNs), an unexplored neuronal population in this DS model. Unbiased stereological analyses of choline acetyltransferase (ChAT)-immunoreactive BFCNs and parvalbumin-immunoreactive BFPNs were conducted using confocal z-stacks of the medial septal nucleus and the vertical limb of the diagonal band (MSN/VDB) in Ts65Dn mice and disomic (2N) littermates at 3-4 and 10-12 months of age. MCS trisomic offspring displayed significant increases in ChAT-immunoreactive neuron number and density compared to unsupplemented counterparts, as well as increases in the area of the MSN/VDB occupied by ChAT-immunoreactive neuropil. MCS also rescued BFPN number and density in Ts65Dn offspring, a novel rescue of a non-cholinergic cell population. Furthermore, MCS prevented age-associated loss of BFCNs and MSN/VDB regional area in 2N offspring, indicating genotype-independent neuroprotective benefits. These findings demonstrate MCS provides neuroprotection of vulnerable BFCNs and non-cholinergic septohippocampal BFPNs, indicating this modality has translational value as an early life therapy for DS, as well as extending benefits to the aging population at large.

Balance and Gait: Associations With Cognitive Impairment and Dementia in Individuals With Down Syndrome

BACKGROUND

Atypical aging in Down syndrome (DS) is associated with neuropathological characteristics consistent with Alzheimer disease. Gait abnormalities have been shown to be associated with an increased risk of dementia for the general population. The aim of this study was to determine whether gait disorders are associated with worse cognitive performance and dementia in adults with DS.

METHODS

We evaluated 66 individuals with DS (≥20 y of age), divided into 3 groups: stable cognition, prodromal dementia, and dementia (presumed Alzheimer disease). Each individual was evaluated with the Performance-Oriented Mobility Assessment (POMA), Timed Up and Go test, and Cambridge Examination for Mental Disorders of Older People with Down's Syndrome and Others with Intellectual Disabilities (CAMDEX-DS), in addition to a comprehensive clinical protocol to ascertain the occurrence of medical or psychiatric comorbidities.

RESULTS

The score on the POMA-Gait subscale score and body mass index were found to be independent predictors of prodromal dementia and dementia ( P <0.001 for both). With the exception of perception, all cognitive domains correlated with the POMA-Total score ( P <0.05).

CONCLUSION

A lower POMA-Gait score increases the chance of prodromal dementia and dementia in adults with DS. Unlike other research, in this study higher body mass index was also found to increase the chance of prodromal dementia and dementia. In those individuals, applying the POMA could facilitate the early diagnosis of dementia, help identify fall risks, and promote the adoption of geriatric interventions focused on improving functional mobility.

The mismatch negativity as an index of cognitive abilities in adults with Down syndrome

Down syndrome (DS) is associated with an ultra-high risk of developing Alzheimer's disease (AD). Understanding variability in pre-AD cognitive abilities may help understand cognitive decline in this population. The mismatch negativity (MMN) is an event-related potential component reflecting the detection of deviant stimuli that is thought to represent underlying memory processes, with reduced MMN amplitudes being associated with cognitive decline. To further understand the MMN in adults with DS without AD, we explored the relationships between MMN, age, and cognitive abilities (memory, language, and attention) in 27 individuals (aged 17-51) using a passive auditory oddball task. Statistically significant MMN was present only in 18 individuals up to 41 years of age and the latency were longer than canonical parameters reported in the literature. Reduced MMN amplitude was associated with lower memory scores, while longer MMN latencies were associated with poorer memory, verbal abilities, and attention. Therefore, the MMN may represent a valuable index of cognitive abilities in DS. In combination with previous findings, we hypothesize that while MMN response and amplitude may be associated with AD-related memory loss, MMN latency may be associated with speech signal processing. Future studies may explore the potential impact of AD on MMN in people with DS.

The use of the cambridge neuropsychological test automated battery for people born with Down syndrome and those born premature: A comparative systematic review

This review aimed to investigate the use of the Cambridge Neuropsychological Automated Testing Battery (CANTAB) for people at risk of cognitive impairment, especially those born with Down syndrome and those born preterm. Six databases were searched according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) standards, in addition to the bibliography index listed in the CANTAB site. Twenty four studies regarding Down syndrome and 17 regarding prematurity were reviewed and are here described. Both cognitive profiles were described, and their performance was compared on specific tasks and CANTAB tests. In this battery of tests, people with Down syndrome usually present impaired key cognitive domains, such as episodic memory and recognition memory. Results were presented considering general aspects described in the studies, specific findings such as dementia, the role of genetics, and cognitive profile, among other descriptions. Comparability between both populations in future studies is discussed.

Down syndrome and Alzheimer's disease: A scoping review of functional performance and fall risk

Introduction

Alzheimer's disease (AD) occurs in aging adults with Down syndrome (DS) at a higher prevalence and an earlier age than in typical aging adults. As with the general aging adult population, there is an urgent need to understand the preclinical and early phases of AD progression in the adult population with DS. The aim of this scoping review was to synthesize the current state of the evidence and identify gaps in the literature regarding functional activity performance and falls and their significance to disease staging (i.e., mild, moderate, and severe defined staging criteria) in relation to Alzheimer's disease and related dementias (ADRD) in adults with DS.

Methods

This scoping review included six electronic databases (e.g., PsycInfo, Academic Search Complete, CINAHL, COCHRANE Library, MEDLINE, and PubMed). Eligible studies included participants with DS ≥25 years of age, studies with functional measures and/or outcomes (e.g., activities of daily living, balance, gait, motor control, speech, behavior, and cognition; falls; and fall risks), and studies that investigated AD pathology and implications.

Results

Fourteen eligible studies were included and categorized through a thematic analysis into the following themes: (1) physical activity and motor coordination (PAMC), (2) cognition, (3) behavior, and (4) sleep. The studies indicated how functional activity performance and engagement may contribute to early identification of those at risk of cognitive decline and AD development and/or progression.

Discussion

There is a need to expand the research regarding ADRD pathology relative to functional outcomes in adults with DS. Functional measures related to disease staging and cognitive impairment are essential to understanding how AD progression is characterized within real-world settings. This scoping review identified the need for additional mixed-methods research to examine the use of assessment and intervention related to function and its detection of cognitive decline and AD progression.

The Global Deterioration Scale for Down Syndrome Population (GDS-DS): A Rating Scale to Assess the Progression of Alzheimer's Disease

The aim of this study is to adapt and validate the global deterioration scale (GDS) for the systematic tracking of Alzheimer's disease (AD) progression in a population with Down syndrome (DS). A retrospective dual-center cohort study was conducted with 83 participants with DS (46.65 ± 5.08 years) who formed the primary diagnosis (PD) group: cognitive stability (n = 48), mild cognitive impairment (n = 24), and Alzheimer's disease (n = 11). The proposed scale for adults with DS (GDS-DS) comprises six stages, from cognitive and/or behavioral stability to advanced AD. Two neuropsychologists placed the participants of the PD group in each stage of the GDS-DS according to cognitive, behavioral and daily living skills data. Inter-rater reliability in staging with the GDS-DS was excellent (ICC = 0.86; CI: 0.80-0.93), and the agreement with the diagnosis categories of the PD group ranged from substantial to excellent with κ values of 0.82 (95% CI: 0.73-0.92) and 0.85 (95% CI: 0.72, 0.99). Performance with regard to the CAMCOG-DS total score and orientation subtest of the Barcelona test for intellectual disability showed a slight progressive decline across all the GDS-DS stages. The GDS-DS scale is a sensitive tool for staging the progression of AD in the DS population, with special relevance in daily clinical practice.

Diagnostic Sensitivity and Specificity of Cognitive Tests for Mild Cognitive Impairment and Alzheimer's Disease in Patients with Down Syndrome: A Systematic Review and Meta-Analysis

BACKGROUND

Improved health care for people with Down syndrome (DS) has resulted in an increase in their life expectancy therefore increasing comorbidities associated with age-related problems in this population, the most frequent being Alzheimer's disease (AD). To date, several cognitive tests have been developed to evaluate cognitive changes related to the development of mild cognitive impairment (MCI) and AD in people with DS.

OBJECTIVE

Identify and evaluate available cognitive tests for the diagnosis of MCI and AD in people with DS.

METHODS

A systematic search of the Pubmed and PsycInfo databases was performed to identify articles published from January 1, 2000 and July 1, 2022. Keysearch terms were DS, AD or MCI, cognition, and assessment. Relevant studies assessing the diagnostic accuracy of cognitive tests for AD or MCI with standard clinical evaluation were extracted. Risk of bias was assessed using the QUADAS 2.

RESULTS

We identified 15 batteries, 2 intelligence scales, 14 memory tests, 11 executive, functioning tests, 11 motor and visuospatial functioning tests, 5 language tests, 3 attention tests, and 2 orientation tests. Analysis showed that the CAMCOG-DS present a fair to excellent diagnostic accuracy for detecting AD in patients with DS. However, for the diagnosis of MCI, this battery showed poor to good diagnostic accuracy.

CONCLUSION

The findings highlight important limitations of the current assessment available for the screening of mild cognitive impairment and AD in patients with DS and support the need for more clinical trials to ensure better screening for this highly at-risk population.

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

BACKGROUND

Important insights into the early pathogenesis of Alzheimer's disease can be provided by studies of autosomal dominant Alzheimer's disease and Down syndrome. However, it is unclear whether the timing and spatial distribution of amyloid accumulation differs between people with autosomal dominant Alzheimer's disease and those with Down syndrome. We aimed to directly compare amyloid changes between these two groups of people.

METHODS

In this cross-sectional study, we included participants (aged ≥25 years) with Down syndrome and sibling controls who had MRI and amyloid PET scans in the first data release (January, 2020) of the Alzheimer's Biomarker Consortium-Down Syndrome (ABC-DS) study. We also included carriers of autosomal dominant Alzheimer's disease genetic mutations and non-carrier familial controls who were within a similar age range to ABC-DS participants (25-73 years) and had MRI and amyloid PET scans at the time of a data freeze (December, 2020) of the Dominantly Inherited Alzheimer Network (DIAN) study. Controls from the two studies were combined into a single group. All DIAN study participants had genetic testing to determine PSEN1, PSEN2, or APP mutation status. APOE genotype was determined from blood samples. CSF samples were collected in a subset of ABC-DS and DIAN participants and the ratio of amyloid β42 (Aβ42) to Aβ40 (Aβ42/40) was measured to evaluate its Spearman's correlation with amyloid PET. Global PET amyloid burden was compared with regards to cognitive status, APOE ɛ4 status, sex, age, and estimated years to symptom onset. We further analysed amyloid PET deposition by autosomal dominant mutation type. We also assessed regional patterns of amyloid accumulation by estimated number of years to symptom onset. Within a subset of participants the relationship between amyloid PET and CSF Aβ42/40 was evaluated.

FINDINGS

192 individuals with Down syndrome and 33 sibling controls from the ABC-DS study and 265 carriers of autosomal dominant Alzheimer's disease mutations and 169 non-carrier familial controls from the DIAN study were included in our analyses. PET amyloid centiloid and CSF Aβ42/40 were negatively correlated in carriers of autosomal dominant Alzheimer's disease mutations (n=216; r=-0·565; p<0·0001) and in people with Down syndrome (n=32; r=-0·801; p<0·0001). There was no difference in global PET amyloid burden between asymptomatic people with Down syndrome (mean 18·80 centiloids [SD 28·33]) versus asymptomatic mutation carriers (24·61 centiloids [30·27]; p=0·11) and between symptomatic people with Down syndrome (77·25 centiloids [41·76]) versus symptomatic mutation carriers (69·15 centiloids [51·10]; p=0·34). APOE ɛ4 status and sex had no effect on global amyloid PET deposition. Amyloid deposition was elevated significantly earlier in mutation carriers than in participants with Down syndrome (estimated years to symptom onset -23·0 vs -17·5; p=0·0002). PSEN1 mutations primarily drove this difference. Early amyloid accumulation occurred in striatal and cortical regions for both mutation carriers (n=265) and people with Down syndrome (n=128). Although mutation carriers had widespread amyloid accumulation in all cortical regions, the medial occipital regions were spared in people with Down syndrome.

INTERPRETATION

Despite minor differences, amyloid PET changes were similar between people with autosomal dominant Alzheimer's disease versus Down syndrome and strongly supported early amyloid dysregulation in individuals with Down syndrome. Individuals with Down syndrome aged at least 35 years might benefit from early intervention and warrant future inclusion in clinical trials, particularly given the relatively high incidence of Down syndrome.

FUNDING

The National Institute on Aging, Riney and Brennan Funds, the Eunice Kennedy Shriver National Institute of Child Health and Human Development, the German Center for Neurodegenerative Diseases, and the Japan Agency for Medical Research and Development.

Neural correlates of episodic memory in adults with Down syndrome and Alzheimer’s disease

Background

Adults with Down syndrome are at an ultra-high risk of developing early-onset Alzheimer’s disease. Episodic memory deficits are one of the earliest signs of the disease, but their association with regional brain atrophy in the population with Down syndrome has not been explored. We aimed to investigate the neuroanatomical correlates of episodic memory in adults with Down syndrome and symptomatic Alzheimer’s disease.

Methods

Single-center, cross-sectional study. A total of 139 adults with Down syndrome (85 asymptomatic and 54 with symptomatic Alzheimer’s disease) were included in the study (mean age 43.6 ± 10.9 years, 46% female). Episodic memory was assessed using the modified Cued Recall Test. Immediate (trial 1 free immediate recall, trial 3 free immediate recall, total free immediate recall score, and total immediate score) and delayed scores (free delayed recall score and total delayed score) were examined. Cortical thickness from magnetic resonance imaging was determined with surface-based morphometry using the FreeSurfer 6.0 software package. The clusters of reduced cortical thickness were compared between symptomatic and asymptomatic participants to create a cortical atrophy map. Then, the correlation between cortical thickness and the modified Cued Recall Test subscores were separately assessed in symptomatic and asymptomatic subjects, controlling for age, sex, and severity of intellectual disability.

Results

Compared with asymptomatic participants, those with symptomatic Alzheimer’s disease showed a pattern of cortical atrophy in posterior parieto-temporo-occipital cortices. In symptomatic subjects, trial 1 immediate free recall significantly correlated with cortical atrophy in lateral prefrontal regions. Trial 3 free immediate recall and total free immediate recall were associated with the most widespread cortical atrophy. Total immediate score was related to posterior cortical atrophy, including lateral parietal and temporal cortex, posterior cingulate cortex, precuneus, and medial temporal lobe areas. Delayed memory scores were associated with cortical atrophy in temporoparietal and medial temporal lobe regions. No significant relationships were observed between episodic memory measures and cortical atrophy in asymptomatic subjects.

Conclusions

Different episodic memory measures were associated with cortical atrophy in specific brain regions in adults with Down syndrome and Alzheimer’s disease. These results overlap with those described in sporadic Alzheimer’s disease and further support the similarities between Down syndrome-associated Alzheimer’s disease and that in the general population.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-022-01064-x.

The Pictorial Screening Memory Test (P-MIS) for Adults with Moderate Intellectual Disability and Alzheimer's Disease

In this study, we examined normative data and diagnostic accuracy of a pictorial screening test to detect memory impairment for mild cognitive impairment (MCI) and Alzheimer's disease (AD) in Spanish-speaking adults with intellectual disability (ID). A total of 94 volunteers with ID (60 controls, 17 MCI, and 17 AD), were evaluated by neuropsychological tests including the PMIS-ID in a cross-sectional validation study. Discriminative validity between the MCI, AD, and control group was analyzed by the area under the ROC curve. A cut-off score of 4.5 on the immediate recall trial had a sensitivity of 69% and a specificity of 80% to detect memory impairment (AUC = 0.685; 95% CI = 0.506-0.863) in the AD group. The PMIS-ID is a useful screening test to rule out a diagnosis of memory decline in people with moderate level of ID and AD, and it shows good psychometric properties.

Longitudinal Clinical and Cognitive Changes Along the Alzheimer Disease Continuum in Down Syndrome

IMPORTANCE

Alzheimer disease (AD) is the main medical problem in adults with Down syndrome (DS). However, the associations of age, intellectual disability (ID), and clinical status with progression and longitudinal cognitive decline have not been established.

OBJECTIVE

To examine clinical progression along the AD continuum and its related cognitive decline and to explore the presence of practice effects and floor effects with repeated assessments.

DESIGN, SETTING, AND PARTICIPANTS

This is a single-center cohort study of adults (aged >18 years) with DS with different ID levels and at least 6 months of follow-up between November 2012 and December 2021. The data are from a population-based health plan designed to screen for AD in adults with DS in Catalonia, Spain. Individuals were classified as being asymptomatic, having prodromal AD, or having AD dementia.

EXPOSURES

Neurological and neuropsychological assessments.

MAIN OUTCOMES AND MEASURES

The main outcome was clinical change along the AD continuum. Cognitive decline was measured by the Cambridge Cognitive Examination for Older Adults With Down Syndrome and the modified Cued Recall Test.

RESULTS

A total of 632 adults with DS (mean [SD] age, 42.6 [11.4] years; 292 women [46.2%]) with 2847 evaluations (mean [SD] follow-up, 28.8 [18.7] months) were assessed. At baseline, there were 436 asymptomatic individuals, 69 patients with prodromal AD, and 127 with AD dementia. After 5 years of follow-up, 17.1% (95% CI, 12.5%-21.5%) of asymptomatic individuals progressed to symptomatic AD in an age-dependent manner (0.6% [95% CI, 0%-1.8%] for age <40 years; 21.1% [95% CI, 8.0%-32.5%] for age 40-44 years; 41.4% [95% CI, 23.1%-55.3%] for age 45-49 years; 57.5% [95% CI, 38.2%-70.8%] for age ≥50 years; P < .001), and 94.1% (95% CI, 84.6%-98.0%) of patients with prodromal AD progressed to dementia with no age dependency. Cognitive decline in the older individuals was most common among those who progressed to symptomatic AD and symptomatic individuals themselves. Importantly, individuals with mild and moderate ID had no differences in longitudinal cognitive decline despite having different performance at baseline. This study also found practice and floor effects, which obscured the assessment of longitudinal cognitive decline.

CONCLUSIONS AND RELEVANCE

This study found an association between the development of symptomatic AD and a high risk of progressive cognitive decline among patients with DS. These results support the need for population health plans to screen for AD-related cognitive decline from the fourth decade of life and provide important longitudinal data to inform clinical trials in adults with DS to prevent AD.

Cognitive outcome measures for tracking Alzheimer's disease in Down syndrome

Down syndrome (DS) is now viewed as a genetic type of Alzheimer's disease (AD), given the near-universal presence of AD pathology in middle adulthood and the elevated risk for developing clinical AD in DS. As the field of DS prepares for AD clinical intervention trials, there is a strong need to identify cognitive measures that are specific and sensitive to the transition from being cognitively stable to the prodromal (e.g., Mild Cognitive Impairment-Down syndrome) and clinical AD (e.g., Dementia) stages of the disease in DS. It is also important to determine cognitive measures that map onto biomarkers of early AD pathology during the transition from the preclinical to the prodromal stage of the disease, as this transition period is likely to be targeted and tracked in AD clinical trials. The present chapter discusses the current state of research on cognitive measures that could be used to screen/select study participants and as potential outcome measures in future AD clinical trials with adults with DS. In this chapter, we also identify key challenges that need to be overcome and questions that need to be addressed by the DS field as it prepares for AD clinical trials in the coming years.

Rodent Modeling of Alzheimer's Disease in Down Syndrome: In vivo and ex vivo Approaches

There are an estimated 6 million people with Down syndrome (DS) worldwide. In developed countries, the vast majority of these individuals will develop Alzheimer's disease neuropathology characterized by the accumulation of amyloid-β (Aβ) plaques and tau neurofibrillary tangles within the brain, which leads to the early onset of dementia (AD-DS) and reduced life-expectancy. The mean age of onset of clinical dementia is ~55 years and by the age of 80, approaching 100% of individuals with DS will have a dementia diagnosis. DS is caused by trisomy of chromosome 21 (Hsa21) thus an additional copy of a gene(s) on the chromosome must cause the development of AD neuropathology and dementia. Indeed, triplication of the gene APP which encodes the amyloid precursor protein is sufficient and necessary for early onset AD (EOAD), both in people who have and do not have DS. However, triplication of other genes on Hsa21 leads to profound differences in neurodevelopment resulting in intellectual disability, elevated incidence of epilepsy and perturbations to the immune system. This different biology may impact on how AD neuropathology and dementia develops in people who have DS. Indeed, genes on Hsa21 other than APP when in three-copies can modulate AD-pathogenesis in mouse preclinical models. Understanding this biology better is critical to inform drug selection for AD prevention and therapy trials for people who have DS. Here we will review rodent preclinical models of AD-DS and how these can be used for both in vivo and ex vivo (cultured cells and organotypic slice cultures) studies to understand the mechanisms that contribute to the early development of AD in people who have DS and test the utility of treatments to prevent or delay the development of disease.

Pharmacological Approaches to the Treatment of Dementia in Down Syndrome: A Systematic Review of Randomized Clinical Studies

Down Syndrome (DS) is considered the most frequent form of Intellectual Disability, with important expressions of cognitive decline and early dementia. Studies on potential treatments for dementia in this population are still scarce. Thus, the current review aims to synthesize the different pharmacological approaches that already exist in the literature, which focus on improving the set of symptoms related to dementia in people with DS. A total of six studies were included, evaluating the application of supplemental antioxidant therapies, such as alpha-tocopherol; the use of acetylcholinesterase inhibitor drugs, such as donepezil; N-methyl-d-aspartate (NMDA) receptor antagonists, such as memantine; and the use of vitamin E and a fast-acting intranasal insulin. Two studies observed important positive changes related to some general functions in people with DS (referring to donepezil). In the majority of studies, the use of pharmacological therapies did not lead to improvement in the set of symptoms related to dementia, such as memory and general functionality, in the population with DS.

Association of Alzheimer Disease With Life Expectancy in People With Down Syndrome

IMPORTANCE

People with Down syndrome have a high risk of developing Alzheimer disease dementia. However, penetrance and age at onset are considered variable, and the association of this disease with life expectancy remains unclear because of underreporting in death certificates.

OBJECTIVE

To assess whether the variability in symptom onset of Alzheimer disease in Down syndrome is similar to autosomal dominant Alzheimer disease and to assess its association with mortality.

DESIGN, SETTING, AND PARTICIPANTS

This study combines a meta-analysis with the assessment of mortality data from US death certificates (n = 77 347 case records with a International Classification of Diseases code for Down syndrome between 1968 to 2019; 37 900 [49%] female) and from a longitudinal cohort study (n = 889 individuals; 46% female; 3.2 [2.1] years of follow-up) from the Down Alzheimer Barcelona Neuroimaging Initiative (DABNI).

MAIN OUTCOMES AND MEASURES

A meta-analysis was conducted to investigate the age at onset, age at death, and duration of Alzheimer disease dementia in Down syndrome. PubMed/Medline, Embase, Web of Science, and CINAHL were searched for research reports, and OpenGray was used for gray literature. Studies with data about the age at onset or diagnosis, age at death, and disease duration were included. Pooled estimates with corresponding 95% CIs were calculated using random-effects meta-analysis. The variability in disease onset was compared with that of autosomal dominant Alzheimer disease. Based on these estimates, a hypothetical distribution of age at death was constructed, assuming fully penetrant Alzheimer disease. These results were compared with real-world mortality data.

RESULTS

In this meta-analysis, the estimate of age at onset was 53.8 years (95% CI, 53.1-54.5 years; n = 2695); the estimate of age at death, 58.4 years (95% CI, 57.2-59.7 years; n = 324); and the estimate of disease duration, 4.6 years (95% CI, 3.7-5.5 years; n = 226). Coefficients of variation and 95% prediction intervals of age at onset were comparable with those reported in autosomal dominant Alzheimer disease. US mortality data revealed an increase in life expectancy in Down syndrome (median [IQR], 1 [0.3-16] years in 1968 to 57 [49-61] years in 2019), but with clear ceiling effects in the highest percentiles of age at death in the last decades (90th percentile: 1990, age 63 years; 2019, age 65 years). The mortality data matched the limits projected by a distribution assuming fully penetrant Alzheimer disease in up to 80% of deaths (corresponding to the highest percentiles). This contrasts with dementia mentioned in 30% of death certificates but is in agreement with the mortality data in DABNI (78.9%). Important racial disparities persisted in 2019, being more pronounced in the lower percentiles (10th percentile: Black individuals, 1 year; White individuals, 30 years) than in the higher percentiles (90th percentile: Black individuals, 64 years; White individuals, 66 years).

CONCLUSIONS AND RELEVANCE

These findings suggest that the mortality data and the consistent age at onset were compatible with fully penetrant Alzheimer disease. Lifespan in persons with Down syndrome will not increase until disease-modifying treatments for Alzheimer disease are available.

Screening for Dementia and Cognitive Decline in Adults With Down Syndrome: A Novel Approach Using the Informant Questionnaire on Cognitive Decline in the Elderly

OBJECTIVE

The aim was to examine the psychometric properties of the Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE) as a diagnostic tool to screen for dementia in aging individuals with Down syndrome (DS).

METHODS

This was a cross-sectional study of 92 individuals with DS 30 y or above of age) evaluated with the IQCODE. Using the informant questionnaire of the Cambridge Examination for Mental Disorders of Older People with Down's Syndrome and Others with Intellectual Disabilities, we divided the subjects into 3 diagnostic groups: stable cognition; prodromal dementia; and dementia. The ability of the IQCODE to discriminate between diagnostic groups was analyzed by calculating the areas under the receiver operator characteristic curves (AUCs).

RESULTS

The optimal IQCODE cutoffs were 3.14 for dementia versus stable cognition (AUC=0.993; P<0.001) and 3.11 for prodromal dementia+dementia versus stable cognition (AUC=0.975; P<0.001), with sensitivity/specificity/accuracy of 100%/96.8%/97.3%, and 93.3%/91.9%/92.4%, respectively. The IQCODE showed a weak-to-moderate correlation with cognitive performance (P<0.05).

CONCLUSION

The IQCODE is a useful tool to screen for cognitive decline in individuals with DS and is suitable for use in a primary care setting.

Primitive Reflexes and Dementia in Adults With Down Syndrome

Background and Objectives

To determine whether primitive reflexes serve as an indicator of dementia in adults with Down syndrome (DS), we collected neurologic examination data, cognitive and behavioral assessments, and clinical consensus diagnoses of dementia from 92 adults with DS.

Methods

In a cross-sectional, observational study of a regional cohort, χ² and Fisher exact tests examined individual reflexes across the diagnostic group (no, possible, or probable dementia). In 64 participants with all 8 reflexes assessed, the number of primitive reflexes was assessed as a predictor of diagnosis using age-controlled multinomial logistic regression and of performance on clinical assessments (Brief Praxis Test [BPT], Severe Impairment Battery [SIB], and the Dementia Questionnaire for People with Learning Disabilities [DLD]) using age-adjusted linear regression.

Results

Primitive palmomental, grasp, snout, and suck reflexes were more frequent in individuals with probable dementia, but all participants showed at least 1 primitive reflex. Multiple primitive reflexes in combination served as a better indicator of dementia, with each additional abnormal reflex tripling probability of the probable dementia group membership controlling for age. Abnormal reflex count was not associated with direct assessment of cognition and praxis (SIB and BPT) but associated with informant ratings of cognitive and behavioral functioning (DLD).

Discussion

The presence of multiple reflexes serves as an indicator of dementia status in DS as a supplement to direct assessment of cognition and praxis. The reflex examination may serve as a tool in the multimethod evaluation for dementia in DS, as it appears unaffected by intellectual disability and language mastery.

Alzheimer's disease associated with Down syndrome: a genetic form of dementia

Adults with Down syndrome develop the neuropathological hallmarks of Alzheimer's disease and are at very high risk of developing early-onset dementia, which is now the leading cause of death in this population. Diagnosis of dementia remains a clinical challenge because of the lack of validated diagnostic criteria in this population, and because symptoms are overshadowed by the intellectual disability associated with Down syndrome. In people with Down syndrome, fluid and imaging biomarkers have shown good diagnostic performances and a strikingly similar temporality of changes with respect to sporadic and autosomal dominant Alzheimer's disease. Most importantly, there are no treatments to prevent Alzheimer's disease, even though adults with Down syndrome could be an optimal population in whom to conduct Alzheimer's disease prevention trials. Unprecedented research activity in Down syndrome is rapidly changing this bleak scenario that will translate into disease-modifying therapies that could benefit other populations.

Proposed diagnostic criteria for mild cognitive impairment in Down syndrome population

BACKGROUND

Despite presenting higher risk of dementia, mild cognitive impairment (MCI) is not well defined in Down syndrome population.

OBJECTIVE

We aimed to describe cognitive and neuropsychological patterns associated with MCI in Down syndrome individuals.

METHOD

Two groups of adults with Down syndrome (control and prodromal) were studied throughout 3 years. Two linear mixed models and a model including the variables that best predicted group membership were built.

RESULTS

Behavioural Regulation Index (BRI) (Behaviour Rating Inventory of Executive Function test) and the model composed of BRI, abstraction and delayed verbal memory were the variable and model best predicting group membership, respectively.

CONCLUSION

Suggest a diagnosis of MCI when BRI is the earliest change perceived by caregivers and this is combined with low scores in abstract thinking, and when an amnesic pattern in delayed verbal memory is observed, but adaptive skills are preserved.

The Clinical and Neuropathological Features of Sporadic (Late-Onset) and Genetic Forms of Alzheimer's Disease

The purpose of this review is to compare and highlight the clinical and pathological aspects of genetic versus acquired Alzheimer's disease: Down syndrome-associated Alzheimer's disease in (DSAD) and Autosomal Dominant Alzheimer's disease (ADAD) are compared with the late-onset form of the disease (LOAD). DSAD and ADAD present in a younger population and are more likely to manifest with non-amnestic (such as dysexecutive function features) in the prodromal phase or neurological features (such as seizures and paralysis) especially in ADAD. The very large variety of mutations associated with ADAD explains the wider range of phenotypes. In the LOAD, age-associated comorbidities explain many of the phenotypic differences.

Patient-specific Alzheimer-like pathology in trisomy 21 cerebral organoids reveals BACE2 as a gene dose-sensitive AD suppressor in human brain

A population of more than six million people worldwide at high risk of Alzheimer's disease (AD) are those with Down Syndrome (DS, caused by trisomy 21 (T21)), 70% of whom develop dementia during lifetime, caused by an extra copy of β-amyloid-(Aβ)-precursor-protein gene. We report AD-like pathology in cerebral organoids grown in vitro from non-invasively sampled strands of hair from 71% of DS donors. The pathology consisted of extracellular diffuse and fibrillar Aβ deposits, hyperphosphorylated/pathologically conformed Tau, and premature neuronal loss. Presence/absence of AD-like pathology was donor-specific (reproducible between individual organoids/iPSC lines/experiments). Pathology could be triggered in pathology-negative T21 organoids by CRISPR/Cas9-mediated elimination of the third copy of chromosome 21 gene BACE2, but prevented by combined chemical β and γ-secretase inhibition. We found that T21 organoids secrete increased proportions of Aβ-preventing (Aβ1-19) and Aβ-degradation products (Aβ1-20 and Aβ1-34). We show these profiles mirror in cerebrospinal fluid of people with DS. We demonstrate that this protective mechanism is mediated by BACE2-trisomy and cross-inhibited by clinically trialled BACE1 inhibitors. Combined, our data prove the physiological role of BACE2 as a dose-sensitive AD-suppressor gene, potentially explaining the dementia delay in ~30% of people with DS. We also show that DS cerebral organoids could be explored as pre-morbid AD-risk population detector and a system for hypothesis-free drug screens as well as identification of natural suppressor genes for neurodegenerative diseases.

Cognitive assessment using the Rapid Assessment for Developmental Disabilities, Second Edition (RADD-2)

BACKGROUND

Individuals with developmental disabilities (DD) often have severe impairments and maladaptive behaviours that make it difficult to reliably assess their cognitive abilities. Given these challenges, the Rapid Assessment of Developmental Disabilities, Second Edition (RADD-2), was designed to measure general cognitive ability in this population. The purpose of this study is to demonstrate the battery's psychometric properties when used with individuals with DD who have challenging behavioural and psychiatric conditions and for those who have limited verbal skills.

METHOD

The cognitive and adaptive behaviour skills of 193 children and adults with DD and considerable medical, behavioural and/or psychiatric problems were evaluated using the first and second editions of the RADD, Kaufmann Brief Intelligence Test - 2nd Edition, and Scales of Independent Behaviour - Revised Edition. Medication side effects and challenging behaviours were assessed using the Aberrant Behaviour Checklist.

RESULTS

There were no floor or ceiling effects on the RADD-2. Both the nonverbal index and total scores had strong concurrent validity with other abbreviated tests of intellectual ability and good discriminant validity from measures of adaptive behaviour and medication side effects. RADD-2 scores also had strong criterion validity as they successfully differentiated between all levels of intellectual functioning. Age and sex did not differentially affect RADD-2 performance, and the co-occurrence of psychiatric conditions did not negatively affect performance. The only medical condition associated with lower RADD-2 performance was epilepsy.

CONCLUSIONS

The RADD-2 can quantify the differential cognitive abilities of individuals with DD, even for those with minimal communication skills, challenging behaviours or severe medication side effects that can typically complicate assessment. This brief cognitive battery can be used to measure changes due to interventions, on the one hand, and progression of neurological disease, on the other.

Cognitive and Behavioral Domains That Reliably Differentiate Normal Aging and Dementia in Down Syndrome

Primary care integration of Down syndrome (DS)-specific dementia screening is strongly advised. The current study employed principal components analysis (PCA) and classification and regression tree (CART) analyses to identify an abbreviated battery for dementia classification. Scale- and subscale-level scores from 141 participants (no dementia n = 68; probable Alzheimer’s disease n = 73), for the Severe Impairment Battery (SIB), Dementia Scale for People with Learning Disabilities (DLD), and Vineland Adaptive Behavior Scales—Second Edition (Vineland-II) were analyzed. Two principle components (PC1, PC2) were identified with the odds of a probable dementia diagnosis increasing 2.54 times per PC1 unit increase and by 3.73 times per PC2 unit increase. CART analysis identified that the DLD sum of cognitive scores (SCS < 35 raw) and Vineland-II community subdomain (<36 raw) scores best classified dementia. No significant difference in the PCA versus CART area under the curve (AUC) was noted (D(65.196) = −0.57683; p = 0.57; PCA AUC = 0.87; CART AUC = 0.91). The PCA sensitivity was 80% and specificity was 70%; CART was 100% and specificity was 81%. These results support an abbreviated dementia screening battery to identify at-risk individuals with DS in primary care settings to guide specialized diagnostic referral.

Building the Future Therapies for Down Syndrome: The Third International Conference of the T21 Research Society

Research focused on Down syndrome has increased in the last several years to advance understanding of the consequences of trisomy 21 (T21) on molecular and cellular processes and, ultimately, on individuals with Down syndrome. The Trisomy 21 Research Society (T21RS) is the premier scientific organization for researchers and clinicians studying Down syndrome. The Third International Conference of T21RS, held June 6-9, 2019, in Barcelona, Spain, brought together 429 scientists, families, and industry representatives to share the latest discoveries on underlying cellular and molecular mechanisms of T21, define cognitive and behavioral challenges and better understand comorbidities associated with Down syndrome, including Alzheimer's disease and leukemia. Presentation of cutting-edge results in neuroscience, neurology, model systems, psychology, cancer, biomarkers and molecular and phar-ma-cological therapeutic approaches demonstrate the compelling interest and continuing advancement in all aspects of understanding and ameliorating conditions associated with T21.

Assessment of dementia in a clinical sample of persons with intellectual disability

BACKGROUND

Assessment of age-associated disorders has become increasingly important.

METHODS

In a clinical setting, people with intellectual disability with and without dementia were assessed retrospectively using the Neuropsychological Test Battery (NTB) and the Dementia Questionnaire for People with Learning Disabilities (DLD) at two different times to analyse neuropsychological changes and diagnostic validity. One group (n = 44) was assessed with both instruments, while the DLD was applied in 71 patients.

RESULTS

In the NTB (n = 44), only patients with dementia (n = 26) showed a decline in the NTB total score and three subscales. Receiver operating characteristic analysis revealed a diagnostic sensitivity of .67, a specificity of .81, and an area under the curve (AUC) of .767. In the DLD group (n = 71), only those with dementia displayed a decrease in the cognitive and social scale; diagnostic sensitivity and specificity values were low (.61/.63) and the AUC was .704.

CONCLUSIONS

Neuropsychological assessment was sensitive to detect cognitive changes over time. Sensitivity values of both instruments suggest a reassessment at a later time point.

Markers of early changes in cognition across cohorts of adults with Down syndrome at risk of Alzheimer's disease

INTRODUCTION

Down syndrome (DS), a genetic variant of early onset Alzheimer's disease (AD), lacks a suitable outcome measure for prevention trials targeting pre-dementia stages.

METHODS

We used cognitive test data collected in several longitudinal aging studies internationally from 312 participants with DS without dementia to identify composites that were sensitive to change over time. We then conducted additional analyses to provide support for the utility of the composites. The composites were presented to an expert panel to determine the most optimal cognitive battery based on predetermined criteria.

RESULTS

There were common cognitive domains across site composites, which were sensitive to early decline. The final composite consisted of memory, language/executive functioning, selective attention, orientation, and praxis tests.

DISCUSSION

We have identified a composite that is sensitive to early decline and thus may have utility as an outcome measure in trials to prevent or delay symptoms of AD in DS.

Optimal age and outcome measures for Alzheimer's disease prevention trials in people with Down syndrome

INTRODUCTION

People with Down syndrome (DS) typically develop Alzheimer's disease (AD) neuropathology before age 40, but a lack of outcome measures and longitudinal data have impeded their inclusion in randomized controlled trials (RCTs).

METHODS

Cohort study. Event-based and dose-response Emax models were fitted to longitudinal cognitive data, to stage AD and determine the earliest ages of decline. Results informed sample size estimations for hypothetical RCTs of disease-modifying treatments that reduced decline by 35% or 75%.

RESULTS

Seventy-five percent of participants progressed or remained stable in the AD staging model; effect sizes varied by age group and tests. Varied treatment effects could be detected with 50-200 people per arm when using sensitive cognitive outcome measures and targeting recruitment to ages 36 to 45 years.

DISCUSSION

Efficient RCTs of AD preventative treatments can be conducted in the DS population using sensitive outcome measures to monitor early decline. Dose-response models could help tailor future RCTs.

[Cognition in Down's Syndrome: Development across the Life Span and Neuropsychological Assessment in Adults]

Das Down-Syndrom ist die häufigste genetische Ursache einer Intelligenzminderung. Da Menschen mit einem Down-Syndrom ein erhöhtes Risiko aufweisen, an einer Alzheimer-Demenz zu erkranken, ist eine umfassende Untersuchung der kognitiven Funktionen indiziert, sowohl im jungen Erwachsenenalter (zur Erhebung des kognitiven Ausgangsniveaus) als auch im Verlauf zur Demenzdiagnostik. Das weite Spektrum an kognitiver Leistungsfähigkeit bei Menschen mit einem Down-Syndrom stellt eine diagnostische Herausforderung dar. Wir möchten daher einen Überblick geben (1) über die kognitive Entwicklung über die Lebensspanne, (2) über verschiedene mögliche Ursachen kognitiver Veränderungen bei erwachsenen Menschen mit einem Down-Syndrom und (3) über neuropsychologische Diagnostik und entsprechende Verfahren für den Erwachsenenbereich. Schließlich geben wir, auf der Grundlage unserer Erfahrungen, (4) allgemeine Empfehlungen zur Untersuchung und Befundinterpretation bei Menschen mit Intelligenzminderung.

TTC3-Mediated Protein Quality Control, A Potential Mechanism for Cognitive Impairment

The tetrapeptide repeat domain 3 (TTC3) gene falls within Down's syndrome (DS) critical region. Cognitive impairment is a common phenotype of DS and Alzheimer’s disease (AD), and overexpression of TTC3 can accelerate cognitive decline, but the specific mechanism is unknown. The TTC3-mediated protein quality control (PQC) mechanism, similar to the PQC system, is divided into three parts: it acts as a cochaperone to assist proteins in folding correctly; it acts as an E3 ubiquitin ligase (E3s) involved in protein degradation processes through the ubiquitin–proteasome system (UPS); and it may also eventually cause autophagy by affecting mitochondrial function. Thus, this article reviews the research progress on the structure, function, and metabolism of TTC3, including the recent research progress on TTC3 in DS and AD; the role of TTC3 in cognitive impairment through PQC in combination with the abovementioned attributes of TTC3; and the potential targets of TTC3 in the treatment of such diseases.

Short forms of Prudhoe Cognitive Function Test in adults and aging people with intellectual disabilities: Italian validation study

BACKGROUND

We aimed to validate the Italian version of the two parallel short forms of the Prudhoe Cognitive Function Test (s-PCFT-I) in adults and seniors with intellectual disabilities (ID) of any aetiology and level of severity.

METHODS

Our validation is a multicentre study attended by 211 subjects with ID, 125 male and 86 female, aged 40 years and above for people with Down syndrome and aged 50 years for people with other forms of disabilities.

RESULTS

The s-PCFT-I shows a wide range of scores in the absence of floor effects with minimal ceiling effects. A Cronbach's α coefficient of 0.85 and a mean inter-item correlation of 0.21 indicate high internal consistency. The tool demonstrates good agreement between testers and near excellent temporal stability with intraclass correlation coefficients respectively of 0.85 and 0.90. s-PCFT-I total scores do not differ by sex or age, while statistically significant differences are observed between people with different levels of severity of ID. Moderate to good and highly significant correlations (-0.40 to -0.66) among the s-PCFT-I total scores and subscores and the Sum of Cognitive Score of the informant-based Dementia Questionnaire for Persons with Intellectual Disabilities suggest an acceptable level of concurrent criterion validity. Cognitive decliners according to Prasher's Dementia Questionnaire for Persons with Intellectual Disabilities cut-off scores perform significantly lower on s-PCFT-I than non-decliners.

CONCLUSIONS

The s-PCFT-I has good psychometric properties and user friendliness and may therefore be a valuable addition to the current informant-rated tools for screening and assessment of cognition in aging people with ID.

Neuropsychiatric Symptoms of Alzheimer's Disease in Down Syndrome and Its Impact on Caregiver Distress

BACKGROUND

Neuropsychiatric symptoms (NPS) are non-cognitive manifestations common to dementia and other medical conditions, with important consequences for the patient, caregivers, and society. Studies investigating NPS in individuals with Down syndrome (DS) and dementia are scarce.

OBJECTIVE

Characterize NPS and caregiver distress among adults with DS using the Neuropsychiatric Inventory (NPI).

METHODS

We evaluated 92 individuals with DS (≥30 years of age), divided by clinical diagnosis: stable cognition, prodromal dementia, and AD. Diagnosis was determined by a psychiatrist using the Cambridge Examination for Mental Disorders of Older People with Down's Syndrome and Others with Intellectual Disabilities (CAMDEX-DS). NPS and caregiver distress were evaluated by an independent psychiatrist using the NPI, and participants underwent a neuropsychological assessment with Cambridge Cognitive Examination (CAMCOG-DS).

RESULTS

Symptom severity differed between-groups for delusion, agitation, apathy, aberrant motor behavior, nighttime behavior disturbance, and total NPI scores, with NPS total score being found to be a predictor of AD in comparison to stable cognition (OR for one-point increase in the NPI = 1.342, p = 0.012). Agitation, apathy, nighttime behavior disturbances, and total NPI were associated with CAMCOG-DS, and 62% of caregivers of individuals with AD reported severe distress related to NPS. Caregiver distress was most impacted by symptoms of apathy followed by nighttime behavior, appetite/eating abnormalities, anxiety, irritability, disinhibition, and depression (R2 = 0.627, F(15,76) = 8.510, p < 0.001).

CONCLUSION

NPS are frequent and severe in individuals with DS and AD, contributing to caregiver distress. NPS in DS must be considered of critical relevance demanding management and treatment. Further studies are warranted to understand the biological underpinnings of such symptoms.

Longitudinal assessment of dementia measures in Down syndrome

INTRODUCTION

Early detection of dementia symptoms is critical in Down syndrome (DS) but complicated by clinical assessment barriers. The current study aimed to characterize cognitive and behavioral impairment using longitudinal trajectories comparing several measures of cognitive and behavioral functioning.

METHODS

Measures included global cognitive status (Severe Impairment Battery [SIB]), motor praxis (Brief Praxis Test [BPT]), and clinical dementia informant ratings (Dementia Questionnaire for People with Learning Disabilities [DLD]). One-year reliability was assessed using a two-way mixed effect, consistency, single measurement intraclass correlation among non-demented participants. Longitudinal assessment of SIB, BPT, and DLD was completed using linear mixed effect models.

RESULTS

One-year reliability (n = 52; 21 male) was moderate for DLD (0.69 to 0.75) and good for SIB (0.87) and BPT (0.80). Longitudinal analysis (n = 72) revealed significant age by diagnosis interactions for SIB (F(2, 115.02) = 6.06, P = .003), BPT (F(2, 85.59) = 4.56, P = .013), and DLD (F(2, 103.56) = 4.48, P = .014). SIB progression (PR) had a faster decline in performance versus no-dementia (ND) (t(159) = -2.87; P = .013). Dementia had a faster decline in BPT performance versus ND (t(112) = -2.46; P = .041). PR showed quickly progressing scores compared to ND (t(128) = -2.86; P = .014).

DISCUSSION

Current measures demonstrated moderate to good reliability. Longitudinal analysis revealed that SIB, BPT, and DLD changed with age depending on diagnostic progression; no change rates were dependent on baseline cognition, indicating usefulness across a variety of severity levels in DS.

Screening of Cognitive Changes in Adults with Intellectual Disabilities: A Systematic Review

Background and Aims: Screening and assessment of cognitive changes in adults with Intellectual Disabilities (ID), mainly Down Syndrome (DS), is crucial to offer appropriate services to their needs. We present a systematic review of the existing instruments assessing dementia, aiming to support researchers and clinicians’ best practice. Methods: Searches were carried out in the databases Web of Science; PubMed; PsycINFO in March 2019 and updated in October 2020. Studies were selected and examined if they: (1) focused on assessing age-related cognitive changes in persons with ID; (2) included adults and/or older adults; (3) included scales and batteries for cognitive assessment. Results: Forty-eight cross-sectional studies and twenty-seven longitudinal studies were selected representing a total sample of 6451 participants (4650 DS and 1801 with other ID). In those studies, we found 39 scales, questionnaires, and inventories, and 13 batteries for assessing cognitive and behavioural changes in adults with DS and other ID. Conclusion: The most used instrument completed by an informant or carer was the Dementia Questionnaire for Learning Disabilities (DLD), and its previous versions. We discuss the strengths and limitations of the instruments and outline recommendations for future use.

The AT(N) framework for Alzheimer's disease in adults with Down syndrome

The National Institute on Aging in conjunction with the Alzheimer's Association (NIA-AA) recently proposed a biological framework for defining the Alzheimer's disease (AD) continuum. This new framework is based upon the key AD biomarkers (amyloid, tau, neurodegeneration, AT[N]) instead of clinical symptoms and represents the latest understanding that the pathological processes underlying AD begin decades before the manifestation of symptoms. By using these same biomarkers, individuals with Down syndrome (DS), who are genetically predisposed to developing AD, can also be placed more precisely along the AD continuum. The A/T(N) framework is therefore thought to provide an objective manner by which to select and enrich samples for clinical trials. This new framework is highly flexible and allows the addition of newly confirmed AD biomarkers into the existing AT(N) groups. As biomarkers for other pathological processes are validated, they can also be added to the AT(N) classification scheme, which will allow for better characterization and staging of AD in DS. These biological classifications can then be merged with clinical staging for an examination of factors that impact the biological and clinical progression of the disease. Here, we leverage previously published guidelines for the AT(N) framework to generate such a plan for AD among adults with DS.

Association of sleep with cognition and beta amyloid accumulation in adults with Down syndrome

Adults with Down syndrome have an increased risk for both disordered sleep and Alzheimer's disease (AD). In the general population, disrupted sleep has been linked to beta amyloid accumulation, an early pathophysiologic feature of AD. In this study, the association among sleep, beta amyloid, and measures of AD-related cognitive decline was examined in 47 non-demented adults with Down syndrome (aged 26-56 years). Sleep was measured using actigraphy over 7 nights. Pittsburgh Compound B positron emission tomography was used to assess global and striatal beta amyloid burden. Participants had the following clinical AD status: 7 (15%) mild cognitive impairment and 40 (85%) cognitively unaffected. Average length of night-time awakenings was significantly positively associated with striatal beta amyloid and decreased cognitive performance in executive functioning and motor planning and coordination. Findings suggest that disrupted sleep is associated with beta amyloid accumulation and cognitive features of preclinical AD in Down syndrome. Early identification and treatment of sleep problems could be a lifestyle intervention that may delay beta amyloid accumulation and cognitive decline in this AD vulnerable group.

Differential Associations of Apolipoprotein E ε4 Genotype With Attentional Abilities Across the Life Span of Individuals With Down Syndrome

IMPORTANCE

Risk of Alzheimer disease (AD) is particularly high for individuals with Down syndrome (DS). The ε4 allele of the apolipoprotein E gene (APOE ε4) is associated with an additional risk for AD. In typical development, there is evidence that the APOE ε4 genotype is associated with an early cognitive advantage. Here we investigate associations of APOE ε4 with attention across the life span of individuals with DS.

OBJECTIVE

To investigate associations between APOE ε4 and attentional abilities in young children and in adults with DS.

DESIGN, SETTINGS, AND PARTICIPANTS

In this cross-sectional study, data were collected from 80 young children with DS (8-62 months of age) and 240 adults with DS (16-71 years of age) during the period from 2013 to 2018 at a research center to examine the association between APOE status (ε4 carrier vs ε4 noncarrier) and attentional abilities.

EXPOSURE

APOE status (ε4 carrier vs ε4 noncarrier).

MAIN OUTCOMES AND MEASURES

For the children, attentional ability was assessed using an eye-tracking paradigm, the gap-overlap task; the size of the gap effect was the primary outcome. For the adults, attentional ability was assessed using the CANTAB simple reaction time task; the standard deviation of response time latencies was the primary outcome. Cross-sectional developmental trajectories were constructed linking attentional ability with age in ε4 carriers and ε4 noncarriers for children and adults separately.

RESULTS

The child sample comprised 23 ε4 carriers and 57 ε4 noncarriers. The adult sample comprised 61 ε4 carriers and 179 ε4 noncarriers. For the children, a significant difference between trajectory intercepts (ηp2 = 0.14) indicated that ε4 carriers (B = 100.24 [95% CI, 18.52-181.96]) exhibited an attentional advantage over ε4 noncarriers (B = 314.78 [95% CI, 252.17-377.39]). There was an interaction between APOE status and age (ηp2 = 0.10); while the gap effect decreased with age for ε4 noncarriers (B = -4.58 [95% CI, -6.67 to -2.48]), reflecting the development of the attention system, there was no change across age in ε4 carriers (B = 0.77 [95% CI, -1.57 to 3.12]). For the adults, there was no main effect of ε4 carrier status, but there was an interaction between APOE status and age (B = 0.02 [95% CI, 0.004-0.07]), so that ε4 carriers had poorer attentional ability than ε4 noncarriers at older ages.

CONCLUSIONS AND RELEVANCE

APOE ε4 is associated with an attentional advantage early in development and a disadvantage later in life for individuals with DS, similar to the pattern reported in typical development. Understanding the differential role of APOE across the life span is an important step toward future interventions.

Language skills as a predictor of cognitive decline in adults with Down syndrome

INTRODUCTION

Adults with Down syndrome (DS) are at high risk for early onset Alzheimer's disease (AD), characterized by a progressive decline in multiple cognitive domains including language, which can impact social interactions, behavior, and quality of life. This cross-sectional study examined the relationship between language skills and dementia.

METHODS

A total of 168 adults with DS (mean age = 51.4 years) received neuropsychological assessments, including Vineland Communication Domain, McCarthy Verbal Fluency, and Boston Naming Test, and were categorized in one of three clinical groups: cognitively stable (CS, 57.8%); mild cognitive impairment (MCI-DS, 22.6%); and probable/definite dementia (AD-DS, 19.6%). Logistic regression was used to determine how well language measures predict group status.

RESULTS

Vineland Communication, particularly receptive language, was a significant predictor of MCI-DS. Semantic verbal fluency was the strongest predictor of AD-DS.

DISCUSSION

Assessment of language skills can aid in the identification of dementia in adults with DS. Clinically, indications of emerging language problems should warrant further evaluation and monitoring.

The Alzheimer's Biomarker Consortium-Down Syndrome: Rationale and methodology

INTRODUCTION

Adults with Down syndrome (DS) are at exceptionally high risk for Alzheimer's disease (AD), with virtually all individuals developing key neuropathological features by age 40. Identifying biomarkers of AD progression in DS can provide valuable insights into pathogenesis and suggest targets for disease modifying treatments.

METHODS

We describe the development of a multi-center, longitudinal study of biomarkers of AD in DS. The protocol includes longitudinal examination of clinical, cognitive, blood and cerebrospinal fluid-based biomarkers, magnetic resonance imaging and positron emission tomography measures (at 16-month intervals), as well as genetic modifiers of AD risk and progression.

RESULTS

Approximately 400 individuals will be enrolled in the study (more than 370 to date). The methodological approach from the administrative, clinical, neuroimaging, omics, neuropathology, and statistical cores is provided.

DISCUSSION

This represents the largest U.S.-based, multi-site, biomarker initiative of AD in DS. Findings can inform other multidisciplinary networks studying AD in the general population.

Promising outcome measures of early Alzheimer's dementia in adults with Down syndrome

INTRODUCTION

Adults with Down syndrome (DS) are at high risk for developing Alzheimer's disease (AD) and its associated dementia, warranting the development of strategies to improve early detection when prevention is possible.

METHODS

Using a broad battery of neuropsychological assessments, informant interviews, and clinical record review, we evaluated the psychometrics of measures in a large sample of 561 adults with DS. We tracked longitudinal stability or decline in functioning in a subsample of 269 participants over a period of 3 years, all initially without indications of clinically significant aging-related decline.

RESULTS

Results identified an array of objective measures that demonstrated sensitivity in distinguishing individuals with incident "mild cognitive impairment" (MCI-DS) as well as subsequent declines occurring with incident dementia.

DISCUSSION

Several instruments showed clear promise for use as outcome measures for future clinical trials and for informing diagnosis of individuals suspected of experiencing early signs and symptoms of a progressive dementia process.

Amnestic and non-amnestic symptoms of dementia: An international study of Alzheimer's disease in people with Down's syndrome

The presence of age-related neuropathology characteristic of Alzheimer's disease (AD) in people with Down syndrome (DS) is well-established. However, the early symptoms of dementia may be atypical and appear related to dysfunction of prefrontal circuitry.

OBJECTIVE

To characterize the initial informant reported age-related neuropsychiatric symptoms of dementia in people with DS, and their relationship to AD and frontal lobe function.

METHODS

Non-amnestic informant reported symptoms (disinhibition, apathy, and executive dysfunction) and amnestic symptoms from the CAMDEX-DS informant interview were analyzed in a cross-sectional cohort of 162 participants with DS over 30 years of age, divided into three groups: stable cognition, prodromal dementia, and AD. To investigate age-related symptoms prior to evidence of prodromal dementia we stratified the stable cognition group by age.

RESULTS

Amnestic and non-amnestic symptoms were present before evidence of informant-reported cognitive decline. In those who received the diagnosis of AD, symptoms tended to be more marked. Memory impairments were more marked in the prodromal dementia than the stable cognition group (OR = 35.07; P < .001), as was executive dysfunction (OR = 7.16; P < .001). Disinhibition was greater in the AD than in the prodromal dementia group (OR = 3.54; P = .04). Apathy was more pronounced in the AD than in the stable cognition group (OR = 34.18; P < .001).

CONCLUSION

Premorbid amnestic and non-amnestic symptoms as reported by informants increase with the progression to AD. For the formal diagnosis of AD in DS this progression of symptoms needs to be taken into account. An understanding of the unique clinical presentation of DS in AD should inform treatment options.

Down syndrome and dementia: advances in the field

PURPOSE OF REVIEW

People with Down syndrome represent the world's largest population with a genetic risk for Alzheimer's disease. This review will provide a short summary of what is known and will include recent findings from the field.

RECENT FINDINGS

There has been an increasing focus on biomarker research in this population, with a number of studies presenting findings on promising new markers - Neurofilament Light (NfL) appears to be one such promising marker that has emerged. Imaging studies have increased our knowledge on the progression of Alzheimer's disease in this population.

SUMMARY

The inclusion of people with Down syndrome in dementia research is vital from a scientific and an equity perspective. Recent advances in the field can have further impact with multisite, cross country collaborative efforts. For this to happen, instruments need to be validated across language and cultures.