Abstract
Background
Understanding the earliest pathophysiological changes in Alzheimer’s disease (AD) is important for development of therapeutic intervention strategies. Studying genetically ...identical twins provides unique information on genetic and environmental influences on development of AD. Here we studied change in AD biomarkers amyloid β1‐42 (aβ42), amyloid β1‐40 (aβ40), phosphorylated tau
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(p‐tau) and total tau (t‐tau) in CSF over time in a cohort of older cognitively normal monozygotic twins and tested the genetic contribution to biomarker concentrations at baseline and to change of biomarker concentrations over time.
Method
We included 103 twins (n
pairs
= 42) from the EMIF‐AD preclinAD study with 2‐4 repeated CSF sampling available across a time period of 4.47±2 years (mean±SD age: 68.8±7 years, 54 (52%) female). We measured aβ42, aβ40, p‐tau and t‐tau using the Lumipulse platform (Fujirebio Diagnostics, Inc.). We used linear mixed models to investigate change in biomarker concentrations over time. We used twin‐pair intraclass correlation (ICC) analysis to estimate the genetic contribution to biomarker concentrations at baseline and at repeated measurements, and to annual change in biomarker concentrations.
Result
At baseline, 25 (24%) individuals had an abnormal aβ42/aβ40 ratio, 27 (26%) abnormal p‐tau and 35 (34%) abnormal t‐tau, and at last measurement respectively 34 (33%), 38 (37%) and 45 (44%). Across the group, aβ42/aβ40 decreased (β±SE ‐0.001±0, p‐value<0.001), and p‐tau and t‐tau increased over time (respectively 1.37±0.3, p‐value<0.001; 6.58±2.3, p‐value = 0.004). Increases in p‐tau levels were most pronounced in amyloid positive individuals (2.72±0.38, p‐value<0.001) compared to amyloid negative individuals (0.65±0.24, p‐value = 0.007; p‐value interaction<0.001). At baseline, the genetic contribution to biomarker concentrations was lowest for t‐tau (ICC = 0.5, p<0.001) and highest for aβ40 (ICC = 0.79, p<0.001). ICC’s remained similar at repeated measurements (table 1). Annual changes of aβ40 and p‐tau showed significant twin‐pair correlations (resp. ICC’s: 0.58 and 0.42; p‐values <0.01; Figure 1), indicating a genetic contribution to change in these concentrations over time.
Conclusion
In this sample of older cognitively normal monozygotic twins, we found that AD biomarkers became increasingly abnormal over time. Our unique twin design further indicates that these very early pathophysiological changes are under moderate to high genetic influence, which also indicates a role of environmental factors.
Background
The retina has become an area of increasing interest as a potential biomarker for neurodegeneration, as it is easily accessible and patient friendly. Previous studies have shown changes in ...the vasculature of the retina in patients with mild cognitive impairment (MCI) and Alzheimer’s disease (AD) in a cross sectional design. In this study we explore longitudinal retinal microvascular changes in amyloid beta positive (AB +) participants compared with amyloid beta negative (AB‐) participants.
Method
We analysed data from 159 cognitively normal participants (mean age 70.6 SD ± 5.91, 55% females) for changes in four microvascular parameters at baseline and 2 year follow up. (mean time between visits 2.2 years ± 0.23 SD) (Table 1) Amyloid status was obtained from positron emission tomography scans (PET) performed in both 2015 and 2019. The Cirrus 5000 Optical Coherence Tomography Angiography (OCT‐A) was used to obtain baseline and follow up measurements of the optic nerve head (ONH) and macula.
Result
In total, data from 123 AB‐ participants and 37 AB+ participants were included in the analysis. AB (+) participants were further divided into converters (AB‐+,n = 19) and those positive on both PET scans. (AB ++, n = 18) A decrease in vessel density (VD) of the ONH in AB++ participants was demonstrated over time, (p = 0.04) however no change over time was found for VD in the macula inner and outer ring or foveal avascular zone (FAZ). (Figure 2) The VD was found to be consistently higher amongst AB++ participants in the macula inner and outer rings (p<0.05) and the FAZ area was higher in AB‐+ participants. (p<0.05)
Conclusion
This study showed change in VD over time for the ONH region in participants who have been AB + for 4 years or longer. These participants further demonstrated a higher VD in the macula inner and outer rings compared to AB—and AB‐+ participants. Additional longitudinal studies where amyloid status is present for longer periods of time amongst cognitively healthy participants should be undertaken to see if these OCTA microvascular changes could be used as a biomarker in preclinical AD.
Tau accumulation starts during the preclinical phase of Alzheimer's disease and is closely associated with cognitive decline. For preventive purposes, it is important to identify factors associated ...with tau accumulation and spread. Studying genetically identical twin-pairs may give insight into genetic and environmental contributions to tau pathology, as similarities in identical twin-pairs largely result from genetic factors, while differences in identical twin-pairs can largely be attributed to non-shared, environmental factors. This study aimed to examine similarities and dissimilarities in a cohort of genetically identical older twin-pairs in 1) tau load and 2) spatial distribution of tau, measured with 18Fflortaucipir PET. We selected 78 genetically identical twins (39 pairs; average age 73 ± 6), enriched for amyloid-β pathology and APOE ε4 carriership, who underwent dynamic 18Fflortaucipir PET. We extracted binding potentials (BPND) in entorhinal, temporal, widespread neocortical and global regions, and examined within-pair similarities in BPND using age and sex corrected intra-class correlations. Furthermore, we tested whether twin-pairs showed a more similar spatial 18Fflortaucipir distribution compared to non-twin pairs, and whether the participant's co-twin could be identified solely based on the spatial 18Fflortaucipir distribution. Last, we explored whether environmental (e.g. physical activity, obesity) factors could explain observed differences in twins of a pair in 18Fflortaucipir BPND. On visual inspection, Alzheimer's disease-like 18Fflortaucipir PET patterns were observed, and although we mainly identified similarities in twin-pairs, some pairs showed strong dissimilarities. 18Fflortaucipir BPND was correlated in twins in the entorhinal (r = 0.40; p = 0.01), neocortical (r = 0.59; p < 0.01) and global (r = 0.56; p < 0.01) regions, but not in the temporal region (r = 0.20; p = 0.10). The 18Fflortaucipir distribution pattern was significantly more similar between twins of the same pair (mean r = 0.27; SD = 0.09) than between non-twin pairings of participants (mean r = 0.01; SD = 0.10) (p < 0.01), also after correcting for proxies of off-target binding. Based on the spatial 18Fflortaucipir distribution, we could identify with an accuracy of 86% which twins belonged to the same pair. Finally, within-pair differences in 18Fflortaucipir BPND were associated with within-pair differences in depressive symptoms (0.37<β<0.56), physical activity (-0.41<β<-0.42) and social activity (-0.32<β<-0.36) (all p < 0.05). Overall, identical twin-pairs were comparable in tau load and spatial distribution, highlighting the important role of genetic factors in the accumulation and spreading of tau pathology. Considering also the presence of dissimilarities in tau pathology in identical twin-pairs, our results additionally support a role for (potentially modifiable) environmental factors in the onset of Alzheimer's disease pathological processes, which may be of interest for future prevention strategies.
Neuroimaging studies have indicated abnormalities in cortico-striato-thalamo-cortical circuits in obsessive-compulsive disorder patients, but results have not been consistent. Since there are ...significant sex differences in human brain anatomy and obsessive-compulsive symptomatology and its developmental trajectories tend to be distinct in males and females, we investigated whether sex is a potential source of heterogeneity in neuroimaging studies on obsessive-compulsive symptoms. We selected male and female twin pairs who were concordant for scoring either high or low for obsessive-compulsive symptoms and a group of discordant pairs where one twin scored high and the co-twin scored low. The design included 24 opposite-sex twin pairs. Magnetic resonance imaging scans of 31 males scoring high for obsessive-compulsive symptoms, 41 low-scoring males, 58 high-scoring females, and 73 low-scoring females were analyzed and the interaction of obsessive-compulsive symptoms by sex on gray matter volume was assessed using voxel-based morphometry. An obsessive-compulsive symptom by sex interaction was observed for the left middle temporal gyrus, the right middle temporal gyrus, and the right precuneus. These interactions acted to reduce or hide a main effect in our study and illustrate the importance of taking sex into account when investigating the neurobiology of obsessive-compulsive symptoms.
Abstract
The amyloid cascade hypothesis has strongly impacted the Alzheimer's disease research agenda and clinical trial designs over the past decades, but precisely how amyloid-β pathology initiates ...the aggregation of neocortical tau remains unclear. We cannot exclude the possibility of a shared upstream process driving both amyloid-β and tau in an independent manner instead of there being a causal relationship between amyloid-β and tau. Here, we tested the premise that if a causal relationship exists, then exposure should be associated with outcome both at the individual level as well as within identical twin-pairs, who are strongly matched on genetic, demographic and shared environmental background. Specifically, we tested associations between longitudinal amyloid-β PET and cross-sectional tau PET, neurodegeneration and cognitive decline using genetically identical twin-pair difference models, which provide the unique opportunity of ruling out genetic and shared environmental effects as potential confounders in an association.
We included 78 cognitively unimpaired identical twins with 18Fflutemetamol (amyloid-β)-PET, 18Fflortaucipir (tau)-PET, MRI (hippocampal volume) and cognitive data (composite memory). Associations between each modality were tested at the individual level using generalized estimating equation models, and within identical twin-pairs using within-pair difference models. Mediation analyses were performed to test for directionality in the associations as suggested by the amyloid cascade hypothesis.
At the individual level, we observed moderate-to-strong associations between amyloid-β, tau, neurodegeneration and cognition. The within-pair difference models replicated results observed at the individual level with comparably strong effect sizes. Within-pair differences in amyloid-β were strongly associated with within-pair differences in tau (β = 0.68, P < 0.001), and moderately associated with within-pair differences in hippocampal volume (β = −0.37, P = 0.03) and memory functioning (β = −0.57, P < 0.001). Within-pair differences in tau were moderately associated with within-pair differences in hippocampal volume (β = −0.53, P < 0.001) and strongly associated with within-pair differences in memory functioning (β = −0.68, P < 0.001). Mediation analyses showed that of the total twin-difference effect of amyloid-β on memory functioning, the proportion mediated through pathways including tau and hippocampal volume was 69.9%, which was largely attributable to the pathway leading from amyloid-β to tau to memory functioning (proportion mediated, 51.6%).
Our results indicate that associations between amyloid-β, tau, neurodegeneration and cognition are unbiased by (genetic) confounding. Furthermore, effects of amyloid-β on neurodegeneration and cognitive decline were fully mediated by tau. These novel findings in this unique sample of identical twins are compatible with the amyloid cascade hypothesis and thereby provide important new knowledge for clinical trial designs.
Coomans & Tomassen et al. test associations between amyloid-β, tau, neurodegeneration and cognitive decline within pairs of identical twins using within-pair difference models, thereby ruling out potential confounding by genetic and shared environmental factors. The results are compatible with the amyloid cascade hypothesis.
Background
We recently identified three distinct spatial‐temporal trajectories of amyloid deposition through the application of a machine‐learning model (i.e., Subtype and Stage Inference SuStaIn) to ...amyloid positron emission tomography (PET) data. These included Frontal, Parietal, and Occipital subtypes, defined by the earliest regions to show abnormality. The current study aimed to determine whether these subtypes of amyloid accumulation hold value in predicting baseline and longitudinal cognitive functioning in addition to a validated measure of global amyloid burden, i.e. Centiloid (CL) units.
Method
The Frontal, Parietal, and Occipital subtypes were applied to the amyloid‐PET standard uptake value ratios (SUVr) of 2,510 subjects from 3 cohorts (ADNI, EMIF‐AD, OASIS‐3). Of these, 570 subjects with a high subtype probability assignment (>50%), assigned stage ≥ 1, and available cognition were included in the analyses. Subtypes were compared on global cognition and several cognitive domains including memory, attention, executive functioning, language, and visuospatial functioning. To assess whether subtype assignment added to baseline CL in predicting baseline and longitudinal cognition (range follow‐up=0.4‐11 years), linear models (predictors: subtype and CL) and linear mixed models (predictors: subtype*time and CL*time) were performed, respectively. All models were adjusted for baseline age, sex, education, and baseline cognitive stage.
Result
Participant characteristics are shown in Table‐1. The majority was assigned to the Frontal subtype (57%), followed by Occipital (22%) and Parietal (20%). After adjusting for baseline CL, the Occipital subtype showed lower baseline language scores than the Parietal subtype (β=‐0.34, p=.046) (Fig‐1A) and lower baseline attention scores than both Frontal (β=‐0.39, p=.047) and Parietal (β=‐0.73, p=.002) subtypes (Fig‐1B, Table‐2). In addition, the Occipital subtype declined faster over time on global cognition (Fig‐2A) and language (Fig‐2B) as compared to the Frontal (βglobal cognition=‐0.35, pglobal cognition=.007; βlanguage=‐0.10, planguage=.015) and Parietal (βglobal cognition=‐0.50, pglobal cognition=.002; βlanguage=‐0.13, planguage=.015) subtypes.
Conclusion
Our results show the added value of amyloid subtype assignment on top of CL measures on baseline and longitudinal cognition. Specifically, the Occipital subtype was associated with lower baseline performance and showed faster rates of cognitive decline. These findings suggest that subtype assignment based on amyloid PET might improve prognosis and patient stratification in clinical trials.
Background
Grey matter covariance networks become disrupted early in Alzheimer’s disease (AD), when amyloid starts aggregating, and before the onset of irreversible atrophy. However, the precise ...relationship of grey matter network breakdown and the AD pathophysiological process remains unclear. Here, we studied to what extent shared familial (genes and family environment) or environmental factors unique to a twin contribute to these relationships in a sample of older monozygotic twins with intact cognition.
Method
From the EMIF‐AD PreclinAD study we included monozygotic twins who had at least an MRI scan (n=197) and CSF available (n=124). We assessed the upper limit of genetic contribution to grey matter network measures (size, degree, connectivity density, clustering, path length, small‐world measures) with within‐twin pair correlations. Associations between CSF AD markers (Aβ42/40, t‐tau, p‐tau) and other markers related to AD pathophysiology (neurogranin, Aβ38, Aβ40, BACE1) with grey matter network disruptions were assessed with linear mixed models. Twin analyses (cross‐twin cross‐trait, twin difference analyses) were used to assess the contribution of shared familial and/or unique environmental factors to these associations.
Result
Twenty individuals (16%) had abnormal CSF Aβ42/40 levels. Grey matter network measures were highly correlated within twin pairs (r=0.54‐0.97; all p<0.001, Fig.1), suggesting a moderate to strong genetic background. Across the whole sample, more abnormal Aβ42/40 ratios were moderately related to lower connectivity density (β±SE = 0.176±0.09, p=0.055, Fig.2). The strongest associations with grey matter network measures were observed for t‐tau and p‐tau levels (range β=‐0.344‐0.182), followed by Aβ production markers (Aβ38, Aβ40, BACE1) (range β=‐0.202‐0.165). We observed no relationships between neurogranin and grey matter network measures. Cross‐twin cross‐trait analyses showed that levels for t‐tau, p‐tau and Aβ38 in one twin were associated with grey matter network measures in their co‐twin (r=‐0.27 to ‐0.21; p range=0.02 to 0.07, Fig.3). Within‐pair differences in BACE1 were related to within‐pair differences in normalized path length values (r=0.35; p=0.01; Fig.4).
Conclusion
Our results suggest a shared familial background for the relationship of grey matter network disruptions and AD‐related processes as measured in CSF. In addition, unique environmental factors influencing BACE1 may also affect grey matter network disruptions.
Background
Grey matter covariance networks become disrupted early in Alzheimer’s disease (AD), when amyloid starts aggregating, and before the onset of irreversible atrophy. However, the precise ...relationship of grey matter network breakdown and the AD pathophysiological process remains unclear. Here, we studied to what extent shared familial (genes and family environment) or environmental factors unique to a twin contribute to these relationships in a sample of older monozygotic twins with intact cognition.
Method
From the EMIF‐AD PreclinAD study we included monozygotic twins who had at least an MRI scan (n=197) and CSF available (n=124). We assessed the upper limit of genetic contribution to grey matter network measures (size, degree, connectivity density, clustering, path length, small‐world measures) with within‐twin pair correlations. Associations between CSF AD markers (Aβ42/40, t‐tau, p‐tau) and other markers related to AD pathophysiology (neurogranin, Aβ38, Aβ40, BACE1) with grey matter network disruptions were assessed with linear mixed models. Twin analyses (cross‐twin cross‐trait, twin difference analyses) were used to assess the contribution of shared familial and/or unique environmental factors to these associations.
Result
Twenty individuals (16%) had abnormal CSF Aβ42/40 levels. Grey matter network measures were highly correlated within twin pairs (r=0.54‐0.97; all p<0.001, Fig.1), suggesting a moderate to strong genetic background. Across the whole sample, more abnormal Aβ42/40 ratios were moderately related to lower connectivity density (β±SE = 0.176±0.09, p=0.055, Fig.2). The strongest associations with grey matter network measures were observed for t‐tau and p‐tau levels (range β=‐0.344‐0.182), followed by Aβ production markers (Aβ38, Aβ40, BACE1) (range β=‐0.202‐0.165). We observed no relationships between neurogranin and grey matter network measures. Cross‐twin cross‐trait analyses showed that levels for t‐tau, p‐tau and Aβ38 in one twin were associated with grey matter network measures in their co‐twin (r=‐0.27 to ‐0.21; p range=0.02 to 0.07, Fig.3). Within‐pair differences in BACE1 were related to within‐pair differences in normalized path length values (r=0.35; p=0.01; Fig.4).
Conclusion
Our results suggest a shared familial background for the relationship of grey matter network disruptions and AD‐related processes as measured in CSF. In addition, unique environmental factors influencing BACE1 may also affect grey matter network disruptions.
Hearing loss in older adults is associated with increased dementia risk. Underlying mechanisms that connect hearing loss with dementia remain largely unclear.
We studied the association of hearing ...loss and biomarkers for dementia risk in two age groups with normal cognition: 65 participants from the European Medical Information Framework (EMIF)-Alzheimer's disease (AD) 90+ study (oldest-old; mean age 92.7 years, 56.9% female) and 60 participants from the EMIF-AD PreclinAD study (younger-old; mean age 74.4, 43.3% female). Hearing function was tested by the 'digits-in-noise test' and cognition by repeated neuropsychological evaluation. Regressions and generalised estimating equations were used to test the association of hearing function and PET-derived amyloid burden, and linear mixed models were used to test the association of hearing function and cognitive decline. In the oldest-old group, mediation analyses were performed to study whether cognitive decline is mediated through regional brain atrophy.
In oldest-old individuals, hearing function was not associated with amyloid pathology (p=0.7), whereas in the younger-old individuals hearing loss was associated with higher amyloid burden (p=0.0034). In oldest-old individuals, poorer hearing was associated with a steeper decline in memory, global cognition and language, and in the younger-old with steeper decline in language only. The hippocampus and nucleus accumbens mediated the effects of hearing loss on memory and global cognition in the oldest-old individuals.
Hearing loss was associated with amyloid binding in younger-old individuals only, and with cognitive decline in both age groups. These results suggest that mechanisms linking hearing loss with risk for dementia depends on age.
Background
Alzheimer’s Disease (AD) plasma biomarkers have been proposed for amyloid positivity identification and for differentiating between diagnoses. Phosphorylated Tau‐217 (pTau‐217) has ...demonstrated good predictive ability for AD vs healthy controls. Neurofilament Light chain (NfL) differentiates between Frontotemporal Dementia (FTD) and other dementia. These factors have not be extensively tested in real‐world cohorts. The aim of this study was to investigate how pTau‐217 and NfL concentrations differ across clinical diagnoses in an unselected, real‐world memory clinic cohort.
Method
We included 418 consecutive patients from the Amsterdam Dementia Cohort. Patients were split among 12 diagnoses, including SCD, Mild Cognitive Impairment (MCI), probable AD, Dementia with Lewy Bodies (DLB) and FTD (Table 1). pTau‐217 was measured using the novel AlzPath assay, while NfL was measured using the Quanterix Simoa assay. were used to classify patients as high or low for pTau‐217 and NfL levels. The pTau‐217 cutoff (0.58 pg/mL) was the Youden index cutoff derived from the present data, based on amyloid‐positive AD vs amyloid‐negative SCD diagnosis (n = 57), using amyloid status derived from cerebrospinal fluid or Amyloid positron emission tomography for classification. (18.2 pg/mL) was chosen based on the sample’s median age (64 years) and taking the value associated with the 90th percentile of normal NfL levels (NfL interface for physicians (shinyapps.io)).
Result
pTau‐217 levels were highest in patients with AD and Primary Progressive Aphasia (PPA), and lowest in those with Vascular Dementia (VaD) and other neurological diagnosis (Figure 1). NfL levels were highest in patients with VaD and FTD, and lowest in SCD and psychiatric diagnoses. The cutoffs highlighted similar trends, with higher proportions patients with elevated pTau‐217 levels observed in possible and probable AD, MCI, and DLB. Higher proportions of patients with high NfL levels were observed in FTD, PPA, VaD, and possible AD (Figure 2).
Conclusion
pTau‐217 concentrations vary as expected across the different diagnoses, with highest concentrations in AD pathology diagnostic groups. The elevated levels observed in DLB and PPA could be due to underlying AD co‐pathology. Following previous results, NfL concentrations were highest in FTD and lowest in psychiatry and SCD.
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