Publications

Abstract

Importance: The amyloid/tau/neurodegeneration (A/T/N) framework uses cerebrospinal fluid (CSF) levels of total tau (tTau) as a marker of neurodegeneration and CSF levels of phosphorylated tau 181 (pTau181) as a marker of tau tangles. However, it is unclear whether CSF levels of tTau and pTau181 have similar or different trajectories over the course of Alzheimer disease.

Objectives: To examine the rates of change in CSF levels of tTau and pTau181 across the Alzheimer disease course and how the rates of change are associated with brain atrophy as measured by magnetic resonance imaging.

Design, Setting, and Participants: This cohort study was set in tertiary research clinics. Each participant was a member of a pedigree with a known mutation for dominantly inherited Alzheimer disease. Participants were divided into 3 groups on the basis of the presence of a mutation and their Clinical Dementia Rating score. Data analysis was performed in June 2019.

Main Outcomes and Measures: Rates of change of CSF tTau and pTau181 levels and their association with the rate of change of brain volume.

Results: Data from 465 participants (283 mutation carriers and 182 noncarriers) were analyzed. The mean (SD) age of the cohort was 37.8 (11.3) years, and 262 (56.3%) were women. The mean (SD) follow-up duration was 2.7 (1.5) years. Two or more longitudinal CSF and magnetic resonance imaging assessments were available for 160 and 247 participants, respectively. Sixty-five percent of mutation carriers (183) did not have symptoms at baseline (Clinical Dementia Rating score, 0). For mutation carriers, the annual rates of change for CSF tTau and pTau181 became significantly different from 0 approximately 10 years before the estimated year of onset (mean [SE] rates of change, 5.5 [2.8] for tTau [P = .05] and 0.7 [0.3] for pTau 181 [P = .04]) and 15 years before onset (mean [SE] rates of change, 5.4 [3.9] for tTau [P = .17] and 1.1 [0.5] for pTau181 [P = .03]), respectively. The rate of change of pTau181 was positive and increased at the early stages of the disease, showing a positive rate of change starting at 15 estimated years before onset until 5 estimated years before onset (mean [SE], 0.4 [0.3]), followed by a positive but decreasing rate of change at year 0 (mean [SE], 0.1 [0.3]) and then negative rates of change at 5 years (mean [SE], −0.3 [0.4]) and 10 years (mean [SE], −0.6 [0.6]) after symptom onset. In individuals without symptoms (Clinical Dementia Rating score, 0), the rates of change of CSF tTau and pTau181 were negatively associated with brain atrophy (high rates of change in CSF measures were associated with low rates of change in brain volume in asymptomatic stages). After symptom onset (Clinical Dementia Rating score, >0), an increased rate of brain atrophy was not associated with rates of change of levels of both CSF tTau and pTau181.

Conclusions and Relevance: These findings suggest that CSF tTau and pTau181 may have different associations with brain atrophy across the disease time course. These results have implications for understanding the dynamics of disease pathobiology and interpreting neuronal injury biomarker concentrations in response to Alzheimer disease progression and disease-modifying therapies.

Abstract

Introduction: Despite the numerous episodic memory tasks used in neuropsychological assessment, relatively few learning tasks are available, with methods lacking the complexity and sophistication to capture very subtle changes in information acquisition.

Method: We adapted a previously validated associative learning task for use within an online framework, utilizing real-world stimuli, in which learning of audio-visual pairs of Chinese characters and English words occurs over 5 days. The aim of this study was to validate our adaptation to the task, provide estimates of rates of learning in both young and older adults, as well as provide a methodological framework for further adaptation and development of the paradigm. A total of 30 young adults and 30 older adults completed 5 days of the Chinese Characters Learning Task (CCLT).

Results: Results indicated that rates of learning on the adapted task were comparable to the original paradigm and consistent across variations to testing frequency and duration. Our results also indicate the presence of a significant age-related impairment in the rate and accuracy of learning, with young adults aged 18–45 years performing significantly better than older adults aged 65–85 years, that was not due to differences in reaction time.

Conclusions: These findings suggest that daily measurement of cognition via an online platform can detect age-related impairments in learning and is therefore applicable for use within the context of age-related disorders of memory and learning.

Abstract

Introduction: Study outcomes can be measured repeatedly based on the clinical trial protocol before randomization during what is known as the “run-in” period. However, it has not been established how best to incorporate run-in data into the primary analysis of the trial.

Methods: We proposed two-period (run-in period and randomization period) linear mixed effects models to simultaneously model the run-in data and the postrandomization data.

Results: Compared with the traditional models, the two-period linear mixed effects models can increase the power up to 15% and yield similar power for both unequal randomization and equal randomization.

Discussion: Given that analysis of run-in data using the two-period linear mixed effects models allows more participants (unequal randomization) to be on the active treatment with similar power to that of the equal-randomization trials, it may reduce the dropout by assigning more participants to the active treatment and thus improve the efficiency of AD clinical trials.

Abstract

Introduction: Large longitudinal biomarkers database focusing on middle age is needed for Alzheimer’s disease (AD) prevention.

Methods: Data for cerebrospinal fluid analytes, molecular imaging of cerebral fibrillar β-amyloid with positron emission tomography, magnetic resonance imaging–based brain structures, and clinical/cognitive outcomes were harmonized across eight AD biomarker studies. Statistical power was estimated.

Results: The harmonized database included 7779 participants with clinical/cognitive data: 3542 were 18∼65 years at the baseline, 5865 had longitudinal cognitive data for a median of 4.7 years, 2473 participated in the cerebrospinal fluid studies (906 had longitudinal data), 2496 participated in the magnetic resonance imaging studies (1283 had longitudinal data), and 1498 participated in the positron emission tomography amyloid studies (849 had longitudinal data). The database provides adequate power for detecting early biomarker changes, and demonstrates the feasibility of AD prevention trials on middle-aged individuals.

Discussion: The harmonized database is an optimum resource to design AD prevention trials decades before symptomatic onset.

Abstract

Introduction: Vascular factors increase the risk of Alzheimer’s disease (AD). We investigated the associations between such factors, longitudinal AD cerebrospinal fluid biomarkers, and cognition.

Methods: 433 cognitively normal participants were classified into four biomarker groups using their baseline amyloid (A+/−) and tau status (T+/−). 184 participants had undergone serial cerebrospinal fluid collection. Frequencies of risk factors and the Framingham Risk Score (FRS) were compared, and we tested the influence of risk factors on change in biomarker concentrations and cognition.

Results: The absence of obesity, presence of hypertension, and a high FRS were associated with an increase in tau levels, particularly in A+T+ individuals. Risk factors were not associated with amyloid. Depression was associated with higher cognitive scores, whereas high FRS was associated with lower scores and a faster decline.

Discussion: Our results demonstrate that vascular risk factors may enhance neurodegeneration but not amyloid accumulation in preclinical AD.

Abstract

Owing to an early and marked deposition of amyloid-β in the basal ganglia, autosomal dominant Alzheimer’s disease could distinctly involve motor symptoms. Therefore, we aimed to assess the prevalence and characteristics of motor signs in autosomal dominant Alzheimer’s disease. Baseline Unified Parkinson Disease Rating Scale part three scores (UPDRS-III) from 433 participants of the Dominantly Inherited Alzheimer’s Network observational study were analysed. Motor symptoms were scrutinized with respect to associations with mutation carrier status, mutation site within PSEN1, basal ganglia amyloid-β as measured by Pittsburgh compound B PET, estimated years to symptom onset and Clinical Dementia Rating Scale-Sum of Boxes. Motor findings in mutation carriers were compared to patients with sporadic Alzheimer’s disease using data of the National Alzheimer’s Coordination Center. Mutation carriers showed motor findings at a higher frequency (28.4% versus 12.8%; P < 0.001) and severity (mean UPDRS-III scores 2.0 versus 0.4; P < 0.001) compared to non-carriers. Eleven of the 27 UPDRS-III items were statistically more frequently affected in mutation carriers after adjustment for multiple comparisons. Ten of these 11 items were subscale components of bradykinesia. In cognitively asymptomatic mutation carriers, dysdiadochokinesia was more frequent compared to non-carriers (right hand: 3.8% versus 0%; adjusted P = 0.023; left: 4.4% versus 0.6%; adjusted P = 0.031). In this cohort, the positive predictive value for mutation carrier status in cognitively asymptomatic participants (50% a priori risk) of dysdiadochokinesia was 100% for the right and 87.5% for the left side. Mutation carriers with motor findings more frequently were basal ganglia amyloid-β positive (84% versus 63.3%; P = 0.006) and showed more basal ganglia amyloid-β deposition (Pittsburgh compound B-standardized uptake value ratio 2.472 versus 1.928; P = 0.002) than those without. Frequency and severity of motor findings were greater in post-codon 200 PSEN1 mutations (36%; mean UPDRS-III score 3.03) compared to mutations pre-codon 200 PSEN1 (19.3%, P = 0.022; 0.91, P = 0.013). In mutation carriers, motor symptom severity was significantly positively correlated with basal ganglia amyloid-β deposition, Clinical Dementia Rating scores and estimated years to symptom onset. Mutation carriers with a Clinical Dementia Rating global score of 2 exhibited more pronounced motor symptoms than sporadic Alzheimer’s disease patients with the same Clinical Dementia Rating global score (mean UPDRS-III scores 20.71 versus 5.96; P < 0.001). With a prevalence of approximately 30% and increasing severity with progression of dementia, motor symptoms are proven as a clinically relevant finding in autosomal dominant Alzheimer’s disease, in particular in advanced dementia stages, that correlates with deposition of amyloid-β in the basal ganglia. In a very small per cent of cognitively asymptomatic members of families with autosomal dominant Alzheimer’s disease, dysdiadochokinesia may increase the chance of an individual’s status as mutation carrier.

Abstract

Tauopathy is a hallmark pathology of Alzheimer’s disease with a strong relationship with cognitive impairment. As such, understanding tau may be a key to clinical interventions. In vivo tauopathy has been measured using cerebrospinal fluid assays, but these do not provide information about where pathology is in the brain. The introduction of PET ligands that bind to paired helical filaments provides the ability to measure the amount and distribution of tau pathology. The heritability of the age of dementia onset tied to the specific mutations found in autosomal dominant Alzheimer’s disease families provides an elegant model to study the spread of tau across the course of the disease as well as the cross-modal relationship between tau and other biomarkers. To better understand the pathobiology of Alzheimer’s disease we measured levels of tau PET binding in individuals with dominantly inherited Alzheimer’s disease using data from the Dominantly Inherited Alzheimer Network (DIAN). We examined cross-sectional
measures of amyloid-b, tau, glucose metabolism, and grey matter degeneration in 15 cognitively normal mutation non-carriers, 20 asymptomatic carriers, and 15 symptomatic mutation carriers. Linear models examined the association of pathology with group, estimated years to symptom onset, as well as cross-modal relationships. For comparison, tau PET was acquired on 17 older adults
with sporadic, late onset Alzheimer disease. Tau PET binding was starkly elevated in symptomatic DIAN individuals throughout the cortex. The brain areas demonstrating elevated tau PET binding overlapped with those seen in sporadic Alzheimer’s disease, but with a greater cortical involvement and greater levels of binding despite similar cognitive impairment. Tau PET binding was elevated in the temporal lobe, but the most prominent loci of pathology were in the precuneus and lateral parietal regions. Symptomatic mutation carriers also demonstrated elevated tau PET binding in the basal ganglia, consistent with prior work with amyloid-b. The degree of tau tracer binding in symptomatic individuals was correlated to other biomarkers, particularly markers of neurodegeneration. In addition to the differences seen with tau, amyloid-b was increased in both asymptomatic and symptomatic groups relative to non-carriers. Glucose metabolism showed decline primarily in the symptomatic group. MRI indicated structural degeneration in both asymptomatic and symptomatic cohorts. We demonstrate that tau PET binding is elevated in symptomatic individuals with dominantly inherited Alzheimer’s disease. Tau PET uptake was tied to the onset of cognitive dysfunction, and there was a higher amount, and different regional pattern of binding compared to late onset, nonfamilial Alzheimer’s disease.

Abstract

In Alzheimer’s disease (AD), a single-nucleotide polymorphism in the gene encoding brain-derived neurotrophic factor (BDNFVal66Met) is associated with worse impact of primary AD pathology (beta-amyloid, Aβ) on neurodegeneration and cognitive decline, rendering BDNFVal66Met an important modulating factor of cognitive impairment in AD. However, the effect of BDNFVal66Met on functional networks that may underlie cognitive impairment in AD is poorly understood. Using a cross-validation approach, we first explored in subjects with autosomal dominant AD (ADAD) from the Dominantly Inherited Alzheimer Network (DIAN) the effect of BDNFVal66Met on resting-state fMRI assessed functional networks. In
seed-based connectivity analysis of six major large-scale networks, we found a stronger decrease of hippocampus (seed) to medial-frontal connectivity in the BDNFVal66Met carriers compared to BDNFVal homozogytes. BDNFVal66Met was not associated with connectivity in any other networks. Next, we tested whether the finding of more pronounced decrease in hippocampal-medial-frontal connectivity in BDNFVal66Met could be also found in elderly subjects with sporadically occurring Aβ, including a group with subjective cognitive decline (N = 149, FACEHBI study) and a group ranging from preclinical to AD dementia (N = 114, DELCODE study). In both of these independently recruited groups, BDNFVal66Met was associated with a stronger effect of more abnormal Aβ-levels (assessed by biofluid-assay or amyloid-PET) on hippocampal-medialfrontal connectivity decreases, controlled for hippocampus volume and other confounds. Lower hippocampal-medial-frontal connectivity was associated with lower global cognitive performance in the DIAN and DELCODE studies. Together these results suggest that BDNFVal66Met is selectively associated with a higher vulnerability of hippocampus-frontal connectivity to primary AD pathology, resulting in greater AD-related cognitive impairment.

Abstract

Introduction: Four less well-studied but promising “emerging” cerebrospinal fluid (CSF) biomarkers are elevated in late-onset Alzheimer disease (AD): neurogranin, synaptosomal-associated protein-25 (SNAP-25), visinin-like protein 1 (VILIP-1), and chitinase-3-like protein 1 (YKL-40). Methods: CSF neurogranin, SNAP-25, VILIP-1, and YKL-40 were measured in families carrying autosomal-dominant AD mutations. Results: The four emerging CSF biomarkers were significantly elevated in the mutation carriers (n = 235) versus noncarriers (n = 145). CSF SNAP-25, VILIP-1, and YKL-40 were altered very early in the AD time course, approximately 15-19 years before estimated symptom onset. All CSF biomarkers predicted important AD-related outcomes including performance on a cognitive composite, brain amyloid burden as measured by amyloid positron emission tomography, and the estimated years from symptom onset. Discussion: Early abnormalities in CSF tTau, pTau, SNAP-25, VILIP-1, and YKL-40 suggest that synaptic damage, neuronal injury, and neuroinflammation begin shortly after the commencement of brain amyloid accumulation.

Abstract

Introduction: Staging preclinical Alzheimer disease (AD) by the expected years to symptom onset (EYO) in autosomal dominant AD (ADAD) through biomarker correlations is important.

Methods: We estimated the correlation matrix between EYO/cognition and imaging/CSF biomarkers, and searched for the EYO cutoff where a change in the correlations occurred before and after the cutoff among the asymptomatic mutation carriers of ADAD. We then estimated the longitudinal rate of change for biomarkers/cognition within each preclinical stage defined by the EYO.

Results: Based on the change in the correlations, the preclinical ADAD was divided by EYOs −7 and −13 years. Mutation carriers demonstrated a temporal ordering of biomarker/cognition changes across the three preclinical stages.

Discussion: Duration of each preclinical stage can be estimated in ADAD, facilitating better planning of prevention trials with the EYO cutoffs under the recently released FDA guidance. The generalization of these results to sporadic AD warrants further investigation.

Abstract

This study examined differences in neuropsychological test scores between individuals with primary age-related tauopathy (PART) and Alzheimer disease (AD) using cross-sectional data from the National Alzheimer’s Coordinating Center. Linear regression tested for differences in 4 cognitive domains stratified by cognitive status (global Clinical Dementia Rating [CDR]). The sample included 240 participants with no neuritic plaques (NP) (definite PART), 186 with sparse NP (possible PART), and 510 with moderate/frequent NP (AD). Four cognitive domain z-score outcome variables (memory, attention, executive function, and semantic memory/language) were calculated using 12 neuropsychological tests. Definite PART participants had a sparing of semantic memory/language compared to those with AD, with a mean adjusted z-score difference of 0.37 (95% confidence interval [CI]: 0.16–0.58) for those with CDR = 0.5 or 1 and of 0.92 (CI: 0.22–1.63) for those with CDR = 2 or 3. Compared to participants with AD, definite PART participants with CDR = 0.5 or 1 had sparing of memory (adjusted z-score difference: 0.61; CI: 0.39–0.84) and definite PART participants with CDR = 2 or 3 had sparing of attention (adjusted z-score difference: 0.76: CI: 0.09–1.43). Patterns of cognitive impairment differed between definite PART and AD, suggesting significant differences in clinical presentation between individuals from these 2 groups.

Abstract

Introduction: Although some members of families with autosomal dominant Alzheimer’s disease mutations learn their mutation status, most do not. How knowledge of mutation status affects clinical disease progression is unknown. This study quantifies the influence of mutation awareness on clinical symptoms, cognition, and biomarkers.

Methods: Mutation carriers and non-carriers from the Dominantly Inherited Alzheimer Network (DIAN) were stratified based on knowledge of mutation status. Rates of change on standard clinical, cognitive, and neuroimaging outcomes were examined.

Results: Mutation knowledge had no associations with cognitive decline, clinical progression, amyloid deposition, hippocampal volume, or depression in either carriers or non-carriers. Carriers who learned their status mid-study had slightly higher levels of depression and lower cognitive scores.

Discussion: Knowledge of mutation status does not affect rates of change on any measured outcome. Learning of status mid-study may confer short-term changes in cognitive functioning, or changes in cognition may influence the determination of mutation status.

Abstract

Parietal cortex RNA-sequencing (RNA-seq) data were generated from individuals with and without Alzheimer disease (AD; n_control = 13; n_AD = 83) from the Knight Alzheimer Disease Research Center (Knight ADRC). Using this and an independent (Mount Sinai Brain Bank (MSBB)) AD RNA-seq dataset, cortical circular RNA (circRNA) expression was quantified in the context of AD. Significant associations were identified between circRNA expression and AD diagnosis, clinical dementia severity and neuropathological severity. It was demonstrated that most circRNA–AD associations are independent of changes in cognate linear messenger RNA expression or estimated brain cell-type proportions. Evidence was provided for circRNA expression changes occurring early in presymptomatic AD and in autosomal dominant AD. It was also observed that AD-associated circRNAs co-expressed with known AD genes. Finally, potential microRNA-binding sites were identified in AD-associated circRNAs for miRNAs predicted to target AD genes. Together, these results highlight the importance of analyzing non-linear RNAs and support future studies exploring the potential roles of circRNAs in AD pathogenesis.