Longitudinal association between astrocyte function and glucose metabolism in autosomal dominant Alzheimer's disease

PURPOSE

The spatial resolution of ¹⁸F-fluorodeoxyglucose PET does not allow the specific cellular origin of its signal to be determined, but it is commonly accepted that transport and trapping of ¹⁸F-fluorodeoxyglucose reflects neuronal glucose metabolism. The main frameworks for the diagnosis of Alzheimer's disease suggest that hypometabolism measured with ¹⁸F-fluorodeoxyglucose PET is a biomarker of neuronal injury and neurodegeneration. There is preclinical evidence to suggest that astrocytes contribute, at least partially, to the in vivo ¹⁸F-fluorodeoxyglucose PET signal. However, due to a paucity of PET tracers for imaging astrocytic processes, the relationship between astrocyte function and glucose metabolism in human brain is not fully understood. The aim of this study was to investigate the longitudinal association between astrocyte function and glucose metabolism in Alzheimer's disease.

METHODS

The current investigation combined longitudinal PET data from patients with autosomal dominant Alzheimer's disease, including data on astrocyte function (¹¹C-deuterium-L-deprenyl binding) and glucose metabolism (¹⁸F-fluorodeoxyglucose uptake). Research participants included 7 presymptomatic and 4 symptomatic mutation carriers (age 44.9 ± 9.8 years and 58.0 ± 3.7 years, respectively) and 16 noncarriers (age 51.1 ± 14.2 years). Eight carriers and eight noncarriers underwent longitudinal follow-up PET imaging at an average of 2.8 ± 0.2 and 3.0 ± 0.5 years from baseline, respectively.

RESULTS

Longitudinal decline in astrocyte function as measured using ¹¹C-deuterium-L-deprenyl PET was significantly associated with progressive hypometabolism (¹⁸F-fluorodeoxyglucose uptake) in mutation carriers; no significant association was observed in noncarriers.

CONCLUSION

The emerging data shift the accepted wisdom that decreases in cerebral metabolism measured with ¹⁸F-fluorodeoxyglucose solely reflect neuronal injury, and places astrocytes more centrally in the development of Alzheimer's disease.

Biological and Cognitive Markers of Presenilin1 E280A Autosomal Dominant Alzheimer's Disease: A Comprehensive Review of the Colombian Kindred

The study of individuals with autosomal dominant Alzheimer's disease affords one of the best opportunities to characterize the biological and cognitive changes of Alzheimer's disease that occur over the course of the preclinical and symptomatic stages. Unifying the knowledge gained from the past three decades of research in the world's largest single-mutation autosomal dominant Alzheimer's disease kindred - a family in Antioquia, Colombia with the E280A mutation in the Presenilin1 gene - will provide new directions for Alzheimer's research and a framework for generalizing the findings from this cohort to the more common sporadic form of Alzheimer's disease. As this specific mutation is virtually 100% penetrant for the development of the disease by midlife, we use a previously defined median age of onset for mild cognitive impairment for this cohort to examine the trajectory of the biological and cognitive markers of the disease as a function of the carriers' estimated years to clinical onset. Studies from this cohort suggest that structural and functional brain abnormalities - such as cortical thinning and hyperactivation in memory networks - as well as differences in biofluid and in vivo measurements of Alzheimer's-related pathological proteins distinguish Presenilin1 E280A mutation carriers from non-carriers as early as childhood, or approximately three decades before the median age of onset of clinical symptoms. We conclude our review with discussion on future directions for Alzheimer's disease research, with specific emphasis on ways to design studies that compare the generalizability of research in autosomal dominant Alzheimer's disease to the larger sporadic Alzheimer's disease population.

Discovery and validation of autosomal dominant Alzheimer's disease mutations

Background

Alzheimer’s disease (AD) is a neurodegenerative disease that is clinically characterized by progressive cognitive decline. Mutations in amyloid-β precursor protein (APP), presenilin 1 (PSEN1), and presenilin 2 (PSEN2) are the pathogenic cause of autosomal dominant AD (ADAD). However, polymorphisms also exist within these genes.

Methods

In order to distinguish polymorphisms from pathogenic mutations, the DIAN Expanded Registry has implemented an algorithm for determining ADAD pathogenicity using available information from multiple domains, including genetic, bioinformatic, clinical, imaging, and biofluid measures and in vitro analyses.

Results

We propose that PSEN1 M84V, PSEN1 A396T, PSEN2 R284G, and APP T719N are likely pathogenic mutations, whereas PSEN1 c.379_382delXXXXinsG and PSEN2 L238F have uncertain pathogenicity.

Conclusions

In defining a subset of these variants as pathogenic, individuals from these families can now be enrolled in observational and clinical trials. This study outlines a critical approach for translating genetic data into meaningful clinical outcomes.

Visual short-term memory relates to tau and amyloid burdens in preclinical autosomal dominant Alzheimer's disease

Background

Over the past decade, visual short-term memory (VSTM) binding tests have been shown to be one of the most sensitive behavioral indicators of Alzheimer’s disease (AD), especially when they require the binding of multiple features (e.g., color and shape). Recently, it has become possible to directly measure amyloid and tau levels in vivo via positron emission tomography (PET). To this point, these behavioral and neurochemical markers have not been compared in humans with AD or at risk for it.

Methods

In a cross-sectional study, we compared VSTM performance to tau and amyloid concentrations, measured by PET, in individuals certain to develop AD by virtue of their inheritance of the presenilin-1 E280A mutation. These included 21 clinically unimpaired subjects and 7 subjects with early mild cognitive impairment (MCI), as well as 30 family members who were not carriers of the mutation.

Results

We found that VSTM performance correlated strongly with tau in entorhinal cortex and inferior temporal lobe, and also with amyloid when examining asymptomatic carriers only. The condition requiring binding was not preferentially linked to tau—in fact, the non-binding “shape only” condition showed a stronger relationship.

Conclusions

The results confirm VSTM’s status as an early marker of AD pathology and raise interesting questions as to the course of binding-specific versus non-binding aspects of VSTM in early AD.

Reduced penetrance of the PSEN1 H163Y autosomal dominant Alzheimer mutation: a 22-year follow-up study

Background

The range of onset ages within some PSEN1 families is wide, and a few cases of reduced penetrance of PSEN1 mutations have been reported. However, published data on reduced penetrance have been limited to clinical histories, often collected retrospectively and lacking biomarker information. We present a case of reduced penetrance of the PSEN1 H163Y mutation in a carrier prospectively followed for 22 years.

Methods

Two brothers (A and B), both carriers of the H163Y mutation, were followed between 1995 and 2017. They underwent repeated clinical evaluations, neuropsychological assessments, and cerebrospinal fluid analyses, as well as brain imaging examinations with structural magnetic resonance, [¹⁸F]fluorodeoxyglucose positron emission tomography, and [¹¹C]Pittsburgh compound B positron emission tomography.

Results

Brother A was followed between 44 and 64 years of age. Cognitive symptoms due to Alzheimer’s disease set in at the age of 54. Gradual worsening of symptoms resulted in admittance to a nursing home owing to dependence on others for all activities of daily living. He showed a curvilinear decline in cognitive function on neuropsychological tests, and changes on magnetic resonance imaging, positron emission tomography, and biomarkers in the cerebrospinal fluid supported a clinical diagnosis of Alzheimer’s disease. Brother A died at the age of 64 and fulfilled the criteria for definitive Alzheimer’s disease according to neuropathological examination results. Brother B was followed between the ages of 43 and 65 and showed no cognitive deterioration on repeated neuropsychological test occasions. In addition, no biomarker evidence of Alzheimer’s disease pathology was detected, either on imaging examinations or in cerebrospinal fluid.

Conclusions

The average (SD) age of symptom onset for PSEN1 H163Y is 51 ± 7 years according to previous studies. However, we present a case of a biomarker-verified reduction in penetrance in a mutation carrier who was still symptom-free at the age of 65. This suggests that other genetic, epigenetic, and/or environmental factors modify the onset age.

Electronic supplementary material

The online version of this article (10.1186/s13195-018-0374-y) contains supplementary material, which is available to authorized users.

Cerebrospinal fluid Presenilin-1 increases at asymptomatic stage in genetically determined Alzheimer's disease

BACKGROUND

Presenilin-1 (PS1), the active component of the intramembrane γ-secretase complex, can be detected as soluble heteromeric aggregates in cerebrospinal fluid (CSF). The aim of this study was to examine the different soluble PS1 complexes in the lumbar CSF (CSF-PS1) of individuals with Alzheimer's disease (AD), particularly in both symptomatic and asymptomatic genetically determined AD, in order to evaluate their potential as early biomarkers.

METHODS

Western blotting, differential centrifugation and co-immunoprecipitation served to determine and characterize CSF-PS1 complexes. We also monitored the assembly of soluble PS1 into complexes in a cell model, and the participation of Aβ in the dynamics and robustness of the stable PS1 complexes.

RESULTS

There was an age-dependent increase in CSF-PS1 levels in cognitively normal controls, the different complexes represented in similar proportions. The total levels of CSF-PS1, and in particular the proportion of the stable 100-150 kDa complexes, increased in subjects with autosomal dominant AD that carried PSEN1 mutations (eight symptomatic and six asymptomatic ADAD) and in Down syndrome individuals (ten demented and ten non-demented DS), compared with age-matched controls (n = 23), even prior to the appearance of symptoms of dementia. The proportion of stable CSF-PS1 complexes also increased in sporadic AD (n = 13) and mild-cognitive impaired subjects (n = 12), relative to age-matched controls (n = 17). Co-immunoprecipitation demonstrated the association of Aβ oligomers with soluble PS1 complexes, particularly the stable complexes.

CONCLUSIONS

Our data suggest that CSF-PS1 complexes may be useful as an early biomarker for AD, reflecting the pathology at asymptomatic state.

The Latin American Spanish version of the Face-Name Associative Memory Exam is sensitive to cognitive and pathological changes in preclinical autosomal dominant Alzheimer's disease

BACKGROUND

To determine whether performance on the Latin American Spanish version of the Face-Name Associative Memory Exam (LAS-FNAME) can differentiate between cognitively intact carriers of an autosomal dominant Alzheimer's disease mutation (E280A) in Presenilin-1, who are genetically determined to develop early-onset dementia, from matched non-carriers. We also sought to examine whether LAS-FNAME performance is associated with amyloid-β and regional tau burden in mutation carriers.

METHODS

A total of 35 cognitively intact mutation carriers (age range 26-41), 19 symptomatic carriers, and 48 matched non-carriers (age range 27-44) completed a neuropsychological assessment including the LAS-FNAME. A subset of participants (31 carriers [12 symptomatic] and 35 non-carriers) traveled from Colombia to Boston to undergo positron emission tomography (PET) using Pittsburgh compound B to measure mean cortical amyloid-β and flortaucipir for regional tau. ANOVA analyses and Spearman correlations were used to examine group differences and relationships among LAS-FNAME performance and amyloid-β and tau accumulation.

RESULTS

Compared to non-carriers, cognitively intact mutation carriers had lower scores on the LAS-FNAME Total Scores (p = .040). Across all carriers (including symptomatic carriers), higher levels of amyloid-β (r = - .436, p = .018) and regional tau in the entorhinal (r = - .394, p = .031) and inferior temporal cortex (r = - .563, p = .001) were associated with lower LAS-FNAME Total Scores.

CONCLUSIONS

Performance on the LAS-FNAME differentiated between cognitively intact mutation carriers from non-carriers and was associated with greater amyloid and tau burden when examining all carriers. Findings suggest that the LAS-FNAME is sensitive to early clinical and pathological changes and can potentially help track disease progression in Spanish-speaking individuals.

The Value of Pre-Screening in the Alzheimer's Prevention Initiative (API) Autosomal Dominant Alzheimer's Disease Trial

The Alzheimer's Prevention Initiative (API) Autosomal Dominant Alzheimer's Disease (ADAD) trial evaluates the anti-amyloid-β antibody crenezumab in cognitively unimpaired persons who, based on genetic background and age, are at high imminent risk of clinical progression, and provides a powerful test of the amyloid hypothesis. The Neurosciences Group of Antioquia implemented a pre-screening process with the goals of decreasing screen failures and identifying participants most likely to adhere to trial requirements of the API ADAD trial in cognitively unimpaired members of Presenilin1 E280A mutation kindreds. The pre-screening failure rate was 48.2%: the primary reason was expected inability to comply with the protocol, chiefly due to work requirements. More carriers compared to non-carriers, and more males compared to females, failed pre-screening. Carriers with illiteracy or learning/comprehension difficulties failed pre-screening more than non-carriers. With the Colombian API Registry and our prescreening efforts, we randomized 169 30-60 year-old cognitively unimpaired carriers and 83 non-carriers who agreed to participate in the trial for at least 60 months. Our findings suggest multiple benefits of implementing a pre-screening process for enrolling prevention trials in ADAD.

Functional Connectivity of Default Mode Network Subsystems in the Presymptomatic Stage of Autosomal Dominant Alzheimer's Disease

BACKGROUND

The default mode network (DMN) could be divided into subsystems, the functional connectivity of which are different across the Alzheimer's disease (AD) spectrum. However, the functional connectivity patterns within the subsystems are unknown in presymptomatic autosomal dominant AD (ADAD).

OBJECTIVE

To investigate functional connectivity patterns within the subsystems of the DMN in presymptomatic subjects carrying PSEN1, PSEN2, or APP gene mutations.

METHODS

Twenty-six presymptomatic mutation carriers (PMC) and twenty-nine cognitively normal non-carriers as normal controls (NC) from the same families underwent resting state functional MRI and structural MRI. Seed-based analyses were done to obtain functional connectivity of posterior and anterior DMN. For the regions that showed significant connectivity difference between PMC and NC, volumes were extracted and compared between the two groups. Connectivity measures were then correlated with cognitive tests scores.

RESULTS

The posterior DMN showed connectivity decrease in the PMC group as compared with the NC group, which was primarily the connectivity of left precuneus with right precuneus and superior frontal gyrus; the anterior DMN showed significant connectivity decrease in the PMC group, which was the connectivity of medial frontal gyrus with middle frontal gyrus. In the brain regions showing connectivity changes in the PMC group, there was no group difference in volume. A positive correlation was observed between the precuneus connectivity value and Mini-Mental State Examination total score.

CONCLUSION

Functional connectivity within both posterior and anterior DMN were disrupted in the presymptomatic stage of ADAD. Connectivity disruption within the posterior DMN may be useful for early identification of general cognitive decline and a potential imaging biomarker for early diagnosis.

Neurophysiological alterations in mice and humans carrying mutations in APP and PSEN1 genes

BACKGROUND

Studies in animal models of Alzheimer's disease (AD) have provided valuable insights into the molecular and cellular processes underlying neuronal network dysfunction. Whether and how AD-related neurophysiological alterations translate between mice and humans remains however uncertain.

METHODS

We characterized neurophysiological alterations in mice and humans carrying AD mutations in the APP and/or PSEN1 genes, focusing on early pre-symptomatic changes. Longitudinal local field potential recordings were performed in APP/PS1 mice and cross-sectional magnetoencephalography recordings in human APP and/or PSEN1 mutation carriers. All recordings were acquired in the left frontal cortex, parietal cortex, and hippocampus. Spectral power and functional connectivity were analyzed and compared with wildtype control mice and healthy age-matched human subjects.

RESULTS

APP/PS1 mice showed increased absolute power, especially at higher frequencies (beta and gamma) and predominantly between 3 and 6 moa. Relative power showed an overall shift from lower to higher frequencies over almost the entire recording period and across all three brain regions. Human mutation carriers, on the other hand, did not show changes in power except for an increase in relative theta power in the hippocampus. Mouse parietal cortex and hippocampal power spectra showed a characteristic peak at around 8 Hz which was not significantly altered in transgenic mice. Human power spectra showed a characteristic peak at around 9 Hz, the frequency of which was significantly reduced in mutation carriers. Significant alterations in functional connectivity were detected in theta, alpha, beta, and gamma frequency bands, but the exact frequency range and direction of change differed for APP/PS1 mice and human mutation carriers.

CONCLUSIONS

Both mice and humans carrying APP and/or PSEN1 mutations show abnormal neurophysiological activity, but several measures do not translate one-to-one between species. Alterations in absolute and relative power in mice should be interpreted with care and may be due to overexpression of amyloid in combination with the absence of tau pathology and cholinergic degeneration. Future studies should explore whether changes in brain activity in other AD mouse models, for instance, those also including tau pathology, provide better translation to the human AD continuum.

PET evidence of preclinical cerebellar amyloid plaque deposition in autosomal dominant Alzheimer's disease-causing Presenilin-1 E280A mutation carriers

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PET evidence of cerebellar Aβ deposition in unimpaired (CU) PSEN1 E280A kindred.

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Cerebellar Aβ PET SUVR began to distinguish CU carriers from non-carriers at age 34.

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Cortical and cerebellar Aβ PET SUVR are positively associated in CU carriers.

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Cerebellar florbetapir SUVR correlated with lower composite score in CU carriers.

Background

In contrast to sporadic Alzheimer’s disease, autosomal dominant Alzheimer’s disease (ADAD) is associated with greater neuropathological evidence of cerebellar amyloid plaque (Aβ) deposition. In this study, we used positron emission tomography (PET) measurements of fibrillar Aβ burden to characterize the presence and age at onset of cerebellar Aβ deposition in cognitively unimpaired (CU) Presenilin-1 (PSEN1) E280A mutation carriers from the world’s largest extended family with ADAD.

Methods

¹⁸F florbetapir and ¹¹C Pittsburgh compound B (PiB) PET data from two independent studies – API ADAD Colombia Trial (NCT01998841) and Colombia-Boston (COLBOS) longitudinal biomarker study were included. The tracers were selected independently by the respective sponsors prior to the start of each study and used exclusively throughout. Template-based cerebellar Aβ-SUVR (standard-uptake value ratios) using a known-to-be-spared pons reference region (cerebellar SUVR_pons), to a) compare 28–56-year-old CU carriers and non-carriers; b) estimate the age at which cerebellar SUVR_pons began to differ significantly in carrier and non-carrier groups; and c) characterize in carriers associations with age, cortical SUVR_pons, delayed recall memory, and API ADAD composite score.

Results

Florbetapir and PiB cerebellar SUVR_pons were significantly higher in carriers than non-carriers (p < 0.0001). Cerebellar SUVR_pons began to distinguish carriers from non-carriers at age 34, 10 years before the carriers’ estimated age at mild cognitive impairment onset. Florbetapir and PiB cerebellar SUVR_pons in carriers were positively correlated with age (r = 0.44 & 0.69, p < 0.001), cortical SUVR_pons (r = 0.55 & 0.69, p < 0.001), and negatively correlated with delayed recall memory (r = −0.21 & −0.50, p < 0.05, unadjusted for cortical SUVR_pons) and API ADAD composite (r = −0.25, p < 0.01, unadjusted for cortical SUVR_pons in florbetapir API ADAD cohort).

Conclusion

This PET study provides evidence of cerebellar Aβ plaque deposition in CU carriers starting about a decade before the clinical onset of ADAD. Additional studies are needed to clarify the impact of using a cerebellar versus pons reference region on the power to detect and track ADAD changes, even in preclinical stages of this disorder.

Global Cardiovascular Risk Profile and Cerebrovascular Abnormalities in Presymptomatic Individuals with CADASIL or Autosomal Dominant Alzheimer's Disease

BACKGROUND

Cardiovascular risk factors increase the risk of developing dementia, including Alzheimer's disease and vascular dementia.

OBJECTIVE

Studying individuals with autosomal dominant mutations leading to the early onset of dementia, this study examines the effect of the global cardiovascular risk profile on early cognitive and neuroimaging features of Alzheimer's disease and vascular dementia.

METHODS

We studied 85 non-demented and stroke-free individuals, including 20 subjects with Presenilin1 (PSEN1) E280A mutation leading to the early onset of autosomal dominant Alzheimer's disease (ADAD), 20 subjects with NOTCH3 mutations leading to cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) and to the early onset of vascular dementia, and 45 non-affected family members (non-carriers). All subjects underwent clinical and neuropsychological evaluations and an MRI. The global cardiovascular risk profile was estimated using the office-based Framingham Cardiovascular Risk Profile (FCRP) score.

RESULTS

In individuals with CADASIL, a higher FCRP score was associated with a reduced hippocampal volume (B = -0.06, p < 0.05) and an increased severity of cerebral microbleeds (B = 0.13, p < 0.001), lacunes (B = 0.30, p < 0.001), and perivascular space enlargement in the basal ganglia (B = 0.50, p < 0.05). There was no significant association between the FCRP score and neuroimaging measures in ADAD or non-carrier subjects. While the FCRP score was related to performance in executive function in non-carrier subjects (B = 0.06, p < 0.05), it was not significantly associated with cognitive performance in individuals with CADASIL or ADAD.

CONCLUSION

Our results suggest that individuals with CADASIL and other forms of vascular cognitive impairment might particularly benefit from early interventions aimed at controlling cardiovascular risks.

Attitudes about involvement in hypothetical clinical trial protocols in Mexican and Mexican-American at risk for autosomal dominant Alzheimer's disease

BACKGROUND

The enrollment into clinical trials of persons at risk for autosomal dominant Alzheimer's disease (ADAD) in whom the onset of disease can be accurately predicted facilitates the interpretation of outcomes (e.g., biomarkers, treatment efficacy). Attitudes toward involvement in such studies are biased by intrinsic cultural and social characteristics. Our objective was to study how demographic factors such as country of residence, age, sex, schooling, parenthood, and urbanization affect attitudes towards participation in hypothetical clinical trials in Mexican families at risk for ADAD living either in Mexico or in the United States.

METHODS

Participants were 74 members of different families known to harbor an ADAD mutation living in Mexico (n = 50) or in the United States (n = 24). Participants were asked, in a written questionnaire, their interest in participating in four hypothetical clinical trial scenarios of increasing perceived invasiveness. The questionnaire then asked about their willingness should there be a 50% chance of being assigned to a placebo group. The influences of demographic variables on decisions were performed using Wilcoxon rank-sum for continuous variables and Fisher's exact test for categorical variables.

RESULTS

Participants who live in Mexico, who have or plan to have children, who do not attend or do not plan to attend school, and who live in rural areas gave more positive responses regarding their willingness to participate compared to those living in the U.S. The 50% chance of being in a placebo group increased the willingness to participate for family members living in Mexico. The main reason for participation was to help future generations, while the main reasons for refusal were not wanting to undergo genetic testing and consideration of adverse effects.

CONCLUSIONS

We found a higher level of willingness to participate in clinical trials among persons living in rural Mexico and our data suggest that altruism towards future generations is a major motivation, though this was balanced against concerns regarding side effects. Our results emphasize the importance of sharing information and assessing its understanding in potential participants with diverse backgrounds in the nature of ADAD and regarding the design of clinical trials prior to their enrollment in such studies.

Spectrum of γ-Secretase dysfunction as a unifying predictor of ADAD age at onset across PSEN1, PSEN2 and APP causal genes

BACKGROUND

Autosomal Dominant Alzheimer's Disease (ADAD), caused by mutations in Presenilins (PSEN1/2) and Amyloid Precursor Protein (APP) genes, typically manifests with early onset (< 65 years). Age at symptom onset (AAO) is relatively consistent among carriers of the same PSEN1 mutation, but more variable for PSEN2 and APP variants, with these mutations associated with later AAOs than PSEN1. Understanding this clinical variability is crucial for understanding disease mechanisms, developing predictive models and tailored interventions in ADAD, with potential implications for sporadic AD.

METHODS

We performed biochemical assessment of γ-secretase dysfunction on 28 PSEN2 and 19 APP mutations, including disease-associated, unclear and benign variants. This analysis has been valuable in the assessment of PSEN1 variant pathogenicity, disease onset and progression.

RESULTS

Our analysis reveals linear correlations between the molecular composition of Aβ profiles and AAO for both PSEN2 (R2 = 0.52) and APP (R2 = 0.69) mutations. The integration of PSEN1, PSEN2 and APP correlation data shows parallel but shifted lines, suggesting a common pathogenic mechanism with gene-specific shifts in onset. We found overall "delays" in AAOs of 27 years for PSEN2 and 8 years for APP variants, compared to PSEN1. Notably, extremely inactivating PSEN1 variants delayed onset, suggesting that reduced contribution to brain APP processing underlies the later onset of PSEN2 variants.

CONCLUSION

This study supports a unified model of ADAD pathogenesis wherein γ-secretase dysfunction and the resulting shifts in Aβ profiles are central to disease onset across all causal genes. While similar shifts in Aβ occur across causal genes, their impact on AAO varies in the function of their contribution to APP processing in the brain. This biochemical analysis establishes quantitative relationships that enable predictive AAO modelling with implications for clinical practice and genetic research. Our findings also support the development of therapeutic strategies modulating γ-secretase across different genetic ADAD forms and potentially more broadly in AD.

Investigating the Aβ and tau pathology in autosomal dominant Alzheimer's disease: insights from hybrid PET/MRI and network mapping

BACKGROUND

Autosomal dominant Alzheimer's disease (ADAD) offers a distinct framework to study the preclinical phase of Alzheimer's disease (AD), due to its predictable symptom onset and high penetrance of causative mutations. The study aims to examine the spatial distribution and temporal progression of amyloid-beta (Aβ) and tau pathologies, along with mapping the pathology-functional connectivity network, in asymptomatic ADAD mutation carriers using hybrid positron emission tomography/magnetic resonance imaging (PET/MRI).

METHODS

Participants were recruited from the Chinese Familial Alzheimer's Disease Network, comprising 14 asymptomatic ADAD mutation carriers and 20 cognitively normal healthy controls (CN). Aβ deposition was evaluated using 11C-PIB PET, while tau aggregation was assessed via 18F-MK6240 PET imaging. Resting-state functional connectivity (rsFC) was analyzed to investigate relationships between pathological burden and neural network changes. Through qualitative analysis, ADAD carriers with marked 18F-MK6240 uptake in intracranial regions were categorized into Group 2, while others were designated as Group 1.

RESULTS

Asymptomatic ADAD carriers demonstrated a significantly greater Aβ burden across the cortex and striatum compared to CN, although tau PET binding did not differ significantly between the groups. Group 2 participants exhibited elevated 11C-PIB uptake in the neocortex and striatum, and increased 18F-MK6240-PET uptake in the medial temporal and other cortical regions. Compared with Group 1, network mapping of rsFC in Group 2 indicated increased connectivity associated with tau deposition in limbic, posterior cortical, and bilateral temporal regions, overlapping with the default mode network, suggesting potential compensatory mechanisms. Additionally, reduced connectivity in the left medial inferior temporal cortex and fusiform gyrus aligned with findings in sporadic AD cases.

CONCLUSIONS

This study shows the spatiotemporal progression of Aβ and tau pathologies in preclinical ADAD, supporting the hypothesis that Aβ deposition precedes tau pathology. The rsFC alterations observed associate with tau deposition in asymptomatic carriers indicate early network disruptions. Tau network mapping presents a valuable approach for assessing individualized brain connectivity changes in preclinical AD, mitigating single-subject variability and advancing precision assessment in early-stage AD diagnosis.

Progressive cognitive impairment and familial spastic paraparesis due to PRESENILIN 1 mutation: anatomoclinical characterization

INTRODUCTION

Autosomal dominant Alzheimer's disease (ADAD) due to presenilin 1 (PSEN1) mutation can induce atypical neurological symptoms such as movement disorders and epileptic seizures in the context of early-onset progressive cognitive impairment.

METHODS

This study includes the anatomoclinical description of three patients of two generations of the same family with movement disorders and progressive cognitive impairment. All were evaluated by trained neurologists, underwent protocolized neuropsychological evaluation, and were assessed by structural (magnetic resonance) and functional (SPECT, PET-18FDG, or PET-18F-Florbetapir) brain imaging tests. A molecular genetic study was performed for all patients, and post-mortem confirmatory anatomopathological evaluation for one of them.

RESULTS

The three female patients had an age of onset of symptoms of 38-51 years. All developed progressive multidomain cognitive impairment, paraparesis, and dysarthria, two with ophthalmoparesis and one with untriggered epileptic seizures since early stages. Bilateral cortical fronto-parietal atrophy and global cortical hypoperfusion or posterior bilateral hypometabolism were detected. PET-18F-Florbetapir, when performed, was positive for amyloid cortical deposit. The molecular genetic study confirmed the PSEN1 mutation c.869-2 A>G. Postmortem study of one of them confirmed Alzheimer's disease anatomopathological features with classic cotton wool plaques (CWP), including coexistence of amyloid angiopathy and Lewy body co-pathology.

DISCUSSION

The phenotype of ADAD due to PSEN1 mutations is very heterogeneous between and across the same family. Family history assessment should include information not only about cognitive decline, but also about movement disorders and untriggered epileptic seizures. Further studies are needed to identify genetic or epigenetic factors that determine phenotypic diversity in this disease.

Impact of APOE ε4 and ε2 on plasma neurofilament light chain and cognition in autosomal dominant Alzheimer's disease

BACKGROUND

Apolipoprotein E (APOE) genotypes have been suggested to influence cognitive impairment and clinical onset in presenilin-1 (PSEN1) E280A carriers for autosomal dominant Alzheimer's disease (ADAD). Less is known about their impact on the trajectory of biomarker changes. Neurofilament light chain (NfL), a marker of neurodegeneration, begins to accumulate in plasma about 20 years prior to the clinical onset of ADAD. In this study we investigated the impact of APOE ε4 and ε2 variants on age-related plasma NfL increases and cognition in PSEN1 E280A mutation carriers.

METHODS

We analyzed cross-sectional data from PSEN1 E280A mutation carriers and non-carriers recruited from the Alzheimer's Prevention Initiative Registry of ADAD. All participants over 18 years with available APOE genotype, plasma NfL, and neuropsychological evaluation were included in this study. APOE genotypes and plasma NfL concentrations were characterized for each participant. Cubic spline models using a Hamiltonian Markov chain Monte Carlo method were used to characterize the respective impact of at least one APOE ε4 or ε2 allele on age-related log-transformed plasma NfL increases. Linear regression models were estimated to explore the impact of APOE ε4 and ε2 variants and plasma NfL on a composite cognitive test score in the ADAD mutation carrier and non-carrier groups.

RESULTS

Analyses included 788 PSEN1 E280A mutation carriers (169 APOE ε4 + , 114 ε2 +) and 650 mutation non-carriers (165 APOE ε4 + , 80 ε2 +), aged 18-75 years. APOE ε4 allele carriers were distinguished from ε4 non-carriers by greater age-related NfL elevations in the ADAD mutation carrier group, beginning about three years after the mutation carriers' estimated median age at mild cognitive impairment onset. APOE ε2 allele carriers had lower plasma NfL concentrations than ε2 non-carriers in both the ADAD mutation carrier and non-carrier groups, unrelated to age, and an attenuated relationship between higher NfL levels on cognitive decline in the ADAD mutation carrier group.

CONCLUSIONS

APOE ε4 accelerates age-related plasma NfL increases and APOE ε2 attenuates the relationship between higher plasma NfL levels and cognitive decline in ADAD. NfL may be a useful biomarker to assess clinical efficacy of APOE-modifying drugs with the potential to help in the treatment and prevention of ADAD.