PSEN1 Mutations Research Articles

The effect of citalopram treatment on amyloid-β precursor protein processing and oxidative stress in human hNSC-derived neurons

Selective Serotonin Reuptake Inhibitors (SSRIs) may hold therapeutic benefits for people with Alzheimer’s disease (AD). SSRIs may perturb AD progression, or the conversion from MCI to AD, via increased neurogenesis, reduced oxidative stress and/or favourable Amyloid-β Precursor Protein (AβPP) processing. This study used iPSC derived cortical neuronal cells carrying 3 different PSEN1 mutations, to investigate the effect of treatment with the SSRI, Citalopram on AβPP processing and oxidative stress. Control and PSEN1 mutation (L286V, A246E, M146L) iPSC-derived neurons were treated with Citalopram for 45 days. ADAM10 activity, AβPP processing and Aβ generation was measured in addition to cellular redox status. Citalopram treatment reduced the Aβ1-42:40 ratio in control but not in fAD PSEN1 cells. ADAM10 activity was increased with Citalopram treatments in fAD PSEN1 cell lines, which was also seen for sAβPPα secretion. Lower superoxide generation in fAD PSEN1 cells following Citalopram treatment was identified, although there was no effect on end markers of oxidative stress. Treatment with Citalopram appears to have little effect on Aβ generation in fADPSEN1 cells, but our findings suggest that treatment can significantly increase non-amyloidogenic AβPP processing and reduce oxidative stress. These changes may explain why SSRIs appear most effective in the prodromal period of the disease progression, as opposed to reducing established AD pathology. Further investigation of specific pathways conferring the beneficial effects of SSRIs treatment are warranted.

PSEN2 Mutation Spectrum and Novel Functionally Validated Mutations in Alzheimer's Disease: Data from PUMCH Dementia Cohort.

Background:The established causative mutations in the APP, PSEN1, and PSEN2 can explain less than 1%,Alzheimer’s disease (AD) patients. Of the identified variants, the PSEN2 mutations are even less common.Objective:With the genetic study from the dementia cohort of Peking Union Medical College Hospital (PUMCH), we aim to illustrate the PSEN2 mutation spectrum and novel functionally validated mutations in Chinese AD patients.Methods:702 AD participants, aged 30–85, were identified in PUMCH dementia cohort. They all received history inquiry, physical examination, biochemical test, cognitive evaluation, brain CT/MRI, and next-generation DNA sequencing. Functional analysis was achieved by transfection of the HEK293 cells with plasmids harboring the wild-type PSEN2 or candidate mutations.Results:Nine PSEN2 rare variants were found, including two reported (M239T, R62C) and seven novel variants (N141S, I368F, L396I, G117X, I146T, S147N, H220Y). The HEK293 cells transfected with the PSEN2 N141S, M239T, I368F plasmids showed higher Aβ42 and Aβ42/Aβ40 levels relative to the wild-type PSEN2. The PSEN2 L396I, G117X, S147N, H220Y, and R62C did not alter Aβ42, Aβ40 levels, or Aβ42/Aβ40 ratio. 1.9%,(13/702) subjects harbored rare PSEN2 variants. 0.4%,(3/702) subjects carried pathogenic/likely pathogenic PSEN2 mutations. The three subjects with the functionally validated PSEN2 mutations were all familial early-onset AD patients. The common symptoms included amnesia and mental symptom. Additionally, the M239T mutation carrier presented with dressing apraxia, visuospatial agraphia, dyscalculia and visual mislocalization.Conclusion:The PSEN2 N141S, M239T, and I368F are functionally validated mutations.

Novel PSEN1 (P284S) Mutation Causes Alzheimer's Disease with Cerebellar Amyloid β-Protein Deposition.

AD-associated PSEN1 mutations exhibit high clinical heterogeneity. The discovery of these mutations and the analysis of their associations with cases such as EOAD should be critical to understanding AD's pathogenesis. We performed clinical analysis, neuroimaging, target region capture and high-throughput sequencing, and Sanger sequencing in a family of 3 generations. The underlying Alzheimer's pathology was evaluated using biomarker evidence obtained from cerebrospinal fluid (CSF) amyloid testing and 18F-florbetapir (AV-45) PET imaging. Target region capture sequencing revealed a novel heterozygous C to T missense point mutation at the base position 284 (c.850 C>T) located in exon 8 of the PSEN1 gene, resulting in a Prolineto- Serine substitution (P284S) at codon position 850. The mutation was also identified by Sanger sequencing in 2 family members, including proband and her daughter and was absent in the other 4 unaffected family members and 50 control subjects. Cerebrospinal fluid (CSF) amyloid test exhibited biomarker evidence of underlying Alzheimer's pathology. 18F-florbetapir (AV-45) PET imaging indicated extensive cerebral cortex and cerebellar Aβ deposition. We discovered a novel PSEN1 pathogenic mutation, P284S, observed for the first time in a Chinese family with early-onset AD.

Aberrant miR-339-5p/neuronatin signaling causes prodromal neuronal calcium dyshomeostasis in mutant presenilin mice.

Mushroom spine loss and calcium dyshomeostasis are early hallmark events of age-related neurodegeneration, such as Alzheimer’s disease (AD), that are connected with neuronal hyperactivity in early pathology of cognitive brain areas. However, it remains elusive how these key events are triggered at the molecular level for the neuronal abnormality that occurs at the initial stage of disease. Here, we identify downregulated miR-339-5p and its upregulated target protein, neuronatin (Nnat), in cortex neurons from the presenilin-1 M146V knockin (PSEN1-M146V KI) mouse model of familial AD (FAD). Inhibition of miR-339-5p or overexpression of Nnat recapitulates spine loss and endoplasmic reticulum calcium overload in cortical neurons with the PSEN1 mutation. Conversely, either overexpression of miR-339-5p or knockdown of Nnat restores spine morphogenesis and calcium homeostasis. We used fiber photometry recording during the object-cognitive process to further demonstrate that the PSEN1 mutant causes defective habituation in neuronal reaction in the retrosplenial cortex and that this can be rescued by restoring the miR-339-5p/Nnat pathway. Our findings thus reveal crucial roles of the miR-339-5p/Nnat pathway in FAD that may serve as potential diagnostic and therapeutic targets for early pathogenesis.

Circular RNA detection identifies circPSEN1 alterations in brain specific to autosomal dominant Alzheimer's disease

BackgroundAutosomal-dominant Alzheimer's disease (ADAD) is caused by pathogenic mutations in APP, PSEN1, and PSEN2, which usually lead to an early age at onset (< 65). Circular RNAs are a family of non-coding RNAs highly expressed in the nervous system and especially in synapses. We aimed to investigate differences in brain gene expression of linear and circular transcripts from the three ADAD genes in controls, sporadic AD, and ADAD.MethodsWe obtained and sequenced RNA from brain cortex using standard protocols. Linear counts were obtained using the TOPMed pipeline; circular counts, using python package DCC. After stringent quality control (QC), we obtained the counts for PSEN1, PSEN2 and APP genes. Only circPSEN1 passed QC. We used DESeq2 to compare the counts across groups, correcting for biological and technical variables. Finally, we performed in-silico functional analyses using the Circular RNA interactome website and DIANA mirPath software.ResultsOur results show significant differences in gene counts of circPSEN1 in ADAD individuals, when compared to sporadic AD and controls (ADAD = 21, AD = 253, Controls = 23—ADADvsCO: log2FC = 0.794, p = 1.63 × 10–04, ADADvsAD: log2FC = 0.602, p = 8.22 × 10–04). The high gene counts are contributed by two circPSEN1 species (hsa_circ_0008521 and hsa_circ_0003848). No significant differences were observed in linear PSEN1 gene expression between cases and controls, indicating that this finding is specific to the circular forms. In addition, the high circPSEN1 levels do not seem to be specific to PSEN1 mutation carriers; the counts are also elevated in APP and PSEN2 mutation carriers. In-silico functional analyses suggest that circPSEN1 is involved in several pathways such as axon guidance (p = 3.39 × 10–07), hippo signaling pathway (p = 7.38 × 10–07), lysine degradation (p = 2.48 × 10–05) or Wnt signaling pathway (p = 5.58 × 10–04) among other KEGG pathways. Additionally, circPSEN1 counts were able to discriminate ADAD from sporadic AD and controls with an AUC above 0.70.ConclusionsOur findings show the differential expression of circPSEN1 is increased in ADAD. Given the biological function previously ascribed to circular RNAs and the results of our in-silico analyses, we hypothesize that this finding might be related to neuroinflammatory events that lead or that are caused by the accumulation of amyloid-beta.

Mutation analysis of disease causing genes in patients with early onset or familial forms of Alzheimer\u2019s disease and frontotemporal dementia

BackgroundMost dementia disorders have a clear genetic background and a number of disease genes have been identified. Mutations in the tau gene (MAPT) lead to frontotemporal dementia (FTD), whereas mutations in the genes for the amyloid-β precursor protein (APP) and the presenilins (PSEN1, PSEN2) cause early-onset, dominantly inherited forms of Alzheimer’s disease (AD).Even if mutations causing Mendelian forms of these diseases are uncommon, elucidation of the pathogenic effects of such mutations have proven important for understanding the pathogenic processes. Here, we performed a screen to identify novel pathogenic mutations in known disease genes among patients undergoing dementia investigation.ResultsUsing targeted exome sequencing we have screened all coding exons in eleven known dementia genes (PSEN1, PSEN2, APP, MAPT, APOE, GRN, TARDBP, CHMP2B, TREM2, VCP and FUS) in 102 patients with AD, FTD, other dementia diagnoses or mild cognitive impairment.We found three AD patients with two previously identified pathogenic mutations in PSEN1 (Pro264Leu and Met146Val). In this screen, we also identified the recently reported APP mutation in two siblings with AD. This mutation, named the Uppsala mutation, consists of a six amino acid intra-amyloid β deletion.In addition, we found several potentially pathogenic mutations in PSEN2, FUS, MAPT, GRN and APOE. Finally, APOE ε4 was prevalent in this patient group with an allele frequency of 54%.ConclusionsAmong the 102 screened patients, we found two disease causing mutations in PSEN1 and one in APP, as well as several potentially pathogenic mutations in other genes related to neurodegenerative disorders. Apart from giving important information to the clinical investigation, the identification of disease mutations can contribute to an increased understanding of disease mechanisms.

The novel I213S mutation in PSEN1 gene is located in a hotspot codon associated with familial early-onset Alzheimer's disease

Mutations in presenilin 1 gene (PSEN1) are the most common causes of autosomal dominant early-onset Alzheimer's disease (EOAD). We report a novel PSEN1 mutation (I213S) that was discovered in an Italian patient with a family history of early-onset dementia, who developed a slowly progressive cognitive decline since the age of 40 years. Clinical investigations, including neuropsychological assessment, brain MRI and 18-fluorodeoxyglucose PET, as well as cerebrospinal fluid biomarkers, supported the diagnosis of EOAD. Genetic studies identified a novel missense mutation at codon 213 (I213S). Three other mutations at the same codon have been described in association with EOAD. Previous in silico, in vitro and in vivo studies indicated that these mutations affect the functional properties of γ-secretase and are most likely pathogenic. In silico algorithms suggested that even the I213S mutation has similar deleterious effects on PSEN1 structure and function. Overall, these data strongly support a role of hotspot site for the codon 213 of PSEN1, and provide evidence that the genetic variants located on this site cause EOAD.

Variant-dependent heterogeneity in amyloid β burden in autosomal dominant Alzheimer's disease: cross-sectional and longitudinal analyses of an observational study

Insights gained from studying individuals with autosomal dominant Alzheimer's disease have broadly influenced mechanistic hypotheses, biomarker development, and clinical trials in both sporadic and dominantly inherited Alzheimer's disease. Although pathogenic variants causing autosomal dominant Alzheimer's disease are highly penetrant, there is substantial heterogeneity in levels of amyloid β (Aβ) between individuals. We aimed to examine whether this heterogeneity is related to disease progression and to investigate the association with mutation location within PSEN1, PSEN2, or APP. We did cross-sectional and longitudinal analyses of data from the Dominantly Inherited Alzheimer's Network (DIAN) observational study, which enrols individuals from families affected by autosomal dominant Alzheimer's disease. 340 participants in the DIAN study who were aged 18 years or older, had a history of autosomal dominant Alzheimer's disease in their family, and who were enrolled between September, 2008, and June, 2019, were included in our analysis. 206 participants were carriers of pathogenic mutations in PSEN1, PSEN2, or APP, and 134 were non-carriers. 62 unique pathogenic variants were identified in the cohort and were grouped in two ways. First, we sorted variants in PSEN1, PSEN2, or APP by the affected protein domain. Second, we divided PSEN1 variants according to position before or after codon 200. We examined variant-dependent variability in Aβ biomarkers, specifically Pittsburgh-Compound-B PET (PiB-PET) signal, levels of CSF Aβ1-42 (Aβ42), and levels of Aβ1-40 (Aβ40). Cortical and striatal PiB-PET signal showed striking variant-dependent variability using both grouping approaches (p<0·0001), despite similar progression on the clinical dementia rating (p>0·7), and CSF Aβ42 levels (codon-based grouping: p=0·49; domain-based grouping: p=0·095). Longitudinal PiB-PET signal also varied across codon-based groups, mirroring cross-sectional analyses. Autosomal dominant Alzheimer's disease pathogenic variants showed highly differential temporal and regional patterns of PiB-PET signal, despite similar functional progression. These findings suggest that although increased PiB-PET signal is generally seen in autosomal dominant Alzheimer's disease, higher levels of PiB-PET signal at an individual level might not reflect more severe or more advanced disease. Our results have high relevance for ongoing clinical trials in autosomal dominant Alzheimer's disease, including those using Aβ PET as a surrogate marker of disease progression. Additionally, and pertinent to both sporadic and autosomal dominant Alzheimer's disease, our results suggest that CSF and PET measures of Aβ levels are not interchangeable and might reflect different Aβ-driven pathobiological processes. National Institute on Aging, Doris Duke Charitable Foundation, German Center for Neurodegenerative Diseases, Japanese Agency for Medical Research and Development.

Effects of TYROBP Deficiency on Neuroinflammation of a Alzheimer’s Disease Mouse Model Carrying a PSEN1 p.G378E Mutation

ObjectiveTo study the effects of TYRO protein kinase-binding protein (TYROBP) deficiency on learning behavior, glia activation and pro-inflammatory cycokines, andTau phosphorylation of a new Alzheimer’s disease (AD) mouse model carrying a PSEN1 p.G378E mutation. MethodsA new AD mouse model carrying PSEN1 p.G378E mutation was built based on our previously found AD family which might be ascribed to the PSEN1 mutation, and then crossed with TYROBP deficient mice to produce the heterozygous hybrid mice (PSEN1G378E/WT; Tyrobp+/–) and the homozygous hybrid mice (PSEN1G378E/G378E; Tyrobp–/–). Water maze test was used to detect spatial learning and memory ability of mice. After the mice were sacrificed, the hippocampus was excised for further analysis. Immunofluorescence was used to identify the cell that expresses TYROBP and the number of microglia and astrocyte. Western blot was used to detect the expression levels of Tau and phosphorylatedTau (p-Tau), and ELISA to measure the levels of pro-inflammatory cytokines. ResultsOur results showed that TYROBP specifically expressed in the microglia of mouse hippocampus. Absence of TYROBP in PSEN1G378E mutation mouse model prevented the deterioration of learning behavior, decreased the numbers of microglia and astrocytes, and the levels of interleukin-6, interleukin-1β and tumor necrosis factor-α in the hippocampus (all P < 0.05). The ratios of AT8/Tau5, PHF1/Tau5, pT181/Tau5, pT231/ Tau5 and p-ERK/ERK were all higher in homozygous hybrid mice (PSEN1G378E/G378E; Tyrobp–/– mice) compared with PSEN1G378E/G378E mice (all P < 0.05). ConclusionsTYROBP deficiency might play a protective role in the modulation of neuroinflammation of AD. However, the relationship between neuroinflammation processes involving microglia and astrocyte activation, and release of pro-inflammatory cytokines, and p-Tau pathology needs further study.

11C-PiB PET can underestimate brain amyloid-β burden when cotton wool plaques are numerous.

Individuals with familial Alzheimer's disease due to PSEN1 mutations develop high cortical fibrillar amyloid-β load but often have lower cortical 11C-Pittsburgh compound B (PiB) retention than Individuals with sporadic Alzheimer's disease. We hypothesized this is influenced by limited interactions of Pittsburgh compound B with cotton wool plaques, an amyloid-β plaque type common in familial Alzheimer's disease but rare in sporadic Alzheimer's disease. Histological sections of frontal and temporal cortex, caudate nucleus and cerebellum were obtained from 14 cases with sporadic Alzheimer's disease, 12 cases with familial Alzheimer's disease due to PSEN1 mutations, two relatives of a PSEN1 mutation carrier but without genotype information and three non-Alzheimer's disease cases. Sections were processed immunohistochemically using amyloid-β-targeting antibodies and the fluorescent amyloid stains cyano-PiB and X-34. Plaque load was quantified by percentage area analysis. Frozen homogenates from the same brain regions from five sporadic Alzheimer's disease and three familial Alzheimer's disease cases were analysed for 3H-PiB in vitro binding and concentrations of amyloid-β1-40 and amyloid-β1-42. Nine sporadic Alzheimer's disease, three familial Alzheimer's disease and three non-Alzheimer's disease participants had 11C-PiB PET with standardized uptake value ratios calculated using the cerebellum as the reference region. Cotton wool plaques were present in the neocortex of all familial Alzheimer's disease cases and one sporadic Alzheimer's disease case, in the caudate nucleus from four familial Alzheimer's disease cases, but not in the cerebellum. Cotton wool plaques immunolabelled robustly with 4G8 and amyloid-β42 antibodies but weakly with amyloid-β40 and amyloid-βN3pE antibodies and had only background cyano-PiB fluorescence despite labelling with X-34. Relative to amyloid-β plaque load, cyano-Pittsburgh compound B plaque load was similar in sporadic Alzheimer's disease while in familial Alzheimer's disease it was lower in the neocortex and the caudate nucleus. In both regions, insoluble amyloid-β1-42 and amyloid-β1-40 concentrations were similar in familial Alzheimer's disease and sporadic Alzheimer's disease groups, while 3H-PiB binding was lower in the familial Alzheimer's disease than the sporadic Alzheimer's disease group. Higher amyloid-β1-42 concentration associated with higher 3H-PiB binding in sporadic Alzheimer's disease but not familial Alzheimer's disease. 11C-PiB retention correlated with region-matched post-mortem amyloid-β plaque load; however, familial Alzheimer's disease cases with abundant cotton wool plaques had lower 11C-PiB retention than sporadic Alzheimer's disease cases with similar amyloid-β plaque loads. PiB has limited ability to detect amyloid-β aggregates in cotton wool plaques and may underestimate total amyloid-β plaque burden in brain regions with abundant cotton wool plaques.

De novo PSEN1 mutation (Pro436Gln) in a very early onset posterior variant of Alzheimer's disease is associated with pyramidal signs.

Alzheimer's disease (AD) is a common cause of dementia even in cases with very early onset, and implication of monogenic mutations in the PSEN1, PSEN2, and APP genes must be considered. Strong family history is the rule in autosomal dominant AD associated with mutations in these genes but, in rare cases, de novo mutations can occur. Case report of a sporadic AD case with onset in his twenties carrying the Pro436Gln mutation (exon 12, TM-9 region) in PSEN1. Comparison with a previously reported familial case carrying the same mutation. A 32 years old male consulted for a 10 years-long mild but slowly progressive learning difficulties, apathy and anxiety. There was no family history of neurologic diseases and both parents were cognitively preserved in their early 70s. The previous two years he had developed progressive visual disturbances including impaired reading, recognizing numbers, letters and faces and, more recently, he had experienced troubles with manual praxias. There were no specific complaints regarding episodic memory. Neuropsychological assessment showed severe visual agnosia and mild impairments in memory, speech, and executive functions. Neurologic examination showed brief distal myoclonus in upper limbs, markedly enhanced reflexes in lower limbs, as well as mild spasticiy. Blood tests, EEG, spinal MRI, and SSEP were normal. Brain MRI and FDG-PET revealed severe parieto-occipital atrophy/hypoperfusion (fig. 1-4). AD CSF biomarkers showed decrease in Ab1-42 and 1-42/1-40 ratio, increased pTau and normal total tau. Amyloid-PET was positive, identifying a high burden of amyloid plaques in posterior cortex. The pathogenic PSEN1 mutation was found in the patient but was absent in his parents. It is remarkable that the phenotype of the previously reported case with this mutation was almost identical as regards onset in the late twenties and associated pyramidalism. PSEN1 mutations should be considered in patients with sporadic very early onset dementia, as de novo mutations may occur. AD CSF biomarkers offer valuable diagnostic information in such cases. The specific mutation has a very strong impact in the clinical phenotype. Further, this case is another example that PSEN1 mutations affecting proline residues have the earliest age at onset.

Single nuclei RNA-sequencing of GWAS loci variant carriers elucidates cell-types and transcriptional profile alterations associated with Alzheimer disease.

AD has a substantial genetic, molecular and cellular heterogeneity associated with its etiology. We sought to investigate the glial and neuronal pathways affected by AD at a cell specific resolution. To do so, we generated single-nuclei RNA-seq (snRNA-seq) from the parietal cortex of Mendelian mutation carriers, sporadic AD and neuropath-free donors from the Knight-ADRC and Dominantly Inherited Alzheimer Network banks. We generated snRNAseq (10X chemistry v3) for 18 APP and PSEN1 mutation carriers, 36 sporadic AD and 9 controls. After data cleaning and quality control, 336,892 nuclei remained for clustering and downstream analyses (Figure 1). Our analytical approach is based on the identification of cellular states (subclusters), their characterization and identification of genes associated with AD genetic strata. We identified a myriad of transcriptional states for the most representative brain cell-types (Figure 1) with distinguishing expression profiles (mean of 600 genes overexpressed; FDR<0.05). We identified that neuronal and glial cells have specific transcriptional states enriched in nuclei from brains with APP and PSEN1 mutations. For example, an astrocyte cell state specific for these brains shows overexpression of genes identified in the Disease Associated Astrocytes (DAA) expression signature. We also noted a microglia cell state enriched for a subset of TREM2 variant carriers showing overexpression of genes related to cell migration and lamellipodium assembly. We developed a unique molecular atlas to study the pathways dysregulated in AD. Our analyses indicate that in the backdrop of neuropath free and even sporadic AD brains, ADAD samples have distinctive cell states and altered pathways in neurons and glia.

Sex differences in blood-based biomarkers in individuals with autosomal dominant Alzheimer's disease.

Blood-based biomarkers are a promising tool for early detection of Alzheimer's disease (AD). We recently showed that individuals with autosomal-dominant AD due to the E280A mutation in the presenilin1 gene (PSEN1) showed elevated levels of plasma tau phosphorylated at threonine 217 (P-tau217) and neurofilament light chain (NfL), as early as approximately 20 years before clinical onset. We examined sex differences in the age-related trajectory of these blood-based biomarkers, and whether they predicted cognitive performance in PSEN1 mutation carriers. Cross-sectional plasma P-tau217 and NfL concentrations were measured using highly sensitive immunoassays from 622 participants, including 259 cognitively-unimpaired mutation carriers (mean age: 31, range 24-39; %male: 45.6), 106 cognitively-impaired mutation carriers (mean age: 49, range 46-52; %male: 45.3), and 257 age-matched noncarriers (mean age: 34, range 25.5-42; %male: 39.3). Bivariate local polynomial regressions (LOESS) were used to characterize relationships between log-transformed P-tau217 and NfL with age. Linear mixed effect models were used to estimate the fixed slope and intercept of female and male among carriers and noncarriers. Linear regressions examined the association between blood biomarkers and CERAD word list delayed recall in mutation carriers. There were no sex differences in the association between age and plasma P-tau217 among mutation carriers (Slope test, p=.055). Female carriers showed a steeper slope for the association between age and plasma NfL, compared to male carriers (Slope test, p=.001). There was a significant interaction between sex and plasma NfL in predicting verbal memory delayed recall (b=.020, p=.000) in mutation carriers. No sex differences were observed in the association between age and any blood biomarkers among noncarriers (Slope tests: NfL, p=.963; P-tau271, p=.867). Our findings indicate that there are no sex differences in plasma tau pathology in PSEN1 carriers and noncarriers. However, female carriers showed greater levels of plasma NfL along their age-related trajectory, compared to male carriers, suggesting that female carriers may be more susceptible to AD-related neurodegeneration. Further research examining sex/gender differences in blood-based biomarkers and its relation to cognitive trajectories is needed to understand mechanisms of resilience and susceptibility in AD.

Clinical and biological heterogeneity in autosomal dominant Alzheimer's disease

AbstractBackgroundPresenilin‐1 (PSEN1) mutations cause early‐onset autosomal dominant Alzheimer’s disease (ADAD) with nearly 100% penetrance, providing an opportunity to characterize the biological changes associated with preclinical AD. Over 280 different ADAD mutations are currently identified. In Antioquia, Colombia, there are two PSEN1 cohorts, including the world’s largest family with the E280A mutation (consisting of over 1,200 mutation carriers). The clinical phenotype of ADAD is similar to sporadic AD, though some cases have atypical presentations and vary in age at clinical onset and disease course. Here, we reviewed the clinical and biological profiles of these two large families with ADAD.MethodMembers of two large Colombian families with ADAD were included (PSEN1 mutations: 60 E280A carriers, 26 Ile416Thr carriers). All participants underwent a comprehensive clinical and cognitive assessment. Diagnosis of Mild Cognitive Impairment (MCI) and dementia was blind to carrier status. A subset of the E280A (n=35) and Ile416Thr (n=3) mutation carriers also underwent tau and amyloid PET imaging.ResultThe PSEN1 E280A clinical profile is characterized by memory decline beginning in the early 30s, followed by progressive impairment of other cognitive functions. These carriers develop MCI around age 44 and dementia around age 49. There is some phenotypic variability in PSEN1 E280A; some carriers present with epilepsy and ataxia. PET imaging of E280A carriers show a pattern of amyloid and tau pathology similar to that seen in sporadic AD. However, a few cases show distinct patterns of tau accumulation, involving early tau pathology in occipital and parietal regions, absence of tau in medial temporal lobe, and variable cognitive profiles. The Ile416Thr cognitive profile consists of early memory and verbal comprehension impairments. Carriers develop MCI at a mean age of 48 and progress to dementia at age 52. PET imaging of Ile416Thr carriers shows an initial pattern of tau accumulation limited to medial temporal lobe regions.ConclusionThe clinical and biological profiles of ADAD mutations can be heterogenous. Variable cognitive and clinical phenotypes may explain different trajectories of disease progression and response to treatments in clinical trials. Future studies should examine other biological similarities and differences among ADAD mutations.

Multi‐tissue proteomic profiling for genetically defined Alzheimer disease cases

AbstractBackgroundAlzheimer disease (AD) is a complex and heterogeneous disease. Most AD cases present sporadically, while 1‐2% of the cases have autosomal dominant AD (ADAD), carrying mutations in APP, PSEN1, and PSEN2. Among sporadic cases, several rare variants in TREM2, which is involved in immune response, are shown to increase AD risk. Most proteomic studies, while instrumental in identifying novel AD genes and pathways, focus on single tissues and mainly sporadic AD cases. Proteomic signatures for each genetically defined AD case will advance the understanding of the underlying biology of this heterogeneous disease and help us create prediction models for AD risk, onset, and progression.MethodWe generated deep proteomic profiles of brain (n=370), cerebrospinal fluid (CSF; n=699), and plasma (n=486) for sporadic AD, ADAD, and TREM2 risk‐variant carriers, from the Knight‐ADRC and DIAN cohorts. After stringent QC, 1079 proteins in brain, 713 in CSF, and 931 in plasma remained.ResultWe identified 150 proteins with differential levels between sporadic cases and controls, 371 for ADAD, and 134 for TREM2 carriers in at least one tissue (with Bonferroni‐corrected statistical significance). Of these, 36, 74 and 31 were replicated across tissue types for sporadic AD, ADAD, and TREM2 carriers, respectively. Using proteins that replicated across tissues, we created a prediction model for CSF and plasma with an AUC (AUC=0.79‐1.0) similar to (or better than) that of the well‐accepted CSF pTau/Aβ42 ratio. A model using 23 TREM2‐specific plasma proteins was able to discriminate between TREM2 carriers and controls (AUC=0.94) or sporadic AD cases (AUC=0.91) with high sensitivity and selectivity. Our pathway enrichment analysis validated pathways previously implicated in AD (such as APP, APOE, GSK3B, NOTCH3, PPP3R1 and PPP3CA) and identified novel pathways such as a Parkinson’s disease pathway (LRRK2 and α‐synuclein) and innate immune response pathways (MEK1, SHC1, and PDGF‐BB), including cytokine‐mediated signaling and a DAP12‐mediated pathway.ConclusionWith the first multi‐tissue proteomic study of genetically defined AD cases, we have uncovered multiple novel AD biomarker candidates. These findings not only help to elucidate specific pathways implicated in AD but ultimately support the clinical utility of predictive models based on proteomic signatures.

Systematic validation of variants of unknown significance in PSEN1

AbstractBackgroundAlzheimer’s disease (AD) is a neurodegenerative disease that is characterized by extracellular amyloid plaques, intracellular neurofibrillary tangles, and progressive cognitive decline. More than 200 mutations in APP, PSEN1, and PSEN2 cause autosomal dominant AD (ADAD). However, common and rare variants also exist within these genes that may be risk factors, protective factors or non‐pathogenic polymorphisms.MethodTo distinguish polymorphisms from pathogenic mutations, we have developed an algorithm for determining ADAD pathogenicity that weighs genetic, bioinformatic, clinical, imaging, and biofluid measures and in vitro analyses. Here, we evaluated 5 novel variants in PSEN1 identified in densely affected AD families in Latin America: p.Val103_Ser104delinsGly, K395I, P264T, A275T and I414T. PSEN1 p.Val103_Ser104delinsGly, K395I, and P264T produced a significant increase in the extracellular A42/40 ratio.ResultPSEN1 p.Val103_Ser104delinsGly, K395I, and P264T produced a significant increase in the extracellular A42/40 ratio. PSEN1 A275T produced a significant increase in A42 and A40 levels, without altering the ratio. PSEN1 I141I, however, failed to significantly alter A levels in a manner consistent with known pathogenic mutations.ConclusionThus, we propose that PSEN1 I414T is a risk factor or non‐pathogenic polymorphism, and PSEN1 p.Val103_Ser104delinsGly, K395I, and P264T represent novel likely pathogenic mutations.

Exploring the basis of phenotypic diversity in Alzheimer’s disease

AbstractBackgroundAlzheimer’s Disease (AD) is the most common type of dementia and affects more than 50 million people around the world. Although there is no effective treatment for the disease at the moment, early detection is still critical to start an early management plan and try out various interventions. Besides the stereotypical Amnestic Syndrome, many atypical pehnotypes exist which make accurate early diagnosis challenging.MethodExamined Corticobasal Syndrome (CBS), behavioural variant of Frontotemporal Dementia (bvFTD), Posterior Cortical Atrophy (PCA), and Primary Progressive Aphasia (PPA) cases correlating with AD's onset. As such, this literature review investigated the reasons underpinning the selective regional vulnerability leading to clinical diversity in AD.ResultThe majority of AD is sporadic, caused by phosphorylated‐tau aggregates and amyloid‐β depositions in neurons or extracellular space. Increasing age is the dominant risk factor for AD development and the major genetic risk factor for sporadic AD is ApoE4. A small proportion of AD is familial, due to mutations in APP, PSEN1, and PSEN2 genes. The available research findings suggest that diverse clinical presentations correlated with selective degeneration and pathology development in different brain regions. The different regions with originally pathological alternations of each phenotype may help explain the conundrum of polytropic presentations, that primary motor cortex is significantly affected in CBS, basal ganglia in bvFTD, posterior part of the brain in PCA, and temporoparietal areas in PPA. Research indicates that the presence of ApoE4 is significant for the development of all AD phenotypes. In addition, while some studies reported several famial cases, these are not typically thought to be representative and thus more studies are needed.ConclusionThe diverse clinical phenotypes of AD, including AS, CBS, bvFTD, PCA, and PPA, share similar pathogenesis and genetic factors, but each phenotype has divergent patterns of regional distribution of the pathology.

Profiling the metabolic landscape of AD

Metabolic dysfunction, including perturbations in lipid, neurotransmitter, and polyamine metabolism, is an early indicator of cognitive impairment and Alzheimer disease (AD) risk. Further investigation is needed to elucidate the role of genetic heterogeneity in these metabolic disturbances. Here, we interrogate metabolomic signatures in the brains of carriers of pathological mutations in APP, PSEN1, and PSEN2 (Autosomal Dominant AD; ADAD), risk variants in TREM2, non-carrier sporadic AD cases (sAD), individuals with neuropathology but without clinical symptoms (Presymptomatic), and neuropathology-free controls (CO). Metabolomic data from parietal brain tissue of donors to the Knight Alzheimer Disease Research Center and the Dominantly Inherited Alzheimer Network (ADAD, n=25; TREM2, n=21; sAD, n=305; Presymptomatic, n=15; CO, n=27) were generated using the Metabolon global metabolomics platform. A total of 627 metabolites passed our QC process. Differential abundance between AD strata and controls was tested using linear regression corrected for sex, age, and post-mortem interval. Age was excluded from ADAD models. Benjamini-Hochberg multiple testing correction was applied, and pathway analysis was performed with MetaboAnalyst and IMPaLA. In total, we identified 138 metabolites associated with distinct genetic strata (FDR q-value<0.05). For sAD, these included tryptophan betaine (β=-0.55) and N-acetylputrescine (β=-0.14). Metabolites associated with both sAD and ADAD were ergothioneine (β=-0.22 and -0.26 respectively) and serotonin (β=-0.34 and -0.57). TREM2 and ADAD showed association with α-tocopherol (β=-0.12 and -0.12). β-citrylglutamate abundance decreased in sAD, ADAD, and TREM2 versus controls (β=-0.14; -0.22; and -0.29). Pathways identified included glutamate, vitamin, and antioxidant metabolism. A 16-metabolite subset showed consistent direction of effect among the genetic strata with the magnitude of effect of ADAD greater than that of TREM2, in turn greater than sAD. A representation of these (eigengene) is associated with disease duration in sAD (p=5.65x10-03 ), possibly driven by tau accumulation. Hierarchical clustering identified 41 "early stage" sAD individuals with Braak tau stage similar to Presymptomatic (p=0.35), but lower than other sAD individuals (β=-0.56, p=3.09x10-04 ) (Figure 1). Our findings suggest distinct and characteristic metabolic perturbations in ADAD and TREM2 brains. Investigation of these differentially abundant metabolites may lead to greater insight into the metabolic etiology of AD and its impact on clinical presentation.

Genome-wide DNA methylation analysis of autosomal dominantly inherited and sporadic Alzheimer disease brains.

Alzheimer's disease (AD) is a multifactorial neurodegenerative disorder with many biological processes, and molecular changes. The etiology of AD is complex and not specific to a single genetic factor. Epigenetic changes could help explain the missing heritability not capture in GWAS chips and determine functional variants in genome-wide significant loci. Our discovery cohort includes 460 post-mortem brains, 452 AD and 25 controls from Knight-ADRC and Dominantly Inherited Alzheimer Network cohorts. Our study included late-onset (LOAD), but also subjects with Mendelian mutations in APP, PSEN1 and PSEN2 genes (Autosomal Dominant AD; ADAD) and controls. We performed a genome-wide methylation study using DNA from parietal cortex. We used Infinium MethylationEPIC Beadchip arrays (Illumina) to measure DNA methylation. All statistical analyses were adjusted for sex, age at death and neuron proportion. Completion of this project will provide an enhanced characterization of the epigenetic factors associated with AD etiology. This study will enhance the understanding of the molecular dynamics underlying the pathophysiology of AD, and may lead to novel clues for its early detection, prevention and treatment. Epigenetics of AD brains have been previously studied, but this is the first study to analyze both LOAD and ADAD. These results will be presented in the conference.

Multi-omics data integration reveals clinically meaningful molecular profiles of Alzheimer disease.

Alzheimer disease (AD) is a complex polygenic disease in which multiple molecular pathways and biological processes are affected in distinct cell-types of the brain. Increasingly, novel machine learning approaches have been applied in other areas of similarly high complexity (e.g., cancer) to integrate different modalities of "-omics" data and provide novel insights. We sought to apply high-throughput "multi-omics" and machine learning approaches to a large assembly of clinically and neuropathologically well-characterized brain samples to identify genes and biological pathways that may lead to new biomarkers and therapies for AD. We analyzed high-throughput transcriptomics, proteomics, metabolomics and lipidomics profiles of postmortem parietal cortex samples from the Knight ADRC (n=328) and the DIAN (n =21) participants including APP, PSEN1 and PSEN2 autosomal dominant AD mutation carriers (ADAD, n=28), sporadic AD (sAD, n=282), presymptomatic AD (preAD, n=14), and controls with minimal neuropathologic changes (n=25). We applied a Bayesian integrative clustering method (iClusterBayes), designed to identify disease subtypes, to cluster sAD samples on the basis of 2,676 transcripts, 1,067 proteins, 350 metabolites, and 277 lipids. Our analyses identified four different molecular signatures among sAD cases (Figure 1A). Cluster 4 was associated with higher Clinical Dementia Rating (CDR; p=2.2 x10-20) scores and shorter life span (p=5.6 x10-3, HR=1.6; Figure 1B). In particular, alpha-synuclein (SNCA) transcriptomic and proteomic levels were differentially expressed between samples in cluster 4 and others representing sAD, ADAD, preAD, and controls (Figure 1C) suggesting a unique role for SNCA in sAD cases with unfavorable outcomes. The lower levels of soluble SNCA protein in AD samples may be associated with insoluble aggregated SNCA (Lewy bodies) reported in 50-60% of sAD. By applying machine learning approaches to sAD samples with high-throughput multi-omic profiles, we identified novel molecular signatures missed by single layer analyses. These signatures are associated with clinical phenotypes and offer new insights into which molecules may wax or wane as cognition declines. The association of SNCA with poor outcomes suggests that concomitant Lewy bodies may be a negative prognostic factor in sAD. Currently, we are extending these analyses to incorporate replication cohorts and to perform downstream pathway and enrichment analyses.