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Abstract Background Epileptic seizures are an established comorbidity of Alzheimer’s disease (AD). Subclinical epileptiform activity (SEA) as detected by 24-h electroencephalography (EEG) or magneto-encephalography (MEG) has been reported in temporal regions of clinically diagnosed AD patients. Although epileptic activity in AD probably arises in the mesial temporal lobe, electrical activity within this region might not propagate to EEG scalp electrodes and could remain undetected by standard EEG. However, SEA might lead to faster cognitive decline in AD. Aims 1. To estimate the prevalence of SEA and interictal epileptic discharges (IEDs) in a well-defined cohort of participants belonging to the AD continuum, including preclinical AD subjects, as compared with cognitively healthy controls. 2. To evaluate whether long-term-EEG (LTM-EEG), high-density-EEG (hd-EEG) or MEG is superior to detect SEA in AD. 3. To characterise AD patients with SEA based on clinical, neuropsychological and neuroimaging parameters. Methods Subjects (n = 49) belonging to the AD continuum were diagnosed according to the 2011 NIA-AA research criteria, with a high likelihood of underlying AD pathophysiology. Healthy volunteers (n = 24) scored normal on neuropsychological testing and were amyloid negative. None of the participants experienced a seizure before. Subjects underwent LTM-EEG and/or 50-min MEG and/or 50-min hd-EEG to detect IEDs. Results We found an increased prevalence of SEA in AD subjects (31%) as compared to controls (8%) (p = 0.041; Fisher’s exact test), with increasing prevalence over the disease course (50% in dementia, 27% in MCI and 25% in preclinical AD). Although MEG (25%) did not withhold a higher prevalence of SEA in AD as compared to LTM-EEG (19%) and hd-EEG (19%), MEG was significantly superior to detect spikes per 50 min (p = 0.002; Kruskall–Wallis test). AD patients with SEA scored worse on the RBANS visuospatial and attention subset (p = 0.009 and p = 0.05, respectively; Mann–Whitney U test) and had higher left frontal, (left) temporal and (left and right) entorhinal cortex volumes than those without. Conclusion We confirmed that SEA is increased in the AD continuum as compared to controls, with increasing prevalence with AD disease stage. In AD patients, SEA is associated with more severe visuospatial and attention deficits and with increased left frontal, (left) temporal and entorhinal cortex volumes. Trial registration Clinicaltrials.gov, NCT04131491. 12/02/2020.

Abstract Background Genome-wide association studies (GWAS) of Alzheimer’s disease (AD) have identified several risk loci, but many remain unknown. Cerebrospinal fluid (CSF) biomarkers may aid in gene discovery and we previously demonstrated that six CSF biomarkers (β-amyloid, total/phosphorylated tau, NfL, YKL-40, and neurogranin) cluster into five principal components (PC), each representing statistically independent biological processes. Here, we aimed to (1) identify common genetic variants associated with these CSF profiles, (2) assess the role of associated variants in AD pathophysiology, and (3) explore potential sex differences. Methods We performed GWAS for each of the five biomarker PCs in two multi-center studies (EMIF-AD and ADNI). In total, 973 participants (n = 205 controls, n = 546 mild cognitive impairment, n = 222 AD) were analyzed for 7,433,949 common SNPs and 19,511 protein-coding genes. Structural equation models tested whether biomarker PCs mediate genetic risk effects on AD, and stratified and interaction models probed for sex-specific effects. Results Five loci showed genome-wide significant association with CSF profiles, two were novel (rs145791381 [inflammation] and GRIN2D [synaptic functioning]) and three were previously described (APOE, TMEM106B, and CHI3L1). Follow-up analyses of the two novel signals in independent datasets only supported the GRIN2D locus, which contains several functionally interesting candidate genes. Mediation tests indicated that variants in APOE are associated with AD status via processes related to amyloid and tau pathology, while markers in TMEM106B and CHI3L1 are associated with AD only via neuronal injury/inflammation. Additionally, seven loci showed sex-specific associations with AD biomarkers. Conclusions These results suggest that pathway and sex-specific analyses can improve our understanding of AD genetics and may contribute to precision medicine.

Abstract Background Alzheimer’s disease (AD) is the leading cause of dementia, clinically characterized by memory deficits and progressive cognitive decline. Despite decades of research effective therapies are lacking, and a large part of the genetic heritability remains unidentified. ABCA7 and ABCA1, members of the ATP-binding cassette subfamily A (ABCA), were identified as AD risk genes in genome-wide association studies. Nevertheless, genetic and/or functional studies propose a link between AD and two other members of the ABCA subclass, i.e., ABCA2 and ABCA5. Main body Changes in expression or dysfunction of these transporters were found to increase amyloid β levels. This might be related to the common role of ABCA transporters in cellular cholesterol homeostasis, for which a prominent role in AD development has been suggested. In this review, we provide a comprehensive overview and discussion on the contribution of the ABCA subfamily to the etiopathogenesis of AD. Conclusions A better understanding of the function and identification of disease-associated genetic variants in ABCA transporters can contribute to the development of novel therapeutic strategies for AD.

Abstract The adenosine triphosphate–binding cassette subfamily A member 7 gene (ABCA7) is associated with Alzheimer’s disease (AD) in large genome-wide association studies. Targeted sequencing of ABCA7 suggests a role for rare premature termination codon (PTC) mutations in AD, with haploinsufficiency through nonsense-mediated mRNA decay as a plausible pathogenic mechanism. Since other classes of rare variants in ABCA7 are poorly understood, we investigated the contribution and pathogenicity of rare missense, indel and splice variants in ABCA7 in Belgian AD patient and control cohorts. We identified 8.36% rare variants in the patient cohort versus 6.05% in the control cohort. For 10 missense mutations identified in the Belgian cohort we analyzed the pathogenetic effect on protein localization in vitro using immunocytochemistry. Our results demonstrate that rare ABCA7 missense mutations can contribute to AD by inducing protein mislocalization, resulting in a lack of functional protein at the plasma membrane. In one pedigree, a mislocalization-inducing missense mutation in ABCA7 (p.G1820S) co-segregated with AD in an autosomal dominant inheritance pattern. Brain autopsy of six patient missense mutation carriers showed typical AD neuropathological characteristics including cerebral amyloid angiopathy type 1. Also, among the rare ABCA7 missense mutations, we observed mutations that affect amino acid residues that are conserved in ABCA1 and ABCA4, of which some correspond to established ABCA1 or ABCA4 disease-causing mutations involved in Tangier or Stargardt disease.

Known genetic loci account for only a fraction of the genetic contribution to Alzheimer’s disease. Here, the authors have performed a large genome-wide meta-analysis comprising 409,435 individuals to discover 6 new loci and demonstrate the efficacy of an Alzheimer’s disease polygenic risk score.

Abstract Knowledge of the molecular etiology of neurodegenerative brain diseases (NBD) has substantially increased over the past three decades. Early genetic studies of NBD families identified rare and highly penetrant deleterious mutations in causal genes that segregate with disease. Large genome-wide association studies uncovered common genetic variants that influenced disease risk. Major developments in next-generation sequencing (NGS) technologies accelerated gene discoveries at an unprecedented rate and revealed novel pathways underlying NBD pathogenesis. NGS technology exposed large numbers of rare genetic variants of uncertain significance (VUS) in coding regions, highlighting the genetic complexity of NBD. Since experimental studies of these coding rare VUS are largely lacking, the potential contributions of VUS to NBD etiology remain unknown. In this review, we summarize novel findings in NBD genetic etiology driven by NGS and the impact of rare VUS on NBD etiology. We consider different mechanisms by which rare VUS can act and influence NBD pathophysiology and discuss why a better understanding of rare VUS is instrumental for deriving novel insights into the molecular complexity and heterogeneity of NBD. New knowledge might open avenues for effective personalized therapies.

Abstract Dementia with Lewy bodies (DLB) and Parkinson’s disease (PD) are clinically, pathologically and etiologically disorders embedded in the Lewy body disease (LBD) continuum, characterized by neuronal α-synuclein pathology. Rare homozygous and compound heterozygous premature termination codon (PTC) mutations in the Vacuolar Protein Sorting 13 homolog C gene (VPS13C) are associated with early-onset recessive PD. We observed in two siblings with early-onset age (

Abstract Background Alzheimer’s disease (AD) mutations in amyloid precursor protein (APP) and presenilins (PSENs) could potentially lead to the production of longer amyloidogenic Aβ peptides. Amongst these, Aβ1–43 is more prone to aggregation and has higher toxic properties than the long-known Aβ1–42. However, a direct effect on Aβ1–43 in biomaterials of individuals carrying genetic mutations in the known AD genes is yet to be determined. Methods N = 1431 AD patients (n = 280 early-onset (EO) and n = 1151 late-onset (LO) AD) and 809 control individuals were genetically screened for APP and PSENs. For the first time, Aβ1–43 levels were analysed in cerebrospinal fluid (CSF) of 38 individuals carrying pathogenic or unclear rare mutations or the common PSEN1 p.E318G variant and compared with Aβ1–42 and Aβ1–40 CSF levels. The soluble sAPPα and sAPPβ species were also measured for the first time in mutation carriers. Results A known pathogenic mutation was identified in 5.7% of EOAD patients (4.6% PSEN1, 1.07% APP) and in 0.3% of LOAD patients. Furthermore, 12 known variants with unclear pathogenicity and 11 novel were identified. Pathogenic and unclear mutation carriers showed a significant reduction in CSF Aβ1–43 levels compared to controls (p = 0.037;

Abstract Parkinson’s disease (PD) and atypical parkinsonian syndromes (APS) are symptomatically characterized by parkinsonism, with the latter presenting additionally a distinctive range of atypical features. Although the majority of patients with PD and APS appear to be sporadic, genetic causes of several rare monogenic disease variants were identified. The knowledge acquired from these genetic factors indicated that defects in vesicular transport pathways, endo-lysosomal dysfunction, impaired autophagy-lysosomal protein and organelle degradation pathways, α-synuclein aggregation and mitochondrial dysfunction play key roles in PD pathogenesis. Moreover, membrane dynamics are increasingly recognized as a key player in the disease pathogenesis due lipid homeostasis alterations, associated with lysosomal dysfunction, caused by mutations in several PD and APS genes. The importance of lysosomal dysfunction and lipid homeostasis is strengthened by both genetic discoveries and clinical epidemiology of the association between parkinsonism and lysosomal storage disorders (LSDs), caused by the disruption of lysosomal biogenesis or function. A synergistic coordination between vesicular trafficking, lysosomal and mitochondria defects exist whereby mutations in PD and APS genes encoding proteins primarily involved one PD pathway are frequently associated with defects in other PD pathways as a secondary effect. Moreover, accumulating clinical and genetic observations suggest more complex inheritance patters of familial PD exist, including oligogenic and polygenic inheritance of genes in the same or interconnected PD pathways, further strengthening their synergistic connection. Here, we provide a comprehensive overview of PD and APS genes with functions in vesicular transport, lysosomal and mitochondrial pathways, and highlight functional and genetic evidence of the synergistic connection between these PD associated pathways.

Alzheimer’s disease (AD) is the most frequent neurodegenerative disease with an increasing prevalence in industrialized, aging populations. AD susceptibility has an established genetic basis which has been the focus of a large number of genome-wide association studies (GWAS) published over the last decade. Most of these GWAS used dichotomized clinical diagnostic status, i.e., case vs. control classification, as outcome phenotypes, without the use of biomarkers. An alternative and potentially more powerful study design is afforded by using quantitative AD-related phenotypes as GWAS outcome traits, an analysis paradigm that we followed in this work. Specifically, we utilized genotype and phenotype data from n = 931 individuals collected under the auspices of the European Medical Information Framework for Alzheimer’s Disease Multimodal Biomarker Discovery (EMIF-AD MBD) study to perform a total of 19 separate GWAS analyses. As outcomes we used five magnetic resonance imaging (MRI) traits and seven cognitive performance traits. For the latter, longitudinal data from at least two timepoints were available in addition to cross-sectional assessments at baseline. Our GWAS analyses revealed several genome-wide significant associations for the neuropsychological performance measures, in particular those assayed longitudinally. Among the most noteworthy signals were associations in or near EHBP1 (EH domain binding protein 1; on chromosome 2p15) and CEP112 (centrosomal protein 112; 17q24.1) with delayed recall as well as SMOC2 (SPARC related modular calcium binding 2; 6p27) with immediate recall in a memory performance test. On the X chromosome, which is often excluded in other GWAS, we identified a genome-wide significant signal near IL1RAPL1 (interleukin 1 receptor accessory protein like 1; Xp21.3). While polygenic score (PGS) analyses showed the expected strong associations with SNPs highlighted in relevant previous GWAS on hippocampal volume and cognitive function, they did not show noteworthy associations with recent AD risk GWAS findings. In summary, our study highlights the power of using quantitative endophenotypes as outcome traits in AD-related GWAS analyses and nominates several new loci not previously implicated in cognitive decline.

Abstract Introduction The bridging integrator 1(BIN1) rs744373 risk polymorphism has been linked to increased [18F]AV1451 signal in non‐demented older adults (ie., mild cognitive impairment [MCI] plus cognitively normal [CN] individuals). However, the association of BIN1 with in vivo tau, amyloid beta (Aβ) burden, and cognitive impairment in the asymptomatic stage of Alzheimer's disease (AD) remains unknown. Methods The BIN1 effect on [18F]AV1451 binding was evaluated in 59 cognitively normal (CN) participants (39% apolipoprotein E [APOE ε4]) from the Flemish Prevent AD Cohort KU Leuven (F‐PACK), as well as in 66 Alzheimer's Disease Neuroimaging Initiative (ADNI) CN participants, using voxelwise and regional statistics. For comparison, 52 MCI patients from ADNI were also studied. Results Forty‐four percent of F‐PACK participants were BIN1 rs744373 risk‐allele carriers, 21% showed high amyloid burden, and 8% had elevated [18F]AV1451 binding. In ADNI, 53% and 50% of CNs and MCIs, respectively, carried the BIN1 rs744373 risk‐allele. Amyloid positivity was present in 23% of CNs and 51% of MCIs, whereas 2% of CNs and 35% of MCIs showed elevated [18F]AV1451 binding. There was no significant effect of BIN1 on voxelwise or regional [18F]AV1451 in F‐PACK or ADNI CNs, or in the pooled CN sample. No significant association between BIN1 and [18F]AV1451 was obtained in ADNI MCI patients. However, in the MCI group, numerically higher [18F]AV1451 binding was observed in the BIN1 risk‐allele group compared to the BIN1 normal group in regions corresponding to more progressed tau pathology. Discussion We could not confirm the association between BIN1 rs744373 risk‐allele and elevated [18F]AV1451 signal in CN older adults or MCI. Numerically higher [18F]AV1451 binding was observed, however, in the MCI BIN1 risk‐allele group, indicating that the previously reported positive effect may be confounded by group. Therefore, when studying how the BIN1 risk polymorphism influences AD pathogenesis, a distinction should be made between asymptomatic, MCI, and dementia stages of AD.

Abstract Technological limitations have hindered the large-scale genetic investigation of tandem repeats in disease. We show that long-read sequencing with a single Oxford Nanopore Technologies PromethION flow cell per individual achieves 30× human genome coverage and enables accurate assessment of tandem repeats including the 10,000-bp Alzheimer’s disease-associated ABCA7 VNTR. The Guppy “flip-flop” base caller and tandem-genotypes tandem repeat caller are efficient for large-scale tandem repeat assessment, but base calling and alignment challenges persist. We present NanoSatellite, which analyzes tandem repeats directly on electric current data and improves calling of GC-rich tandem repeats, expanded alleles, and motif interruptions.

Abstract Background Charcot-Marie-Tooth (CMT) disease is the most common inherited neuromuscular disorder characterized by wide clinical, genetic and pathomechanistic heterogeneity. Recently, the gene encoding peripheral myelin protein 2 (PMP2) was identified as a novel cause for CMT neuropathy with three mutations that structurally cluster together (p.Ile43Asn, p.Thr51Pro, p.Ile52Thr) reported in five families. Results Using whole exome sequencing and cohort screening we identified two novel missense substitutions in PMP2 in Bulgarian (p.Met114Thr, c.341C > T) and German (p.Val115Ala, c.344 T > C) families. The mutations affect adjacent and highly conserved amino acid residues outside of the known mutation-rich region in the protein. Crystal structure analysis positions the affected residues within a cluster of highly conserved fatty acid coordinating residues implying their functional significance. The clinical, electrophysiological and imaging features in both families were consistent with a childhood onset polyneuropathy with variable patterns of demyelination, slow to very slow progression, and most severe involvement of the peroneal muscles. Conclusions We expand the genetic and phenotypic spectrum of PMP2-related peripheral neuropathy. Our findings reveal a second mutational cluster in the protein.

Neurodegenerative disorders like frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) are pathologically characterized by toxic protein deposition in the cytoplasm or nucleus of affected neurons and glial cells. Many of these aggregated proteins belong to the class of RNA binding proteins (RBP), and, when mutated, account for a significant subset of familial ALS and FTD cases. Here, we present first genetic evidence for the RBP gene RBM45 in the FTD-ALS spectrum. RBM45 shows many parallels with other FTD-ALS associated genes and proteins. Multiple lines of evidence have demonstrated that RBM45 is an RBP that, upon mutation, redistributes to the cytoplasm where it co-aggregates with other RBPs into cytoplasmic stress granules (SG), evolving to persistent toxic TDP-43 immunoreactive inclusions. Exome sequencing in two affected first cousins of a heavily affected early-onset dementia family listed a number of candidate genes. The gene with the highest pathogenicity score was the RBP gene RBM45. In the family, the RBM45 Arg183* nonsense mutation co-segregated in both affected cousins. Validation in an unrelated patient (n = 548) / control (n = 734) cohort identified an additional RBM45 Arg183* carrier with bvFTD on a shared 4 Mb haplotype. Transcript and protein expression analysis demonstrated loss of nuclear RBM45, suggestive of a loss-of-function disease mechanism. Further, two more ultra-rare VUS, one in the nuclear localization signal (NLS, p.Lys456Arg) in an ALS patient and one in the intrinsically disordered homo-oligomer assembly (HOA) domain (p.Arg314Gln) in a patient with nfvPPA were detected.Our findings suggest that the pathomechanisms linking RBM45 with FTD and ALS may be related to its loss of nuclear function as a mediator of mRNA splicing, cytoplasmic retention or its inability to form homo-oligomers, leading to aggregate formation with trapping of other RBPs including TDP-43, which may accumulate into persisted TDP-43 inclusions.

Abstract Early‐onset Alzheimer's disease (EOAD) is generally known as a dominant disease due to highly penetrant pathogenic mutations in the amyloid precursor protein, presenilin 1 and 2. However, they explain only a fraction of EOAD patients (5% to 10%). Furthermore, only 10% to 15% of EOAD families present with clear autosomal dominant inheritance. Studies showed that only 35% to 60% of EOAD patients have at least one affected first‐degree relative. Parent–offspring concordance in EOAD was estimated to be

Background: Sporadic Creutzfeldt–Jakob disease (sCJD) is the most common type of a group of transmissible spongiform encephalopathies (prion diseases). The etiology of the sporadic form of CJD is still unclear. sCJD can occur in combination with other neurodegenerative diseases, which further complicates the diagnosis. Alzheimer's disease (AD), e.g., is often seen in conjunction with sCJD.Method: In this study, we performed a systematic analysis of 15 genes related to the most important neurodegenerative diseases - AD, frontotemporal dementia, amyotrophic lateral sclerosis, prion disease, and Parkinson's disease - in a cohort of sCJD and sCJD in comorbidity with AD and primary age-related proteinopathy (PART). A total of 30 neuropathologically verified cases of sCJD with and without additional proteinopathies were included in the study. In addition, we compared microtubule-associated protein tau (MAPT) haplotypes between sCJD patients and patients with sCJD and PART or sCJD and AD. Then we studied the interaction between the Apolipoprotein E gene (APOE) and PRNP in sCJD patients.Results: We did not find any causal mutations in the neurodegenerative disease genes. We did detect a p.E318G missense variant of uncertain significance (VUS) in PSEN1 in three patients. In PRNP, we also found a previously described non-pathogenic insertion (p.P84_Q91Q).Conclusion: Our pilot study failed to find any critical differences between pure sCJD and sCJD in conjunction with other comorbid neurodegenerative diseases. Further investigations are needed to better understand this phenomenon.

BackgroundThe ε4 allele of apolipoprotein E (APOE) gene and increasing age are two of the most important known risk factors for developing Alzheimer disease (AD). The diagnosis of AD based on clinical symptoms alone is known to have poor specificity; recently developed diagnostic criteria based on biomarkers that reflect underlying AD neuropathology allow better assessment of the strength of the associations of risk factors with AD. Accordingly, we examined the global and age-specific association between APOE genotype and AD by using the A/T/N classification, relying on the cerebrospinal fluid (CSF) levels of β-amyloid peptide (A, β-amyloid deposition), phosphorylated tau (T, pathologic tau), and total tau (N, neurodegeneration) to identify patients with AD.Methods and findingsThis case-control study included 1,593 white AD cases (55.4% women; mean age 72.8 [range = 44-96] years) with abnormal values of CSF biomarkers from nine European memory clinics and the American Alzheimer's Disease Neuroimaging Initiative (ADNI) study. A total of 11,723 dementia-free controls (47.1% women; mean age 65.6 [range = 44-94] years) were drawn from two longitudinal cohort studies (Whitehall II and Three-City), in which incident cases of dementia over the follow-up were excluded from the control population. Odds ratio (OR) and population attributable fraction (PAF) for AD associated with APOE genotypes were determined, overall and by 5-year age categories. In total, 63.4% of patients with AD and 22.6% of population controls carried at least one APOE ε4 allele. Compared with non-ε4 carriers, heterozygous ε4 carriers had a 4.6 (95% confidence interval 4.1-5.2; p < 0.001) and ε4/ε4 homozygotes a 25.4 (20.4-31.2; p < 0.001) higher OR of AD in unadjusted analysis. This association was modified by age (p for interaction < 0.001). The PAF associated with carrying at least one ε4 allele was greatest in the 65-70 age group (69.7%) and weaker before 55 years (14.2%) and after 85 years (22.6%). The protective effect of APOE ε2 allele for AD was unaffected by age. Main study limitations are that analyses were based on white individuals and AD cases were drawn from memory centers, which may not be representative of the general population of patients with AD.ConclusionsIn this study, we found that AD diagnosis based on biomarkers was associated with APOE ε4 carrier status, with a higher OR than previously reported from studies based on only clinical AD criteria. This association differs according to age, with the strongest effect at 65-70 years. These findings highlight the need for early interventions for dementia prevention to mitigate the effect of APOE ε4 at the population level.

Recently, disease-associated variants of the TUBA4A gene were identified in patients with amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Here, we present the neuropathological report of a patient with the semantic variant of primary progressive aphasia with a family history of Parkinsonism, harboring a novel frameshift mutation c.187del (p.Arg64Glyfs*90) in TUBA4A. Immunohistochemistry showed abundant TAR DNA-binding protein 43 kDa (TDP-43) dystrophic neurite pathology in the frontal and temporal cortex and the dentate gyrus of the hippocampus, consistent with frontotemporal lobar degeneration (FTLD). The observed pathology pattern fitted best with that of FTLD-TDP Type C. qPCR showed the presence of mutant TUBA4A mRNA. However, no truncated TUBA4A was detected at the protein level. A decrease in total TUBA4A mRNA and protein levels suggests loss-of-function as a potential pathogenic mechanism. This report strengthens the idea that N-terminal TUBA4A mutations are associated with FTLD-TDP. These N-terminal mutations possibly exert their pathogenic effects through haploinsufficiency, contrary to C-terminal TUBA4A mutations which are thought to disturb the microtubule network via a dominant-negative mechanism.

Abstract Background With the shift of research focus towards the pre-dementia stage of Alzheimer’s disease (AD), there is an urgent need for reliable, non-invasive biomarkers to predict amyloid pathology. The aim of this study was to assess whether easily obtainable measures from structural MRI, combined with demographic data, cognitive data and apolipoprotein E (APOE) ε4 genotype, can be used to predict amyloid pathology using machine-learning classification. Methods We examined 810 subjects with structural MRI data and amyloid markers from the European Medical Information Framework for Alzheimer’s Disease Multimodal Biomarker Discovery study, including subjects with normal cognition (CN, n = 337, age 66.5 ± 7.2, 50% female, 27% amyloid positive), mild cognitive impairment (MCI, n = 375, age 69.1 ± 7.5, 53% female, 63% amyloid positive) and AD dementia (n = 98, age 67.0 ± 7.7, 48% female, 97% amyloid positive). Structural MRI scans were visually assessed and Freesurfer was used to obtain subcortical volumes, cortical thickness and surface area measures. We first assessed univariate associations between MRI measures and amyloid pathology using mixed models. Next, we developed and tested an automated classifier using demographic, cognitive, MRI and APOE ε4 information to predict amyloid pathology. A support vector machine (SVM) with nested 10-fold cross-validation was applied to identify a set of markers best discriminating between amyloid positive and amyloid negative subjects. Results In univariate associations, amyloid pathology was associated with lower subcortical volumes and thinner cortex in AD-signature regions in CN and MCI. The multi-variable SVM classifier provided an area under the curve (AUC) of 0.81 ± 0.07 in MCI and an AUC of 0.74 ± 0.08 in CN. In CN, selected features for the classifier included APOE ε4, age, memory scores and several MRI measures such as hippocampus, amygdala and accumbens volumes and cortical thickness in temporal and parahippocampal regions. In MCI, the classifier including demographic and APOE ε4 information did not improve after additionally adding imaging measures. Conclusions Amyloid pathology is associated with changes in structural MRI measures in CN and MCI. An automated classifier based on clinical, imaging and APOE ε4 data can identify the presence of amyloid pathology with a moderate level of accuracy. These results could be used in clinical trials to pre-screen subjects for anti-amyloid therapies.

Abstract Background There is an urgent need for novel, noninvasive biomarkers to diagnose Alzheimer’s disease (AD) in the predementia stages and to predict the rate of decline. Therefore, we set up the European Medical Information Framework for Alzheimer’s Disease Multimodal Biomarker Discovery (EMIF-AD MBD) study. In this report we describe the design of the study, the methods used and the characteristics of the participants. Methods Participants were selected from existing prospective multicenter and single-center European studies. Inclusion criteria were having normal cognition (NC) or a diagnosis of mild cognitive impairment (MCI) or AD-type dementia at baseline, age above 50 years, known amyloid-beta (Aβ) status, availability of cognitive test results and at least two of the following materials: plasma, DNA, magnetic resonance imaging (MRI) or cerebrospinal fluid (CSF). Targeted and untargeted metabolomic and proteomic analyses were performed in plasma, and targeted and untargeted proteomics were performed in CSF. Genome-wide SNP genotyping, next-generation sequencing and methylation profiling were conducted in DNA. Visual rating and volumetric measures were assessed on MRI. Baseline characteristics were analyzed using ANOVA or chi-square, rate of decline analyzed by linear mixed modeling. Results We included 1221 individuals (NC n = 492, MCI n = 527, AD-type dementia n = 202) with a mean age of 67.9 (SD 8.3) years. The percentage Aβ+ was 26% in the NC, 58% in the MCI, and 87% in the AD-type dementia groups. Plasma samples were available for 1189 (97%) subjects, DNA samples for 929 (76%) subjects, MRI scans for 862 (71%) subjects and CSF samples for 767 (63%) subjects. For 759 (62%) individuals, clinical follow-up data were available. In each diagnostic group, the APOE ε4 allele was more frequent amongst Aβ+ individuals (p

Human lymphoblast cells from a male diagnosed with Alzheimer's disease (AD) expressing the TREM2 p.R47H variant were used to generate integration-free induced pluripotent stem cells (iPSCs) by over-expressing episomal-based plasmids harbouring OCT4, SOX2, KLF4, LIN28, L-MYC and p53 shRNA. The derived iPSC line – AD-TREM2-3 was defined as pluripotent based on (i) expression of pluripotency-associated markers (ii) embryoid body-based differentiation into cell types representative of the three germ layers and (iii) the similarity between the transcriptome of the iPSC line and the human embryonic stem cell line H1 with a Pearson correlation of 0.940.

Human lymphoblast cells from a male diagnosed with Alzheimer's disease (AD) expressing the TREM2 p.R47H variant were used to generate integration-free induced pluripotent stem cells (iPSCs) by over-expressing episomal-based plasmids harbouring OCT4, SOX2, NANOG, LIN28, c-MYC and L-MYC. AD-TREM2–1 was defined as pluripotent based on (i) expression of pluripotency-associated markers (ii) embryoid body-based differentiation into cell types representative of the three germ layers and (iii) the similarity between the transcriptome of the iPSC line and the human embryonic stem cell line H1 with a Pearson correlation of 0.947.

Abstract CHCHD10 mutations are linked to amyotrophic lateral sclerosis, but their mode of action is unclear. In a 29‐year‐old patient with rapid disease progression, we discovered a novel mutation (Q108P) in a conserved residue within the coiled‐coil‐helix‐coiled‐coil‐helix (CHCH) domain. The aggressive clinical phenotype prompted us to probe its pathogenicity. Unlike the wild‐type protein, mitochondrial import of CHCHD10 Q108P was blocked nearly completely resulting in diffuse cytoplasmic localization and reduced stability. Other CHCHD10 variants reported in patients showed impaired mitochondrial import (C122R) or clustering within mitochondria (especially G66V and E127K) often associated with reduced expression. Truncation experiments suggest mitochondrial import of CHCHD10 is mediated by the CHCH domain rather than the proposed N‐terminal mitochondrial targeting signal. Knockdown of Mia40, which introduces disulfide bonds into CHCH domain proteins, blocked mitochondrial import of CHCHD10. Overexpression of Mia40 rescued mitochondrial import of CHCHD10 Q108P by enhancing disulfide‐bond formation. Since reduction in CHCHD10 inhibits respiration, mutations in its CHCH domain may cause aggressive disease by impairing mitochondrial import. Our data suggest Mia40 upregulation as a potential therapeutic salvage pathway.

Abstract Background We explored the diagnostic performance of cerebrospinal fluid (CSF) biomarkers in allowing differentiation between frontotemporal lobar degeneration (FTLD) and Alzheimer’s disease (AD), as well as between FTLD pathological subtypes. Methods CSF levels of routine AD biomarkers (phosphorylated tau (p-tau181), total tau (t-tau), and amyloid-beta (Aβ)1–42) and neurofilament proteins, as well as progranulin levels in both CSF and serum were quantified in definite FTLD (n = 46), clinical AD (n = 45), and cognitively healthy controls (n = 20). FTLD subgroups were defined by genetic carrier status and/or postmortem neuropathological confirmation (FTLD-TDP: n = 34, including FTLD-C9orf72: n = 19 and FTLD-GRN: n = 9; FTLD-tau: n = 10). Results GRN mutation carriers had significantly lower progranulin levels compared to other FTLD patients, AD, and controls. Both t-tau and p-tau181 were normal in FTLD patients, even in FTLD-tau. Aβ1–42 levels were very variable in FTLD. Neurofilament light chain (Nf-L) was significantly higher in FTLD compared with AD and controls. The reference logistic regression model based on the established AD biomarkers could be improved by the inclusion of CSF Nf-L, which was also important for the differentiation between FTLD and controls. Within the FTLD cohort, no significant differences were found between FTLD-TDP and FTLD-tau, but GRN mutation carriers had higher t-tau and Nf-L levels than C9orf72 mutation carriers and FTLD-tau patients. Conclusions There is an added value for Nf-L in the differential diagnosis of FTLD. Progranulin levels in CSF depend on mutation status, and GRN mutation carriers seem to be affected by more severe neurodegeneration.

Mutation A713T in the amyloid precursor protein (APP) has been linked to cases of Alzheimer’s disease (AD), cerebral amyloid angiopathy (CAA) and cerebrovascular disease. Despite its rarity, it has been observed in several families from the same geographical area, in the Calabria region in Southern Italy. Genotyping of 720,000 genome-wide SNPs with the HumanOmniExpress BeadChip was performed for six patients that were representative of apparently unrelated Calabrian families, as well as a Belgian subject of Italian descent (all with the same A713T mutation and disease). Their genomic structure and genetic relationships were analyzed. Demographic reconstruction and coalescent theory were applied to estimate the time of the most recent common ancestor (tMRCA) among patients. Results show that all A713T carriers fell into the genetic variability of Southern Italy and were not more closely related to each other than to any other healthy Calabrian individual. However, five out of seven patients shared a 1.7 Mbp-long DNA segment centered on the A713T mutation, making it possible to estimate a tMRCA for its common origin in the Calabrian region dating back over 1000 years. The analysis of affected individuals with methodologies based on human population genomics thus provides informative insights in support of clinical observations and biomedical research.

Human lymphoblast cells were used to generate integration-free induced pluripotent stem cells (iPSCs) employing episomal-based plasmids expressing OCT4, SOX2, NANOG, LIN28, c-MYC and L-MYC. The derived iPSCs were defined as pluripotent based on (i) expression of pluripotency-associated markers, (ii) embryoid body-based differentiation into cell types representative of the three germ layers and (iii) the similarity between the transcriptomes of the iPSC line and the human embryonic stem cell line H1 with a Pearson correlation of 0.95.

Abstract Background In this paper, we describe the clinical and neuropathological findings of nine members of the Belgian progranulin gene (GRN) founder family. In this family, the loss-of-function mutation IVS1 + 5G > C was identified in 2006. In 2007, a clinical description of the mutation carriers was published that revealed the clinical heterogeneity among IVS1 + 5G > C carriers. We report our comparison of our data with the published clinical and neuropathological characteristics of other GRN mutations as well as other frontotemporal lobar degeneration (FTLD) syndromes, and we present a review of the literature. Methods For each case, standardized sampling and staining were performed to identify proteinopathies, cerebrovascular disease, and hippocampal sclerosis. Results The neuropathological substrate in the studied family was compatible in all cases with transactive response DNA-binding protein (TDP) proteinopathy type A, as expected. Additionally, most of the cases presented also with primary age-related tauopathy (PART) or mild Alzheimer’s disease (AD) neuropathological changes, and one case had extensive Lewy body pathology. An additional finding was the presence of cerebral small vessel changes in every patient in this family. Conclusions Our data show not only that the IVS1 + 5G > C mutation has an exclusive association with FTLD-TDP type A proteinopathy but also that other proteinopathies can occur and should be looked for. Because the penetrance rate of the clinical phenotype of carriers of GRN mutations is age-dependent, further research is required to investigate the role of co-occurring age-related pathologies such as AD, PART, and cerebral small vessel disease.

Abstract Background The Alzheimer’s disease (AD) cerebrospinal fluid (CSF) biomarkers Aβ1–42, t-tau, and p-tau181 overlap with other diseases. New tau modifications or epitopes, such as the non-phosphorylated tau fraction (p-taurel), may improve differential dementia diagnosis. The goal of this study is to investigate if p-taurel can improve the diagnostic performance of the AD CSF biomarker panel for differential dementia diagnosis. Methods The study population consisted of 45 AD, 45 frontotemporal lobar degeneration (FTLD), 45 dementia with Lewy bodies (DLB), and 21 Creutzfeldt-Jakob disease (CJD) patients, and 20 cognitively healthy controls. A substantial subset of the patients was pathology-confirmed. CSF levels of Aβ1–42, t-tau, p-tau181, and p-taurel were determined with commercially available single-analyte enzyme-linked immunosorbent assay (ELISA) kits. Diagnostic performance was evaluated by receiver operating characteristic (ROC) curve analyses, and area under the curve (AUC) values were compared using DeLong tests. Results The diagnostic performance of single markers as well as biomarker ratios was determined for each pairwise comparison of different dementia groups and controls. The addition of p-taurel to the AD biomarker panel decreased its diagnostic performance when discriminating non-AD, FTLD, and DLB from AD. As a single marker, p-taurel increased the diagnostic performance for CJD. No significant difference was found in AUC values with the addition of p-taurel when differentiating between AD or non-AD dementias and controls. Conclusions The addition of p-taurel to the AD CSF biomarker panel failed to improve differentiation between AD and non-AD dementias.

Abstract Alzheimer disease (AD) is a progressive neurodegenerative disorder and the most common form of dementia. The majority of AD cases are sporadic, while up to 5% are families with an early onset AD (EOAD). Mutations in one of the three genes: amyloid beta precursor protein (APP), presenilin 1 (PSEN1) or presenilin 2 (PSEN2) can be disease causing. However, most EOAD families do not carry mutations in any of these three genes, and candidate genes, such as the sortilin-related receptor 1 (SORL1), have been suggested to be potentially causative. To identify AD causative variants, we performed whole-exome sequencing on five individuals from a family with EOAD and a missense variant, p.Arg1303Cys (c.3907C > T) was identified in SORL1 which segregated with disease and was further characterized with immunohistochemistry on two post mortem autopsy cases from the same family. In a targeted re-sequencing effort on independent index patients from 35 EOAD-families, a second SORL1 variant, c.3050-2A > G, was found which segregated with the disease in 3 affected and was absent in one unaffected family member. The c.3050-2A > G variant is located two nucleotides upstream of exon 22 and was shown to cause exon 22 skipping, resulting in a deletion of amino acids Gly1017- Glu1074 of SORL1. Furthermore, a third SORL1 variant, c.5195G > C, recently identified in a Swedish case control cohort included in the European Early-Onset Dementia (EU EOD) consortium study, was detected in two affected siblings in a third family with familial EOAD. The finding of three SORL1-variants that segregate with disease in three separate families with EOAD supports the involvement of SORL1 in AD pathology. The cause of these rare monogenic forms of EOAD has proven difficult to find and the use of exome and genome sequencing may be a successful route to target them.

Stress granules (SGs) are dynamic membraneless compartments composed out of RNA-binding proteins (RBPs) and RNA molecules that assemble temporarily to allow the cell to cope with cellular stress by stalling mRNA translation and moving synthesis towards cytoprotective proteins. Aberrant SGs have become prime suspects in the nucleation of toxic protein aggregation in frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). Perturbed SG dynamics appears to be mediated by alterations in RNA binding proteins (RBP). Indeed, a growing number of FTD and/or ALS related RBPs coding genes (TDP43, FUS, EWSR1, TAF15, hnRNPA1, hnRNPA2B1, ATXN2, TIA1) have been identified to interfere with SG formation through mutation of their low-complexity domain (LCD), and thereby cause or influence disease. Interestingly, disease pathways associated to the C9orf72 repeat expansion, the leading genetic cause of the FTD-ALS spectrum, intersect with SG-mediated protein aggregate formation. In this review, we provide a comprehensive overview of known SG proteins and their genetic contribution to the FTD-ALS spectrum. Importantly, multiple LCD-baring RBPs have already been identified in FTD-ALS that have not yet been genetically linked to disease. These should be considered candidate genes and offer opportunities for gene prioritization when mining sequencing data of unresolved FTD and ALS. Further, we zoom into the current understanding of the molecular processes of perturbed RBP function leading to disturbed SG dynamics, RNA metabolism, and pathological inclusions. Finally, we indicate how these gained insights open new avenues for therapeutic strategies targeting phase separation and SG dynamics to reverse pathological protein aggregation and protect against toxicity.

Within the wide range of neurodegenerative brain diseases, the differential diagnosis of frontotemporal dementia (FTD) frequently poses a challenge. Often, signs and symptoms are not characteristic of the disease and may instead reflect atypical presentations. Consequently, the use of disease biomarkers is of importance to correctly identify the patients. Here, we describe how neuropsychological characteristics, neuroimaging and neurochemical biomarkers and screening for causal gene mutations can be used to differentiate FTD from other neurodegenerative diseases as well as to distinguish between FTD subtypes. Summarizing current evidence, we propose a stepwise approach in the diagnostic evaluation. Clinical consensus criteria that take into account a full neuropsychological examination have relatively good accuracy (sensitivity [se] 75–95%, specificity [sp] 82–95%) to diagnose FTD, although misdiagnosis (mostly AD) is common. Structural brain MRI (se 70–94%, sp 89–99%) and FDG PET (se 47–90%, sp 68–98%) or SPECT (se 36–100%, sp 41–100%) brain scans greatly increase diagnostic accuracy, showing greater involvement of frontal and anterior temporal lobes, with sparing of hippocampi and medial temporal lobes. If these results are inconclusive, we suggest detecting amyloid and tau cerebrospinal fluid (CSF) biomarkers that can indicate the presence of AD with good accuracy (se 74–100%, sp 82–97%). The use of P-tau181 and the Aβ1–42/Aβ1–40 ratio significantly increases the accuracy of correctly identifying FTD vs. AD. Alternatively, an amyloid brain PET scan can be performed to differentiate FTD from AD. When autosomal dominant inheritance is suspected, or in early onset dementia, mutation screening of causal genes is indicated and may also be offered to at-risk family members. We have summarized genotype–phenotype correlations for several genes that are known to cause familial frontotemporal lobar degeneration, which is the neuropathological substrate of FTD. The genes most commonly associated with this disease (C9orf72, MAPT, GRN, TBK1) are discussed, as well as some less frequent ones (CHMP2B, VCP). Several other techniques, such as diffusion tensor imaging, tau PET imaging and measuring serum neurofilament levels, show promise for future implementation as diagnostic biomarkers.

Abstract TREM2 is an innate immune receptor expressed on the surface of microglia. Loss‐of‐function mutations of TREM2 are associated with increased risk of Alzheimer's disease (AD). TREM2 is a type‐1 protein with an ectodomain that is proteolytically cleaved and released into the extracellular space as a soluble variant (sTREM2), which can be measured in the cerebrospinal fluid (CSF). In this cross‐sectional multicenter study, we investigated whether CSF levels of sTREM2 are changed during the clinical course of AD, and in cognitively normal individuals with suspected non‐AD pathology (SNAP). CSF sTREM2 levels were higher in mild cognitive impairment due to AD than in all other AD groups and controls. SNAP individuals also had significantly increased CSF sTREM2 compared to controls. Moreover, increased CSF sTREM2 levels were associated with higher CSF total tau and phospho‐tau181P, which are markers of neuronal degeneration and tau pathology. Our data demonstrate that CSF sTREM2 levels are increased in the early symptomatic phase of AD, probably reflecting a corresponding change of the microglia activation status in response to neuronal degeneration.

Disease-modifying treatment trials are increasingly advanced to the prodromal or preclinical phase of Alzheimer's disease (AD), and inclusion criteria are based on biomarkers rather than clinical symptoms. Therefore, it is of great interest to determine which biomarkers should be combined to accurately predict conversion from mild cognitive impairment (MCI) to AD dementia. However, up to date, only few studies performed a complete A/T/N subject characterization using each of the CSF and imaging markers, or they only investigated long-term (≥ 2 years) prognosis. This study aimed to investigate the association between cerebrospinal fluid (CSF), magnetic resonance imaging (MRI), amyloid- and 18F-FDG positron emission tomography (PET) measures at baseline, in relation to cognitive changes and conversion to AD dementia over a short-term (12-month) period. We included 13 healthy controls, 49 MCI and 16 AD dementia patients with a clinical-based diagnosis and a complete A/T/N characterization at baseline. Global cortical amyloid-β (Aβ) burden was quantified using the 18F-AV45 standardized uptake value ratio (SUVR) with two different reference regions (cerebellar grey and subcortical white matter), whereas metabolism was assessed based on 18F-FDG SUVR. CSF measures included Aβ1–42, Aβ1–40, T-tau, P-tau181, and their ratios, and MRI markers included hippocampal volumes (HV), white matter hyperintensities, and cortical grey matter volumes. Cognitive functioning was measured by MMSE and RBANS index scores. All statistical analyses were corrected for age, sex, education, and APOE ε4 genotype. As a result, faster cognitive decline was most strongly associated with hypometabolism (posterior cingulate) and smaller hippocampal volume (e.g., Δstory recall: β = +0.43 [p

TDP-43 proteinopathy is strongly implicated in the pathogenesis of amyotrophic lateral sclerosis and related neurodegenerative disorders. Whether TDP-43 neurotoxicity is caused by a novel toxic gain-of-function mechanism of the aggregates or by a loss of its normal function is unknown. We increased and decreased expression of TDP-43 (dTDP-43) in Drosophila. Although upregulation of dTDP-43 induced neuronal ubiquitin and dTDP-43-positive inclusions, both up- and downregulated dTDP-43 resulted in selective apoptosis of bursicon neurons and highly similar transcriptome alterations at the pupal-adult transition. Gene network analysis and genetic validation showed that both up- and downregulated dTDP-43 directly and dramatically increased the expression of the neuronal microtubule-associated protein Map205, resulting in cytoplasmic accumulations of the ecdysteroid receptor (EcR) and a failure to switch EcR-dependent gene programs from a pupal to adult pattern. We propose that dTDP-43 neurotoxicity is caused by a loss of its normal function.