Genetic architecture of common non-Alzheimer's disease dementias

Genetic influences on brain and cognitive health and their interactions with cardiovascular conditions and depression

Approximately 40% of dementia cases could be prevented or delayed by modifiable risk factors related to lifestyle and environment. These risk factors, such as depression and vascular disease, do not affect all individuals in the same way, likely due to inter-individual differences in genetics. However, the precise nature of how genetic risk profiles interact with modifiable risk factors to affect brain health is poorly understood. Here we combine multiple data resources, including genotyping and postmortem gene expression, to map the genetic landscape of brain structure and identify 367 loci associated with cortical thickness and 13 loci associated with white matter hyperintensities (P < 5×10-8), with several loci also showing a significant association with cognitive function. We show that among 220 unique genetic loci associated with cortical thickness in our genome-wide association studies (GWAS), 95 also showed evidence of interaction with depression or cardiovascular conditions. Polygenic risk scores based on our GWAS of inferior frontal thickness also interacted with hypertension in predicting executive function in the Canadian Longitudinal Study on Aging. These findings advance our understanding of the genetic underpinning of brain structure and show that genetic risk for brain and cognitive health is in part moderated by treatable mid-life factors.

Genetic and clinical landscape of Chinese frontotemporal dementia: dominance of TBK1 and OPTN mutations

BACKGROUND

Our study aims to evaluate the genetic and phenotypic spectrum of Frontotemporal dementia (FTD) gene variant carriers in Chinese populations, investigate mutation frequencies, and assess the functional properties of TBK1 and OPTN variants.

METHODS

Clinically diagnosed FTD patients underwent genetic analysis through exome sequencing, repeat-primed polymerase chain reaction, and Sanger sequencing. TBK1 and OPTN variants were biologically characterized in vitro using immunofluorescence, immunoprecipitation, and immunoblotting analysis. The frequencies of genes implicated in FTD in China were analyzed through a literature review and meta-analysis.

RESULTS

Of the 261 Chinese FTD patients, 61 (23.4%) carried potential causative variants in FTD-related genes, including MAPT (n = 17), TBK1 (n = 7), OPTN (n = 6), GRN (n = 6), ANXA11 (n = 4), CHMP2B (n = 3), C9orf72 GGGGCC repeats (n = 2), CYLD (n = 2), PRNP (n = 2), SQSTM1 (n = 2), TARDBP (n = 2), VCP (n = 1), CCNF (n = 1), CHCHD10 (n = 1), SIGMAR1 (n = 1), CHCHD2 (n = 1), FUS (n = 1), TMEM106B (n = 1), and UBQLN2 (n = 1). 29 variants can be considered novel, including the MAPT p.D54N, p.E342K, p.R221P, p.T263I, TBK1 p.E696G, p.I37T, p.E232Q, p.S398F, p.T78A, p.Q150P, p.W259fs, OPTN p.R144G, p.F475V, GRN p.V473fs, p.C307fs, p.R101fs, CHMP2B p.K6N, p.R186Q, ANXA11 p.Q155*, CYLD p.T157I, SQSTM1 p.S403A, UBQLN2 p.P509H, CCNF p.S160N, CHCHD10 p.A8T, SIGMAR1 p.S117L, CHCHD2 p.P53fs, FUS p.S235G & p.S236G, and TMEM106B p.L144V variants. Patients with TBK1 and OPTN variants presented with heterogeneous clinical phenotypes. Functional analysis demonstrated that TBK1 I37T and E232Q mutants showed decreased autophosphorylation, and the OPTN phosphorylation was reduced by the TBK1 I37T mutant. The OPTN-TBK1 complex formation was enhanced by the TBK1 E696G mutant, while OPTN R144G and F475V mutants exhibited reduced recruitment to autophagosomes compared to the wild-type. The overall frequency of TBK1 and OPTN in Chinese FTD patients was 2.0% and 0.3%, respectively.

CONCLUSIONS

Our study demonstrates the extensive genetic and phenotypic heterogeneity of Chinese FTD patients. TBK1 mutations are the second most frequent cause of clinical FTD after MAPT in the Chinese.

Atrial Fibrillation and Other Cardiovascular Factors and the Risk of Dementia: An Italian Case-Control Study

Dementia is a major neurologic syndrome characterized by severe cognitive decline, and it has a detrimental impact on overall physical health, leading to conditions such as frailty, changes in gait, and fall risk. Depending on whether symptoms occur before or after the age of 65, it can be classified as early-onset (EOD) or late-onset (LOD) dementia. The present study is aimed at investigating the role of cardiovascular factors on EOD and LOD risk in an Italian population. Using a case-control study design, EOD and LOD cases were recruited at the Modena Cognitive Neurology Centers in 2016-2019. Controls were recruited among caregivers of all the dementia cases. Information about their demographics, lifestyles, and medical history were collected through a tailored questionnaire. We used the odds ratio (OR) and 95% confidence interval (CI) to estimate the EOD and LOD risk associated with the investigated factors after adjusting for potential confounders. Of the final 146 participants, 58 were diagnosed with EOD, 34 with LOD, and 54 were controls. According to their medical history, atrial fibrillation was associated with increased disease risk (ORs 1.90; 95% CI 0.32-11.28, and 3.64; 95% CI 0.32-41.39 for EOD and LOD, respectively). Dyslipidemia and diabetes showed a positive association with EOD, while the association was negative for LOD. We could not evaluate the association between myocardial infarction and EOD, while increased risk was observed for LOD. No clear association emerged for carotid artery stenosis or valvular heart disease. In this study, despite the limited number of exposed subjects and the high imprecision of the estimates, we found positive associations between cardiovascular disease, particularly dyslipidemia, diabetes, and atrial fibrillation, and EOD.

Drug repurposing for neurodegenerative diseases

Neurodegenerative diseases (NDDs) are neuronal problems that include the brain and spinal cord and result in loss of sensory and motor dysfunction. Common NDDs include Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), Multiple Sclerosis (MS), and Amyotrophic Lateral Sclerosis (ALS) etc. The occurrence of these diseases increases with age and is one of the challenging problems among elderly people. Though, several scientific research has demonstrated the key pathologies associated with NDDs still the underlying mechanisms and molecular details are not well understood and need to be explored and this poses a lack of effective treatments for NDDs. Several lines of evidence have shown that NDDs have a high prevalence and affect more than a billion individuals globally but still, researchers need to work forward in identifying the best therapeutic target for NDDs. Thus, several researchers are working in the directions to find potential therapeutic targets to alter the disease pathology and treat the diseases. Several steps have been taken to identify the early detection of the disease and drug repurposing for effective treatment of NDDs. Moreover, it is logical that current medications are being evaluated for their efficacy in treating such disorders; therefore, drug repurposing would be an efficient, safe, and cost-effective way in finding out better medication. In the current manuscript we discussed the utilization of drugs that have been repurposed for the treatment of AD, PD, HD, MS, and ALS.

Genetic-based patient stratification in Alzheimer's disease

Alzheimer's disease (AD) shows a high pathological and symptomatological heterogeneity. To study this heterogeneity, we have developed a patient stratification technique based on one of the most significant risk factors for the development of AD: genetics. We addressed this challenge by including network biology concepts, mapping genetic variants data into a brain-specific protein-protein interaction (PPI) network, and obtaining individualized PPI scores that we then used as input for a clustering technique. We then phenotyped each obtained cluster regarding genetics, sociodemographics, biomarkers, fluorodeoxyglucose-positron emission tomography (FDG-PET) imaging, and neurocognitive assessments. We found three clusters defined mainly by genetic variants found in MAPT, APP, and APOE, considering known variants associated with AD and other neurodegenerative disease genetic architectures. Profiling of these clusters revealed minimal variation in AD symptoms and pathology, suggesting different biological mechanisms may activate the neurodegeneration and pathobiological patterns behind AD and result in similar clinical and pathological presentations, even a shared disease diagnosis. Lastly, our research highlighted MAPT, APP, and APOE as key genes where these genetic distinctions manifest, suggesting them as potential targets for personalized drug development strategies to address each AD subgroup individually.

A Drosophila model for mechanistic investigation of tau protein spread

Brain protein aggregates are a hallmark of neurodegenerative disease. Previous work indicates that specific protein components of these aggregates are toxic, including tau in Alzheimer's disease and related tauopathies. Increasing evidence also indicates that these toxic proteins traffic between cells in a prion-like fashion, thereby spreading pathology from one brain region to another. However, the mechanisms involved in trafficking are poorly understood. We therefore developed a transgenic Drosophila model to facilitate rapid evaluation of candidate tau trafficking modifiers. Our model uses the bipartite Q system to drive co-expression of tau and GFP in the fly eye. We find age-dependent tau spread into the brain, represented by detection of tau, but not GFP in the brain. We also found that tau trafficking was attenuated upon inhibition of the endocytic factor dynamin or the kinase glycogen synthase kinase-3β ( GSK-3β ). Further work revealed that dynamin promotes tau uptake in recipient tissues, whereas GSK-3β appears to promote tau spread via direct phosphorylation of tau. Our robust and flexible system will promote the identification of tau trafficking components involved in the pathogenesis of neurodegenerative diseases.

SUMMARY STATEMENT

The trafficking of toxic proteins in neurodegenerative disease is well-known but poorly understood. Our model will allow rapid and new insight into molecular mechanisms underlying this process.

Genomic Insights into Dementia: Precision Medicine and the Impact of Gene-Environment Interaction

The diagnosis, treatment, and management of dementia provide significant challenges due to its chronic cognitive impairment. The complexity of this condition is further highlighted by the impact of gene-environment interactions. A recent strategy combines advanced genomics and precision medicine methods to explore the complex genetic foundations of dementia. Utilizing the most recent research in the field of neurogenetics, the importance of precise genetic data in explaining the variation seen in dementia patients can be investigated. Gene-environment interactions are important because they influence genetic susceptibilities and aid in the development and progression of dementia. Modified to each patient's genetic profile, precision medicine has the potential to detect groups at risk and make previously unheard-of predictions about the course of diseases. Precision medicine techniques have the potential to completely transform treatment and diagnosis methods. Targeted medications that target genetic abnormalities will probably appear, providing the possibility for more efficient and customized medical interventions. Investigating the relationship between genes and the environment may lead to preventive measures that would enable people to change their surroundings and minimize the risk of dementia, leading to the improved lifestyle of affected people. This paper provides a comprehensive overview of the genomic insights into dementia, emphasizing the pivotal role of precision medicine, and gene-environment interactions.

Factors affecting progression of non-Alzheimer dementia: a retrospective analysis with long-term follow-up

Background

Non-Alzheimer's dementias, including vascular dementia (VaD), frontotemporal dementia (FTD), Lewy body dementia (LBD), and Parkinson's disease dementia (PDD), possess unique characteristics and prognostic factors that remain poorly understood. This study aims to investigate the temporal course of these subtypes and identify the impact of functional, neuropsychiatric, and comorbid medical conditions on prognosis. Additionally, the relationship between hippocampal atrophy, white matter intensities, and disease progression will be examined, along with the identification of key covariates influencing slow or fast progression in non-Alzheimer's dementias.

Methods

A total of 196 patients with non-Alzheimer's dementias who underwent at least three comprehensive evaluations were included, with proportions of VaD, FTD, LBD, and PDD being 50, 19.39, 19.90, and 10.71%, respectively. Patient demographics, comorbidities, neuropsychiatric and neuroimaging parameters, and global evaluation were analyzed using appropriate statistical methods. The study followed patients for a mean duration of 62.57 ± 33.45 months (ranging from 11 to 198 months).

Results

The results from three different visits for each non-AD dementia case demonstrated significant differences in various measures across visits, including functional capacity (BDLAS), cognition (MMSE), and other neuropsychological tests. Notably, certain genotypes and hippocampal atrophy grades were more prevalent in specific subtypes. The results indicate that Fazekas grading and hippocampal atrophy were significant predictors of disease progression, while epilepsy, extrapyramidal symptoms, thyroid dysfunction, coronary artery disease, diabetes mellitus, hypertension, stroke, hyperlipidemia, sleep disorders, smoking, and family history of dementia were not significant predictors. BDLAS and EDLAS scores at the first and second visits showed significant associations with disease progression, while scores at the third visit did not. Group-based trajectory analysis revealed that non-AD cases separated into two reliable subgroups with slow/fast prognosis, showing high reliability (Entropy = 0.790, 51.8 vs. 48.2%).

Conclusion

This study provides valuable insights into the temporal course and prognostic factors of non-Alzheimer's dementias. The findings underscore the importance of considering functional, neuropsychological, and comorbid medical conditions in understanding disease progression. The significant associations between hippocampal atrophy, white matter intensities, and prognosis highlight potential avenues for further research and therapeutic interventions.

Focusing on oligomeric tau as a therapeutic target in Alzheimer's disease and other tauopathies

INTRODUCTION

Tau has commanded much attention as a potential therapeutic target in neurodegenerative diseases. Tau pathology is a hallmark of primary tauopathies, such as progressive supranuclear palsy (PSP), corticobasal syndrome (CBS), and subtypes of frontotemporal dementia (FTD), as well as secondary tauopathies, such as Alzheimer's disease (AD). The development of tau therapeutics must reconcile with the structural complexity of the tau proteome, as well as an incomplete understanding of the role of tau in both physiology and disease.

AREAS COVERED

This review offers a current perspective on tau biology, discusses key barriers to the development of effective tau-based therapeutics, and promotes the idea that pathogenic (as opposed to merely pathological) tau should be at the center of drug development efforts.

EXPERT OPINION

An efficacious tau therapeutic will exhibit several primary features: 1) selectivity for pathogenic tau versus other tau species; 2) blood-brain barrier and cell membrane permeability, enabling access to intracellular tau in disease-relevant brain regions; and 3) minimal toxicity. Oligomeric tau is proposed as a major pathogenic form of tau and a compelling drug target in tauopathies.

The genetic overlap between Alzheimer’s disease, amyotrophic lateral sclerosis, Lewy body dementia, and Parkinson’s disease

Neurodegenerative diseases are a group of disorders characterized by neuronal cell death causing a variety of physical and mental problems. While these disorders can be characterized by their phenotypic presentation within the nervous system, their aetiologies differ to varying degrees. The majority of previous genetic evidence for overlap between neurodegenerative diseases has been pairwise. In this study, we aimed to identify overlap between the 4 investigated neurodegenerative disorders (Alzheimer's disease, amyotrophic lateral sclerosis, Lewy body dementia, and Parkinson's disease) at the variant, gene, genomic locus, gene-set, cell, or tissue level, with specific interest in overlap between 3 or more diseases. Using local genetic correlation, we found 2 loci (TMEM175 and HLA) that were shared across 3 disorders. We also highlighted genes, genomic loci, gene sets, cell types, and tissue types which may be important to 2 or more disorders by analyzing the association of variants with a common factor estimated from the 4 disorders. Our study successfully highlighted genetic loci and tissues associated with 2 or more neurodegenerative diseases.

Genetic Spectrum and Clinical Heterogeneity of Chinese Frontotemporal Dementia Patients: Data from PUMCH Dementia Cohort

Background:

There are relatively few data on the genetic spectrum of Chinese frontotemporal dementia (FTD) population.

Objective:

With the dementia cohort of Peking Union Medical College Hospital, we aim to illustrate the genetic spectrum of FTD patients, as well as the phenotypic heterogeneity of FTD-gene variant carriers.

Methods:

204 unrelated, clinically diagnosed FTD patients of Chinese ancestry were enrolled. All the participants received demographic survey, history inquiry, physical examination, cognitive assessment, blood biochemical test, brain CT/MRI, and gene sequencing.

Results:

56.4% (115/204) participants were clinically diagnosed with behavioral variant of FTD, 20.6% (42/204) with nonfluent/agrammatic variant primary progressive aphasia (PPA), 20.1% (41/204) with semantic variant PPA, and 2.9% (6/204) with mixed variant PPA. 11.8% (24/204) subjects harbored the potential causative variants in FTD-related genes, including the MAPT (n = 7), TBK1 (n = 7), GRN (n = 2), TBK1+GRN (n = 1), VCP (n = 1), TARDBP (n = 1), UBQLN2 (n = 1), SQSTM1 (n = 1), DCTN1 (n = 1), HNRNPA1 (n = 1), and C9orf72 GGGGCC repeats (n = 1). The TBK1 T31fs, T457fs, K622fs, c.359-1G>A, the VCP P188T, and the GRN P50fs, P439fs were novel pathogenic/likely pathogenic variants. The TBK1 carriers showed a later disease onset and a higher incidence of parietal atrophy relative to the MAPTcarriers.

Conclusion:

There is genetic and clinical heterogeneity among Chinese FTD population. The TBK1 has a high mutation frequency in Chinese FTD patients.

Exome Sequencing of a Portuguese Cohort of Frontotemporal Dementia Patients: Looking Into the ALS-FTD Continuum

Introduction

Frontotemporal dementia (FTD) is considered to be part of a continuum with amyotrophic lateral sclerosis (ALS). Many genes are associated with both ALS and FTD. Yet, many genes associated with ALS have not been shown to cause FTD. We aimed to study a Portuguese cohort of FTD patients, searching for variants in genes associated with both FTD and/or ALS.

Methods

We included 57 thoroughly characterized index FTD patients from our memory clinic, who were not carriers of pathogenic variants in GRN, MAPT or C9orf72. We performed exome sequencing and 1) prioritized potential FTD and ALS causing variants by using Exomiser to annotate and filter results; and 2) looked specifically at rare variability in genes associated with FTD (excluding GRN, MAPT and C9ORF72) and/or ALS.

Results

We identified 13 rare missense variants in 10 patients (three patients had two variants) in the following genes: FUS, OPTN, CCNF, DCTN1, TREM2, ERBB4, ANG, CHRNA4, CHRNB4 and SETX. We found an additional frameshift variant on GLT8D1 in one patient. One variant (ERBB4 p.Arg1112His) gathered enough evidence to be classified as likely pathogenic by the ACMG criteria.

Discussion

We report, for the first time, an expanded study of genes known to cause FTD-ALS, in the Portuguese population. Potentially pathogenic variants in ERBB4, FUS, SETX, ANG, CHRNA4 and CHRNB4 were identified in FTD patients. These findings provide additional evidence for the potential role of rare variability in ALS-associated genes in FTD, expanding the genetic spectrum between the two diseases.

Recent Updates on the Genetics of Amyotrophic Lateral Sclerosis and Frontotemporal Dementia

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) primarily affect the motor and frontotemporal areas of the brain, respectively. These disorders share clinical, genetic, and pathological similarities, and approximately 10-15% of ALS-FTD cases are considered to be multisystemic. ALS-FTD overlaps have been linked to families carrying an expansion in the intron of C9orf72 along with inclusions of TDP-43 in the brain. Other overlapping genes (VCP, FUS, SQSTM1, TBK1, CHCHD10) are also involved in similar functions that include RNA processing, autophagy, proteasome response, protein aggregation, and intracellular trafficking. Recent advances in genome sequencing have identified new genes that are involved in these disorders (TBK1, CCNF, GLT8D1, KIF5A, NEK1, C21orf2, TBP, CTSF, MFSD8, DNAJC7). Additional risk factors and modifiers have been also identified in genome-wide association studies and array-based studies. However, the newly identified genes show higher disease frequencies in combination with known genes that are implicated in pathogenesis, thus indicating probable digenetic/polygenic inheritance models, along with epistatic interactions. Studies suggest that these genes play a pleiotropic effect on ALS-FTD and other diseases such as Alzheimer's disease, Ataxia, and Parkinsonism. Besides, there have been numerous improvements in the genotype-phenotype correlations as well as clinical trials on stem cell and gene-based therapies. This review discusses the possible genetic models of ALS and FTD, the latest therapeutics, and signaling pathways involved in ALS-FTD.

Heterozygous and Homozygous Variants in SORL1 Gene in Alzheimer's Disease Patients: Clinical, Neuroimaging and Neuropathological Findings

In the last few years, the SORL1 gene has been strongly implicated in the development of Alzheimer’s disease (AD). We performed whole-exome sequencing on 37 patients with early-onset dementia or family history suggestive of autosomal dominant dementia. Data analysis was based on a custom panel that included 46 genes related to AD and dementia. SORL1 variants were present in a high proportion of patients with candidate variants (15%, 3/20). We expand the clinical manifestations associated with the SORL1 gene by reporting detailed clinical and neuroimaging findings of six unrelated patients with AD and SORL1 mutations. We also present for the first time a patient with the homozygous truncating variant c.364C>T (p.R122*) in SORL1, who also had severe cerebral amyloid angiopathy. Furthermore, we report neuropathological findings and immunochemistry assays from one patient with the splicing variant c.4519+5G>A in the SORL1 gene, in which AD was confirmed by neuropathological examination. Our results highlight the heterogeneity of clinical presentation and familial dementia background of SORL1-associated AD and suggest that SORL1 might be contributing to AD development as a risk factor gene rather than as a major autosomal dominant gene.

Functional Connectivity of the Brain Across Rodents and Humans

Resting-state functional magnetic resonance imaging (rs-fMRI), which measures the spontaneous fluctuations in the blood oxygen level-dependent (BOLD) signal, is increasingly utilized for the investigation of the brain's physiological and pathological functional activity. Rodents, as a typical animal model in neuroscience, play an important role in the studies that examine the neuronal processes that underpin the spontaneous fluctuations in the BOLD signal and the functional connectivity that results. Translating this knowledge from rodents to humans requires a basic knowledge of the similarities and differences across species in terms of both the BOLD signal fluctuations and the resulting functional connectivity. This review begins by examining similarities and differences in anatomical features, acquisition parameters, and preprocessing techniques, as factors that contribute to functional connectivity. Homologous functional networks are compared across species, and aspects of the BOLD fluctuations such as the topography of the global signal and the relationship between structural and functional connectivity are examined. Time-varying features of functional connectivity, obtained by sliding windowed approaches, quasi-periodic patterns, and coactivation patterns, are compared across species. Applications demonstrating the use of rs-fMRI as a translational tool for cross-species analysis are discussed, with an emphasis on neurological and psychiatric disorders. Finally, open questions are presented to encapsulate the future direction of the field.

Rare variants in TP73 in a Frontotemporal Dementia cohort link this gene with primary progressive aphasia phenotypes

OBJECTIVE

TP73 was recently reported to cause Amyotrophic Lateral Sclerosis (ALS). ALS and Frontotemporal Dementia (FTD) are considered to be part of a continuum. We aimed to investigate whether TP73 variants may be associated with FTD.

METHODS

We studied a thoroughly investigated cohort of 65 Portuguese Frontotemporal Dementia patients by Whole-Exome Sequencing. Patients had no other known genetic cause for their disease (C9orf72 expansion was also excluded).

RESULTS

Of the 65 patients studied, two had rare variants in TP73 (p.Gly605Ser and p.Arg347Trp). Both had MAF<0.001 and are predicted to be pathogenic in silico. Both patients showed a phenotype with predominant language impairment, suggestive of non-fluent progressive aphasia.

CONCLUSION

We show that thoroughly studied patients without other known genetic changes harbour TP73 rare variants, which are pathogenic in silico. This adds evidence to the role of TP73 in the ALS-FTD spectrum and especially in primary progressive aphasia cases.

Effects of functional variants of vitamin C transporter genes on apolipoprotein E E4-associated risk of cognitive decline: The Nakajima study

Apolipoprotein E E4 (APOE4) is a risk factor for cognitive decline. A high blood vitamin C (VC) level reduces APOE4-associated risk of developing cognitive decline in women. In the present study, we aimed to examine the effects of functional variants of VC transporter genes expressed in the brain (SLC2A1, SLC2A3, and SLC23A2) on APOE4-associated risk of developing cognitive decline. This case–control study involved 393 Japanese subjects: 252 cognitively normal and 141 cognitively impaired individuals (87 mild cognitive impairment and 54 dementia). Database searches revealed that rs1279683 of SLC23A2, and rs710218 and rs841851 of SLC2A1 are functional variants that are significantly associated with the altered expression of the respective genes and genotyped as three single nucleotide variants (SNVs). When stratified by SNV genotype, we found a significant association between APOE4 and cognitive decline in minor allele carriers of rs1279683 (odds ratio [OR] 2.02, 95% CI, 1.05–3.87, p = 0.035) but not in the homozygote carriers of the major allele. Significant associations between APOE4 and cognitive decline were also observed in participants with major allele homozygotes of rs710218 (OR 2.35, 95% CI, 1.05–5.23, p = 0.037) and rs841851 (OR 3.2, 95% CI, 1.58–6.46, p = 0.0012), but not in minor allele carriers of the respective SNVs. In contrast, the three functional SNVs showed no significant effect on cognitive decline. Our results imply that functional SNVs of VC transporter genes can affect APOE4-associated risk of developing cognitive decline via altered VC levels in the brain.

Neuronal VPS35 deletion induces spinal cord motor neuron degeneration and early post-natal lethality

Neurodegenerative diseases are characterized by the selective degeneration of neuronal populations in different brain regions and frequently the formation of distinct protein aggregates that often overlap between diseases. While the causes of many sporadic neurodegenerative diseases are unclear, genes associated with familial or sporadic forms of disease and the underlying cellular pathways involved tend to support common disease mechanisms. Underscoring this concept, mutations in the Vacuolar Protein Sorting 35 Orthologue (VPS35) gene have been identified to cause late-onset, autosomal dominant familial Parkinson's disease, whereas reduced VPS35 protein levels are reported in vulnerable brain regions of subjects with Alzheimer's disease, neurodegenerative tauopathies such as progressive supranuclear palsy and Pick's disease, and amyotrophic lateral sclerosis. Therefore, VPS35 is commonly implicated in many neurodegenerative diseases. VPS35 plays a critical role in the retromer complex that mediates the retrieval and recycling of transmembrane protein cargo from endosomes to the trans-Golgi network or plasma membrane. VPS35 and retromer function are highly conserved in eukaryotic cells, with the homozygous deletion of VPS35 inducing early embryonic lethality in mice that has hindered an understanding of its role in the brain. Here, we develop conditional knockout mice with the selective deletion of VPS35 in neurons to better elucidate its role in neuronal viability and its connection to neurodegenerative diseases. Surprisingly, the pan-neuronal deletion of VPS35 induces a progressive and rapid disease with motor deficits and early post-natal lethality. Underlying this neurological phenotype is the relatively selective and robust degeneration of motor neurons in the spinal cord. Neuronal loss is accompanied and preceded by the formation of p62-positive protein inclusions and robust reactive astrogliosis. Our study reveals a critical yet unappreciated role for VPS35 function in the normal maintenance and survival of motor neurons during post-natal development that has important implications for neurodegenerative diseases, particularly amyotrophic lateral sclerosis.

Serum neurofilament light chain as a surrogate of cognitive decline in sporadic and familial frontotemporal dementia

BACKGROUND AND PURPOSE

Neurofilament light chain (NfL) has recently been proposed as a promising biomarker in frontotemporal dementia (FTD). We investigated the correlation of both cerebrospinal fluid (CSF) and serum NfL with detailed neuropsychological data and cognitive decline in a cohort of sporadic and familial FTD.

METHODS

CSF and serum NfL, as well as conventional CSF Alzheimer's disease (AD) biomarkers (Aβ42, t-Tau, p-Tau181), were determined in 63 FTD patients (30 sporadic-FTD, 20 with progranulin (GRN) mutations [FTD-GRN], 13 with chromosome 9 open reading frame 72 [C9orf72] expansions [C9orf72-FTD]), 37 AD patients, and 31 neurologic controls. Serum NfL was also quantified in 37 healthy individuals. Correlations between baseline CSF and serum NfL levels, standardized neuropsychological tests, and the rate of cognitive decline in FTD patients were assessed.

RESULTS

CSF and serum NfL presented with significantly higher levels in FTD than in AD patients and both control groups. Within FTD subtypes, genetic cases, and particularly FTD-GRN, had higher CSF and serum NfL levels. Significant correlations between NfL levels and overall cognitive function, abstract reasoning (CSF and serum), executive functions, memory, and language (serum) were found. A relationship between increased baseline CSF and serum NfL and a decay in cognitive performance over time was also observed.

CONCLUSIONS

Our findings highlight the potential of serum NfL as a useful surrogate end point of disease severity in upcoming targeted treatments.

Neurodegenerative movement disorders: An epigenetics perspective and promise for the future

Neurodegenerative movement disorders (NMDs) are age‐dependent disorders that are characterised by the degeneration and loss of neurons, typically accompanied by pathological accumulation of different protein aggregates in the brain, which lead to motor symptoms. NMDs include Parkinson's disease, multiple system atrophy, progressive supranuclear palsy, and Huntington's disease, among others. Epigenetic modifications are responsible for functional gene regulation during development, adult life and ageing and have progressively been implicated in complex diseases such as cancer and more recently in neurodegenerative diseases, such as NMDs. DNA methylation is by far the most widely studied epigenetic modification and consists of the reversible addition of a methyl group to the DNA without changing the DNA sequence. Although this research field is still in its infancy in relation to NMDs, an increasing number of studies point towards a role for DNA methylation in disease processes. This review addresses recent advances in epigenetic and epigenomic research in NMDs, with a focus on human brain DNA methylation studies. We discuss the current understanding of the DNA methylation changes underlying these disorders, the potential for use of these DNA modifications in peripheral tissues as biomarkers in early disease detection, classification and progression as well as a promising role in future disease management and therapy.

Genetic Counselling Improves the Molecular Characterisation of Dementing Disorders

Dementing disorders are a complex group of neurodegenerative diseases characterised by different, but often overlapping, pathological pathways. Genetics have been largely associated with the development or the risk to develop dementing diseases. Recent advances in molecular technologies permit analyzing of several genes in a small time, but the interpretation analysis is complicated by several factors: the clinical complexity of neurodegenerative disorders, the frequency of co-morbidities, and the high phenotypic heterogeneity of genetic diseases. Genetic counselling supports the diagnostic path, providing an accurate familial and phenotypic characterisation of patients. In this review, we summarise neurodegenerative dementing disorders and their genetic determinants. Genetic variants and associated phenotypes will be divided into high and low impact, in order to reflect the pathologic continuum between multifactorial and mendelian genetic factors. Moreover, we report a molecular characterisation of genes associated with neurodegenerative disorders with cognitive impairment. In particular, the high frequency of rare coding genetic variants in dementing genes strongly supports the role of geneticists in both, clinical phenotype characterisation and interpretation of genotypic data. The smart application of exome analysis to dementia patients, with a pre-analytical selection on familial, clinical, and instrumental features, improves the diagnostic yield of genetic test, reduces time for diagnosis, and allows a rapid and personalised management of disease.

Chromosome Instability, Aging and Brain Diseases

Chromosome instability (CIN) has been repeatedly associated with aging and progeroid phenotypes. Moreover, brain-specific CIN seems to be an important element of pathogenic cascades leading to neurodegeneration in late adulthood. Alternatively, CIN and aneuploidy (chromosomal loss/gain) syndromes exhibit accelerated aging phenotypes. Molecularly, cellular senescence, which seems to be mediated by CIN and aneuploidy, is likely to contribute to brain aging in health and disease. However, there is no consensus about the occurrence of CIN in the aging brain. As a result, the role of CIN/somatic aneuploidy in normal and pathological brain aging is a matter of debate. Still, taking into account the effects of CIN on cellular homeostasis, the possibility of involvement in brain aging is highly likely. More importantly, the CIN contribution to neuronal cell death may be responsible for neurodegeneration and the aging-related deterioration of the brain. The loss of CIN-affected neurons probably underlies the contradiction between reports addressing ontogenetic changes of karyotypes within the aged brain. In future studies, the combination of single-cell visualization and whole-genome techniques with systems biology methods would certainly define the intrinsic role of CIN in the aging of the normal and diseased brain.

Neuropsychological features of progranulin-associated frontotemporal dementia: a nested case-control study

The distinction between sporadic and genetic behavioural-variant frontotemporal dementia (bvFTD) regarding some neuropsychological (NP) features remains challenging. Specifically, progranulin (GRN)-associated bvFTD frequently presents with early episodic memory impairment and some degree of parietal dysfunction which are supporters of Alzheimer's disease (AD) diagnosis. In this context, we aimed to characterize the NP profile of GRN-bvFTD as compared to sporadic-bvFTD and AD in patients with mild dementia (Mini-Mental State Examination score ≥ 17 and Clinical Dementia Rating Scale score ≤ 1. We identified 21 patients at Centro Hospitalar e Universitário de Coimbra, Portugal with GRN mutations belonging to fifteen different families. As our focus was bvFTD variants, FTD-related aphasic forms (3 patients) were excluded. The remaining 18 GRN-bvFTD were further matched with 18 sporadic-bvFTD and 18 AD patients according to disease staging, age and education. All patients completed the Mini-Mental State Examination, Montreal Cognitive Assessment (MoCA) and a comprehensive NP assessment battery. Results were converted into z-scores. Differences between groups in individual NP measures and NP domains were assessed through non-parametric tests (Kruskal-Wallis test analysis) and eta squared (ŋ2) was calculated as a measure of effect size. Group comparisons show that GRN patients have worse performances on verbal retrieval processes (P = 0.039, ŋ2 = 0.110) and visuoconstructive abilities (P = 0.039, ŋ2 = 0.190) than sporadic bvFTD forms. When compared to AD, GRN patients present a higher impairment in frontal (P = 0.001, ŋ2 = 0.211) and parietal (P = 0.041, ŋ2 = 0.129) measures and a better performance in memory tasks (P = 0.020, ŋ2 = 0.120). Sporadic-bvFTD forms are worse than AD in frontal measures (P = 0.032, ŋ2 = 0.200), being better in both memory (P = 0.010, ŋ2 = 0.131) and visuospatial skills (P = 0.023, ŋ2 = 0.231). Considering these results, we conclude that GRN-bvFTD patients present a NP profile that associates the typical patterns of FTD and AD deficits. This is particularly expressive in visuoconstructive abilities, which was the more discriminative feature between groups, followed by episodic verbal memory. This study was approved by the Institutional Ethics Committee of Centro Hospitalar e Universitário de Coimbra, Portugal (CE-029/2019) on June 24, 2019.

How understudied populations have contributed to our understanding of Alzheimer's disease genetics

The majority of genome-wide association studies have been conducted using samples with a broadly European genetic background. As a field, we acknowledge this limitation and the need to increase the diversity of populations studied. A major challenge when designing and conducting such studies is to assimilate large samples sizes so that we attain enough statistical power to detect variants associated with disease, particularly when trying to identify variants with low and rare minor allele frequencies. In this review, we aimed to illustrate the benefits to genetic characterization of Alzheimer's disease, in researching currently understudied populations. This is important for both fair representation of world populations and the translatability of findings. To that end, we conducted a literature search to understand the contributions of studies, on different populations, to Alzheimer's disease genetics. Using both PubMed and Alzforum Mutation Database, we systematically quantified the number of studies reporting variants in known disease-causing genes, in a worldwide manner, and discuss the contributions of research in understudied populations to the identification of novel genetic factors in this disease. Additionally, we compared the effects of genome-wide significant single nucleotide polymorphisms across populations by focusing on loci that show different association profiles between populations (a key example being APOE). Reports of variants in APP, PSEN1 and PSEN2 can initially determine whether patients from a country have been studied for Alzheimer's disease genetics. Most genome-wide significant associations in non-Hispanic white genome-wide association studies do not reach genome-wide significance in such studies of other populations, with some suggesting an opposite effect direction; this is likely due to much smaller sample sizes attained. There are, however, genome-wide significant associations first identified in understudied populations which have yet to be replicated. Familial studies in understudied populations have identified rare, high effect variants, which have been replicated in other populations. This work functions to both highlight how understudied populations have furthered our understanding of Alzheimer's disease genetics, and to help us gauge our progress in understanding the genetic architecture of this disease in all populations.

Non-coding variants in MYH11, FZD3, and SORCS3 are associated with dementia in women

INTRODUCTION

Recent studies suggest that both sex-specific genetic risk factors and those shared between dementia and stroke are involved in dementia pathogenesis.

METHODS

We performed both single-variant and gene-based genome-wide association studies of >11,000 whole genome sequences from the Women's Health Initiative cohort to discover loci associated with dementia, with adjustment for age, ethnicity, stroke, and venous thromboembolism status. Evidence for prior evidence of association and differential gene expression in dementia-related tissues and samples was gathered for each locus.

RESULTS

Our multiethnic studies identified significant associations between variants within APOE, MYH11, FZD3, SORCS3, and GOLGA8B and risk of dementia. Ten genes implicated by these loci, including MYH11, FZD3, SORCS3, and GOLGA8B, were differentially expressed in the context of Alzheimer's disease.

DISCUSSION

Our association of MYH11, FZD3, SORCS3, and GOLGA8B with dementia is supported by independent functional studies in human subjects, model systems, and associations with shared risk factors for stroke and dementia.

A Non-APOE Polygenic Risk Score for Alzheimer's Disease Is Associated With Cerebrospinal Fluid Neurofilament Light in a Representative Sample of Cognitively Unimpaired 70-Year Olds

The effect of Alzheimer's disease (AD) polygenic risk scores (PRS) on amyloid and tau pathophysiology and neurodegeneration in cognitively unimpaired older adults is not known in detail. This study aims to investigate non-APOE AD-PRS and APOE ε4 in relation to AD pathophysiology evaluated by cerebrospinal fluid (CSF) biomarkers in a population-based sample of 70-year olds. A total of 303 dementia-free individuals from the Gothenburg H70 Birth Cohort Studies were included. Genotyping was performed using the NeuroChip, and AD-PRS were calculated. CSF levels of amyloid-β (Aβ42), total tau (t-tau), phosphorylated tau (p-tau), neurogranin (Ng), and neurofilament light (NfL) were measured with enzyme-linked immunosorbent assay. Associations were found between non-APOE PRS and both NfL (p = .001) and Aβ42 (p = .02), and between APOE ε4 and Aβ42 (p = 1e-10), t-tau (p = 5e-4), and p-tau (p = .002). Similar results were observed when only including individuals with CDR = 0, except for no evidence of an association between non-APOE PRS and Aβ42. There was an interaction between non-APOE PRS and Aβ42 pathology status in relation to NfL (p = .005); association was only present in individuals without Aβ42 pathology (p = 3e-4). In relation to Aβ42, there was a borderline interaction (p = .06) between non-APOE PRS and APOE ε4; association was present in ε4 carriers only (p = .03). Similar results were observed in individuals with CDR = 0 (n = 246). In conclusion, among cognitively healthy 70-year olds from the general population, genetic risk of AD beyond the APOE locus was associated with NfL in individuals without Aβ42 pathology, and with Aβ42 in APOE ε4 carriers, suggesting these associations are driven by different mechanisms.

Network analysis of the progranulin-deficient mouse brain proteome reveals pathogenic mechanisms shared in human frontotemporal dementia caused by GRN mutations

Heterozygous, loss-of-function mutations in the granulin gene (GRN) encoding progranulin (PGRN) are a common cause of frontotemporal dementia (FTD). Homozygous GRN mutations cause neuronal ceroid lipofuscinosis-11 (CLN11), a lysosome storage disease. PGRN is a secreted glycoprotein that can be proteolytically cleaved into seven bioactive 6 kDa granulins. However, it is unclear how deficiency of PGRN and granulins causes neurodegeneration. To gain insight into the mechanisms of FTD pathogenesis, we utilized Tandem Mass Tag isobaric labeling mass spectrometry to perform an unbiased quantitative proteomic analysis of whole-brain tissue from wild type (Grn^+/+) and Grn knockout (Grn^-/-) mice at 3- and 19-months of age. At 3-months lysosomal proteins (i.e. Gns, Scarb2, Hexb) are selectively increased indicating lysosomal dysfunction is an early consequence of PGRN deficiency. Additionally, proteins involved in lipid metabolism (Acly, Apoc3, Asah1, Gpld1, Ppt1, and Naaa) are decreased; suggesting lysosomal degradation of lipids may be impaired in the Grn^-/- brain. Systems biology using weighted correlation network analysis (WGCNA) of the Grn^-/- brain proteome identified 26 modules of highly co-expressed proteins. Three modules strongly correlated to Grn deficiency and were enriched with lysosomal proteins (Gpnmb, CtsD, CtsZ, and Tpp1) and inflammatory proteins (Lgals3, GFAP, CD44, S100a, and C1qa). We find that lysosomal dysregulation is exacerbated with age in the Grn^-/- mouse brain leading to neuroinflammation, synaptic loss, and decreased markers of oligodendrocytes, myelin, and neurons. In particular, GPNMB and LGALS3 (galectin-3) were upregulated by microglia and elevated in FTD-GRN brain samples, indicating common pathogenic pathways are dysregulated in human FTD cases and Grn^-/- mice. GPNMB levels were significantly increased in the cerebrospinal fluid of FTD-GRN patients, but not in MAPT or C9orf72 carriers, suggesting GPNMB could be a biomarker specific to FTD-GRN to monitor disease onset, progression, and drug response. Our findings support the idea that insufficiency of PGRN and granulins in humans causes neurodegeneration through lysosomal dysfunction, defects in autophagy, and neuroinflammation, which could be targeted to develop effective therapies.