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Hexanucleotide repeat expansion (HRE) withinC9orf72is the most common genetic cause of frontotemporal dementia (FTD). Thalamic atrophy occurs in both sporadic and familial FTD but is thought to distinctly affect HRE carriers. Separately, emerging evidence suggests widespread derepression of transposable elements (TEs) in the brain in several neurodegenerative diseases, includingC9orf72HRE-mediated FTD (C9-FTD). Whether TE activation can be measured in peripheral blood and how the reduction in peripheralC9orf72expression observed in HRE carriers relates to atrophy and clinical impairment remain unknown. We used FreeSurfer software to assess the effects ofC9orf72HRE and clinical diagnosis (n= 78 individuals, male and female) on atrophy of thalamic nuclei. We also generated a novel, human, whole-blood RNA-sequencing dataset to determine the relationships among peripheralC9orf72expression, TE activation, thalamic atrophy, and clinical severity (n= 114 individuals, male and female). We confirmed global thalamic atrophy and reducedC9orf72expression in HRE carriers. Moreover, we identified disproportionate atrophy of the right mediodorsal lateral nucleus in HRE carriers and showed thatC9orf72expression associated with clinical severity, independent of thalamic atrophy. Strikingly, we found global peripheral activation of TEs, including the human endogenous LINE-1 elementL1HS.L1HSlevels were associated with atrophy of multiple pulvinar nuclei, a thalamic region implicated in C9-FTD. Integration of peripheral transcriptomic and neuroimaging data from human HRE carriers revealed atrophy of specific thalamic nuclei, demonstrated thatC9orf72levels relate to clinical severity, and identified marked derepression of TEs, includingL1HS, which predicted atrophy of FTD-relevant thalamic nuclei.SIGNIFICANCE STATEMENTPathogenic repeat expansion inC9orf72is the most frequent genetic cause of FTD and amyotrophic lateral sclerosis (ALS; C9-FTD/ALS). The clinical, neuroimaging, and pathologic features of C9-FTD/ALS are well characterized, whereas the intersections of transcriptomic dysregulation and brain structure remain largely unexplored. Herein, we used a novel radiogenomic approach to examine the relationship between peripheral blood transcriptomics and thalamic atrophy, a neuroimaging feature disproportionately impacted in C9-FTD/ALS. We confirmed reduction ofC9orf72in blood and found broad dysregulation of transposable elements—genetic elements typically repressed in the human genome—in symptomaticC9orf72expansion carriers, which associated with atrophy of thalamic nuclei relevant to FTD.C9orf72expression was also associated with clinical severity, suggesting that peripheralC9orf72levels capture disease-relevant information.

Early-onset Alzheimer’s disease (EOAD) is a rare but particularly devastating form of AD. Though notable for its high degree of clinical heterogeneity, EOAD is defined by the same neuropathological hallmarks underlying the more common, late-onset form of AD. In this review, we describe the various clinical syndromes associated with EOAD, including the typical amnestic phenotype as well as atypical variants affecting visuospatial, language, executive, behavioral, and motor functions. We go on to highlight advances in fluid biomarker research and describe how molecular, structural, and functional neuroimaging can be used not only to improve EOAD diagnostic acumen but also enhance our understanding of fundamental pathobiological changes occurring years (and even decades) before the onset of symptoms. In addition, we discuss genetic variation underlying EOAD, including pathogenic variants responsible for the well-known mendelian forms of EOAD as well as variants that may increase risk for the much more common forms of EOAD that are either considered to be sporadic or lack a clear autosomal-dominant inheritance pattern. Intriguingly, specific pathogenic variants in PRNP and MAPT—genes which are more commonly associated with other neurodegenerative diseases—may provide unexpectedly important insights into the formation of AD tau pathology. Genetic analysis of the atypical clinical syndromes associated with EOAD will continue to be challenging given their rarity, but integration of fluid biomarker data, multimodal imaging, and various ‘omics techniques and their application to the study of large, multicenter cohorts will enable future discoveries of fundamental mechanisms underlying the development of EOAD and its varied clinical presentations.

Hexanucleotide repeat expansion (HRE) within C9orf72 is the most common genetic cause of frontotemporal dementia (FTD). Thalamic atrophy occurs in both sporadic and familial FTD but is thought to distinctly affect HRE carriers. Separately, emerging evidence suggests widespread de-repression of transposable elements (TEs) in the brain in several neurodegenerative diseases, including C9orf72 HRE-mediated FTD (C9-FTD). Whether TE activation can be measured in peripheral blood and how the reduction in peripheral C9orf72 expression observed in HRE carriers relates to atrophy and clinical impairment remain unknown. We used the FreeSurfer pipeline and its extensions to assess the effects of C9orf72 HRE and clinical diagnosis (n = 78) on atrophy of thalamic nuclei. We also generated a novel, whole-blood RNA-seq dataset to determine the relationships between peripheral C9orf72 expression, TE activation, thalamic atrophy, and clinical severity (n = 114). We confirmed global thalamic atrophy and reduced C9orf72 expression in HRE carriers. Moreover, we identified disproportionate atrophy of the right mediodorsal lateral nucleus in HRE carriers and showed that C9orf72 expression associated with clinical severity, independent of thalamic atrophy. Strikingly, we found global peripheral activation of TEs, including the human endogenous LINE-1 element, L1HS. L1HS levels were associated with atrophy of multiple pulvinar nuclei, a thalamic region implicated in C9-FTD. Integration of peripheral transcriptomic and neuroimaging data from HRE carriers revealed atrophy of specific thalamic nuclei; demonstrated that C9orf72 levels relate to clinical severity; and identified marked de-repression of TEs, including L1HS, which predicted atrophy of FTD-relevant thalamic nuclei.Significance StatementPathogenic repeat expansion in C9orf72 is the most frequent genetic cause of frontotemporal dementia and amyotrophic lateral sclerosis (C9-FTD/ALS). The clinical, neuroimaging, and pathological features of C9-FTD/ALS are well-characterized, whereas the intersections of transcriptomic dysregulation and brain structure remain largely unexplored. Herein, we utilized a novel radiogenomic approach to examine the relationship between peripheral blood transcriptomics and thalamic atrophy, a neuroimaging feature disproportionately impacted in C9-FTD/ALS. We confirmed reduction of C9orf72 in blood and found broad dysregulation of transposable elements—genetic elements typically repressed in the human genome—in symptomatic C9orf72 expansion carriers, which associated with atrophy of thalamic nuclei relevant to FTD. C9orf72 expression was also associated with clinical severity, suggesting that peripheral C9orf72 levels capture disease-relevant information.

BackgroundGlobal brain health initiatives call for improving methods for the diagnosis of Alzheimer's disease (AD) and frontotemporal dementia (FTD) in underrepresented populations. However, diagnostic procedures in upper-middle-income countries (UMICs) and lower-middle income countries (LMICs), such as Latin American countries (LAC), face multiple challenges. These include the heterogeneity in diagnostic methods, lack of clinical harmonisation, and limited access to biomarkers.MethodsThis cross-sectional observational study aimed to identify the best combination of predictors to discriminate between AD and FTD using demographic, clinical and cognitive data among 1794 participants [904 diagnosed with AD, 282 diagnosed with FTD, and 606 healthy controls (HCs)] collected in 11 clinical centres across five LAC (ReDLat cohort).FindingsA fully automated computational approach included classical statistical methods, support vector machine procedures, and machine learning techniques (random forest and sequential feature selection procedures). Results demonstrated an accurate classification of patients with AD and FTD and HCs. A machine learning model produced the best values to differentiate AD from FTD patients with an accuracy = 0.91. The top features included social cognition, neuropsychiatric symptoms, executive functioning performance, and cognitive screening; with secondary contributions from age, educational attainment, and sex.InterpretationResults demonstrate that data-driven techniques applied in archival clinical datasets could enhance diagnostic procedures in regions with limited resources. These results also suggest specific fine-grained cognitive and behavioural measures may aid in the diagnosis of AD and FTD in LAC. Moreover, our results highlight an opportunity for harmonisation of clinical tools for dementia diagnosis in the region.FundingThis work was supported by the Multi-Partner Consortium to Expand Dementia Research in Latin America (ReDLat), funded by NIA/NIH (R01AG057234), Alzheimer's Association (SG-20-725707-ReDLat), Rainwater Foundation, Takeda (CW2680521), Global Brain Health Institute; as well as CONICET; FONCYT-PICT (2017-1818, 2017-1820); PIIECC, Facultad de Humanidades, Usach; Sistema General de Regalías de Colombia (BPIN2018000100059), Universidad del Valle (CI 5316); ANID/FONDECYT Regular (1210195, 1210176, 1210176); ANID/FONDAP (15150012); ANID/PIA/ANILLOS ACT210096; and Alzheimer's Association GBHI ALZ UK-22-865742.

Global initiatives call for further understanding of the impact of inequity on aging across underserved populations. Previous research in low- and middle-income countries (LMICs) presents limitations in assessing combined sources of inequity and outcomes (i.e., cognition and functionality). In this study, we assessed how social determinants of health (SDH), cardiometabolic factors (CMFs), and other medical/social factors predict cognition and functionality in an aging Colombian population. We ran a cross-sectional study that combined theory- (structural equation models) and data-driven (machine learning) approaches in a population-based study (N = 23,694;M = 69.8 years) to assess the best predictors of cognition and functionality. We found that a combination of SDH and CMF accurately predicted cognition and functionality, although SDH was the stronger predictor. Cognition was predicted with the highest accuracy by SDH, followed by demographics, CMF, and other factors. A combination of SDH, age, CMF, and additional physical/psychological factors were the best predictors of functional status. Results highlight the role of inequity in predicting brain health and advancing solutions to reduce the cognitive and functional decline in LMICs.

BackgroundRisk factors associated with sporadic non-amnestic and early-onset Alzheimer’s disease remain underexamined. We investigated a large, clinically heterogeneous Alzheimer’s disease cohort for frequencies of established Alzheimer’s disease risk factors (hypertension, hyperlipidemia, diabetes mellitus,APOE-ɛ4 frequency, and years of education), alongside a suite of novel factors with historical theoretical association (non-right-handedness, learning disability, seizures, and autoimmune disease).MethodsIn this case-control study, we screened the demographic and health histories of 750 consecutive early-onset and 750 late-onset Alzheimer’s disease patients from the University of California San Francisco Memory and Aging Center for the prevalence of conventional risk and novel Alzheimer’s disease factors and compared these results with 8,859 Alzheimer’s disease individuals from the National Alzheimer’s Coordinating Center, Amsterdam University Medical Center, Amsterdam, and Mayo Clinic, Jacksonville.ResultsEarly-onset Alzheimer’s disease was associated with significantly lower frequencies of established risk factors (hypertension, hyperlipidemia, diabetes mellitus, allpAPOE-ɛ4,p=0.03) and significantly higher frequencies of novel factors (non-right-handedness, learning disability, active seizure, allpp=0.002, and autoimmune disease,p=0.007). Logistic regressions predicting EOAD vs. LOAD controlling for sex, education,APOE-ɛ4 status, typical, and novel risk factors, produced findings consistent with the above. Principal component analysis loaded novel factors into two components, non-right-handedness and learning disability versus seizure and autoimmune disease, and the combination of factors from both components resulted in an exponential decrease in age at onset from any single factor alone.APOE-ɛ4 provided no additional contribution to age at onset decreases within the non-amnestic Alzheimer’s disease cohort but shifted the age of onset 3 years earlier within amnestic presentations (p=0.013).ConclusionsWe identified non-right-handedness, learning disability, seizures, and autoimmune disease as novel factors that affect both the age at onset and phenotypical targeting of Alzheimer’s disease. Together these results support a new theoretical framework of neurodegenerative disease susceptibility and that through the collection of detailed developmental and health history, neurodegenerative disease risk in some may be highly predictable, offering new opportunities towards early detection, monitoring, therapeutic intervention, and ultimately disease prevention.

Study ObjectivesDespite its association with severe health conditions, the etiology of sleep apnea (SA) remains understudied. This study sought to identify genetic variants robustly associated with SA risk.MethodsWe performed a genome-wide association study (GWAS) meta-analysis of SA across five cohorts (NTotal = 523 366), followed by a multi-trait analysis of GWAS (multi-trait analysis of genome-wide association summary statistics [MTAG]) to boost power, leveraging the high genetic correlation between SA and snoring. We then adjusted our results for the genetic effects of body mass index (BMI) using multi-trait-based conditional and joint analysis (mtCOJO) and sought replication of lead hits in a large cohort of participants from 23andMe, Inc (NTotal = 1 477 352; Ncases = 175 522). We also explored genetic correlations with other complex traits and performed a phenome-wide screen for causally associated phenotypes using the latent causal variable method.ResultsOur SA meta-analysis identified five independent variants with evidence of association beyond genome-wide significance. After adjustment for BMI, only one genome-wide significant variant was identified. MTAG analyses uncovered 49 significant independent loci associated with SA risk. Twenty-nine variants were replicated in the 23andMe GWAS adjusting for BMI. We observed genetic correlations with several complex traits, including multisite chronic pain, diabetes, eye disorders, high blood pressure, osteoarthritis, chronic obstructive pulmonary disease, and BMI-associated conditions.ConclusionOur study uncovered multiple genetic loci associated with SA risk, thus increasing our understanding of the etiology of this condition and its relationship with other complex traits.

Emergence of novel visual artistic skills has been described in neurodegenerative disorders, particularly in the frontotemporal dementia - amyotrophic lateral sclerosis (FTD-ALS) spectrum, but associated clinical and genetic features and the underlying neural mechanisms have not been systematically examined. We aimed to address these gaps.We performed comprehensive chart review of all 734 participants in the University of California San Francisco FTD Program Project Grant who had a clinical syndrome within the FTD-ALS spectrum. This review allowed us to ascertain subjects meeting current FTD-ALS clinical research criteria who had: (1) an emergence of novel visual artistic skills or (2) a change in the style of visual art produced or (3) a significant increase in quantity of visual art produced. Clinical data, imaging studies, and genetic information were collected and analyzed.Among the 734 patients screened, 45 were excluded due to lack of available research notes. We identified a change in visual artistic creativity in 17/689 patients (prevalence 2.5%). Mean age of FTD symptom onset was 57.4 (±10.4), and the visual artistic creativity (VAC) change was reported an average of 0.7 years (±10.1) prior to FTD symptom onset. Of the 17 patients with VAC, 8 exhibited no prior interest in art, 2 were professional visual artists who experienced a change in artistic style, and 7 reported some prior interest in art but a substantial change of style or quantity. Artistic output was diverse however bright colors and non-human subjects were prominent. VAC occurred in patients with semantic variant primary progressive aphasia (8), behavioral variant FTD (3), nonfluent variant primary progressive aphasia (2), progressive supranuclear palsy - Richardson's syndrome (2), corticobasal syndrome (1), and ALS (1). None carried a common pathogenic variant in a FTD gene.Change in VAC is an uncommon but early positive symptom that occurs in patients across the FTD-ALS clinical spectrum but appears most common in patients with anterior temporal lobe degeneration. We are pursuing the neural mechanisms of VAC through structural and functional neuroimaging studies.

BackgroundEmerging evidence from mouse models is beginning to elucidate the brain’s immune response to tau pathology, but little is known about the nature of this response in humans. In addition, it remains unclear to what extent tau pathology and the local inflammatory response within the brain influence the broader immune system.MethodsTo address these questions, we performed single-cell RNA sequencing (scRNA-seq) of peripheral blood mononuclear cells (PBMCs) from carriers of pathogenic variants inMAPT, the gene encoding tau.ResultsAnalysis of ∼181,000 individual PBMC transcriptomes fromMAPTpathogenic variant carriers (n= 8) and healthy non-carrier controls (n= 8) demonstrated striking differential expression in monocytes and natural killer (NK) cells. We observed a marked reduction in the expression ofCX3CR1– the gene encoding the fractalkine receptor that is known to modulate tau pathology in mouse models – in monocytes and NK cells. We also observed a significant reduction in the abundance of nonclassical monocytes and dysregulated expression of nonclassical monocyte marker genes, includingFCGR3A. Finally, we identified reductions inTMEM176AandTMEM176B, genes thought to be involved in the inflammatory response in human microglia. We confirmed differential expression of select biologically relevant genes dysregulated in our scRNA-seq data using droplet digital PCR as an orthogonal technique for quantitative validation.ConclusionsOur results suggest that human peripheral immune cell expression and abundance are modulated by tau-associated pathophysiologic changes.CX3CR1and nonclassical monocytes in particular will be a focus of future work exploring the role of these peripheral signals in additional tau-associated neurodegenerative diseases.

Background: Frontotemporal dementia (FTD) has a complex genetic aetiology, with mutations in several genes associated with different forms of the disease. However, the precise mechanisms underlying the selective vulnerability of the frontal and temporal brain regions remain unknown. Methods: We leveraged summary-based data from genome-wide association studies (GWASs) and performed LD-score regression to estimate pairwise genetic correlations between FTD risk and cortical brain imaging phenotypes. Then, we followed up strongly-correlated brain measures with GWAS-pairwise analyses to isolate specific genomic loci with a shared aetiology between FTD and brain structure. We also performed functional annotation and summary-based-data Mendelian randomisation for eQTL data for genes within the overlapping genomic loci of interest using human peripheral blood and brain tissue. We evaluated the gene expression in mice targeted brain regions to better understand the dynamics of the FTD candidate genes. Results: Pairwise genetic correlation estimates between FTD and brain morphology measures were high but not statistically significant. We identified five brain regions with a strong genetic correlation (rg > 0.45) with FTD risk. A genomic region in chromosome 17 was aetiologically shared between FTD, the right inferior parietal surface area, and the right medial orbitofrontal cortical thickness. Functional annotation identified eight protein-coding genes and NSF gene expression shared between FTD and variation in the two brain structure phenotypes. Building upon these findings, we show in a mouse model of FTD that cortical NSF expression decreases with age, corresponding closely with the steadily increasing burden of tau pathology in the cortex. Conclusions: Our results highlight the molecular and genetic overlap between brain morphology and higher risk for FTD, specifically for the right inferior parietal surface area and right medial orbitofrontal cortical thickness. In addition, our findings implicate NSF gene expression in the aetiology of FTD and elucidate how NSF expression changes uniquely contribute to risk for and the pathophysiology of frontotemporal lobar degeneration independent of its association with the MAPT locus.

BACKGROUND: Cognitive trajectory varies widely and can distinguish those that develop dementia from those that remain cognitively normal. Variation in cognitive trajectory is only partially explained by traditional neuropathologies. Here, we sought to identify novel genes associated with cognitive trajectory using DNA methylation profiles from human post-mortem brain. METHODS: We performed a brain epigenome-wide association study of cognitive trajectory in 636 participants from the Religious Order Study and the Rush Memory and Aging Project (ROS/MAP) using DNA methylation profiles of the dorsal lateral prefrontal cortex (dPFC). To maximize our power to detect epigenetic associations, we used the recently developed Gene Association with Multiple Traits (GAMuT) test to analyze the five measured cognitive domains simultaneously. RESULTS: We found an epigenome-wide association for differential methylation of sites in the Claudin-5 (CLDN5) locus and cognitive trajectory (p-value = 9.96 × 10(−7)), which was robust to adjustment for cell type proportions (p-value = 8.52 × 10(−7)). This association was primarily driven by association with declines in episodic (p-value = 4.65 x 10(−6)) and working memory (p-value = 2.54 × 10(−7)). This association between methylation in CLDN5 and cognitive decline was even significant in participants with no or little signs of beta-amyloid and neurofibrillary tangle pathology. CONCLUSIONS: Differential methylation of CLDN5, an important protein of the blood-brain barrier, is associated with cognitive trajectory beyond traditional Alzheimer Disease (AD) pathologies. The association between CLDN5 and cognitive trajectory in people with low pathology suggests an early role for CLDN5 and blood-brain barrier dysfunction in cognitive decline and AD.

Genome-wide association studies (GWAS) of Alzheimer’s disease are predominantly carried out in European ancestry individuals despite the known variation in genetic architecture and disease prevalence across global populations. We leveraged published GWAS summary statistics from European, East Asian, and African American populations, and an additional GWAS from a Caribbean Hispanic population using previously reported genotype data to perform the largest multi-ancestry GWAS meta-analysis of Alzheimer’s disease and related dementias to date. This method allowed us to identify two independent novel disease-associated loci on chromosome 3. We also leveraged diverse haplotype structures to fine-map nine loci with a posterior probability >0.8 and globally assessed the heterogeneity of known risk factors across populations. Additionally, we compared the generalizability of multi-ancestry- and single-ancestry-derived polygenic risk scores in a three-way admixed Colombian population. Our findings highlight the importance of multi-ancestry representation in uncovering and understanding putative factors that contribute to risk of Alzheimer’s disease and related dementias.

Hexanucleotide repeat expansion (HRE) within

IMPORTANCEThe neurological substrates of visual creativity are unknown. We demonstrate the role of dorsomedial visual cortex in emergence of visual artistic creativity (VAC) in the setting of dementia. Our findings illuminate neural substrates of human creativity and suggest that hyperactivation of specific brain areas may manifest as enhanced cognitive or behavioral capacities.OBJECTIVETo determine the anatomical and physiological underpinnings of VAC in dementia.DESIGN, SETTING, AND PARTICIPANTSAs part of a prospective, longitudinal cohort study focused on frontotemporal dementia (FTD), 734 patients met research criteria for an FTD spectrum disorder between 2002 and 2019. Of these, seventeen showed emergence of visual artistic creativity (VAC-FTD). Two control groups (n = 51 each) were matched to VAC-FTD based on demographic and clinical parameters: (1) Not Visually Artistic FTD (NVA-FTD) and (2) Healthy Controls (HC).MAIN OUTCOMES AND MEASURESClinical, neuropsychological, genetic and neuroimaging data were analyzed to characterize VAC-FTD and compare VAC-FTD to control groups.RESULTSEmergence of VAC occurred around the time of onset of symptoms, and was disproportionately seen in patients with temporal lobe predominant degeneration (n = 8/17). Atrophy network mapping identified a dorsomedial occipital region whose activity inversely correlated, in healthy brains, with activity in the patient-specific atrophy patterns in VAC-FTD (n = 17/17) and NVA-FTD (n = 45/51). Structural covariance analysis revealed that volume of this dorsal occipital region was strongly correlated, in VAC-FTD, but not in NVA-FTD or HC, with a volume in the primary motor cortex corresponding to the right hand representation. One patient, who underwent fluorodeoxyglucose positron emission tomography before and after VAC onset, showed increasing glucose metabolism in the dorsal occipital region over the interval when creativity emerged.CONCLUSIONS AND RELEVANCEFTD lesion-induced intensification of dorsal visual association cortex structure and function predisposes to emergence of VAC in certain environmental or genetic conditions. Paradoxical gains of function are early manifestations of neurodegenerative disease, and this study delineates a specific brain region associated with the emergence of VAC.

Though distinct pathological entities, corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP) share multiple biochemical and genetic features suggesting overlapping pathophysiolog...

Microglia play a critical but poorly understood role in promoting white-matter homeostasis. In this review, we leverage advances in human genetics and mouse models of leukodystrophies to delineate our current knowledge and identify outstanding questions regarding the impact of microglia on central nervous system white matter. We first focus on the role of pathogenic mutations in genes, such as TREM2, TYROBP, and CSF1R, that cause leukodystrophies in which the primary deficit is thought to originate in microglia. We next discuss recent advances in disorders such as adrenoleukodystrophy and Krabbe disease, in which microglia play an increasingly recognized role. We conclude by reviewing the roles of GRN and related genes, such as TMEM106B, PSAP, and SORT1, that affect microglial biology and associate with several types of disease, including multiple leukodystrophies as well as forms of frontotemporal dementia (FTD) presenting with white-matter abnormalities. Taken together, mouse and human data support the notion that loss of microglia-facilitated white-matter homeostasis plays an important role in the development of leukodystrophies and suggest novel mechanisms contributing to FTD.

Alzheimer’s disease (AD) in its most common form results in cognitive changes in memory function leading to dementia due to underlying neurodegenerative disease. Recent research advancements in AD ...

Objective: MAPT mutations typically cause behavioral variant frontotemporal dementia with or without parkinsonism. Previous studies have shown that symptomatic MAPT mutation carriers have frontotemporal atrophy, yet studies have shown mixed results as to whether presymptomatic carriers have low gray matter volumes. To elucidate whether presymptomatic carriers have lower structural brain volumes within regions atrophied during the symptomatic phase, we studied a large cohort of MAPT mutation carriers using a voxelwise approach. Methods: We studied 22 symptomatic carriers (age 54.7 ± 9.1, 13 female) and 43 presymptomatic carriers (age 39.2 ± 10.4, 21 female). Symptomatic carriers’ clinical syndromes included: behavioral variant frontotemporal dementia (18), an amnestic dementia syndrome (2), Parkinson’s disease (1), and mild cognitive impairment (1). We performed voxel-based morphometry on T1 images and assessed brain volumetrics by clinical subgroup, age, and mutation subtype. Results: Symptomatic carriers showed gray matter atrophy in bilateral frontotemporal cortex, insula, and striatum, and white matter atrophy in bilateral corpus callosum and uncinate fasciculus. Approximately 20% of presymptomatic carriers had low gray matter volumes in bilateral hippocampus, amygdala, and lateral temporal cortex. Within these regions, low gray matter volumes emerged in a subset of presymptomatic carriers as early as their thirties. Low white matter volumes arose infrequently among presymptomatic carriers. Interpretation: A subset of presymptomatic MAPT mutation carriers showed low volumes in mesial temporal lobe, the region ubiquitously atrophied in all symptomatic carriers. With each decade of age, an increasing percentage of presymptomatic carriers showed low mesial temporal volume, suggestive of early neurodegeneration.

Limited knowledge on dementia biomarkers in Latin American and Caribbean (LAC) countries remains a serious barrier. Here, we reported a survey to explore the ongoing work, needs, interests, potential barriers, and opportunities for future studies related to biomarkers. The results show that neuroimaging is the most used biomarker (73%), followed by genetic studies (40%), peripheral fluids biomarkers (31%), and cerebrospinal fluid biomarkers (29%). Regarding barriers in LAC, lack of funding appears to undermine the implementation of biomarkers in clinical or research settings, followed by insufficient infrastructure and training. The survey revealed that despite the above barriers, the region holds a great potential to advance dementia biomarkers research. Considering the unique contributions that LAC could make to this growing field, we highlight the urgent need to expand biomarker research. These insights allowed us to propose an action plan that addresses the recommendations for a biomarker framework recently proposed by regional experts.

BackgroundThe triggering receptor expressed on myeloid cell 2 (TREM2) is a major regulator of neuroinflammatory processes in neurodegeneration. To date, the p.H157Y variant ofTREM2has been reported only in patients with Alzheimer’s disease. Here, we report three patients with frontotemporal dementia (FTD) from three unrelated families with heterozygous p.H157Y variant ofTREM2: two patients from Colombian families (study 1) and a third Mexican origin case from the USA (study 2).MethodsTo determine if the p.H157Y variant might be associated with a specific FTD presentation, we compared in each study the cases with age-matched, sex-matched and education-matched groups—a healthy control group (HC) and a group with FTD with neitherTREM2mutations nor family antecedents (Ng-FTD and Ng-FTD-MND).ResultsThe two Colombian cases presented with early behavioural changes, greater impairments in general cognition and executive function compared with both HC and Ng-FTD groups. These patients also exhibited brain atrophy in areas characteristic of FTD. Furthermore, TREM2 cases showed increased atrophy compared with Ng-FTD in frontal, temporal, parietal, precuneus, basal ganglia, parahippocampal/hippocampal and cerebellar regions. The Mexican case presented with FTD and motor neuron disease (MND), showing grey matter reduction in basal ganglia and thalamus, and extensive TDP-43 type B pathology.ConclusionIn all TREM2 cases, multiple atrophy peaks overlapped with the maximum peaks ofTREM2gene expression in crucial brain regions including frontal, temporal, thalamic and basal ganglia areas. These results provide the first report of an FTD presentation potentially associated with the p.H157Y variant with exacerbated neurocognitive impairments.

Radiogenomics, defined as the integrated analysis of radiologic imaging and genetic data, is a well-established tool shown to augment neuroimaging in the clinical diagnosis, prognostication, and scientific study of late-onset Alzheimer disease (LOAD). Early work using candidate single nucleotide polymorphisms (SNPs) identified genetic variation in APOE, BIN1, CLU, and CR1 as key modifiers of brain structure and function using magnetic resonance imaging (MRI). More recently, polygenic risk scores used in conjunction with MRI and positron emission tomography have shown great promise as a risk-stratification tool for clinical trials and care-management decisions. In addition, recent work using multimodal MRI and positron emission tomography as proxies of LOAD progression has identified novel risk variants that are enhancing our understanding of LOAD pathophysiology and progression. Herein, we highlight key studies and trends in the radiogenomics of LOAD over the past two decades and their implications for clinical practice and scientific research.

Early-onset Alzheimer's disease (EOAD) is a rare but particularly devastating form of AD. Though notable for its high degree of clinical heterogeneity, EOAD is defined by the same neuropathological hallmarks underlying the more common, late-onset form of AD. In this review, we describe the various clinical syndromes associated with EOAD, including the typical amnestic phenotype as well as atypical variants affecting visuospatial, language, executive, behavioral, and motor functions. We go on to highlight advances in fluid biomarker research and describe how molecular, structural, and functional neuroimaging can be used not only to improve EOAD diagnostic acumen but also enhance our understanding of fundamental pathobiological changes occurring years (and even decades) before the onset of symptoms. In addition, we discuss genetic variation underlying EOAD, including pathogenic variants responsible for the well-known mendelian forms of EOAD as well as variants that may increase risk for the much more common forms of EOAD that are either considered to be sporadic or lack a clear autosomal-dominant inheritance pattern. Intriguingly, specific pathogenic variants in PRNP and MAPT-genes which are more commonly associated with other neurodegenerative diseases-may provide unexpectedly important insights into the formation of AD tau pathology. Genetic analysis of the atypical clinical syndromes associated with EOAD will continue to be challenging given their rarity, but integration of fluid biomarker data, multimodal imaging, and various 'omics techniques and their application to the study of large, multicenter cohorts will enable future discoveries of fundamental mechanisms underlying the development of EOAD and its varied clinical presentations.

Description, TSC1/hamartin haploinsufficiency increases risk for tauopathy by promoting tau acetylation and accumulation., Age-associated neurodegenerative disorders demonstrating tau-laden intracellular inclusions are known as tauopathies. We previously linked a loss-of-function mutation in the TSC1 gene to tau accumulation and frontotemporal lobar degeneration. Now, we have identified genetic variants in TSC1 that decrease TSC1/hamartin levels and predispose to tauopathies such as Alzheimer’s disease and progressive supranuclear palsy. Cellular and murine models of TSC1 haploinsufficiency, as well as human brains carrying a TSC1 risk variant, accumulated tau protein that exhibited aberrant acetylation. This acetylation hindered tau degradation via chaperone-mediated autophagy, thereby leading to its accumulation. Aberrant tau acetylation in TSC1 haploinsufficiency resulted from the dysregulation of both p300 acetyltransferase and SIRT1 deacetylase. Pharmacological modulation of either enzyme restored tau levels. This study substantiates TSC1 as a novel tauopathy risk gene and includes TSC1 haploinsufficiency as a genetic model for tauopathies. In addition, these findings promote tau acetylation as a rational target for tauopathy therapeutics and diagnostic.