John Hardy

Linkage, whole genome sequence, and biological data implicate variants in RAB10 in Alzheimer’s disease resilience

BackgroundWhile age and the APOE ε4 allele are major risk factors for Alzheimer’s disease (AD), a small percentage of individuals with these risk factors exhibit AD resilience by living well beyond 75xa0years of age without any clinical symptoms of cognitive decline.MethodsWe used over 200 “AD resilient” individuals and an innovative, pedigree-based approach to identify genetic variants that segregate with AD resilience. First, we performed linkage analyses in pedigrees with resilient individuals and a statistical excess of AD deaths. Second, we used whole genome sequences to identify candidate SNPs in significant linkage regions. Third, we replicated SNPs from the linkage peaks that reduced risk for AD in an independent dataset and in a gene-based test. Finally, we experimentally characterized replicated SNPs.ResultsRs142787485 in RAB10 confers significant protection against AD (p valueu2009=u20090.0184, odds ratiou2009=u20090.5853). Moreover, we replicated this association in an independent series of unrelated individuals (p valueu2009=u20090.028, odds ratiou2009=u20090.69) and used a gene-based test to confirm a role for RAB10 variants in modifying AD risk (p valueu2009=u20090.002). Experimentally, we demonstrated that knockdown of RAB10 resulted in a significant decrease in Aβ42 (p valueu2009=u20090.0003) and in the Aβ42/Aβ40 ratio (p valueu2009=u20090.0001) in neuroblastoma cells. We also found that RAB10 expression is significantly elevated in human AD brains (p valueu2009=u20090.04).ConclusionsOur results suggest that RAB10 could be a promising therapeutic target for AD prevention. In addition, our gene discovery approach can be expanded and adapted to other phenotypes, thus serving as a model for future efforts to identify rare variants for AD and other complex human diseases.

Functional Studies of Missense TREM2 Mutations in Human Stem Cell-Derived Microglia

Summary The derivation of microglia from human stem cells provides systems for understanding microglial biology and enables functional studies of disease-causing mutations. We describe a robust method for the derivation of human microglia from stem cells, which are phenotypically and functionally comparable with primary microglia. We used stem cell-derived microglia to study the consequences of missense mutations in the microglial-expressed protein triggering receptor expressed on myeloid cells 2 (TREM2), which are causal for frontotemporal dementia-like syndrome and Nasu-Hakola disease. We find that mutant TREM2 accumulates in its immature form, does not undergo typical proteolysis, and is not trafficked to the plasma membrane. However, in the absence of plasma membrane TREM2, microglia differentiate normally, respond to stimulation with lipopolysaccharide, and are phagocytically competent. These data indicate that dementia-associated TREM2 mutations have subtle effects on microglia biology, consistent with the adult onset of disease in individuals with these mutations.

CXCR4 involvement in neurodegenerative diseases

Neurodegenerative diseases likely share common underlying pathobiology. Although prior work has identified susceptibility loci associated with various dementias, few, if any, studies have systematically evaluated shared genetic risk across several neurodegenerative diseases. Using genome-wide association data from large studies (total nu2009=u200982,337 cases and controls), we utilized a previously validated approach to identify genetic overlap and reveal common pathways between progressive supranuclear palsy (PSP), frontotemporal dementia (FTD), Parkinson’s disease (PD) and Alzheimer’s disease (AD). In addition to the MAPT H1 haplotype, we identified a variant near the chemokine receptor CXCR4 that was jointly associated with increased risk for PSP and PD. Using bioinformatics tools, we found strong physical interactions between CXCR4 and four microglia related genes, namely CXCL12, TLR2, RALB, and CCR5. Evaluating gene expression from post-mortem brain tissue, we found that expression of CXCR4 and microglial genes functionally related to CXCR4 was dysregulated across a number of neurodegenerative diseases. Furthermore, in a mouse model of tauopathy, expression of CXCR4 and functionally associated genes was significantly altered in regions of the mouse brain that accumulate neurofibrillary tangles most robustly. Beyond MAPT, we show dysregulation of CXCR4 expression in PSP, PD, and FTD brains, and mouse models of tau pathology. Our multi-modal findings suggest that abnormal signaling across a ‘network’ of microglial genes may contribute to neurodegeneration and may have potential implications for clinical trials targeting immune dysfunction in patients with neurodegenerative diseases.

An Aged Canid with Behavioral Deficits Exhibits Blood and Cerebrospinal Fluid Amyloid Beta Oligomers

Many of the molecular and pathological features associated with human Alzheimer disease (AD) are mirrored in the naturally occurring age-associated neuropathology in the canine species. In aged dogs with declining learned behavior and memory the severity of cognitive dysfunction parallels the progressive build up and location of Aβ in the brain. The main aim of this work was to study the biological behavior of soluble oligomers isolated from an aged dog with cognitive dysfunction through investigating their interaction with a human cell line and synthetic Aβ peptides. We report that soluble oligomers were specifically detected in the dogs blood and cerebrospinal fluid (CSF) via anti-oligomer- and anti-Aβ specific binders. Importantly, our results reveal the potent neurotoxic effects of the dogs CSF on cell viability and the seeding efficiency of the CSF-borne soluble oligomers on the thermodynamic activity and the aggregation kinetics of synthetic human Aβ. The value of further characterizing the naturally occurring Alzheimer-like neuropathology in dogs using genetic and molecular tools is discussed.

Aging related cognitive changes associated with Alzheimer's disease in Down syndrome

Individuals with Down syndrome (DS) have an extremely high genetic risk for Alzheimers disease (AD), however, the course of cognitive decline associated with progression to dementia is ill‐defined. Data‐driven methods can estimate long‐term trends from cross‐sectional data while adjusting for variability in baseline ability, which complicates dementia assessment in those with DS.

Parkinson's disease genetics: identifying novel risk loci, providing causal insights and improving estimates of heritable risk.

We performed the largest genetic study of Parkinson9s disease to date, involving analysis of 11.4M SNPs in 37.7K cases, 18.6K 9proxy-cases9 and 1.4M controls, discovering 39 novel risk loci. In total, we identified 92 putative independent genome-wide significant signals including 53 at previously published loci. Next, we dissected risk within these loci, identifying 22 candidate independent risk variants in close proximity to one another representing multiple risk signals in one locus (20 variants proximal to known risk loci). We then employed tests of causality within a Mendelian randomization framework to infer functional genomic consequences for genes within loci of interest in concert with protein-centric network analyses to nominate likely candidates for follow-up investigation. This report also shows expression network signatures of PD loci to be heavily brain enriched and different in comparison to Alzheimer9s disease. We also used risk scoring methods to improve genetic predictions of disease risk, and show that GWAS signals explain 11-15% of the heritable risk of PD at thresholds below genome-wide significance. Additionally, these data also suggest genetic correlations relating to risk overlapping with brain morphology, smoking status and educational attainment. Further analyses of smoking initiation and cognitive performance relating to PD risk in more comprehensive datasets show complex etiological links between PD risk and these traits. These data in sum provide the most comprehensive understanding of the genetic architecture of PD to date, revealing a large number of additional loci, and demonstrating that there remains a considerable genetic component of this disease that has not yet been discovered.We performed the largest genome-wide association study of PD to date, involving the analysis of 7.8M SNPs in 37.7K cases, 18.6K UK Biobank proxy-cases, and 1.4M controls. We identified 90 independent genome-wide significant signals across 78 loci, including 38 independent risk signals in 37 novel loci. These variants explained 26-36% of the heritable risk of PD. Tests of causality within a Mendelian randomization framework identified putatively causal genes for 70 risk signals. Tissue expression enrichment analysis suggested that signatures of PD loci were heavily brain-enriched, consistent with specific neuronal cell types being implicated from single cell expression data. We found significant genetic correlations with brain volumes, smoking status, and educational attainment. In sum, these data provide the most comprehensive understanding of the genetic architecture of PD to date by revealing many additional PD risk loci, providing a biological context for these risk factors, and demonstrating that a considerable genetic component of this disease remains unidentified.

A rare loss-of-function variant of ADAM17 is associated with late-onset familial Alzheimer disease

Common variants of about 20 genes contributing to AD risk have so far been identified through genome-wide association studies (GWAS). However, there is still a large proportion of heritability that might be explained by rare but functionally important variants. One of the so far identified genes with rare AD causing variants is ADAM10 . Using whole-genome sequencing we now identified a single rare nonsynonymous variant (SNV) rs142946965 [p.R215I] in ADAM17 co-segregating with an autosomal-dominant pattern of late-onset AD in one family. Subsequent genotyping and analysis of available whole-exome sequencing data of additional case/control samples from Germany, UK, and USA identified five variant carriers among AD patients only. The mutation inhibits pro-protein cleavage and the formation of the active enzyme, thus leading to loss-of-function of ADAM17 alpha-secretase. Further, we identified a strong negative correlation between ADAM17 and APP gene expression in human brain and present in vitro evidence that ADAM17 negatively controls the expression of APP . As a consequence, p.R215I mutation of ADAM17 leads to elevated Aß formation in vitro. Together our data supports a causative association of the identified ADAM17 variant in the pathogenesis of AD.

Features of GBA-associated Parkinson's disease at presentation in the UK Tracking Parkinson's study.

Objectives To examine the influence of the glucocerebrosidase (GBA) mutation carrier state on age at onset of Parkinson’s disease (PD), the motor phenotype and cognitive function at baseline assessment in a large cohort of UK patients. We also analysed the prevalence of mood and behavioural problems that may confound the assessment of cognitive function. Methods We prospectively recruited patients with PD in the Tracking Parkinson’s study. We fully sequenced the GBA gene in all recently diagnosed patients (≤3.5 years). We examined cognitive (Montreal Cognitive Assessment) and motor (Movement Disorder Society Unified Parkinson’s Disease Rating Scale part 3) function at a baseline assessment, at an average of 1.3 years after diagnosis. We used logistic regression to determine predictors of PD with mild cognitive impairment and PD with dementia. Results We studied 1893 patients with PD: 48 (2.5%) were heterozygous carriers for known Gaucher’s disease (GD) causing pathogenic mutations; 117 (6.2%) had non-synonymous variants, previously associated with PD, and 28 (1.5%) patients carried variants of unknown significance in the GBA gene. L444P was the most common pathogenic GBA mutation. Patients with pathogenic GBA mutations were on average 5 years younger at disease onset compared with non-carriers (P=0.02). PD patients with GD-causing mutations did not have an increased family risk of PD. Patients with GBA mutations were more likely to present with the postural instability gait difficulty phenotype compared with non-carriers (P=0.02). Patients carrying pathogenic mutations in GBA had more advanced Hoehn and Yahr stage after adjustment for age and disease duration compared with non-carriers (P=0.005). There were no differences in cognitive function between GBA mutation carriers and non-carriers at this early disease stage. Conclusions Our study confirms the influence of GBA mutations on the age of onset, disease severity and motor phenotype in patients with PD. Cognition did not differ between GBA mutation carriers and non-carriers at baseline, implying that cognitive impairment/dementia, reported in other studies at a later disease stage, is not present in recently diagnosed cases. This offers an important window of opportunity for potential disease-modifying therapy that may protect against the development of dementia in GBA-PD. Clinical trial registration NCT02881099; Results.

Genetics of dementia in a Finnish cohort

Alzheimer’s disease (AD) and frontotemporal dementia (FTD) are the two most common neurodegenerative dementias. Variants in APP, PSEN1 and PSEN2 are typically linked to early-onset AD, and several genetic risk loci are associated with late-onset AD. Inherited FTD can be caused by hexanucleotide expansions in C9orf72, or variants in GRN, MAPT or CHMP2B. Several other genes have also been linked to FTD or FTD with motor neuron disease. Here we describe a cohort of 60 Finnish families with possible inherited dementia. Our aim was to clarify the genetic background of dementia in this cohort by analysing both known dementia-associated genes (APOE, APP, C9ORF72, GRN, PSEN1 and PSEN2) and searching for rare or novel segregating variants with exome sequencing. C9orf72 repeat expansions were detected in 12 (20%) of the 60 families, including, in addition to FTD, a family with neuropathologically verified AD. Twelve families (10 with AD and 2 with FTD) with representative samples from affected and unaffected subjects and without C9orf72 expansions were selected for whole-exome sequencing. Exome sequencing did not reveal any variants that could be regarded unequivocally causative, but revealed potentially damaging variants in UNC13C and MARCH4.