Genetic and immunopathological analysis of CHCHD10 in Australian amyotrophic lateral sclerosis and frontotemporal dementia and transgenic TDP-43 mice.

OBJECTIVE: Since the first report of CHCHD10 gene mutations in amyotrophiclateral sclerosis (ALS)/frontotemporaldementia (FTD) patients, genetic variation in CHCHD10 has been inconsistently linked to disease. A pathological assessment of the CHCHD10 protein in patient neuronal tissue also remains to be reported. We sought to characterise the genetic and pathological contribution of CHCHD10 to ALS/FTD in Australia. METHODS: Whole-exome and whole-genome sequencing data from 81 familial and 635 sporadic ALS, and 108 sporadic FTD cases, were assessed for genetic variation in CHCHD10. CHCHD10 protein expression was characterised by immunohistochemistry, immunofluorescence and western blotting in control, ALS and/or FTD postmortem tissues and further in a transgenic mouse model of TAR DNA-binding protein 43 (TDP-43) pathology. RESULTS: No causal, novel or disease-associated variants in CHCHD10 were identified in Australian ALS and/or FTD patients. In human brain and spinal cord tissues, CHCHD10 was specifically expressed in neurons. A significant decrease in CHCHD10 protein level was observed in ALS patient spinal cord and FTD patient frontal cortex. In a TDP-43 mouse model with a regulatable nuclear localisation signal (rNLS TDP-43 mouse), CHCHD10 protein levels were unaltered at disease onset and early in disease, but were significantly decreased in cortex in mid-stage disease. CONCLUSIONS: Genetic variation in CHCHD10 is not a common cause of ALS/FTD in Australia. However, we showed that in humans, CHCHD10 may play a neuron-specific role and a loss of CHCHD10 function may be linked to ALS and/or FTD. Our data from the rNLS TDP-43 transgenic mice suggest that a decrease in CHCHD10 levels is a late event in aberrant TDP-43-induced ALS/FTD pathogenesis.

The underacknowledged PPA-ALS: A unique clinicopathologic subtype with strong heritability.

OBJECTIVE: To assess the incidence, heritability, and neuropathology of primary progressive aphasia (PPA) with amyotrophic lateral sclerosis (ALS) in a large Australian cohort. METHODS: A total of 130 patients with a primary nonfluent variant of PPA (nfvPPA) or semantic variant of PPA (svPPA) were assessed for concomitant ALS and a strong family history of neurodegenerative diseases (Goldman score ≤3). Neuropathologic examination was carried out in 28% (n = 36) of these PPA and PPA-ALS cases that had come to autopsy. RESULTS: ALS was identified in 18% of patients with nfvPPA and 5% of patients with svPPA. PPA-ALS but not PPA was found to have a strong family history. At autopsy, frontotemporal lobar degeneration (FTLD)-TDP was identified in 100% of nfvPPA-ALS cases, 100% of svPPA-ALS cases, 24% of nfvPPA cases, and 78% of svPPA cases. Clinicopathologic assessments revealed a significant association between a strong family history and underlying FTLD-TDP pathology. Pathogenic mutations in known frontotemporal dementia (FTD)/ALS genes were identified in 100% of these familial PPA cases but only 50% of familial PPA-ALS cases, suggesting the involvement of novel genetic variants in this underacknowledged phenotype. CONCLUSION: The present study identified ALS in 12% of a large cohort of patients with nfvPPA and svPPA, which is comparable to the 10%-15% reported in FTD overall, indicating that a third of patients with FTD-ALS will have a predominant language profile. These findings highlight the importance of assessing for ALS in PPA, particularly since this is the only PPA phenotype in which a perfect clinicopathologic association has been reported in to date.

Effect of Fluvoxamine on Amyloid-ß Peptide Generation and Memory.

Alzheimer's disease is characterized by abnormal amyloid-ß (Aß) peptide accumulation beginning decades before symptom onset. An effective prophylactic treatment aimed at arresting the amyloidogenic pathway would therefore need to be initiated prior to the occurrence of Aß pathology. The SIGMAR1 gene encodes a molecular chaperone that modulates processing of the amyloid-ß protein precursor (AßPP). Fluvoxamine is a selective serotonin reuptake inhibitor and a potent SIGMAR1 agonist. We therefore hypothesized that fluvoxamine treatment would reduce Aß production and improve cognition. We firstly investigated the impact of SIGMAR1 on AßPP processing, and found that overexpression and knockdown of SIGMAR1 significantly affected γ-secretase activity in SK-N-MC neuronal cells. We then tested the impact of fluvoxamine on Aß production in an amyloidogenic cell model, and found that fluvoxamine significantly reduced Aß production by inhibiting γ-secretase activity. Finally, we assessed the efficacy of long-term treatment (i.e., ∼8 months) of 10 mg/kg/day fluvoxamine in the J20 amyloidogenic mouse model; the treatment was initiated prior to the occurrence of predicted Aß pathology. Physical examination of the animals revealed no overt pathology or change in weight. We conducted a series of behavioral tests to assess learning and memory, and found that the fluvoxamine treatment significantly improved memory function as measured by novel object recognition task. Two other tests revealed no significant change in memory function. In conclusion, fluvoxamine has a clear impact on γ-secretase activity and AßPP processing to generate Aß, and may have a protective effect on cognition in the J20 mice.

Assessment of amyloid ß in pathologically confirmed frontotemporal dementia syndromes.

INTRODUCTION: The diagnostic utility of in vivo amyloid ß (Aß) imaging to aid in the clinical distinction between frontotemporal dementia (FTD) and Alzheimer's disease remains unclear without data on the prevalence and severity of Aß in pathologically confirmed FTD syndromes. METHODS: Aß was assessed in 98 autopsy-confirmed FTD and 36 control cases, and the pathological accuracy of 11C-Pittsburgh compound B (PiB)-positron emission tomography imaging was assessed in a subset of FTD cases (n = 15). RESULTS: Aß was identified in a similar proportion of FTD syndromes and age-matched controls and increases with age. Alzheimer's disease pathology was identified in all cases with high PiB retention and in one case with low PiB retention. We further demonstrate a strong regional correlation between volume fraction of histological Aß with PiB standard uptake value ratio scaled to the white matter. DISCUSSION: The present study provides a pathologic reference to assist in the interpretation of in vivo assessments in FTD syndromes.

Finding MAPT Mutations in Frontotemporal Dementia and Other Tauopathies.

Sanger sequencing is a classic technique in molecular genetics to detect single nucleotide DNA variants in genomic DNA. Here we describe the detection of MAPT mutations by polymerase chain reaction amplification of patient genomic DNA followed by bidirectional Sanger sequencing. Exon trapping is a technique whereby genomic DNA covering the exon of interest and flanking intronic sequence is cloned into the intron of an expression vector and transfected into human cell lines. RNA is extracted and splicing products are examined by reverse-transcriptase PCR and agarose gel electrophoresis. We outline the application of this technique to assess the effect of novel DNA variants on the splicing efficiency of MAPT exon 10, a common mechanism of disease for pathogenic MAPT mutations.

TDP-43 in the hypoglossal nucleus identifies amyotrophic lateral sclerosis in behavioral variant frontotemporal dementia.

The hypoglossal nucleus was recently identified as a key brain region in which the presence of TDP-43 pathology could accurately discriminate TDP-43 proteinopathy cases with clinical amyotrophic lateral sclerosis (ALS). The objective of the present study was to assess the hypoglossal nucleus in behavioral variant frontotemporal dementia (bvFTD), and determine whether TDP-43 in this region is associated with clinical ALS. Twenty-nine cases with neuropathological FTLD-TDP and clinical bvFTD that had not been previously assessed for hypoglossal TDP-43 pathology were included in this study. Of these 29 cases, 41% (n=12) had a dual diagnosis of bvFTD-ALS at presentation, all 100% (n=12) of which demonstrated hypoglossal TDP-43 pathology. Of the 59% (n=17) cohort that presented with pure bvFTD, 35% (n=6) were identified with hypoglossal TDP-43 pathology. Review of the case files of all pure bvFTD cases revealed evidence of possible or probable ALS in 5 of the 6 hypoglossal-positive cases (83%) towards the end of disease, and this was absent from all cases without such pathology. In conclusion, the present study validates grading the presence of TDP-43 in the hypoglossal nucleus for the pathological identification of bvFTD cases with clinical ALS, and extends this to include the identification of cases with possible ALS at end-stage.

Role of the Long Non-Coding RNA MAPT-AS1 in Regulation of Microtubule Associated Protein Tau (MAPT) Expression in Parkinson's Disease.

Studies investigating the pathogenic role of the microtubule associated protein tau (MAPT) gene in Parkinson's disease (PD) have indicated that DNA methylation of the promoter region is aberrant in disease, leading to dysregulated MAPT expression. We examined two potential regulators of MAPT gene expression in respect to PD, a promoter-associated long non-coding RNA MAPT-AS1, and DNA methyltransferases (DNMTs), enzymes responsible for new and maintenance of DNA methylation. We assessed the relationship between expression levels of MAPT and the candidate MAPT-AS1, DNMT1, DNMT3A and DNMT3B transcripts in four brain regions with varying degrees of cell loss and pathology (putamen, anterior cingulate cortex, visual cortex and cerebellum) in N = 10 PD and N = 10 controls. We found a significant decrease in MAPT-AS1 expression in PD (p = 7.154 x 10-6). The transcript levels of both MAPT-AS1 (p = 2.569 x 10-4) and DNMT1 (p = 0.001) correlated with those of MAPT across the four brain regions, but not with each other. Overexpression of MAPT-AS1 decreased MAPT promoter activity by ∼2.2 to 4.3 fold in an in vitro luciferase assay performed in two cell lines (p ≤ 2.678 x 10-4). Knock-down expression of MAPT-AS1 led to a 1.3 to 6.3 fold increase in methylation of the endogenous MAPT promoter (p ≤ 0.011) and a 1.2 to 1.5 fold increased expression of the 4-repeat MAPT isoform transcript (p ≤ 0.013). In conclusion, MAPT-AS1 and DNMT1 have been identified as potential epigenetic regulators of MAPT expression in PD across four different brain regions. Our data also suggest that increased MAPT expression could be associated with disease state, but not with PD neuropathology severity.

Genetic factors and epigenetic mechanisms of longevity: current perspectives.

The exceptional longevity phenotype, defined as living beyond the age of 95, results from complex interactions between environmental and genetic factors. Epigenetic mechanisms, such as DNA methylation and histone modifications, mediate the interaction of these factors. This review will provide an overview of animal model studies used to examine age-related epigenetic modifications. Key human studies will be used to illustrate the progress made in the identification of the genetic loci associated with exceptional longevity, including APOE and FOXO3 and genes/loci that are also differentially methylated between long-lived individuals and younger controls. Future studies should focus on elucidating whether identified longevity genetic loci directly influence epigenetic mechanisms, especially on differentially methylated regions associated with longevity.

Physiologically generated presenilin 1 lacking exon 8 fails to rescue brain PS1-/- phenotype and forms complexes with wildtype PS1 and nicastrin.

The presenilin 1 (PSEN1) L271V mutation causes early-onset familial Alzheimer's disease by disrupting the alternative splicing of the PSEN1 gene, producing some transcripts harboring the L271V point mutation and other transcripts lacking exon 8 (PS1(∆exon8)). We previously reported that PS1 L271V increased amyloid beta (Aß) 42/40 ratios, while PS1(∆exon8) reduced Aß42/40 ratios, indicating that the former and not the exon 8 deletion transcript is amyloidogenic. Also, PS1(∆exon8) did not rescue Aß generation in PS1/2 double knockout cells indicating its identity as a severe loss-of-function splice form. PS1(∆exon8) is generated physiologically raising the possibility that we had identified the first physiological inactive PS1 isoform. We studied PS1(∆exon8) in vivo by crossing PS1(∆exon8) transgenics with either PS1-null or Dutch APP(E693Q) mice. As a control, we crossed APP(E693Q) with mice expressing a deletion in an adjacent exon (PS1(∆exon9)). PS1(∆exon8) did not rescue embryonic lethality or Notch-deficient phenotypes of PS1-null mice displaying severe loss of function in vivo. We also demonstrate that this splice form can interact with wildtype PS1 using cultured cells and co-immunoprecipitation (co-IP)/bimolecular fluorescence complementation. Further co-IP demonstrates that PS1(∆exon8) interacts with nicastrin, participating in the γ-secretase complex formation. These data support that catalytically inactive PS1(∆exon8) is generated physiologically and participates in protein-protein interactions.

Investigating the influence of KIBRA and CLSTN2 genetic polymorphisms on cross-sectional and longitudinal measures of memory performance and hippocampal volume in older individuals.

The variability of episodic memory decline and hippocampal atrophy observed with increasing age may partly be explained by genetic factors. KIBRA (kidney and brain expressed protein) and CLSTN2 (calsyntenin 2) are two candidate genes previously linked to episodic memory performance and volume of the hippocampus, a key memory structure. However, whether polymorphisms in these two genes also influence age-related longitudinal memory decline and hippocampal atrophy is still unknown. Using data from two independent cohorts, the Sydney Memory and Ageing Study and the Older Australian Twins Study, we investigated whether the KIBRA and CLSTN2 genetic polymorphisms (rs17070145 and rs6439886) are associated with episodic memory performance and hippocampal volume in older adults (65-90 years at baseline). We were able to examine these polymorphisms in relation to memory and hippocampal volume using cross-sectional data and, more importantly, also using longitudinal data (2 years between testing occasions). Overall we did not find support for an association of KIBRA either alone or in combination with CLSTN2 with memory performance or hippocampal volume, nor did variation in these genes influence longitudinal memory decline or hippocampal atrophy in two cohorts of older adults.

TDP-43 proteinopathies: pathological identification of brain regions differentiating clinical phenotypes.

The pathological sequestration of TAR DNA-binding protein 43 (TDP-43, encoded by TARDBP) into cytoplasmic pathological inclusions characterizes the distinct clinical syndromes of amyotrophic lateral sclerosis and behavioural variant frontotemporal dementia, while also co-occurring in a proportion of patients with Alzheimer's disease, suggesting that the regional concentration of TDP-43 pathology has most relevance to specific clinical phenotypes. This has been reflected in the three different pathological staging schemes for TDP-43 pathology in these different clinical syndromes, with none of these staging schemes including a preclinical phase similar to that which has proven beneficial in other neurodegenerative diseases. To apply each of these three staging schemes for TDP-43 pathology, the clinical phenotype must be known undermining the potential predictive value of the pathological examination. The present study set out to test whether a more unified approach could accurately predict clinical phenotypes based solely on the regional presence and severity of TDP-43 pathology. The selection of brain regions of interest was based on key regions routinely sampled for neuropathological assessment under current consensus criteria that have also been used in the three TDP-43 staging schemes. The severity of TDP-43 pathology in these regions of interest was assessed in four clinicopathological phenotypes: amyotrophic lateral sclerosis (n = 27, 47-78 years, 15 males), behavioural variant frontotemporal dementia (n = 15, 49-82 years, seven males), Alzheimer's disease (n = 26, 51-90 years, 11 males) and cognitively normal elderly individuals (n = 17, 80-103 years, nine males). Our results demonstrate that the presence of TDP-43 in the hypoglossal nucleus discriminates patients with amyotrophic lateral sclerosis with an accuracy of 98%. The severity of TDP-43 deposited in the anterior cingulate cortex identifies patients with behavioural variant frontotemporal dementia with an accuracy of 99%. This identification of regional pathology associated with distinct clinical phenotypes suggests key regions on which probabilistic pathological criteria, similar to those currently available for Alzheimer's disease and dementia with Lewy bodies, can be developed for TDP-43 proteinopathies. We propose and validate a simplified probabilistic statement that involves grading the presence of TDP-43 in the hypoglossal nucleus and the severity of TDP-43 in the anterior cingulate for the pathological identification of TDP-43 proteinopathy cases with clinical amyotrophic lateral sclerosis and behavioural variant frontotemporal dementia.

Effect of PSEN1 mutations on MAPT methylation in early-onset Alzheimer's disease.

The MAPT gene is a risk locus for multiple neurodegenerative diseases, including idiopathic Parkinson's and Alzheimer's disease. We examined whether altered DNA methylation of the MAPT promoter, with its potential to modulate gene expression, was a common phenomenon in Alzheimer's disease patients with differing aetiologies. We measured MAPT promoter methylation in a brain tissue cohort of early-onset Alzheimer's disease (EOAD) with defined causative mutations in the PSEN1 gene (Normal = 10, PSEN1 AD = 10), and idiopathic late-onset Alzheimer's disease (Normal = 12, LOAD = 12). We found a brain-region-specific decrease in MAPT promoter methylation in PSEN1 AD patients. Overexpression of PSEN1 reduced MAPT promoter activity in an in vitro luciferase study, and led to an increase in methylation of the endogenous MAPT promoter. Overexpression of PSEN1 with a deletion of exon 9 mutation (Δex9) led to a smaller reduction in MAPT promoter activity relative to wild-type PSEN1 in the luciferase assay, consistent with a decreased ability to modulate endogenous MAPT gene methylation. Our study indicates a novel effect of PSEN1 on MAPT methylation, and suggests a mutation-specific effect of the PSEN1 Δex9 mutation.

SNCA Gene, but Not MAPT, Influences Onset Age of Parkinson's Disease in Chinese and Australians.

BACKGROUND: α-Synuclein (SNCA) and microtubule-associated protein tau (MAPT) are the two major genes independently, but not jointly, associated with susceptibility for Parkinson's disease (PD). The SNCA gene has recently been identified as a major modifier of age of PD onset. Whether MAPT gene synergistically influences age of onset of PD is unknown. Objective. To investigate independent and joint effects of MAPT and SNCA on PD onset age. METHODS: 412 patients with PD were recruited from the Australian PD Research Network (123) and the Neurology Department, Ruijin Hospital Affiliated to Shanghai Jiaotong University, China (289). MAPT (rs17650901) tagging H1/H2 haplotype and SNCA (Rep1) were genotyped in the Australian cohort, and MAPT (rs242557, rs3744456) and SNCA (rs11931074, rs894278) were genotyped in the Chinese cohort. SPSS regression analysis was used to test genetic effects on age at onset of PD in each cohort. RESULTS: SNCA polymorphisms associated with the onset age of PD in both populations. MAPT polymorphisms did not enhance such association in either entire cohort. CONCLUSION: This study suggests that, in both ethnic groups, SNCA gene variants influence the age at onset of PD and α-synuclein plays a key role in the disease course of PD.

DNA methylation in the apolipoprotein-A1 gene is associated with episodic memory performance in healthy older individuals.

BACKGROUND: DNA methylation variation has been implicated in memory, cognitive performance, and dementia. Plasma apolipoprotein-A1 (ApoA1) levels may act as a biomarker of age-associated cognitive performance and decline. OBJECTIVES: To estimate the heritability of plasma ApoA1 protein levels; to examine DNA methylation variation within the APOA1 gene; and to investigate whether APOA1 methylation is associated with plasma ApoA1 levels and episodic memory performance. METHOD: Heritability of ApoA1 protein levels in Older Australian Twins Study (OATS) was assessed using structural equation modelling. APOA1 methylation levels were assayed in two cohorts of cognitively normal older individuals. The methylation status of 12 CpGs in 24 twin pairs from OATS was assayed using the Illumina 450K methylation array. Candidate CpGs were assayed in 454 individuals from Sydney Memory and Ageing Study (Sydney MAS) using pyrosequencing. Regression analyses assessed associations between APOA1 methylation levels, ApoA1 plasma levels, and memory performance. RESULTS: No significant heritability was observed for ApoA1 protein levels. APOA1 candidate-gene analyses revealed CpG sites associated with memory performance in the twin study (p < 0.050). Replication of an association between methylation of a specific CpG (cg03010018) in APOA1 and memory performance was observed in Sydney MAS (ß = -0.145, p = 0.010). Methylation of this CpG site was also significantly correlated with ApoA1 protein levels (ß = 0.161, p = 0.019). However, no relationship between a composite memory domain score and methylation was observed (p = 0.389). CONCLUSION: Findings demonstrated that epigenetic control of APOA1 expression and DNA methylation levels are associated with episodic memory performance in older adults.

Genetics of microstructure of the corpus callosum in older adults.

The current study sought to examine the relative influence of genetic and environmental factors on corpus callosum (CC) microstructure in a community sample of older adult twins. Analyses were undertaken in 284 healthy older twins (66% female; 79 MZ and 63 DZ pairs) from the Older Australian Twins Study. The average age of the sample was 69.82 (SD = 4.76) years. Brain imaging scans were collected and DTI measures were estimated for the whole CC as well as its five subregions. Parcellation of the CC was performed using Analyze. In addition, white matter lesion (WMLs) burden was estimated. Heritability and genetic correlation analyses were undertaken using the SOLAR software package. Age, sex, scanner, handedness and blood pressure were considered as covariates. Heritability (h(2)) analysis for the DTI metrics of whole CC, indicated significant h(2) for fractional anisotropy (FA) (h(2) = 0.56; p = 2.89×10(-10)), mean diffusivity (MD) (h(2) = 0.52; p = 0.30×10(-6)), radial diffusivity (RD) (h(2) = 0.49; p = 0.2×10(-6)) and axial diffusivity (AD) (h(2) = 0.37; p = 8.15×10(-5)). We also performed bivariate genetic correlation analyses between (i) whole CC DTI measures and (ii) whole CC DTI measures with total brain WML burden. Across the DTI measures for the whole CC, MD and RD shared 84% of the common genetic variance, followed by MD-AD (77%), FA-RD (52%), RD-AD (37%) and FA-MD (11%). For total WMLs, significant genetic correlations indicated that there was 19% shared common genetic variance with whole CC MD, followed by CC RD (17%), CC AD (16%) and CC FA (5%). Our findings suggest that the CC microstructure is under moderate genetic control. There was also evidence of shared genetic factors between the CC DTI measures. In contrast, there was less shared genetic variance between WMLs and the CC DTI metrics, suggesting fewer common genetic variants.

Heritability in frontotemporal dementia: more missing pieces?

Frontotemporal dementia (FTD) is reportedly highly heritable, even though a recognized genetic cause is often absent. To explain this contradiction, we explored the "strength" of family history in FTD, Alzheimer's disease (AD), and controls. Clinical syndromes associated with heritability of FTD and AD were also examined. FTD and AD patients were recruited from an FTD-specific research clinic, and patients were further sub-classified into FTD or AD phenotypes. The strength of family history was graded using the Goldman score (GS), and GS of 1-3 was regarded as a "strong" family history. A subset of FTD patients underwent screening for the main genetic causes of FTD. In total, 307 participants were included (122 FTD, 98 AD, and 87 controls). Although reported positive family history did not differ between groups, a strong family history was more common in FTD (FTD 17.2 %, AD 5.1 %, controls 2.3 %, P < 0.001). The bvFTD and FTD-ALS groups drove heritability, but 12.2 % of atypical AD patients also had a strong family history. A pathogenic mutation was identified in 16 FTD patients (10 C9ORF72 repeat expansion, 5 GRN, 1 MAPT), but more than half of FTD patients with a strong family history had no mutation detected. FTD is a highly heritable disease, even more than AD, and patients with bvFTD and FTD-ALS drive this heritability. Atypical AD also appears to be more heritable than typical AD. These results suggest that further genetic influences await discovery in FTD.

Concordance between direct and imputed APOE genotypes using 1000 Genomes data.

There are a growing number of large cohorts of older persons with genome-wide genotyping data available, but APOE is not included in any of the common microarray platforms. We compared directly measured APOE genotypes with those imputed using microarray data and the "1000 Genomes" dataset in a sample of 320 Caucasians. We find 90% agreement for ε2/ε3/ε4 genotypes and 93% agreement for predicting ε4 status, yielding kappa values of 0.81 and 0.84, respectively. More stringent thresholds around allele number estimates can increase this agreement to 90-97% and kappas of 0.90-0.93.

Frontotemporal dementia and its subtypes: a genome-wide association study.

BACKGROUND: Frontotemporal dementia (FTD) is a complex disorder characterised by a broad range of clinical manifestations, differential pathological signatures, and genetic variability. Mutations in three genes-MAPT, GRN, and C9orf72--have been associated with FTD. We sought to identify novel genetic risk loci associated with the disorder. METHODS: We did a two-stage genome-wide association study on clinical FTD, analysing samples from 3526 patients with FTD and 9402 healthy controls. To reduce genetic heterogeneity, all participants were of European ancestry. In the discovery phase (samples from 2154 patients with FTD and 4308 controls), we did separate association analyses for each FTD subtype (behavioural variant FTD, semantic dementia, progressive non-fluent aphasia, and FTD overlapping with motor neuron disease [FTD-MND]), followed by a meta-analysis of the entire dataset. We carried forward replication of the novel suggestive loci in an independent sample series (samples from 1372 patients and 5094 controls) and then did joint phase and brain expression and methylation quantitative trait loci analyses for the associated (p<5 × 10(-8)) single-nucleotide polymorphisms. FINDINGS: We identified novel associations exceeding the genome-wide significance threshold (p<5 × 10(-8)). Combined (joint) analyses of discovery and replication phases showed genome-wide significant association at 6p21.3, HLA locus (immune system), for rs9268877 (p=1·05 × 10(-8); odds ratio=1·204 [95% CI 1·11-1·30]), rs9268856 (p=5·51 × 10(-9); 0·809 [0·76-0·86]) and rs1980493 (p value=1·57 × 10(-8), 0·775 [0·69-0·86]) in the entire cohort. We also identified a potential novel locus at 11q14, encompassing RAB38/CTSC (the transcripts of which are related to lysosomal biology), for the behavioural FTD subtype for which joint analyses showed suggestive association for rs302668 (p=2·44 × 10(-7); 0·814 [0·71-0·92]). Analysis of expression and methylation quantitative trait loci data suggested that these loci might affect expression and methylation in cis. INTERPRETATION: Our findings suggest that immune system processes (link to 6p21.3) and possibly lysosomal and autophagy pathways (link to 11q14) are potentially involved in FTD. Our findings need to be replicated to better define the association of the newly identified loci with disease and to shed light on the pathomechanisms contributing to FTD. FUNDING: The National Institute of Neurological Disorders and Stroke and National Institute on Aging, the Wellcome/MRC Centre on Parkinson's disease, Alzheimer's Research UK, and Texas Tech University Health Sciences Center.

Association of SORL1 gene variants with hippocampal and cerebral atrophy and Alzheimer's disease.

BACKGROUND: Sortilin-related receptor, Sorl1, is a neuronal receptor that interacts with the amyloid precursor protein to regulate amyloidogenesis. Variants in the gene encoding Sorl1 are associated with Alzheimer's disease (AD), as well as its neuroimaging markers. OBJECTIVES: To investigate the relationship between SORL1 gene variants with ADrelated brain morphologies and AD, testing for sex-specific effects. METHODS: The sample comprised 292 individuals aged ≥ 75 years participating in the longitudinal Sydney Older Persons Study. A sub-sample also underwent a brain MRI scan (n=102, 53 males; 49 females). The relationships of three SORL1 single nucleotide polymorphisms (SNPs): rs4935774, rs2298813, rs1133174 with brain MRI measures, and AD were determined. RESULTS: Significant associations of SORL1 variants with cross-sectional brain MRI measures and AD were observed only when the sample was stratified by sex. The most common haplotype (H1), comprising rs4935774-T, rs2298813-G, and rs1133174-G alleles (T/G/G) was associated with whole brain atrophy in both males and females (p=0.012 & p=0.013; respectively). Only SNP rs1133174 was individually associated with hippocampal atrophy in males (p= 0.039) and females (p=0.025). Of the 292 participants, 111 had either probable or possible AD. A significant association of H1 with AD (p = 0.017) was observed in females. A nominally significant association of SNP rs1133174 with AD (p = 0.051) was also observed in the whole cohort. CONCLUSION: The results provide evidence that the association of polymophisms in the sortilin-related receptor gene (SORL1) with AD and its MRI biomarkers of brain and hippocampal atrophy are moderated by sex.