High-density SNP haplotyping suggests altered regulation of tau gene expression in progressive supranuclear palsy

Endoplasmic reticulum stress and its role in various neurodegenerative diseases

The Endoplasmic reticulum (ER), a critical cellular organelle, maintains cellular homeostasis by regulating calcium levels and orchestrating essential functions such as protein synthesis, folding, and lipid production. A pivotal aspect of ER function is its role in protein quality control. When misfolded proteins accumulate within the ER due to factors like protein folding chaperone dysfunction, toxicity, oxidative stress, or inflammation, it triggers the Unfolded protein response (UPR). The UPR involves the activation of chaperones like calnexin, calreticulin, glucose-regulating protein 78 (GRP78), and Glucose-regulating protein 94 (GRP94), along with oxidoreductases like protein disulphide isomerases (PDIs). Cells employ the Endoplasmic reticulum-associated degradation (ERAD) mechanism to counteract protein misfolding. ERAD disruption causes the detachment of GRP78 from transmembrane proteins, initiating a cascade involving Inositol-requiring kinase/endoribonuclease 1 (IRE1), Activating transcription factor 6 (ATF6), and Protein kinase RNA-like endoplasmic reticulum kinase (PERK) pathways. The accumulation and deposition of misfolded proteins within the cell are hallmarks of numerous neurodegenerative diseases. These aberrant proteins disrupt normal neuronal signalling and contribute to impaired cellular homeostasis, including oxidative stress and compromised protein degradation pathways. In essence, ER stress is defined as the cellular response to the accumulation of misfolded proteins in the endoplasmic reticulum, encompassing a series of signalling pathways and molecular events that aim to restore cellular homeostasis. This comprehensive review explores ER stress and its profound implications for the pathogenesis and progression of neurodegenerative diseases.

Association of Structural Forms of 17q21.31 with the Risk of Progressive Supranuclear Palsy and MAPT Sub-haplotypes

Importance

The chromosome 17q21.31 region, containing a 900 Kb inversion that defines H1 and H2 haplotypes, represents the strongest genetic risk locus in progressive supranuclear palsy (PSP). In addition to H1 and H2, various structural forms of 17q21.31, characterized by the copy number of α, β, and γ duplications, have been identified. However, the specific effect of each structural form on the risk of PSP has never been evaluated in a large cohort study.

Objective

To assess the association of different structural forms of 17q.21.31, defined by the copy numbers of α, β, and γ duplications, with the risk of PSP and MAPT sub-haplotypes.

Design setting and participants

Utilizing whole genome sequencing data of 1,684 (1,386 autopsy confirmed) individuals with PSP and 2,392 control subjects, a case-control study was conducted to investigate the association of copy numbers of α, β, and γ duplications and structural forms of 17q21.31 with the risk of PSP. All study subjects were selected from the Alzheimer's Disease Sequencing Project (ADSP) Umbrella NG00067.v7. Data were analyzed between March 2022 and November 2023.

Main outcomes and measures

The main outcomes were the risk (odds ratios [ORs]) for PSP with 95% CIs. Risks for PSP were evaluated by logistic regression models.

Results

The copy numbers of α and β were associated with the risk of PSP only due to their correlation with H1 and H2, while the copy number of γ was independently associated with the increased risk of PSP. Each additional duplication of γ was associated with 1.10 (95% CI, 1.04-1.17; P = 0.0018) fold of increased risk of PSP when conditioning H1 and H2. For the H1 haplotype, addition γ duplications displayed a higher odds ratio for PSP: the odds ratio increases from 1.21 (95%CI 1.10-1.33, P = 5.47 × 10-5) for H1β1γ1 to 1.29 (95%CI 1.16-1.43, P = 1.35 × 10-6) for H1β1γ2, 1.45 (95%CI 1.27-1.65, P = 3.94 × 10-8) for H1β1γ3, and 1.57 (95%CI 1.10-2.26, P = 1.35 × 10-2) for H1β1γ4. Moreover, H1β1γ3 is in linkage disequilibrium with H1c (R2 = 0.31), a widely recognized MAPT sub-haplotype associated with increased risk of PSP. The proportion of MAPT sub-haplotypes associated with increased risk of PSP (i.e., H1c, H1d, H1g, H1o, and H1h) increased from 34% in H1β1γ1 to 77% in H1β1γ4.

Conclusions and relevance

This study revealed that the copy number of γ was associated with the risk of PSP independently from H1 and H2. The H1 haplotype with more γ duplications showed a higher odds ratio for PSP and were associated with MAPT sub-haplotypes with increased risk of PSP. These findings expand our understanding of how the complex structure at 17q21.31 affect the risk of PSP.

Different MAPT haplotypes influence expression of total MAPT in postmortem brain tissue

The MAPT gene, encoding the microtubule-associated protein tau on chromosome 17q21.31, is result of an inversion polymorphism, leading to two allelic variants (H1 and H2). Homozygosity for the more common haplotype H1 is associated with an increased risk for several tauopathies, but also for the synucleinopathy Parkinson's disease (PD). In the present study, we aimed to clarify whether the MAPT haplotype influences expression of MAPT and SNCA, encoding the protein α-synuclein (α-syn), on mRNA and protein levels in postmortem brains of PD patients and controls. We also investigated mRNA expression of several other MAPT haplotype-encoded genes. Postmortem tissues from cortex of fusiform gyrus (ctx-fg) and of the cerebellar hemisphere (ctx-cbl) of neuropathologically confirmed PD patients (n = 95) and age- and sex-matched controls (n = 81) were MAPT haplotype genotyped to identify cases homozygous for either H1 or H2. Relative expression of genes was quantified using real-time qPCR; soluble and insoluble protein levels of tau and α-syn were determined by Western blotting. Homozygosity for H1 versus H2 was associated with increased total MAPT mRNA expression in ctx-fg regardless of disease state. Inversely, H2 homozygosity was associated with markedly increased expression of the corresponding antisense MAPT-AS1 in ctx-cbl. PD patients had higher levels of insoluble 0N3R and 1N4R tau isoforms regardless of the MAPT genotype. The increased presence of insoluble α-syn in PD patients in ctx-fg validated the selected postmortem brain tissue. Our findings in this small, but well controlled cohort of PD and controls support a putative biological relevance of tau in PD. However, we did not identify any link between the disease-predisposing H1/H1 associated overexpression of MAPT with PD status. Further studies are required to gain a deeper understanding of the potential regulatory role of MAPT-AS1 and its association to the disease-protective H2/H2 condition in the context of PD.

Phosphorylated Tau in Alzheimer's Disease and Other Tauopathies

Alzheimer's disease (AD) is the leading cause of dementia in elderly people. Amyloid beta (Aβ) deposits and neurofibrillary tangles are the major pathological features in an Alzheimer's brain. These proteins are highly expressed in nerve cells and found in most tissues. Tau primarily provides stabilization to microtubules in the part of axons and dendrites. However, tau in a pathological state becomes hyperphosphorylated, causing tau dysfunction and leading to synaptic impairment and degeneration of neurons. This article presents a summary of the role of tau, phosphorylated tau (p-tau) in AD, and other tauopathies. Tauopathies, including Pick's disease, frontotemporal dementia, corticobasal degeneration, Alzheimer's disease, argyrophilic grain disease, progressive supranuclear palsy, and Huntington's disease, are the result of misprocessing and accumulation of tau within the neuronal and glial cells. This article also focuses on current research on the post-translational modifications and genetics of tau, tau pathology, the role of tau in tauopathies and the development of new drugs targeting p-tau, and the therapeutics for treating and possibly preventing tauopathies.

Genetics of progressive supranuclear palsy in a Chinese population

BACKGROUND

Genetics plays an important role in progressive supranuclear palsy (PSP) and remains poorly understood. A detailed literature search identified 19 PSP-associated genes: MAPT, LRRK2, LRP10, DCTN1, GRN, NPC1, PARK, TARDBP, TBK1, BSN, GBA, STX6, EIF2AK3, MOBP, DUSP10, SLCO1A2, RUNX2, CXCR4, and APOE. To date, genetic studies on PSP have focused on Caucasian population. The gaps in PSP genetic study on East Asian populations need to be filled.

METHODS

Exon and flanking regions of the PSP-associated genes were sequenced in 104 patients with PSP and 488 healthy controls. Common variant-based association analysis and gene-based association tests of rare variants were performed using PLINK 1.9 and the sequence kernel association test-optimal, respectively. Additionally, the association of APOE and MAPT genotypes with PSP was evaluated. The above association analyses were repeated among probable PSP patients. Finally, PLINK 1.9 was used to test variants associated with the onset age of PSP.

RESULTS

A rare non-pathogenic variant of MAPT (c.425C > T,p.A142V) was detected in a PSP patient. No common variants were significantly associated with PSP. In both the rare-variant and the rare-damaging-variant groups, the combined effect for GBA reached statistical significance (p = 1.43 × 10^-3, p = 4.98 × 10^-4). The result between APOE, MAPT genotypes and PSP risk were inconsistent across all PSP group and probably PSP group.

CONCLUSIONS

The pathogenic variant in MAPT were uncommon in PSP patients. Moreover, GBA gene was likely to increase the risk of PSP, and GBA-associated diseases were beyond α-synucleinopathies. The association between APOE, MAPT and PSP is still unclear among the non-Caucasian population.

Tau and MAPT genetics in tauopathies and synucleinopathies

MAPT encodes the microtubule-associated protein tau, which is the main component of neurofibrillary tangles (NFTs) and found in other protein aggregates. These aggregates are among the pathological hallmarks of primary tauopathies such as frontotemporal dementia (FTD). Abnormal tau can also be observed in secondary tauopathies such as Alzheimer's disease (AD) and synucleinopathies such as Parkinson's disease (PD). On top of pathological findings, genetic data also links MAPT to these disorders. MAPT variations are a cause or risk factors for many tauopathies and synucleinopathies and are associated with certain clinical and pathological features in affected individuals. In addition to clinical, pathological, and genetic overlap, evidence also suggests that tau and alpha-synuclein may interact on the molecular level, and thus might collaborate in the neurodegenerative process. Understanding the role of MAPT variations in tauopathies and synucleinopathies is therefore essential to elucidate the role of tau in the pathogenesis and phenotype of those disorders, and ultimately to develop targeted therapies. In this review, we describe the role of MAPT genetic variations in tauopathies and synucleinopathies, several genotype-phenotype and pathological features, and discuss their implications for the classification and treatment of those disorders.

Latent trait modeling of tau neuropathology in progressive supranuclear palsy

Progressive supranuclear palsy (PSP) is the second most common neurodegenerative Parkinsonian disorder after Parkinson's disease, and is characterized as a primary tauopathy. Leveraging the considerable clinical and neuropathologic heterogeneity associated with PSP, we measured tau neuropathology as quantitative traits to perform a genome-wide association study (GWAS) within PSP to identify genes and biological pathways that underlie the PSP disease process. In 882 PSP cases, semi-quantitative scores for phosphorylated tau-immunoreactive coiled bodies (CBs), neurofibrillary tangles (NFTs), tufted astrocytes (TAs), and tau threads were documented from 18 brain regions, and converted to latent trait (LT) variables using the R ltm package. LT analysis utilizes a multivariate regression model that links categorical responses to unobserved covariates allowing for a reduction of dimensionality, generating a single, continuous variable to account for the multiple lesions and brain regions assessed. We first tested for association with PSP LTs and the top PSP GWAS susceptibility loci. Significant SNP/LT associations were identified at rs242557 (MAPT H1c sub-haplotype) with hindbrain CBs and rs1768208 (MOBP) with forebrain tau threads. Digital microscopy was employed to quantify phosphorylated tau burden in midbrain tectum and red nucleus in 795 PSP cases and tau burdens were used as quantitative phenotypes in GWAS. Top associations were identified at rs1768208 with midbrain tectum and red nucleus tau burden. Additionally, we performed a PSP LT GWAS on an initial cohort, a follow-up SNP panel (37 SNPs, P < 10-5) in an extended cohort, and a combined analysis. Top SNP/LT associations were identified at SNPs in or near SPTBN5/EHD4, SEC13/ATP2B2, EPHB1/PPP2R3A, TBC1D8, IFNGR1/OLIG3, ST6GAL1, HK1, CALB1, and SGCZ. Finally, testing for SNP/transcript associations using whole transcriptome and whole genome data identified significant expression quantitative trait loci at rs3088159/SPTBN5/EHD4 and rs154239/GHRL. Modeling tau neuropathology heterogeneity using LTs as quantitative phenotypes in a GWAS may provide substantial insight into biological pathways involved in PSP by affecting regional tau burden.

Genetics of Progressive Supranuclear Palsy: A Review

Progressive supranuclear palsy (PSP) is an atypical parkinsonism with prominent 4R-tau neuropathology, and the classical clinical phenotype is characterized by vertical supranuclear gaze palsy, unprovoked falls, akinetic-rigid syndrome and cognitive decline. Though PSP is generally regarded as sporadic, there is increasing evidence suggesting that a series of common and rare genetic variants impact on sporadic and familial forms of PSP. To date, more than 10 genes have been reported to show a potential association with PSP. Among these genes, the microtubule-associated protein tau (MAPT) is the risk locus with the strongest effect size on sporadic PSP in the case-control genome-wide association studies (GWAS). Additionally, MAPT mutations are the most common cause of familial PSP while the leucine-rich repeat kinase 2 (LRRK2) is a rare monogenic cause of PSP, and several other gene mutations may mimic the PSP phenotype, like the dynactin subunit 1 (DCTN1). In total, 15 MAPT mutations have been identified in cases with PSP, and the mean age at onset is much earlier than in cases carrying LRRK2 or DCTN1 mutations. GWAS have further identified several risk loci of PSP, proposing molecular pathways related to PSP. The present review focused on genetic studies on PSP and summarized genetic factors of PSP, which may help to elucidate the underlying pathogenesis and provide new perspectives for therapeutic strategies.

Prion-Like Propagation Mechanisms in Tauopathies and Traumatic Brain Injury: Challenges and Prospects

The accumulation of tau protein in the form of filamentous aggregates is a hallmark of many neurodegenerative diseases such as Alzheimer's disease (AD) and chronic traumatic encephalopathy (CTE). These dementias share traumatic brain injury (TBI) as a prominent risk factor. Tau aggregates can transfer between cells and tissues in a "prion-like" manner, where they initiate the templated misfolding of normal tau molecules. This enables the spread of tau pathology to distinct parts of the brain. The evidence that tauopathies spread via prion-like mechanisms is considerable, but work detailing the mechanisms of spread has mostly used in vitro platforms that cannot fully reveal the tissue-level vectors or etiology of progression. We review these issues and then briefly use TBI and CTE as a case study to illustrate aspects of tauopathy that warrant further attention in vivo. These include seizures and sleep/wake disturbances, emphasizing the urgent need for improved animal models. Dissecting these mechanisms of tauopathy progression continues to provide fresh inspiration for the design of diagnostic and therapeutic approaches.

Association of MAPT subhaplotypes with clinical and demographic features in Parkinson's disease

Objective

To determine whether distinct microtubule‐associated protein tau MAPT H1 subhaplotypes are associated with clinical and demographic features in Parkinson’s disease.

Methods

A retrospective cohort study included 855 unrelated Caucasian patients with Parkinson’s disease who were seen by Movement Disorder specialists at the Mayo Clinic Florida between 1998 and 2016. The primary outcome measures were specific demographic and clinical features of Parkinson’s disease, including age at onset, disease progression, survival, motor signs, dementia, dystonia, dyskinesia, autonomic dysfunction, impulse control disorder, psychiatric features, REM sleep behavior disorder, restless legs syndrome, and Parkinson’s disease subtype. Specific clinical features were measured at the initial visit and most recent visit. These outcomes were assessed for association with MAPT H1 subhaplotypes, which were defined by six haplotype tagging variants.

Results

Median onset age was 64 years (range: 22‐94 years); 548 (64%) of patients were male. Significant associations (P < 0.0029) were observed between MAPT H1b and orthostatic hypotension (OR = 1.72, P = 0.001); between H1j and rest tremor (OR = 0.15; P < 0.001) as well as REM sleep behavior disorder (OR = 3.87, P < 0.001); between H1r and bradykinesia (OR = 0.11; P < 0.001); and between H1v and restless legs syndrome (OR = 4.02, P = 0.002).

Interpretation

Four MAPT H1 subhaplotypes, but not the H2 haplotype, were significantly associated with specific clinical features in Parkinson’s disease. MAPT haplotypic structure may explain some of the phenotypic variability in disease. Replication of our findings will be critical to fully resolve the Parkinson’s disease risk association signal at Chr17q21.

Genetics of Chronic Traumatic Encephalopathy

Although chronic traumatic encephalopathy (CTE) garners substantial attention in the media and there have been marked scientific advances in the last few years, much remains unclear about the role of genetic risk in CTE. Two athletes with comparable contact-sport exposure may have varying amounts of CTE neuropathology, suggesting that other factors, including genetics, may contribute to CTE risk and severity. In this review, we explore reasons why genetics may be important for CTE, concepts in genetic study design for CTE (including choosing controls, endophenotypes, gene by environment interaction, and epigenetics), implicated genes in CTE (including APOE, MAPT, and TMEM106B), and whether predictive genetic testing for CTE should be considered.

MAPT rs242557 variant is associated with hippocampus tau uptake on 18F-AV-1451 PET in non-demented elders

The microtubule-associated protein tau gene (MAPT) rs242557 variant is associated with multiple tauopathies and dementia. This study investigated whether it was correlated with brain tau-PET uptake in non-demented elders. Ninety non-demented elders were identified from the Alzheimer's Disease Neuroimaging Initiative cohort. We compared standardized uptake value ratios (SUVRs) of tau-PET tracer ¹⁸F-AV-1451 between rs242557 variant carriers and non-carriers in 25 regions of interest (ROIs). The minor allele A was associated with increased hippocampus ¹⁸F-AV-1451 uptake in non-demented elders (left: β = 0.111, Bonferroni corrected p = 0.035; right: β = 0.103, Bonferroni corrected p = 0.031). Aβ-positive participants (left: β = 0.206, Bonferroni corrected p = 0.029; right: β = 0.198, Bonferroni corrected p = 0.035) and APOE ε4 non-carriers (left: β = 0.140, Bonferroni corrected p = 0.006; right: β = 0.134, Bonferroni corrected p = 0.004) exhibited approximately the same findings in hippocampus. Considering no obvious associations in other regions, we confirmed the significant correlation of MAPT rs242557 risk variant with increased hippocampus tau deposition in non-demented elders. With higher magnitude signals in the hippocampus that is more likely to be uniquely affected in AD, the tau PET ligand ¹⁸F-AV-1451 seemed to possess a specific binding property for AD-like tau pathology.

Association of MAPT Subhaplotypes With Risk of Progressive Supranuclear Palsy and Severity of Tau Pathology

Importance

The association between the microtubule-associated protein tau (MAPT) H1 haplotype and the risk of progressive supranuclear palsy (PSP) has been well documented. However, the specific H1 subhaplotypes that drive the association have not been evaluated in large studies, nor have they been studied in relation to neuropathologic severity of disease.

Objective

To comprehensively evaluate the associations of MAPT haplotypes with the risk of PSP and the severity of tau pathology using a large series of neuropathologically confirmed PSP cases.

Design, Setting, and Participants

A case-control study was used to investigate the associations between MAPT haplotypes and the risk of PSP, and a case series was conducted for examination of associations of MAPT haplotypes with the severity of tau pathology. All 802 neuropathologically confirmed PSP cases were obtained from a neurodegenerative disorders brain bank between January 1, 1998, and December 31, 2013, and 1312 clinical controls were obtained from the neurology department of the Mayo Clinic. Statistical analysis was performed from February 17 to December 12, 2018.

Main Outcomes and Measures

Presence of PSP in case-control analysis and semiquantitative tau pathology scores for neurofibrillary tangles, neuropil threads, tufted astrocytes, and oligodendroglial coiled bodies in PSP cases.

Results

For 802 patients with PSP (376 women and 426 men), the median age at death was 75 years (range, 52-98 years). For 1312 controls (701 women and 611 men), the median age at blood collection was 69 years (range, 45-92 years). After adjustment for multiple testing, known associations with risk of PSP were observed for the H2 and H1c haplotypes. Novel associations with PSP were observed for 3 H1 subhaplotypes, including H1d (odds ratio, 1.86; 95% CI, 1.43-2.42; P = 2 × 10-6), H1g (odds ratio, 3.64; 95% CI, 2.04-6.50; P = 2 × 10-6), and H1o (odds ratio, 2.60; 95% CI, 1.63-4.16; P = 2 × 10-5). Although not significant after multiple testing adjustment, 3 of these PSP risk haplotypes (H2, H1c, and H1d) were also nominally associated with measures of severity of tau pathology in PSP cases. Nominally significant associations with severity of tau pathology were also noted for the H1e and H1q haplotypes.

Conclusions and Relevance

This study has identified novel associations with risk of PSP for 3 MAPT H1 subhaplotypes. In addition, potential weaker associations between several haplotypes (including several PSP risk haplotypes) and severity of tau pathology were observed. These findings expand the current understanding of the role of MAPT haplotypic variation in susceptibility to and neuropathologic severity of PSP.

Neglected Functions of TFCP2/TFCP2L1/UBP1 Transcription Factors May Offer Valuable Insights into Their Mechanisms of Action

In recent years, the TFCP2 (transcription factor cellular promoter 2)/TFCP2L1 (TFCP2-like 1)/UBP1 (upstream binding protein 1) subfamily of transcription factors has been attracting increasing attention in the scientific community. These factors are very important in cancer, Alzheimer’s disease, and other human conditions, and they can be attractive targets for drug development. However, the interpretation of experimental results is complicated, as in principle, any of these factors could substitute for the lack of another. Thus, studying their hitherto little known functions should enhance our understanding of mechanisms of their functioning, and analogous mechanisms might govern their functioning in medically relevant contexts. For example, there are numerous parallels between placental development and cancer growth; therefore, investigating the roles of TFCP2, TFCP2L1, and UBP1 in the placenta may help us better understand their functioning in cancer, as is evidenced by the studies of various other proteins and pathways. Our review article aims to call the attention of the scientific community to these neglected functions, and encourage further research in this field. Here, we present a systematic review of current knowledge of the TFCP2/TFCP2L1/UBP1 subfamily in reproduction, embryonic development, renal function, blood-pressure regulation, brain function, and other processes, where their involvement has not been studied much until now.

Meta-analysis of the association between variants in MAPT and neurodegenerative diseases

Microtubule-associated protein tau (MAPT) gene is compelling among the susceptibility genes of neurodegenerative diseases which include Alzheimer’s disease (AD), Parkinson’s disease (PD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). Our meta-analysis aimed to find the association between MAPT and the risk of these diseases. Published literatures were retrieved from MEDLINE and other databases, and 82 case-control studies were recruited. Six haplotype tagging single-nucleotide polymorphisms (rs1467967, rs242557, rs3785883, rs2471738, del-In9 and rs7521) and haplotypes (H2 and H1c) were significantly associated with the above diseases. The odds ratios (ORs) and 95 % confidence intervals (CIs) were evaluated by comparison in minor and major allele frequency using the R software. This study demonstrated that different variants in MAPT were associated with AD (rs2471738: OR= 1.04, 95%CI = 1.00 - 1.09; H2: OR = 0.94, 95% CI = 0.91 - 0.97), PD (H2: OR = 0.76, 95% CI = 0.74 - 0.79), PSP (rs242557: OR = 1. 96, 95% CI = 1. 71 - 2.25; rs2471738: OR = 1. 85, 95% CI = 1. 48 - 2.31; H2: OR = 0.20, 95% CI = 0.18 - 0.23), CBD (rs242557: OR = 2.51, 95%CI = 1. 66 -3.78; rs2471738: OR = 2.07, 95%CI = 1. 32 -3.23; H2: OR = OR = 0.30, 95% CI = 0.23 - 0.41) and ALS (H2: OR = 0.92, 95% CI = 0.86 - 0.98) instead of FTD (H2: OR = 1.02, 95% CI = 0.78 - 1.32). In conclusion, MAPT is associated with risk of neurodegenerative diseases, suggesting crucial roles of tau in neurodegenerative processes.

Clinical variability and onset age modifiers in an extended Belgian GRN founder family

We previously reported a granulin (GRN) null mutation, originating from a common founder, in multiple Belgian families with frontotemporal dementia. Here, we used data of a 10-year follow-up study to describe in detail the clinical heterogeneity observed in this extended founder pedigree. We identified 85 patients and 40 unaffected mutation carriers, belonging to 29 branches of the founder pedigree. Most patients (74.4%) were diagnosed with frontotemporal dementia, while others had a clinical diagnosis of unspecified dementia, Alzheimer's dementia or Parkinson's disease. The observed clinical heterogeneity can guide clinical diagnosis, genetic testing, and counseling of mutation carriers. Onset of initial symptomatology is highly variable, ranging from age 45 to 80 years. Analysis of known modifiers, suggested effects of GRN rs5848, microtubule-associated protein tau H1/H2, and chromosome 9 open reading frame 72 G₄C₂ repeat length on onset age but explained only a minor fraction of the variability. Contrary, the extended GRN founder family is a valuable source for identifying other onset age modifiers based on exome or genome sequences. These modifiers might be interesting targets for developing disease-modifying therapies.

Interaction with the MAPT H1H1 Genotype Increases Dementia Risk in APOE ε4 Carriers in a Population of Southern India

BACKGROUND

This study delineates the role of the interaction of apolipoprotein E (APOE) and MAPT alleles in contributing to disease risks of dementia in a southern Indian population.

METHODS

A sample of 419 patients comprising Alzheimer's disease (AD; n = 156), mild cognitive impairment (MCI; n = 87), frontotemporal dementia (FTD; n = 127), vascular dementia (VD; n = 37), and dementia with Lewy bodies (DLB; n = 12) was analysed in comparison with a control group (n = 138). APOE genotyping and MAPT haplotyping were performed on all study subjects.

RESULTS

Multivariate logistic regression analysis showed that variability on the APOE locus influenced the relative risk of dementia in the study population. The APOE ε4 allele increased the disease risk most significantly for AD (OR = 3.468, p < 0.0001) and MCI (OR = 2.901, p < 0.0001). The APOE ε2 allele remained protective for AD (OR = 0.205, p < 0.05). For FTD, VD, and DLB, the APOE ε4 allele was ineffectual in modulating disease risk. The MAPT H1 haplotype was not an overrepresented marker of neurodegenerative diseases. The H1H1 genotype had an additive effect in contributing to either disease risk in combination with the APOE ε4 allele or protection in combination with the APOE ε2 or ε3 allele.

CONCLUSIONS

This study is a reappraisal of the strong association of APOE variability with AD in southern India when compared to other dementia groups, while the transcriptional differences between MAPT haplotypes have a limited role in Indian dementia patients.

Slowly progressive dementia caused by MAPT R406W mutations: longitudinal report on a new kindred and systematic review

Background

The MAPT c.1216C > T (p.Arg406Trp; R406W) mutation is a known cause of frontotemporal dementia with Parkinsonism linked to chromosome 17 tau with Alzheimer’s disease-like clinical features.

Methods

We compiled clinical data from a new Swedish kindred with R406W mutation. Seven family members were followed longitudinally for up to 22 years. Radiological examinations were performed in six family members and neuropathological examinations in three. We systematically reviewed the literature and compiled clinical, radiological, and neuropathological data on 63 previously described R406W heterozygotes and 3 homozygotes.

Results

For all cases combined, the median age of onset was 56 years and the median disease duration was 13 years. Memory impairment was the most frequent symptom, behavioral disturbance and language impairment were less common, and Parkinsonism was rare. Disease progression was most often slow. The most frequent clinical diagnosis was Alzheimer’s disease. R406W homozygotes had an earlier age at onset and a higher frequency of behavioral symptoms and Parkinsonism than heterozygotes. In the new Swedish kindred, a consistent imaging finding was ventromedial temporal lobe atrophy, which was evident also in early disease stages as a widening of the collateral sulcus with ensuing atrophy of the parahippocampal gyrus. Unlike previously published R406W carriers, all three autopsied patients from the novel family showed neuropathological similarities with progressive supranuclear palsy, with predominant four-repeat (exon 10+) tau isoform (4R) tauopathy and neurofibrillary tangles accentuated in the basal-medial temporal lobe. Amyloid-β pathology was absent.

Conclusions

Dominance of 4R over three-repeat (exon 10−) tau isoforms contrasts with earlier reports of R406W patients and was not sufficiently explained by the presence of H1/H2 haplotypes in two of the autopsied patients. R406W patients often show a long course of disease with marked memory deficits. Both our neuropathological results and our imaging findings revealed that the ventromedial temporal lobes were extensively affected in the disease. We suggest that this area may represent the point of origin of tau deposition in this disease with relatively isolated tauopathy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13195-017-0330-2) contains supplementary material, which is available to authorized users.

Atypical parkinsonian syndromes: a general neurologist's perspective

The differential diagnosis of atypical parkinsonian syndromes is challenging. These severe and often rapidly progressive neurodegenerative disorders are clinically heterogeneous and show significant phenotypic overlap. Here, clinical, imaging, neuropathological and genetic features of multiple system atrophy, progressive supranuclear palsy, corticobasal degeneration and frontotemporal lobar degeneration (FTLD) are reviewed. The terms corticobasal degeneration and FTLD refer to pathologically confirmed cases of corticobasal syndrome and frontotemporal dementia (FTD). Frontotemporal lobar degeneration clinically presents as the behavioral variant FTD, semantic variant primary progressive aphasia (PPA), non-fluent agrammatic variant PPA, logopenic variant PPA and FTD associated with motor neuron disease. While progressive supranuclear palsy and corticobasal syndrome have been called Parkinson-plus syndromes in the past, they are now classified as FTD-related disorders, reflecting that they pathologically differ from α-synucleinopathies like multiple system atrophy and Parkinson disease. The contribution of genetic factors to atypical parkinsonian syndromes is increasingly recognized. Genes involved in the etiology of FTLD include MAPT, GRN and C9orf72. Novel neuroimaging techniques, including tau positron emission tomography imaging, are being investigated. Multimodal magnetic resonance imaging approaches and automated magnetic resonance imaging volume segmentation techniques are being evaluated for optimized differential diagnosis. Current treatment options are symptomatic, and disease modifying therapies are under active investigation.

Current Understanding of Neurodegenerative Diseases Associated With the Protein Tau

Primary tauopathies are a group of neurodegenerative diseases in which tau is believed to be the major contributing factor of the neurodegenerative process. In primary tauopathies, there is a disassociation between tau (a microtubule-associated protein) and microtubules as a result of tau hyperphosphorylation. This disassociation between tau and microtubules results in tau fibrillization and inclusion formation as well as in microtubule dysfunction. There are different clinical syndromes associated with different primary tauopathies, and some clinical syndromes can be associated with multiple primary tauopathies. Hence, although some clinical syndromes are highly specific and almost diagnostic of a primary tauopathy, many are not, making it difficult to diagnose a primary tauopathy. Recently, radioligands that bind to tau and can be combined with positron emission tomography to detect fibrillary tau antemortem have been developed, although preliminary data suggest that these ligands may not be sensitive in detecting tau associated with many primary tauopathies. Another recent advancement in the field is evidence suggesting that tau may exhibit properties similar to those of prions, although infective transmission has not been shown. There have been a few clinical trials targeting tau and microtubule dysfunction, although none have had any disease-modifying effects. Understanding tau biology is critical to the development of pharmacological agents that could have disease-modifying effects on primary tauopathies.

A clinicopathological approach to the diagnosis of dementia

The most definitive classification systems for dementia are based on the underlying pathology which, in turn, is categorized largely according to the observed accumulation of abnormal protein aggregates in neurons and glia. These aggregates perturb molecular processes, cellular functions and, ultimately, cell survival, with ensuing disruption of large-scale neural networks subserving cognitive, behavioural and sensorimotor functions. The functional domains affected and the evolution of deficits in these domains over time serve as footprints that the clinician can trace back with various levels of certainty to the underlying neuropathology. The process of phenotyping and syndromic classification has substantially improved over decades of careful clinicopathological correlation, and through the discovery of in vivo biomarkers of disease. Here, we present an overview of the salient features of the most common dementia subtypes - Alzheimer disease, vascular dementia, frontotemporal dementia and related syndromes, Lewy body dementias, and prion diseases - with an emphasis on neuropathology, relevant epidemiology, risk factors, and signature signs and symptoms.

Genome-wide association study identifies MAPT locus influencing human plasma tau levels

OBJECTIVE

To identify genetic loci associated with plasma tau concentrations in healthy elders and individuals with Alzheimer disease.

METHODS

Four hundred sixty-three non-Hispanic white individuals exceeding quality control criteria were included from the Alzheimer's Disease Neuroimaging Initiative (ADNI-1) cohort. Association of plasma tau with genetic polymorphisms was performed with a linear regression model. Significant associations were validated in an independent replication cohort consisting of 431 healthy elders or individuals with mild cognitive impairment recruited from the University of California, San Francisco Memory and Aging Center.

RESULTS

The minor allele (A) of rs242557 in the microtubule-associated protein tau gene (MAPT) was associated with higher plasma tau levels at genome-wide significance (p = 4.85 × 10^-9, empiric family-wise error corrected p = 0.0024) in a dose-dependent fashion. This association was also observed in the replication cohort (p = 1.0 × 10^-5; joint analysis p = 1.2 × 10^-12). Single nucleotide polymorphisms near PARK2 (rs2187213) (p = 6.15 × 10^-6), IL2RA (rs7072793, rs7073236) (p = 7.89 × 10^-6), and an intergenic locus on 9p21.3 (rs7047280) (p = 8.13 × 10^-6) were identified as suggestive loci associated with plasma tau levels.

CONCLUSIONS

MAPT H1c haplotype (rs242557) has previously been identified as a genetic risk factor for progressive supranuclear palsy and corticobasal degeneration. The current findings suggest that plasma tau concentration could be an endophenotype for identifying risk for 4-repeat tauopathies in older individuals.

Tau mis-splicing in the pathogenesis of neurodegenerative disorders

Tau proteins, which stabilize the structure and regulate the dynamics of microtubules, also play important roles in axonal transport and signal transduction. Tau proteins are missorted, aggregated, and found as tau inclusions under many pathological conditions associated with neurodegenerative disorders, which are collectively known as tauopathies. In the adult human brain, tau protein can be expressed in six isoforms due to alternative splicing. The aberrant splicing of tau pre-mRNA has been consistently identified in a variety of tauopathies but is not restricted to these types of disorders as it is also present in patients with non-tau proteinopathies and RNAopathies. Tau mis-splicing results in isoform-specific impairments in normal physiological function and enhanced recruitment of excessive tau isoforms into the pathological process. A variety of factors are involved in the complex set of mechanisms underlying tau mis-splicing, but variation in the cis-element, methylation of the MAPT gene, genetic polymorphisms, the quantity and activity of spliceosomal proteins, and the patency of other RNA-binding proteins, are related to aberrant splicing. Currently, there is a lack of appropriate therapeutic strategies aimed at correcting the tau mis-splicing process in patients with neurodegenerative disorders. Thus, a more comprehensive understanding of the relationship between tau mis-splicing and neurodegenerative disorders will aid in the development of efficient therapeutic strategies for patients with a tauopathy or other, related neurodegenerative disorders. [BMB Reports 2016; 49(8): 405-413]

Gene expression, methylation and neuropathology correlations at progressive supranuclear palsy risk loci

To determine the effects of single nucleotide polymorphisms (SNPs) identified in a genome-wide association study of progressive supranuclear palsy (PSP), we tested their association with brain gene expression, CpG methylation and neuropathology. In 175 autopsied PSP subjects, we performed associations between seven PSP risk variants and temporal cortex levels of 20 genes in-cis, within ±100 kb. Methylation measures were collected using reduced representation bisulfite sequencing in 43 PSP brains. To determine whether SNP/expression associations are due to epigenetic modifications, CpG methylation levels of associated genes were tested against relevant variants. Quantitative neuropathology endophenotypes were tested for SNP associations in 422 PSP subjects. Brain levels of LRRC37A4 and ARL17B were associated with rs8070723; MOBP with rs1768208 and both ARL17A and ARL17B with rs242557. Expression associations for LRRC37A4 and MOBP were available in an additional 100 PSP subjects. Meta-analysis revealed highly significant associations for PSP risk alleles of rs8070723 and rs1768208 with higher LRRC37A4 and MOBP brain levels, respectively. Methylation levels of one CpG in the 3' region of ARL17B associated with rs242557 and rs8070723. Additionally, methylation levels of an intronic ARL17A CpG associated with rs242557 and that of an intronic MOBP CpG with rs1768208. MAPT and MOBP region risk alleles also associated with higher levels of neuropathology. Strongest associations were observed for rs242557/coiled bodies and tufted astrocytes; and for rs1768208/coiled bodies and tau threads. These findings suggest that PSP variants at MAPT and MOBP loci may confer PSP risk via influencing gene expression and tau neuropathology. MOBP, LRRC37A4, ARL17A and ARL17B warrant further assessment as candidate PSP risk genes. Our findings have implications for the mechanism of action of variants at some of the top PSP risk loci.

The Role of MAPT Haplotype H2 and Isoform 1N/4R in Parkinsonism of Older Adults

Background and Objective

Recently, we have shown that the Parkinson’s disease (PD) susceptibility locus MAPT (microtubule associated protein tau) is associated with parkinsonism in older adults without a clinical diagnosis of PD. In this study, we investigated the relationship between parkinsonian signs and MAPT transcripts by assessing the effect of MAPT haplotypes on alternative splicing and expression levels of the most common isoforms in two prospective clinicopathologic studies of aging.

Materials and Methods

using regression analysis, controlling for age, sex, study and neuropathology, we evaluated 976 subjects with clinical, genotyping and brain pathology data for haplotype analysis. For transcript analysis, we obtained MAPT gene and isoform-level expression from the dorsolateral prefrontal cortex for 505 of these subjects.

Results

The MAPT H2 haplotype was associated with lower total MAPT expression (p = 1.2x10-14) and global parkinsonism at both study entry (p = 0.001) and proximate to death (p = 0.050). Specifically, haplotype H2 was primarily associated with bradykinesia in both assessments (p<0.001 and p = 0.008). MAPT total expression was associated with age and decreases linearly with advancing age (p<0.001). Analysing MAPT alternative splicing, the expression of 1N/4R isoform was inversely associated with global parkinsonism (p = 0.008) and bradykinesia (p = 0.008). Diminished 1N/4R isoform expression was also associated with H2 (p = 0.001).

Conclusions

Overall, our results suggest that age and H2 are associated with higher parkinsonism score and decreased total MAPT RNA expression. Additionally, we found that H2 and parkinsonism are associated with altered expression levels of specific isoforms. These findings may contribute to the understanding of the association between MAPT locus and parkinsonism in elderly subjects and in some extent to age-related neurodegenerative diseases.

MAPT haplotype diversity in multiple system atrophy

INTRODUCTION

Multiple system atrophy (MSA) is a rare progressive neurodegenerative disorder. MSA was originally considered exclusively sporadic but reports of association with genes such as SNCA, COQ2 and LRRK2 have demonstrated that there is a genetic contribution to the disease. MAPT has been associated with several neurodegenerative diseases and we previously reported a protective association of the MAPT H2 haplotype with MSA in 61 pathologically confirmed cases.

METHODS

In the present study, we assessed the full MAPT haplotype diversity in MSA patients using six MAPT tagging SNPs. We genotyped a total of 127 pathologically confirmed MSA cases, 86 patients with clinically diagnosed MSA and 1312 controls.

RESULTS

We identified four significant association signals in our pathologically confirmed cases, two from the protective haplotypes H2 (MSA:16.2%,

CONTROLS

22.7%, p = 0.024) and H1E (MSA:3.0%,

CONTROLS

9.0%, p = 0.014), and two from the rare risk haplotypes H1x (MSA:3.7%,

CONTROLS

1.3%, p = 0.030) and H1J (MSA:3.0%,

CONTROLS

0.9%, p = 0.021). We evaluated the association of MSA subtypes with the common protective H2 haplotype and found a significant difference with controls for MSA patients with some degree of MSA-C (MSA-C or MSA-mixed), for whom H2 occurred in only 8.6% of patients in our pathologically confirmed series (P < 0.0001).

CONCLUSIONS

Our findings provide further evidence that MAPT variation is associated with risk of MSA. Interestingly, our results suggest a greater effect size in the MSA-C compared to MSA-P for H2. Additional genetic studies in larger pathologically confirmed MSA series and meta-analytic studies will be needed to fully assess the role of MAPT and other genes in MSA.

Tremor in progressive supranuclear palsy

INTRODUCTION

Tremor is thought to be a rare feature of progressive supranuclear palsy (PSP).

METHODS

We retrospectively reviewed the database of the CurePSP brain bank at Mayo Clinic Florida to retrieve all available clinical information for PSP patients. All patients underwent a standard neuropathological assessment and an immunohistochemical evaluation for tau and α-synuclein. DNA was genotyped for the MAPT H1/H2 haplotype.

RESULTS

Of the 375 PSP patients identified, 344 had a documented presence or absence of tremor, which included 146 (42%) with tremor, including 29 (20%) with postural/action tremors, 16 (11%) with resting tremor, 7 (5%) with intention tremor, 20 (14%) with a combination of different types of tremor, and 74 (51%) patients who had tremor at some point during their illness, but details were unavailable. The tremor severity of 96% of the patients (54/55) who had this data was minimal to mild. The probability of observing a tremor during a neurological examination during the patient's illness was estimated to be ∼22%. PSP patients with postural/action tremors and PSP patients with resting tremor responded to carbidopa-levodopa therapy more frequently than PSP patients without tremor, although the therapy response was always transient. There were no significant differences in pathological findings between the tremor groups.

CONCLUSIONS

Tremor is an inconspicuous feature of PSP; however, 42% (146/344) of the PSP patients in our study presented some form of tremor. Because there is no curative therapy for PSP, carbidopa/levodopa therapy should be tried for patients with postural, action, and resting tremor.

The Genetic Basis of Cognitive Impairment and Dementia in Parkinson's Disease

Cognitive dysfunction is a common feature of Parkinson's disease (PD) with mild cognitive impairment affecting around a quarter of patients in the early stages of their disease, and approximately half developing dementia by 10 years from diagnosis. However, the pattern of cognitive impairments and their speed of evolution vary markedly between individuals. While some of this variability may relate to extrinsic factors and comorbidities, inherited genetic heterogeneity is also known to play an important role. A number of common genetic variants have been identified, which contribute to cognitive function in PD, including variants in catechol-O-methyltransferase, microtubule-associated protein tau, and apolipoprotein E. Furthermore, rarer mutations in glucocerebrosidase and α-synuclein and are strongly associated with dementia risk in PD. This review explores the functional impact of these variants on cognition in PD and discusses how such genotype-phenotype associations provide a window into the mechanistic basis of cognitive heterogeneity in this disorder. This has consequent implications for the development of much more targeted therapeutic strategies for cognitive symptoms in PD.

Glycation alter the process of Tau phosphorylation to change Tau isoforms aggregation property

The risk of tauopathies depends in part on the levels and modified composition of six Tau isoforms in the human brain. Abnormal phosphorylation of the Tau protein and the shift of the ratio of 3R Tau to 4R Tau are presumed to result in neurofibrillary pathology and neurodegeneration. Glycation has recently been linked to dementia and metabolic syndrome. To determine the contribution of Tau protein glycation and phosphorylation on Tau aggregation propensity, the assembled kinetics were examined in vitro using Thioflavin T fluorescence assays. We found that glycation and phosphorylation have different effects on aggregation propensity in different Tau isoforms. Different Tau proteins play important parts in each tauopathies, but 3R0N, fetal Tau protein, has no effect on tauopathies. Conversely, 4R2N has more modified sites and a higher tendency to aggregate, playing the most important role in 4R tauopathies. Finally, Glycation, which could modulate Tau phosphorylation, may occur before any other modification. It also regulates the 3R to 4R ratio and promotes 4R2N Tau protein aggregation. Decreasing the sites of glycation, as well as shifting other Tau proteins to 3R0N Tau proteins has potential therapeutic implications for tauopathies.

Chronic traumatic encephalopathy pathology in a neurodegenerative disorders brain bank

Chronic traumatic encephalopathy (CTE) is a progressive neurodegenerative disorder linked to repetitive traumatic brain injury (TBI) and characterized by deposition of hyperphosphorylated tau at the depths of sulci. We sought to determine the presence of CTE pathology in a brain bank for neurodegenerative disorders for individuals with and without a history of contact sports participation. Available medical records of 1721 men were reviewed for evidence of past history of injury or participation in contact sports. Subsequently, cerebral cortical samples were processed for tau immunohistochemistry in cases with a documented history of sports exposure as well as age- and disease-matched men and women without such exposure. For cases with available frozen tissue, genetic analysis was performed for variants in APOE, MAPT, and TMEM106B. Immunohistochemistry revealed 21 of 66 former athletes had cortical tau pathology consistent with CTE. CTE pathology was not detected in 198 individuals without exposure to contact sports, including 33 individuals with documented single-incident TBI sustained from falls, motor vehicle accidents, domestic violence, or assaults. Among those exposed to contact sports, those with CTE pathology did not differ from those without CTE pathology with respect to noted clinicopathologic features. There were no significant differences in genetic variants for those with CTE pathology, but we observed a slight increase in MAPT H1 haplotype, and there tended to be fewer homozygous carriers of the protective TMEM106B rs3173615 minor allele in those with sports exposure and CTE pathology compared to those without CTE pathology. In conclusion, this study has identified a small, yet significant, subset of individuals with neurodegenerative disorders and concomitant CTE pathology. CTE pathology was only detected in individuals with documented participation in contact sports. Exposure to contact sports was the greatest risk factor for CTE pathology. Future studies addressing clinical correlates of CTE pathology are needed.

Variants in GBA, SNCA, and MAPT influence Parkinson disease risk, age at onset, and progression

Multiple genetic variants have been linked to risk of Parkinson disease (PD), but known mutations do not explain a large proportion of the total PD cases. Similarly, multiple loci have been associated with PD risk by genome-wide association studies (GWAS). The influence that genetic factors confer on phenotypic diversity remains unclear. Few studies have been performed to determine whether the GWAS loci are also associated with age at onset (AAO) or motor progression. We used 2 PD case-control data sets (Washington University and the Parkinson's Progression Markers Initiative) to determine whether polymorphisms located at the GWAS top hits (GBA, ACMSD/TMEM163, STK39, MCCC1/LAMP3, GAK/TMEM175, SNCA, and MAPT) show association with AAO or motor progression. We found associations between single nucleotide polymorphisms at the GBA and MAPT loci and PD AAO and progression. These findings reinforce the complex genetic basis of PD and suggest that distinct genes and variants explain the genetic architecture of PD risk, onset, and progression.

Genetics of Progressive Supranuclear Palsy

Progressive supranuclear palsy (PSP) is a neurodegenerative syndrome that is clinically characterized by progressive postural instability, supranuclear gaze palsy, parkinsonism and cognitive decline. Pathologically, diagnosis of PSP is based on characteristic features, such as neurofibrillary tangles, neutrophil threads, tau-positive astrocytes and their processes in basal ganglia and brainstem, and the accumulation of 4 repeat tau protein. PSP is generally recognized as a sporadic disorder; however, understanding of genetic background of PSP has been expanding rapidly. Here we review relevant publications to outline the genetics of PSP. Although only small number of familial PSP cases have been reported, the recognition of familial PSP has been increasing. In some familial cases of clinically probable PSP, PSP pathologies were confirmed based on NINDS neuropathological diagnostic criteria. Several mutations in MAPT, the gene that causes a form of familial frontotemporal lobar degeneration with tauopathy, have been identified in both sporadic and familial PSP cases. The H1 haplotype of MAPT is a risk haplotype for PSP, and within H1, a sub-haplotype (H1c) is associated with PSP. A recent genome-wide association study on autopsyproven PSP revealed additional PSP risk alleles in STX6 and EIF2AK3. Several heredodegenerative parkinsonian disorders are referred to as PSP-look-alikes because their clinical phenotype, but not their pathology, mimics PSP. Due to the fast development of genomics and bioinformatics, more genetic factors related to PSP are expected to be discovered. Undoubtedly, these studies will provide a better understanding of the pathogenesis of PSP and clues for developing therapeutic strategies.

A geographical cluster of progressive supranuclear palsy in northern France

OBJECTIVE

To describe a cluster of progressive supranuclear palsy (PSP) in northern France. PSP has not been reported in geographical, temporal, or occupational clusters. A unit of Neurology and Neurogeriatrics opened in 2005 at the Centre Hospitalier de Wattrelos, serving the population of Wattrelos and Leers (combined population 51,551) and parts of neighboring towns. For most of the 20th century, this area was a center for chromate and phosphate ore processing, textile dyeing, and tanning. Significant industrial waste persists close to residential areas.

METHODS

From 2005 to 2014, 92 patients with PSP at Centre Hospitalier de Wattrelos were identified and studied. Detailed residential data were available in the medical records. Eighty cases have had magnetic resonance head scanning and 60 have died, of whom 13 have been examined neuropathologically.

RESULTS

The ratio of observed to expected PSP incidence over the period 2005 to 2012 was 12.3 (95% confidence interval: 7.4-35.9). Mean onset age was 74.3 years. The Richardson syndrome/PSP-parkinsonism ratio was 43%/42%. Four other phenotypes each occurred in 2% to 5%. Onset was gait/balance difficulty in 52%. None of the 92 affected patients were relatives and 7 were of North African ancestry. MRI was compatible with a clinical diagnostic of PSP in all cases. Histopathologic examination confirmed neurofibrillary degeneration and tufted astrocytes in all autopsied cases. Western blots revealed a typical tau 4R doublet. The tau H1 haplotype occurred in 95.8% of cases' chromosomes.

CONCLUSIONS

We have identified a cluster of PSP in a geographical area with severe environmental contamination by industrial metals.

Regulation of human MAPT gene expression

The number of known pathologies involving deregulated Tau expression/metabolism is increasing. Indeed, in addition to tauopathies, which comprise approximately 30 diseases characterized by neuronal aggregation of hyperphosphorylated Tau in brain neurons, this protein has also been associated with various other pathologies such as cancer, inclusion body myositis, and microdeletion/microduplication syndromes, suggesting its possible function in peripheral tissues. In addition to Tau aggregation, Tau deregulation can occur at the expression and/or splicing levels, as has been clearly demonstrated in some of these pathologies. Here, we aim to review current knowledge regarding the regulation of human MAPT gene expression at the DNA and RNA levels to provide a better understanding of its possible deregulation. Several aspects, including repeated motifs, CpG island/methylation, and haplotypes at the DNA level, as well as the key regions involved in mRNA expression and stability and the splicing patterns of different mRNA isoforms at the RNA level, will be discussed.

Genome-wide association study of corticobasal degeneration identifies risk variants shared with progressive supranuclear palsy

Corticobasal degeneration (CBD) is a neurodegenerative disorder affecting movement and cognition, definitively diagnosed only at autopsy. Here, we conduct a genome-wide association study (GWAS) in CBD cases (n=152) and 3,311 controls, and 67 CBD cases and 439 controls in a replication stage. Associations with meta-analysis were 17q21 at MAPT (P=1.42 × 10(-12)), 8p12 at lnc-KIF13B-1, a long non-coding RNA (rs643472; P=3.41 × 10(-8)), and 2p22 at SOS1 (rs963731; P=1.76 × 10(-7)). Testing for association of CBD with top progressive supranuclear palsy (PSP) GWAS single-nucleotide polymorphisms (SNPs) identified associations at MOBP (3p22; rs1768208; P=2.07 × 10(-7)) and MAPT H1c (17q21; rs242557; P=7.91 × 10(-6)). We previously reported SNP/transcript level associations with rs8070723/MAPT, rs242557/MAPT, and rs1768208/MOBP and herein identified association with rs963731/SOS1. We identify new CBD susceptibility loci and show that CBD and PSP share a genetic risk factor other than MAPT at 3p22 MOBP (myelin-associated oligodendrocyte basic protein).

Studying tauopathies in Drosophila: A fruitful model

Tauopathies are a group of neurodegenerative disorders that include hereditary frontotemporal dementias (FTDs) such as FTD with parkinsonism linked to chromosome 17 (FTDP-17), as well as sporadic variants of FTDs like progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and Pick's disease. These diverse diseases all have in common the presence of abnormally phosphorylated tau aggregates. In this review, we will summarize key features of transgenic Drosophila models of tauopathies and a number of insights into disease mechanisms as well as therapeutic implications gained from the fruit fly models.

Association between MAPT haplotype and memory function in patients with Parkinson's disease and healthy aging individuals

Genetic variation is associated with differences in the function of the brain as well as its susceptibility to disease. The common H1 haplotypic variant of the microtubule-associated protein tau gene (MAPT) has been related to an increased risk for Parkinson's disease (PD). Furthermore, among PD patients, H1 homozygotes have an accelerated progression to dementia. We investigated the neurocognitive correlates of MAPT haplotypes using functional magnetic resonance imaging. Thirty-seven nondemented patients with PD (19 H1/H1, 18 H2 carriers) and 40 age-matched controls (21 H1/H1, 19 H2 carriers) were scanned during performance of a picture memory encoding task. Behaviorally, H1 homozygosity was associated with impaired picture recognition memory in PD patients and control subjects. These impairments in the H1 homozygotes were accompanied by an altered blood-oxygen level-dependent response in the medial temporal lobe during successful memory encoding. Additional age-related differences in blood-oxygen level-dependent response were observed in the medial temporal lobes of H1 homozygotes with PD. These results suggest that common variation in MAPT is not only associated with the dementia of PD but also differences in the neural circuitry underlying aspects of cognition in normal aging.

Association of MAPT haplotypes with Alzheimer's disease risk and MAPT brain gene expression levels

Introduction

MAPT encodes for tau, the predominant component of neurofibrillary tangles that are neuropathological hallmarks of Alzheimer’s disease (AD). Genetic association of MAPT variants with late-onset AD (LOAD) risk has been inconsistent, although insufficient power and incomplete assessment of MAPT haplotypes may account for this.

Methods

We examined the association of MAPT haplotypes with LOAD risk in more than 20,000 subjects (n-cases = 9,814, n-controls = 11,550) from Mayo Clinic (n-cases = 2,052, n-controls = 3,406) and the Alzheimer’s Disease Genetics Consortium (ADGC, n-cases = 7,762, n-controls = 8,144). We also assessed associations with brain MAPT gene expression levels measured in the cerebellum (n = 197) and temporal cortex (n = 202) of LOAD subjects. Six single nucleotide polymorphisms (SNPs) which tag MAPT haplotypes with frequencies greater than 1% were evaluated.

Results

H2-haplotype tagging rs8070723-G allele associated with reduced risk of LOAD (odds ratio, OR = 0.90, 95% confidence interval, CI = 0.85-0.95, p = 5.2E-05) with consistent results in the Mayo (OR = 0.81, p = 7.0E-04) and ADGC (OR = 0.89, p = 1.26E-04) cohorts. rs3785883-A allele was also nominally significantly associated with LOAD risk (OR = 1.06, 95% CI = 1.01-1.13, p = 0.034). Haplotype analysis revealed significant global association with LOAD risk in the combined cohort (p = 0.033), with significant association of the H2 haplotype with reduced risk of LOAD as expected (p = 1.53E-04) and suggestive association with additional haplotypes. MAPT SNPs and haplotypes also associated with brain MAPT levels in the cerebellum and temporal cortex of AD subjects with the strongest associations observed for the H2 haplotype and reduced brain MAPT levels (β = -0.16 to -0.20, p = 1.0E-03 to 3.0E-03).

Conclusions

These results confirm the previously reported MAPT H2 associations with LOAD risk in two large series, that this haplotype has the strongest effect on brain MAPT expression amongst those tested and identify additional haplotypes with suggestive associations, which require replication in independent series. These biologically congruent results provide compelling evidence to screen the MAPT region for regulatory variants which confer LOAD risk by influencing its brain gene expression.

An epigenetic signature in peripheral blood associated with the haplotype on 17q21.31, a risk factor for neurodegenerative tauopathy

Little is known about how changes in DNA methylation mediate risk for human diseases including dementia. Analysis of genome-wide methylation patterns in patients with two forms of tau-related dementia--progressive supranuclear palsy (PSP) and frontotemporal dementia (FTD)--revealed significant differentially methylated probes (DMPs) in patients versus unaffected controls. Remarkably, DMPs in PSP were clustered within the 17q21.31 region, previously known to harbor the major genetic risk factor for PSP. We identified and replicated a dose-dependent effect of the risk-associated H1 haplotype on methylation levels within the region in blood and brain. These data reveal that the H1 haplotype increases risk for tauopathy via differential methylation at that locus, indicating a mediating role for methylation in dementia pathophysiology.

Novel mutation in MAPT exon 13 (p.N410H) causes corticobasal degeneration

In order to determine the frequency of microtubule-associated protein tau gene (MAPT) mutations and rare variants in CBD, we performed a systematic sequence analysis of MAPT coding and 3′ untranslated region (3′UTR) in a large cohort of autopsy-confirmed CBD patients (N = 109). This identified a novel MAPT mutation in exon 13, p.N410H, in a case that is neuropathologically indistinguishable from sporadic CBD. On immunoblot, the p.N410H mutation carrier had the same insoluble tau profile as seen in CBD. Additionally, tau expression analysis in brain tissue found a significant increase in the 4R/3R tau mRNA ratio (P = 0.04), indicating that p.N410H disrupts tau isoform homeostasis. Biochemically, recombinant tau protein with p.N410H showed a marked increase in tau filament formation compared to wild-type tau (P < 0.001), had a 19.2% decrease in rate of microtubule assembly (P < 0.05), and a 10.3% reduction in the extent of total microtubule polymerization (P < 0.01). Sequence analysis of the complete MAPT 3′UTR in autopsy-confirmed CBD cases further identified two rare variants with nominally significant association with CBD. An ATC nucleotide insertion (“MAPTv8”) was found in 4.6% of CBD patients compared to 1.2% of controls (P = 0.031, OR = 3.71), and rs186977284 in 4.6% CBD patients, but only 0.9% of controls (P = 0.04, OR = 3.58). Rs186977284 was also present in 2.7% of a large cohort of autopsy-confirmed PSP patients (N = 566) and only 0.9% of an additional control series (P = 0.034, OR = 3.08), extending the association to PSP. Our findings show that mutations in MAPT can cause CBD and MAPT non-coding variants may increase the risk of complex 4R tauopathies.

Brain pathology in myotonic dystrophy: when tauopathy meets spliceopathy and RNAopathy

Myotonic dystrophy (DM) of type 1 and 2 (DM1 and DM2) are inherited autosomal dominant diseases caused by dynamic and unstable expanded microsatellite sequences (CTG and CCTG, respectively) in the non-coding regions of the genes DMPK and ZNF9, respectively. These mutations result in the intranuclear accumulation of mutated transcripts and the mis-splicing of numerous transcripts. This so-called RNA gain of toxic function is the main feature of an emerging group of pathologies known as RNAopathies. Interestingly, in addition to these RNA inclusions, called foci, the presence of neurofibrillary tangles (NFT) in patient brains also distinguishes DM as a tauopathy. Tauopathies are a group of nearly 30 neurodegenerative diseases that are characterized by intraneuronal protein aggregates of the microtubule-associated protein Tau (MAPT) in patient brains. Furthermore, a number of neurodegenerative diseases involve the dysregulation of splicing regulating factors and have been characterized as spliceopathies. Thus, myotonic dystrophies are pathologies resulting from the interplay among RNAopathy, spliceopathy, and tauopathy. This review will describe how these processes contribute to neurodegeneration. We will first focus on the tauopathy associated with DM1, including clinical symptoms, brain histology, and molecular mechanisms. We will also discuss the features of DM1 that are shared by other tauopathies and, consequently, might participate in the development of a tauopathy. Moreover, we will discuss the determinants common to both RNAopathies and spliceopathies that could interfere with tau-related neurodegeneration.

Clinicopathologic assessment and imaging of tauopathies in neurodegenerative dementias

Microtubule-associated protein tau encoded by the MAPT gene binds to microtubules and is important for maintaining neuronal morphology and function. Alternative splicing of MAPT pre-mRNA generates six major tau isoforms in the adult central nervous system resulting in tau proteins with three or four microtubule-binding repeat domains. In a group of neurodegenerative disorders called tauopathies, tau becomes aberrantly hyperphosphorylated and dissociates from microtubules, resulting in a progressive accumulation of intracellular tau aggregates. The spectrum of sporadic frontotemporal lobar degeneration associated with tau pathology includes progressive supranuclear palsy, corticobasal degeneration, and Pick’s disease. Alzheimer’s disease is considered the most prevalent tauopathy. This review is divided into two broad sections. In the first section we discuss the molecular classification of sporadic tauopathies, with a focus on describing clinicopathologic relationships. In the second section we discuss the neuroimaging methodologies that are available for measuring tau pathology (directly using tau positron emission tomography ligands) and tau-mediated neuronal injury (magnetic resonance imaging and fluorodeoxyglucose positron emission tomography). Both sections have detailed descriptions of the following neurodegenerative dementias – Alzheimer’s disease, progressive supranuclear palsy, corticobasal degeneration and Pick’s disease.

Genetic and neuroanatomic associations in sporadic frontotemporal lobar degeneration

Genome-wide association studies have identified single nucleotide polymorphisms (SNPs) that are sensitive for tau or TDP-43 pathology in frontotemporal lobar degeneration (FTLD). Neuroimaging analyses have revealed distinct distributions of disease in FTLD patients with genetic mutations. However, genetic influences on neuroanatomic structure in sporadic FTLD have not been assessed. In this report, we use novel multivariate tools, Eigenanatomy, and sparse canonical correlation analysis to identify associations between SNPs and neuroanatomic structure in sporadic FTLD. Magnetic resonance imaging analyses revealed that rs8070723 (MAPT) was associated with gray matter variance in the temporal cortex. Diffusion tensor imaging analyses revealed that rs1768208 (MOBP), rs646776 (near SORT1), and rs5848 (PGRN) were associated with white matter variance in the midbrain and superior longitudinal fasciculus. In an independent autopsy series, we observed that rs8070723 and rs1768208 conferred significant risk of tau pathology relative to TDP-43, and rs646776 conferred increased risk of TDP-43 pathology relative to tau. Identified brain regions and SNPs may help provide an in vivo screen for underlying pathology in FTLD and contribute to our understanding of sporadic FTLD.

MAPT gene rs1052553 variant is not associated with the risk for multiple sclerosis

BACKGROUND/OBJECTIVES

Some experimental data suggest a possible role of tau protein in the pathogenesis of multiple sclerosis (MS) and in experimental autoimmune encephalomyelitis. The aim of this study was to investigate a possible influence of the SNP rs1052553 in the MAPT gene in the risk for relapsing bout onset (relapsing-remitting and secondary progressive) MS.

METHODS

We analyzed the allelic and genotype frequency of MAPT rs1052553, which has been associated with some neurodegenerative diseases, in 259 patients with relapsing bout onset MS and 291 healthy controls, using TaqMan Assays.

RESULTS

MAPT rs1052553 allelic and genotype frequencies did not differ significantly between relapsing bout onset MS patients and controls, and were unrelated with the age of onset of MS or gender.

CONCLUSIONS

These results suggest that MAPT rs1052553 polymorphism is not related with the risk for relapsing bout onset MS.

The unfolded protein response is activated in disease-affected brain regions in progressive supranuclear palsy and Alzheimer's disease

Background

Progressive supranuclear palsy (PSP) is a neurodegenerative disorder pathologically characterized by intracellular tangles of hyperphosphorylated tau protein distributed throughout the neocortex, basal ganglia, and brainstem. A genome-wide association study identified EIF2AK3 as a risk factor for PSP. EIF2AK3 encodes PERK, part of the endoplasmic reticulum’s (ER) unfolded protein response (UPR). PERK is an ER membrane protein that senses unfolded protein accumulation within the ER lumen. Recently, several groups noted UPR activation in Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis, multiple system atrophy, and in the hippocampus and substantia nigra of PSP subjects. Here, we evaluate UPR PERK activation in the pons, medulla, midbrain, hippocampus, frontal cortex and cerebellum in subjects with PSP, AD, and in normal controls.

Results

We found UPR activation primarily in disease-affected brain regions in both disorders. In PSP, the UPR was primarily activated in the pons and medulla and to a much lesser extent in the hippocampus. In AD, the UPR was extensively activated in the hippocampus. We also observed UPR activation in the hippocampus of some elderly normal controls, severity of which positively correlated with both age and tau pathology but not with Aβ plaque burden. Finally, we evaluated EIF2AK3 coding variants that influence PERK activation. We show that a haplotype associated with increased PERK activation is genetically associated with increased PSP risk.

Conclusions

The UPR is activated in disease affected regions in PSP and the genetic evidence shows that this activation increases risk for PSP and is not a protective response.