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

Genetic forms of tauopathies: inherited causes and implications of Alzheimer's disease-like TAU pathology in primary and secondary tauopathies

Tauopathies are a heterogeneous group of neurologic diseases characterized by pathological axodendritic distribution, ectopic expression, and/or phosphorylation and aggregation of the microtubule-associated protein TAU, encoded by the gene MAPT. Neuronal dysfunction, dementia, and neurodegeneration are common features of these often detrimental diseases. A neurodegenerative disease is considered a primary tauopathy when MAPT mutations/haplotypes are its primary cause and/or TAU is the main pathological feature. In case TAU pathology is observed but superimposed by another pathological hallmark, the condition is classified as a secondary tauopathy. In some tauopathies (e.g. MAPT-associated frontotemporal dementia (FTD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and Alzheimer's disease (AD)) TAU is recognized as a significant pathogenic driver of the disease. In many secondary tauopathies, including Parkinson's disease (PD) and Huntington's disease (HD), TAU is suggested to contribute to the development of dementia, but in others (e.g. Niemann-Pick disease (NPC)) TAU may only be a bystander. The genetic and pathological mechanisms underlying TAU pathology are often not fully understood. In this review, the genetic predispositions and variants associated with both primary and secondary tauopathies are examined in detail, assessing evidence for the role of TAU in these conditions. We highlight less common genetic forms of tauopathies to increase awareness for these disorders and the involvement of TAU in their pathology. This approach not only contributes to a deeper understanding of these conditions but may also lay the groundwork for potential TAU-based therapeutic interventions for various tauopathies.

MAPT H2 haplotype and risk of Pick's disease in the Pick's disease International Consortium: a genetic association study

BACKGROUND

Pick's disease is a rare and predominantly sporadic form of frontotemporal dementia that is classified as a primary tauopathy. Pick's disease is pathologically defined by the presence in the frontal and temporal lobes of Pick bodies, composed of hyperphosphorylated, three-repeat tau protein, encoded by the MAPT gene. MAPT has two distinct haplotypes, H1 and H2; the MAPT H1 haplotype is the major genetic risk factor for four-repeat tauopathies (eg, progressive supranuclear palsy and corticobasal degeneration), and the MAPT H2 haplotype is protective for these disorders. The primary aim of this study was to evaluate the association of MAPT H2 with Pick's disease risk, age at onset, and disease duration.

METHODS

In this genetic association study, we used data from the Pick's disease International Consortium, which we established to enable collection of data from individuals with pathologically confirmed Pick's disease worldwide. For this analysis, we collected brain samples from individuals with pathologically confirmed Pick's disease from 35 sites (brainbanks and hospitals) in North America, Europe, and Australia between Jan 1, 2020, and Jan 31, 2023. Neurologically healthy controls were recruited from the Mayo Clinic (FL, USA, or MN, USA between March 1, 1998, and Sept 1, 2019). For the primary analysis, individuals were directly genotyped for the MAPT H1-H2 haplotype-defining variant rs8070723. In a secondary analysis, we genotyped and constructed the six-variant-defined (rs1467967-rs242557-rs3785883-rs2471738-rs8070723-rs7521) MAPT H1 subhaplotypes. Associations of MAPT variants and MAPT haplotypes with Pick's disease risk, age at onset, and disease duration were examined using logistic and linear regression models; odds ratios (ORs) and β coefficients were estimated and correspond to each additional minor allele or each additional copy of the given haplotype.

FINDINGS

We obtained brain samples from 338 people with pathologically confirmed Pick's disease (205 [61%] male and 133 [39%] female; 338 [100%] White) and 1312 neurologically healthy controls (611 [47%] male and 701 [53%] female; 1312 [100%] White). The MAPT H2 haplotype was associated with increased risk of Pick's disease compared with the H1 haplotype (OR 1·35 [95% CI 1·12 to 1·64], p=0·0021). MAPT H2 was not associated with age at onset (β -0·54 [95% CI -1·94 to 0·87], p=0·45) or disease duration (β 0·05 [-0·06 to 0·16], p=0·35). Although not significant after correcting for multiple testing, associations were observed at p less than 0·05: with risk of Pick's disease for the H1f subhaplotype (OR 0·11 [0·01 to 0·99], p=0·049); with age at onset for H1b (β 2·66 [0·63 to 4·70], p=0·011), H1i (β -3·66 [-6·83 to -0·48], p=0·025), and H1u (β -5·25 [-10·42 to -0·07], p=0·048); and with disease duration for H1x (β -0·57 [-1·07 to -0·07], p=0·026).

INTERPRETATION

The Pick's disease International Consortium provides an opportunity to do large studies to enhance our understanding of the pathobiology of Pick's disease. This study shows that, in contrast to the decreased risk of four-repeat tauopathies, the MAPT H2 haplotype is associated with an increased risk of Pick's disease in people of European ancestry. This finding could inform development of isoform-related therapeutics for tauopathies.

FUNDING

Wellcome Trust, Rotha Abraham Trust, Brain Research UK, the Dolby Fund, Dementia Research Institute (Medical Research Council), US National Institutes of Health, and the Mayo Clinic Foundation.

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.

Detecting and Validating MAPT Mutations in Neurodegeneration Patients and Analysis of Exon Splicing Consequences

Mutation of MAPT has been observed in patients with parkinsonism, progressive supranuclear palsy, and corticobasal degeneration and is a significant cause of frontotemporal dementia. In this chapter, we discuss considerations for next-generation sequencing analysis to identify MAPT mutations in patient genomic DNA and describe the validation of these mutations by Sanger sequencing. One of the most common effects of MAPT mutations is differential splicing of exon 10, which leads to an imbalance in the proportion of 3-repeat and 4-repeat tau isoforms. We describe how to investigate the effect of novel DNA variants on the splicing efficiency of this exon in vitro using the exon-trapping technique, also known as the splicing reporter minigene assay.

Creating the Pick's disease International Consortium: Association study of MAPT H2 haplotype with risk of Pick's disease

Background

Pick's disease (PiD) is a rare and predominantly sporadic form of frontotemporal dementia that is classified as a primary tauopathy. PiD is pathologically defined by argyrophilic inclusion Pick bodies and ballooned neurons in the frontal and temporal brain lobes. PiD is characterised by the presence of Pick bodies which are formed from aggregated, hyperphosphorylated, 3-repeat tau proteins, encoded by the MAPT gene. The MAPT H2 haplotype has consistently been associated with a decreased disease risk of the 4-repeat tauopathies of progressive supranuclear palsy and corticobasal degeneration, however its role in susceptibility to PiD is unclear. The primary aim of this study was to evaluate the association between MAPT H2 and risk of PiD.

Methods

We established the Pick's disease International Consortium (PIC) and collected 338 (60.7% male) pathologically confirmed PiD brains from 39 sites worldwide. 1,312 neurologically healthy clinical controls were recruited from Mayo Clinic Jacksonville, FL (N=881) or Rochester, MN (N=431). For the primary analysis, subjects were directly genotyped for MAPT H1-H2 haplotype-defining variant rs8070723. In secondary analysis, we genotyped and constructed the six-variant MAPT H1 subhaplotypes (rs1467967, rs242557, rs3785883, rs2471738, rs8070723, and rs7521).

Findings

Our primary analysis found that the MAPT H2 haplotype was associated with increased risk of PiD (OR: 1.35, 95% CI: 1.12-1.64 P=0.002). In secondary analysis involving H1 subhaplotypes, a protective association with PiD was observed for the H1f haplotype (0.0% vs. 1.2%, P=0.049), with a similar trend noted for H1b (OR: 0.76, 95% CI: 0.58-1.00, P=0.051). The 4-repeat tauopathy risk haplotype MAPT H1c was not associated with PiD susceptibility (OR: 0.93, 95% CI: 0.70-1.25, P=0.65).

Interpretation

The PIC represents the first opportunity to perform relatively large-scale studies to enhance our understanding of the pathobiology of PiD. This study demonstrates that in contrast to its protective role in 4R tauopathies, the MAPT H2 haplotype is associated with an increased risk of PiD. This finding is critical in directing isoform-related therapeutics for tauopathies.

Genome-wide association study stratified by MAPT haplotypes identifies potential novel loci in Parkinson's disease

Objective

To identify genetic factors that may modify the effects of the MAPT locus in Parkinson's disease (PD).

Methods

We used data from the International Parkinson's Disease Genomics Consortium (IPDGC) and the UK biobank (UKBB). We stratified the IPDGC cohort for carriers of the H1/H1 genotype (PD patients n=8,492 and controls n=6,765) and carriers of the H2 haplotype (with either H1/H2 or H2/H2 genotypes, patients n=4,779 and controls n=4,849) to perform genome-wide association studies (GWASs). Then, we performed replication analyses in the UKBB data. To study the association of rare variants in the new nominated genes, we performed burden analyses in two cohorts (Accelerating Medicines Partnership - Parkinson Disease and UKBB) with a total sample size PD patients n=2,943 and controls n=18,486.

Results

We identified a novel locus associated with PD among MAPT H1/H1 carriers near EMP1 (rs56312722, OR=0.88, 95%CI= 0.84-0.92, p= 1.80E-08), and a novel locus associated with PD among MAPT H2 carriers near VANGL1 (rs11590278, OR=1.69 95%CI=1.40-2.03, p=2.72E-08). Similar analysis of the UKBB data did not replicate these results and rs11590278 near VANGL1 did have similar effect size and direction in carriers of H2 haplotype, albeit not statistically significant (OR= 1.32, 95%CI= 0.94-1.86, p=0.17). Rare EMP1 variants with high CADD scores were associated with PD in the MAPT H2 stratified analysis (p=9.46E-05), mainly driven by the p.V11G variant.

Interpretation

We identified several loci potentially associated with PD stratified by MAPT haplotype and larger replication studies are required to confirm these associations.

Pathomechanisms of cognitive impairment in progressive supranuclear palsy

Progressive supranuclear palsy (PSP) is a neurodegenerative disorder characterized by early postural instability and falls, oculomotor dysfunction (vertical supranuclear gaze palsy), parkinsonism with poor response to levodopa, pseudobulbar palsy, and cognitive impairment. This four-repeat tauopathy is morphologically featured by accumulation of tau protein in neurons and glia causing neuronal loss and gliosis in the extrapyramidal system associated with cortical atrophy and white matter lesions. Cognitive impairment being frequent in PSP and more severe than in multiple system atrophy and Parkinson disease, is dominated by executive dysfunction, with milder difficulties in memory, and visuo-spatial and naming dysfunctions. Showing longitudinal decline, it has been related to a variety of pathogenic mechanisms associated with the underlying neurodegenerative process, such as involvement of cholinergic and muscarinergic dysfunctions, and striking tau pathology in frontal and temporal cortical regions associated with reduced synaptic density. Altered striatofrontal, fronto-cerebellar, parahippocampal, and multiple subcortical structures, as well as widespread white matter lesions causing extensive connectivity disruptions in cortico-subcortical and cortico-brainstem connections, support the concept that PSP is a brain network disruption disorder. The pathophysiology and pathogenesis of cognitive impairment in PSP, as in other degenerative movement disorders, are complex and deserve further elucidation as a basis for adequate treatment to improve the quality of life of patients with this fatal disease.

17q21.31 sub-haplotypes underlying H1-associated risk for Parkinson's disease are associated with LRRC37A/2 expression in astrocytes

BACKGROUND

Parkinson's disease (PD) is genetically associated with the H1 haplotype of the MAPT 17q.21.31 locus, although the causal gene and variants underlying this association have not been identified.

METHODS

To better understand the genetic contribution of this region to PD and to identify novel mechanisms conferring risk for the disease, we fine-mapped the 17q21.31 locus by constructing discrete haplotype blocks from genetic data. We used digital PCR to assess copy number variation associated with PD-associated blocks, and used human brain postmortem RNA-seq data to identify candidate genes that were then further investigated using in vitro models and human brain tissue.

RESULTS

We identified three novel H1 sub-haplotype blocks across the 17q21.31 locus associated with PD risk. Protective sub-haplotypes were associated with increased LRRC37A/2 copy number and expression in human brain tissue. We found that LRRC37A/2 is a membrane-associated protein that plays a role in cellular migration, chemotaxis and astroglial inflammation. In human substantia nigra, LRRC37A/2 was primarily expressed in astrocytes, interacted directly with soluble α-synuclein, and co-localized with Lewy bodies in PD brain tissue.

CONCLUSION

These data indicate that a novel candidate gene, LRRC37A/2, contributes to the association between the 17q21.31 locus and PD via its interaction with α-synuclein and its effects on astrocytic function and inflammatory response. These data are the first to associate the genetic association at the 17q21.31 locus with PD pathology, and highlight the importance of variation at the 17q21.31 locus in the regulation of multiple genes other than MAPT and KANSL1, as well as its relevance to non-neuronal cell types.

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.

Genetic architecture of primary tauopathies

Primary Tauopathies are a group of diseases defined by the accumulation of Tau, in which the alteration of this protein is the primary driver of the neurodegenerative process. In addition to the classical syndromes (Pick's disease (PiD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and argyrophilic grain disease (AGD)), new entities, like primary age-related Tauopathy (PART), have been recently described. Except for the classical Richardson's syndrome phenotype in PSP, the correlation between the clinical picture of the primary Tauopathies and underlying pathology is poor. This fact has challenged genetic studies. However, thanks to multicenter collaborations, several genome-wide association studies are helping us unravel the genetic structure of these diseases. The most relevant risk factor revealed by these studies is the Tau gene (MAPT), which, in addition to mutations causing rare familial forms, plays a fundamental role in sporadic cases of PSP and CBD in which there is a strong predominance of the H1 and H1c haplotypes. But outside of MAPT, several other genes have been robustly associated with PSP. These findings, pointing towards multifactorial causation, imply the participation of several pathways involving the myelin sheath integrity, the endoplasmic reticulum unfolded protein response, microglia, intracellular vesicle trafficking, or the ubiquitin-proteasome system. Additionally, GWAS show a high degree of genetic overlap across different Tauopathies. This is especially salient between PSP and CBD, but also GWAS studying the recently described PART phenotype shows genetic overlap with genes that promote Tau pathology and with others associated with Alzheimer's disease.

Tauopathies: new perspectives and challenges

BACKGROUND

Tauopathies are a class of neurodegenerative disorders characterized by neuronal and/or glial tau-positive inclusions.

MAIN BODY

Clinically, tauopathies can present with a range of phenotypes that include cognitive/behavioral-disorders, movement disorders, language disorders and non-specific amnestic symptoms in advanced age. Pathologically, tauopathies can be classified based on the predominant tau isoforms that are present in the inclusion bodies (i.e., 3R, 4R or equal 3R:4R ratio). Imaging, cerebrospinal fluid (CSF) and blood-based tau biomarkers have the potential to be used as a routine diagnostic strategy and in the evaluation of patients with tauopathies. As tauopathies are strongly linked neuropathologically and genetically to tau protein abnormalities, there is a growing interest in pursuing of tau-directed therapeutics for the disorders. Here we synthesize emerging lessons on tauopathies from clinical, pathological, genetic, and experimental studies toward a unified concept of these disorders that may accelerate the therapeutics.

CONCLUSIONS

Since tauopathies are still untreatable diseases, efforts have been made to depict clinical and pathological characteristics, identify biomarkers, elucidate underlying pathogenesis to achieve early diagnosis and develop disease-modifying therapies.

Protracted Course-Progressive Supranuclear Palsy (PC-PSP)

BACKGROUND

Progressive Supranuclear Palsy (PSP) encompasses a broader range of disease courses than previously appreciated. The most frequent clinical presentations of PSP are Richardson's Syndrome (RS) and PSP with a predominant Parkinsonism phenotype (PSP-P). Time to reach gait dependence and cognitive impairment have been proposed as prognostic disease milestones. Genetic polymorphisms in TRIM11 and SLC2A13 genes have been associated with longer disease duration (DD).

METHODS

Retrospective chart review, genetic single nucleotide polymorphism (SNP) analyses (in 3 cases), and neuropathology.

RESULTS

We identified four cases with long (>10-15 years) or very long (>15 years) DD. Stage 1 PSP tau pathology was present in 2 cases (one PSP-P and one undifferentiated phenotype), whereas pallido-nigro-Luysian atrophy (PSP-RS) and stage 4/6 (PSP-P) PSP pathology was found in the other 2 cases. Three cases were homozygous for the rs564309-C allele in the TRIM11 gene and the H1 MAPT haplotype. Two were heterozygous for rs2242367 (G/A) in SLC2A13, while the third was homozygous for the G-allele.

CONCLUSIONS

We propose a protracted course subtype of PSP (PC-PSP) based on clinical or neuropathological criteria in 2 cases with anatomically restricted PSP pathology, and very long DD and slower clinical progression in 2 cases. The presence of the rs564309-C allele may influence the protracted disease course. Crystallizing the concept of PC-PSP is important to further understand the pathobiology of tauopathies in line with current hypotheses of protein misfolding, seeding activity and propagation.

Genetic and Epigenetic Constructs of Progressive Supranuclear Palsy

BACKGROUND

Progressive supranuclear palsy (PSP) is a rapidly progressive primary tauopathy characterized by vertical gaze palsy, postural instability, and mild dementia. PSP shows high clinical and pathologic heterogeneity. Although a few risk factors exist, such as advanced age and environmental toxins, the precise etiology remains largely elusive. Compelling evidence now suggests that genetic background plays a pivotal role in the pathogenetic pathways of PSP. Notably, PSP is genetically and phenotypically a complex disorder. Given the tau pathology, several studies in the past have identified microtubule-associated protein tau (MAPT) gene mutations/variations and its haplotype as the major genetic risk factor of PSP, both in the sporadic and the familial forms. Subsequently, genome-wide association studies (GWAS) also identified several novel risk variants. However, these genetic risk determinants fail to explain the pathogenetic basis of PSP and its phenotypic spectrum in majority of the cases. Some genetic variants are known to confer the risk, while others seem to act as modifier genes.

SUMMARY

Besides the complex genetic basis of PSP, the pathobiological mechanisms, differential diagnosis, and management of patients with PSP have further been complicated by genetic conditions that mimic the phenotypes of PSP. This is now becoming increasingly apparent that interactions between genetic and environmental factors significantly contribute to PSP development. Further, the effect of environmental factors seems to be mediated through epigenetic modifications.

KEY MESSAGE

Herein, we provide a comprehensive overview of the genetic and epigenetic constructs of PSP and highlight the relevance of genetic and epigenetic findings in the pathobiology of PSP.

Is the Phenotype Designation by PSP-MDS Criteria Stable Throughout the Disease Course and Consistent With Tau Distribution?

Introduction

The MDS-PSP criteria have shown high sensitivity for the PSP diagnosis, but do not discriminate the phenotype diversity. Our purpose was to search for anatomopathological differences among PSP phenotypes resulting from the application of the MDS-PSP criteria comparing with the previous ones.

Methods

Thirty-four PSP cases from a single brain bank were retrospectively classified according to the criteria used by Respondek et al. in 2014 and the PSP-MDS criteria at 3 years (MDS-3y), 6 years (MDS-6y) and at the last clinical evaluation before death (MDS-last). Semiquantitative measurement of total, cortical and subcortical tau load was compared. For comparative analysis, PSP-Richardson syndrome and PSP postural instability were grouped (PSP-RS/PI) as well as the PSP atypical cortical phenotypes (PSP-Cx).

Results

Applying the Respondek's criteria, PSP phenotypes were distributed as follow: 55.9% PSP-RS/PI, 26.5% PSP-Cx, 11.8% PSP-Parkinsonism (PSP-P), and 5.9% PSP-Cerebellum. PSP-RS/PI and PSP-Cx had a higher total tau load than PSP-P; PSP-Cx showed a higher cortical tau load than PSP-RS/PI and PSP-P; and PSP-RS/PI had a higher subcortical tau load than PSP-P. Applying the MDS-3y, MDS-6y and MDS-last criteria; the PSP-RS/PI group increased (67.6, 70.6 and 70.6% respectively) whereas the PSP-Cx group decreased (8.8, and 8.8 and 11.8%). Then, only differences in total and subcortical tau burden between PSP-RS/PI and PSP-P were observed.

Interpretation

After the retrospective application of the new MDS-PSP criteria, total and subcortical tau load is higher in PSP-RS/PI than in PSP-P whereas no other differences in tau load between phenotypes were found, as a consequence of the loss of phenotypic diversity.

Semantic Recollection in Parkinson's Disease: Functional Reconfiguration and MAPT Variants

Decline in semantic cognition in early stages of Parkinson’s disease (PD) is a leading risk factor for future dementia, yet the underlying neural mechanisms are not understood. The present study addressed this gap by investigating the functional connectivity of regions involved in semantic recollection. We further examined whether microtubule-associated protein tau (MAPT) risk variants, which may accelerate cognitive decline, altered the strength of regional functional connections. Cognitively normal PD and healthy elder controls underwent fMRI while performing a fame-discrimination task, which activates the semantic network. Analyses focused on disturbances in fame-modulated functional connectivity in PD for regions that govern semantic recollection and interrelated processes. Group differences were found in multiple connectivity features, which were reduced into principal components that reflected the strength of fame-modulated regional couplings with other brain areas. Despite the absence of group differences in semantic cognition, two aberrant connectivity patterns were uncovered in PD. One pattern was related to a loss in frontal, parietal, and temporal connection topologies that governed semantic recollection in older controls. Another pattern was characterized by functional reconfiguration, wherein frontal, parietal, temporal and caudate couplings were strengthened with areas that were not recruited by controls. Correlations between principal component scores and cognitive measures suggested that reconfigured frontal coupling topologies in PD supported compensatory routes for accessing semantic content, whereas reconfigured parietal, temporal, and caudate connection topologies were detrimental or unrelated to cognition. Increased tau transcription diminished recruitment of compensatory frontal topologies but amplified recruitment of parietal topologies that were unfavorable for cognition. Collectively, the findings provide a new understanding of early vulnerabilities in the functional architecture of regional connectivity during semantic recollection in cognitively normal PD. The findings also have implications for tracking cognitive progression and selecting patients who stand to benefit from therapeutic interventions.

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.

Evolving concepts in progressive supranuclear palsy and other 4-repeat tauopathies

Tauopathies are classified according to whether tau deposits predominantly contain tau isoforms with three or four repeats of the microtubule-binding domain. Those in which four-repeat (4R) tau predominates are known as 4R-tauopathies, and include progressive supranuclear palsy, corticobasal degeneration, argyrophilic grain disease, globular glial tauopathies and conditions associated with specific MAPT mutations. In these diseases, 4R-tau deposits are found in various cell types and anatomical regions of the brain and the conditions share pathological, pathophysiological and clinical characteristics. Despite being considered 'prototype' tauopathies and, therefore, ideal for studying neuroprotective agents, 4R-tauopathies are still severe and untreatable diseases for which no validated biomarkers exist. However, advances in research have addressed the issues of phenotypic overlap, early clinical diagnosis, pathophysiology and identification of biomarkers, setting a road map towards development of treatments. New clinical criteria have been developed and large cohorts with early disease are being followed up in prospective studies. New clinical trial readouts are emerging and biomarker research is focused on molecular pathways that have been identified. Lessons learned from failed trials of neuroprotective drugs are being used to design new trials. In this Review, we present an overview of the latest research in 4R-tauopathies, with a focus on progressive supranuclear palsy, and discuss how current evidence dictates ongoing and future research goals.

Tau Seeding Mouse Models with Patient Brain-Derived Aggregates

Tauopathies are a heterogeneous class of neurodegenerative diseases characterized by intracellular inclusions of aggregated tau proteins. Tau aggregates in different tauopathies have distinct structural features and can be found in different cell types. Transgenic animal models overexpressing human tau have been used for over two decades in the research of tau pathology. However, these models poorly recapitulate the heterogeneity of tauopathies found in human brains. Recent findings demonstrate that injection of purified tau aggregates from the brains of human tauopathy patients recapitulates both the structural features and cell-type specificity of the tau pathology of the donor tauopathy. These models may therefore have unique translational value in the study of functional consequences of tau pathology, tau-based diagnostics, and tau targeting therapeutics. This review provides an update of the literature relating to seeding-based tauopathy and their potential applications.

Molecular Genetics of Early- and Late-Onset Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia in the elderly and this complex disorder is associated with environmental as well as genetic factors. Early-onset AD (EOAD) and late-onset AD (LOAD, more common) are major identified types of AD. The genetics of EOAD is extensively understood, with three gene variants such as APP, PSEN1, and PSEN2 leading to the disease. Some common alleles, including APOE, are effectively associated with LOAD identified, but the genetics of LOAD is not clear to date. It has been accounted that about 5-10% of EOAD patients can be explained through mutations in the three familiar genes of EOAD. The APOE ε4 allele augmented the severity of EOAD risk in carriers, and the APOE ε4 allele was considered as a hallmark of EOAD. A great number of EOAD patients, who are not genetically explained, indicate that it is not possible to identify disease-triggering genes yet. Although several genes have been identified by using the technology of next-generation sequencing in EOAD families, including SORL1, TYROBP, and NOTCH3. A number of TYROBP variants are identified through exome sequencing in EOAD patients and these TYROBP variants may increase the pathogenesis of EOAD. The existence of the ε4 allele is responsible for increasing the severity of EOAD. However, several ε4 allele carriers propose the presence of other LOAD genetic as well as environmental risk factors that are not identified yet. It is urgent to find out missing genetics of EOAD and LOAD etiology to discover new potential genetic facets which will assist in understanding the pathological mechanism of AD. These investigations should contribute to developing a new therapeutic candidate for alleviating, reversing and preventing AD. This article, based on current knowledge, represents the overview of the susceptible genes of EOAD, and LOAD. Next, we represent the probable molecular mechanism that might elucidate the genetic etiology of AD and highlight the role of massively parallel sequencing technologies for novel gene discoveries.

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.

MAPT subhaplotypes in corticobasal degeneration: assessing associations with disease risk, severity of tau pathology, and clinical features

The microtubule-associated protein tau (MAPT) H1 haplotype is the strongest genetic risk factor for corticobasal degeneration (CBD). However, the specific H1 subhaplotype association is not well defined, and it is not clear whether any MAPT haplotypes influence severity of tau pathology or clinical presentation in CBD. Therefore, in the current study we examined 230 neuropathologically confirmed CBD cases and 1312 controls in order to assess associations of MAPT haplotypes with risk of CBD, severity of tau pathology (measured as semi-quantitative scores for coiled bodies, neurofibrillary tangles, astrocytic plaques, and neuropil threads), age of CBD onset, and disease duration. After correcting for multiple testing (P < 0.0026 considered as significant), we confirmed the strong association between the MAPT H2 haplotype and decreased risk of CBD (Odds ratio = 0.26, P = 2 × 10⁻¹²), and also observed a novel association between the H1d subhaplotype and an increased CBD risk (Odds ratio = 1.76, P = 0.002). Additionally, although not statistically significant after correcting for multiple testing, the H1c haplotype was associated with a higher risk of CBD (Odds ratio = 1.49, P = 0.009). No MAPT haplotypes were significantly associated with any tau pathology measures, age of CBD onset, or disease duration. Though replication will be important and there is potential that population stratification could have influenced our findings, these results suggest that several MAPT H1 subhaplotypes are primarily responsible for the strong association between MAPT H1 and risk of CBD, but that H1 subhaplotypes are unlikely to play a major role in driving tau pathology or clinical features. Our findings also indicate that similarities in MAPT haplotype risk-factor profile exist between CBD and the related tauopathy progressive supranuclear palsy, with H2, H1d, and H1c displaying associations with both diseases.

Variants in PPP2R2B and IGF2BP3 are associated with higher tau deposition

Tau deposition is a key biological feature of Alzheimer’s disease that is closely related to cognitive impairment. However, it remains poorly understood why certain individuals may be more susceptible to tau deposition while others are more resistant. The recent availability of in vivo assessment of tau burden through positron emission tomography provides an opportunity to test the hypothesis that common genetic variants may influence tau deposition. We performed a genome-wide association study of tau-positron emission tomography on a sample of 754 individuals over age 50 (mean age 72.4 years, 54.6% men, 87.6% cognitively unimpaired) from the population-based Mayo Clinic Study of Aging. Linear regression was performed to test nucleotide polymorphism associations with AV-1451 (¹⁸F-flortaucipir) tau-positron emission tomography burden in an Alzheimer’s-signature composite region of interest, using an additive genetic model and covarying for age, sex and genetic principal components. Genome-wide significant associations with higher tau were identified for rs76752255 (P = 9.91 × 10⁻⁹, β = 0.20) in the tau phosphorylation regulatory gene PPP2R2B (protein phosphatase 2 regulatory subunit B) and for rs117402302 (P  = 4.00 × 10⁻⁸, β = 0.19) near IGF2BP3 (insulin-like growth factor 2 mRNA-binding protein 3). The PPP2R2B association remained genome-wide significant after additionally covarying for global amyloid burden and cerebrovascular disease risk, while the IGF2BP3 association was partially attenuated after accounting for amyloid load. In addition to these discoveries, three single nucleotide polymorphisms within MAPT (microtubule-associated protein tau) displayed nominal associations with tau-positron emission tomography burden, and the association of the APOE (apolipoprotein E) ɛ4 allele with tau-positron emission tomography was marginally nonsignificant (P  = 0.06, β = 0.07). No associations with tau-positron emission tomography burden were identified for other single nucleotide polymorphisms associated with Alzheimer’s disease clinical diagnosis in prior large case–control studies. Our findings nominate PPP2R2B and IGF2BP3 as novel potential influences on tau pathology which warrant further functional characterization. Our data are also supportive of previous literature on the associations of MAPT genetic variation with tau, and more broadly supports the inference that tau accumulation may have a genetic architecture distinct from known Alzheimer’s susceptibility genes, which may have implications for improved risk stratification and therapeutic targeting.

Associations of mitochondrial genomic variation with corticobasal degeneration, progressive supranuclear palsy, and neuropathological tau measures

Mitochondrial health is important in ageing and dysfunctional oxidative phosphorylation (OXPHOS) accelerates ageing and influences neurodegeneration. Mitochondrial DNA (mtDNA) codes for vital OXPHOS subunits and mtDNA background has been associated with neurodegeneration; however, no study has characterised mtDNA variation in Progressive supranuclear palsy (PSP) or Corticobasal degeneration (CBD) risk or pathogenesis. In this case-control study, 910 (42.6% male) neurologically-healthy controls, 1042 (54.1% male) pathologically-confirmed PSP cases, and 171 (52.0% male) pathologically-confirmed CBD cases were assessed to determine how stable mtDNA polymorphisms, in the form of mtDNA haplogroups, were associated with risk of PSP, risk of CBD, age of PSP onset, PSP disease duration, and neuropathological tau pathology measures for neurofibrillary tangles (NFT), neuropil threads (NT), tufted astrocytes (TA), astrocytic plaques (AP), and oligodendroglial coiled bodies (CB). 764 PSP cases and 150 CBD cases had quantitative tau pathology scores. mtDNA was genotyped for 39 unique SNPs using Agena Bioscience iPlex technologies and mitochondrial haplogroups were defined to mitochondrial phylogeny. After adjustment for multiple testing, we observed an association with risk of CBD for mtDNA sub-haplogroup H4 (OR = 4.51, P = 0.001) and the HV/HV0a haplogroup was associated with a decreased severity of NT tau pathology in PSP cases (P = 0.0023). Our study reports that mitochondrial genomic background may be associated with risk of CBD and may be influencing tau pathology measures in PSP. Replication of these findings will be important.

Screening non-MAPT genes of the Chr17q21 H1 haplotype in Parkinson's disease

INTRODUCTION

The microtubule-associated protein tau (MAPT) gene is considered a strong genetic risk factor for Parkinson's disease (PD) in Caucasians. MAPT is located within an inversion region of high linkage disequilibrium designated as H1 and H2 haplotype, and contains eight other genes which have been implicated in neurodegeneration. The aim of the current study was to identify common coding variants in strong linkage disequilibrium (LD) within the associated loci on chr17q21 harboring MAPT.

METHODS

Sanger sequencing of coding exons in 90 Caucasian late-onset PD (LOPD) patients was performed. Specific gene sequencing for LRRC37A, LRRC37A2, ARL17A and ARL17B was not possible given the high homology, presence of pseudogenes and copy number variants that are in the region, and therefore four genes (NSF, KANSL1, SPPL2C, and CRHR1) were included in the analysis. Coding variants from these four genes that did not perfectly tag (r² = 1) the MAPT H1/H2 haplotype were genotyped in an independent replication series of Caucasian PD cases (N = 851) and controls (N = 730).

RESULTS

In the 90 LOPD cases we identified 30 coding variants. Eleven non-synonymous variants tagged the MAPT H1/H2 haplotype, including two SPPL2C variants (rs12185233 and rs12373123) that had high pathogenic combined annotation dependent depletion (CADD) scores of >20. In the replication series, the non-synonymous KANSL1 rs17585974 variant was in very strong LD with MAPT H1/H2 and had a high CADD score of 24.7.

CONCLUSION

We have identified several non-synonymous variants across neighboring genes of MAPT that may warrant further genetic and functional investigation within the biological etiology of PD.

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.

Association of Tripartite Motif Containing 11 rs564309 With Tau Pathology in Progressive Supranuclear Palsy

BACKGROUND

Intronic variant rs564309 in tripartite motif containing 11 (TRIM11) is associated with clinical phenotypic differences in progressive supranuclear palsy (PSP), whereby the minor allele (A) is more common in atypical PSP than typical PSP (PSP-Richardson's syndrome). However, rs564309 has not been investigated relative to neuropathological outcomes.

OBJECTIVE

Evaluate the association of rs564309 with the neuropathologically assessed severity of tau pathology, as measured by semi-quantitative scores for neurofibrillary tangles, tufted astrocytes, neuropil threads, and oligodendroglial coiled bodies.

METHODS

797 neuropathologically confirmed PSP cases were genotyped for TRIM11 rs564309 and assessed for tau pathology across 20 neuroanatomical regions. Tau pathology measures and age at death were examined for association with TRIM11 rs564309-A using multivariable linear regression models.

RESULTS

TRIM11 rs564309-A was associated with increased neurofibrillary tangles pathology (P = 0.050), but was not significantly associated with age at death, neuropil threads, coiled bodies, or tufted astrocytes tau pathology scores.

CONCLUSIONS

TRIM11 rs564309 may influence burden of neurofibrillary tangles tau pathology in PSP; further study is warranted. © 2020 International Parkinson and Movement Disorder Society.

The MAPT H1 Haplotype Is a Risk Factor for Alzheimer's Disease in APOE ε4 Non-carriers

An ancestral inversion of 900 kb on chromosome 17q21, which includes the microtubule-associated protein tau (MAPT) gene, defines two haplotype clades in Caucasians (H1 and H2). The H1 haplotype has been linked inconsistently with AD. In a previous study, we showed that an SNP tagging this haplotype (rs1800547) was associated with AD risk in a large population from the Dementia Genetics Spanish Consortium (DEGESCO) including 4435 cases and 6147 controls. The association was mainly driven by individuals that were non-carriers of the APOE ε4 allele. Our aim was to replicate our previous findings in an independent sample of 4124 AD cases and 3290 controls from Spain (GR@ACE project) and to analyze the effect of the H1 sub-haplotype structure on the risk of AD. The H1 haplotype was associated with AD risk (OR = 1.12; p = 0.0025). Stratification analysis showed that this association was mainly driven by the APOE ε4 non-carriers (OR = 1.15; p = 0.0022). Pooled analysis of both Spanish datasets (n = 17,996) showed that the highest AD risk related to the MAPT H1/H2 haplotype was in those individuals that were the oldest [third tertile (>77 years)] and did not carry APOE ε4 allele (p = 0.001). We did not find a significant association between H1 sub-haplotypes and AD. H1c was nominally associated but lost statistical significance after adjusting by population sub-structure. Our results are consistent with the hypothesis that genetic variants linked to the MAPT H1/H2 are tracking a genuine risk allele for AD. The fact that this association is stronger in APOE ε4 non-carriers partially explains previous controversial results and might be related to a slower alternative causal pathway less dependent on brain amyloid load.

Cellular and regional vulnerability in frontotemporal tauopathies

The frontotemporal tauopathies all deposit abnormal tau protein aggregates, but often of only certain isoforms and in distinguishing pathologies of five main types (neuronal Pick bodies, neurofibrillary tangles, astrocytic plaques, tufted astrocytes, globular glial inclusions and argyrophilic grains). In those with isoform specific tau aggregates glial pathologies are substantial, even though there is limited evidence that these cells normally produce tau protein. This review will assess the differentiating features and clinicopathological correlations of the frontotemporal tauopathies, the genetic predisposition for these different pathologies, their neuroanatomical selectivity, current observations on how they spread through the brain, and any potential contributing cellular and molecular changes. The findings show that diverse clinical phenotypes relate most to the brain region degenerating rather than the type of pathology involved, that different regions on the MAPT gene and novel risk genes are associated with specific tau pathologies, that the 4-repeat glial tauopathies do not follow individual patterns of spreading as identified for neuronal pathologies, and that genetic and pathological data indicate that neuroinflammatory mechanisms are involved. Each pathological frontotemporal tauopathy subtype with their distinct pathological features differ substantially in the cell type affected, morphology, biochemical and anatomical distribution of inclusions, a fundamental concept central to future success in understanding the disease mechanisms required for developing therapeutic interventions. Tau directed therapies targeting genetic mechanisms, tau aggregation and pathological spread are being trialled, although biomarkers that differentiate these diseases are required. Suggested areas of future research to address the regional and cellular vulnerabilities in frontotemporal tauopathies are discussed.

Frontrunner in Translation: Progressive Supranuclear Palsy

Progressive supranuclear palsy (PSP) is a four-repeat tau proteinopathy. Abnormal tau deposition is not unique for PSP and is the basic pathologic finding in some other neurodegenerative disorders such as Alzheimer's disease (AD), age-related tauopathy, frontotemporal degeneration, corticobasal degeneration, and chronic traumatic encephalopathy. While AD research has mostly been focused on amyloid beta pathology until recently, PSP as a prototype of a primary tauopathy with high clinical-pathologic correlation and a rapid course is a crucial candidate for tau therapeutic research. Several novel approaches to slow disease progression are being developed. It is expected that the benefits of translational research in this disease will extend beyond the PSP population. This article reviews advances in the diagnosis, epidemiology, pathology, hypothesized etiopathogenesis, and biomarkers and disease-modifying therapeutic approaches of PSP that is leading it to become a frontrunner in translation.

Association of MAPT H1 subhaplotypes with neuropathology of lewy body disease

BACKGROUND

Genetic variation at the microtubule-associated protein tau locus is associated with clinical parkinsonism. However, it is unclear as to whether microtubule-associated protein tau H1 subhaplotypes are associated with the burden of neuropathological features of Lewy body disease.

OBJECTIVES

To evaluate associations of microtubule-associated protein tau haplotypes with severity of Lewy body pathology and markers of SN neuronal loss in Lewy body disease cases.

METHODS

Five hundred eighty-five autopsy-confirmed Lewy body disease cases were included. Six microtubule-associated protein tau variants (rs1467967, rs242557, rs3785883, rs2471738, rs8070723, and rs7521) were genotyped to define common microtubule-associated protein tau haplotypes. Lewy body counts were measured in five cortical regions. Ventrolateral and medial SN neuronal loss were assessed semiquantitatively. Nigrostriatal dopaminergic degeneration was quantified by image analysis of tyrosine hydroxylase immunoreactivity in the dorsolateral and ventromedial putamen.

RESULTS

The common microtubule-associated protein tau H2 haplotype did not show a strong effect on pathological burden in Lewy body disease. The rare H1j haplotype (1.3%) was significantly associated with a lower dorsolateral putaminal tyrosine hydroxylase immunoreactivity (and therefore greater dopaminergic degeneration) compared to other microtubule-associated protein tau haplotypes (P = 0.0016). Microtubule-associated protein tau H1j was also nominally (P ≤ 0.05) associated with a lower ventromedial putaminal tyrosine hydroxylase immunoreactivity (P = 0.010), but this did not survive multiple testing correction. Other nominally significant associations between microtubule-associated protein tau H1 subhaplotypes and neuropathological outcomes were observed.

CONCLUSIONS

A rare microtubule-associated protein tau H1 subhaplotype (H1j) may be associated with more severe putaminal dopaminergic degeneration in Lewy body disease cases. Microtubule-associated protein tau H1j has been associated previously with an increased risk of PD, and therefore our exploratory findings provide insight into the mechanism by which H1j modulates PD risk. © 2019 International Parkinson and Movement Disorder Society.

Four-repeat tauopathies

Tau is a microtubule-associated protein with versatile functions in the dynamic assembly of the neuronal cytoskeleton. Four-repeat (4R-) tauopathies are a group of neurodegenerative diseases defined by cytoplasmic inclusions predominantly composed of tau protein isoforms with four microtubule-binding domains. Progressive supranuclear palsy, corticobasal degeneration, argyrophilic grain disease or glial globular tauopathy belong to the group of 4R-tauopathies. The present review provides an introduction in the current concept of 4R-tauopathies, including an overview of the neuropathological and clinical spectrum of these diseases. It describes the genetic and environmental etiological factors, as well as the contemporary knowledge about the pathophysiological mechanisms, including post-translational modifications, aggregation and fragmentation of tau, as well as the role of protein degradation mechanisms. Furthermore, current theories about disease propagation are discussed, involving different extracellular tau species and their cellular release and uptake mechanisms. Finally, molecular diagnostic tools for 4R-tauopathies, including tau-PET and fluid biomarkers, and investigational therapeutic strategies are presented. In summary, we report on 4R-tauopathies as overarching disease concept based on a shared pathophysiological concept, and highlight the challenges and opportunities on the way towards a causal therapy.

Neuropathology and pathogenesis of extrapyramidal movement disorders: a critical update-I. Hypokinetic-rigid movement disorders

Extrapyramidal movement disorders include hypokinetic rigid and hyperkinetic or mixed forms, most of them originating from dysfunction of the basal ganglia (BG) and their information circuits. The functional anatomy of the BG, the cortico-BG-thalamocortical, and BG-cerebellar circuit connections are briefly reviewed. Pathophysiologic classification of extrapyramidal movement disorder mechanisms distinguish (1) parkinsonian syndromes, (2) chorea and related syndromes, (3) dystonias, (4) myoclonic syndromes, (5) ballism, (6) tics, and (7) tremor syndromes. Recent genetic and molecular-biologic classifications distinguish (1) synucleinopathies (Parkinson's disease, dementia with Lewy bodies, Parkinson's disease-dementia, and multiple system atrophy); (2) tauopathies (progressive supranuclear palsy, corticobasal degeneration, FTLD-17; Guamian Parkinson-dementia; Pick's disease, and others); (3) polyglutamine disorders (Huntington's disease and related disorders); (4) pantothenate kinase-associated neurodegeneration; (5) Wilson's disease; and (6) other hereditary neurodegenerations without hitherto detected genetic or specific markers. The diversity of phenotypes is related to the deposition of pathologic proteins in distinct cell populations, causing neurodegeneration due to genetic and environmental factors, but there is frequent overlap between various disorders. Their etiopathogenesis is still poorly understood, but is suggested to result from an interaction between genetic and environmental factors. Multiple etiologies and noxious factors (protein mishandling, mitochondrial dysfunction, oxidative stress, excitotoxicity, energy failure, and chronic neuroinflammation) are more likely than a single factor. Current clinical consensus criteria have increased the diagnostic accuracy of most neurodegenerative movement disorders, but for their definite diagnosis, histopathological confirmation is required. We present a timely overview of the neuropathology and pathogenesis of the major extrapyramidal movement disorders in two parts, the first one dedicated to hypokinetic-rigid forms and the second to hyperkinetic disorders.