Differences in a dinucleotide repeat polymorphism in the tau gene between Caucasian and Japanese populations: implication for progressive supranuclear palsy

Tau pathology in neurodegenerative disease: disease mechanisms and therapeutic avenues

Tauopathies are disorders associated with tau protein dysfunction and insoluble tau accumulation in the brain at autopsy. Multiple lines of evidence from human disease, as well as nonclinical translational models, suggest that tau has a central pathologic role in these disorders, historically thought to be primarily related to tau gain of toxic function. However, a number of tau-targeting therapies with various mechanisms of action have shown little promise in clinical trials in different tauopathies. We review what is known about tau biology, genetics, and therapeutic mechanisms that have been tested in clinical trials to date. We discuss possible reasons for failures of these therapies, such as use of imperfect nonclinical models that do not predict human effects for drug development; heterogeneity of human tau pathologies which may lead to variable responses to therapy; and ineffective therapeutic mechanisms, such as targeting of the wrong tau species or protein epitope. Innovative approaches to human clinical trials can help address some of the difficulties that have plagued our field's development of tau-targeting therapies thus far. Despite limited clinical success to date, as we continue to refine our understanding of tau's pathogenic mechanism(s) in different neurodegenerative diseases, we remain optimistic that tau-targeting therapies will eventually play a central role in the treatment of tauopathies.

Novel tau filament fold in corticobasal degeneration

Corticobasal degeneration (CBD) is a neurodegenerative tauopathy that is characterised by motor and cognitive disturbances (1–3). A higher frequency of the H1 haplotype of MAPT, the tau gene, is present in cases of CBD than in controls (4,5) and genome-wide association studies have identified additional risk factors (6). By histology, astrocytic plaques are diagnostic of CBD (7,8), as are detergent-insoluble tau fragments of 37 kDa by SDS-PAGE (9). Like progressive supranuclear palsy (PSP), globular glial tauopathy (GGT) and argyrophilic grain disease (AGD) (10), CBD is characterised by abundant filamentous tau inclusions that are made of isoforms with four microtubule-binding repeats (4R) (11–15). This distinguishes 4R tauopathies from Pick’s disease, filaments of which are made of three-repeat (3R) tau isoforms, and from Alzheimer’s disease and chronic traumatic encephalopathy (CTE), where both 3R and 4R tau isoforms are found in the filaments (16). Here we report the structures of tau filaments extracted from the brains of three individuals with CBD using electron cryo-microscopy (cryo-EM). They were identical between cases, but distinct from those of Alzheimer’s disease, Pick’s disease and CTE (17–19). The core of CBD filaments comprises residues K274-E380 of tau, spanning the last residue of R1, the whole of R2, R3 and R4, as well as 12 amino acids after R4. It adopts a novel four-layered fold, which encloses a large non-proteinaceous density. The latter is surrounded by the side chains of lysine residues 290 and 294 from R2 and 370 from the sequence after R4. CBD is the first 4R tauopathy with filaments of known structure.

Clinical and Genetic Study of the First Japanese FTDP-17 Patient with a Mutation of +3 in Intron 10 in the MAPT Gene

Frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17) with mutations in the MAPT gene is a hereditary neurodegenerative tauopathy with various clinical phenotypes. We herein report the first Japanese patient with FTDP-17 caused by an IVS10+3G>A mutation in the MAPT gene, which is linked to an H1M haplotype. The present study suggests that the IVS10+3G>A mutation in the MAPT gene can have originated from a non-Caucasian population. In the disease course, myoclonus and respiratory failure can be observed. This study may expand on the clinical and genetic findings for FTDP-17 with mutations in the MAPT gene.

Tau and TDP-43 proteinopathies: kindred pathologic cascades and genetic pleiotropy

We review the literature on Tau and TDP-43 proteinopathies in aged human brains and the relevant underlying pathogenetic cascades. Complex interacting pathways are implicated in Alzheimer's disease and related dementias (ADRD), wherein multiple proteins tend to misfold in a manner that is "reactive," but, subsequently, each proteinopathy may contribute strongly to the clinical symptoms. Tau proteinopathy exists in brains of individuals across a broad spectrum of primary underlying conditions-e.g., developmental, traumatic, and inflammatory/infectious diseases. TDP-43 proteinopathy is also expressed in a wide range of clinical disorders.  Although TDP-43 proteinopathy was first described in the central nervous system of patients with amyotrophic lateral sclerosis (ALS) and in subtypes of frontotemporal dementia (FTD/FTLD), TDP-43 proteinopathy is also present in chronic traumatic encephalopathy, cognitively impaired persons in advanced age with hippocampal sclerosis, Huntington's disease, and other diseases. We list known Tau and TDP-43 proteinopathies.  There is also evidence of cellular co-localization between Tau and TDP-43 misfolded proteins, suggesting common pathways or protein interactions facilitating misfolding in one protein by the other. Multiple pleiotropic gene variants can alter risk for Tau or TDP-43 pathologies, and certain gene variants (e.g., APOE ε4, Huntingtin triplet repeats) are associated with increases of both Tau and TDP-43 proteinopathies. Studies of genetic risk factors have provided insights into multiple nodes of the pathologic cascades involved in Tau and TDP-43 proteinopathies. Variants from a specific gene can be either a low-penetrant risk factor for a group of diseases, or alternatively, a different variant of the same gene may be a disease-driving allele that is associated with a relatively aggressive and early-onset version of a clinically and pathologically specific disease type. Overall, a complex but enlightening paradigm has emerged, wherein both Tau and TDP-43 proteinopathies are linked to numerous overlapping upstream influences, and both are associated with multiple downstream pathologically- and clinically-defined deleterious effects.

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.

Clinical features and disability milestones in multiple system atrophy and progressive supranuclear palsy

Multiple system atrophy (MSA) and progressive supranuclear palsy (PSP) are an adult-onset progressive neurodegenerative disorder that are known to display diverse clinical features and disease progression. We aim to characterize the clinical features and disease progression in patients with MSA and PSP by using a number of relevant disability milestones in Koreans. Forty-one patients with MSA and 14 patients with PSP had been enrolled. The mean age at onset of MSA-C, MSA-P and PSP was 56.7 ± 7.8, 62.5 ± 8.0, 68.9 ± 6.1 years respectively. The most commonly reported symptom at disease onset is disequilibrium/dizziness in MSA-C, tremor in MSA-P and frequent falling in PSP. The mean duration of reaching milestones after disease onset in MSA-C were as followings: 20.8 (urinary incontinence), 22.9 (frequent falling), 27.8 (wheelchair bound), 31.8 (dysarthria) and 35.8 months (diagnosis). The mean duration of reaching milestones after disease onset were 22.0 (urinary incontinence), 32.6 (frequent falling and diagnosis), 41.2 (dysarthria), 61.4 months (wheelchair bound) in MSA-P and 16.8 (dysarthria), 21.6 (diagnosis), 21.7 (frequent falling), 24.0 months (wheel chair bound) in PSP. In the case of MSA, dizziness may occur for the first time. Thus, when the patient complains of non-specific dizziness, a follow-up examination to distinguish it from MSA can be helpful. There was a trend for patients with MSA-C to reach more disability milestones than in MSA-P and PSP before diagnosis. It may explain why patients with MSA-C are required more detail history taking and neurologic examination at an earlier stage.

H1 tau haplotype-related genomic variation at 17q21.3 as an Asian heritage of the European Gypsy population

In this study, we examine the frequency of a 900 kb inversion at 17q21.3 in the Gypsy and Caucasian populations of Hungary, which may reflect the Asian origin of Gypsy populations. Of the two haplotypes (H1 and H2), H2 is thought to be exclusively of Caucasian origin, and its occurrence in other racial groups is likely to reflect admixture. In our sample, the H1 haplotype was significantly more frequent in the Gypsy population (89.8 vs 75.5%, P<0.001) and was in Hardy-Weinberg disequilibrium (P=0.017). The 17q21.3 region includes the gene of microtubule-associated protein tau, and this result might imply higher sensitivity to H1 haplotype-related multifactorial tauopathies among Gypsies.

Frontotemporal dementia with tau pathology

Tau is a microtubule-associated protein involved in microtubule assembly and stabilization. Filamentous deposits made of tau constitute a major defining characteristic of several neurodegenerative diseases known as tauopathies including Alzheimer's disease. The involvement of tau in neurodegeneration has been clarified by the identification of genetic mutations in the tau gene in cases with familial frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17). Although the mechanism through which tau mutations lead to neuronal death is still unresolved, it is clear that tau mutations lead to formation of tau filaments that have a different morphology, contain different types of tau isoforms and produce distinct tau deposits. The range of tau pathology identified in FTDP-17 recapitulates the tau pathology present in sporadic tauopathies and indicates that tau dysfunction plays a major role also in these diseases.

Progressive supranuclear palsy: pathology and genetics

Progressive supranuclear palsy (PSP) is an atypical Parkinsonian disorder associated with progressive axial rigidity, vertical gaze palsy, dysarthria and dysphagia. Neuropathologically, the subthalamic nucleus and brainstem, especially the midbrain tectum and the superior cerebellar peduncle, show atrophy. The substantia nigra shows loss of pigment corresponding to nigrostriatal dopaminergic degeneration. Microscopic findings include neuronal loss, gliosis and neurofibrillary tangles in basal ganglia, diencephalon and brainstem. Characteristic tau pathology is also found in glia. The major genetic risk factor for sporadic PSP is a common variant in the gene encoding microtubule-associated protein tau (MAPT) and recent studies have suggested that this may result in the altered expression of specific tau protein isoforms. Imaging studies suggest that there may be sensitive and specific means to differentiate PSP from other parkinsonian disorders, but identification of a diagnostic biomarker is still elusive.

Functional MAPT haplotypes: bridging the gap between genotype and neuropathology

The microtubule-associated protein tau (MAPT) locus has long been associated with sporadic neurodegenerative disease, notably progressive supranuclear palsy and corticobasal degeneration, and more recently with Alzheimer's disease and Parkinson's disease. However, the functional biological mechanisms behind the genetic association have only now started to emerge. The genomic architecture in the region spanning MAPT is highly complex, and includes a approximately 1.8 Mb block of linkage disequilibrium (LD). The region is divided into two major haplotypes, H1 and H2, defined by numerous single nucleotide polymorphisms and a 900 kb inversion which suppresses recombination. Fine mapping of the MAPT region has identified sub-clades of the MAPT H1 haplotype which are specifically associated with neurodegenerative disease. Here we briefly review the role of MAPT in sporadic and familial neurodegenerative disease, and then discuss recent work which, for the first time, proposes functional mechanisms to link MAPT haplotypes with the neuropathology seen in patients.

Clinical and genetic features of families with frontotemporal dementia and parkinsonism linked to chromosome 17 with a P301S tau mutation

In 9 patients with frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) with a P301S tau mutation, the predominant phenotype was frontotemporal dementia in 3 and parkinsonism in 6. Comparison of the tau genotype/haplotype carrying the mutation and the initial clinical sign showed association between H1/H1 and parkinsonism and between H1/H2 and personality change. Thus, the tau haplotype carrying the mutation and the tau genotype may be related to the clinical phenotype throughout the disease course.

Untangling the tau gene association with neurodegenerative disorders

Pathological tau protein inclusions have long been recognized to define the diverse range of neurodegenerative disorders called the tauopathies, which include Alzheimer's disease (AD), progressive supranuclear palsy (PSP) and frontotemporal lobar degeneration. Mutations in the tau gene, MAPT, cause familial frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17), and common variation in MAPT is strongly associated with the risk of PSP, corticobasal degeneration and, to a lesser extent, AD and Parkinson's disease (PD), implicating the involvement of tau in common neurodegenerative pathway(s). This review will discuss recent work towards the unravelling of the functional basis of this MAPT gene association. The region of chromosome 17q21 containing MAPT locus is characterized by the complex genomic architecture, including a large inversion that leads to a bipartite haplotype architecture, an inversion-mediated deletion and multiplications resulting from non-allelic homologous recombination between the MAPT family of low-copy repeats.

Correlation of tau gene polymorphism with age at onset of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease and its prevalence increases with age. The microtubule-associated protein tau (MAPT) is thought to be implicated in the pathogenesis of PD. Association of the MAPT H1 haplotype with PD in Caucasians has been extensively studied, however, the results were inconsistent. In this study, we investigated whether MAPT gene variants contribute to the pathogenesis process including the age at onset in Japanese PD. Promoter region of MAPT gene was analyzed to find polymorphisms in Japanese population. Two single nucleotide polymorphisms (SNPs), C-639T and Del-568TIns, in promoter region were found. C-639T was novel. Unlike Caucasians, the -226C and -45A alleles consisting of the H1 haplotype were monomorphic in Japanese population. Association analysis was performed using 240 PD and 191 controls in these SNPs. No significant association was observed between these SNPs and PD. Haplotype analysis also showed no significant association (P=0.72). However, the age at onset showed significant correlation with the genotypes of Del-568TIns in PD samples when analyzed by Kendall rank correlation test (Kendall tau=-0.098, P=0.0243). These results suggested that MAPT gene variants may modify the pathogenesis process of PD.

Effect of MAPT and APOE on prognosis of progressive supranuclear palsy

To assess genetic influence on the clinical presentation of progressive supranuclear palsy (PSP), the genetic effect on disease course was examined for variants in the tau gene (MAPT) and the gene for apolipoprotein E (APOE) in 58 cases of pathologically confirmed PSP. Clinical indicators of disease course included age at symptomatic onset (AAO), age at death (AAD), and disease duration (DD) and the genetic effects examined included MAPT haplotypes and APOE genotypes. From linear regression analysis, the MAPT H1/H1 genotype was associated with significantly earlier AAO (P=0.038). The MAPT genotype did not significantly influence DD or AAD. The APOE epsilon4 allele did not significantly influence AAO, AAD, or DD. Male sex was a predictor for earlier AAO (P=0.015). The interaction between MAPT and APOE was not significant for AAD and DD, but a significant negative coefficient was found for AAO suggesting their combination does not have an additive effect. These results support the assertion that the H1/H1 genotype may contribute to the earlier occurrence of clinical symptoms.

Comparative biochemistry of tau in progressive supranuclear palsy, corticobasal degeneration, FTDP-17 and Pick's disease

Neurodegenerative disorders referred to as tauopathies have cellular hyperphosphorylated tau protein aggregates in the absence of amyloid deposits. Comparative biochemistry of tau aggregates shows that they differ in both phosphorylation and content of tau isoforms. The six tau isoforms found in human brain contain either three (3R) or four microtubule-binding domains (4R). In Alzheimer's disease, all six tau isoforms are abnormally phosphorylated and aggregate into paired helical filaments. They are detected by immunoblotting as a major tau triplet (tau55, 64 and 69). In corticobasal degeneration and progressive supranuclear palsy, only 4R-tau isoforms aggregate into twisted and straight filaments respectively. They appear as a major tau doublet (tau64 and 69). Finally, in Pick's disease, only 3R-tau isoforms aggregate into random coiled filaments. They are characterized by another major tau doublet (tau55 and 64). These differences in tau isoforms may be related to either the degeneration of particular cell populations in a given disorder or aberrant cell trafficking of particular tau isoforms. Finally, recent findings provide a direct link between a genetic defect in tau and its abnormal aggregation into filaments in fronto-temporal dementia with Parkinsonism linked to chromosome 17, demonstrating that tau aggregation is sufficient for nerve cell degeneration. Thus, tau mutations and polymorphisms may also be instrumental in many neurodegenerative disorders.

Tau-positive glial inclusions in progressive supranuclear palsy, corticobasal degeneration and Pick's disease

The presence of tau-positive glial inclusions has been recently found a consistent feature in the brains of patients with progressive supranuclear palsy (PSP), corticobasal degeneration (CBD) and Pick's disease (PiD). These inclusions are classified based on cellular origin as tau-positive astrocytes, presumably either fibrillary or protoplasmic, coiled bodies and glial threads. Immunohistochemically, their major structural component is abnormal tau proteins, similar to those found in Alzheimer's disease. Nevertheless, their morphology, including ultrastructural profile, has been suggested to be distinctive for each disease. The profile and extent of particular glial inclusions correlate well with disease phenotype. Highly characteristic correlations include tufts of abnormal fibers in PSP, astrocytic plaques and dense glial threads in CBD and ramified astrocytes and small Pick body-like inclusions in PiD. The significance of the inclusions in disease pathogenesis and their biochemical characteristics remain to be clarified. Nevertheless, these distinctive glial lesions most likely reflect fundamental alterations in isoform composition of tau as well as its specific cellular and regional expression in sporadic tauopathies.

The Effect of tau genotype on clinical features in FTDP-17

The clinical phenotype of frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17) varies. This variability is seen not only between kindreds with different mutations but also in families sharing the same mutation. Inheritance of tau haplotype (H1) and genotype (H1/H1) has been established as a risk factor for some neurodegenerative disorders with parkinsonism. We assessed the effect of tau polymorphism on the clinical features of FTDP-17 in 61 cases from 30 separately ascertained families with four different tau mutations, including P301L, +16, N279K, and P301S. There were no significant differences of age at symptomatic onset and disease duration between H1/H1 and H1/H2 genotypes. The comparison between tau genotype and type of initial clinical sign showed an association between the H1/H1 genotype and parkinsonian phenotype and between the H1/H2 genotype and frontotemporal dementia phenotype (OR=11.7; 95% confidence interval, 1.4-98.7; P=0.008). Our results suggest that tau genotype does not influence the disease course. However, it may predispose to a specific clinical sign in the early stage of FTDP-17.

Microtubule-associated protein tau gene: a risk factor in human neurodegenerative diseases

Tau is a microtubule-associated protein mainly expressed in neurons of central nervous system, which is crucial in the maintenance of these cells. It has a central role in the polymerization and stabilization of microtubules and in the traffic of organelles along axons and dendrites. Aggregates of hyperphosphorylated forms of tau protein participate in the formation of neurofibrillary tangles, which characterize numerous neurodegenerative disorders named tauopathies. The analysis of tau gene and the study of familial cases of tauopathies have led to the discovery of tau gene mutations that cause inherited dementia designated as Frontotemporal dementia (FTD) with parkinsonism linked to chromosome 17 (FTDP-17). However, these familial cases remain rare compared to the sporadic tauopathies, the later involving both genetic and environmental etiologic factors. As tau pathology represents a primary pathogenic event in various neurodegenerative diseases, the hypothesis that tau genotype could influence the development of these diseases was tested by several groups. This review summarizes advances in the molecular genetics of the tau gene, as well as recent studies addressing the disease incidence of novel tau polymorphisms in different neurodegenerative diseases. Hopefully, the identification of several genetic defects of the tau gene will be helpful in improving our understanding of the role of tau protein in the pathogenesis of various neurodegenerative diseases.

Tau gene mutations: dissecting the pathogenesis of FTDP-17

Tau is a microtubule-associated protein involved in microtubule assembly and stabilization. Abnormal filamentous tau deposits constitute a major defining characteristic of several neurodegenerative diseases, including Alzheimer's disease. Although the presence of tau pathology correlates with the symptoms of Alzheimer's disease, there was no genetic evidence linking tau to neurodegeneration until recently. However, since 1998, the identification of more than 25 mutations in the tau gene, associated with frontotemporal dementia and parkinsonism linked to chromosome 17, has demonstrated that tau dysfunction can lead to neurodegeneration and the development of clinical symptoms.

Parkinson's genetics: molecular insights for the new millennium

In idiopathic Parkinson's disease and familial parkinsonism, the limited number of overlapping clinical and pathological outcomes argue that a common underlying molecular pathway is perturbed. Genetic methods are a powerful approach to identify molecular components of disease. We summarize recent attempts to identify the genetic components of familial parkinsonism, without a priori assumptions about disease causation. Much effort has been expended on mapping in families with early-onset disease, in which parkinsonism appears inherited as a Mendelian trait. More recently, association methods have been employed in late-onset disease using affected sib-pairs and population isolates. These findings have been extrapolated to Parkinson's disease in the community with some success. We review the molecular synthesis now emerging from a genetic perspective.

Expression patterns of tau mRNA isoforms correlate with susceptible lesions in progressive supranuclear palsy and corticobasal degeneration

Deposition of hyperphosphorylated tau (p-tau) has been observed in several neurodegenerative diseases. The six isoforms of tau are divided into two main groups including three repeat (3R) and four repeat (4R) microtubule-binding domains. Using quantitative RT-PCR method and immunohistochemistry with phosphorylation dependent anti-tau antibody (AT8), we investigated the expression level of tau mRNA isoforms in the frontal cortex and globus pallidus of patients with progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD) to determine whether altered expression patterns of tau mRNA isoforms correlate with p-tau accumulation. The 4R/3R ratios in frontal cortices of CBD and globus pallidus of PSP and CBD were significantly higher than the control (P<0.05). There was no correlation between the expression patterns of tau mRNA isoforms and p-tau accumulation. Our findings suggest that neurodegeneration of PSP and CBD could be regulated by alternative splicing of tau mRNA to yield high 4R/3R ratio. In addition, the lack of correlation between the expression pattern of tau mRNA isoforms and p-tau accumulation suggests that not only alternative splicing of tau mRNA, but also other factors such as post-transcriptional or translational modifications may play a role in the pathogenesis of specific neurodegeneration in PSP and CBD.

Progressive supranuclear palsy: clinical and genetic aspects

PURPOSE OF THE REVIEW

This review focuses on the recent additions to the literature in the clinical and genetic aspects of progressive supranuclear palsy.

RECENT FINDINGS

Clinical features of progressive supranuclear palsy are reasonably well established and known to be quite characteristic. Recent epidemiological studies suggest that the disorder is more common than previously considered and that it is frequently misdiagnosed. New laboratory and novel imaging techniques are being tested and cerebrospinal fluid levels of tau protein have been found helpful in diagnosis. Pathological and biochemical studies in progressive supranuclear palsy brains have shown the predominance of hyperphosphorylated tau isoforms which contain the sequence encoded by exon 10 (4R) aggregated into filaments. Familial tauopathies linked to tau gene mutations showing clinical and neuropathological overlap with sporadic progressive supranuclear palsy have been described. Despite recent discoveries of the strong genetic association of sporadic progressive supranuclear palsy with tau gene polymorphisms, a specific risk allele for developing the palsy has not yet been identified yet.

SUMMARY

Recent clinical studies and clinicopathological correlations are contributing significantly to the delineation of the clinical features of progressive supranuclear palsy. These features and the appropriate use of laboratory tests allow for an earlier identification of the disease and a more accurate premortem diagnosis. However, no specific biological markers for the disorder are available yet, and consequently diagnosis in the early stages or when some of the characteristic signs and symptoms are missing, remains a major challenge. Despite the recent advances in the understanding of genetic factors involved in progressive supranuclear palsy, the cause of the disease still remains unknown. Biochemical studies in brains from progressive supranuclear palsy patients provide a potential helpful instrument to improve the characterization of this disorder.

Cortical synapse loss in progressive supranuclear palsy

Cortical synapse loss, the probable substrate of cognitive impairment in Alzheimer disease (AD), has not previously been evaluated in progressive supranuclear palsy (PSP). Hypothesizing that synapse loss would be greater in demented than non-demented PSP patients, we examined synaptophysin concentrations in 8 cases of PSP (5 demented and 3 nondemented cases). We found a decrease in mean synaptophysin concentration in these 8 cases in frontal, temporal, and parietal lobes, and in cerebellum, compared to the means in corresponding lobes of 16 controls. The decreases were similar to those in 28 cases of AD, but not as great. We determined synaptophysin concentration from motor cortex in only 4 of our PSP cases, 2 demented and 2 non-demented. The average concentrations in these 4 cases were lower than in AD motor cortex; both were lower than controls. When demented and non-demented PSP cases were compared, neocortical synaptophysin concentrations in non-demented PSP cases were lower than in demented cases. There appears to be a link between AD and PSP, in that synapse loss is found in both. However, the basis and significance of the prominent neocortical synapse loss in PSP, especially in non-demented subjects, remain to be explored.

Increased risk for frontotemporal dementia through interaction between tau polymorphisms and apolipoprotein E epsilon4

The tau gene has an important role in frontotemporal dementia (FTD) as pathogenic mutations have been found in hereditary forms of the disease. Furthermore, a certain extended tau haplotype has been shown to increase the risk for progressive supranuclear palsy, corticobasal degeneration, Parkinson's disease and, in interaction with the apolipoprotein E (apoE) epsilon4 allele, Alzheimer's disease. By microsatellite analysis we investigated an intronic tau polymorphism, in linkage disequilibrium with the extended tau haplotype, in FTD patients (n = 36) and healthy controls (n = 39). No association between any of the tau alleles/genotypes and FTD was seen, but certain tau alleles and apoE epsilon4 interactively increased the risk of FTD (p = 0.006). We thus propose that this extended tau haplotype in combination with apoE epsilon4 is a genetic risk factor for FTD.

Tau polymorphisms are not associated with Alzheimer's disease

Alzheimer's disease (AD) is one of a number of neurodegenerative conditions including frontotemporal dementia and progressive supranuclear palsy that are associated with abnormal tau protein aggregates in neurons. Mutations in the tau gene cause familial forms of frontotemporal dementia and alleles of the tau gene have been associated with risk for progressive supranuclear palsy. However, studies evaluating whether polymorphic variation in tau is associated with AD have produced conflicting results. We investigated the role of the tau exon 2 polymorphism in a large sample of AD cases and controls and found no evidence that polymorphic variation in tau is associated AD.

Recent advances in atypical parkinsonian disorders

Recent advances in epidemiologic, diagnostic, pathologic, and management aspects of atypical parkinsonian disorders are reviewed and placed in perspective. The implications of considering progressive supranuclear palsy and corticobasal degeneration as tauopathies, and multiple system atrophy and dementia with Lewy bodies as alpha-synucleopathies are discussed.