The novel Tau mutation G335S: clinical, neuropathological and molecular characterization

Extremely Early-Onset Frontotemporal Dementia: A Case Report and Literature Review

BACKGROUND

In most cases, the onset of frontotemporal dementia (FTD) occurs between the ages of 45 and 65 years. However, some patients experience an extremely early disease onset.

OBJECTIVE

To investigate the clinical, genetic, and pathological features of extremely early-onset FTD.

METHODS

We conducted a comprehensive clinical, genetic, and neuropathological analysis of a 25-year-old patient experiencing the onset of behavioral variant frontotemporal dementia (bvFTD). In addition, we conducted a literature review and summarized the clinical, genetic, and pathological features of patients with FTD with onset age≤25 years.

RESULTS

The patient was diagnosed with bvFTD; however, there was no family history of FTD, no positive genetic test results and no deposition of TDP43, tau, ubiquitin, and synuclein in the brain. Literature screening identified 18 patients with onset age ≤25 years with FTD. The youngest patient was 14 years of age. Most patients (8/14) had a positive family history. The most common clinical phenotype was the behavioral variant (12/14). Genetic results were reported for 11 patients; the most common pathogenic gene was MAPT (10/12), with four cases of G389 R, two cases of P301 S, one case of G335 S, one case of G335A, one case of G335 V, and one case of L315 R. Pathological results were reported for 13 patients; the most common pathological subtype was tau (8/13).

CONCLUSION

FTD can start at an extremely early age. The most common phenotype of extremely early onset FTD was the behavioral variant, the most common pathogenic gene was MAPT, and the most common neuropathological type was tau.

Very early-onset behavioral variant frontotemporal dementia in a patient with a variant of uncertain significance of a FUS gene mutation

The behavioral variant of Frontotemporal dementia (bvFTD) has typically a progressive course with cognitive and behavioral changes that manifests between 50 and 70 years. Very early-onset bvFTD with rapid progression is a rare syndrome under the frontotemporal lobar degeneration (FTLD) umbrella that has been associated with a variety of protein deposition and genetic mutations. We present a case of a 24-year-old man who developed behavioral symptoms and progressed with severe cognitive impairment and functional loss within months.   Genetic testing identified a variant of uncertain significance (VUS) mutation in the FUS gene.

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.

The Q336H MAPT Mutation Linked to Pick's Disease Leads to Increased Binding of Tau to the Microtubule Network via Altered Conformational and Phosphorylation Effects

Tauopathies are neurodegenerative disorders characterized by Tau aggregation. Genetic studies on familial cases allowed for the discovery of mutations in the MAPT gene that increase Tau propensity to detach from microtubules and to form insoluble cytoplasmic Tau aggregates. Recently, the rare mutation Q336H has been identified to be associated with Pick’s disease (PiD) and biochemical analyses demonstrated its ability to increase the microtubules (MTs) polymerization, thus revealing an opposite character compared to other Tau mutations studied so far. Here we investigated the biophysical and molecular properties of Tau^Q336H in living cells by the employment of the conformational Tau biosensor CST. We found that this mutation alters Tau conformation on microtubules, stabilizes its binding to tubulin, and is associated with a paradoxical lower level of Tau phosphorylation. Moreover, we found that this mutation impacts the cytoskeletal complexity by increasing the tubulin filament length and the number of branches. However, despite these apparently non-pathological traits, we observed the formation of intracellular inclusions confirming that Q336H leads to aggregation. Our results suggest that the Tau aggregation process might be triggered by molecular mechanisms other than Tau destabilization or post-translational modifications which are likely to be detrimental to neuronal function in vivo.

Recommendations to distinguish behavioural variant frontotemporal dementia from psychiatric disorders

The behavioural variant of frontotemporal dementia (bvFTD) is a frequent cause of early-onset dementia. The diagnosis of bvFTD remains challenging because of the limited accuracy of neuroimaging in the early disease stages and the absence of molecular biomarkers, and therefore relies predominantly on clinical assessment. BvFTD shows significant symptomatic overlap with non-degenerative primary psychiatric disorders including major depressive disorder, bipolar disorder, schizophrenia, obsessive-compulsive disorder, autism spectrum disorders and even personality disorders. To date, ∼50% of patients with bvFTD receive a prior psychiatric diagnosis, and average diagnostic delay is up to 5-6 years from symptom onset. It is also not uncommon for patients with primary psychiatric disorders to be wrongly diagnosed with bvFTD. The Neuropsychiatric International Consortium for Frontotemporal Dementia was recently established to determine the current best clinical practice and set up an international collaboration to share a common dataset for future research. The goal of the present paper was to review the existing literature on the diagnosis of bvFTD and its differential diagnosis with primary psychiatric disorders to provide consensus recommendations on the clinical assessment. A systematic literature search with a narrative review was performed to determine all bvFTD-related diagnostic evidence for the following topics: bvFTD history taking, psychiatric assessment, clinical scales, physical and neurological examination, bedside cognitive tests, neuropsychological assessment, social cognition, structural neuroimaging, functional neuroimaging, CSF and genetic testing. For each topic, responsible team members proposed a set of minimal requirements, optimal clinical recommendations, and tools requiring further research or those that should be developed. Recommendations were listed if they reached a ≥ 85% expert consensus based on an online survey among all consortium participants. New recommendations include performing at least one formal social cognition test in the standard neuropsychological battery for bvFTD. We emphasize the importance of 3D-T1 brain MRI with a standardized review protocol including validated visual atrophy rating scales, and to consider volumetric analyses if available. We clarify the role of 18F-fluorodeoxyglucose PET for the exclusion of bvFTD when normal, whereas non-specific regional metabolism abnormalities should not be over-interpreted in the case of a psychiatric differential diagnosis. We highlight the potential role of serum or CSF neurofilament light chain to differentiate bvFTD from primary psychiatric disorders. Finally, based on the increasing literature and clinical experience, the consortium determined that screening for C9orf72 mutation should be performed in all possible/probable bvFTD cases or suspected cases with strong psychiatric features.

Impaired tau-microtubule interactions are prevalent among pathogenic tau variants arising from missense mutations

tau is a microtubule (MT)-associated protein that promotes tubulin assembly and stabilizes MTs by binding longitudinally along the MT surface. tau can aberrantly aggregate into pathological inclusions that define Alzheimer's disease, frontotemporal dementias, and other tauopathies. A spectrum of missense mutations in the tau-encoding gene microtubule-associated protein tau (MAPT) can cause frontotemporal dementias. tau aggregation is postulated to spread by a prion-like mechanism. Using a cell-based inclusion seeding assay, we recently reported that only a few tau variants are intrinsically prone to this type of aggregation. Here, we extended these studies to additional tau mutants and investigated their MT binding properties in mammalian cell-based assays. A limited number of tau variants exhibited modest aggregation propensity in vivo, but most tau mutants did not aggregate. Reduced MT binding appeared to be the most common dysfunction for the majority of tau variants due to missense mutations, implying that MT-targeting therapies could potentially be effective in the management of tauopathies.

MAPT mutations, tauopathy, and mechanisms of neurodegeneration

In multiple neurodegenerative diseases, including Alzheimer's disease (AD), a prominent pathological feature is the aberrant aggregation and inclusion formation of the microtubule-associated protein tau. Because of the pathological association, these disorders are often referred to as tauopathies. Mutations in the MAPT gene that encodes tau can cause frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17), providing the clearest evidence that tauopathy plays a causal role in neurodegeneration. However, large gaps in our knowledge remain regarding how various FTDP-17-linked tau mutations promote tau aggregation and neurodegeneration, and, more generally, how the tauopathy is linked to neurodegeneration. Herein, we review what is known about how FTDP-17-linked pathogenic MAPT mutations cause disease, with a major focus on the prion-like properties of wild-type and mutant tau proteins. The hypothesized mechanisms by which mutations in the MAPT gene promote tauopathy are quite varied and may not provide definitive insights into how tauopathy arises in the absence of mutation. Further, differences in the ability of tau and mutant tau proteins to support prion-like propagation in various model systems raise questions about the generalizability of this mechanism in various tauopathies. Notably, understanding the mechanisms of tauopathy induction and spread and tau-induced neurodegeneration has important implications for tau-targeting therapeutics.

Ordered Assembly of Tau Protein and Neurodegeneration

Tau filaments with distinct morphologies and/or isoform compositions underlie a large number of human neurodegenerative diseases. Their formation is important, because dominantly inherited mutations in MAPT, the tau gene, cause frontotemporal dementia with abundant filamentous tau inclusions. Assembly of tau may begin in a specific region of the brain, from where it spreads to other areas. It remains to be seen if the molecular species underlying tau aggregate-mediated neurodegeneration and propagation are the same or different. In the brains of mice transgenic for human mutant P301S tau, small tau filaments are the predominant seed-competent species. It has been suggested that different conformers of assembled tau may give rise to different human tauopathies, but until recently, it was not possible to study this directly. Electron cryo-microscopy can now be used to determine high-resolution structures of amyloid filaments from human brain. Paired helical and straight tau filaments of Alzheimer's disease are ultrastructural polymorphs. Each filament core is composed of two identical protofilaments extending from G273/304-E380 (in the numbering of the 441 amino acid isoform of human tau), which adopt a combined cross-β/β-helix structure. They comprise the ends of the first or second microtubule-binding repeat (R1 or R2), the whole of R3 and R4, as well as 12 amino acids after R4. By contrast, the core of the narrow filament of Pick's disease consists of a single protofilament extending from K254-F378 of 3R tau, which adopts a cross-β structure. It comprises the last 21 amino acids of R1, all of R3 and R4, as well as 10 amino acids after R4. Wide tau filaments of Pick's disease, which are in the minority, consist of two narrow filaments packed against each other. The tau filament folds of Alzheimer's and Pick's diseases appear to be conserved between different cases of disease. These findings show that filamentous tau adopts one fold in Alzheimer's disease and a different fold in Pick's disease, establishing the existence of distinct conformers.

Frontotemporal dementia

Frontotemporal dementia (FTD) is the second commonest cause of young onset dementia. Our understanding of FTD and its related syndromes has advanced significantly in recent years. Among the most prominent areas of progress is the overlap between FTD, MND, and other neurodegenerative conditions at a clinicopathologic and genetic level. In parallel major advances in neuroimaging techniques, the discovery of new genetic mutations as well as the development of potential biomarkers may serve to further expand knowledge of the biologic processes at play in FTD and may in turn propel research toward identifying curative and preventative pharmacologic therapies. The aim of this chapter is to discuss the clinical, pathologic, and genetic complexities of FTD and related disorders.

FTDP-17 Mutations Alter the Aggregation and Microtubule Stabilization Propensity of Tau in an Isoform-Specific Fashion

More than 50 different intronic and exonic autosomal dominant mutations in the tau gene have been linked to the neurodegenerative disorder frontotemporal dementia with Parkinsonism linked to chromosome-17 (FTDP-17). Although the pathological and clinical presentation of this disorder is heterogeneous among patients, the deposition of tau as pathological aggregates is a common feature. Collectively, FTDP-17 mutations have been shown to alter tau's ability to stabilize microtubules, enhance its aggregation, alter mRNA splicing, or induce its hyperphosphorylation, among other effects. Previous in vitro studies from our lab revealed that these mutations differ markedly from each other in the longest 2N4R isoform of tau. However, it is not entirely known whether the effect of a single mutation varies when compared between different isoforms of tau. Differences in the isoelectric points of the N-terminal region of tau isoforms lead to changes in their biochemical properties, raising the possibility that isoforms could also be disproportionately affected by disease-related mechanisms such as mutations. We therefore performed a comparative study of three FTDP-17 mutations present in different regions of tau (R5L, P301L, and R406W) in the three 4R isoforms of tau. We observed significant differences in the effect these mutations exert on the total amount and kinetics of aggregation, aggregate length distributions, and microtubule stabilizing propensity of 4R tau isoforms for all three selected mutants. These results demonstrate that different combinations of FTDP-17 mutations and tau isoforms are functionally distinct and could have important implications for our understanding of disease and animal models of tauopathies.

Protein astrogliopathies in human neurodegenerative diseases and aging

Neurodegenerative diseases are characterized by progressive dysfunction and loss of neurons associated with depositions of pathologically altered proteins showing hierarchical involvement of brain regions. The role of astrocytes in the pathogenesis of neurodegenerative diseases is explored as contributors to neuronal degeneration or neuroprotection pathways, and also as potential mediators of the transcellular spreading of disease-associated proteins. Protein astrogliopathy (PAG), including deposition of amyloid-β, prion protein, tau, α-synuclein, and very rarely transactive response DNA-binding protein 43 (TDP-43) is not unprecedented or unusual in neurodegenerative diseases. Morphological characterization of PAG is considered, however, only for the neuropathological diagnosis and classification of tauopathies. Astrocytic tau pathology is seen in primary frontotemporal lobar degeneration (FTLD) associated with tau pathologies (FTLD-Tau), and also in the form of aging-related tau astrogliopathy (ARTAG). Importantly, ARTAG shares common features with primary FTLD-Tau as well as with the astroglial tau pathologies that are thought to be hallmarks of a brain injury-related tauopathy known as chronic traumatic encephalopathy (CTE). Supported by experimental observations, the morphological variability of PAG might reflect distinct pathogenic involvement of different astrocytic populations. PAG might indicate astrocytic contribution to spreading or clearance of disease-associated proteins, however, this might lead to astrocytic dysfunction and eventually contribute to the degeneration of neurons. Here, we review recent advances in understanding ARTAG and other related forms of PAG.

Propagation of Tau Aggregates and Neurodegeneration

A pathway from the natively unfolded microtubule-associated protein Tau to a highly structured amyloid fibril underlies human Tauopathies. This ordered assembly causes disease and represents the gain of toxic function. In recent years, evidence has accumulated to suggest that Tau inclusions form first in a small number of brain cells, from where they propagate to other regions, resulting in neurodegeneration and disease. Propagation of pathology is often called prion-like, which refers to the capacity of an assembled protein to induce the same abnormal conformation in a protein of the same kind, initiating a self-amplifying cascade. In addition, prion-like encompasses the release of protein aggregates from brain cells and their uptake by neighboring cells. In mice, the intracerebral injection of Tau inclusions induces the ordered assembly of monomeric Tau, followed by its spreading to distant brain regions. Conformational differences between Tau aggregates from transgenic mouse brain and in vitro assembled recombinant protein account for the greater seeding potency of brain aggregates. Short fibrils constitute the major species of seed-competent Tau in the brains of transgenic mice. The existence of multiple human Tauopathies with distinct fibril morphologies has led to the suggestion that different molecular conformers (or strains) of aggregated Tau exist.

Characterization of Movement Disorder Phenomenology in Genetically Proven, Familial Frontotemporal Lobar Degeneration: A Systematic Review and Meta-Analysis

Background

Mutations in granulin (PGRN) and tau (MAPT), and hexanucleotide repeat expansions near the C9orf72 genes are the most prevalent genetic causes of frontotemporal lobar degeneration. Although behavior, language and movement presentations are common, the relationship between genetic subgroup and movement disorder phenomenology is unclear.

Objective

We conducted a systematic review and meta-analysis of the literature characterizing the spectrum and prevalence of movement disorders in genetic frontotemporal lobar degeneration.

Methods

Electronic databases were searched using terms related to frontotemporal lobar degeneration and movement disorders. Articles were included when cases had a proven genetic cause. Study-specific prevalence estimates for clinical features were transformed using Freeman-Tukey arcsine transformation, allowing for pooled estimates of prevalence to be generated using random-effects models.

Results

The mean age at onset was earlier in those with MAPT mutations compared to PGRN (p<0.001) and C9orf72 (p = 0.024). 66.5% of subjects had an initial non-movement presentation that was most likely a behavioral syndrome (35.7%). At any point during the disease, parkinsonism was the most common movement syndrome reported in 79.8% followed by progressive supranuclear palsy (PSPS) and corticobasal (CBS) syndromes in 12.2% and 10.7%, respectively. The prevalence of movement disorder as initial presentation was higher in MAPT subjects (35.8%) compared to PGRN subjects (10.1). In those with a non-movement presentation, language disorder was more common in PGRN subjects (18.7%) compared to MAPT subjects (5.4%).

Summary

This represents the first systematic review and meta-analysis of the occurrence of movement disorder phenomenology in genetic frontotemporal lobar degeneration. Standardized prospective collection of clinical information in conjunction with genetic characterization will be crucial for accurate clinico-genetic correlation.

A Novel Tau Mutation in Exon 12, p.Q336H, Causes Hereditary Pick Disease

Pick disease (PiD) is a frontotemporal lobar degeneration with distinctive neuronal inclusions (Pick bodies) that are enriched in 3-repeat (3R) tau. Although mostly sporadic, mutations in the tau gene (MAPT) have been reported. We screened 24 cases of neuropathologically confirmed PiD for MAPT mutations and found a novel mutation (c.1008G>C, p.Q336H) in 1 patient. Pathogenicity was confirmed on microtubule assembly and tau filament formation assays. The patient was compared with sporadic PiD and PiD associated with MAPT mutations from a review of the literature. The patient had behavioral changes at 55 years of age, followed by reduced verbal fluency, parkinsonism, and death at 63 years of age. His mother and maternal uncle had similar symptoms. Recombinant tau with p.Q336H mutation formed filaments faster than wild-type tau, especially with 3R tau. It also promoted more microtubule assembly than wild-type tau. We conclude that mutations in MAPT, including p.Q336H, can be associated with clinical, pathologic, and biochemical features that are similar to those in sporadic PiD. The pathomechanism of p.Q336H, and another previously reported variant at the same codon (p.Q336R), seems to be unique to MAPT mutations in that they not only predispose to abnormal tau filament formation but also facilitate microtubule assembly in a 3R tau-dependent manner.

Genetics in degenerative dementia: current status and applicability

An increasing number of hereditary neurodegenerative diseases, including autosomal-dominant Alzheimer disease (AD), familial autosomal-dominant frontotemporal dementia (FTD), and heritable Lewy body disease (LBD) have been defined at the molecular level in recent years, making it possible to determine the genotype before the onset of symptoms. The identification of deterministic genes for these common adult-onset genetic diseases is moving the field of genetic counseling toward a new and challenging direction. With the identification of genes associated with AD and FTD, there is considerable interest in the clinical application of genetic information in genetic counseling and testing. Progress in the genetics of dementing disorders and the availability of clinical tests for practicing physicians therefore increases the need for a better understanding of the multifaceted issues associated with genetic testing. The aims of this systematic review are: (1) to underline the need to consider a genetic etiology of AD, FTD, and LBD; (2) to provide clinicians with information necessary to effectively translate genetic diagnosis into clinical practice; and (3) to highlight gaps and uncertainties in the field which will need to be addressed by future research.

A network of RNA and protein interactions in Fronto Temporal Dementia

Frontotemporal dementia (FTD) is a neurodegenerative disorder characterized by degeneration of the fronto temporal lobes and abnormal protein inclusions. It exhibits a broad clinicopathological spectrum and has been linked to mutations in seven different genes. We will provide a picture, which connects the products of these genes, albeit diverse in nature and function, in a network. Despite the paucity of information available for some of these genes, we believe that RNA processing and post-transcriptional regulation of gene expression might constitute a common theme in the network. Recent studies have unraveled the role of mutations affecting the functions of RNA binding proteins and regulation of microRNAs. This review will combine all the recent findings on genes involved in the pathogenesis of FTD, highlighting the importance of a common network of interactions in order to study and decipher the heterogeneous clinical manifestations associated with FTD. This approach could be helpful for the research of potential therapeutic strategies.

Invited review: Frontotemporal dementia caused by microtubule-associated protein tau gene (MAPT) mutations: a chameleon for neuropathology and neuroimaging

Hereditary frontotemporal dementia associated with mutations in the microtubule-associated protein tau gene (MAPT) is a protean disorder. Three neuropathologic subtypes can be recognized, based on the presence of inclusions made of tau isoforms with three and four repeats, predominantly three repeats and mostly four repeats. This is relevant for establishing a correlation between structural magnetic resonance imaging and positron emission tomography using tracers specific for aggregated tau. Longitudinal studies will be essential to determine the evolution of anatomical alterations from the asymptomatic stage to the various phases of disease following the onset of symptoms.

The genetics of dystonias

Dystonia has been defined as a syndrome of involuntary, sustained muscle contractions affecting one or more sites of the body, frequently causing twisting and repetitive movements or abnormal postures. Dystonia is also a clinical sign that can be the presenting or prominent manifestation of many neurodegenerative and neurometabolic disorders. Etiological categories include primary dystonia, secondary dystonia, heredodegenerative diseases with dystonia, and dystonia plus. Primary dystonia includes syndromes in which dystonia is the sole phenotypic manifestation with the exception that tremor can be present as well. Most primary dystonia begins in adults, and approximately 10% of probands report one or more affected family members. Many cases of childhood- and adolescent-onset dystonia are due to mutations in TOR1A and THAP1. Mutations in THAP1 and CIZ1 have been associated with sporadic and familial adult-onset dystonia. Although significant recent progress had been made in defining the genetic basis for most of the dystonia-plus and heredodegenerative diseases with dystonia, a major gap remains in understanding the genetic etiologies for most cases of adult-onset primary dystonia. Common themes in the cellular biology of dystonia include G1/S cell cycle control, monoaminergic neurotransmission, mitochondrial dysfunction, and the neuronal stress response.

Pathogenic missense MAPT mutations differentially modulate tau aggregation propensity at nucleation and extension steps

Mutations in the MAPT gene encoding tau protein lead to neurofibrillary lesion formation, neurodegeneration, and cognitive decline associated with frontotemporal lobar degeneration. While some pathogenic mutations affect MAPT introns, resulting in abnormal splicing patterns, the majority occur in the tau coding sequence leading to single amino acid changes in tau primary structure. Depending on their location within the polypeptide chain, tau missense mutations have been reported to augment aggregation propensity. To determine the mechanisms underlying mutation-associated changes in aggregation behavior, the fibrillization of recombinant pathogenic mutants R5L, G272V, P301L, V337M, and R406W prepared in a full-length four-repeat human tau background was examined in vitro as a function of time and submicromolar tau concentrations using electron microscopy assay methods. Kinetic constants for nucleation and extension phases of aggregation were then estimated by direct measurement and mathematical simulation. Results indicated that the mutants differ from each other and from wild-type tau in their aggregation propensity. G272V and P301L mutations increased the rates of both filament nucleation and extension reactions, whereas R5L and V337M increased only the nucleation phase. R406W did not differ from wild-type in any kinetic parameter. The results show that missense mutations can directly promote tau filament formation at different stages of the aggregation pathway.

In vivo and postmortem clinicoanatomical correlations in frontotemporal dementia and parkinsonism linked to chromosome 17

BACKGROUND

Frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) is associated with mutations in the Microtubule-Associated Protein Tau(MAPT) gene or the Progranulin(PGRN) gene. MAPT mutations lead to widespread deposition of hyperphosphorylated tau protein (FTDP-17T). PGRN mutations are associated with ubiquitin- and TDP-43-positive inclusions in the frontotemporal cortex, striatum and hippocampus (FTDP-17U). Despite the differences, FTDP-17T and FTDP-17U share a largely overlapping clinical phenotype.

OBJECTIVE

To determine whether neuroimaging studies may allow an in vivo early differentiation between FTDP-17T and FTDP-17U.

METHODS

We studied 25 individuals affected with FTDP-17T associated with either the exon 10+3 (24 subjects) or the G335S (1 subject) MAPT mutation, as well as 3 FTDP-17U individuals, who were carriers of the A9D, IVS6-2A>G or R493X PGRN mutation. Neuroimaging studies, obtained along the course of the disease, were compared to the neuropathologic findings.

RESULTS

FTDP-17T cases were associated with symmetric frontotemporal atrophy. Behavioral changes constituted the predominant clinical presentation. Conversely, an asymmetric degenerative process was seen in all 3 PGRN cases, who presented with either corticobasal syndrome (A9D) or frontotemporal dementia and language deterioration (IVS6-2A>G and R493X).

CONCLUSION

Neuroimaging data, in the early disease stage of FTDP-17, may offer the possibility of an early differentiation of FTDP-17T and FTDP-17U phenotypes, independent of the genetic analysis.

Hereditary frontotemporal dementia caused by Tau gene mutations

Tau protein is involved in microtubule assembly and stabilization. Filamentous deposits made of tau constitute a defining characteristic of several neurodegenerative diseases. The relevance of tau dysfunction for neurodegeneration has been clarified through the identification of mutations in the Tau gene in cases with frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17). Although the mechanisms by which these mutations lead to nerve cell death are only incompletely understood, it is clear that they cause the formation of tau filaments with distinct morphologies and isoform compositions. The range of tau pathology identified in FTDP-17 recapitulates that in sporadic tauopathies, indicating a major role for tau dysfunction in these diseases.