Rapidly progressive autosomal dominant parkinsonism and dementia with pallido-ponto-nigral degeneration

Prominent loss of striatal dopamine transporter binding in frontotemporal lobar degeneration with the MAPT N279K mutation present as early as at prodromal stage without parkinsonism

Our research found out, from 123I-FP-CIT SPECT scans of three familial frontotemporal dementia (fFTD) individuals with MAPT N279K mutation and similar autopsy findings of frontotemporal degeneration with severe neuronal loss in the substantia nigra, that prominent decrease of dopamine transporter binding (z-score < -5.0) was present at prodromal fFTD without parkinsonism.

Osteopontin drives neuroinflammation and cell loss in MAPT-N279K frontotemporal dementia patient neurons

Frontotemporal dementia (FTD) is an incurable group of early-onset dementias that can be caused by the deposition of hyperphosphorylated tau in patient brains. However, the mechanisms leading to neurodegeneration remain largely unknown. Here, we combined single-cell analyses of FTD patient brains with a stem cell culture and transplantation model of FTD. We identified disease phenotypes in FTD neurons carrying the MAPT-N279K mutation, which were related to oxidative stress, oxidative phosphorylation, and neuroinflammation with an upregulation of the inflammation-associated protein osteopontin (OPN). Human FTD neurons survived less and elicited an increased microglial response after transplantation into the mouse forebrain, which we further characterized by single nucleus RNA sequencing of microdissected grafts. Notably, downregulation of OPN in engrafted FTD neurons resulted in improved engraftment and reduced microglial infiltration, indicating an immune-modulatory role of OPN in patient neurons, which may represent a potential therapeutic target in FTD.

HCS-Splice: A High-Content Screening Method to Advance the Discovery of RNA Splicing-Modulating Therapeutics

Nucleic acid therapeutics have demonstrated an impressive acceleration in recent years. They work through multiple mechanisms of action, including the downregulation of gene expression and the modulation of RNA splicing. While several drugs based on the former mechanism have been approved, few target the latter, despite the promise of RNA splicing modulation. To improve our ability to discover novel RNA splicing-modulating therapies, we developed HCS-Splice, a robust cell-based High-Content Screening (HCS) assay. By implementing the use of a two-colour (GFP/RFP) fluorescent splicing reporter plasmid, we developed a versatile, effective, rapid, and robust high-throughput strategy for the identification of potent splicing-modulating molecules. The HCS-Splice strategy can also be used to functionally confirm splicing mutations in human genetic disorders or to screen drug candidates. As a proof-of-concept, we introduced a dementia-related splice-switching mutation in the Microtubule-Associated Protein Tau (MAPT) exon 10 splicing reporter. We applied HCS-Splice to the wild-type and mutant reporters and measured the functional change in exon 10 inclusion. To demonstrate the applicability of the method in cell-based drug discovery, HCS-Splice was used to evaluate the efficacy of an exon 10-targeting siRNA, which was able to restore the correct alternative splicing balance.

Genetically Engineered Triple MAPT-Mutant Human-Induced Pluripotent Stem Cells (N279K, P301L, and E10+16 Mutations) Exhibit Impairments in Mitochondrial Bioenergetics and Dynamics

Pathological abnormalities in the tau protein give rise to a variety of neurodegenerative diseases, conjointly termed tauopathies. Several tau mutations have been identified in the tau-encoding gene MAPT, affecting either the physical properties of tau or resulting in altered tau splicing. At early disease stages, mitochondrial dysfunction was highlighted with mutant tau compromising almost every aspect of mitochondrial function. Additionally, mitochondria have emerged as fundamental regulators of stem cell function. Here, we show that compared to the isogenic wild-type triple MAPT-mutant human-induced pluripotent stem cells, bearing the pathogenic N279K, P301L, and E10+16 mutations, exhibit deficits in mitochondrial bioenergetics and present altered parameters linked to the metabolic regulation of mitochondria. Moreover, we demonstrate that the triple tau mutations disturb the cellular redox homeostasis and modify the mitochondrial network morphology and distribution. This study provides the first characterization of disease-associated tau-mediated mitochondrial impairments in an advanced human cellular tau pathology model at early disease stages, ranging from mitochondrial bioenergetics to dynamics. Consequently, comprehending better the influence of dysfunctional mitochondria on the development and differentiation of stem cells and their contribution to disease progression may thus assist in the potential prevention and treatment of tau-related neurodegeneration.

In Vivo 18 F-APN-1607 Tau Positron Emission Tomography Imaging in MAPT Mutations: Cross-Sectional and Longitudinal Findings

BACKGROUND

Frontotemporal lobar degeneration with tauopathy caused by MAPT (microtubule-associated protein tau) mutations is a highly heterogenous disorder. The ability to visualize and longitudinally monitor tau deposits may be beneficial to understand disease pathophysiology and predict clinical trajectories.

OBJECTIVE

The aim of this study was to investigate the cross-sectional and longitudinal ¹⁸ F-APN-1607 positron emission tomography/computed tomography (PET/CT) imaging findings in MAPT mutation carriers.

METHODS

Seven carriers of MAPT mutations (six within exon 10 and one outside of exon 10) and 15 healthy control subjects were included. All participants underwent ¹⁸ F-APN-1607 PET/CT at baseline. Three carriers of exon 10 mutations received follow-up ¹⁸ F-APN-1607 PET/CT scans. Standardized uptake value ratio (SUVR) maps were obtained using the cerebellar gray matter as the reference region. SUVR values observed in MAPT mutation carriers were normalized to data from healthy control subjects. A regional SUVR z score ≥ 2 was used as the criterion to define positive ¹⁸ F-APN-1607 PET/CT findings.

RESULTS

Although the seven study patients had heterogenous clinical phenotypes, all showed a significant ¹⁸ F-APN-1607 uptake characterized by high-contrast signals. However, the anatomical localization of tau deposits differed in patients with distinct clinical symptoms. Follow-up imaging data, which were available for three patients, demonstrated worsening trends in patterns of tau accumulation over time, which were paralleled by a significant clinical deterioration.

CONCLUSIONS

Our data represent a promising step in understanding the usefulness of ¹⁸ F-APN-1607 PET/CT imaging for detecting tau accumulation in MAPT mutation carriers. Our preliminary follow-up data also suggest the potential value of ¹⁸ F-APN-1607 PET/CT for monitoring the longitudinal trajectories of frontotemporal lobar degeneration caused by MAPT mutations. © 2021 International Parkinson and Movement Disorder Society.

Pallidal degenerations and related disorders: an update

Neurodegenerative disorders involving preferentially the globus pallidus, its efferet and afferent circuits and/or related neuronal systems are rare. They include a variety of both familial and sporadic progressive movement disorders, clinically manifesting as choreoathetosis, dystonia, Parkinsonism, akinesia or myoclonus, often associated with seizures, mental impairment and motor or cerebellar symptoms. Based on the involved neuronal systems, this heterogenous group has been classified into several subgroups: "pure" pallidal atrophy (PPA) and extended forms, pallidonigral and pallidonigrospinal degeneration (PND, PNSD), pallidopyramidal syndrome (PPS), a highly debatable group, pallidopontonigral (PPND), nigrostriatal-pallidal-pyramidal degeneration (NSPPD) (Kufor-Rakeb syndrome /KRS), pallidoluysian degeneration (PLD), pallidoluysionigral degeneration (PLND), pallidoluysiodentate atrophy (PLDA), the more frequent dentatorubral-pallidoluysian atrophy (DRPLA), and other hereditary multisystem disorders affecting these systems, e.g., neuroferritinopathy (NF). Some of these syndromes are sporadic, others show autosomal recessive or dominant heredity, and for some specific gene mutations have been detected, e.g., ATP13A2/PARK9 (KRS), FTL1 or ATP13A2 (neuroferritinopathy), CAG triple expansions in gene ATN1 (DRPLA) or pA152T variant in MAPT gene (PNLD). One of the latter, and both PPND and DRPLA are particular subcortical 4-R tauopathies, related to progressive supranuclear palsy (PSP), corticobasal degeneration (CBD) and frontotemporal lobe degeneration-17 (FTLD-17), while others show additional 3-R and 4-R tauopathies or TDP-43 pathologies. The differential diagnosis includes a large variety of neurodegenerations ranging from Huntington and Joseph-Machado disease, tauopathies (PSP), torsion dystonia, multiple system atrophy, neurodegeneration with brain iron accumulation (NBIA), and other extrapyramidal disorders. Neuroimaging data and biological markers have been published for only few syndromes. In the presence of positive family histories, an early genetic counseling may be effective. The etiology of most phenotypes is unknown, and only for some pathogenic mechanisms, like polyglutamine-induced oxidative stress and autophagy in DRPLA, mitochondrial dysfunction induced by oxidative stress in KRS or ferrostasis/toxicity and protein aggregation in NF, have been discussed. Currently no disease-modifying therapy is available, and symptomatic treatment of hypo-, hyperkinetic, spastic or other symptoms may be helpful.

Japanese Familial Cases of Frontotemporal Dementia and Parkinsonism with N279K Tau Gene Mutation

Background

Mutations in the tau gene linked to chromosome 17 cause frontotemporal dementia and parkinsonism (FTDP-17).

Objective

This study presents 3 Japanese familial cases diagnosed with N279K tau gene mutation, including 1 autopsy-confirmed case.

Methods

We compared the clinical presentations, cognitive functions, and images between the 3 familial cases diagnosed with N279K mutation.

Results

All 3 patients presented symptoms in their early 40s. One patient showed severe cognitive dysfunction and died in his sixth year after onset. The remaining 2 cases presented with parkinsonism-dominant clinical features. Among the 2 cases, 1 presented the characteristic symptoms of progressive supranuclear palsy. The pathological features of the dementia-dominant case showed frontal and temporal lobe-dominant neuronal loss and gliosis. Tau-positive neuronal and glial inclusions were found throughout. Further, tufted astrocytes and globose tangles were present whereas there were no Pick bodies and astrocytic plaques, compatible with pathology-confirmed frontotemporal lobar degeneration (FTLD) -tau subtypes.

Conclusions

Patients with FTDP-17 can be classified into the following 2 major groups: dementia and parkinsonism-plus predominant phenotypes. Among our 3 cases, 1 showed dementia predominance whereas the other 2 showed parkinsonism predominance. Mutations in the microtubule-associated protein tau (MAPT) present with several pathological features. Clinically, our case presented a behavioral variant frontotemporal dementia (bvFTD). However, morphologically, the observed glial and neuronal pathology met the criteria for progressive supranuclear palsy (PSP). This study highlights the clinical heterogeneity within and between families with same MAPT mutation. Few pathologically confirmed PSP cases have been reported with mutations in MAPT.

Modelling frontotemporal dementia using patient-derived induced pluripotent stem cells

Frontotemporal dementia (FTD) describes a group of clinically heterogeneous conditions that frequently affect people under the age of 65 (Le Ber et al., 2013). There are multiple genetic causes of FTD, including coding or splice-site mutations in MAPT, GRN mutations that lead to haploinsufficiency of progranulin protein, and a hexanucleotide GGGGCC repeat expansion in C9ORF72. Pathologically, FTD is characterised by abnormal protein accumulations in neurons and glia. These aggregates can be composed of the microtubule-associated protein tau (observed in FTD with MAPT mutations), the DNA/RNA-binding protein TDP-43 (seen in FTD with mutations in GRN or C9ORF72 repeat expansions) or dipeptide proteins generated by repeat associated non-ATG translation of the C9ORF72 repeat expansion. There are currently no disease-modifying therapies for FTD and the availability of in vitro models that recapitulate pathologies in a disease-relevant cell type would accelerate the development of novel therapeutics. It is now possible to generate patient-specific stem cells through the reprogramming of somatic cells from a patient with a genotype/phenotype of interest into induced pluripotent stem cells (iPSCs). iPSCs can subsequently be differentiated into a plethora of cell types including neurons, astrocytes and microglia. Using this approach has allowed researchers to generate in vitro models of genetic FTD in human cell types that are largely inaccessible during life. In this review we explore the recent progress in the use of iPSCs to model FTD, and consider the merits, limitations and future prospects of this approach.

Imaging Biomarkers for Neurodegeneration in Presymptomatic Familial Frontotemporal Lobar Degeneration

Frontotemporal lobar degeneration (FTLD) is a neurodegenerative disorder characterized by behavioral changes, language abnormality, as well as executive function deficits and motor impairment. In about 30-50% of FTLD patients, an autosomal dominant pattern of inheritance was found with major mutations in the MAPT, GRN, and the C9orf72 repeat expansion. These mutations could lead to neurodegenerative pathology years before clinical symptoms onset. With potential disease-modifying treatments that are under development, non-invasive biomarkers that help determine the early brain changes in presymptomatic FTLD patients will be critical for tracking disease progression and enrolling the right participants into the clinical trials at the right time during the disease course. In recent years, there is increasing evidence that a number of imaging biomarkers show the abnormalities during the presymptomatic stage. Imaging biomarkers of presymptomatic familial FTLD may provide insight into the underlying neurodegenerative process years before symptom onset. Structural magnetic resonance imaging (MRI) has demonstrated cortical degeneration with a mutation-specific neurodegeneration pattern years before onset of clinical symptoms in presymptomatic familial FTLD mutation carriers. In addition, diffusion tensor imaging (DTI) has shown the loss of white matter microstructural integrity in the presymptomatic stage of familial FTLD. Furthermore, proton magnetic resonance spectroscopy (¹H MRS), which provides a non-invasive measurement of brain biochemistry, has identified early neurochemical abnormalities in presymptomatic MAPT mutation carriers. Positron emission tomography (PET) imaging with [¹⁸F]-fluorodeoxyglucose (FDG) has demonstrated the glucose hypometabolism in the presymptomatic stage of familial FTLD. Also, a novel PET ligand, ¹⁸F-AV-1451, has been used in this group to evaluate tau deposition in the brain. Promising imaging biomarkers for presymptomatic familial FTLD have been identified and assessed for specificity and sensitivity for accurate prediction of symptom onset and tracking disease progression during the presymptomatic stage when clinical measures are not useful. Furthermore, identifying imaging biomarkers for the presymptomatic stage is important for the design of disease-modifying trials. We review the recent progress in imaging biomarkers of the presymptomatic phase of familial FTLD and discuss the imaging techniques and analysis methods, with a focus on the potential implication of these imaging techniques and their utility in specific mutation types.

Rates of lobar atrophy in asymptomatic MAPT mutation carriers

INTRODUCTION

The aim of this study was to investigate the rates of lobar atrophy in the asymptomatic microtubule-associated protein tau (MAPT) mutation carriers.

METHODS

MAPT mutation carriers (n = 14; 10 asymptomatic, 4 converters from asymptomatic to symptomatic) and noncarriers (n = 13) underwent structural magnetic resonance imaging and were followed annually with a median of 9.2 years. Longitudinal changes in lobar atrophy were analyzed using the tensor-based morphometry with symmetric normalization algorithm.

RESULTS

The rate of temporal lobe atrophy in asymptomatic MAPT mutation carriers was faster than that in noncarriers. Although the greatest rate of atrophy was observed in the temporal lobe in converters, they also had increased atrophy rates in the frontal and parietal lobes compared to noncarriers.

DISCUSSION

Accelerated decline in temporal lobe volume occurs in asymptomatic MAPT mutation carriers followed by the frontal and parietal lobe in those who have become symptomatic. The findings have implications for monitoring the progression of neurodegeneration during clinical trials in asymptomatic MAPT mutation carriers.

Frontal lobe 1H MR spectroscopy in asymptomatic and symptomatic MAPT mutation carriers

OBJECTIVE

To determine the frontal lobe proton magnetic resonance spectroscopy (¹H MRS) abnormalities in asymptomatic and symptomatic carriers of microtubule-associated protein tau (MAPT) mutations.

METHODS

We recruited patients with MAPT mutations from 5 individual families, who underwent single voxel ¹H MRS from the medial frontal lobe at 3T (n = 19) from the Longitudinal Evaluation of Familial Frontotemporal Dementia Subjects (LEFFTDS) Study at the Mayo Clinic site. Asymptomatic MAPT mutation carriers (n = 9) had Frontotemporal Lobar Degeneration Clinical Dementia Rating Sum of Boxes (FTLD-CDR SOB) score of zero, and symptomatic MAPT mutation carriers (n = 10) had a median FTLD-CDR SOB score of 5. Noncarriers from healthy first-degree relatives of the patients were recruited as controls (n = 25). The demographic aspects and ¹H MRS metabolite ratios were compared by use of the Fisher exact test for sex and linear mixed models to account for within-family correlations. We used Tukey contrasts for pair-wise comparisons.

RESULTS

Asymptomatic MAPT mutation carriers had lower neuronal marker N-acetylaspartate (NAA)/creatine (Cr) (p = 0.001) and lower NAA/myo-inositol (mI) (p = 0.026) than noncarriers after adjustment for age. Symptomatic MAPT mutation carriers had lower NAA/Cr (p = 0.01) and NAA/mI (p = 0.01) and higher mI/Cr (p = 0.02) compared to noncarriers after adjustment for age. Furthermore, NAA/Cr (p = 0.006) and NAA/mI (p < 0.001) ratios decreased, accompanied by an increase in mI/Cr ratio (p = 0.001), as the ages of carriers approached and passed the age at symptom onset.

CONCLUSION

Frontal lobe neurochemical alterations measured with ¹H MRS precede the symptom onset in MAPT mutation carriers. Frontal lobe ¹H MRS is a potential biomarker for early neurodegenerative processes in MAPT mutation carriers.

Clinical heterogeneity of frontotemporal dementia and Parkinsonism linked to chromosome 17 caused by MAPT N279K mutation in relation to tau positron emission tomography features

BACKGROUND

While mechanistic links between tau abnormalities and neurodegeneration have been proven in frontotemporal dementia and parkinsonism linked to chromosome 17 caused by MAPT mutations, variability of the tau pathogenesis and its relation to clinical progressions in the same MAPT mutation carriers are yet to be clarified.

OBJECTIVES

The present study aimed to analyze clinical profiles, tau accumulations, and their correlations in 3 kindreds with frontotemporal dementia and parkinsonism linked to chromosome 17 attributed to the MAPT N279K mutation.

METHODS

Four patients with N279K mutant frontotemporal dementia and parkinsonism linked to chromosome 17/MAPT underwent [¹¹ C]PBB3-PET to estimate regional tau loads.

RESULTS

Haplotype assays revealed that these kindreds originated from a single founder. Despite homogeneity of the disease-causing MAPT allele, clinical progression was more rapid in 2 kindreds than in the other. The kindred with slow progression showed mild tau depositions, mostly confined to the midbrain and medial temporal areas. In contrast, kindreds with rapid progression showed profoundly increased [¹¹ C]PBB3 binding in widespread regions from an early disease stage.

CONCLUSIONS

[¹¹ C]PBB3-PET can capture four-repeat tau pathologies characteristic of N279K mutant frontotemporal dementia and parkinsonism linked to chromosome 17/MAPT. Our findings indicate that, in addition to the mutated MAPT allele, genetic and/or epigenetic modifiers of tau pathologies lead to heterogeneous clinicopathological features. © 2019 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

In vivo 18F-AV-1451 tau PET signal in MAPT mutation carriers varies by expected tau isoforms

OBJECTIVE

To evaluate 18F-AV-1451 tau PET binding among microtubule-associated protein tau (MAPT) mutation carriers.

METHODS

Using a case-control study, we quantitatively and qualitatively compared tau PET scans in 10 symptomatic and 3 asymptomatic MAPT mutation carriers (n = 13, age range 42-67 years) with clinically normal (CN) participants (n = 241, age range 42-67 years) and an Alzheimer disease (AD) dementia cohort (n = 30, age range 52-67 years). Eight participants had MAPT mutations that involved exon 10 (N279K n = 5, S305N n = 2, P301L n = 1) and tend to form 4R tau pathology, and 5 had mutations outside exon 10 (V337M n = 2, R406W n = 3) and tend to form mixed 3R/4R tau pathology.

RESULTS

Tau PET signal was qualitatively and quantitatively different between participants with AD, CN participants, and MAPT mutation carriers, with the greatest signal intensity in those with AD and minimal regional signal in MAPT mutation carries with mutations in exon 10. However, MAPT mutation carriers with mutations outside exon 10 had uptake levels within the AD range, which was significantly higher than both MAPT mutation carriers with mutations in exon 10 and controls.

CONCLUSIONS

Tau PET shows higher magnitude of binding in MAPT mutation carriers who harbor mutations that are more likely to produce AD-like tau pathology (e.g., in our series, the non-exon 10 families tend to accumulate mixed 3R/4R aggregates). Exon 10 splicing determines the balance of 3R and 4R tau isoforms, with some mutations involving exon 10 predisposing to a greater proportion of 4R aggregates and consequently a lower level of AV-1451 binding, as seen in this case series, thus supporting the notion that this tau PET ligand has specific binding properties for AD-like tau pathology.

Axonal Degeneration in Tauopathies: Disease Relevance and Underlying Mechanisms

Tauopathies are a diverse group of diseases featuring progressive dying-back neurodegeneration of specific neuronal populations in association with accumulation of abnormal forms of the microtubule-associated protein tau. It is well-established that the clinical symptoms characteristic of tauopathies correlate with deficits in synaptic function and neuritic connectivity early in the course of disease, but mechanisms underlying these critical pathogenic events are not fully understood. Biochemical in vitro evidence fueled the widespread notion that microtubule stabilization represents tau's primary biological role and that the marked atrophy of neurites observed in tauopathies results from loss of microtubule stability. However, this notion contrasts with the mild phenotype associated with tau deletion. Instead, an analysis of cellular hallmarks common to different tauopathies, including aberrant patterns of protein phosphorylation and early degeneration of axons, suggests that alterations in kinase-based signaling pathways and deficits in axonal transport (AT) associated with such alterations contribute to the loss of neuronal connectivity triggered by pathogenic forms of tau. Here, we review a body of literature providing evidence that axonal pathology represents an early and common pathogenic event among human tauopathies. Observations of axonal degeneration in animal models of specific tauopathies are discussed and similarities to human disease highlighted. Finally, we discuss potential mechanistic pathways other than microtubule destabilization by which disease-related forms of tau may promote axonopathy.

Genetics of Frontotemporal Dementia

Frontotemporal dementia (FTD) is the second most common cause of dementia following Alzheimer's disease (AD). Between 20 and 50% of cases are familial. Mutations in MAPT, GRN and C9orf72 are found in 60% of familial FTD cases. C9orf72 mutations are the most common and account for 25%. Rarer mutations (<5%) occur in other genes such as VPC, CHMP2B, TARDP, FUS, ITM2B, TBK1 and TBP. The diagnosis is often challenging due to symptom overlap with AD and other conditions. We review the genetics, clinical presentations, neuroimaging, neuropathology, animal studies and therapeutic trials in FTD. We describe clinical scenarios including the original family with the tau stem loop mutation (+14) and also the recently discovered 'missing tau' mutation +15 that 'closed the loop' in 2015.

Assessment of Olfactory Function in MAPT-Associated Neurodegenerative Disease Reveals Odor-Identification Irreproducibility as a Non-Disease-Specific, General Characteristic of Olfactory Dysfunction

Olfactory dysfunction is associated with normal aging, multiple neurodegenerative disorders, including Parkinson's disease, Lewy body disease and Alzheimer's disease, and other diseases such as diabetes, sleep apnea and the autoimmune disease myasthenia gravis. The wide spectrum of neurodegenerative disorders associated with olfactory dysfunction suggests different, potentially overlapping, underlying pathophysiologies. Studying olfactory dysfunction in presymptomatic carriers of mutations known to cause familial parkinsonism provides unique opportunities to understand the role of genetic factors, delineate the salient characteristics of the onset of olfactory dysfunction, and understand when it starts relative to motor and cognitive symptoms. We evaluated olfactory dysfunction in 28 carriers of two MAPT mutations (p.N279K, p.P301L), which cause frontotemporal dementia with parkinsonism, using the University of Pennsylvania Smell Identification Test. Olfactory dysfunction in carriers does not appear to be allele specific, but is strongly age-dependent and precedes symptomatic onset. Severe olfactory dysfunction, however, is not a fully penetrant trait at the time of symptom onset. Principal component analysis revealed that olfactory dysfunction is not odor-class specific, even though individual odor responses cluster kindred members according to genetic and disease status. Strikingly, carriers with incipient olfactory dysfunction show poor inter-test consistency among the sets of odors identified incorrectly in successive replicate tests, even before severe olfactory dysfunction appears. Furthermore, when 78 individuals without neurodegenerative disease and 14 individuals with sporadic Parkinson's disease were evaluated twice at a one-year interval using the Brief Smell Identification Test, the majority also showed inconsistency in the sets of odors they identified incorrectly, independent of age and cognitive status. While these findings may reflect the limitations of these tests used and the sample sizes, olfactory dysfunction appears to be associated with the inability to identify odors reliably and consistently, not with the loss of an ability to identify specific odors. Irreproducibility in odor identification appears to be a non-disease-specific, general feature of olfactory dysfunction that is accelerated or accentuated in neurodegenerative disease. It may reflect a fundamental organizational principle of the olfactory system, which is more "error-prone" than other sensory systems.

The long journey to the discovery of PARK2: The 50th Anniversary of Japanese Society of Neuropathology

Research into familial Parkinson's disease (PD) remained at a virtual standstill in Europe and the US for several decades until a re-challenge by Japanese neurologists regarding an autosomal recessive form of PD. In 1965, our research group at Nagoya University examined familial cases of early-onset parkinsonism characterized by autosomal recessive inheritance, diurnal fluctuation of symptoms (alleviation after sleep), foot dystonia, good response to medication, and benign course without dementia. An inborn error of metabolism in some dopamine-related pathway was suspected. The clinical study of four families with the disease, named as "early-onset parkinsonism with diurnal fluctuation (EPDF)", was published in Neurology in 1973. The pathological study of a case in 1993 revealed neuronal loss without Lewy bodies in the substantia nigra. Based on these clinical and pathological evidences, EPDF was defined as a distinct disease entity. Screening for the EPDF gene was started in 1994 in collaboration with Juntendo University. With the discovery of parkin gene in 1998, EPDF was designated as PARK2. Of our 16 families examined for gene analysis, 15 proved to be PARK2, and the remaining one, PARK6.

Behind the curtain of tauopathy: a show of multiple players orchestrating tau toxicity

tau, a microtubule-associated protein, directly binds with microtubules to dynamically regulate the organization of cellular cytoskeletons, and is especially abundant in neurons of the central nervous system. Under disease conditions such as Pick's disease, progressive supranuclear palsy, frontotemporal dementia, parkinsonism linked to chromosome 17 and Alzheimer's disease, tau proteins can self-assemble to paired helical filaments progressing to neurofibrillary tangles. In these diseases, collectively referred to as "tauopathies", alterations of diverse tau modifications including phosphorylation, metal ion binding, glycosylation, as well as structural changes of tau proteins have all been observed, indicating the complexity and variability of factors in the regulation of tau toxicity. Here, we review our current knowledge and hypotheses from relevant studies on tau toxicity, emphasizing the roles of phosphorylations, metal ions, folding and clearance control underlining tau etiology and their regulations. A summary of clinical efforts and associated findings of drug candidates under development is also presented. It is hoped that a more comprehensive understanding of tau regulation will provide us with a better blueprint of tau networking in neuronal cells and offer hints for the design of more efficient strategies to tackle tau-related diseases in the future.

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.

Primary dystonias and genetic disorders with dystonia as clinical feature of the disease

Dystonia is probably the most common form of movement disorder encountered in the clinical practice. It is characterized by sustained muscle contractions, usually producing twisting and repetitive movements or abnormal postures or positions. Dystonias can be classified in several ways, including primarily by the clinical phenomenology or by the underlining etiology, in particular to understand if the presentation is genetically determined. By advances of genetics, including contemporary genomic technologies, there is a growing understanding of the molecular underpinnings of genetically determined dystonias. The intricacy of information requires a user friendly, novel database that may efficiently serve clinicians to inform of advances of the field and to diagnose and manage these often complex cases. Here we present an up to date, comprehensive review - in tabulated formats - of genetically determined primary dystonias and complex Mendelian disorders with dystonia as central feature. The detailed search up to December 24, 2012, identified 24 hereditary primary dystonias (DYT1 to DYT 25) that are mostly monogenic disorders, and a larger group (>70) of genetic syndromes in which dystonia is one of the characteristic clinical features. We organized the findings not only by individual information (name of the conditions, pattern of inheritance, chromosome and gene abnormality, clinical features, relevant ancillary tests and key references), but also provide symptom-oriented organization of the clinical entities for efficient inquiries.

Rapidly progressive autosomal dominant Parkinsonism and dementia with Pallido-Ponto-Nigral Gegeneration (PPND) and Disinhibition-Dementia-Parkinsonism-Amyotrophy Complex (DDPAC) are clinically distinct conditions that are both linked to 17q21-22

Genetic analysis provides specific etiologic information about disease that cannot be deduced by clinical and pathologic investigations alone. Two large families have been characterized with multi-system degeneration: rapidly progressive autosomal dominant parkinsonism and dementia with pallido-ponto-nigral degeneration (PPND) and disinhibition-dementia-parkinsonism-amyotrophy complex (DDPAC). Linkage analysis identified a locus, wld, on-17q21-22 that is responsible for DDPAC. Analysis of a PPND family shows that PPND is also due to a gene on 17q21-22. Comparison of genealogic, clinical, diagnostic, and pathologic data shows that DDPAC and PPND are distinct disorders suggesting two different mutations in wld. Literature review identifies many kindreds with multi-system degeneration that may be allelic.

The genetics and neuropathology of Parkinson's disease

There has been tremendous progress toward understanding the genetic basis of Parkinson's disease and related movement disorders. We summarize the genetic, clinical and pathological findings of autosomal dominant disease linked to mutations in SNCA, LRRK2, ATXN2, ATXN3, MAPT, GCH1, DCTN1 and VPS35. We then discuss the identification of mutations in PARK2, PARK7, PINK1, ATP13A2, FBXO7, PANK2 and PLA2G6 genes. In particular we discuss the clinical and pathological characterization of these forms of disease, where neuropathology has been important in the likely coalescence of pathways highly relevant to typical PD. In addition to the identification of the causes of monogenic forms of PD, significant progress has been made in defining genetic risk loci for PD; we discuss these here, including both risk variants at LRRK2 and GBA, in addition to discussing the results of recent genome-wide association studies and their implications for PD. Finally, we discuss the likely path of genetic discovery in PD over the coming period and the implications of these findings from a clinical and etiological perspective.

Creation of an open-access, mutation-defined fibroblast resource for neurological disease research

Our understanding of the molecular mechanisms of many neurological disorders has been greatly enhanced by the discovery of mutations in genes linked to familial forms of these diseases. These have facilitated the generation of cell and animal models that can be used to understand the underlying molecular pathology. Recently, there has been a surge of interest in the use of patient-derived cells, due to the development of induced pluripotent stem cells and their subsequent differentiation into neurons and glia. Access to patient cell lines carrying the relevant mutations is a limiting factor for many centres wishing to pursue this research. We have therefore generated an open-access collection of fibroblast lines from patients carrying mutations linked to neurological disease. These cell lines have been deposited in the National Institute for Neurological Disorders and Stroke (NINDS) Repository at the Coriell Institute for Medical Research and can be requested by any research group for use in in vitro disease modelling. There are currently 71 mutation-defined cell lines available for request from a wide range of neurological disorders and this collection will be continually expanded. This represents a significant resource that will advance the use of patient cells as disease models by the scientific community.

Anatomy of disturbed sleep in pallido-ponto-nigral degeneration

OBJECTIVE

Pallido-ponto-nigral degeneration (PPND), caused by an N279K mutation of the MAPT gene, is 1 of a family of disorders collectively referred to as frontotemporal dementia and parkinsonism linked to chromosome 17. This study aims to characterize the nature of the sleep disturbance in PPND and compare these findings to those in other progressive neurological illnesses. Pathological findings are also provided.

METHODS

Ten subjects were recruited from the PPND kindred; 5 affected and 5 unaffected. The subjects underwent clinical assessment, polysomnography, and wrist actigraphy. Available sleep-relevant areas (pedunculopontine/laterodorsal tegmentum, nucleus basalis of Meynert, thalamus, and locus ceruleus) of affected subjects were analyzed postmortem.

RESULTS

The affected group's total sleep time was an average of 130.8 minutes compared to 403.6 minutes in the control group (p < 0.01). Initial sleep latency was significantly longer in affected subjects (range, 58-260 minutes vs 3-34 minutes). Affected subjects also had an increase in stage I sleep (8.5% vs 1%), and less stage III/IV sleep (8.5% vs 17%). At the time of autopsy, all cases had severe neuronal tau pathology in wake-promoting nuclei, as well as decreases in thalamic cholinergic innervations. There was no difference in orexinergic fiber density in nucleus basalis of Meynert or locus ceruleus compared to controls.

INTERPRETATION

The PPND kindred showed severe sleep disturbance. Sleep abnormalities are common in neurodegenerative illnesses, but this is the first study of sleep disorders in PPND. Unlike most neurodegenerative conditions, PPND is characterized by decreased total sleep time, increased sleep latency, and decreased sleep efficiency, without daytime hypersomnolence.

Altered functional connectivity in asymptomatic MAPT subjects: a comparison to bvFTD

OBJECTIVE

To determine whether functional connectivity is altered in subjects with mutations in the microtubule associated protein tau (MAPT) gene who were asymptomatic but were destined to develop dementia, and to compare these findings to those in subjects with behavioral variant frontotemporal dementia (bvFTD).

METHODS

In this case-control study, we identified 8 asymptomatic subjects with mutations in MAPT and 8 controls who screened negative for mutations in MAPT. Twenty-one subjects with a clinical diagnosis of bvFTD were also identified and matched to 21 controls. All subjects had resting-state fMRI. In-phase functional connectivity was assessed between a precuneus seed in the default mode network (DMN) and a fronto-insular cortex seed in the salience network, and the rest of the brain. Atlas-based parcellation was used to assess functional connectivity and gray matter volume across specific regions of interest.

RESULTS

The asymptomatic MAPT subjects and subjects with bvFTD showed altered functional connectivity in the DMN, with reduced in-phase connectivity in lateral temporal lobes and medial prefrontal cortex, compared to controls. Increased in-phase connectivity was also observed in both groups in the medial parietal lobe. Only the bvFTD group showed altered functional connectivity in the salience network, with reduced connectivity in the fronto-insular cortex and anterior cingulate. Gray matter loss was observed across temporal, frontal, and parietal regions in bvFTD, but not in the asymptomatic MAPT subjects.

CONCLUSIONS

Functional connectivity in the DMN is altered in MAPT subjects before the occurrence of both atrophy and clinical symptoms, suggesting that changes in functional connectivity are early features of the disease.

MRS in presymptomatic MAPT mutation carriers: a potential biomarker for tau-mediated pathology

OBJECTIVE

To determine the proton magnetic resonance spectroscopy ((1)H MRS) changes in carriers of microtubule-associated protein (MAPT) mutations in a case-control study.

METHODS

Patients with MAPT mutations (N279K, V337M, R406W, IVS9-10G>T, P301L) from 5 different families (n = 24) underwent MRI and single voxel (1)H MRS from the posterior cingulate gyrus inferior precuneus at 3 T. Ten of the patients were symptomatic with median Clinical Dementia Rating sum of boxes score (CDR-SOB) of 6.5 and 14 patients were presymptomatic with CDR-SOB of 0. Age- and sex-matched controls (n = 24) were recruited.

RESULTS

Symptomatic MAPT mutation carriers were characterized by decreased N-acetylaspartate/creatine (NAA/Cr) ratio, an index of neuronal integrity, increased myoinositol (mI)/Cr ratio, a possible marker for glial activity, decreased NAA/mI, and hippocampal atrophy (p < 0.001). Whereas presymptomatic MAPT mutation carriers had elevated mI/Cr and decreased NAA/mI (p < 0.001), NAA/Cr levels and hippocampal volumes were not different from controls. Decrease in NAA/Cr (R(2) = 0. 22; p = 0.021) and hippocampal volumes (R(2) = 0.46; p < 0.001) were associated with proximity to the expected or actual age at symptom onset in MAPT mutation carriers.

CONCLUSION

(1)H MRS metabolite abnormalities characterized by an elevated mI/Cr and decreased NAA/mI are present several years before the onset of symptoms in MAPT mutation carriers. The data suggest an ordered sequencing of the (1)H MRS and MRI biomarkers. MI/Cr, a possible index of glial proliferation, precedes the decrease in neuronal integrity marker NAA/Cr and hippocampal atrophy. (1)H MRS may be a useful inclusion biomarker for preventive trials in presymptomatic carriers of MAPT mutations and possibly other proteinopathies.

Two distinct subtypes of right temporal variant frontotemporal dementia

BACKGROUND

Right temporal frontotemporal dementia (FTD) is an anatomic variant of FTD associated with relatively distinct behavioral and cognitive symptoms. We aimed to determine whether right temporal FTD is a homogeneous clinical, imaging, and pathologic/genetic entity.

METHODS

In this case-control study, 101 subjects with FTD were identified. Atlas-based parcellation generated temporal, frontal, and parietal grey matter volumes which were used to identify subjects with a right temporal dominant atrophy pattern. Clinical, neuropsychological, genetic, and neuropathologic features were reviewed. The subjects with right temporal FTD were grouped by initial clinical diagnosis and voxel-based morphometry was used to assess grey matter loss in the different groups, compared to controls, and each other.

RESULTS

We identified 20 subjects with right temporal FTD. Twelve had been initially diagnosed with behavioral variant FTD (bvFTD), and the other 8 with semantic dementia (SMD). Personality change and inappropriate behaviors were more frequent in the bvFTD group, while prosopagnosia, word-finding difficulties, comprehension problems, and topographagnosia were more frequent in the SMD group. The bvFTD group showed greater loss in frontal lobes than the SMD group. The SMD group showed greater fusiform loss than the bvFTD group. All 8 bvFTD subjects with pathologic/genetic diagnosis showed abnormalities in tau protein (7 with tau mutations), while all three SMD subjects with pathology showed abnormalities in TDP-43 (p = 0.006).

CONCLUSIONS

We have identified 2 subtypes of right temporal variant frontotemporal dementia (FTD) allowing further differentiation of FTD subjects with underlying tau pathology from those with TDP-43 pathology.

Atrophy patterns in IVS10+16, IVS10+3, N279K, S305N, P301L, and V337M MAPT mutations

OBJECTIVE

To use a case-control study to assess and compare patterns of gray matter loss across groups of subjects with different mutations in the microtubule-associated protein tau (MAPT) gene.

METHODS

We identified all subjects from Mayo Clinic, Rochester, Minnesota, that screened positive for mutations in MAPT and had a head MRI (n = 22). Voxel-based morphometry was used to assess patterns of gray matter atrophy in groups of subjects with the IVS10+16, IVS10+3, N279K, S305N, P301L, and V337M mutations compared with age- and sex-matched controls.

RESULTS

All MAPT groups showed gray matter loss in the anterior temporal lobes, with varying degrees of involvement of the frontal and parietal lobes. Within the temporal lobe, the subjects with IVS10+16, IVS10+3, N279K, and S305N mutations (mutations that influence the alternative splicing of tau pre-messenger RNA) all showed gray matter loss focused on the medial temporal lobes. In contrast to these groups, the subjects with P301L or V337M mutations (mutations that affect the structure of the tau protein) both showed gray matter loss focused on the lateral temporal lobes, with a relative sparing of the medial temporal lobe.

CONCLUSION

There seem to be differences in patterns of temporal lobe atrophy across the MAPT mutations, which may aid in the differentiation of the different mutation carriers. Furthermore, there seems to be a possible association between mutation function and pattern of temporal lobe atrophy.

Clinical genetics of Parkinson's disease and related disorders

Our knowledge regarding the genetics of Parkinson's disease (PD) and parkinsonism has evolved dramatically during the past decade, with the discovery of numerous loci and genes. The LRRK2 gene has emerged as the most commonly involved in both familial and sporadic PD. Several variants in LRRK2 and SNCA have been associated with an increased risk of sporadic PD. PRKN, PINK1 and DJ1 mutations cause early-onset recessively inherited PD. Autosomal dominant dementia and parkinsonism is caused by mutations in the MAPT gene, and in the most recently discovered PGRN gene.

Voxel-based morphometry patterns of atrophy in FTLD with mutations in MAPT or PGRN

OBJECTIVE

To compare patterns of gray matter loss in subjects with mutations in the progranulin (PGRN) gene to subjects with mutations in the microtubule-associated protein tau (MAPT) gene.

METHODS

We identified all subjects seen at the Mayo Clinic, Rochester, MN, who had screened positive for mutations in PGRN or MAPT and had a head MRI. Twelve cases with mutations in the PGRN gene were matched by time from disease onset to scan to 12 subjects with mutations in the MAPT gene. Voxel-based morphometry was used to assess patterns of gray matter loss in the PGRN and MAPT groups compared to a control cohort, and compared to each other. MAPT subjects were younger than the PGRN subjects; therefore, each group was also compared to a specific age-matched control group.

RESULTS

Both PGRN and MAPT groups showed gray matter loss in frontal, temporal, and parietal lobes compared to controls, although loss was predominantly identified in posterior temporal and parietal lobes in PGRN and anteromedial temporal lobes in MAPT. The MAPT group had greater loss compared to healthy subjects of the same age than the PGRN subjects when compared to healthy subjects of the same age. The MAPT subjects showed greater gray matter loss in the medial temporal lobes, insula, and putamen than the PGRN subjects.

CONCLUSION

These results increase understanding of the biology of these disorders and suggest that patterns of atrophy on MRI may be useful to aid in the differentiation of groups of PGRN and MAPT mutation carriers.

The genetics of frontotemporal dementia

This article describes the remarkable progress that has been made over the past decade in identifying the genetic contribution to frontotemporal dementia. The clinical and neuropathologic features of frontotemporal dementia with parkinsonism linked to chromosome 17 and the nature of the mutations in the progranulin and microtubule-associated protein tau genes are emphasized.

The tau N279K exon 10 splicing mutation recapitulates frontotemporal dementia and parkinsonism linked to chromosome 17 tauopathy in a mouse model

Intracellular tau deposits are characteristic of several neurodegenerative disorders called tauopathies. The tau protein regulates the stability and assembly of microtubules by binding to microtubules through three or four microtubule-binding repeats (3R and 4R). The number of microtubule-binding repeats is determined by the inclusion or exclusion of the second microtubule-binding repeat encoded by exon 10 of the TAU gene. TAU gene mutations that alter the inclusion of exon 10, and hence the 4R:3R ratio, are causal in the tauopathy frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17). A mutation located in exon 10 has been identified in several FTDP-17 families that present with increased exon 10 inclusion in both mRNA and protein, parkinsonism, movement disorders, and dementia. We have engineered a human tau minigene construct that was designed to allow alternative splicing of the tau exon 10. Here we demonstrate that transgenic mice expressing human tau protein with this mutation develop neurodegeneration as result of aberrant splicing. The mice recapitulate many of the disease hallmarks that are seen in patients with this mutation, including increased tau exon 10 inclusion in both mRNA and protein, motor and behavioral deficits, and tau protein accumulation in neurons and tufted astrocytes. Furthermore, these mice present with degeneration of the nigrostriatal dopaminergic pathway, suggesting a possible mechanism for parkinsonism in FTDP-17. Additionally, activated caspase-3 immunoreactivity in both neurons and astrocytes implicates the involvement of the apoptotic pathway in the pathology of these mice.

Lrrk2 and chronic inflammation are linked to pallido-ponto-nigral degeneration caused by the N279K tau mutation

Mutations in the leucine-rich repeat kinase 2 gene (LRRK2) have been identified in families with autosomal dominant late-onset Parkinson disease (PD). Lrrk2 is a phylogenetically conserved, ubiquitous protein, which is constitutively expressed in various cells including neurons and glial cells of human brain. We recently reported that Lrrk2 is identified in Lewy bodies in PD as well as in neuronal and glial inclusions in several other neurodegenerative disorders. Here we show that Lrrk2 is closely associated with the tau-positive inclusions in eight members of a family with frontotemporal dementia of the pallido-ponto-nigral degeneration type linked to the chromosome 17 N279K tau mutation (N279K/FTDP-17/PPND). Lrrk2 is colocalized with tau in oligodendroglial coiled bodies and intracytoplasmic neuronal inclusions. HLA-DR positive reactive microglia and ICAM-1 positive reactive astrocytes accumulated in affected areas demonstrating that inflammatory processes are also involved in the disease pathogenesis. Western blot analysis of soluble extracts of N279K/FTDP-17/PPND brain tissue suggests that C-terminal fragment(s) of apparent 64-75 kDa molecular weight may be the major Lrrk2 species in pathological deposits. The possibility that Lrrk2 is linked with various neurodegenerative disorders through the ubiquitin proteosome pathway is discussed. The results indicate that Lrrk2 is linked to frontotemporal atrophy of PPND type caused by N279K tau mutation. They also show that chronic inflammation is involved in the pathogenesis of N279K/FTDP-17/PPND.

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.

Accumulation of pathological tau species and memory loss in a conditional model of tauopathy

Neurofibrillary tangles (NFTs) are a pathological hallmark of Alzheimer's disease and other tauopathies, but recent studies in a conditional mouse model of tauopathy (rTg4510) have suggested that NFT formation can be dissociated from memory loss and neurodegeneration. This suggests that NFTs are not the major neurotoxic tau species, at least during the early stages of pathogenesis. To identify other neurotoxic tau protein species, we performed biochemical analyses on brain tissues from the rTg4510 mouse model and then correlated the levels of these tau proteins with memory loss. We describe the identification and characterization of two forms of tau multimers (140 and 170 kDa), whose molecular weight suggests an oligomeric aggregate, that accumulate early in the pathogenic cascade in this mouse model. Similar tau multimers were detected in a second mouse model of tauopathy (JNPL3) and in tissue from patients with Alzheimer's disease and FTDP-17 (frontotemporal dementia and parkinsonism linked to chromosome 17). Moreover, levels of the tau multimers correlated consistently with memory loss at various ages in the rTg4510 mouse model. Our findings suggest that accumulation of early-stage aggregated tau species, before the formation of NFT, is associated with the development of functional deficits during the pathogenic progression of tauopathy.

Frontotemporal dementia and parkinsonism linked to chromosome 17 with the N279K tau mutation

We present a case of frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) harboring the N279K mutation in the MAPT gene from the family known as pallido-ponto-nigral degeneration (PPND). This 49-year-old man was followed for 17 years. He presented at age 41 years with left leg stiffness and en-bloc turning. During the course of his illness he developed a constellation of symptoms including parkinsonism, pyramidal signs, vertical gaze palsy, dysphagia, dystonia, personality and cognitive dysfunction, weight loss and mutism. Gross neuropathological examination showed mild atrophy of the cerebral cortex, hippocampal formation, amygdala, thalamus, subthalamic nucleus and depigmentation of the substantia nigra. Microscopy revealed neuronal loss and gliosis in the same regions. Tau immunohistochemistry showed pretangles, numerous threads, grain-like structures and oligodendroglial tau-positive inclusions ("coiled bodies"). In the spinal cord the tau pathology was more abundant in gray than white matter. Pretangles and threads were present in the anterior and, to a lesser extent, in the posterior horns. FTDP-17 should be suspected in patients with a history of familial parkinsonism combined with behavioral and cognitive changes, onset before age 65 years and an aggressive clinical course.

Clinical-pathologic study of biomarkers in FTDP-17 (PPND family with N279K tau mutation)

The objective of this clinical-pathologic study was to identify biomarkers for a pallidopontonigral degeneration (PPND) kindred of frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) harboring the N279K tau mutation. Five affected subjects, one at-risk who later became symptomatic, and one at-risk asymptomatic mutation carrier, had abnormal (18)fluorodeoxyglucose PET demonstrating asymmetric temporal lobe hypometabolism. All except the asymptomatic mutation carrier had abnormal brain MRI. Parkinsonism, myoclonus, anosmia, insomnia, speech, and autonomic dysfunction were identified. Autopsy of six affected subjects showed frontotemporal degeneration with extensive tauopathy. Further studies of FTDP-17 patients are needed to replicate these findings.

Alzheimer's disease and frontotemporal dementia: prospects of a tailored therapy?

Alzheimer's disease (AD) is the most prevalent dementia (accounting for 50%-75% of cases of dementia in people aged over 65 years), followed by frontotemporal dementia (FTD) (10%-20% of cases). AD is characterised histopathologically by Abeta-containing amyloid plaques and tau-containing neurofibrillary tangles, whereas FTD exhibits neurofibrillary tangles alone. Current symptomatic treatments of AD are of limited benefit, as they are not directed at the underlying biological basis of the disease. The development of transgenic animal models has provided insight into disease mechanisms and helped define novel drug targets. More than 50 drugs are currently in clinical trials, and novel and more effective drugs targeting both AD and FTD are expected to become available within 5-10 years.

Frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17)

Frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) is an autosomal dominant neurodegenerative disorder, which has three cardinal features: behavioral and personality changes, cognitive impairment, and motor symptoms. FTDP-17 was defined during the International Consensus Conference in Ann Arbor, Michigan, in 1996. The prevalence and incidence remain unknown but FTDP-17 is an extremely rare condition. It is caused by mutations in the tau gene, which encodes a microtubule-binding protein. Over 100 families with 38 different mutations in the tau gene have been identified worldwide. The phenotype of FTDP-17 varies not only between families carrying different mutations but also between and within families carrying the same mutations. The pathogenetic mechanisms underlying the disorder are thought to be related to the altered proportion of tau isoforms or to the ability of tau to bind microtubules and to promote microtubule assembly. Definitive diagnosis of FTDP-17 requires a combination of characteristic clinical and pathological features and molecular genetic analysis. Genetic counseling should be offered to affected and at-risk individuals; for most subtypes, penetrance is incomplete. Currently, treatment for FTDP-17 is only symptomatic and supportive. The prognosis and rate of the disease's progression vary considerably among individual patients and genetic kindreds, ranging from life expectancies of several months to several years, and, in exceptional cases, as long as two decades.