Dementia lacking distinctive histologic features: a common non-Alzheimer degenerative dementia

Frontotemporal dementia: Past, present, and future

INTRODUCTION

The history of frontotemporal dementia (FTD) is both old and new. This study explores its historical roots, dating back to the 19th century, while recognizes it as a distinct neurological entity only a few decades ago.

METHODS

This qualitative study and literature review provides an overview of FTD's historical background, birth, evolution, and future directions.

RESULTS

Recognition of FTD was hindered by rigid perceptions of dementia, the division between neurology and psychiatry, reliance on IQ-based assessment, limited neuroimaging capabilities, and lack of pathological proof. Overcoming these barriers involved revisiting early pioneers' approaches, focusing on focal impairment, establishing non-Alzheimer's disease cohorts, fostering collaboration, and developing diagnostic criteria. Current gaps include the need for biology-oriented psychiatry education, biological biomarkers, and culturally sensitive, objective clinical instruments predicting underlying pathology.

DISCUSSION

Independent multidisciplinary centers are essential. The future of FTD lies in disease-modifying therapies, presenting new opportunities for healthcare professionals and researchers.

Neuropathological fingerprints of survival, atrophy and language in primary progressive aphasia

Primary progressive aphasia is a neurodegenerative disease that selectively impairs language without equivalent impairment of speech, memory or comportment. In 118 consecutive autopsies on patients with primary progressive aphasia, primary diagnosis was Alzheimer's disease neuropathological changes (ADNC) in 42%, corticobasal degeneration or progressive supranuclear palsy neuropathology in 24%, Pick's disease neuropathology in 10%, transactive response DNA binding proteinopathy type A [TDP(A)] in 10%, TDP(C) in 11% and infrequent entities in 3%. Survival was longest in TDP(C) (13.2 ± 2.6 years) and shortest in TDP(A) (7.1 ± 2.4 years). A subset of 68 right-handed participants entered longitudinal investigations. They were classified as logopenic, agrammatic/non-fluent or semantic by quantitative algorithms. Each variant had a preferred but not invariant neuropathological correlate. Seventy-seven per cent of logopenics had ADNC, 56% of agrammatics had corticobasal degeneration/progressive supranuclear palsy or Pick's disease and 89% of semantics had TDP(C). Word comprehension impairments had strong predictive power for determining underlying neuropathology positively for TDP(C) and negatively for ADNC. Cortical atrophy was smallest in corticobasal degeneration/progressive supranuclear palsy and largest in TDP(A). Atrophy encompassed posterior frontal but not temporoparietal cortex in corticobasal degeneration/progressive supranuclear palsy, anterior temporal but not frontoparietal cortex in TDP(C), temporofrontal but not parietal cortex in Pick's disease and all three lobes with ADNC or TDP(A). There were individual deviations from these group patterns, accounting for less frequent clinicopathologic associations. The one common denominator was progressive asymmetric atrophy overwhelmingly favouring the left hemisphere language network. Comparisons of ADNC in typical amnestic versus atypical aphasic dementia and of TDP in type A versus type C revealed fundamental biological and clinical differences, suggesting that members of each pair may constitute distinct clinicopathologic entities despite identical downstream proteinopathies. Individual TDP(C) participants with unilateral left temporal atrophy displayed word comprehension impairments without additional object recognition deficits, helping to dissociate semantic primary progressive aphasia from semantic dementia. When common and uncommon associations were considered in the set of 68 participants, one neuropathology was found to cause multiple clinical subtypes, and one subtype of primary progressive aphasia to be caused by multiple neuropathologies, but with different probabilities. Occasionally, expected clinical manifestations of atrophy sites were absent, probably reflecting individual peculiarities of language organization. The hemispheric asymmetry of neurodegeneration and resultant language impairment in primary progressive aphasia reflect complex interactions among the cellular affinities of the degenerative disease, the constitutive biology of language cortex, familial or developmental vulnerabilities of this network and potential idiosyncrasies of functional anatomy in the affected individual.

Frontotemporal lobar degeneration with TAR DNA-binding protein 43 (TDP-43): its journey of more than 100 years

Frontotemporal lobar degeneration (FTLD) with TDP-43-immunoreactive inclusions (FTLD-TDP) is a neurodegenerative disease associated with clinical, genetic, and neuropathological heterogeneity. An association between TDP-43, FTLD and amyotrophic lateral sclerosis (ALS) was first described in 2006. However, a century before immunohistochemistry existed, atypical dementias displaying behavioral, language and/or pyramidal symptoms and showing non-specific FTLD with superficial cortical neuronal loss, gliosis and spongiosis were often confused with Alzheimer's or Pick's disease. Initially this pathology was termed dementia lacking distinctive histopathology (DLDH), but this was later renamed when ubiquitinated inclusions originally found in ALS were also discovered in (DLDH), thus warranting a recategorization as FTLD-U (ubiquitin). Finally, the ubiquitinated protein was identified as TDP-43, which aggregates in cortical, subcortical, limbic and brainstem neurons and glial cells. The topography and morphology of TDP-43 inclusions associate with specific clinical syndromes and genetic mutations which implies different pathomechanisms that are yet to be discovered; hence, the TDP-43 journey has actually just begun. In this review, we describe how FTLD-TDP was established and defined clinically and neuropathologically throughout the past century.

Review: Neuropathology of non-tau frontotemporal lobar degeneration

Frontotemporal dementia (FTD) is a heterogeneous clinical syndrome associated with frontotemporal lobar degeneration (FTLD) as a relatively consistent neuropathological hallmark feature. However, the discoveries in the past decade of many of the relevant pathological proteins aggregating in human FTD brains in addition to several new FTD causing gene mutations underlined that FTD is a diverse condition on the neuropathological and genetic basis. This resulted in a novel molecular classification of these conditions based on the predominant protein abnormality and allows most cases of FTD to be placed now into one of three broad molecular subgroups; FTLD with tau, TAR DNA-binding protein 43 or FET protein accumulation (FTLD-tau, FTLD-TDP and FTLD-FET respectively). This review will provide an overview of the molecular neuropathology of non-tau FTLD, insights into disease mechanisms gained from the study of human post mortem tissue as well as discussion of current controversies in the field.

Development of disease-modifying drugs for frontotemporal dementia spectrum disorders

Frontotemporal dementia (FTD) encompasses a spectrum of clinical syndromes characterized by progressive executive, behavioural and language dysfunction. The various FTD spectrum disorders are associated with brain accumulation of different proteins: tau, the transactive response DNA binding protein of 43 kDa (TDP43), or fused in sarcoma (FUS) protein, Ewing sarcoma protein and TATA-binding protein-associated factor 15 (TAF15) (collectively known as FET proteins). Approximately 60% of patients with FTD have autosomal dominant mutations in C9orf72, GRN or MAPT genes. Currently available treatments are symptomatic and provide limited benefit. However, the increased understanding of FTD pathogenesis is driving the development of potential disease-modifying therapies. Most of these drugs target pathological tau - this category includes tau phosphorylation inhibitors, tau aggregation inhibitors, active and passive anti-tau immunotherapies, and MAPT-targeted antisense oligonucleotides. Some of these therapeutic approaches are being tested in phase II clinical trials. Pharmacological approaches that target the effects of GRN and C9orf72 mutations are also in development. Key results of large clinical trials will be available in a few years. However, clinical trials in FTD pose several challenges, and the development of specific brain imaging and molecular biomarkers could facilitate the recruitment of clinically homogenous groups to improve the chances of positive clinical trial results.

FTLD-TDP With and Without GRN Mutations Cause Different Patterns of CA1 Pathology

Heterozygous loss-of-function mutations in the GRN gene lead to progranulin (PGRN) haploinsufficiency and cause frontotemporal lobar degeneration with TDP-43 pathology type A (FTLD-TDP type A). PGRN is a highly conserved, secreted glycoprotein and functions in the central nervous system as a key modulator of microglial function. Hence, altered microglial function caused by PGRN deficiency may be tied to the pathogenesis of FTLD-TDP. Our previous studies showed that haploinsufficiency of GRN mutations extends to microglial PGRN expression in the hippocampal CA1 region. In this study, we found that the CA1 sector was associated with less neuronal loss and more frequent TDP-43 inclusions in FTLD-TDP type A cases with GRN mutations than in sporadic cases. In addition, the CA1 region in GRN mutation cases contained more rod-like microglia, which also had reduced PGRN expression. These findings suggest that the profile of TDP-43 inclusions, neuronal number, and microgliosis in the CA1 sector of FTLD-TDP type A cases may be influenced by GRN gene expression status.

The Use of Biomarkers and Genetic Screening to Diagnose Frontotemporal Dementia: Evidence and Clinical Implications

Within the wide range of neurodegenerative brain diseases, the differential diagnosis of frontotemporal dementia (FTD) frequently poses a challenge. Often, signs and symptoms are not characteristic of the disease and may instead reflect atypical presentations. Consequently, the use of disease biomarkers is of importance to correctly identify the patients. Here, we describe how neuropsychological characteristics, neuroimaging and neurochemical biomarkers and screening for causal gene mutations can be used to differentiate FTD from other neurodegenerative diseases as well as to distinguish between FTD subtypes. Summarizing current evidence, we propose a stepwise approach in the diagnostic evaluation. Clinical consensus criteria that take into account a full neuropsychological examination have relatively good accuracy (sensitivity [se] 75–95%, specificity [sp] 82–95%) to diagnose FTD, although misdiagnosis (mostly AD) is common. Structural brain MRI (se 70–94%, sp 89–99%) and FDG PET (se 47–90%, sp 68–98%) or SPECT (se 36–100%, sp 41–100%) brain scans greatly increase diagnostic accuracy, showing greater involvement of frontal and anterior temporal lobes, with sparing of hippocampi and medial temporal lobes. If these results are inconclusive, we suggest detecting amyloid and tau cerebrospinal fluid (CSF) biomarkers that can indicate the presence of AD with good accuracy (se 74–100%, sp 82–97%). The use of P-tau₁₈₁ and the Aβ_1–42/Aβ_1–40 ratio significantly increases the accuracy of correctly identifying FTD vs. AD. Alternatively, an amyloid brain PET scan can be performed to differentiate FTD from AD. When autosomal dominant inheritance is suspected, or in early onset dementia, mutation screening of causal genes is indicated and may also be offered to at-risk family members. We have summarized genotype–phenotype correlations for several genes that are known to cause familial frontotemporal lobar degeneration, which is the neuropathological substrate of FTD. The genes most commonly associated with this disease (C9orf72, MAPT, GRN, TBK1) are discussed, as well as some less frequent ones (CHMP2B, VCP). Several other techniques, such as diffusion tensor imaging, tau PET imaging and measuring serum neurofilament levels, show promise for future implementation as diagnostic biomarkers.

Progress and Challenges in Frontotemporal Dementia Research: A 20-Year Review

The landscape of frontotemporal dementia (FTD) has evolved remarkably in recent years and is barely recognizable from two decades ago. Knowledge of the clinical phenomenology, cognition, neuroimaging, genetics, pathology of the different subtypes of FTD, and their relations to other neurodegenerative conditions, has increased rapidly, due in part, to the growing interests into these neurodegenerative brain conditions. This article reviews the major advances in the field of FTD over the past 20 years, focusing primarily on the work of Frontier, the frontotemporal dementia clinical research group, based in Sydney, Australia. Topics covered include clinical presentations (cognition, behavior, neuroimaging), pathology, genetics, and disease progression, as well as interventions and carer directed research. This review demonstrates the improvement in diagnostic accuracy and capacity to provide advice on genetic risks, prognosis, and outcome. The next major challenge will be to capitalize on these research findings to develop effective disease modifying drugs, which are currently lacking.

FDG-PET patterns associated with underlying pathology in corticobasal syndrome

OBJECTIVE

To evaluate brain ¹⁸Fluorodeoxyglucose PET (FDG-PET) differences among patients with a clinical diagnosis of corticobasal syndrome (CBS) and distinct underling primary pathologies.

METHODS

We studied 29 patients with a diagnosis of CBS who underwent FDG-PET scan and postmortem neuropathologic examination. Patients were divided into subgroups on the basis of primary pathologic diagnosis: CBS-corticobasal degeneration (CBS-CBD) (14 patients), CBS-Alzheimer disease (CBS-AD) (10 patients), and CBS-progressive supranuclear palsy (CBS-PSP) (5 patients). Thirteen age-matched healthy patients who underwent FDG-PET were the control group (HC). FDG-PET scans were compared between the subgroups and the HC using SPM-12, with a threshold of p _FWE < 0.05.

RESULTS

There were no differences in Mattis Dementia Rating Scale or finger tapping scores between CBS groups. Compared to HC, the patients with CBS presented significant hypometabolism in frontoparietal regions, including the perirolandic area, basal ganglia, and thalamus of the clinically more affected hemisphere. Patients with CBS-CBD showed a similar pattern with a more marked, bilateral involvement of the basal ganglia. Patients with CBS-AD presented with posterior, asymmetric hypometabolism, including the lateral parietal and temporal lobes and the posterior cingulate. Finally, patients with CBS-PSP disclosed a more anterior hypometabolic pattern, including the medial frontal regions and the anterior cingulate. A conjunction analysis revealed that the primary motor cortex was the only common area of hypometabolism in all groups, irrespective of pathologic diagnosis.

DISCUSSION AND CONCLUSIONS

In patients with CBS, different underling pathologies are associated with different patterns of hypometabolism. Our data suggest that FDG-PET scans could help in the etiologic diagnosis of CBS.

Demographic and neuropsychiatric factors associated with off-label medication use in frontotemporal dementia and Alzheimer's disease

OBJECTIVES

Off-label medication use for treating cognitive impairments and neuropsychiatric symptoms occurs in frontotemporal dementia (FTD) and Alzheimer disease (AD). We compared the use of cognitive and psychiatric medications in FTD and AD and evaluated the relationship between neuropsychiatric symptoms and medication use.

METHODS

Cognitive and psychiatric medication use, demographic variables, and Neuropsychiatric Inventory (NPI) subscale symptoms were obtained from the National Alzheimer's Coordinating Center Uniform Data Set (n=3958, 8.1% FTD). Bivariate statistics and logistic regressions were calculated to evaluate which demographic or NPI subscale symptoms predicted medication use.

RESULTS

Although cognitive medication was used more commonly in AD (78%), it was also commonly used off-label in FTD (56%). Psychiatric medications were in greater use in FTD than in AD (68% vs. 45%, respectively, P<0.001). In FTD, cognitive medication use was associated with elevated NPI elation scores and psychiatric medication use was associated with history of prior psychiatric disease. In AD, demographic variables (white, longer disease duration, higher education, more severe disease, or being male) were most predictive of cognitive medication use, whereas having psychiatric disease, being white, having longer disease duration, being younger, greater disease severity, and being disinhibited or anxious were associated with psychiatric medication use. Off-label antipsychotics were used by 4.7% of patients with AD and 10% of patients with FTD.

CONCLUSIONS

Our results revealed significant off-label medication use in both FTD and AD. A notable finding from this study was the lack of consistent relationships between medication use and neuropsychiatric symptoms across the 2 illnesses.

Visuoperception test predicts pathologic diagnosis of Alzheimer disease in corticobasal syndrome

OBJECTIVE

To use the Visual Object and Space Perception Battery (VOSP) to distinguish Alzheimer disease (AD) from non-AD pathology in corticobasal syndrome (CBS).

METHODS

This clinicopathologic study assessed 36 patients with CBS on the VOSP. All were autopsied. The primary dependent variable was a binary pathologic outcome: patients with CBS who had primary pathologic diagnosis of AD (CBS-AD, n = 10) vs patients with CBS without primary pathologic diagnosis of AD (CBS-nonAD, n = 26). We also determined sensitivity and specificity of individual VOSP subtests.

RESULTS

Patients with CBS-AD had younger onset (54.5 vs 63.6 years, p = 0.001) and lower memory scores on the Mattis Dementia Rating Scale-2 (16 vs 22 points, p = 0.003). Failure on the VOSP subtests Incomplete Letters (odds ratio [OR] 11.5, p = 0.006), Position Discrimination (OR 10.86, p = 0.008), Number Location (OR 12.27, p = 0.026), and Cube Analysis (OR 45.71 p = 0.0001) had significantly greater odds of CBS-AD than CBS-nonAD. These associations remained when adjusting for total Mattis Dementia Rating score, disease laterality, education, age, and sex. Receiver operating characteristic curves demonstrated significant accuracy for Incomplete Letters and all VOSP spatial subtests, with Cube Analysis performing best (area under the curve 0.91, p = 0.0004).

CONCLUSIONS

In patients with CBS, failure on specific VOSP subtests is associated with greater odds of having underlying AD. There may be preferential involvement of the dorsal stream in CBS-AD.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that some subtests of the VOSP accurately distinguish patients with CBS-AD from those without AD pathology (e.g., Cube Analysis sensitivity 100%, specificity 77%).

Frontotemporal dementia and amyotrophic lateral sclerosis: revisiting one of the first case reports with neuropathology examination

The occurrence of dementia in amyotrophic lateral sclerosis (ALS) was only widely recognized in the late 20^th century. Hitherto, it was believed that dementia was a rare event due to the fortuitous association with other diseases. In 1924, Kostantin Nikolaevich Tretiakoff and Moacyr de Freitas Amorim reported a case of dementia with features of frontotemporal dementia (FTD) that preceded the motor signs of ALS. Neuropathological examination confirmed ALS and found no signs of other dementia-causing diseases. The authors hypothesized that dementia was part of ALS and recommended the search for signs of involvement of motor neurons in cases of dementia with an ill-defined clinical picture, a practice currently accepted in the investigation of cases of FTD. This was one of the first descriptions of dementia preceding the motor impairments of ALS and was published in Portuguese and French in Memórias do Hospício de Juquery.

Asymmetry and heterogeneity of Alzheimer's and frontotemporal pathology in primary progressive aphasia

Fifty-eight autopsies of patients with primary progressive aphasia are reported. Twenty-three of these were previously described (Mesulam et al., 2008) but had their neuropathological diagnoses updated to fit current criteria. Thirty-five of the cases are new. Their clinical classification was guided as closely as possible by the 2011 consensus guidelines (Gorno-Tempini et al., 2011). Tissue diagnoses included Alzheimer's disease in 45% and frontotemporal lobar degeneration (FTLD) in the others, with an approximately equal split between TAR DNA binding protein 43 proteinopathies and tauopathies. The most common and distinctive feature for all pathologies associated with primary progressive aphasia was the asymmetric prominence of atrophy, neuronal loss, and disease-specific proteinopathy in the language-dominant (mostly left) hemisphere. The Alzheimer's disease pathology in primary progressive aphasia displayed multiple atypical features. Males tended to predominate, the neurofibrillary pathology was more intense in the language-dominant hemisphere, the Braak pattern of hippocampo-entorhinal prominence was tilted in favour of the neocortex, and the APOE e4 allele was not a risk factor. Mean onset age was under 65 in the FTLD as well as Alzheimer's disease groups. The FTLD-TAR DNA binding protein 43 group had the youngest onset and fastest progression whereas the Alzheimer's disease and FTLD-tau groups did not differ from each other in either onset age or progression rate. Each cellular pathology type had a preferred but not invariant clinical presentation. The most common aphasic manifestation was of the logopenic type for Alzheimer pathology and of the agrammatic type for FTLD-tau. The progressive supranuclear palsy subtype of FTLD-tau consistently caused prominent speech abnormality together with agrammatism whereas FTLD-TAR DNA binding protein 43 of type C consistently led to semantic primary progressive aphasia. The presence of agrammatism made Alzheimer's disease pathology very unlikely whereas the presence of a logopenic aphasia or word comprehension impairment made FTLD-tau unlikely. The association of logopenic primary progressive aphasia with Alzheimer's disease pathology was much more modest than has been implied by results of in vivo amyloid imaging studies. Individual features of the aphasia, such as agrammatism and comprehension impairment, were as informative of underlying pathology as more laborious subtype diagnoses. At the single patient level, no clinical pattern was pathognomonic of a specific neuropathology type, highlighting the critical role of biomarkers for diagnosing the underlying disease. During clinical subtyping, some patients were unclassifiable by the 2011 guidelines whereas others simultaneously fit two subtypes. Revisions of criteria for logopenic primary progressive aphasia are proposed to address these challenges.

Frontotemporal dementia and primary progressive aphasia, a review

Frontotemporal dementias are neurodegenerative diseases in which symptoms of frontal and/or temporal lobe disease are the first signs of the illness, and as the diseases progress, they resemble a focal left hemisphere process such as stroke or traumatic brain injury, even more than a neurodegenerative disease. Over time, some patients develop a more generalized dementia. Four clinical subtypes characterize the predominant presentations of this illness: behavioral or frontal variant FTD, progressive nonfluent aphasia, semantic dementia, and logopenic primary progressive aphasia. These clinical variants correlate with regional patterns of atrophy on brain imaging studies such as MRI and PET scanning, as well as with biochemical and molecular genetic variants of the disorder. The treatment is as yet only symptomatic, but advances in molecular genetics promise new therapies.

Clinical diagnostic criteria and classification controversies in frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) can manifest as a spectrum of clinical syndromes, ranging from behavioural impairment to language or motor dysfunction. Recently, revised diagnostic criteria have been proposed for the behavioural and progressive aphasia syndromes associated with frontotemporal degeneration. The present review will summarize these diagnostic guidelines and highlight some lingering controversies in the classification of FTLD clinical syndromes. We will discuss common tools and methods used to identify the insidious changes of behavioural variant frontotemporal dementia (bvFTD), the value of new, patient-based tasks of orbitofrontal function, and the issue of a benign or 'phenocopy' variant of bvFTD. With regard to primary progressive aphasia (PPA), we will discuss the scope of the semantic disorder in semantic-variant PPA, the nature of the speech disorder in non-fluent, agrammatic PPA, and the preliminary utility of a logopenic PPA classification.

Corticospinal tract degeneration associated with TDP-43 type C pathology and semantic dementia

Four subtypes of frontotemporal lobar degeneration with TDP-43 immunoreactive inclusions have been described (types A-D). Of these four subtypes, motor neuron disease is more commonly associated with type B pathology, but has also been reported with type A pathology. We have noted, however, the unusual occurrence of cases of type C pathology having corticospinal tract degeneration. We aimed to assess the severity of corticospinal tract degeneration in a large cohort of cases with type C (n = 31). Pathological analysis included semi-quantitation of myelin loss of fibres of the corticospinal tract and associated macrophage burden, as well as axonal loss, at the level of the medullary pyramids. We also assessed for motor cortex degeneration and fibre loss of the medial lemniscus/olivocerebellar tract. All cases were subdivided into three groups based on the degree of corticospinal tract degeneration: (i) no corticospinal tract degeneration; (ii) equivocal corticospinal tract degeneration; and (iii) moderate to very severe corticospinal tract degeneration. Clinical, genetic, pathological and imaging comparisons were performed across groups. Eight cases had no corticospinal tract degeneration, and 14 cases had equivocal to mild corticospinal tract degeneration. Nine cases, however, had moderate to very severe corticospinal tract degeneration with myelin and axonal loss. In these nine cases, there was degeneration of the motor cortex without lower motor neuron degeneration or involvement of other brainstem tracts. These cases most commonly presented as semantic dementia, and they had longer disease duration (mean: 15.3 years) compared with the other two groups (10.8 and 9.9 years; P = 0.03). After adjusting for disease duration, severity of corticospinal tract degeneration remained significantly different across groups. Only one case, without corticospinal tract degeneration, was found to have a hexanucleotide repeat expansion in the C9ORF72 gene. All three groups were associated with anterior temporal lobe atrophy on MRI; however, the cases with moderate to severe corticospinal tract degeneration showed right-sided temporal lobe asymmetry and greater involvement of the right temporal lobe and superior motor cortices than the other groups. In contrast, the cases with no or equivocal corticospinal tract degeneration were more likely to show left-sided temporal lobe asymmetry. For comparison, the corticospinal tract was assessed in 86 type A and B cases, and only two cases showed evidence of corticospinal tract degeneration without lower motor neuron degeneration. These findings confirm that there exists a unique association between frontotemporal lobar degeneration with type C pathology and corticospinal tract degeneration, with this entity showing a predilection to involve the right temporal lobe.

[Frontotemporal lobar degeneration (FTLD) concept and classification update]

FTLD is a neuroanatomical disease concept defined only by the presence of degeneration of the frontal and temporal lobes regardless of the underlying histopathological features, and therefore inevitably includes heterogeneous diseases that affect those cerebral regions. The ambiguous idea of Pick disease, the prototype of FTLD, constantly caused great nosological confusion as to FTLD. Progress in molecular neuropathology aimed at clarification of the protein constituents of the inclusion bodies seen in conditions causing FTLD, however, has resolved this problem by providing FTLD with a new concise nomenclature and classification based on the inclusion body proteins. The substances in inclusions in FTLD with ubiquitin-only inclusions (FTLD-U) have been discovered one after another; TDP-43 was the first, being found in inclusions in ALS and ALS with dementia (ALSD) too, and soon FUS/TLS was identified in some TDP-43-negative FTLD-U groups. Thus, FTLD has been divided into three main subgroups; 1) FTLD-tau, which includes Pick disease, PSP, CBD, etc., 2) FTLD-TDP, which is further divided to types A-D, ALSD belonging to type B, and 3) FTLD-FUS, which includes aFTLD-U, NIFID, and BIBD. Further deciphering of yet-unidentified proteins of some FTLD-U subsets will add more subclasses.

Advances in understanding the molecular basis of frontotemporal dementia

Frontotemporal dementia (FTD) is a clinical syndrome with a heterogeneous molecular basis. Until recently, the underlying cause was known in only a minority of cases that were associated with abnormalities of the tau protein or gene. In 2006, however, mutations in the progranulin gene were discovered as another important cause of familial FTD. That same year, TAR DNA-binding protein 43 (TDP-43) was identified as the pathological protein in the most common subtypes of FTD and amyotrophic lateral sclerosis (ALS). Since then, substantial efforts have been made to understand the functions and regulation of progranulin and TDP-43, as well as their roles in neurodegeneration. More recently, other DNA/RNA binding proteins (FET family proteins) have been identified as the pathological proteins in most of the remaining cases of FTD. In 2011, abnormal expansion of a hexanucleotide repeat in the gene C9orf72 was found to be the most common genetic cause of both FTD and ALS. All common FTD-causing genes have seemingly now been discovered and the main pathological proteins identified. In this Review, we highlight recent advances in understanding the molecular aspects of FTD, which will provide the basis for improved patient care through the development of more-targeted diagnostic tests and therapies.

The neuropsychological profile of Alzheimer disease

Neuropsychological assessment has featured prominently over the past 30 years in the characterization of dementia associated with Alzheimer disease (AD). Clinical neuropsychological methods have identified the earliest, most definitive cognitive and behavioral symptoms of illness, contributing to the identification, staging, and tracking of disease. With increasing public awareness of dementia, disease detection has moved to earlier stages of illness, at a time when deficits are both behaviorally and pathologically selective. For reasons that are not well understood, early AD pathology frequently targets large-scale neuroanatomical networks for episodic memory before other networks that subserve language, attention, executive functions, and visuospatial abilities. This chapter reviews the pathognomonic neuropsychological features of AD dementia and how these differ from "normal," age-related cognitive decline and from other neurodegenerative diseases that cause dementia, including cortical Lewy body disease, frontotemporal lobar degeneration, and cerebrovascular disease.

Pathologic lesions in neurodegenerative diseases

This chapter will discuss two of the most widely used approaches to assessing brain structure: neuroimaging and neuropathology. Whereas neuropathologic approaches to studying the central nervous system have been utilized for many decades and have provided insights into morphologic correlates of dementia for over 100 years, accurate structural imaging techniques "blossomed" with the development and refinement of computerized tomographic scanning and magnetic resonance imaging (MRI), beginning in the late 1970s. As Alzheimer disease progresses over time, there is progressive atrophy of the hippocampus and neocortex--this can be quantified and regional accentuation of the atrophy can be evaluated using quantitative MRI scanning. Furthermore, ligands for amyloid proteins have recently been developed--these can be used in positron emission tomography studies to localize amyloid proteins, and (in theory) study the dynamics of their deposition (and clearance) within the brain over time. Neuropathologic studies of the brain, using highly specific antibodies, can demonstrate synapse loss and the deposition of proteins important in AD progression--specifically ABeta and phosphor-tau. Finally, neuropathologic assessment of (autopsy) brain specimens can provide important correlation with sophisticated neuroimaging techniques.

Gains or losses: molecular mechanisms of TDP43-mediated neurodegeneration

RNA-binding proteins, and in particular TAR DNA-binding protein 43 (TDP43), are central to the pathogenesis of motor neuron diseases and related neurodegenerative disorders. Studies on human tissue have implicated several possible mechanisms of disease and experimental studies are now attempting to determine whether TDP43-mediated neurodegeneration results from a gain or a loss of function of the protein. In addition, the distinct possibility of pleotropic or combined effects - in which gains of toxic properties and losses of normal TDP43 functions act together - needs to be considered.

Update on frontotemporal dementia

BACKGROUND

Frontotemporal dementia has recently been recognized as a common cause of young-onset dementia.

OBJECTIVE

To review the current approach to the clinical evaluation, understanding of pathophysiology, and management of frontotemporal dementia.

RESULTS

Two main clinical presentations are: (1) behavioral, with impulsive behaviors and disinhibition, change in personality such as apathy and indifference, and poor judgment, and (2) language, with a nonfluent aphasia with anomia (primary progressive aphasia), or a fluent aphasia with early loss of word meaning (semantic dementia). The differential diagnosis includes other neurodegenerative dementias, vascular and other conditions affecting the brain, and psychiatric diseases. Investigations, including neuropsychological testing, and structural and functional brain imaging, may help support the diagnosis. Recent advances in understanding the pathophysiology have suggested that most cases have underlying ubiquitin-positive inclusions, whereas some have tau-positive inclusions. Genetic mutations, particularly on chromosome 17 in the tau or progranulin genes, have been identified. Management includes a trial of symptomatic medications and a multifaceted approach, including environmental modification and long-term care planning.

CONCLUSION

Medical researchers studying frontotemporal dementia aim to identify disease-modifying drugs and, ultimately, a cure for this devastating disease.

Review: Recent progress in frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) is a highly familial condition and is increasingly being recognized as an important form of dementia. The literature published on this disease is often difficult to collate due to the wide range in nomenclature used. Thankfully, consensus recommendations have now been published to address this issue and hopefully the community will adopt these as intended. Much progress has been made in our understanding of the clinical, pathological and genetic understanding of FTLD in recent years. Progranulin and TDP-43 have recently been identified as new important proteins involved in the pathophysiology of FTLD and this latter protein may have potential as a biomarker of this disease. However, much remains before we have a full picture of the genes that cause FTLD and the biological pathways in which they function. The purpose of this review is to summarize the current concepts and recent advances in our knowledge of this disease.

The molecular basis of frontotemporal dementia

Frontotemporal dementia (FTD) is a clinical syndrome with a heterogeneous molecular basis. Familial FTD has been linked to mutations in several genes, including those encoding the microtubule-associated protein tau (MAPT), progranulin (GRN), valosin-containing protein (VCP) and charged multivescicular body protein 2B (CHMP2B). The associated neuropathology is characterised by selective degeneration of the frontal and temporal lobes (frontotemporal lobar degeneration, FTLD), usually with the presence of abnormal intracellular protein accumulations. The current classification of FTLD neuropathology is based on the identity of the predominant protein abnormality, in the belief that this most closely reflects the underlying pathogenic process. Major subgroups include those characterised by the pathological tau, TDP-43, intermediate filaments and a group with cellular inclusions composed of an unidentified ubiquitinated protein. This review will focus on the current understanding of the molecular basis of each of the major FTLD subtypes. It is anticipated that this knowledge will provide the basis of future advances in the diagnosis and treatment of FTD.

Frontotemporal lobar degeneration and dementia with Lewy bodies: clinicopathological issues associated with antemortem diagnosis

Currently, the clinical diagnostic criteria of frontotemporal lobar degeneration (FTLD) and dementia with Lewy bodies (DLB) are well known to neurologists and psychiatrists. However, the accuracy of the clinical diagnosis of these diseases in autopsy series is not always adequate. For example, FTLD is a syndrome rather than a clinicopathological disease entity that is comprised of various pathological substrates, including Pick's disease, FTLD with microtubule-associated protein tau gene mutation, FTLD with tau-negative ubiquitin-positive inclusions (FTLD-U), FTLD-U with progranulin gene mutation, corticobasal degeneration, basophilic inclusion body disease, and neuronal intermediate filament inclusion disease. Whether these underlying pathologies can be identified clinically is one of the greatest interests in neuropathological research. The pathophysiological relationship between Lewy pathology and Alzheimer pathology in DLB is explored with interest because it may be associated with the accuracy of clinical diagnoses. For example, although Lewy pathology may progress from the brain stem nuclei to the cerebral cortex in Parkinson's disease, recent studies have demonstrated that the progression pattern in DLB is not always identical to that in Parkinson's disease. It is also considered that the progression pattern of Lewy pathology correlates with the evolution of clinical symptoms and that the progression pattern of Lewy pathology may be altered when Alzheimer pathology coexists. In the present paper, the clinicopathological features of two demented cases are presented, and some pathological issues associated with the clinical diagnosis of FTLD and DLB are discussed.

Clinicopathological characterization of Pick's disease versus frontotemporal lobar degeneration with ubiquitin/TDP-43-positive inclusions

Although frontotemporal lobar degeneration with ubiquitin/TDP-43-positive inclusions (FTLD-TDP) and Pick's disease are common pathological substrates in sporadic FTLD, clinical differentiation of these diseases is difficult. We performed a retrospective review of medical records and semiquantitative examination of neuronal loss of 20 sporadic FTLD-TDP and 19 Pick's disease cases. Semantic dementia as the first syndrome developed only in FTLD-TDP patients. Impaired speech output in the early stage was five times more frequent in Pick's disease than in FTLD-TDP. The total frequency of asymmetric motor disturbances (e.g., parkinsonism, pyramidal signs, and contracture) during the course was significantly more frequent in FTLD-TDP (78%) than in Pick's disease cases (14%). Asymmetric pyramidal signs were found in 7 of 13 FTLD-TDP cases with corticospinal tract degeneration similar to primary lateral sclerosis. Frontotemporal dementia as the first syndrome was noted in both FTLD-TDP (28%) and Pick's disease cases (64%); however, only FTLD-TDP cases subsequently developed asymmetric motor disturbances, and some of the cases further exhibited hemineglect. Concordant with these clinical findings, degeneration in the temporal cortex, caudate nucleus, putamen, globus pallidus, substantia nigra, and corticospinal tract was significantly more severe in FTLD-TDP, and degeneration in the frontal cortex tended to be more severe in Pick's disease. Given these findings, the initial impairment of semantic memory or comprehension and subsequent asymmetric motor disturbances in sporadic FTLD patients predict sporadic FTLD-TDP rather than Pick's disease, while initial behavioral symptoms or non-fluent aphasia without subsequent asymmetric motor disturbances predict Pick's disease rather than sporadic FTLD-TDP.

Understanding hippocampal sclerosis in the elderly: epidemiology, characterization, and diagnostic issues

Hippocampal sclerosis (HS) is a pathologic term used to describe severe loss of neurons and reactive gliosis without cystic cavitation in the CA1 sector of the hippocampus. In late life, HS is associated with hippocampal atrophy, severe amnesia, and slowly progressive dementia without clinical seizure activity. HS is difficult to distinguish clinically from Alzheimer's disease and is often diagnosed postmortem. In autopsy series, HS may be found without significant other pathology (2%-4% of cases), but it occurs frequently in combination with other vascular and neurodegenerative disorders (12%-20% of cases). HS is found bilaterally in 50% of cases and unilaterally in 50% of cases, with similar predilection for the right versus left hemisphere. The pathogenesis of HS is unknown and may be multifactorial in origin, possibly due to anoxic/ischemic injury or TDP-43-related neurodegeneration. Little is known about the prevention and treatment of late-life HS, although circumstantial evidence suggests the importance of identifying and treating vascular risk factors.

Update on recent molecular and genetic advances in frontotemporal lobar degeneration

Great strides have been made in the last 2 years in the field of frontotemporal lobar degeneration (FTLD), particularly with respect to the genetics and molecular biology of FTLD with ubiquitinated inclusions. It is now clear that most cases of familial FTLD with ubiquitinated inclusions have mutations in the progranulin gene, located on chromosome 17. It is also clear that most ubiquitinated inclusions in FTLD with ubiquitinated inclusions are composed primarily of TAR DNA-binding protein-43. Thus, FTLDs can be separated into 2 major groups (i.e. tauopathies and ubiquitinopathies), and most of the ubiquitinopathies can now be defined as TAR DNA-binding protein-43 proteinopathies. Many of the familial FTLDs are linked to chromosome 17, including both the familial tauopathies and the familial TAR DNA-binding protein-43 proteinopathies with progranulin mutations. This review highlights the neuropathologic features and the most important discoveries of the last 2 years and places these findings into the historical context of FTLD.

Gene expression study on peripheral blood identifies progranulin mutations

Peripheral blood is a readily available tissue source allowing relatively noninvasive screening for a host of medical conditions. We screened total-blood progranulin (PGRN) levels in 107 patients with neurodegenerative dementias and related conditions, and 36 control subjects, and report the following findings: (1) confirmation of high progranulin expression levels in peripheral blood; (2) two subjects with reduced progranulin levels and mutations in the PGRN gene confirmed by direct sequencing; and (3) greater PGRN messenger RNA levels in patients with clinical diagnosis of Alzheimer's disease. This proof-of-principle report supports the use of gene quantification as diagnostic screen for PGRN mutations and suggests a potential role for progranulin in Alzheimer's disease.

Frontotemporal dementia and related disorders: deciphering the enigma

In the past century, particularly the last decade, there has been enormous progress in our understanding of frontotemporal dementia, a non-Alzheimer's type dementia. Large clinicopathological series have been published that have clearly demonstrated an overlap between the clinical syndromes subsumed under the term frontotemporal dementia and the progressive supranuclear palsy syndrome, corticobasal syndrome, and motor neuron disease. There have also been significant advancements in brain imaging, neuropathology, and molecular genetics that have led to different approaches to classification. Unfortunately, the field is complicated by a barrage of overlapping clinical syndromes and histopathological diagnoses that does not allow one to easily identify relations between individual clinical syndromic presentations and underlying neuropathology. This review deciphers this web of terminology and highlights consistent, and hence important, associations between individual clinical syndromes and neuropathology. These associations could ultimately allow the identification of appropriate patient phenotypes for future targeted treatments.

Frontotemporal lobar degeneration with ubiquitin-positive, but TDP-43-negative inclusions

Frontotemporal lobar degeneration (FTLD) can be pathologically subdivided into tau-positive and tau-negative types. The most common tau-negative variant is FTLD with ubiquitin-immunoreactive lesions (FTLD-U). Recently, the TAR DNA binding protein 43 (TDP-43) was identified in neuronal inclusions in FTLD-U. After applying TDP-43 immunohistochemistry to a series of 44 cases of FTLD-U with no secondary pathology, three cases (7%) were identified with ubiquitin- and p62-positive neuronal cytoplasmic inclusions (NCI) that were negative for TDP-43. All the three cases had marked brain atrophy with striking atrophy of the striatum. Cases 1 and 2 presented at ages 43 and 38, respectively, as behavioral variant frontotemporal dementia (1 with positive family history) and had ubiquitin- and p62-positive NCI in frontotemporal neocortex and dentate granule cells of the hippocampus. Case 3 presented with the corticobasal syndrome. Unlike the other two cases, ubiquitin- and p62-positive NCI were also visible on hematoxylin and eosin stain. There were no neuronal intranuclear inclusions. Electron microscopic examination of the NCI in cases 2 and 3 revealed granulofilamentous inclusions. These cases confirm the existence of TDP-43-negative FTLD-U and extend the clinical and pathological spectrum of this disorder. The findings raise the possibly of an as yet identified protein that may play a pathogenic role in tau-negative FTLD.

TDP-43-negative FTLD-U is a significant new clinico-pathological subtype of FTLD

Frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U) is the most common neuropathological subtype of frontotemporal dementias. While TDP-43 is the pathologic protein in the majority of FTLD-U cases, small numbers of cases have recently been reported with TDP-43-negative FTLD-U pathology. To determine the frequency and to define the clinico-pathological spectrum of TDP-43-negative FTLD-U, we re-evaluated 44 cases with a previous diagnosis of FTLD-U or dementia lacking distinctive histopathology. We identified nine cases (20%) with TDP-43-negative FTLD-U pathology by immunohistochemistry and confirmed the absence of pathological TDP-43 by biochemical analysis. All patients presented with sporadic early-onset frontotemporal dementia with predominant behavioral and personality changes. Besides ubiquitin-positive neuronal cytoplasmic inclusions, the most intriguing neuropathological feature was the presence of ubiquitin-positive neuronal intranuclear inclusions (NIIs), often with curved or twisted morphology, in the neocortex, hippocampus, brainstem, and spinal cord. Double-label immunofluorescence revealed an unusual and distinct immunoreactivity profile for these NIIs, with ubiquitin-immunoreactivity, but absence of p62 labeling. The highly consistent clinical and neuropathological phenotype supports the concept that TDP-43-negative FTLD-U should be considered as a new clinicopathological FTLD entity.

TAR DNA-binding protein 43 immunohistochemistry reveals extensive neuritic pathology in FTLD-U: a midwest-southwest consortium for FTLD study

TAR DNA-binding protein 43 (TDP-43) is a major component of the inclusions in frontotemporal lobar degeneration with ubiquitinated inclusions (FTLD-U). We studied TDP-43 pathology in the hippocampus and frontal cortex of autopsy brains from patients with FTLD-U (n = 68), dementia lacking distinctive histopathology (n = 4), other neurodegenerative diseases (n = 23), and controls (n = 12) using a sensitive immunohistochemistry protocol. Marked enhancement of staining of TDP-43-positive dystrophic neurites (DNs) was obtained, and we observed 2 previously unrecognized pathologic patterns (i.e. frequent long DNs in the CA1 region and frequent dot-like DNs in the neocortical layer 2) in 39% and 15% of the FTLD-U cases, respectively. Frequent long DNs, but not dot-like DNs, were significantly associated with progranulin mutations. Based on this evaluation, 4 FTLD-U cases showed no TDP-43 pathology and were reclassified as "FTLD-U, non-TDP-43 proteinopathy," and 3 cases of dementia lacking distinctive histopathology were reclassified as FTLD-U. Of the cases with other neurodegenerative diseases, 43% showed TDP-43 pathology in the hippocampus, but only 4% showed TDP-43 pathology in the frontal cortex. No TDP-43 pathology was seen in controls. These results indicate that the sensitivity of the TDP-43 immunohistochemistry method affects both the extent and type of abnormalities detected. Moreover, assessment of abnormalities in both the hippocampus and frontal cortex may be diagnostically important in FTLD-U.

Mutations in progranulin gene: clinical, pathological, and ribonucleic acid expression findings

BACKGROUND

There is an increasing interest in the clinico-pathological correlation of mutations in progranulin (PGRN) and frontotemporal lobar degeneration (FTLD) complex diseases. We aim to study the PGRN expression variability in patients with different clinical features for a better understanding of its roles in FTLD disease.

METHODS

We sequenced the PGRN gene in 72 patients suffering from FTLD (25 familial and 47 sporadic cases) and in 24 asymptomatic at-risk relatives. We also analyzed PGRN expression in blood by quantitative real-time polymerase chain reaction from 37 patients, 8 asymptomatic mutation carriers, and 10 control subjects as well as in brain tissue from 16 patients and 9 control subjects.

RESULTS

Four novel mutations were associated with familial and sporadic FTLD and familial dementia associated with amyotrophic lateral sclerosis. We identified a close association between the IVS6-1G>A mutation in PGRN and corticobasal syndrome. Brain tissue was available for carriers of two of the four mutations (IVS6-1 G>A and P357HfsX3). Immunohistochemical analysis revealed ubiquitin- and TDP-43positive and tau/alpha-synuclein negative immunoreactive neuronal intranuclear inclusions. The relative expression of PGRN in the clinical sample was significantly lower in carriers of the IVS6-1 G>A than in control subjects.

CONCLUSIONS

Progranulopathies are a major cause of the main phenotypes included in the FTLD complex. According to our results, the level of expression of PGRN in blood could be a useful marker both for diagnostics of part of the spectrum of FTLD conditions and for monitoring future treatments that might boost the level of PGRN in this disorder.