Frontotemporal dementia: clinicopathological correlations

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.

Recent insights into the molecular genetics of dementia

Our understanding of the molecular genetic basis of two common neurodegenerative dementias, Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD), has greatly advanced in recent years. Progranulin mutations were identified as a major cause of FTLD and a potential susceptibility factor for other forms of dementia. In addition, through copy-number analyses of previously identified disease genes and the study of microRNA regulation in dementia, new evidence emerged to support the view that subtle variability in the expression of known disease proteins could increase the risk for sporadic forms of dementia. Finally, in late-onset AD populations, the first genome-wide association studies were performed and novel potential AD susceptibility genes reported. These exciting findings provide novel insights into the disease mechanisms underlying dementia and hold promise for the development of potential treatments.

[Pick's disease: clinicopathological features for antemortem diagnosis]

Frontotemporal lobar degeneration (FTLD) with ubiquitin/TDP-43-positive inclusions (FTLD-TDP) and Pick's disease are two major pathological substrates in sporadic FTLD patients. Although identifying these underlying pathologies during the life of the patient is crucial for specific pathology-based treatment in the future, adequate clinical data to infer pathologies are not available. Several recent studies demonstrated that Pick's disease cases tend to present clinically with frontotemporal dementia (FTD) or progressive non-fluent aphasia as the first syndrome, while sporadic FTLD-TDP cases frequently show semantic dementia. Some asymmetric motor disturbances (e.g., pyramidal signs, parkinsonism, and contracture) are frequent in sporadic FTLD-TDP during the course, but rare in Pick's disease. On the other hand, several previous studies have demonstrated that the most frequent first syndrome of FTLD-TDP with progranulin gene (PGRN) mutations is FTD and that neuronal loss in the frontal cortex is more severe than that in the temporal cortex. Therefore, it is plausible that the clinicopathological features of sporadic FTLD-TDP are different from those of Pick's disease and FTLD-TDP with PGRN mutations. Given that in vivo Abeta imaging will soon be put to practical use, clinical data useful for clinical differentiation of pathological subtypes of FTLD besides AD with atypical cerebral atrophy will be essential in the future.

Atrophy patterns in histologic vs clinical groupings of frontotemporal lobar degeneration

OBJECTIVE

Predictable patterns of atrophy are associated with the clinical subtypes of frontotemporal dementia (FTD): behavioral variant (bvFTD), semantic dementia (SEMD), and progressive nonfluent aphasia (PNFA). Some studies of pathologic subtypes have also suggested specific atrophy patterns; however, results are inconsistent. Our aim was to test the hypothesis that clinical, but not pathologic, classification (FTD with ubiquitin inclusions [FTD-U] and FTD with tau inclusions [FTD-T]) is associated with predictable patterns of regional atrophy.

METHODS

Magnetic resonance scans of nine FTD-U and six FTD-T patients (histologically confirmed) were compared with 25 controls using voxel-based morphometry (VBM). Analyses were conducted with the patient group classified according to histologic or clinical variant. Additionally, three Alzheimer pathology patients who had the syndrome of SEMD in life (FTD-A) were analyzed.

RESULTS

The VBM studies in clinical variants confirmed established patterns of atrophy (SEMD, rostral temporal; bvFTD, mesial frontal; PNFA, left insula). FTD-U and FTD-T VBM results were very similar, showing severe atrophy in the temporal poles, mesial frontal lobe, and insulae. A conjunction analysis confirmed this similarity. Subgroup analysis found that SEMD associated with either FTD-T or FTD-U was associated with similar rostral temporal atrophy; however, FTD-A had a qualitatively different pattern of left hippocampal atrophy.

CONCLUSIONS

While there is predictable atrophy for clinical variants of frontotemporal dementia (FTD), histologic FTD variants show no noticeable differences. Reports of specific atrophy profiles are likely the result of idiosyncrasies in small groups. Semantic dementia associated with Alzheimer pathology, however, presented a distinct atrophy pattern.

Automated MRI-based classification of primary progressive aphasia variants

Degeneration of language regions in the dominant hemisphere can result in primary progressive aphasia (PPA), a clinical syndrome characterized by progressive deficits in speech and/or language function. Recent studies have identified three variants of PPA: progressive non-fluent aphasia (PNFA), semantic dementia (SD) and logopenic progressive aphasia (LPA). Each variant is associated with characteristic linguistic features, distinct patterns of brain atrophy, and different likelihoods of particular underlying pathogenic processes, which makes correct differential diagnosis highly clinically relevant. Evaluation of linguistic behavior can be challenging for non-specialists, and neuroimaging findings in single subjects are often difficult to evaluate by eye. We investigated the utility of automated structural MR image analysis to discriminate PPA variants (N=86) from each other and from normal controls (N=115). T1 images were preprocessed to obtain modulated grey matter (GM) images. Feature selection was performed with principal components analysis (PCA) on GM images as well as images of lateralized atrophy. PC coefficients were classified with linear support vector machines, and a cross-validation scheme was used to obtain accuracy rates for generalization to novel cases. The overall mean accuracy in discriminating between pairs of groups was 92.2%. For one pair of groups, PNFA and SD, we also investigated the utility of including several linguistic variables as features. Models with both imaging and linguistic features performed better than models with only imaging or only linguistic features. These results suggest that automated methods could assist in the differential diagnosis of PPA variants, enabling therapies to be targeted to likely underlying etiologies.

Neuropsychological decline in frontotemporal lobar degeneration: a longitudinal analysis

Few studies have assessed whether the patterns of neuropsychological impairment in patients with different frontotemporal lobar degeneration (FTLD) subtypes remain distinct over the duration of their illness or devolve into a common, undifferentiated neuropsychological state. A longitudinal neuropsychological analysis was obtained over 100 months assessing executive control, language/naming, and visuoconstruction in 441 patients diagnosed with Alzheimer's disease (AD) and four FTLD subtypes, i.e., a social comportment/dysexecutive (SOC/EXEC) disorder; progressive non-fluent aphasia (PNFA); semantic dementia (SemD); and corticobasal degeneration (CBD). Initial group differences on each measure were maintained over the duration of illness, including several double dissociations. For example, AD patients exhibited a decline in 'animal' fluency; PNFA patients had difficulty on tests of executive control, SemD maintained their impairment on tests of naming, and CBD had presented with performance on visuoconstructional tests. None of the group by neuropsychological task interactions evaluating longitudinal decline was significant, suggesting that performance does not converge onto a common subtype over time. These data indicate that distinct patterns of neuropsychological impairment are maintained longitudinally, reflecting the unique anatomic distribution of relative disease burden in AD and FTLD.

Apraxia of speech and nonfluent aphasia: a new clinical marker for corticobasal degeneration and progressive supranuclear palsy

PURPOSE OF REVIEW

To highlight the fact that patients with corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP) can sometimes present with a progressive apraxia of speech, nonfluent aphasia, or a combination of the two disorders.

RECENT FINDINGS

Corticobasal degeneration and PSP are neurodegenerative diseases characterized by neuronal loss and gliosis in cardinal brain regions, as well as the abnormal deposition of the microtubule associated protein tau in cell bodies and cell processes. The typical presenting features of CBD and PSP are akinesia and rigidity that are levodopa unresponsive, although there has been evidence that both diseases, moreso CBD, can present with a dementia syndrome. Recent clinicopathological studies have now also demonstrated that a subset of patients with CBD and PSP present with a progressive apraxia of speech, nonfluent aphasia, or a combination of the two disorders.

SUMMARY

Presenting features of progressive apraxia of speech or nonfluent aphasia are strongly associated with a diagnosis of CBD, PSP, or both.

Rapidly progressive neurodegenerative dementias

BACKGROUND

Neurodegenerative dementias are typically characterized by an insidious onset and a relatively slowly progressive course. Less common are patients with a rapidly progressive course to death.

OBJECTIVE

To characterize patients with a neurodegenerative disease and a rapidly progressive course to death.

DESIGN, SETTING, AND PATIENTS

Using a text word search for "rapid" and "dementia" in the same sentence, the Mayo Clinic Medical Records Linkage system was used to identify all patients evaluated between January 1, 2000, and September 30, 2007, with brain autopsy (N = 96) at a tertiary care medical center. Of these 96 patients, we included only those with disease duration of less than 4 years to death and with histological diagnosis of a neurodegenerative disease.

MAIN OUTCOME MEASURES

Rapidly progressive dementia with death sooner than 4 years after onset and pathological diagnosis at our institution of a neurodegenerative disease.

RESULTS

We included 22 patients (10 men). Although 8 cases (36%) had Creutzfeldt-Jakob disease (CJD), the rest had frontotemporal lobar degeneration with motor neuron degeneration (5 cases [23%]), a tauopathy (progressive supranuclear palsy or corticobasal degeneration) (4 cases [18%]), diffuse Lewy body disease (3 cases [14%]), or Alzheimer disease (2 cases [9%]). All of the patients with CJD died 12 months or sooner after onset, whereas the others had an illness duration longer than 12 months. Notably, all of the 3 patients with diffuse Lewy body disease but no others initially experienced a transient postoperative or illness-associated encephalopathy, then relative normality for 2 years, and finally a rapidly progressive dementia and decline to death in 4 to 12 months.

CONCLUSIONS

Based on this cohort, although CJD is the most likely cause of a rapidly progressive neurodegenerative dementia, frontotemporal lobar degeneration with motor neuron degeneration, diffuse Lewy body disease, tauopathies, and Alzheimer disease can also cause a rapidly progressive dementia. If illness duration is beyond 12 months, a non-CJD neurodegenerative disease may be more likely than CJD to be the diagnosis.

Cerebrospinal fluid biomarker signature in Alzheimer's disease neuroimaging initiative subjects

OBJECTIVE

Develop a cerebrospinal fluid biomarker signature for mild Alzheimer's disease (AD) in Alzheimer's Disease Neuroimaging Initiative (ADNI) subjects.

METHODS

Amyloid-beta 1 to 42 peptide (A beta(1-42)), total tau (t-tau), and tau phosphorylated at the threonine 181 were measured in (1) cerebrospinal fluid (CSF) samples obtained during baseline evaluation of 100 mild AD, 196 mild cognitive impairment, and 114 elderly cognitively normal (NC) subjects in ADNI; and (2) independent 56 autopsy-confirmed AD cases and 52 age-matched elderly NCs using a multiplex immunoassay. Detection of an AD CSF profile for t-tau and A beta(1-42) in ADNI subjects was achieved using receiver operating characteristic cut points and logistic regression models derived from the autopsy-confirmed CSF data.

RESULTS

CSF A beta(1-42) was the most sensitive biomarker for AD in the autopsy cohort of CSF samples: receiver operating characteristic area under the curve of 0.913 and sensitivity for AD detection of 96.4%. In the ADNI cohort, a logistic regression model for A beta(1-42), t-tau, and APO epsilon 4 allele count provided the best assessment delineation of mild AD. An AD-like baseline CSF profile for t-tau/A beta(1-42) was detected in 33 of 37 ADNI mild cognitive impairment subjects who converted to probable AD during the first year of the study.

INTERPRETATION

The CSF biomarker signature of AD defined by A beta(1-42) and t-tau in the autopsy-confirmed AD cohort and confirmed in the cohort followed in ADNI for 12 months detects mild AD in a large, multisite, prospective clinical investigation, and this signature appears to predict conversion from mild cognitive impairment to AD.

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.

MRI correlates of protein deposition and disease severity in postmortem frontotemporal lobar degeneration

BACKGROUND

Frontotemporal lobar degeneration (FTLD) can be classified based on the presence of the microtubule-associated protein tau and the TAR DNA binding protein-43 (TDP-43). Future treatments will likely target these proteins, therefore it is important to identify biomarkers to help predict protein biochemistry.

OBJECTIVE

To determine whether there is an MRI signature pattern of tau or TDP-43 using a large cohort of FTLD subjects and to investigate how patterns of atrophy change according to disease severity using a large autopsy-confirmed cohort of FTLD subjects.

METHODS

Patterns of gray matter loss were assessed using voxel-based morphometry in 37 tau-positive and 44 TDP-43-positive subjects compared to 35 age and gender-matched controls, and compared to each other. Comparisons were also repeated in behavioral variant frontotemporal dementia (bvFTD) subjects (n = 15 tau-positive and n = 30 TDP-43-positive). Patterns of atrophy were also assessed according to performance on the Clinical Dementia Rating (CDR) scale and Mini-Mental State Examination (MMSE).

RESULTS

The tau-positive and TDP-43-positive groups showed patterns of frontotemporal gray matter loss compared to controls with no differences observed between the groups, for all subjects and for bvFTD subjects. Patterns of gray matter loss increased in a graded manner by CDR and MMSE with loss in the frontal lobes, insula and hippocampus in mild subjects, spreading to the temporal and parietal cortices and striatum in more advanced disease.

CONCLUSION

There is no signature pattern of atrophy for tau or TDP-43; however, patterns of atrophy in FTLD progress with measures of clinical disease severity.

Diminished self-conscious emotional responding in frontotemporal lobar degeneration patients

Frontotemporal lobar degeneration (FTLD) is a neurodegenerative disease that dramatically alters social and emotional behavior. Recent work has suggested that self-conscious emotions (e.g., embarrassment) may be particularly vulnerable to disruption in this disease. Self-conscious emotions require the ability to monitor the self in relation to others. These abilities are thought to be subserved by brain regions (e.g., medial prefrontal, anterior cingulate, and insula) that are particularly vulnerable to damage in FTLD. This study examined emotional responding (expressive behavior, peripheral physiology, and subjective experience) in 24 FTLD patients and 16 cognitively normal control participants using a karaoke task known to elicit self-conscious emotion reliably and a nonemotional control task (isometric handgrip). Results indicated that FTLD patients showed diminished self-conscious emotional behavior (embarrassment and amusement) and diminished physiological responding while watching themselves singing. No differences were found between patients and controls in the nonemotional control task. These findings offer evidence of marked disruption of self-conscious emotional responding in FTLD. Diminished self-conscious emotional responding likely contributes significantly to social inappropriateness and other behavioral abnormalities in FTLD.

Apolipoprotein E epsilon4 is associated with disease-specific effects on brain atrophy in Alzheimer's disease and frontotemporal dementia

Apolipoprotein epsilon4 (apoE4) has been strongly linked with Alzheimer's disease (AD) and contributes to several other neurological disorders. We investigated the influence of epsilon4 allele carrier status on the pattern of gray matter atrophy and disease severity in 51 patients with probable AD and 31 patients with behavioral variant frontotemporal dementia (bvFTD), compared with 56 healthy controls. Voxel-based morphometry was performed by using statistical parametric mapping. The epsilon4 allele frequency was higher in the AD group (P < 0.001) than the controls but not in the bvFTD group. No differences in demographic or cognitive profiles were observed between epsilon4 allele carriers and noncarriers within any of the diagnostic groups. However, epsilon4 carrier status was associated with more severe brain atrophy in disease-specific regions compared with noncarriers in both AD and bvFTD. AD epsilon4 carriers showed greater atrophy in the bilateral parietal cortex and right hippocampus, and bvFTD epsilon4 carriers demonstrated greater atrophy in the bilateral medial, dorsolateral, and orbital frontal cortex, anterior insula, and cingulate cortex with right predominance. This regional epsilon4 effect is consistent with the hypothesis that apoE may affect the morphologic expression uniquely in different neurodegenerative diseases. The atrophy patterns in epsilon4 carriers may indicate that they are at greater risk for clinical progression.

Molecular neuropathology of TDP-43 proteinopathies

The identification of TDP-43 as the major component of the pathologic inclusions in most forms of sporadic and familial frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U) and amyotrophic lateral sclerosis (ALS) resolved a long-standing enigma concerning the nature of the ubiquitinated disease protein under these conditions. Anti-TDP-43 immunohistochemistry and the recent development of novel tools, such as phosphorylation-specific TDP-43 antibodies, have increased our knowledge about the spectrum of pathological changes associated with FTLD-U and ALS and moreover, facilitated the neuropathological routine diagnosis of these conditions. This review summarizes the recent advances in our understanding on the molecular neuropathology and pathobiology of TDP-43 in FTLD and ALS.

Granulin mutations associated with frontotemporal lobar degeneration and related disorders: an update

Mutations in the gene encoding granulin (HUGO gene symbol GRN, also referred to as progranulin, PGRN), located at chromosome 17q21, were recently linked to tau-negative ubiquitin-positive frontotemporal lobar degeneration (FTLDU). Since then, 63 heterozygous mutations were identified in 163 families worldwide, all leading to loss of functional GRN, implicating a haploinsufficiency mechanism. Together, these mutations explained 5 to 10% of FTLD. The high mutation frequency, however, might still be an underestimation because not all patient samples were examined for all types of loss-of-function mutations and because several variants, including missense mutations, have a yet uncertain pathogenic significance. Although the complete phenotypic spectrum associated with GRN mutations is not yet fully characterized, it was shown that it is highly heterogeneous, suggesting the influence of modifying factors. A role of GRN in neuronal survival was suggested but the exact mechanism by which neurodegeneration and deposition of pathologic brain inclusions occur still has to be clarified.

Abeta amyloid and glucose metabolism in three variants of primary progressive aphasia

OBJECTIVE

Alzheimer's disease (AD) is found at autopsy in up to one third of patients with primary progressive aphasia (PPA), but clinical features that predict AD pathology in PPA are not well defined. We studied the relationships between language presentation, Abeta amyloidosis, and glucose metabolism in three PPA variants using [11C]-Pittsburgh compound B ([11C]PIB) and [18F]-labeled fluorodeoxyglucose positron emission tomography ([18F]FDG-PET).

METHODS

Patients meeting PPA criteria (N = 15) were classified as logopenic aphasia (LPA), progressive nonfluent aphasia (PNFA), or semantic dementia (SD) based on language testing. [11C]PIB distribution volume ratios were calculated using Logan graphical analysis (cerebellar reference). [18F]FDG images were normalized to pons. Partial volume correction was applied.

RESULTS

Elevated cortical PIB (by visual inspection) was more common in LPA (4/4 patients) than in PNFA (1/6) and SD (1/5) (p < 0.02). In PIB-positive PPA, PIB uptake was diffuse and indistinguishable from the pattern in matched AD patients (n = 10). FDG patterns were focal and varied by PPA subtype, with left temporoparietal hypometabolism in LPA, left frontal hypometabolism in PNFA, and left anterior temporal hypometabolism in SD. FDG uptake was significant asymmetric (favoring left hypometabolism) in PPA (p < 0.005) but not in AD.

INTERPRETATION

LPA is associated with Abeta amyloidosis, suggesting that subclassification of PPA based on language features can help predict the likelihood of AD pathology. Language phenotype in PPA is closely related to metabolic changes that are focal and anatomically distinct between subtypes, but not to amyloid deposition patterns that are diffuse and similar to AD.

Multiple system atrophy: a primary oligodendrogliopathy

To this day, the cause of multiple system atrophy (MSA) remains stubbornly enigmatic. A growing body of observations regarding the clinical, morphological, and biochemical phenotypes of MSA has been published, but the interested student is still left without a clue as to its underlying cause. MSA has long been considered a rare cousin of Parkinson's disease and cerebellar degeneration; it is rich in acronyms but poor in genetic and environmental leads. Because of the worldwide research efforts conducted over the last two decades and the discovery of the alpha-synuclein-encoding SNCA gene as a cause of rare familial Parkinson's disease, the MSA field has seen advances on three fronts: the identification of its principal cellular target, that is, oligodendrocytes; the characterization of alpha-synuclein-rich glial cytoplasmic inclusions as a suitable marker at autopsy; and improved diagnostic accuracy in living patients resulting from detailed clinicopathological studies. The working model of MSA as a primary glial disorder was recently strengthened by the finding of dysregulation in the metabolism of myelin basic protein and p25alpha, a central nervous system-specific phosphoprotein (also called tubulin polymerization promoting protein, TPPP). Intriguingly, in early cases of MSA, the oligodendrocytic changes in myelin basic protein and p25alpha processing were recorded even before formation of glial cytoplasmic inclusions became detectable. Here, we review the evolving concept that MSA may not just be related to Parkinson's disease but also share traits with the family of demyelinating disorders. Although these syndromes vary in their respective cause of oligodendrogliopathy, they have in common myelin disruption that is often followed by axonal dysfunction.

The contribution of TMS to frontotemporal dementia variants

OBJECTIVE

Frontotemporal lobar degeneration (FTLD) includes different heterogeneous conditions mainly characterized by personality changes and cognitive deficits in language and executive functions; movement disorders have also been associated with FTLD. The present study aimed to measure the primary motor cortex (M1) inhibitory and facilitatory functions in patients affected by FTLD.

MATERIALS AND METHODS

The study included 17 FTLD patients, 8 age-matched healthy controls and 8 Alzheimer's disease (AD) patients. Transcranial magnetic stimulation (TMS) was used to study intracortical inhibition (ICI) and facilitation (ICF) by using a double-pulse paradigm.

RESULTS

FTLD patients were comparable with controls and AD patients for ICI and ICF. Corticobasal degeneration (CBD) patients presented significant reduced inhibition at ISI3; moreover two out of seven CBD patients had only ipsilateral responses.

DISCUSSION

The present study reveals a selective impairment of M1 ICI inhibitory response in CBD, which may help in distinguishing among the FTLD clinical spectrum.

Development of methodology for conducting clinical trials in frontotemporal lobar degeneration

To design clinical trials for the frontotemporal lobar degenerations (FTLD), knowledge about measurement of disease progression is needed to estimate power and enable the choice of optimal outcome measures. The aim here was to conduct a multicentre, 1 year replica of a clinical trial in patients with one of four FTLD syndromes, behavioural variant frontotemporal dementia (bvFTD), progressive nonfluent aphasia (PNFA), progressive logopenic aphasia (PLA) and semantic dementia (SMD). Patients with one of the four FTLD syndromes were recruited from five academic medical centres over a 2 year period. Standard operationalized diagnostic criteria were used. In addition to clinical inclusion and exclusion criteria, patients were required to exhibit focal frontal, temporal or insular brain atrophy or dysfunction by neuroimaging. Patients underwent neuropsychological, functional, behavioural, neurological and MR imaging assessment at baseline and approximately 12 months later. Potential outcome measures were examined for their rates of floor and ceiling values at baseline and end of study, their mean changes and variances. The neuropsychological tests were combined into two cognitive composites -- one for language functions and the other for executive functions. There were 107 patients who underwent baseline assessment and 78 who completed a follow-up assessment within 10-16 months. Two global measures, the FTLD-modified Clinical Dementia Rating (FTLD-modified CDR) and the Clinical Global Impression of Change (CGIC) demonstrated decline in the majority of patients. Several cognitive measures showed negligible floor or ceiling scores either at baseline or follow-up. Scores declined at follow-up in the majority of patients. The cognitive, executive and combined composites were shown to be sensitive to change across all FTLD syndromes. Patients improved at follow-up on the behavioural scales -- the Frontal Behavioural Inventory (22%) and the Neuropsychiatric Inventory (28%) -- suggesting that these instruments may not be ideal for clinical trial use. It was feasible to recruit FTLD patients in a simulated multi-centre trial. There are several candidate outcome measures -- including the FTLD-CDR and the cognitive composites -- that could be used in clinical trials across the spectrum of FTLD.

Biomarkers for cognitive impairment and dementia in elderly people

The threat of a looming pandemic of dementia in elderly people highlights the compelling need for the development and validation of biomarkers that can be used to identify pre-clinical and prodromal stages of disease in addition to fully symptomatic dementia. Although predictive risk factors and correlative neuroimaging measures will have important roles in these efforts, this Review describes recent progress in the discovery, validation, and standardisation of molecular biomarkers--small molecules and macromolecules whose concentration in the brain or biological fluids can aid diagnosis at different stages of the more common dementing diseases and in the assessment of disease progression and response to therapeutics. An approach that efficiently combines independent information from risk-factor assessment, neuroimaging measures, and biomarkers might soon guide clinicians in the early diagnosis and management of cognitive impairment in elderly people.

Impaired action knowledge in amyotrophic lateral sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative condition affecting the motor system, but recent work also shows more widespread cognitive impairment. This study examined performance on measures requiring knowledge of actions, and related performance to MRI cortical atrophy in ALS.

METHODS

A total of 34 patients with ALS performed measures requiring word-description matching and associativity judgments with actions and objects. Voxel-based morphometry was used to relate these measures to cortical atrophy using high resolution structural MRI.

RESULTS

Patients with ALS were significantly more impaired on measures requiring knowledge of actions than measures requiring knowledge of objects. Difficulty on measures requiring action knowledge correlated with cortical atrophy in motor cortex, implicating degraded knowledge of action features represented in motor cortex of patients with ALS. Performance on measures requiring object knowledge did not correlate with motor cortex atrophy. Several areas correlated with difficulty for both actions and objects, implicating these brain areas in components of semantic memory that are not dedicated to a specific category of knowledge.

CONCLUSION

Patients with amyotrophic lateral sclerosis are impaired on measures involving action knowledge, and this appears to be due to at least two sources of impairment: degradation of knowledge about action features represented in motor cortex and impairment on multicategory cognitive components contributing more generally to semantic memory.

TDP-43 in neurodegenerative disorders

BACKGROUND

The number of neurodegenerative diseases associated with pathological aggregates of transactivation response element (TAR)-DNA-binding protein 43 (TDP-43) has increased, leading to the new designation 'TDP-43 proteinopathy.' Biochemically, TDP-43 proteinopathies are characterized by decreased solubility, hyperphosphorylation, and cleavage of TDP-43 into 25- and 35-kDa fragments, and by altered cellular localization.

OBJECTIVE

This review summarizes research characterizing the distribution of TDP-43 pathology in human postmortem brain tissue and discusses possible therapeutic strategies based on genetic and in vitro studies.

METHODS

We reviewed recent studies of TDP-43 proteinopathy.

RESULTS/CONCLUSION

Given that several different mutations can lead to TDP-43 proteinopathies, including mutations in progranulin and valosin-containing protein, research is needed to decipher and potentially exploit the link between these mutations and TDP-43 pathology.

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.

TDP-43 protein in plasma may index TDP-43 brain pathology in Alzheimer's disease and frontotemporal lobar degeneration

Autopsy studies have shown that about 55% of patients with frontotemporal lobar degeneration (FTLD) and 25% of patients with Alzheimer’s disease (AD) harbour TDP-43 immunoreactive pathological changes in their brains. Using ELISA, we investigated whether we could detect the presence, or increased amounts, of TDP-43 in plasma of patients with FTLD and AD compared to normal control subjects. We detected elevated levels of TDP-43 protein in plasma of 46% patients with FTLD with clinical frontotemporal dementia (FTD) and 22% patients with AD, compared to 8% of control subjects. The proportions of patients with FTD and AD showing raised plasma TDP-43 levels correspond closely to those proportions known from autopsy studies to contain TDP-43 pathological changes in their brains. Raised TDP-43 plasma levels may thereby index TDP-43 pathology within the brain. Plasma TDP-43 levels may be a biomarker that can provide a laboratory test capable of identifying the presence of TDP-43 brain pathology in neurodegenerative disease during life. It may help to distinguish those cases of FTLD with ubiquitin/TDP-43 pathology in their brains from those with tauopathy. As a predictive test, plasma TDP-43 level may have great practical value in directing therapeutic strategies aimed at preventing or removing tau or TDP-43 pathological changes from the brain in FTLD and AD.

Concomitant TAR-DNA-binding protein 43 pathology is present in Alzheimer disease and corticobasal degeneration but not in other tauopathies

Pathologic TAR-DNA-binding protein 43 (TDP-43) is a disease protein in frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U) and amyotrophic lateral sclerosis. We studied the presence, frequency, and distribution of TDP-43 pathology by immunohistochemistry and biochemistry in a series of clinically well-characterized tauopathy patient brains, including 182 Alzheimer disease (AD), 39 corticobasal degeneration, 77 progressive supranuclear palsy, and 12 Pick disease cases and investigated the clinical impact of concomitant TDP-43 pathology in these cases. TAR-DNA-binding protein 43 pathology was found in 25.8% of AD cases. It was restricted to the dentate gyrus and entorhinal cortex in approximately 75% of cases; approximately 25% showed more widespread TDP-43 pathology in frontal and temporal cortices, resembling the FTLD-U subtype associated with progranulin mutations. TAR-DNA-binding protein 43 pathology in AD was associated with significantly longer disease duration, but there was no association with the clinical presentation (148 cases diagnosed as AD and 34 cases diagnosed as frontotemporal lobar degeneration). Progressive supranuclear palsy and Pick disease cases showed no TDP-43 inclusions and no biochemical alterations of TDP-43. There was, however, a unique, predominantly glial TDP-43 pathology with staining of astrocytic plaque-like structures and coiled bodies in 15.4% of corticobasal degeneration cases; this was associated with biochemical TDP-43 changes similar to those in FTLD-U. These findings provide further insight into the burden and clinical significance of TDP-43 pathology in disorders other than FTLD-U and amyotrophic lateral sclerosis.

Individual patient diagnosis of AD and FTD via high-dimensional pattern classification of MRI

The purpose of this study is to determine the diagnostic accuracy of MRI-based high-dimensional pattern classification in differentiating between patients with Alzheimer's disease (AD), Frontotemporal Dementia (FTD), and healthy controls, on an individual patient basis. MRI scans of 37 patients with AD and 37 age-matched cognitively normal elderly individuals, as well as 12 patients with FTD and 12 age-matched cognitively normal elderly individuals, were analyzed using voxel-based analysis and high-dimensional pattern classification. Diagnostic sensitivity and specificity of spatial patterns of regional brain atrophy found to be characteristic of AD and FTD were determined via cross-validation and via split-sample methods. Complex spatial patterns of relatively reduced brain volumes were identified, including temporal, orbitofrontal, parietal and cingulate regions, which were predominantly characteristic of either AD or FTD. These patterns provided 100% diagnostic accuracy, when used to separate AD or FTD from healthy controls. The ability to correctly distinguish AD from FTD averaged 84.3%. All estimates of diagnostic accuracy were determined via cross-validation. In conclusion, AD- and FTD-specific patterns of brain atrophy can be detected with high accuracy using high-dimensional pattern classification of MRI scans obtained in a typical clinical setting.

Lexical acquisition in progressive aphasia and frontotemporal dementia

We investigated the characteristics of language difficulty in frontotemporal dementia (FTD) by exposing these patients to a new verb in a naturalistic manner and then assessing acquisition of the grammatical, semantic, and thematic matrix information associated with the new word. We found that FTD patients have difficulty relative to healthy seniors in their acquisition of the new verb, but that progressive nonfluent aphasia (PNFA), semantic dementia (SD), and social/dysexecutive variant (SOC/EXEC) subgroups of FTD demonstrate relatively distinct impairment profiles. Specifically, PNFA patients showed relative difficulty assigning the new verb to its correct grammatical form class, reflecting compromised processing of the associated grammatical information. SD patients were impaired at associating the new word with its pictorial representation, suggesting impaired processing of the new verb's semantic attributes. SOC/EXEC patients showed their greatest difficulty judging violations of the new word's associated thematic roles, implying that limited executive resources underlie in part the difficulty in integrating grammatical and semantic information into a coherent thematic matrix. Similar impairment profiles were seen during a follow-up session one week after the initial evaluation. These deficits in lexical acquisition reflect the breakdown of a language-processing system that consists of highly interactive but partially dissociable grammatical, semantic, and resource-based components, leading to relatively distinct language-processing deficits in each subgroup of patients with FTD.

Neuropathologic features of frontotemporal lobar degeneration with ubiquitin-positive inclusions visualized with ubiquitin-binding protein p62 immunohistochemistry

Genetic, clinical, and neuropathologic heterogeneity have been observed in frontotemporal lobar degeneration with ubiquitin (Ubq)-positive inclusions (FTLD-U) and FTLD-U with motor neuron disease. Here, the distribution and morphologic features of neuronal and glial inclusions in the brains of 20 FTLD-U and 2 FTLD-U/motor neuron disease cases were assessed using immunohistochemistry for Ubq-binding protein p62. Eighteen cases displayed TAR DNA-binding protein 43-immunoreactive lesions and were classified as Types 3 (neuronal cytoplasmic inclusions and neurites; 72%), 2 (primarily neuronal cytoplasmic inclusions; 17%), or 1 (primarily neurites; 11%) FTLD-U. The distribution of p62-immunoreactivity varied considerably in each type. Of 4 unclassifiable cases, 2 displayed p62-immunoreactive lesions suggestive of FTLD-U with a mutation in the charged multivesicular body protein 2B gene; 1 suggested basophilic inclusion body disease, and 1 was of a type not previously described. By immunohistochemistry for Ubq-binding protein p62, the distribution of abnormalities was wider than expected; in approximately half of the cases, there were p62-positive but TAR DNA-binding protein 43-negative inclusions in the cerebellum, a region not previously considered to be affected. In other regions, TAR DNA-binding protein 43-, Ubq-, and Ubq-binding protein p62 labeling of inclusions was variable. Whether variations in inclusion morphologies, immunoreactivity, and topographic distribution are due to methodologic factors, different stages of inclusion and disease evolution, different disease entities or biologic modifications of the same disease are presently unclear.

CSF biomarkers in frontotemporal lobar degeneration with known pathology

OBJECTIVE

To evaluate the diagnostic value of CSF biomarkers in patients with known pathology due to frontotemporal lobar degeneration (FTLD).

BACKGROUND

It is important to distinguish FTLD from other neurodegenerative diseases like Alzheimer disease (AD), but this may be difficult clinically because of atypical presentations.

METHODS

Patients with FTLD (n = 30) and AD (n = 19) were identified at autopsy or on the basis of genetic testing at University of Pennsylvania and Erasmus University Medical Center. CSF was obtained during a diagnostic lumbar puncture and was analyzed using assays for total tau and amyloid-beta 1-42 (A beta(42)). Patients also were assessed with a brief neuropsychological battery.

RESULTS

CSF total tau level and the ratio of CSF total tau to A beta(42) (tau/A beta(42)) were significantly lower in FTLD than in AD. Receiver operating characteristic curve analyses confirmed that the CSF tau/A beta(42) ratio is sensitive and specific at discriminating between FTLD and AD, and is more successful at this than CSF total tau alone. Although some neuropsychological measures are significantly different in autopsy-proven FTLD and AD, combining these neuropsychological measures with CSF biomarkers did not improve the ability to distinguish FTLD from AD.

CONCLUSIONS

The ratio of CSF tau/A beta(42) is a sensitive and specific biomarker at discriminating frontotemporal lobar degeneration from Alzheimer disease in patients with known pathology.

A yeast TDP-43 proteinopathy model: Exploring the molecular determinants of TDP-43 aggregation and cellular toxicity

Protein misfolding is intimately associated with devastating human neurodegenerative diseases, including Alzheimer's, Huntington's, and Parkinson's. Although disparate in their pathophysiology, many of these disorders share a common theme, manifested in the accumulation of insoluble protein aggregates in the brain. Recently, the major disease protein found in the pathological inclusions of two of these diseases, amyotrophic lateral sclerosis (ALS) and frontal temporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U), was identified as the 43-kDa TAR-DNA-binding protein (TDP-43), providing a molecular link between them. TDP-43 is a ubiquitously expressed nuclear protein that undergoes a pathological conversion to an aggregated cytoplasmic localization in affected regions of the nervous system. Whether TDP-43 itself can convey toxicity and whether its abnormal aggregation is a cause or consequence of pathogenesis remain unknown. We report a yeast model to define mechanisms governing TDP-43 subcellular localization and aggregation. Remarkably, this simple model recapitulates several salient features of human TDP-43 proteinopathies, including conversion from nuclear localization to cytoplasmic aggregation. We establish a connection between this aggregation and toxicity. The pathological features of TDP-43 are distinct from those of yeast models of other protein-misfolding diseases, such as polyglutamine. This suggests that the yeast model reveals specific aspects of the underlying biology of the disease protein rather than general cellular stresses associated with accumulating misfolded proteins. This work provides a mechanistic framework for investigating the toxicity of TDP-43 aggregation relevant to human disease and establishes a manipulable, high-throughput model for discovering potential therapeutic strategies.

Longitudinal decline in autopsy-defined frontotemporal lobar degeneration

BACKGROUND

The natural history of patients with pathologically proven frontotemporal lobar degeneration (FTLD) is important from clinical and biologic perspectives, but is not well documented quantitatively.

METHODS

We examine longitudinal decline in cognitive functioning in an autopsy-proven cohort of patients with the clinical diagnosis of a FTLD spectrum disorder or FTLD pathology using a panel of neuropsychological measures. Patients are categorized according to findings at autopsy into tau-positive FTLD, tau-negative FTLD, and frontal variant-Alzheimer disease (fvAD) subgroups.

RESULTS

Patients decline significantly over time on all neuropsychological measures. Moreover, several measures differentiate between histopathologically distinct subgroups throughout the course of the disease process. This includes a significant double dissociation involving relative difficulty on a visual constructional measure in tau-positive patients compared to relatively impaired visual confrontation naming in tau-negative patients. Longitudinal measures of FAS naming fluency and animal naming fluency also distinguish tau-positive patients and tau-negative patients with FTLD from patients with fvAD. Other measures show significant decline but do not distinguish between histopathologic groups longitudinally.

CONCLUSION

Our findings suggest different longitudinal patterns of cognitive decline in pathologically defined subgroups of patients. Measures consistently distinguishing between patient subgroups can be used to bolster diagnostic accuracy throughout the course of these diseases, while measures demonstrating undifferentiated longitudinal decline may serve as useful endpoints in treatment trials.

Patient care and management of frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) is a neurodegenerative disease that affects frontal and temporal regions of the brain. Two proteins indicated in the pathology are tau and the recently discovered TDP-43. Major manifestations include progressive aphasia and a disorder of social comportment. The diagnosis of a patient includes a detailed cognitive exam, clinical testing, and neuroimaging techniques. The current goal of therapy for FTLD is symptomatic management with medications borrowed from other conditions. Nonpharmacologic management such as behavioral interventions and environmental engineering are also efficacious in optimizing quality of life.

Diagnostic accuracy of consensus diagnostic criteria for frontotemporal dementia in a memory clinic population

BACKGROUND/AIMS

The goal of the present study was to evaluate the diagnostic accuracy of the core diagnostic criteria for frontotemporal dementia (FTD) [Neary D, et al: Neurology 1998;51:1546-1554] within a memory clinic population.

METHODS

The 5 core diagnostic criteria for FTD were operationalised in an informant-based written questionnaire. For a diagnosis of FTD the total clinical picture was weighted with findings on additional investigations and possible exclusion criteria, with follow-up of at least 1 year.

RESULTS

The operationalised core criteria for FTD had a sensitivity of 79% (95% CI = 57-92) and a specificity of 90% (95% CI = 85-94).

CONCLUSION

The core diagnostic criteria for FTD applied in a caregiver questionnaire have good diagnostic accuracy among subjects without advanced dementia attending a memory clinic. This stresses the importance of the informant-based history in the differential diagnosis of dementia.

Oculomotor function in frontotemporal lobar degeneration, related disorders and Alzheimer's disease

Frontotemporal lobar degeneration (FTLD) often overlaps clinically with corticobasal syndrome (CBS) and progressive supranuclear palsy (PSP), both of which have prominent eye movement abnormalities. To investigate the ability of oculomotor performance to differentiate between FTLD, Alzheimer's disease, CBS and PSP, saccades and smooth pursuit were measured in three FTLD subtypes, including 24 individuals with frontotemporal dementia (FTD), 19 with semantic dementia (SD) and six with progressive non-fluent aphasia (PA), as compared to 28 individuals with Alzheimer's disease, 15 with CBS, 10 with PSP and 27 control subjects. Different combinations of oculomotor abnormalities were identified in all clinical syndromes except for SD, which had oculomotor performance that was indistinguishable from age-matched controls. Only PSP patients displayed abnormalities in saccade velocity, whereas abnormalities in saccade gain were observed in PSP > CBS > Alzheimer's disease subjects. All patient groups except those with SD were impaired on the anti-saccade task, however only the FTLD subjects and not Alzheimer's disease, CBS or PSP groups, were able to spontaneously self-correct anti-saccade errors as well as controls. Receiver operating characteristic statistics demonstrated that oculomotor findings were superior to neuropsychological tests in differentiating PSP from other disorders, and comparable to neuropsychological tests in differentiating the other patient groups. These data suggest that oculomotor assessment may aid in the diagnosis of FTLD and related disorders.

The spectrum of recurrent thoughts and behaviors in frontotemporal dementia

This article describes the spectrum of recurrent thoughts and behaviors that can result from frontotemporal dementia (FTD) and its variants. Although repetitive behaviors can result from a range of brain disorders, FTD is the most common neurologic cause of new-onset recurrent thoughts and behaviors in middle or late life. Patients with FTD can manifest typical or bizarre compulsions, hoarding, verbal and motor stereotypies and complex tics; self-injurious acts, perseverations; and fixed, obsessional thoughts. The frequency and variability of these repetitive behaviors suggest a common disturbance of orbitofrontal-basal ganglia circuits involved in response inhibition. The amelioration of these recurrent events with the administration of serotonin selective reuptake inhibitors further suggests a serotonergic deficit.

Clinical features and survival of 3R and 4R tauopathies presenting as behavioral variant frontotemporal dementia

We compared the clinical characteristics of 3 repeat (3R) and 4 repeat (4R) tau-positive cases (tauopathies) presenting as behavior variant frontotemporal dementia (bv-FTD). We identified and retrospectively reviewed demographics and clinical features of patients with pathologically confirmed tau-positive frontotemporal lobar degeneration in a blinded fashion. Those presenting as bv-FTD were divided according to their tau isoform, 3R versus 4R, and compared with age-matched and sex-matched control patients with 4R tauopathies but presenting clinical syndromes other than bv-FTD. Twenty-four cases with tau-positive bv-FTD and 18 4R tau-positive controls were included in the study. Patients with 4R tauopathies had significantly shorter disease duration than patients with 3R tauopathy (median, 6.5 y vs. 9.5 y; P<0.05), despite similar age of disease onset and regardless of whether bv-FTD was the presenting clinical syndrome. Among bv-FTD cases, those with 4R tauopathies were more likely to display behavioral underactivity than those with 3R tauopathy (P=0.03), although 3R and 4R tauopathy patients shared many similar clinical features. In summary, survival in 4R tauopathies seemed independent of the presenting clinical phenotype, and there may be subtle clinical differences between bv-FTD patients with 3R and 4R tauopathies.

Frontotemporal dementia and semantic dementia: anatomic variations on the same disease or distinctive entities?

Research into the non-Alzheimer dementias has exploded over the last 2 decades, and frontotemporal lobar degeneration has emerged as the most common cause of dementia in patients below the age of 65. In 1998, an international consortium of investigators focusing on this disease entity met and agreed upon the classification of 3 subtypes of frontotemporal lobar degeneration, using regional atrophy to distinguish them. These are: a frontally predominant form called frontotemporal dementia, a temporally predominant form called semantic dementia, and a left-frontally predominant syndrome, called progressive nonfluent aphasia. With the rise of genetic and neuropathologic findings, however, the usefulness of this subtype classification has been called into question. This paper discusses the major pertinent findings, and the implications of classifying the disease on the basis of atrophy versus genetic or molecular mechanisms.

Screening for frontotemporal dementias and Alzheimer's disease with the Philadelphia Brief Assessment of Cognition: a preliminary analysis

BACKGROUND

A neuropsychological screening instrument sensitive to neuropsychological deficits associated with Alzheimer's disease (AD) and patients with frontotemporal dementia (FTD) would be valuable for diagnostic evaluation.

METHODS

The Philadelphia Brief Assessment of Cognition (PBAC) assesses working memory/executive control, language, visuospatial operations, verbal/visual episodic memory, and behavior/social comportment and can be administered and scored in 15-20 min. Participants included 149 patients with AD and four groups of FTD patients - i.e., patients with a decline in social comportment, personality, and executive functioning (SOC/EXEC), semantic dementia (SemD), progressive nonfluent aphasia (PNFA), and corticobasal syndrome (CBS).

RESULTS

The total PBAC score correlated with the Mini-Mental State Examination. Between-group analysis of PBAC subscales and the results of logistic regression analyses produced substantial between-group differences, emphasizing the sensitivity of the test to differentiate dementia subtypes. AD patients were impaired on tests of episodic memory, SOC/EXEC patients were impaired on a measure of social comportment/behavioral disturbance, PNFA patients obtained low scores on tests of working memory/executive control, SemD patients obtained lower scores on language-mediated measures, and CBS patients were impaired on visuospatial/visual memory tests.

CONCLUSION

These data support the usefulness of the PBAC as a relatively brief screening test of overall dementia severity across a wide range of dementia patients.

Progranulin locus deletion in frontotemporal dementia

Ubiquitin-positive, tau-negative, frontotemporal dementia (FTD) is caused by null mutations in progranulin (PGRN; HUGO gene symbol GRN), suggesting a haploinsufficiency mechanism. Since whole gene deletions also lead to the loss of a functional allele, we performed systematic quantitative analyses of PGRN in a series of 103 Belgian FTD patients. We identified in one patient (1%) a genomic deletion that was absent in 267 control individuals. The deleted segment was between 54 and 69 kb in length and comprised PGRN and two centromeric neighboring genes RPIP8 (HUGO gene symbol RUNDC3A) and SLC25A39. The patient presented clinically with typical FTD without additional symptoms, consistent with haploinsufficiency of PGRN being the only gene contributing to the disease phenotype. This study demonstrates that reduced PGRN in absence of mutant protein is sufficient to cause neurodegeneration and that previously reported PGRN mutation frequencies are underestimated.

Variations in the progranulin gene affect global gene expression in frontotemporal lobar degeneration

Frontotemporal lobar degeneration is a fatal neurodegenerative disease that results in progressive decline in behavior, executive function and sometimes language. Disease mechanisms remain poorly understood. Recently, however, the DNA- and RNA-binding protein TDP-43 has been identified as the major protein present in the hallmark inclusion bodies of frontotemporal lobar degeneration with ubiquitinated inclusions (FTLD-U), suggesting a role for transcriptional dysregulation in FTLD-U pathophysiology. Using the Affymetrix U133A microarray platform, we profiled global gene expression in both histopathologically affected and unaffected areas of human FTLD-U brains. We then characterized differential gene expression with biological pathway analyses, cluster and principal component analyses, and subgroup analyses based on brain region and progranulin (GRN) gene status. Comparing 17 FTLD-U brains to 11 controls, we identified 414 upregulated and 210 downregulated genes in frontal cortex (P-value < 0.001). Moreover, cluster and principal component analyses revealed that samples with mutations or possibly pathogenic variations in the GRN gene (GRN+, 7/17) had an expression signature that was distinct from both normal controls and FTLD-U samples lacking GRN gene variations (GRN-, 10/17). Within the subgroup of GRN+ FTLD-U, we found >1300 dysregulated genes in frontal cortex (P-value < 0.001), many participating in pathways uniquely dysregulated in the GRN+ cases. Our findings demonstrate a distinct molecular phenotype for GRN+ FTLD-U, not readily apparent on clinical or histopathological examination, suggesting distinct pathophysiological mechanisms for GRN+ and GRN- subtypes of FTLD-U. In addition, these data from a large number of human brains provide a valuable resource for future testing of disease hypotheses.

Frequency and clinical characteristics of progranulin mutation carriers in the Manchester frontotemporal lobar degeneration cohort: comparison with patients with MAPT and no known mutations

Two hundred and twenty-three consecutive patients fulfilling clinical diagnostic criteria for frontotemporal lobar degeneration (FTLD), and 259 patients with motor neuron disease (MND), for whom genomic DNA was available, were investigated for the presence of mutations in tau (MAPT) and progranulin (PGRN) genes. All FTLD patients had undergone longitudinal neuropsychological and clinical assessment, and in 44 cases, the diagnosis had been pathologically confirmed at post-mortem. Six different PGRN mutations were found in 13 (6%) patients with FTLD. Four apparently unrelated patients shared exon Q415X 10 stop codon mutation. However, genotyping data revealed all four patients shared common alleles of 15 SNPs from rs708386 to rs5848, defining a 45.8-kb haplotype containing the whole PGRN gene, suggesting they are related. Three patients shared exon 11 R493X stop codon mutation. Four patients shared exon 10 V452WfsX38 frameshift mutation. Two of these patients were siblings, though not apparently related to the other patients who in turn appeared unrelated. One patient had exon 1 C31LfsX34 frameshift mutation, one had exon 4 Q130SfsX130 frameshift mutation and one had exon 10 Q468X stop codon mutation. In addition, two non-synonymous changes were detected: G168S change in exon 5 was found in a single patient, with no family history, who showed a mixed FTLD/MND picture and A324T change in exon 9 was found in two cases; one case of frontotemporal dementia (FTD) with a sister with FTD+MND and the other in a case of progressive non-fluent aphasia (PNFA) without any apparent family history. MAPT mutations were found in 17 (8%) patients. One patient bore exon 10 + 13 splice mutation, and 16 patients bore exon 10 + 16 splice mutation. When PGRN and MAPT mutation carriers were excluded, there were no significant differences in either the allele or genotype frequencies, or haplotype frequencies, between the FTLD cohort as a whole, or for any clinical diagnostic FTLD subgroup, and 286 controls or between MND cases and controls. However, possession of the A allele of SNP rs9897526, in intron 4 of PGRN, delayed mean age at onset by approximately 4 years. Patients with PGRN and MAPT mutations did not differ significantly from other FTLD cases in terms of gender distribution or total duration of illness. However, a family history of dementia in a first-degree relative was invariably present in MAPT cases, but not always so in PGRN cases. Onset of illness was earlier in MAPT cases compared to PGRN and other FTLD cases. PNFA, combined with limb apraxia was significantly more common in PGRN mutation cases than other FTLD cases. By contrast, the behavioural disorder of FTD combined with semantic impairment was a strong predictor of MAPT mutations. These findings complement recent clinico-pathological findings in suggesting identifiable associations between clinical phenotype and genotype in FTLD.

Pathological TDP-43 in parkinsonism-dementia complex and amyotrophic lateral sclerosis of Guam

Pathological TDP-43 is the major disease protein in frontotemporal lobar degeneration characterized by ubiquitin inclusions (FTLD-U) with/without motor neuron disease (MND) and in amyotrophic lateral sclerosis (ALS). As Guamanian parkinsonism-dementia complex (PDC) or Guamanian ALS (G-PDC or G-ALS) of the Chamorro population may present clinically similar to FTLD-U and ALS, TDP-43 pathology may be present in the G-PDC and G-ALS. Thus, we examined cortical or spinal cord samples from 54 Guamanian subjects for evidence of TDP-43 pathology. In addition to cortical neurofibrillary and glial tau pathology, G-PDC was associated with cortical TDP-43 positive dystrophic neurites and neuronal and glial inclusions in gray and/or white matter. Biochemical analyses showed the presence of FTLD-U-like insoluble TDP-43 in G-PDC, but not in Guam controls (G-C). Spinal cord pathology of G-PDC or G-ALS was characterized by tau positive tangles as well as TDP-43 positive inclusions in lower motor neurons and glial cells. G-C had variable tau and negligible TDP-43 pathology. These results indicate that G-PDC and G-ALS are associated with pathological TDP-43 similar to FTLD-U with/without MND as well as ALS, and that neocortical or hippocampal TDP-43 pathology distinguishes controls from disease subjects better than tau pathology. Finally, we conclude that the spectrum of TDP-43 proteinopathies should be expanded to include neurodegenerative cognitive and motor diseases, affecting the Chamorro population of Guam.

Word-finding difficulty: a clinical analysis of the progressive aphasias

The patient with word-finding difficulty presents a common and challenging clinical problem. The complaint of 'word-finding difficulty' covers a wide range of clinical phenomena and may signify any of a number of distinct pathophysiological processes. Although it occurs in a variety of clinical contexts, word-finding difficulty generally presents a diagnostic conundrum when it occurs as a leading or apparently isolated symptom, most often as the harbinger of degenerative disease: the progressive aphasias. Recent advances in the neurobiology of the focal, language-based dementias have transformed our understanding of these processes and the ways in which they breakdown in different diseases, but translation of this knowledge to the bedside is far from straightforward. Speech and language disturbances in the dementias present unique diagnostic and conceptual problems that are not fully captured by classical models derived from the study of vascular and other acute focal brain lesions. This has led to a reformulation of our understanding of how language is organized in the brain. In this review we seek to provide the clinical neurologist with a practical and theoretical bridge between the patient presenting with word-finding difficulty in the clinic and the evidence of the brain sciences. We delineate key illustrative speech and language syndromes in the degenerative dementias, compare these syndromes with the syndromes of acute brain damage, and indicate how the clinical syndromes relate to emerging neurolinguistic, neuroanatomical and neurobiological insights. We propose a conceptual framework for the analysis of word-finding difficulty, in order both better to define the patient's complaint and its differential diagnosis for the clinician and to identify unresolved issues as a stimulus to future work.

Severe subcortical TDP-43 pathology in sporadic frontotemporal lobar degeneration with motor neuron disease

Recently, TDP-43, a 43 kDa nuclear TAR DNA-binding protein, was identified as the major disease protein in frontotemporal lobar degeneration with ubiquitinated inclusions (FTLD-U), FTLD-U with motor neuron disease (FTLD-MND), and amyotrophic lateral sclerosis. To date, TDP-43 pathology in sporadic FTLD-MND has been reported only in select central nervous system areas. However, this distribution of lesions is insufficient to explain all clinical signs of FTLD-MND and the extent of TDP-43 pathology, throughout the brain, remains unknown. Therefore, as a pilot study, we performed an immunohistochemical whole brain scan of two cases diagnosed clinically as FTLD-MND and two control subjects. We found evidence of both neuronal and glial TDP-43 pathology in multiple brain areas including the nigro-striatal system, neo- and allocortical brain areas, with varying frequency, morphology, and degree, and nowhere in control tissue. The finding of a distinct cytopathological profile consisting of a cell nucleus devoid of endogenous TDP-43 staining coupled with diffuse/granular cytoplasmic staining ("pre-inclusion") was prominent in a couple of brain areas. These pre-inclusions were not or only weakly ubiquitin-immunoreactive. While the findings of severe involvement of extracortical or extrapyramidal areas are strongly suggestive for FTLD-MND being a TDP-43 multisystem proteinopathy rather than a disease predominantly affecting the cortex and spinal cord, more detailed clinicopathological studies of larger cohorts are needed to fully elucidate the distribution and severity of pathological TDP-43 in this disease.

TDP-43 proteinopathies: neurodegenerative protein misfolding diseases without amyloidosis

In this review, we summarize recent advances in understanding frontotemporal lobar degeneration (FTLD), amyotrophic lateral sclerosis (ALS) and related neurodegenerative disorders that are collectively known as TDP-43 proteinopathies, since transactive response DNA-binding protein 43 (TDP-43) was recently shown to be the major component of the ubiquitinated inclusions that are their pathological hallmarks. TDP-43 proteinopathies are distinct from most other neurodegenerative disorders because TDP-43 inclusions are not amyloid deposits. Besides TDP-43-positive inclusions, both sporadic and familial forms of FTLD and ALS have the pathologic TDP-43 signature of abnormal hyperphosphorylation, ubiquitination and C-terminal fragments in affected brain and spinal cord, suggesting that they share a common mechanism of pathogenesis. Thus, these findings support the concept that FTLD and ALS represent a clinicopathologic spectrum of one disease, that is, TDP-43 proteinopathy.

PENN biomarker core of the Alzheimer's disease Neuroimaging Initiative

There is a pressing need to develop effective prevention and disease-modifying treatments for Alzheimer's disease (AD), a dreaded affliction whose incidence increases almost logarithmically with age starting at about 65 years. A key need in the field of AD research is the validation of imaging and biochemical biomarkers. Biomarker tests that are shown to reliably predict the disease before it is clinically expressed would permit testing of new therapeutics at the earliest time point possible in order to give the best chance for delaying the onset of dementia in these patients. In this review the current state of AD biochemical biomarker research is discussed. A new set of guidelines for the diagnosis of AD in the research setting places emphasis on the inclusion of selected imaging and biochemical biomarkers, in addition to neuropsychological behavioral testing. Importantly, the revised guidelines were developed to identify patients at the earliest stages prior to full-blown dementia as well as patients with the full spectrum of the disease. The Alzheimer's Disease Neuroimaging Initiative is a multicenter consortium study that includes as one of its primary goals the development of standardized neuroimaging and biochemical biomarker methods for AD clinical trials, as well as using these to measure changes over time in mildly cognitively impaired patients who convert to AD as compared to the natural variability of these in control subjects and their further change over time in AD patients. Validation of the biomarker results by correlation analyses with neuropsychological and neurobehavioral test data is one of the primary outcomes of this study. This validation data will hopefully provide biomarker test performance needed for effective measurement of the efficacy of new treatment and prevention therapeutic agents.