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Background:

We sought to describe the antemortem clinical and neuroimaging features among patients with frontotemporal lobar degeneration with TDP-43 immunoreactive inclusions (FTLD-TDP).

Methods:

Subjects were recruited from a consecutive series of patients with a primary neuropathologic diagnosis of FTLD-TDP and antemortem MRI. Twenty-eight patients met entry criteria: 9 with type 1, 5 with type 2, and 10 with type 3 FTLD-TDP. Four patients had too sparse FTLD-TDP pathology to be subtyped. Clinical, neuropsychological, and neuroimaging features of these cases were reviewed. Voxel-based morphometry was used to assess regional gray matter atrophy in relation to a group of 50 cognitively normal control subjects.

Results:

Clinical diagnosis varied between the groups: semantic dementia was only associated with type 1 pathology, whereas progressive nonfluent aphasia and corticobasal syndrome were only associated with type 3. Behavioral variant frontotemporal dementia and frontotemporal dementia with motor neuron disease were seen in type 2 or type 3 pathology. The neuroimaging analysis revealed distinct patterns of atrophy between the pathologic subtypes: type 1 was associated with asymmetric anterior temporal lobe atrophy (either left- or right-predominant) with involvement also of the orbitofrontal lobes and insulae; type 2 with relatively symmetric atrophy of the medial temporal, medial prefrontal, and orbitofrontal-insular cortices; and type 3 with asymmetric atrophy (either left- or right-predominant) involving more dorsal areas including frontal, temporal, and inferior parietal cortices as well as striatum and thalamus. No significant atrophy was seen among patients with too sparse pathology to be subtyped.

Conclusions:

FTLD-TDP subtypes have distinct clinical and neuroimaging features, highlighting the relevance of FTLD-TDP subtyping to clinicopathologic correlation.

GLOSSARY

= behavioral variant frontotemporal dementia;

= corticobasal syndrome;

= Clinical Dementia Rating;

= false discovery rate;

= frontotemporal dementia;

= frontotemporal lobar degeneration;

= frontotemporal lobar degeneration with TDP-43 immunoreactive inclusions;

= fused in sarcoma;

= Mini-Mental State Examination;

= motor neuron disease;

= progressive nonfluent aphasia;

= TAR DNA-binding protein of 43 kDa;

= University of California, San Francisco;

= voxel-based morphometry.

Objective:

To determine whether TDP-43 type is associated with distinct patterns of brain atrophy on MRI in subjects with pathologically confirmed frontotemporal lobar degeneration (FTLD).

Methods:

In this case-control study, we identified all subjects with a pathologic diagnosis of FTLD with TDP-43 immunoreactive inclusions (FTLD-TDP) and at least one volumetric head MRI scan (n = 42). In each case we applied published criteria for subclassification of FTLD-TDP into FTLD-TDP types 1-3. Voxel-based morphometry was used to compare subjects with each of the different FTLD-TDP types to age- and gender-matched normal controls (n = 30). We also assessed different pathologic and genetic variants within, and across, the different types.

Results:

Twenty-two subjects were classified as FTLD-TDP type 1, 9 as type 2, and 11 as type 3. We identified different patterns of atrophy across the types with type 1 showing frontotemporal and parietal atrophy, type 2 predominantly anterior temporal lobe atrophy, and type 3 predominantly posterior frontal atrophy. Within the FTLD-TDP type 1 group, those with a progranulin mutation had significantly more lateral temporal lobe atrophy than those without. All type 2 subjects were diagnosed with semantic dementia. Subjects with a pathologic diagnosis of FTLD with motor neuron degeneration had a similar pattern of atrophy, regardless of whether they were type 1 or type 3.

Conclusions:

Although there are different patterns of atrophy across the different FTLD-TDP types, it appears that genetic and pathologic factors may also affect the patterns of atrophy.

GLOSSARY

= Alzheimer disease;

= Alzheimer's Disease Research Center;

= behavioral variant frontotemporal dementia;

= corticobasal syndrome;

= Clinical Dementia Rating scale sum of boxes;

= frontotemporal lobar degeneration;

= frontotemporal lobar degeneration with motor neuron degeneration;

= frontotemporal lobar degeneration with TDP-43 immunoreactive inclusions;

= Mini-Mental State Examination;

= neuronal cytoplasmic inclusion;

= progressive nonfluent aphasia;

= semantic dementia;

= Short Test of Mental Status;

= voxel-based morphometry.

Objective:

To identify antemortem CSF diagnostic biomarkers that can potentially distinguish between the 2 main causes of frontotemporal lobar degeneration (FTLD), i.e., FTLD with TDP-43 pathology (FTLD-TDP) and FTLD with tau pathology (FTLD-tau).

Methods:

CSF samples were collected antemortem from 23 patients with FTLD with known pathology to form a autopsy cohort as part of a comparative biomarker study that additionally included 33 living cognitively normal subjects and 66 patients with autopsy-confirmed Alzheimer disease (AD). CSF samples were also collected from 80 living patients clinically diagnosed with frontotemporal dementia (FTD). Levels of 151 novel analytes were measured via a targeted multiplex panel enriched in neuropeptides, cytokines, and growth factors, along with levels of CSF biomarkers for AD.

Results:

CSF levels of multiple analytes differed between FTLD-TDP and FTLD-tau, including Fas, neuropeptides (agouti-related peptide and adrenocorticotropic hormone), and chemokines (IL-23, IL-17). Classification by random forest analysis achieved high sensitivity for FTLD-TDP (86%) with modest specificity (78%) in the autopsy cohort. When the classification algorithm was applied to a living FTD cohort, semantic dementia was the phenotype with the highest predicted proportion of FTLD-TDP. When living patients with behavioral variant FTD were examined in detail, those predicted to have FTLD-TDP demonstrated neuropsychological differences vs those predicted to have FTLD-tau in a pattern consistent with previously reported trends in autopsy-confirmed cases.

Conclusions:

Clinical cases with FTLD-TDP and FTLD-tau pathology can be potentially identified antemortem by assaying levels of specific analytes that are well-known and readily measurable in CSF.

GLOSSARY

= Alzheimer disease;

= Aguti-related protein;

= angiopoietin-2;

= adrenocorticotropic hormone;

= amyotrophic lateral sclerosis;

= apolipoprotein B;

= behavioral variant FTD;

= corticobasal syndrome;

= frontotemporal dementia;

= frontotemporal lobar degeneration;

= frontotemporal lobar degeneration with tau pathology;

= frontotemporal lobar degeneration with TDP-43 pathology;

= interleukin;

= macrophage-derived chemokine;

= progressive nonfluent aphasia;

= primary progressive aphasia;

= progressive supranuclear palsy;

= S100 calcium binding protein b;

= semantic dementia;

= tumor necrosis factor-related apoptosis-inducing ligand receptor 3.

SUMMARY

Neurodegenerative disorders are pathologically characterized by the deposition of abnormal proteins in the brain. It is likely that future treatment trials will target the underlying protein biochemistry and it is therefore increasingly important to be able to distinguish between different pathologies during life. The aim of this study was to determine whether rates of brain atrophy differ in neurodegenerative dementias that vary by pathological diagnoses and characteristic protein biochemistry. Fifty-six autopsied subjects were identified with a clinical diagnosis of dementia and two serial head MRI. Subjects were subdivided based on pathological diagnoses into Alzheimer's disease (AD), dementia with Lewy bodies (DLB), mixed AD/DLB, frontotemporal lobar degeneration with ubiquitin-only-immunoreactive changes (FTLD-U), corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP). Twenty-five controls were matched by age, gender, and scan interval, to the study cohort. The boundary-shift integral was used to calculate change over time in whole brain (BBSI) and ventricular volume (VBSI). All BSI results were annualized by adjusting for scan interval. The rates of whole brain atrophy and ventricular expansion were significantly increased compared to controls in the AD, mixed AD/DLB, FTLD-U, CBD and PSP groups. However, atrophy rates in the DLB group were not significantly different from control rates of atrophy. The largest rates of atrophy were observed in the CBD group which had a BBSI of 2.3% and VBSI of 16.2%. The CBD group had significantly greater rates of BBSI and VBSI than the DLB, mixed AD/DLB, AD and PSP groups, with a similar trend observed when compared to the FTLD-U group. The FTLD-U group showed the next largest rates with a BBSI of 1.7% and VBSI of 9.6% which were both significantly greater than the DLB group. There was no significant difference in the rates of atrophy between the AD, mixed AD/DLB and PSP groups, which all showed similar rates of atrophy; BBSI of 1.1, 1.3 and 1.0% and VBSI of 8.3, 7.2 and 10.9% respectively. Rates of atrophy therefore differ according to the pathological diagnoses and underlying protein biochemistry. While rates are unlikely to be useful in differentiating AD from cases with mixed AD/DLB pathology, they demonstrate important pathophysiological differences between DLB and those with mixed AD/DLB and AD pathology, and between those with CBD and PSP pathology.

Frontotemporal lobar degeneration (FTLD) is a clinically, genetically and pathologically heterogeneous disorder. Within FTLD with ubiquitin-positive inclusions (FTLD-U), a new pathological subtype named FTLD-FUS was recently found with fused in sarcoma (FUS) positive, TDP-43-negative inclusions, and striking atrophy of the caudate nucleus. The aim of this study was to determine the frequency of FTLD-FUS in our pathological FTLD series, and to describe the clinical, neuroimaging and neuropathological features of FTLD-FUS, especially caudate atrophy. Demographic and clinical data collected prospectively from 387 patients with frontotemporal dementia (FTD) yielded 74 brain specimens. Immunostaining was carried out using a panel of antibodies, including AT-8, ubiquitin, p62, FUS, and TDP-43. Cortical and caudate atrophy on MRI (n = 136) was rated as normal, mild-moderate or severe. Of the 37 FTLD-U cases, 33 were reclassified as FTLD-TDP and four (0.11, 95%: 0.00–0.21) as FTLD-FUS, with ubiquitin and FUS-positive, p62 and TDP-43-negative neuronal intranuclear inclusions (NII). All four FTLD-FUS cases had a negative family history, behavioural variant FTD (bvFTD), and three had an age at onset ≤40 years. MRI revealed mild-moderate or severe caudate atrophy in all, with a mean duration from onset till MRI of 63 months (range 16–119 months). In our total clinical FTD cohort, we found 11 patients (0.03; 95% CI: 0.01–0.05) with bvFTD, negative family history, and age at onset ≤40 years. Caudate atrophy was present in 10 out of 136 MRIs, and included all four FUS-cases. The newly identified FTLD-FUS has a frequency of 11% in FTLD-U, and an estimated frequency of three percent in our clinical FTD cohort. The existence of this pathological subtype can be predicted with reasonable certainty by age at onset ≤40 years, negative family history, bvFTD and caudate atrophy on MRI.

Background and Purpose

Frontotemporal lobar degeneration (FTLD) can be subdivided into those in which the abnormal protein is tau (FTLD-TAU), the TAR DNA binding protein 43 (FTLD-TDP) and the fused in sarcoma protein (FTLD-FUS). We have observed severe caudate atrophy at autopsy in FTLD-FUS, and hence we aimed to determine whether caudate atrophy on MRI is a feature that can distinguish FTLD-FUS from FTLD-TDP and FTLD-TAU.

Methods

From a cohort of 207 cases of FTLD we identified all cases of FTLD-FUS that had a volumetric antemortem head MRI (n=3). Caudate and frontal lobe volumes were measured in all three cases using atlas based parcellation and SPM5, and were compared to 10 randomly selected cases of FTLD-TDP and 10 randomly selected cases of FTLD-TAU. Total grey matter volumes were also calculated for all cases.

Results

The FTLD-FUS cases had significantly smaller caudate volumes (p=0.02) yet similar frontal lobe grey matter volumes (p=0.12) compared to FTLD-TDP and FTLD-TAU. Caudate volumes when corrected for total grey matter volume (p=0.01) or frontal lobe grey matter volume (p=0.01) were significantly smaller in FTLD-FUS than FTLD-TDP and FTLD-TAU, and showed no overlap with the other two groups.

Conclusions

Caudate atrophy on MRI appears to be significantly greater in FTLD-FUS compared with FTLD-TDP and FTLD-TAU suggesting that severe caudate atrophy may be a useful clinical feature to predict FTLD-FUS pathology.

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.

Using post-embedding immunogold electron microscopy, TAR DNA-binding protein of 43 kDa (TDP-43) was localized to neuronal cytoplasmic (NCI) and intranuclear (NII) inclusions, as well as unmyelinated neurites, in frontotemporal lobar degeneration with ubiquitinated inclusions (FTLD-U), amyotrophic lateral sclerosis (ALS), Alzheimer’s (AD), Pick’s disease (PiD) and Lewy body disease (LBD). The TDP-43 immunoreactive structures were morphologically heterogeneous. The most common was characterized by bundles of 10–20 nm diameter straight filaments with electron dense granular material within NCI, NII and neurites. This type of pathology was found in FTLD-U, ALS and some cases of AD. Less often inclusions in neuritic processes of FTLD-U and some cases of AD contained 10–17 nm diameter straight filaments without granular material. A final type of TDP-43 immunoreactivity was labeling of filaments and granular material associated tau filaments in neurofibrillary tangles of AD and Pick bodies of PiD or α-synuclein filaments in Lewy bodies of LBD. The results suggest that TDP-43 is the primary component of the granulofilamentous inclusions in FTLD-U and ALS. Similar inclusions sometimes accompany filamentous aggregates composed of other abnormal proteins in AD, PiD and LBD.

The aim of this study was to improve the neuropathologic recognition and provide criteria for the pathological diagnosis in the neurodegenerative diseases grouped as frontotemporal lobar degeneration (FTLD); revised criteria are proposed. Recent advances in molecular genetics, biochemistry, and neuropathology of FTLD prompted the Midwest Consortium for Frontotemporal Lobar Degeneration and experts at other centers to review and revise the existing neuropathologic diagnostic criteria for FTLD. The proposed criteria for FTLD are based on existing criteria, which include the tauopathies [FTLD with Pick bodies, corticobasal degeneration, progressive supranuclear palsy, sporadic multiple system tauopathy with dementia, argyrophilic grain disease, neurofibrillary tangle dementia, and FTD with microtubule-associated tau (MAPT) gene mutation, also called FTD with parkinsonism linked to chromosome 17 (FTDP-17)]. The proposed criteria take into account new disease entities and include the novel molecular pathology, TDP-43 proteinopathy, now recognized to be the most frequent histological finding in FTLD. TDP-43 is a major component of the pathologic inclusions of most sporadic and familial cases of FTLD with ubiquitin-positive, tau-negative inclusions (FTLD-U) with or without motor neuron disease (MND). Molecular genetic studies of familial cases of FTLD-U have shown that mutations in the progranulin (PGRN) gene are a major genetic cause of FTLD-U. Mutations in valosin-containing protein (VCP) gene are present in rare familial forms of FTD, and some families with FTD and/or MND have been linked to chromosome 9p, and both are types of FTLD-U. Thus, familial TDP-43 proteinopathy is associated with defects in multiple genes, and molecular genetics is required in these cases to correctly identify the causative gene defect. In addition to genetic heterogeneity amongst the TDP-43 proteinopathies, there is also neuropathologic heterogeneity and there is a close relationship between genotype and FTLD-U sub-type. In addition to these recent significant advances in the neuropathology of FTLD-U, novel FTLD entities have been further characterized, including neuronal intermediate filament inclusion disease. The proposed criteria incorporate up-to-date neuropathology of FTLD in the light of recent immunohistochemical, biochemical, and genetic advances. These criteria will be of value to the practicing neuropathologist and provide a foundation for clinical, clinico-pathologic, mechanistic studies and in vivo models of pathogenesis of FTLD.

Background

The pathology causing progressive aphasia is typically a variant of frontotemporal lobar degeneration, especially with ubiquitin-positive-inclusions (FTLD-U). Less commonly the underlying pathology is Alzheimer disease (AD).

Objective

To compare clinicopathological and MRI features of subjects with progressive aphasia and AD pathology, to subjects with aphasia and FTLD-U pathology, and subjects with typical AD.

Methods

We identified 5 subjects with aphasia and AD pathology and 5 with aphasia and FTLD-U pathology with an MRI from a total of 216 aphasia subjects. Ten subjects with typical AD clinical features and AD pathology were also identified. All subjects with AD pathology underwent pathological re-analysis with TDP-43 immunohistochemistry. Voxel-based morphometry (VBM) was used to assess patterns of grey matter atrophy in the aphasia cases with AD pathology, aphasia cases with FTLD-U, and typical AD cases with AD pathology, compared to a normal control group.

Results

All aphasic subjects had fluent speech output. However, those with AD pathology had better processing speed than those with FTLD-U pathology. Immunohistochemistry with TDP-43 antibodies was negative. VBM revealed grey matter atrophy predominantly in the temporoparietal cortices with notable sparing of the hippocampus in the aphasia with AD subjects. In comparison, the aphasic subjects with FTLD-U showed sparing of the parietal lobe. Typical AD subjects showed temporoparietal and hippocampal atrophy.

Conclusions

A temporoparietal pattern of atrophy on MRI in patients with progressive fluent aphasia and relatively preserved processing speed is suggestive of underlying AD pathology rather than FTLD-U.

Neuronal and glial changes associated with tau, TAR DNA binding protein of ~43 kD (TDP-43), and fused in sarcoma (FUS) together constitute the pathologic spectrum of frontotemporal lobar degeneration (FTLD). Most patients with FTLD present with prominent behavior or language changes, sometimes accompanied by extrapyramidal symptoms or motor neuron disease. Identification of FTLD patients with mutations in genes for tau, TDP-43, and FUS lends strong support for their pathogenic roles in FTLD, and elucidation of their dysfunction will pave the way for development of substrate specific therapy. However, there remains no reliable biomarker for early detection of FTLD or prediction of underlying FTLD pathologic change. Clinical syndromes usually reflects the earliest affected brain regions where atrophy can be visualized on structural MRI, but neither clinical nor structural imaging-based biomarkers has been accurately correlated with underlying pathology on the individual patient level. Biochemical markers in the cerebrospinal fluid (CSF) have also been investigated in FTLD and related disorders, including amyotrophic lateral sclerosis (ALS) and progressive supranuclear palsy (PSP). However, their accuracy and pathologic significance need to be confirmed in future multi-center studies. Here we review the progress made in FTLD biomarkers, including clinical phenotype/feature characterization, neuropsychological analysis, CSF and plasma analytes, and patterns of brain atrophy and network dysfunction detectable on brain imaging. Given the pathologic overlap of FTLD with ALS and PSP, collaboration with specialists in those fields will be essential in the translation of promising FTLD biomarkers into clinical practice.

Background:

Corticobasal syndrome (CBS) can be associated with different underlying pathologies that are difficult to predict based on clinical presentation. The aim of this study was to determine whether patterns of atrophy on imaging could be useful to help predict underlying pathology in CBS.

Methods:

This was a case-control study of 24 patients with CBS who had undergone MRI during life and came to autopsy. Pathologic diagnoses included frontotemporal lobar degeneration (FTLD) with TDP-43 immunoreactivity in 5 (CBS-TDP), Alzheimer disease (AD) in 6 (CBS-AD), corticobasal degeneration in 7 (CBS-CBD), and progressive supranuclear palsy in 6 (CBS-PSP). Voxel-based morphometry and atlas-based parcellation were used to assess atrophy across the CBS groups and compared to 24 age- and gender-matched controls.

Results:

All CBS pathologic groups showed gray matter loss in premotor cortices, supplemental motor area, and insula on imaging. However, CBS-TDP and CBS-AD showed more widespread patterns of loss, with frontotemporal loss observed in CBS-TDP and temporoparietal loss observed in CBS-AD. CBS-TDP showed significantly greater loss in prefrontal cortex than the other groups, whereas CBS-AD showed significantly greater loss in parietal lobe than the other groups. The focus of loss was similar in CBS-CBD and CBS-PSP, although more severe in CBS-CBD.

Conclusions:

Imaging patterns of atrophy in CBS vary according to pathologic diagnosis. Widespread atrophy points toward a pathologic diagnosis of FTLD-TDP or AD, with frontotemporal loss suggesting FTLD-TDP and temporoparietal loss suggesting AD. On the contrary, more focal atrophy predominantly involving the premotor and supplemental motor area suggests CBD or PSP pathology.

GLOSSARY

= automated anatomic labeling;

= Alzheimer disease;

= corticobasal degeneration;

= corticobasal syndrome;

= Clinical Dementia Rating sum of boxes;

= false discovery rate;

= frontotemporal lobar degeneration;

= Mini-Mental State Examination;

= progressive supranuclear palsy;

= region of interest;

= supplemental motor area;

= TDP-43 immunoreactivity;

= total intracranial volume;

= voxel-based morphometry.

Background

Hippocampal atrophy on magnetic resonance imaging (MRI) is an early characteristic of Alzheimer's disease. However, hippocampal atrophy may also occur in other dementias, such as frontotemporal lobar degeneration (FTLD).

Objective

To investigate hippocampal atrophy on MRI in FTLD and its three clinical subtypes, in comparison with Alzheimer's disease, using volumetry and a visual rating scale.

Methods

42 patients with FTLD (17 frontotemporal dementia, 13 semantic dementia, and 12 progressive non‐fluent aphasia), 103 patients with Alzheimer's disease, and 73 controls were included. Hippocampal volumetry and the easily applicable medial temporal lobe atrophy (MTA) rating scale were applied to assess hippocampal atrophy.

Results

Multivariate analysis of variance for repeated measures showed an effect of diagnostic group on hippocampal volume. There was a significant diagnosis by side (left v right) interaction. Both FTLD and Alzheimer's disease showed hippocampal atrophy compared with controls. Results of the visual MTA rating scale confirmed these findings. Within the FTLD subtypes there were marked differences in hippocampal atrophy. Frontotemporal dementia and semantic dementia showed bilateral hippocampal atrophy, and in semantic dementia the left hippocampus was smaller than in Alzheimer's disease. No significant hippocampal atrophy was detected in non‐fluent progressive aphasia.

Conclusions

Hippocampal atrophy is not only a characteristic of Alzheimer's disease but also occurs in FTLD. The three clinical subtypes of FTLD show different patterns of hippocampal atrophy.

Transactive response DNA-binding protein of 43 kDa (TDP-43), an RNA and DNA binding protein involved in transcriptional repression, RNA splicing and RNA metabolism during the stress response, is the major component of neuronal inclusions in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with ubiquitin inclusions, now referred to as FTLD-TDP. While initially thought to be relatively specific to ALS and FTLD-TDP, TDP-43 pathology has now been detected in a number of other neurodegenerative diseases, many associated with tau pathology, including Guam Parkinson dementia complex and Alzheimer's disease (AD). TDP-43 pathology is detected in 25% to 50% of AD cases, especially those with more severe clinical phenotype and greater Alzheimer type pathology, as well as AD cases with hippocampal sclerosis (HS). HS is characterized by selective neuronal loss affecting CA1 sector of the hippocampus, and most cases of HS, with or without AD, have TDP-43 pathology. Whether TDP-43 pathology is merely an incidental finding in AD or actually contributing to the more severe clinical phenotype remains unresolved. Presence of TDP-43 in normal elderly, who are at increased risk for AD, would strengthen the argument that it is not merely a secondary or incidental finding in end stage AD. Limited studies suggest that TDP-43 pathology is infrequent in neurologically normal elderly (3% or less). We provide an overview of what is known about TDP-43 in AD, normal aging and in other disorders and suggest that TDP-43 proteinopathies be considered in two classes - primary and secondary.

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 with FTLD-U (n=68), dementia lacking distinctive histopathology (n=4), other neurodegenerative diseases (n=23), and controls (n=12). A marked enhancement of TDP-43-positive dystrophic neurites (DN) was obtained by using a sensitive immunohistochemistry protocol. Two previously unrecognized patterns of pathology were observed: frequent long DN in the CA1 region and frequent dot-like DN in the neocortical layer II, which were seen in 39% and 15% of the FTLD-U cases, respectively. Four FTLD-U cases showed no TDP-43 pathology and were reclassified as FTLD-U, non-TDP-43 proteinopathy. Frequent long DN, but not dot-like DN, were significantly associated with progranulin mutations. Three of the DLDH cases were reclassified as FTLD-U. Of the cases with other neurodegenerative diseases, 43% showed TDP-43-pathology in the hippocampus but only 4% 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 quantity of the pathology and the types of pathology that can be detected. Involvement of both the hippocampus and frontal cortex may be a diagnostically important feature in FTLD-U.

Risks associated with brain biopsy limit availability of tissues and the role of brain biopsy in diagnosing neurodegeneration is unclear. We developed a simulated brain biopsy paradigm to comprehensively evaluate potential accuracy of detecting neurodegeneration in biopsies. Postmortem tissue from the frontal, temporal and parietal cortices and basal ganglia from 73 cases including Alzheimer’s disease (AD), Lewy body disease (LBD), frontotemporal lobar degeneration-TDP43 (FTLD-TDP), multiple system atrophy (MSA), Pick’s disease (PiD), corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP) were evaluated using H&E and immunostains. Brain biopsy was simulated in a blinded manner by masking each slide with opaque tape except for an area measuring 10 mm in diameter. Diagnoses obtained from frontal cortex only or all 4-brain regions were then compared with autopsy diagnoses. Diagnostic sensitivity in frontal cortex was highest in FTLD-TDP (88%), AD (80%) and LBD (79%); intermediate for MSA (71%), CBD (66%) and PiD (66%) and lowest for PSP (0%) (average 64%). Specificity was 43%. Sensitivities were enhanced with all 4-brain regions: FTLD-TDP (100%), AD (80%), LBD (100%), MSA (100%), CBD (83%), PiD (100%) and PSP (88%) (average 92%). Specificity was 71%. Simulated brain biopsy addressed limitations of standard brain biopsies such as tissue availability and lack of autopsy confirmation of diagnoses. These data could inform efforts to establish criteria for biopsy diagnosis of neurodegenerative disorders to guide care of individuals who undergo biopsy for enigmatic causes of cognitive impairment or when evidence of an underlying neurodegenerative disease may influence future therapy.

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 grey 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 grey matter loss compared to controls with no differences observed between the groups, for all subjects and for bvFTD subjects. Patterns of grey 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.

In 2006, TAR DNA-binding protein 43 (TDP-43), a highly conserved nuclear protein, was identified as the major disease protein in amyotrophic lateral sclerosis (ALS) and in the most common variant of frontotemporal lobar degeneration (FTLD), FTLD-U, which is characterized by cytoplasmic inclusions that stain positive for ubiquitin but negative for tau and α-synuclein. Since then, rapid advances have been made in our understanding of the physiological function of TDP-43 and the role of this protein in neurodegeneration. These advances link ALS and FTLD-U (now designated FTLD-TDP) to a shared mechanism of disease. In this Review, we summarize the current evidence regarding the normal function of TDP-43 and the TDP-43 pathology observed in FTLD-TDP, ALS, and other neurodegenerative diseases wherein TDP-43 pathology co-occurs with other disease-specific lesions (for example, with amyloid plaques and neurofibrillary tangles in Alzheimer disease). Moreover, we discuss the accumulating data that support our view that FTLD-TDP and ALS represent two ends of a spectrum of primary TDP-43 proteinopathies. Finally, we comment on the importance of recent advances in TDP-43-related research to neurological practice, including the new opportunities to develop better diagnostics and disease-modifying therapies for ALS, FTLD-TDP, and related disorders exhibiting TDP-43 pathology.

Pathology underlying behavioral variant frontotemporal dementia (bvFTD) is heterogeneous, with the most common pathologies being Pick’s disease (PiD), corticobasal degeneration (CBD), and FTLD-TDP type 1. Clinical features are unhelpful in differentiating these pathologies. We aimed to determine whether imaging atrophy patterns differ across these pathologies in bvFTD subjects. We identified 15 bvFTD subjects that had volumetric MRI during life and autopsy: five with PiD, five CBD and five FTLD-TDP type 1. Voxel-based morphometry was used to assess atrophy patterns in each bvFTD group compared to 20 age and gender-matched controls. All three pathological groups showed grey matter loss in frontal lobes, although specific patterns of atrophy differed across groups: PiD showed widespread loss in frontal lobes with additional involvement of anterior temporal lobes; CBD showed subtle patterns of loss involving posterior lateral and medial superior frontal lobe; FTLD-TDP type 1 showed widespread loss in frontal, temporal and parietal lobes. Greater parietal loss was observed in FTLD-TDP type 1 compared to both other groups, and greater anterior temporal and medial frontal loss was observed in PiD compared to CBD. Imaging patterns of atrophy in bvFTD vary according to pathological diagnosis and may therefore be helpful in predicting these pathologies in bvFTD.

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.

We applied optimized voxel-based morphometry (VBM) to brain MRIs from autopsy-proven cases of tau-positive frontotemporal lobar degeneration (FTLD-T, N = 6), ubiquitin and TDP-43-positive/tau-negative FTLD (FTLD-U, N = 8) and cognitively normal controls (N = 61). The analysis revealed that FTLD-T and FTLD-U both show atrophy in the frontal cortex and striatum, but striatal atrophy is more severe in FTLD-T. Manual region-of-interest (ROI) tracing of caudate and putamen volumes confirmed the VBM findings. These anatomic differences may help distinguish between FTLD spectrum pathologic subtypes in vivo.

We applied optimised voxel based morphometry (VBM) to brain MRIs from autopsy proven cases of tau positive frontotemporal lobar degeneration (FTLD‐T, n = 6), ubiquitin and TDP‐43 positive/tau negative FTLD (FTLD‐U, n = 8) and cognitively normal controls (n = 61). The analysis revealed that FTLD‐T and FTLD‐U both show atrophy in the frontal cortex and striatum, but striatal atrophy is more severe in FTLD‐T. Manual region of interest tracing of caudate and putamen volumes confirmed the VBM findings. These anatomical differences may help distinguish between FTLD spectrum pathological subtypes in vivo.

Objective

Frontotemporal lobar degeneration (FTLD) is characterized by impairments in social, behavioral, and/or language function, but postmortem studies indicate that multiple neuropathological entities lead to FTLD. This study assessed whether specific clinical features predict the underlying pathology.

Methods

A clinicopathological correlation was performed on 90 consecutive patients with a pathological diagnosis of frontotemporal dementia and was compared with an additional 24 cases accrued during the same time period with a clinical diagnosis of FTLD, but with pathology not typically associated with frontotemporal dementia.

Results

Postmortem examination showed multiple pathologies including tauopathies (46%), FTLD with ubiquitin-positive inclusions (29%), and Alzheimer’s disease (17%). The pathological groups manifested some distinct demographic, clinical, and neuropsychological features, although these attributes showed only a statistical association with the underlying pathology. FTLD with ubiquitin-positive inclusions was more likely to present with both social and language dysfunction, and motor neuron disease was more likely to emerge in these patients. Tauopathies were more commonly associated with an extrapyramidal disorder. Alzheimer’s disease was associated with relatively greater deficits in memory and executive function.

Interpretation

Clinical and neuropsychological features contribute to delineating the spectrum of pathology underlying a patient diagnosed with FTLD, but biomarkers are needed that, together with the clinical phenotype, can predict the underlying neuropathology.

Major discoveries have been made in the recent past in the genetics, biochemistry and neuropathology of frontotemporal lobar degeneration (FTLD). TAR DNA-binding protein 43 (TDP-43), encoded by the TARDBP gene, has been identified as the major pathological protein of FTLD with ubiquitin-immunoreactive (ub-ir) inclusions (FTLD-U) with or without amyotrophic lateral sclerosis (ALS) and sporadic ALS. Recently, mutations in the TARDBP gene in familial and sporadic ALS have been reported which demonstrate that abnormal TDP-43 alone is sufficient to cause neurodegeneration. Several familial cases of FTLD-U, however, are now known to have mutations in the progranulin (GRN) gene, but granulin is not a component of the TDP-43- and ub-ir inclusions. Further, TDP-43 is found to be a component of the inclusions of an increasing number of neurodegenerative diseases. Other FTLD-U entities with TDP-43 proteinopathy include: FTLD-U with valosin-containing protein (VCP) gene mutation and FTLD with ALS linked to chromosome 9p. In contrast, chromosome 3-linked dementia, FTLD-U with chromatin modifying protein 2B (CHMP2B) mutation, has ub-ir, TDP-43-negative inclusions. In summary, recent discoveries have generated new insights into the pathogenesis of a spectrum of disorders called TDP-43 proteinopathies including: FTLD-U, FTLD-U with ALS, ALS, and a broadening spectrum of other disorders. It is anticipated that these discoveries and a revised nosology of FTLD will contribute toward an accurate diagnosis, and facilitate the development of new diagnostic tests and therapeutics.

Background

Hippocampal sclerosis (HpScl) is common in elderly subjects with dementia, either alone or accompanied by other pathologic processes. It is also found in >70% of frontotemporal lobar degeneration with TDP-43 immunoreactive inclusions (FTLD-TDP). TDP-43 inclusions are detected in >20% of Alzheimer disease (AD) and >70% of HpScl cases. The most common cause of FTLD-TDP is mutation in the progranulin gene (GRN). Recently, a common genetic variant in the 3′ untranslated region (3′UTR) of GRN (rs5848; c.*78C>T) located in a microRNA binding site regulated progranulin expression, and the T-allele was increased in FTLD-TDP compared to controls.

Objective

The goal of this study was to determine if the 3′UTR variant in GRN was associated with TDP-43 immunoreactivity in AD with and without HpScl.

Methods

644 cases of pathologically confirmed AD, including 57 with HpScl, were screened for TDP-43 immunoreactivity and were genotyped at the GRN 3′UTR single-nucleotide polymorphism rs5848 using previously published methods.

Results

There was a trend (p = 0.06) for TDP-43 immunoreactivity, but a very significant (p = 0.005) association of HpScl with the variant, with 72% of AD with HpScl carrying a T-allele, compared to 51% of AD without HpScl carrying a T-allele.

Conclusion

The results suggest that a genetic variant in GRN leading to decreased levels of progranulin may be a risk factor for HpScl in AD, while its role in TDP-43 immunoreactivity in AD remains less certain.