Update on recent molecular and genetic advances in frontotemporal lobar degeneration

A structural haplotype in the 17q21.31 MAPT region is associated with increased risk for chronic traumatic encephalopathy endophenotypes

Chronic traumatic encephalopathy (CTE) is a neurodegenerative tauopathy associated with repetitive head impact (RHI) exposure. Genetic variation in the 17q21.31 region, containing microtubule-associated protein tau (MAPT), has been implicated in tauopathies but has not been investigated in CTE. The region includes a megabase-long inversion (H1/H2) and copy-number variations, including α, β, and γ segments, which can be characterized as nine segregating structural haplotypes. We leveraged array SNP data and a reference panel across the 17q21.31 region to impute structural haplotypes and test their association with CTE endophenotypes in 447 European ancestry brain donors with RHI exposure. The H1β1γ1 haplotype was significantly associated with dementia and semi-quantitative tau burden in multiple cortical and medial temporal regions commonly affected in CTE. H1β1γ1 differential expression analyses in dorsolateral frontal cortex implicated cis-acting genes and inflammatory pathways. Taken together, the H1β1γ1 haplotype may help explain CTE heterogeneity among those with similar RHI exposure.

18F-MK-6240 tau PET in patients at-risk for chronic traumatic encephalopathy

BACKGROUND

Molecular biomarkers of chronic traumatic encephalopathy (CTE) are lacking. We evaluated 18F-MK-6240 tau PET as a biomarker for CTE. Two studies were done: (1) 3H-MK-6240 autoradiography and an in-vitro brain homogenate binding studies on postmortem CTE tissue, (2) an in-vivo 18F-MK-6240 tau PET study in former American football players.

METHODS

Autoradiography and in-vitro binding studies were done using 3H-MK-6240 on frozen temporal and frontal cortex tissue from six autopsy cases with stage III CTE compared to Alzheimer's disease. Thirty male former National Football League (NFL) players with cognitive concerns (mean age = 58.9, SD = 7.8) completed tau (18F-MK-6240) and Aβ (18F-Florbetapir) PET. Controls included 39 Aβ-PET negative, cognitively normal males (mean age = 65.7, SD = 6.3). 18F-MK-6240 SUVr images were created using 70-90 min post-injection data with inferior cerebellar gray matter as the reference. We compared SUVr between players and controls using voxelwise and region-of-interest approaches. Correlations between 18F-MK-6240 SUVr and cognitive scores were tested.

RESULTS

All six CTE stage III cases had Braak NFT stage III but no neuritic plaques. Two had Thal Phase 1 for Aβ; one showed a laminar pattern of 3H-MK-6240 autoradiography binding in the superior temporal cortex and less so in the dorsolateral frontal cortex, corresponding to tau-immunoreactive lesions detected using the AT8 antibody (pSer202/pThr205 tau) in adjacent tissue sections. The other CTE cases had low frequencies of cortical tau-immunoreactive deposits and no well-defined autoradiography binding. In-vitro 3H-MK-6240 binding studies to CTE brain homogenates in the case with autoradiography signal indicated high binding affinity (KD = 2.0 ± 0.9 nM, Bmax = 97 ± 24 nM, n = 3). All NFL players had negative Aβ-PET. There was variable, low-to-intermediate intensity 18F-MK-6240 uptake across participants: 16 had no cortical signal, 7 had medial temporal lobe (MTL) uptake, 2 had frontal uptake, and 4 had MTL and frontal uptake. NFL players had higher SUVr in the entorhinal cortex (d = 0.86, p = 0.001), and the parahippocampal gyrus (d = 0.39, p = 0.08). Voxelwise regressions showed increased uptake in NFL players in two bilateral anterior MTL clusters (p < 0.05 FWE). Higher parahippocampal and frontal-temporal SUVrs correlated with worse memory (r = -0.38, r = -0.40) and semantic fluency (r = -0.38, r = -0.48), respectively.

CONCLUSION

We present evidence of 3H-MK-6240 in-vitro binding to post-mortem CTE tissue homogenates and in vivo 18F-MK-6240 PET binding in the MTL among a subset of participants. Additional studies in larger samples and PET-to-autopsy correlations are required to further elucidate the potential of 18F-MK-6240 to detect tau pathology in CTE.

Decreased myelin proteins in brain donors exposed to football-related repetitive head impacts

American football players and other individuals exposed to repetitive head impacts can exhibit a constellation of later-life cognitive and neuropsychiatric symptoms. While tau-based diseases such as chronic traumatic encephalopathy can underpin certain symptoms, contributions from non-tau pathologies from repetitive head impacts are increasingly recognized. We examined cross-sectional associations between myelin integrity using immunoassays for myelin-associated glycoprotein and proteolipid protein 1 with risk factors and clinical outcomes in brain donors exposed to repetitive head impacts from American football. Immunoassays for myelin-associated glycoprotein and proteolipid protein 1 were conducted on dorsolateral frontal white matter tissue samples of 205 male brain donors. Proxies of exposure to repetitive head impacts included years of exposure and age of first exposure to American football play. Informants completed the Functional Activities Questionnaire, Behavior Rating Inventory of Executive Function-Adult Version (Behavioral Regulation Index), and Barratt Impulsiveness Scale-11. Associations between myelin-associated glycoprotein and proteolipid protein 1 with exposure proxies and clinical scales were tested. Of the 205 male brain donors who played amateur and professional football, the mean age was 67.17 (SD = 16.78), and 75.9% (n = 126) were reported by informants to be functionally impaired prior to death. Myelin-associated glycoprotein and proteolipid protein 1 correlated with the ischaemic injury scale score, a global indicator of cerebrovascular disease (r = -0.23 and -0.20, respectively, Ps < 0.01). Chronic traumatic encephalopathy was the most common neurodegenerative disease (n = 151, 73.7%). Myelin-associated glycoprotein and proteolipid protein 1 were not associated with chronic traumatic encephalopathy status, but lower proteolipid protein 1 was associated with more severe chronic traumatic encephalopathy (P = 0.03). Myelin-associated glycoprotein and proteolipid protein 1 were not associated with other neurodegenerative disease pathologies. More years of football play was associated with lower proteolipid protein 1 [beta = -2.45, 95% confidence interval (CI) [-4.52, -0.38]] and compared with those who played <11 years of football (n = 78), those who played 11 or more years (n = 128) had lower myelin-associated glycoprotein (mean difference = 46.00, 95% CI [5.32, 86.69]) and proteolipid protein 1 (mean difference = 24.72, 95% CI [2.40, 47.05]). Younger age of first exposure corresponded to lower proteolipid protein 1 (beta = 4.35, 95% CI [0.25, 8.45]). Among brain donors who were aged 50 or older (n = 144), lower proteolipid protein 1 (beta = -0.02, 95% CI [-0.047, -0.001]) and myelin-associated glycoprotein (beta = -0.01, 95% CI [-0.03, -0.002]) were associated with higher Functional Activities Questionnaire scores. Lower myelin-associated glycoprotein correlated with higher Barratt Impulsiveness Scale-11 scores (beta = -0.02, 95% CI [-0.04, -0.0003]). Results suggest that decreased myelin may represent a late effect of repetitive head impacts that contributes to the manifestation of cognitive symptoms and impulsivity. Clinical-pathological correlation studies with prospective objective clinical assessments are needed to confirm our findings.

Associations between near end-of-life flortaucipir PET and postmortem CTE-related tau neuropathology in six former American football players

PURPOSE

Flourine-18-flortaucipir tau positron emission tomography (PET) was developed for the detection for Alzheimer's disease. Human imaging studies have begun to investigate its use in chronic traumatic encephalopathy (CTE). Flortaucipir-PET to autopsy correlation studies in CTE are needed for diagnostic validation. We examined the association between end-of-life flortaucipir PET and postmortem neuropathological measurements of CTE-related tau in six former American football players.

METHODS

Three former National Football League players and three former college football players who were part of the DIAGNOSE CTE Research Project died and agreed to have their brains donated. The six players had flortaucipir (tau) and florbetapir (amyloid) PET prior to death. All brains from the deceased participants were neuropathologically evaluated for the presence of CTE. On average, the participants were 59.0 (SD = 9.32) years of age at time of PET. PET scans were acquired 20.33 (SD = 13.08) months before their death. Using Spearman correlation analyses, we compared flortaucipir standard uptake value ratios (SUVRs) to digital slide-based AT8 phosphorylated tau (p-tau) density in a priori selected composite cortical, composite limbic, and thalamic regions-of-interest (ROIs).

RESULTS

Four brain donors had autopsy-confirmed CTE, all with high stage disease (n = 3 stage III, n = 1 stage IV). Three of these four met criteria for the clinical syndrome of CTE, known as traumatic encephalopathy syndrome (TES). Two did not have CTE at autopsy and one of these met criteria for TES. Concomitant pathology was only present in one of the non-CTE cases (Lewy body) and one of the CTE cases (motor neuron disease). There was a strong association between flortaucipir SUVRs and p-tau density in the composite cortical (ρ = 0.71) and limbic (ρ = 0.77) ROIs. Although there was a strong association in the thalamic ROI (ρ = 0.83), this is a region with known off-target binding. SUVRs were modest and CTE and non-CTE cases had overlapping SUVRs and discordant p-tau density for some regions.

CONCLUSIONS

Flortaucipir-PET could be useful for detecting high stage CTE neuropathology, but specificity to CTE p-tau is uncertain. Off-target flortaucipir binding in the hippocampus and thalamus complicates interpretation of these associations. In vivo biomarkers that can detect the specific p-tau of CTE across the disease continuum are needed.

Ante-mortem plasma phosphorylated tau (181) predicts Alzheimer's disease neuropathology and regional tau at autopsy

Blood-based biomarkers such as tau phosphorylated at threonine 181 (phosphorylated-tau181) represent an accessible, cost-effective and scalable approach for the in vivo detection of Alzheimer's disease pathophysiology. Plasma-pathological correlation studies are needed to validate plasma phosphorylated-tau181 as an accurate and reliable biomarker of Alzheimer's disease neuropathological changes. This plasma-to-autopsy correlation study included participants from the Boston University Alzheimer's Disease Research Center who had a plasma sample analysed for phosphorylated-tau181 between 2008 and 2018 and donated their brain for neuropathological examination. Plasma phosphorelated-tau181 was measured with single molecule array technology. Of 103 participants, 62 (60.2%) had autopsy-confirmed Alzheimer's disease. Average time between blood draw and death was 5.6 years (standard deviation = 3.1 years). Multivariable analyses showed higher plasma phosphorylated-tau181 concentrations were associated with increased odds for having autopsy-confirmed Alzheimer's disease [AUC = 0.82, OR = 1.07, 95% CI = 1.03-1.11, P < 0.01; phosphorylated-tau standardized (z-transformed): OR = 2.98, 95% CI = 1.50-5.93, P < 0.01]. Higher plasma phosphorylated-tau181 levels were associated with increased odds for having a higher Braak stage (OR = 1.06, 95% CI = 1.02-1.09, P < 0.01) and more severe phosphorylated-tau across six cortical and subcortical brain regions (ORs = 1.03-1.06, P < 0.05). The association between plasma phosphorylated-tau181 and Alzheimer's disease was strongest in those who were demented at time of blood draw (OR = 1.25, 95%CI = 1.02-1.53), but an effect existed among the non-demented (OR = 1.05, 95% CI = 1.01-1.10). There was higher discrimination accuracy for Alzheimer's disease when blood draw occurred in years closer to death; however, higher plasma phosphorylated-tau181 levels were associated with Alzheimer's disease even when blood draw occurred >5 years from death. Ante-mortem plasma phosphorylated-tau181 concentrations were associated with Alzheimer's disease neuropathology and accurately differentiated brain donors with and without autopsy-confirmed Alzheimer's disease. These findings support plasma phosphorylated-tau181 as a scalable biomarker for the detection of Alzheimer's disease.

Characterizing tau deposition in chronic traumatic encephalopathy (CTE): utility of the McKee CTE staging scheme

Chronic traumatic encephalopathy (CTE) is a tauopathy associated with repetitive head impacts (RHI) that has been neuropathologically diagnosed in American football players and other contact sport athletes. In 2013, McKee and colleagues proposed a staging scheme for characterizing the severity of the hyperphosphorylated tau (p-tau) pathology, the McKee CTE staging scheme. The staging scheme defined four pathological stages of CTE, stages I(mild)-IV(severe), based on the density and regional deposition of p-tau. The objective of this study was to test the utility of the McKee CTE staging scheme, and provide a detailed examination of the regional distribution of p-tau in CTE. We examined the relationship between the McKee CTE staging scheme and semi-quantitative and quantitative assessments of regional p-tau pathology, age at death, dementia, and years of American football play among 366 male brain donors neuropathologically diagnosed with CTE (mean age 61.86, SD 18.90). Spearman's rho correlations showed that higher CTE stage was associated with higher scores on all semi-quantitative and quantitative assessments of p-tau severity and density (p's < 0.001). The severity and distribution of CTE p-tau followed an age-dependent progression: older age was associated with increased odds for having a higher CTE stage (p < 0.001). CTE stage was independently associated with increased odds for dementia (p < 0.001). K-medoids cluster analysis of the semi-quantitative scales of p-tau across 14 regions identified 5 clusters of p-tau that conformed to increasing CTE stage (stage IV had 2 slightly different clusters), age at death, dementia, and years of American football play. There was a predilection for p-tau pathology in five regions: dorsolateral frontal cortex (DLF), superior temporal cortex, entorhinal cortex, amygdala, and locus coeruleus (LC), with CTE in the youngest brain donors and lowest CTE stage restricted to DLF and LC. These findings support the usefulness of the McKee CTE staging scheme and demonstrate the regional distribution of p-tau in CTE.

Neuropathological profile of long-duration amyotrophic lateral sclerosis in military Veterans

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder affecting both the upper and lower motor neurons. Although ALS typically leads to death within 3 to 5 years after initial symptom onset, approximately 10% of patients with ALS live more than 10 years after symptom onset. We set out to determine similarities and differences in clinical presentation and neuropathology in persons with ALS with long vs. those with standard duration. Participants were United States military Veterans with a pathologically confirmed diagnosis of ALS (n = 179), dichotomized into standard duration (<10 years) and long-duration (≥10 years). The ALS Functional Rating Scale-Revised (ALSFRS-R) was administered at study entry and semi-annually thereafter until death. Microglial density was determined in a subset of participants. long-duration ALS occurred in 76 participants (42%) with a mean disease duration of 16.3 years (min/max = 10.1/42.2). Participants with long-duration ALS were younger at disease onset (P = 0.002), had a slower initial ALS symptom progression on the ALSFRS-R (P < 0.001) and took longer to diagnose (P < 0.002) than standard duration ALS. Pathologically, long-duration ALS was associated with less frequent TDP-43 pathology (P < 0.001). Upper motor neuron degeneration was similar; however, long-duration ALS participants had less severe lower motor neuron degeneration at death (P < 0.001). In addition, the density of microglia was decreased in the corticospinal tract (P = 0.017) and spinal cord anterior horn (P = 0.009) in long-duration ALS. Notably, many neuropathological markers of ALS were similar between the standard and long-duration groups and there was no difference in the frequency of known ALS genetic mutations. These findings suggest that the lower motor neuron system is relatively spared in long-duration ALS and that pathological progression is likely slowed by as yet unknown genetic and environmental modifiers.

Chronic Traumatic Encephalopathy Within an Amyotrophic Lateral Sclerosis Brain Bank Cohort

Chronic traumatic encephalopathy (CTE) is a progressive neurodegenerative disorder linked to repetitive head impacts and has been associated with amyotrophic lateral sclerosis (ALS), a fatal, degenerative neuromuscular disorder. The Department of Veterans Affairs Biorepository Brain Bank (VABBB) is a tissue repository that collects antemortem disease progression data and postmortem central nervous system tissue from veterans with ALS. We set out to determine the frequency of co-morbid ALS and CTE in the VABBB cohort and to characterize the clinical, genetic, and pathological distinctions between participants with ALS only and those with both ALS and CTE (ALS+CTE). Of 155 participants, 9 (5.8%) had neuropathologically confirmed ALS+CTE. Participants with ALS+CTE were more likely to have a history of traumatic brain injury (p < 0.001), served during the first Persian Gulf War (p < 0.05), and to have more severe tau pathology within the frontal cortex and spinal cord (p < 0.05). The most common exposures to head impacts included contact sports (n = 5) and military service (n = 2). Clinically, participants with ALS+CTE were more likely to have bulbar onset ALS (p = 0.006), behavioral changes (p = 0.002), and/or mood changes (p < 0.001). Overall, compared with ALS in isolation, comorbid ALS+CTE is associated with a history of TBI and has a distinct clinical and pathological presentation.

Variation in TMEM106B in chronic traumatic encephalopathy

The genetic basis of chronic traumatic encephalopathy (CTE) is poorly understood. Variation in transmembrane protein 106B (TMEM106B) has been associated with enhanced neuroinflammation during aging and with TDP-43-related neurodegenerative disease, and rs3173615, a missense coding SNP in TMEM106B, has been implicated as a functional variant in these processes. Neuroinflammation and TDP-43 pathology are prominent features in CTE. The purpose of this study was to determine whether genetic variation in TMEM106B is associated with CTE risk, pathological features, and ante-mortem dementia. Eighty-six deceased male athletes with a history of participation in American football, informant-reported Caucasian, and a positive postmortem diagnosis of CTE without comorbid neurodegenerative disease were genotyped for rs3173615. The minor allele frequency (MAF = 0.42) in participants with CTE did not differ from previously reported neurologically normal controls (MAF = 0.43). However, in a case-only analysis among CTE cases, the minor allele was associated with reduced phosphorylated tau (ptau) pathology in the dorsolateral frontal cortex (DLFC) (AT8 density, odds ratio [OR] of increasing one quartile = 0.42, 95% confidence interval [CI] 0.22–0.79, p = 0.008), reduced neuroinflammation in the DLFC (CD68 density, OR of increasing one quartile = 0.53, 95% CI 0.29–0.98, p = 0.043), and increased synaptic protein density (β = 0.306, 95% CI 0.065–0.546, p = 0.014). Among CTE cases, TMEM106B minor allele was also associated with reduced ante-mortem dementia (OR = 0.40, 95% CI 0.16–0.99, p = 0.048), but was not associated with TDP-43 pathology. All case-only models were adjusted for age at death and duration of football play. Taken together, variation in TMEM106B may have a protective effect on CTE-related outcomes.

CCL11 is increased in the CNS in chronic traumatic encephalopathy but not in Alzheimer's disease

CCL11, a protein previously associated with age-associated cognitive decline, is observed to be increased in the brain and cerebrospinal fluid (CSF) in chronic traumatic encephalopathy (CTE) compared to Alzheimer's disease (AD). Using a cohort of 23 deceased American football players with neuropathologically verified CTE, 50 subjects with neuropathologically diagnosed AD, and 18 non-athlete controls, CCL11 was measured with ELISA in the dorsolateral frontal cortex (DLFC) and CSF. CCL11 levels were significantly increased in the DLFC in subjects with CTE (fold change = 1.234, p < 0.050) compared to non-athlete controls and AD subjects with out a history of head trauma. This increase was also seen to correlate with years of exposure to American football (β = 0.426, p = 0.048) independent of age (β = -0.046, p = 0.824). Preliminary analyses of a subset of subjects with available post-mortem CSF showed a trend for increased CCL11 among individuals with CTE (p = 0.069) mirroring the increase in the DLFC. Furthermore, an association between CSF CCL11 levels and the number of years exposed to football (β = 0.685, p = 0.040) was observed independent of age (β = -0.103, p = 0.716). Finally, a receiver operating characteristic (ROC) curve analysis demonstrated CSF CCL11 accurately distinguished CTE subjects from non-athlete controls and AD subjects (AUC = 0.839, 95% CI 0.62-1.058, p = 0.028). Overall, the current findings provide preliminary evidence that CCL11 may be a novel target for future CTE biomarker studies.

Clinicopathological Evaluation of Chronic Traumatic Encephalopathy in Players of American Football

IMPORTANCE

Players of American football may be at increased risk of long-term neurological conditions, particularly chronic traumatic encephalopathy (CTE).

OBJECTIVE

To determine the neuropathological and clinical features of deceased football players with CTE.

DESIGN, SETTING, AND PARTICIPANTS

Case series of 202 football players whose brains were donated for research. Neuropathological evaluations and retrospective telephone clinical assessments (including head trauma history) with informants were performed blinded. Online questionnaires ascertained athletic and military history.

EXPOSURES

Participation in American football at any level of play.

MAIN OUTCOMES AND MEASURES

Neuropathological diagnoses of neurodegenerative diseases, including CTE, based on defined diagnostic criteria; CTE neuropathological severity (stages I to IV or dichotomized into mild [stages I and II] and severe [stages III and IV]); informant-reported athletic history and, for players who died in 2014 or later, clinical presentation, including behavior, mood, and cognitive symptoms and dementia.

RESULTS

Among 202 deceased former football players (median age at death, 66 years [interquartile range, 47-76 years]), CTE was neuropathologically diagnosed in 177 players (87%; median age at death, 67 years [interquartile range, 52-77 years]; mean years of football participation, 15.1 [SD, 5.2]), including 0 of 2 pre-high school, 3 of 14 high school (21%), 48 of 53 college (91%), 9 of 14 semiprofessional (64%), 7 of 8 Canadian Football League (88%), and 110 of 111 National Football League (99%) players. Neuropathological severity of CTE was distributed across the highest level of play, with all 3 former high school players having mild pathology and the majority of former college (27 [56%]), semiprofessional (5 [56%]), and professional (101 [86%]) players having severe pathology. Among 27 participants with mild CTE pathology, 26 (96%) had behavioral or mood symptoms or both, 23 (85%) had cognitive symptoms, and 9 (33%) had signs of dementia. Among 84 participants with severe CTE pathology, 75 (89%) had behavioral or mood symptoms or both, 80 (95%) had cognitive symptoms, and 71 (85%) had signs of dementia.

CONCLUSIONS AND RELEVANCE

In a convenience sample of deceased football players who donated their brains for research, a high proportion had neuropathological evidence of CTE, suggesting that CTE may be related to prior participation in football.

Assessing clinicopathological correlation in chronic traumatic encephalopathy: rationale and methods for the UNITE study

INTRODUCTION

Chronic traumatic encephalopathy (CTE) is a progressive neurodegeneration associated with repetitive head impacts. Understanding Neurologic Injury and Traumatic Encephalopathy (UNITE) is a U01 project recently funded by the National Institute of Neurological Disorders and Stroke and the National Institute of Biomedical Imaging and Bioengineering. The goal of the UNITE project is to examine the neuropathology and clinical presentation of brain donors designated as "at risk" for the development of CTE based on prior athletic or military exposure. Here, we present the rationale and methodology for UNITE.

METHODS

Over the course of 4 years, we will analyze the brains and spinal cords of 300 deceased subjects who had a history of repetitive head impacts sustained during participation in contact sports at the professional or collegiate level or during military service. Clinical data are collected through medical record review and retrospective structured and unstructured family interviews conducted by a behavioral neurologist or neuropsychologist. Blinded to the clinical data, a neuropathologist conducts a comprehensive assessment for neurodegenerative disease, including CTE, using published criteria. At a clinicopathological conference, a panel of physicians and neuropsychologists, blinded to the neuropathological data, reaches a clinical consensus diagnosis using published criteria, including proposed clinical research criteria for CTE.

RESULTS

We will investigate the validity of these clinical criteria and sources of error by using recently validated neuropathological criteria as a gold standard for CTE diagnosis. We also will use statistical modeling to identify diagnostic features that best predict CTE pathology.

CONCLUSIONS

The UNITE study is a novel and methodologically rigorous means of assessing clinicopathological correlation in CTE. Our findings will be critical for developing future iterations of CTE clinical diagnostic criteria.

Emerging concepts in Alzheimer's disease

Alzheimer's disease/senile dementia of the Alzheimer type (AD/SDAT) is the most common neuropathologic substrate of dementia. It is characterized by synapse loss (predominantly within neocortex) as well as deposition of certain distinctive lesions (the result of protein misfolding) throughout the brain. The latter include senile plaques, composed mainly of an amyloid (Aβ) core and a neuritic component; neurofibrillary tangles, composed predominantly of hyperphosphorylated tau; and cerebral amyloid angiopathy, a microangiopathy affecting both cerebral cortical capillaries and arterioles and resulting from Aβ deposition within their walls or (in the case of capillaries) immediately adjacent brain parenchyma. In this article, I discuss the hypothesized role these lesions play in causing cerebral dysfunction, as well as CSF and neuroimaging biomarkers (for dementia) that are especially relevant as immunotherapeutic approaches are being developed to remove Aβ from the brain parenchyma. In addition, I address the role of neuropathology in characterizing the sequelae of new AD/SDAT therapies and helping to validate CSF and neuroimaging biomarkers of disease. Comorbidity of AD/SDAT and various types of cerebrovascular disease is a major theme in dementia research, especially as cognitive impairment develops in the oldest old, who are especially vulnerable to ischemic and hemorrhagic brain lesions.

Progranulin-associated PiB-negative logopenic primary progressive aphasia

The logopenic variant of primary progressive aphasia (lvPPA) strongly associates with Alzheimer's disease, but can also associate with frontotemporal lobar degeneration. We aimed to assess the frequency of lvPPA in patients with speech and language disorders without β-amyloid deposition, and to perform detailed neuroimaging and genetic testing in such lvPPA patients. Seventy-six patients with a neurodegenerative speech and language disorder and Pittsburgh compound B (PiB) PET imaging demonstrating no β-amyloid deposition were analyzed. Six lvPPA patients (8 %) were identified. All six underwent progranulin (GRN) gene testing. Structural abnormality index maps and Cortex ID analysis were utilized to assess individual patterns of grey matter atrophy on MRI and hypometabolism on 18-F fluorodeoxyglucose (FDG) PET. Statistical parametric mapping was used to perform MRI and FDG-PET group comparisons between those with (GRN-positive) and without (GRN-negative) progranulin mutations. All six lvPPA patients showed left temporoparietal atrophy and hypometabolism. Three patients (50 %) were GRN-positive. Speech, language, and neurological and neuropsychological profiles did not differ between GRN-positive and negative patients, although GRN-positive patients had family histories, were on average 8 years younger, and had lower PiB-PET ratios. All six patients showed similar patterns of atrophy and hypometabolism, although, as a group, GRN-positive patients had more severe abnormalities, particularly in anteromedial temporal lobes. Logopenic PPA accounts for a small minority of neurodegenerative speech and language disorders not associated with β-amyloid deposition. Identification of such patients, however, should prompt testing for GRN mutations, since GRN-positive patients do not have distinctive features, yet account for 50 % of this patient population.

Frontotemporal dementia and primary progressive aphasia, a review

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

The spectrum of disease in chronic traumatic encephalopathy

Chronic traumatic encephalopathy is a progressive tauopathy that occurs as a consequence of repetitive mild traumatic brain injury. We analysed post-mortem brains obtained from a cohort of 85 subjects with histories of repetitive mild traumatic brain injury and found evidence of chronic traumatic encephalopathy in 68 subjects: all males, ranging in age from 17 to 98 years (mean 59.5 years), including 64 athletes, 21 military veterans (86% of whom were also athletes) and one individual who engaged in self-injurious head banging behaviour. Eighteen age- and gender-matched individuals without a history of repetitive mild traumatic brain injury served as control subjects. In chronic traumatic encephalopathy, the spectrum of hyperphosphorylated tau pathology ranged in severity from focal perivascular epicentres of neurofibrillary tangles in the frontal neocortex to severe tauopathy affecting widespread brain regions, including the medial temporal lobe, thereby allowing a progressive staging of pathology from stages I-IV. Multifocal axonal varicosities and axonal loss were found in deep cortex and subcortical white matter at all stages of chronic traumatic encephalopathy. TAR DNA-binding protein 43 immunoreactive inclusions and neurites were also found in 85% of cases, ranging from focal pathology in stages I-III to widespread inclusions and neurites in stage IV. Symptoms in stage I chronic traumatic encephalopathy included headache and loss of attention and concentration. Additional symptoms in stage II included depression, explosivity and short-term memory loss. In stage III, executive dysfunction and cognitive impairment were found, and in stage IV, dementia, word-finding difficulty and aggression were characteristic. Data on athletic exposure were available for 34 American football players; the stage of chronic traumatic encephalopathy correlated with increased duration of football play, survival after football and age at death. Chronic traumatic encephalopathy was the sole diagnosis in 43 cases (63%); eight were also diagnosed with motor neuron disease (12%), seven with Alzheimer's disease (11%), 11 with Lewy body disease (16%) and four with frontotemporal lobar degeneration (6%). There is an ordered and predictable progression of hyperphosphorylated tau abnormalities through the nervous system in chronic traumatic encephalopathy that occurs in conjunction with widespread axonal disruption and loss. The frequent association of chronic traumatic encephalopathy with other neurodegenerative disorders suggests that repetitive brain trauma and hyperphosphorylated tau protein deposition promote the accumulation of other abnormally aggregated proteins including TAR DNA-binding protein 43, amyloid beta protein and alpha-synuclein.

Pathologic lesions in neurodegenerative diseases

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

Frontotemporal dementias: Recent advances and current controversies

Frontotemporal dementia (FTD) syndromes comprise a heterogeneous group of neurodegenerative conditions characterized by atrophy in the frontal and temporal lobes. Three main clinical variants are recognized: Behavioral variant (bv-FTD), Semantic dementia (SD), and Progressive nonfluent aphasia (PNFA). However, logopenic/phonological (LPA) variant has been recently described, showing a distinctive pattern of brain atrophy and often associated to Alzheimer's disease pathology. The diagnosis of FTD is challenging, since there is clinical, pathological, and genetic overlap between the variants and other neurodegenerative diseases, such as motoneuron disease (MND) and corticobasal degeneration (CBD). In addition, patients with gene mutations (tau and progranulin) display an inconsistent clinical phenotype and the correspondence between the clinical variant and its pathology is unpredictable. New cognitive tests based on social cognition and emotional recognition together with advances in molecular pathology and genetics have contributed to an improved understanding. There is now a real possibility of accurate biomarkers for early diagnosis. The present review concentrates on new insights and debates in FTD.

TARDBP 3'-UTR variant in autopsy-confirmed frontotemporal lobar degeneration with TDP-43 proteinopathy

Pathogenic mutations in the gene encoding TDP-43, TARDBP, have been reported in familial amyotrophic lateral sclerosis (FALS) and, more recently, in families with a heterogeneous clinical phenotype including both ALS and frontotemporal lobar degeneration (FTLD). In our previous study, sequencing analyses identified one variant in the 3'-untranslated region (3'-UTR) of the TARDBP gene in two affected members of one family with bvFTD and ALS and in one unrelated clinically assessed case of FALS. Since that study, brain tissue has become available and provides autopsy confirmation of FTLD-TDP in the proband and ALS in the brother of the bvFTD-ALS family and the neuropathology of those two cases is reported here. The 3'-UTR variant was not found in 982 control subjects (1,964 alleles). To determine the functional significance of this variant, we undertook quantitative gene expression analysis. Allele-specific amplification showed a significant increase of 22% (P < 0.05) in disease-specific allele expression with a twofold increase in total TARDBP mRNA. The segregation of this variant in a family with clinical bvFTD and ALS adds to the spectrum of clinical phenotypes previously associated with TARDBP variants. In summary, TARDBP variants may result in clinically and neuropathologically heterogeneous phenotypes linked by a common molecular pathology called TDP-43 proteinopathy.

TARDBP variation associated with frontotemporal dementia, supranuclear gaze palsy, and chorea

TDP-43 has been identified as the pathological protein in the majority of cases of frontotemporal lobar degeneration and amyotrophic lateral sclerosis (ALS). TARDBP mutations have so far been uniquely associated with familial and sporadic ALS. We describe clinicopathological and genetic findings in a carrier of the novel K263E TARDBP variation, who developed frontotemporal dementia, supranuclear palsy, and chorea, but no signs of motor neuron disease. Neuropathologic examination revealed neuronal and glial TDP-43-immunoreactive deposits, predominantly in subcortical nuclei and brainstem. This is the first report of a TARDBP variation associated with a neurodegenerative syndrome other than ALS.

Twin pairs discordant for neuropathologically confirmed Lewy body dementia

AIM

Little is known about the concordance rate in twins for dementia with Lewy bodies (DLB). The rate of agreement between clinical and pathological diagnoses for DLB is typically low, necessitating confirmation of the diagnosis neuropathologically.

METHODS

Participants were 17 twin pairs enrolled in the Duke Twins Study of Memory in Aging in which at least one member of the pair had an autopsy confirmed diagnosis of DLB, Alzheimer's disease (AD) with Lewy bodies or frontotemporal dementia with Lewy bodies. The characteristics of those with dementia were assessed and rates of concordance for pathological confirmed dementia were examined.

RESULTS

Four monozygotic twin pairs had a proband with neuropathologically confirmed pure DLB; all remained discordant for dementia for periods up to 16 years or more. Five of 13 pairs in which the proband had AD plus DLB were concordant for dementia but only one pair was concordant for AD plus DLB, while the co-twins in the other four pairs had other types of dementia.

CONCLUSIONS

The present study indicates that even among twins, a diagnosis of DLB in one twin does not predict the same diagnosis in the other twin. Neuropathological discordance in type of dementia among monozygotic pairs hints at environmental or epigenetic factors playing a role in Lewy body pathology.

Clinical and pathological continuum of multisystem TDP-43 proteinopathies

OBJECTIVE

To determine the extent of transactivation response DNA-binding protein with a molecular weight of 43 kDa (TDP-43) pathology in the central nervous system of patients with clinically and autopsy-confirmed diagnoses of frontotemporal lobar degeneration with and without motor neuron disease and amyotrophic lateral sclerosis with and without cognitive impairment.

DESIGN

Performance of immunohistochemical whole-central nervous system scans for evidence of pathological TDP-43 and retrospective clinical medical record review.

SETTING

An academic medical center.

PARTICIPANTS

We included 64 patients with clinically and pathologically confirmed frontotemporal lobar degeneration with ubiquitinated inclusions with or without motor neuron disease and amyotrophic lateral sclerosis with or without cognitive impairment.

MAIN OUTCOME MEASURE

Neuronal and glial TDP-43 pathology.

RESULTS

We found evidence of neuronal and glial TDP-43 pathology in all disease groups throughout the neuraxis, albeit with variations in the frequency, morphology, and distribution of TDP-43 lesions. Moreover, the major clinical manifestations (eg, cognitive impairments, motor neuron signs, extrapyramidal symptoms, neuropsychiatric features) were reflected by the predominant distribution and burden of TDP-43 pathology.

CONCLUSION

These findings strongly suggest that amyotrophic lateral sclerosis, frontotemporal lobar degeneration with amyotrophic lateral sclerosis or motor neuron disease, and frontotemporal lobar degeneration with ubiquitinated inclusions are different manifestations of a multiple-system TDP-43 proteinopathy linked to similar mechanisms of neurodegeneration.

Amyotrophic lateral sclerosis, frontotemporal dementia and beyond: the TDP-43 diseases

Ever since the significance of pathological 43-kDa transactivating responsive sequence DNA-binding protein (TDP-43) for human disease has been recognized in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with ubiquitin positive inclusions (FTLD-U), a number of publications have emerged reporting on this pathology in a variety of neurodegenerative diseases. Given the heterogeneous and, in part, conflicting nature of the recent findings, we here review pathological TDP-43 and its relationship to human disease with a special focus on ALS and FTLD-U. To this end, we propose a classification scheme in which pathological TDP-43 is the major disease defining pathology in one group, or is present in addition to other neurodegenerative hallmark pathologies in a second category. We conclude that the TDP-43 proteinopathies represent a novel class of neurodegenerative disorders akin to alpha-synucleinopathies and tauopathies, with the concept of ALS and FTLD-U to be widened to a broad clinico-pathological multisystem disease, i.e., TDP-43 proteinopathy.