Distinct clinical and pathological characteristics of frontotemporal dementia associated with C9ORF72 mutations

Dissociation of Structural and Functional Integrities of the Motor System in Amyotrophic Lateral Sclerosis and Behavioral-Variant Frontotemporal Dementia

Background and Purpose

This study investigated the structural and functional changes in the motor system in amyotrophic lateral sclerosis (ALS; n=25) and behavioral-variant fronto-temporal dementia (bvFTD; n=17) relative to healthy controls (n=37).

Methods

Structural changes were examined using a region-of-interest approach, applying voxel-based morphometry for gray-matter changes and diffusion tensor imaging for white-matter changes. Functional changes in the motor system were elucidated using threshold-tracking transcranial magnetic stimulation (TMS) measurements of upper motor-neuron excitability.

Results

The structural analyses showed that in ALS there were more white-matter changes in the corticospinal and motor-cortex regions and more gray-matter changes in the cerebellum in comparison to controls. bvFTD showed substantial gray- and white-matter changes across virtually all motor-system regions compared to controls, although the brainstem was affected less than the other regions. Direct comparisons across patient groups showed that the gray- and white-matter motor-system changes inclusive of the motor cortex were greater in bvFTD than in ALS. By contrast, the functional integrity of the motor system was more adversely affected in ALS than in bvFTD, with both patient groups showing increased excitability of upper motor neurons compared to controls.

Conclusions

Cross-correlation of structural and functional data further revealed a neural dissociation of different motor-system regions and tracts covarying with the TMS excitability across both patient groups. The structural and functional motor-system integrities appear to be dissociated between ALS and bvFTD, which represents useful information for the diagnosis of motor-system changes in these two disorders.

Diversity of Cognitive Phenotypes Associated with C9ORF72 Hexanucleotide Expansion

For diagnostic purposes, we screened for the C9ORF72 mutation in a) 162 FTLD cases, and b) 145 cases with other diagnoses but with some frontotemporal features or manifestations previously reported in C9 carriers. Ten cases (onset 50 to 75 years) harbored the expansion: seven had FTLD syndromes (4.3% of total, 11% of familial cases), and three (2%) had a different diagnosis. All positive cases had family history of dementia, psychiatric disease, or ALS, but only 20% of families with mixed FTLD/ALS phenotypes carried the expansion. Language impairment was the most common symptom, followed by behavioral changes, memory deficits, and parkinsonism. C9ORF72 mutation has a low frequency in our dementia series and very diverse clinical manifestations.

Parkinsonism, movement disorders and genetics in frontotemporal dementia

Frontotemporal dementia (FTD) refers to a group of clinically and genetically heterogeneous neurodegenerative disorders that are a common cause of adult-onset behavioural and cognitive impairment. FTD often presents in combination with various hyperkinetic or hypokinetic movement disorders, and evidence suggests that various genetic mutations underlie these different presentations. Here, we review the known syndromatic-genetic correlations in FTD. Although no direct genotype-phenotype correlations have been identified, mutations in multiple genes have been associated with various presentations. Mutations in the genes that encode microtubule-associated protein tau (MAPT) and progranulin (PGRN) can manifest as symmetrical parkinsonism, including the phenotypes of Richardson syndrome and corticobasal syndrome (CBS). Expansions in the C9orf72 gene are most frequently associated with familial FTD, typically combined with motor neuron disease, but other manifestations, such as symmetrical parkinsonism, CBS and multiple system atrophy-like presentations, have been described in patients with these mutations. Less common gene mutations, such as those in TARDBP, CHMP2B, VCP, FUS and TREM2, can also present as atypical parkinsonism. The most common hyperkinetic movement disorders in FTD are motor and vocal stereotypies, which have been observed in up to 78% of patients with autopsy-proven FTD. Other hyperkinetic movements, such as chorea, orofacial dyskinesias, myoclonus and dystonia, are also observed in some patients with FTD.

Atypical parkinsonism in C9orf72 expansions: a case report and systematic review of 45 cases from the literature

While C9orf72 repeat expansions usually present with frontotemporal dementia (FTD) and/or amyotrophic lateral sclerosis (ALS), an increasing number of reports suggests that the primary phenotype of C9orf72 patients may also include movement disorders. We here provide the first systematic clinical characterisation of C9orf72-associated parkinsonism. We report a C9orf72 expansion carrier presenting with a clinical syndrome of progressive supranuclear palsy (PSP), pronounced mesencephalic atrophy on MRI and PSP-characteristic electrooculography findings. Moreover, we systematically review all previous reports on C9orf72 patients with parkinsonian features. Review of 28 reports revealed 45 C9orf72-positive patients with hypokinesia, rigidity and/or resting tremor. C9orf72-associated parkinsonism predominantly consisted in a hypokinetic-rigid syndrome without resting tremor (61%), with both asymmetric (59%) and symmetric (41%) distributions. Additional features included upper motor neuron signs (60%), lower motor neuron signs (36%), cognitive dysfunction (85%), behaviour and/or personality change (55%) and psychiatric symptoms (29%). Vertical supranuclear gaze palsy was reported in three further cases and cerebellar dysfunction in four cases. Family history frequently yielded evidence of ALS (31%) and FTD (21%). Atypical parkinsonism is a recurrent phenotypic manifestation of C9orf72 expansions. It occurs as part of a broad spectrum of C9orf72-related multi-system neurodegeneration, which can include basal ganglia, mesencephalic and cerebellar dysfunction. C9orf72 genotyping should be considered in those patients with atypical parkinsonism who present with a family history of ALS or FTD, upper or lower motor neuron signs and/or cognitive dysfunction with pronounced frontotemporal impairment.

Early-onset Alzheimer's disease versus frontotemporal dementia: resolution with genetic diagnoses?

We report a diagnostically challenging case of a 64-year-old man with a history of remote head trauma who developed mild behavioral changes and dyscalculia. He was diagnosed with clinical Alzheimer's disease (AD), with additional features consistent with behavioral variant frontotemporal dementia. Structural magnetic resonance imaging revealed atrophy in bilateral frontal and parietal cortices and hippocampi on visual inspection and left frontal pole and bilateral anterior temporal encephalomalacia, suspected to be due to head trauma. Consistent with the diagnosis of Alzheimer's pathology, positron emission tomography (PET) with Pittsburgh compound B suggested the presence of beta-amyloid. Fluorodeoxyglucose PET demonstrated hypometabolism in bilateral frontal and temporoparietal cortices. Voxel-based morphometry showed atrophy predominant in ventral frontal regions (bilateral orbitofrontal cortex, pregenual anterior cingulate/medial superior frontal gyrus), bilateral mid cingulate, bilateral lateral temporal cortex, and posterior insula. Bilateral caudate, thalamus, hippocampi, and cerebellum were prominently atrophied. Unexpectedly, a pathologic hexanucleotide repeat expansion in C9ORF72 was identified in this patient. This report underscores the clinical variability in C9ORF72 expansion carriers and the need to consider mixed pathologies, particularly when imaging studies are inconsistent with a single syndrome or pathology.

Characterization of an FTLD-PDB family with the coexistence of SQSTM1 mutation and hexanucleotide (G₄C₂) repeat expansion in C9orf72 gene

The C9orf72 expansion is considered a major genetic cause of familial frontotemporal dementia (FTD) in several patients' cohorts. Interestingly, C9orf72 expansion carriers, present also abundant neuronal p62-positive inclusions. Although p62/SQSTM1 mutations were initially associated with Paget disease of bone (PDB), they have been also identified in FTD. We describe an FTD-PDB family in which the proband presented with behavioral FTD phenotype and concomitant Paget disease. The molecular genetic analysis revealed the co-occurrence of 2 mutations; the pathogenic C9orf72 expansion and p.P392L heterozygous missense mutation in SQSTM1 gene. Amongst the 6 family members analyzed, the p.P392L SQSTM1 mutation segregated as expected with PDB, whereas the C9orf72 expansion segregated with frontal cognitive impairment or dementia in all but one carrier. The coexistence of these conditions could be underestimated since neither patients with FTD nor patients with PDB undergo bone scintigraphy or cognitive assessment, respectively. The number of cases with double mutations could also be over looked as the molecular strategy adopted in most laboratories ends with the identification of one pathogenic mutation in one of the known causative genes. Therefore, we advocate for further clinical and molecular evaluation in suspect cases.

Quantitative analysis and clinico-pathological correlations of different dipeptide repeat protein pathologies in C9ORF72 mutation carriers

Hexanucleotide repeat expansion in C9ORF72 is the most common genetic cause of frontotemporal dementia and motor neuron disease. One consequence of the mutation is the formation of different potentially toxic polypeptides composed of dipeptide repeats (DPR) (poly-GA, -GP, -GR, -PA, -PR) generated by repeat-associated non-ATG (RAN) translation. While previous studies focusing on poly-GA pathology have failed to detect any clinico-pathological correlations in C9ORF72 mutation cases, recent data from animal and cell culture models suggested that it may be only specific DPR species that are toxic and only when accumulated in certain intracellular compartments. Therefore, we performed a systematic clinico-pathological correlative analysis with counting of actual numbers of distinct types of inclusion (neuronal cytoplasmic and intranuclear inclusions, dystrophic neurites) for each DPR protein in relevant brain regions (premotor cortex, lower motor neurons) in a cohort of 35 C9ORF72 mutation cases covering the clinical spectrum from those with pure MND, mixed FTD/MND and pure FTD. While each DPR protein pathology had a similar pattern of anatomical distribution, the total amount of inclusions for each DPR protein varied remarkably (poly-GA > GP > GR > PR/PA), indicating that RAN translation seems to be more effective from sense than from antisense transcripts. Importantly, with the exception of moderate associations for the amount of poly-GA-positive dystrophic neurites with degeneration in the frontal cortex and total burden of poly-GA pathology with disease onset, no relationship was identified for any other DPR protein pathology with degeneration or phenotype. Biochemical analysis revealed a close correlation between insoluble DPR protein species and numbers of visible inclusions, while we did not find any evidence for the presence of soluble DPR protein species. Thus, overall our findings strongly argue against a role of DPR protein aggregation as major and exclusive pathomechanism in C9ORF72 pathogenesis. However, this does not exclude that DPR protein formation might be essential in C9ORF72 pathogenesis in interplay with other consequences associated with the C9ORF72 repeat expansion.

C9ORF72 and the FTD-ALS spectrum: A systematic review of neuroimaging studies

Objective

To perform a systematic review of the literature on the neuroimaging investigation of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) associated with C9ORF72 mutation.

Methods

The search was performed on PubMed and LILACS with the following terms: C9ORF72, MRI, SPECT, PET, ALS, FTD. No filters were added.

Results

Twenty articles were selected. Most studies found consistent involvement of frontotemporal regions in C9ORF72 carriers, including prefrontal cortex, and also cingulate, subcortical regions, especially the thalami, and posterior regions such as the parietal and occipital lobes. Functional connectivity was also explored and impaired sensorimotor connectivity in striatum and thalami was found in behavioral variant FTD C9ORF72 carriers. Some papers have reported an absence of significant abnormalities on brain imaging.

Conclusion

The inclusion of patients at different stages of the disease, differences in neuroimaging methods across studies, and distinct clinical phenotypes associated with C9ORF72 may account for the heterogeneity of results.

Psychiatric symptoms in frontotemporal dementia: epidemiology, phenotypes, and differential diagnosis

Frontotemporal dementia (FTD) is the most frequently occurring dementia in the presenile population. Despite epidemiologic data showing that patients with FTD may have experienced previous psychiatric disorders and that patients with psychotic disorders may develop dementia more often than expected in the nonaffected population, the overlap between these two conditions has been underestimated. Nevertheless, the identification in recent years of several genetic causes of FTD associated with heterogeneous and atypical presentations, including pure psychiatric symptoms, has shifted scientific interest back to obtaining a better understanding of common mechanisms between FTD and psychotic disorders. We review the current knowledge of the FTD spectrum and common features shared by FTD and some psychiatric diseases, starting from Pick's clinical description of the disease, moving toward pathogenic aspects of the disease and genetic causes and associated phenotypes, and finishing with analysis of crossing borders between FTD and psychiatric disorders (mainly represented by schizophrenia and bipolar spectrum disorders) in clinical practice in terms of overlapping symptoms, differential diagnosis, comorbidity, and treatment issues.

Familial Amyotrophic Lateral Sclerosis

Genes linked to amyotrophic lateral sclerosis (ALS) susceptibility are being identified at an increasing rate owing to advances in molecular genetic technology. Genetic mechanisms in ALS pathogenesis seem to exert major effects in about 10% of patients, but genetic factors at some level may be important components of disease risk in most patients with ALS. Identification of gene variants associated with ALS has informed concepts of the pathogenesis of ALS, aided the identification of therapeutic targets, facilitated research to develop new ALS biomarkers, and supported the establishment of clinical diagnostic tests for ALS-linked genes.

Brain morphologic changes in asymptomatic C9orf72 repeat expansion carriers

OBJECTIVE

To investigate possible effects of the C9orf72 repeat expansion before disease onset, we assessed brain morphology in asymptomatic carriers.

METHODS

Aiming to diminish the effects of genetic variation between subjects, apart from the C9orf72 repeat expansion, 16 carriers of the repeat expansion were compared with 23 noncarriers from the same large family with a history of amyotrophic lateral sclerosis (ALS). Cortical thickness, subcortical volumes, and white matter connectivity, as assessed from high-resolution T1-weighted and diffusion-weighted MRIs, were evaluated. For comparison, we included 14 C9orf72 carriers with ALS and 28 healthy, unrelated controls.

RESULTS

We found temporal, parietal, and occipital regions to be thinner (p < 0.05) and the left caudate and putamen to be smaller (p < 0.05) in asymptomatic carriers compared with noncarriers. Cortical thinning of the primary motor cortex and decreased connectivity of white matter pathways (global, corticospinal tract, and corpus callosum) were observed in patients with C9orf72-associated ALS, but not in asymptomatic carriers.

CONCLUSIONS

Asymptomatic C9orf72 carriers show cortical and subcortical differences compared with noncarriers from the same family, possibly effects of the C9orf72 repeat expansion on the brain. Of note, changes in the primary motor regions and motor-related tracts were found exclusively in patients with ALS, indicating that such motor changes may be a disease phenomenon.

Cerebrospinal fluid biomarkers for Alzheimer's disease in patients with frontotemporal lobar degeneration and amyotrophic lateral sclerosis with the C9ORF72 repeat expansion

BACKGROUND

The C9ORF72 expansion is one of the most common causes of frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS). The C9ORF72 expansion is associated with TDP-43 and p62 neuropathology, and amyloid plaques and neurofibrillary tangles are not common in patients with the C9ORF72 expansion. Therefore, we hypothesized that cerebrospinal fluid (CSF) biomarkers for Alzheimer's disease [AD; Aβ1-42, total tau (T-tau) and phospho-tau] are normal in these patients.

METHODS

The CSF Aβ1-42, T-tau and phospho-tau levels were measured in 40 Finnish patients with the C9ORF72 expansion (29 FTLD, 10 ALS and 1 FTLD-ALS) using ELISA.

RESULTS

A decreased Aβ1-42 level was found in 25% of cases, while there were only single cases with changes in the t-Tau or phospho-tau level. The patients with abnormal biomarkers fulfilled the clinical criteria of the behavioral variant frontotemporal dementia and expressed no clinical signs of AD.

CONCLUSIONS

In clinical diagnostics, a decreased CSF Aβ1-42 level does not exclude the C9ORF72 expansion associated with FTLD.

Distinct clinical and pathological phenotypes in frontotemporal dementia associated with MAPT, PGRN and C9orf72 mutations

Our objective was to compare the clinical and pathological characteristics of frontotemporal dementia patients with MAPT, GRN and C9orf72 gene mutations. We carried out a cross-sectional comparative study of 74 gene-positive patients (15 MAPT, 17 GRN and 42 C9orf72). Thirty had post mortem pathological data permitting clinico-pathological correlation. MAPT patients were younger than other groups, and showed more frequent behavioural disinhibition, repetitive and stereotyped behaviours, semantic impairment and temporal predominance of atrophy. GRN patients were older at death and more likely to present with non-fluent aphasia. C9orf72 patients alone showed a co-occurrence of ALS. They showed more psychotic symptoms and irrational behaviour, yet were more often reported clinically as socially appropriate and warm. They showed less dietary change than other groups. C9orf72 patients with and without ALS differed only in frequency of psychosis. Greater clinical overlap was observed between GRN and C9orf72 compared to MAPT cases. MAPT cases had tau and GRN and C9orf72, with one exception, TDP-43 pathology. Non-fluent aphasia was linked to TDP subtype A in both GRN and C9orf72 cases and ALS with subtype B. In conclusion, the findings reinforce clinical heterogeneity in FTD and strengthen evidence that genotype influences clinical presentation. Clinical features may inform targeted genetic testing.

Pain and temperature processing in dementia: a clinical and neuroanatomical analysis

Symptoms suggesting altered pain and temperature processing have been described in dementia diseases. Using a semi-structured caregiver questionnaire and MRI voxel-based morphometry in patients with frontotemporal degeneration or Alzheimer’s disease, Fletcher et al. show that these symptoms are underpinned by atrophy in a distributed thalamo-temporo-insular network implicated in somatosensory processing.

Symptoms suggesting altered processing of pain and temperature have been described in dementia diseases and may contribute importantly to clinical phenotypes, particularly in the frontotemporal lobar degeneration spectrum, but the basis for these symptoms has not been characterized in detail. Here we analysed pain and temperature symptoms using a semi-structured caregiver questionnaire recording altered behavioural responsiveness to pain or temperature for a cohort of patients with frontotemporal lobar degeneration (n = 58, 25 female, aged 52–84 years, representing the major clinical syndromes and representative pathogenic mutations in the C9orf72 and MAPT genes) and a comparison cohort of patients with amnestic Alzheimer’s disease (n = 20, eight female, aged 53–74 years). Neuroanatomical associations were assessed using blinded visual rating and voxel-based morphometry of patients’ brain magnetic resonance images. Certain syndromic signatures were identified: pain and temperature symptoms were particularly prevalent in behavioural variant frontotemporal dementia (71% of cases) and semantic dementia (65% of cases) and in association with C9orf72 mutations (6/6 cases), but also developed in Alzheimer’s disease (45% of cases) and progressive non-fluent aphasia (25% of cases). While altered temperature responsiveness was more common than altered pain responsiveness across syndromes, blunted responsiveness to pain and temperature was particularly associated with behavioural variant frontotemporal dementia (40% of symptomatic cases) and heightened responsiveness with semantic dementia (73% of symptomatic cases) and Alzheimer’s disease (78% of symptomatic cases). In the voxel-based morphometry analysis of the frontotemporal lobar degeneration cohort, pain and temperature symptoms were associated with grey matter loss in a right-lateralized network including insula (P < 0.05 corrected for multiple voxel-wise comparisons within the prespecified anatomical region of interest) and anterior temporal cortex (P < 0.001 uncorrected over whole brain) previously implicated in processing homeostatic signals. Pain and temperature symptoms accompanying C9orf72 mutations were specifically associated with posterior thalamic atrophy (P < 0.05 corrected for multiple voxel-wise comparisons within the prespecified anatomical region of interest). Together the findings suggest candidate cognitive and neuroanatomical bases for these salient but under-appreciated phenotypic features of the dementias, with wider implications for the homeostatic pathophysiology and clinical management of neurodegenerative diseases.

C9ORF72 expression and cellular localization over mouse development

INTRODUCTION

A majority of familial frontotemporal lobar dementia and amyotrophic lateral sclerosis cases are associated with a large repeat expansion in a non-coding region of the C9ORF72 gene. Currently, little is known about the normal function and the expression pattern of the C9ORF72 protein. The aims of this study were to characterize the expression pattern and cellular localization of the three reported mouse isoforms of C9orf72, over a developmental time-course in primary cultured cortical neurons and brain tissue from C57BL/6 mice.

RESULTS

We demonstrated that the different isoforms of C9ORF72 at the mRNA and protein level undergo alterations in expression during development and into adulthood. Cellular fractionation and immunofluorescence demonstrated that levels of nuclear and cytoplasmic expression of isoforms changed significantly over the time course. Additionally, immunofluorescence studies showed C9ORF72 labeling as puncta throughout neurons, extending beyond the microtubule cytoskeleton into actin-rich structures such as filopodia and growth cones. Finally, synaptosome preparations demonstrated the presence of C9ORF72 isoform 1 in synaptic-rich fractions from adult mouse brain.

CONCLUSION

In summary, the presence of C9ORF72 as puncta and within synaptic-rich fractions may indicate involvement at the synapse and differential expression of isoforms in nuclei and cytoplasm may suggest distinct roles for the isoforms. Determining the physiological role of C9ORF72 protein may help to determine the role it plays in disease.

Frontotemporal Dysfunction and Dementia in Amyotrophic Lateral Sclerosis

Although amyotrophic lateral sclerosis (ALS) is classically considered a disorder exclusively affecting motor neurons, there is substantial clinical, neuroimaging, and neuropathologic evidence that more than half of patients have an associated syndrome of frontotemporal dysfunction. These syndromes range from frontotemporal dementia to behavioral or cognitive syndromes. Neuroimaging and neuropathologic findings are consistent with frontotemporal lobar degeneration that underpins alterations in network connectivity. Future clinical trials need to be stratified based on the presence or absence of frontotemporal dysfunction on the disease course of ALS.

Phenotypic Heterogeneity of Monogenic Frontotemporal Dementia

Frontotemporal dementia (FTD) is a genetically and pathologically heterogeneous disorder characterized by personality changes, language impairment, and deficits of executive functions associated with frontal and temporal lobe degeneration. Different phenotypes have been defined on the basis of presenting clinical symptoms, i.e., the behavioral variant of FTD, the agrammatic variant of primary progressive aphasia, and the semantic variant of PPA. Some patients have an associated movement disorder, either parkinsonism, as in progressive supranuclear palsy and corticobasal syndrome, or motor neuron disease (FTD-MND). A family history of dementia is found in 40% of cases of FTD and about 10% have a clear autosomal-dominant inheritance. Genetic studies have identified several genes associated with monogenic FTD: microtubule-associated protein tau, progranulin, TAR DNA-binding protein 43, valosin-containing protein, charged multivesicular body protein 2B, fused in sarcoma, and the hexanucleotide repeat expansion in intron 1 of the chromosome 9 open reading frame 72. Patients often present with an extensive phenotypic variability, even among different members of the same kindred carrying an identical disease mutation. The objective of the present work is to review and evaluate available literature data in order to highlight recent advances in clinical, biological, and neuroimaging features of monogenic frontotemporal lobar degeneration and try to identify different mechanisms underlying the extreme phenotypic heterogeneity that characterizes this disease.

Isoform-specific antibodies reveal distinct subcellular localizations of C9orf72 in amyotrophic lateral sclerosis

OBJECTIVE

A noncoding hexanucleotide repeat expansion in C9orf72 is the most common cause of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). It has been reported that the repeat expansion causes a downregulation of C9orf72 transcripts, suggesting that haploinsufficiency may contribute to disease pathogenesis. Two protein isoforms are generated from three alternatively spliced transcripts of C9orf72; a long form (C9-L) and a short form (C9-S), and their function(s) are largely unknown owing to lack of specific antibodies.

METHODS

To investigate C9orf72 protein properties, we developed novel antibodies that recognize either C9-L or C9-S. Multiple techniques, including Western blot, immunohistochemistry, and coimmunoprecipitation, were used to determine the expression levels and subcellular localizations of C9-L and C9-S.

RESULTS

Investigation of expression of C9-L and C9-S demonstrated distinct biochemical profiles, region-specific changes, and distinct subcellular localizations in ALS tissues. In particular, C9-L antibody exhibited a diffuse cytoplasmic staining in neurons and labeled large speckles in cerebellar Purkinje cells. In contrast, C9-S antibody gave very specific labeling of the nuclear membrane in healthy neurons, with apparent relocalization to the plasma membrane of diseased motor neurons in ALS. Coimmunoprecipitation experiments revealed an interaction of the C9-isoforms with both Importin β1 and Ran-GTPase, components of the nuclear pore complex.

INTERPRETATION

Using these antibodies, we have shown that C9orf72 may be involved in nucleocytoplasmic shuttling and this may have relevance to pathophysiology of ALS/FTLD. Our antibodies have provided improved detection of C9orf72 protein isoforms, which will help elucidate its physiological function and role in ALS/FTLD.

Hippocampal Sclerosis of Aging Can Be Segmental: Two Cases and Review of the Literature

Hippocampal sclerosis of aging (HS-Aging) is a neurodegenerative disease that mimics Alzheimer disease (AD) clinically and has a prevalence rivaling AD in advanced age. Whereas clinical biomarkers are not yet optimized, HS-Aging has distinctive pathological features that distinguish it from other diseases with "hippocampal sclerosis" pathology, such as epilepsy, cerebrovascular perturbations, and frontotemporal lobar degeneration. By definition, HS-Aging brains show neuronal cell loss and gliosis in the hippocampal formation out of proportion to AD-type pathology; it is strongly associated with aberrant TDP-43 pathology and arteriolosclerosis. Here, we describe 2 cases of "segmental" HS-Aging in which "sclerosis" in the hippocampus was evident only in a subset of brain sections by hematoxylin and eosin (H&E) stain. In these cases, TDP-43 pathology was more widespread on immunostained sections than the neuronal cell loss and gliosis seen in H&E stains. The 2 patients were cognitively intact at baseline and were tracked longitudinally over a decade using cognitive studies with at least 1 neuroimaging scan. We discuss the relevant HS-Aging literature, which indicates the need for a clearer consensus-based delineation of "hippocampal sclerosis" and TDP-43 pathologies in aged subjects.

Neuropsychiatric effects of neurodegeneration of the medial versus lateral ventral prefrontal cortex in humans

Animal evidence suggests that a brain network involving the medial and rostral ventral prefrontal cortex (PFC) is central for threat response and arousal and a network involving the lateral and caudal PFC plays an important role in reward learning and behavioral control. In this study, we contrasted the neuropsychiatric effects of degeneration of the medial versus lateral PFC in 43 patients with Frontotemporal dementia (FTD) and 11 patients with Corticobasal Syndrome (CBS) using MRI, the Neuropsychiatric Inventory (NPI), and the Sorting, Tower, Twenty Questions, and Fluency tests of the Delis-Kaplan Executive Function System (D-KEFS). Deviations in MRI grey matter volume from 86 age-matched healthy control subjects were determined for the patients using FreeSurfer. Multivariate regression was used to determine which brain areas were associated with specific neuropsychiatric and cognitive symptoms. Decreased grey matter volume of the right medial ventral PFC was associated with increased anxiety and apathy, decreased volume of the right lateral ventral PFC with apathy and inappropriate repetitive behaviors, and of the left lateral ventral PFC with poor performance on the sorting and Twenty Questions task in patients with FTD and CBS. Similar to in animal studies, damage to the medial OFC appears to be associated with a disruption of arousal, and damage to the lateral OFC appears to be associated with deficits in trial-and-error learning and behavioral dysregulation. Studies of brain dysfunction in humans are valuable to bridge animal and human neuropsychiatric research.

Frontotemporal dementia: diagnosis, deficits and management

Frontotemporal dementia (FTD) is a progressive neurologic syndrome with diverse clinical presentations and attendant underlying pathologies. Psychiatric prodrome, neuropsychiatric symptoms and language difficulties are common in FTD, but the diversity of presentation raises unique diagnostic challenges that can significantly impact patient care and counsel for caregivers regarding clinical status and prognosis. While neuropsychiatric symptom measures are helpful, more sensitive assessments delineating the specific behavioral and linguistic deficits accompanying FTD are needed. Comprehensive clinical assessment in combination with evaluation of language, socio-emotional functioning, cognition and neuroimaging aid in accurate and early diagnosis and treatment planning. In what follows, we review each of the FTD syndromes, highlight current research investigating the cognitive, behavioral and socio-emotional deficits observed with this disease, address common diagnostic challenges and summarize best practices associated with management of FTD.

C9orf72-related disorders: expanding the clinical and genetic spectrum of neurodegenerative diseases

Neurodegenerative diseases represent a heterogeneous group of neurological conditions primarily involving dementia, motor neuron disease and movement disorders. They are mostly related to different pathophysiological processes, notably in family forms in which the clinical and genetic heterogeneity are lush. In the last decade, much knowledge has been acumulated about the genetics of neurodegenerative diseases, making it essential in cases of motor neuron disease and frontotemporal dementia the repeat expansions of C9orf72 gene. This review analyzes the main clinical, radiological and genetic aspects of the phenotypes related to the hexanucleotide repeat expansions (GGGGCC) of C9orf72 gene. Future studies will aim to further characterize the neuropsychological, imaging and pathological aspects of the extra-motor features of motor neuron disease, and will help to provide a new classification system that is both clinically and biologically relevant.

The Phenotype of the C9ORF72 Expansion Carriers According to Revised Criteria for bvFTD

Background

The C9ORF72 expansion is one of the most common genetic etiologies observed with behavioural variant frontotemporal dementia (bvFTD). Revised diagnostic criteria for bvFTD (FTDC) were recently introduced but only a few studies have evaluated the accuracy of these criteria.

Objective

The objective of the study was to evaluate the applicability of the FTDC criteria and assess the psychiatric history of these patients.

Methods

The study examined 36 patients carrying the C9ORF72 expansion and suffering from bvFTD (N = 32) or from bvFTD with motor neuron disease (bvFTD-MND, N = 4). Neuropsychological, neuropsychiatric, structural brain imaging and PET/SPECT data were evaluated.

Results

We found 0.75 sensitivity (SD 0.44, 95%CI 0.57–0.87) for possible bvFTD and 0.64 (SD 0.44, 95%CI 0.57–0.87) for probable bvFTD. The sensitivity was even higher in bvFTD patients without MND, i.e., 0.81 for possible bvFTD and 0.69 for probable bvFTD. PET/SPECT was normal in 17.6% of scanned patients with bvFTD. A history of psychiatric symptoms (psychotic and/or mood symptoms) was detected in 61% of cases.

Conclusions

The FTDC possible and probable bvFTD criteria seem to identify the majority of the C9ORF72 expansion carriers with bvFTD, even though they exhibit only a limited number of behavioral criteria but a significant amount of psychiatric symptoms. The presence of a normal PET/SPECT does not exclude the possibility the C9ORF72 associated bvFTD.

Drosha inclusions are new components of dipeptide-repeat protein aggregates in FTLD-TDP and ALS C9orf72 expansion cases

Supplemental digital content is available in the text.

Frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS) are 2 neurodegenerative disorders that share clinical, genetic, and neuropathologic features. The presence of abnormal expansions of GGGGCC repeats (G4C2 repeats) in a noncoding region of the Chromosome 9 open reading frame 72 (C9orf72) gene is the major genetic cause of both FTLD and ALS. Transcribed G4C2 repeats can form nuclear RNA foci and recruit RNA-binding proteins, thereby inhibiting their normal function. Moreover, through a repeat-associated non-ATG translation mechanism, G4C2 repeats translation leads to dipeptide-repeat protein aggregation in the cytoplasm of neurons. Here, we identify Drosha protein as a new component of these dipeptide-repeat aggregates. In C9orf72 mutation cases of FTLD-TDP (c9FTLD-TDP) and ALS (c9ALS), but not in FTLD or ALS cases without C9orf72 mutation, Drosha is mislocalized to form neuronal cytoplasmic inclusions in the hippocampus, frontal cortex, and cerebellum. Further characterization of Drosha-positive neuronal cytoplasmic inclusions in the hippocampus, frontal cortex, and cerebellum revealed colocalization with p62 and ubiquilin-2, 2 pathognomonic signatures of c9FTLD-TDP and c9ALS cases; however, Drosha inclusions rarely colocalized with TDP-43 pathology. We conclude that Drosha may play a unique pathogenic role in the onset or progression of FTLD-TDP/ALS in patients with the C9orf72 mutation.

Sleep disorders and respiratory function in amyotrophic lateral sclerosis

Sleep disorders in amyotrophic lateral sclerosis (ALS) present a significant challenge to the management of patients. Issues include the maintenance of adequate ventilatory status through techniques such as non-invasive ventilation, which has the ability to modulate survival and improve patient quality of life. Here, a multidisciplinary approach to the management of these disorders is reviewed, from concepts about the underlying neurobiological basis, through to current management approaches and future directions for research.

Clinicopathological Study of Patients With C9ORF72-Associated Frontotemporal Dementia Presenting With Delusions

BACKGROUND

Several clinical studies point to a high prevalence of psychotic symptoms in frontotemporal dementia associated with C9ORF72 mutations, but clinicopathological studies addressing the association between C9ORF72 mutations and delusions are lacking.

METHOD

Seventeen patients with pathologically proven frontotemporal lobar degeneration (FTLD) associated with C9ORF72 mutations were identified from Neurodegenerative Disease Brain Bank. Of the 17 cases with C9ORF72 mutation, 4 exhibited well-defined delusions. The clinical history, neurological examination, neuropsychological testing, neuroimaging analysis, and postmortem assessment of the patients with delusions were evaluated and compared with the other cases.

RESULT

The content of the delusions was mixed including persecution, infidelity, and grandiosity. All cases showed parkinsonism; voxel-based morphometry analysis showed greater precuneus atrophy in patients with delusions than those without delusions. All 4 had unclassifiable FTLD with TAR DNA-binding protein inclusions, with characteristics of both type A and type B. Three cases had additional τ pathology and another had α-synuclein pathology.

CONCLUSION

C9ORF72 carriers with well-defined delusions likely associated with additional pathologies and parietal atrophy in neuroimaging. Patients presenting with middle-aged onset of delusions should be screened for C9ORF72 mutations, especially if family history and parkinsonism are present.

Delusion of pregnancy: an unusual symptom in the context of dementia

BACKGROUND

Delusions can complicate practically all brain disorders. They may be dramatic and bizarre. An example is the so-called delusion of pregnancy.

OBJECTIVE

To identify the characteristic of a psychotic symptom, the phenomenon of delusion of pregnancy, in the context of dementia.

METHOD

MEDLINE and Google Scholar searches were conducted for relevant articles, chapters, and books published before 2014. Search terms used included delusion of pregnancy, uncommon presentation, behavioral and psychological symptoms, dementia, Alzheimer's disease, and frontotemporal dementia (FTD). Publications found through this indexed search were reviewed for further relevant references. We included case reports that highlight the relationship and overlap between dementia presenting as schizophrenia-like psychosis and schizophrenia.

RESULTS

Literature on delusion of pregnancy in the course of dementia consists mostly of case reports and small samples of patients.

CONCLUSION

Psychotic phenomena such as delusion of pregnancy may be a feature in some cases of dementia. If this bizarre features of dementia appears as early presentation of FTD whose usual onset is in the presenium, it may be mistaken for schizophrenia.

The neuropsychiatric examination of the young-onset dementias

Young-onset dementias frequently present with prominent behavioral features and constitute a diagnostic challenge. Most cases are secondary to neurodegenerative conditions, including the behavioral variant of frontotemporal dementia, which has overlapping symptoms with many primary psychiatric disorders. This article reviews the differential diagnosis and neuropsychiatric assessment of young-onset dementia, which includes detailed history taking, family history, mental status examination, office-based cognitive tests, and a focused neurologic examination. The clinical examination serves to establish the presence of a dementia and the specific clinical syndrome. Biomarkers can be subsequently integrated in a probabilistic model to determine the most likely neuropathological process.

The frontotemporal dementias

Frontotemporal dementia (FTD) is a heterogeneous group of hereditary and sporadic neurodegenerative disorders affecting frontotemporal areas. FTD, a leading cause of young-onset dementia, is often initially mistaken for primary psychiatric disorders. Based on early and predominant symptoms, different clinical syndromes can be distinguished: the behavioral variant and 2 variants of progressive aphasia; semantic dementia and progressive nonfluent aphasia. Neuropathological classification is based on protein accumulation in the brain. Pathogenic mutations in different genes have been identified. Specific pharmacological treatment is the main research goal. Meanwhile the management must focus on early correct diagnosis, symptom alleviation, caregiver support and educational interventions.

Frontotemporal lobar dementia and amyotrophic lateral sclerosis associated with c9orf72 expansion

An intronic GGGGCC repeat expansion in c9orf72 gene has been identified as the most common genetic cause of frontotemporal lobar dementia (FTLD), amyotrophic lateral sclerosis (ALS) and FTLD-ALS. The discovery of c9orf72 gene has led to important scientific progresses and has considerably changed our clinical practice over the last few years. This paper summarizes the common and less typical phenotypes associated with c9orf72 expansion, the complex pathological pattern characterized by p62/dipeptide repeat aggregates, as well as the pathological mechanisms by which the expansion might produce neurodegeneration implicating loss-of-function, RNA toxicity, RNA-binding protein sequestration and accumulation of dipeptide repeats. We also discuss the recommendations and limits for genetic testing and counseling in clinical practice.

Patterns of microglial cell activation in frontotemporal lobar degeneration

AIMS

Pathological heterogeneity within patients with frontotemporal lobar degeneration (FTLD) in general precludes the accurate assignment of diagnostic subtype in life. The aim of this study was to assess the extent of microglial cell activation in FTLD in order to determine whether it might be possible to employ this as a diagnostic marker in vivo using PET ligand [11C](R)-PK11195 in order to differentiate cases of FTLD according to histological subtype.

METHODS

The distribution and extent of microglial cell activation was assessed semi-quantitatively in cortical grey and subcortical white matter of CD68 immunostained sections of frontal and temporal cortex from 78 pathologically confirmed cases of FTLD, 13 of Alzheimer's disease (AD) and 13 controls.

RESULTS

Significantly higher levels of microglial cell activation than controls occurred in all four regions in FTLD, and in three of the four regions in AD. Microglial activation was greater in frontal subcortical white matter in FTLD than AD, whereas it was higher in temporal cortical grey matter in AD than FTLD. Microglial cell activation was significantly higher in temporal subcortical white matter in FTLD-MAPT than in other genetic (GRN, C9ORF72) or non-genetic forms of FTLD.

CONCLUSIONS

The present study suggests that high levels of microglial cell involvement in temporal lobe (subcortical white matter) might serve as a marker of inherited FTLD associated with intronic mutations in MAPT, with a relatively intense signal in this region in PET studies using [11C](R)-PK11195 as microglial cell marker could indicate the presence of MAPT mutation in vivo.

Accumulation of dipeptide repeat proteins predates that of TDP-43 in frontotemporal lobar degeneration associated with hexanucleotide repeat expansions in C9ORF72 gene

AIMS

Frontotemporal lobar degeneration (FTLD) and motor neurone disease are linked by the possession of a hexanucleotide repeat expansion in C9ORF72, and both show neuronal cytoplasmic inclusions within cerebellar and hippocampal neurones which are TDP-43 negative but immunoreactive for p62 and dipeptide repeat proteins (DPR), these being generated by a non-ATG RAN translation of the expanded region of the gene.

METHODS

Twenty-two cases of FTLD from Newcastle were analysed for an expansion in C9ORF72 by repeat primed PCR and Southern blot. Detailed case note analysis was performed, and blinded retrospective clinical impressions were achieved by review of clinical histories. Sections from all major brain regions were immunostained for TDP-43, p62 and DPR. The extent of TDP-43 and DPR pathology in expansion bearers was compared with that in 13 other previously identified cases from the Manchester Brain Bank with established disease.

RESULTS

Three Newcastle patients bearing an expansion in C9ORF72 were identified. These three patients died prematurely, two from bronchopneumonia within 10 months and 3 years of onset, and one from myocardial infarction 3 years after onset. In all three, DPR were plentiful throughout all cerebral cortical regions, hippocampus and cerebellum, but TDP-43 pathological changes were sparse. The severity of DPR pathological changes in these three patients was similar to that in the Manchester series, although the extent of TDP-43 pathology was significantly less.

CONCLUSION

Widespread accumulation of DPR within nerve cells may occur much earlier than that of TDP-43 in patients with FTLD bearing expansion in C9ORF72.

Psychotic symptoms in frontotemporal dementia: a diagnostic dilemma?

BACKGROUND

Frontotemporal dementia (FTD) constitutes a spectrum of neurodegenerative disorders associated with degeneration of, predominantly, the frontal and temporal lobes. The clinical heterogeneity is evident, and early diagnosis is a challenge. The primary objectives were to characterize psychotic symptoms, initial clinical diagnoses and family history in neuropathologically verified FTD-patients and to analyze possible correlations with different neuropathological findings.

METHODS

The medical records of 97 consecutive patients with a neuropathological diagnosis of frontotemporal lobar degeneration (FTLD) were reevaluated. Psychotic symptoms (hallucinations, delusions, paranoid ideas), initial diagnosis and family history for psychiatric disorders were analyzed.

RESULTS

Psychotic symptoms were present in 31 patients (32%). There were no significant differences in age at onset, disease duration or gender between patients with and without psychotic symptoms. Paranoid ideas were seen in 20.6%, and hallucinations and delusions in 17.5% in equal measure. Apart from a strong correlation between psychotic symptoms and predominantly right-sided brain degeneration, the majority of patients (77.4%) were tau-negative. Only 14.4% of the patients were initially diagnosed as FTD, while other types of dementia were seen in 34%, other psychiatric disorders in 42%, and 9.2% with other cognitive/neurological disorders. The patients who were initially diagnosed with a psychiatric disorder were significantly younger than the patients with other initial clinical diagnoses. A positive heredity for dementia or other psychiatric disorder was seen in 42% and 26% of the patients respectively.

CONCLUSIONS

Psychotic symptoms, not covered by current diagnostic criteria, are common and may lead to clinical misdiagnosis in FTD.

Frontotemporal lobar degeneration: defining phenotypic diversity through personalized medicine

Frontotemporal lobar degeneration (FTLD) comprises two main classes of neurodegenerative diseases characterized by neuronal/glial proteinaceous inclusions (i.e., proteinopathies) including tauopathies (i.e., FTLD-Tau) and TDP-43 proteinopathies (i.e., FTLD-TDP) while other very rare forms of FTLD are known such as FTLD with FUS pathology (FTLD-FUS). This review focuses mainly on FTLD-Tau and FLTD-TDP, which may present as several clinical syndromes: a behavioral/dysexecutive syndrome (behavioral variant frontotemporal dementia); language disorders (primary progressive aphasia variants); and motor disorders (amyotrophic lateral sclerosis, corticobasal syndrome, progressive supranuclear palsy syndrome). There is considerable heterogeneity in clinical presentations of underlying neuropathology and current clinical criteria do not reliably predict underlying proteinopathies ante-mortem. In contrast, molecular etiologies of hereditary FTLD are consistently associated with specific proteinopathies. These include MAPT mutations with FTLD-Tau and GRN, C9orf72, VCP and TARDBP with FTLD-TDP. The last decade has seen a rapid expansion in our knowledge of the molecular pathologies associated with this clinically and neuropathologically heterogeneous group of FTLD diseases. Moreover, in view of current limitations to reliably diagnose specific FTLD neuropathologies prior to autopsy, we summarize the current state of the science in FTLD biomarker research including neuroimaging, biofluid and genetic analyses. We propose that combining several of these biomarker modalities will improve diagnostic specificity in FTLD through a personalized medicine approach. The goals of these efforts are to enhance power for clinical trials focused on slowing or preventing progression of spread of tau, TDP-43 and other FTLD-associated pathologies and work toward the goal of defining clinical endophenotypes of FTD.

The Spectrum of C9orf72-mediated Neurodegeneration and Amyotrophic Lateral Sclerosis

The discovery that a hexanucleotide repeat expansion in C9orf72 is the most numerous genetic variant of both amyotrophic lateral sclerosis and frontotemporal dementia has opened a rapidly growing field, which may provide long hoped for advances in the understanding and treatment of these devastating diseases. In this review we describe the various phenotypes, clinical and pathological, associated with expansion of C9orf72, which go beyond amyotrophic lateral sclerosis and frontotemporal dementia to include neurodegeneration more broadly. Next we take a step back and summarize the current understanding of the C9orf72 expansion and its protein products at a molecular level. Three mechanisms are prominent: toxicity mediated directly by RNA transcribed from the repeat; toxicity mediated by dipeptide repeat proteins translated from the repeat sequence; and haploinsufficiency resulting from reduced transcription of the C9orf72 exonic sequence. A series of exciting advances have recently described how dipeptide repeat proteins might interfere with the normal role of the nucleolus in maturation of RNA binding proteins and in production of ribosomes. Importantly, these mechanisms are unlikely to be mutually exclusive. We draw attention to the fact that clinical and pathological similarities to other genetic variants without a repeat expansion must not be overlooked in ascribing a pathogenic mechanism to C9orf72-disease. Finally, with a view to impact on patient care, we discuss current practice with respect to genetic screening in patients with and without a family history of disease, and the most promising developments towards therapy that have been reported to date.

A network of RNA and protein interactions in Fronto Temporal Dementia

Frontotemporal dementia (FTD) is a neurodegenerative disorder characterized by degeneration of the fronto temporal lobes and abnormal protein inclusions. It exhibits a broad clinicopathological spectrum and has been linked to mutations in seven different genes. We will provide a picture, which connects the products of these genes, albeit diverse in nature and function, in a network. Despite the paucity of information available for some of these genes, we believe that RNA processing and post-transcriptional regulation of gene expression might constitute a common theme in the network. Recent studies have unraveled the role of mutations affecting the functions of RNA binding proteins and regulation of microRNAs. This review will combine all the recent findings on genes involved in the pathogenesis of FTD, highlighting the importance of a common network of interactions in order to study and decipher the heterogeneous clinical manifestations associated with FTD. This approach could be helpful for the research of potential therapeutic strategies.

Pathology in primary progressive aphasia syndromes

'Primary progressive aphasia' (PPA) refers to core linguistic disorders caused by neurodegenerative disease. Three main PPA variants are recognized: nonfluent/agrammatic, semantic and logopenic. Correctly classifying patients during life according to the underlying histopathology will become increasingly important as cause-specific treatments become available. This article reviews clinical and histopathological studies of PPA, with particular reference to updated PPA classifications. Currently, one-to-one relationships do not exist within PPA subtypes. The semantic variant has the best correspondence between the clinical syndrome and the underlying pathological cause and the logopenic variant the worst correspondence. The use of future biomarkers should facilitate accurate clinicopathological correlation of patients during life.

Clinical and molecular delineation of duplication 9p24.3q21.11 in a patient with psychotic behavior

This article describes a 19-year-old female with mild facial dysmorphism, asociality, decreased school performance, and psychotic behavior in whom the karyotype showed an extra-chromosomal marker characterized as 9p24.3-9q21.11 duplication by array-CGH. The 69Mbp duplicated segment in this patient includes the critical 9p duplication syndrome region, the GLDC and C90RF72 genes associated with psychotic behavior and other conduct disorders, and a potential locus for autism.

Slowly progressive frontotemporal lobar degeneration caused by the C9ORF72 repeat expansion: a 20-year follow-up study

A hexanucleotide expansion in chromosome 9 open-reading frame 72 (C9ORF72) has been found to be a major cause of frontotemporal lobar degeneration (FTLD). We describe a 20-year follow-up of a unique case with very slowly progressive FTLD caused by the C9ORF72 repeat expansion. In serial neuropsychological examinations, the patient's cognitive decline was exceptionally slow and after 20 years the patient still was mainly independent in activities of daily living. Our case indicates that there is great individual variation in the progression and duration of C9ORF72-associated FTLD, and also language variants or mixed phenotypes may be present.

Binge eating and fast cognitive worsening in an early-onset bvFTD patient carrying C9ORF72 expansion

An expanded hexanucleotide (GGGGCC) repeat in a non-coding promoter region of open reading frame 72 of chromosome 9 (C9ORF72) has been recently identified as a major cause of familial and sporadic frontotemporal lobar degeneration. We describe the clinical picture of a 64-year-old woman carrying the hexanucleotide repeat expansion, who developed a sporadic early-onset form of behavioral variant frontotemporal dementia characterized by the occurrence of uncommon behavioral manifestations such as binge eating disturbance and by a rapid worsening of cognitive abilities. Our report confirms previous studies asserting that C9ORF72 repeats may sustain heterogeneous clinical syndromes.

Hypermethylation of repeat expanded C9orf72 is a clinical and molecular disease modifier

C9orf72 promoter hypermethylation inhibits the accumulation of pathologies which have been postulated to be neurotoxic. We tested here whether C9orf72 hypermethylation is associated with prolonged disease in C9orf72 mutation carriers. C9orf72 methylation was quantified from brain or blood using methylation-sensitive restriction enzyme digest-qPCR in a cross-sectional cohort of 118 C9orf72 repeat expansion carriers and 19 non-carrier family members. Multivariate regression models were used to determine whether C9orf72 hypermethylation was associated with age at onset, disease duration, age at death, or hexanucleotide repeat expansion size. Permutation analysis was performed to determine whether C9orf72 methylation is heritable. We observed a high correlation between C9orf72 methylation across tissues including cerebellum, frontal cortex, spinal cord and peripheral blood. While C9orf72 methylation was not significantly different between ALS and FTD and did not predict age at onset, brain and blood C9orf72 hypermethylation was associated with later age at death in FTD (brain: β = 0.18, p = 0.006; blood: β = 0.15, p < 0.001), and blood C9orf72 hypermethylation was associated with longer disease duration in FTD (β = 0.03, p = 0.007). Furthermore, C9orf72 hypermethylation was associated with smaller hexanucleotide repeat length (β = -16.69, p = 0.033). Finally, analysis of pedigrees with multiple mutation carriers demonstrated a significant association between C9orf72 methylation and family relatedness (p < 0.0001). C9orf72 hypermethylation is associated with prolonged disease in C9orf72 repeat expansion carriers with FTD. The attenuated clinical phenotype associated with C9orf72 hypermethylation suggests that slower clinical progression in FTD is associated with reduced expression of mutant C9orf72. These results support the hypothesis that expression of the hexanucleotide repeat expansion is associated with a toxic gain of function.

Clinical heterogeneity of the C9orf72 genetic mutation in frontotemporal dementia

The C9orf72 genetic mutation represents the most common cause of familial frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). Studies over the last 2 years have revealed a number of key features of this mutation in the fields of clinical neurology, imaging, pathology, and genetics. Despite these efforts, the clinical phenotype appears to extend beyond FTD and ALS into the realm of psychiatric disease, and while highly variable survival rates have been reported, the clinical course of carriers remains relatively unexplored. This report describes two contrasting C9orf72 cases, one with a protracted indolent course dominated by neuropsychiatric features and the other with a rapidly progressive dementia. In both cases, initial structural brain imaging was relatively normal.

Frontotemporal dementia: a bridge between dementia and neuromuscular disease

The concept that frontotemporal dementia (FTD) is a purely cortical dementia has largely been refuted by the recognition of its close association with motor neuron disease, and the identification of transactive response DNA-binding protein 43 (TDP-43) as a major pathological substrate underlying both diseases. Genetic findings have transformed this field and revealed connections between disorders that were previous thought clinically unrelated. The discovery that the C9ORF72 locus is responsible for the majority of hereditary FTD, amyotrophic lateral sclerosis (ALS), and FTD-ALS cases and the understanding that repeat-containing RNA plays a crucial role in pathogenesis of both disorders has paved the way for the development of potential biomarkers and therapeutic targets for these devastating diseases. In this review, we summarize the historical aspects leading up to our current understanding of the genetic, clinical, and neuropathological overlap between FTD and ALS, and include brief discussions on chronic traumatic encephalopathy (CTE), given its association with TDP-43 pathology, its associated increased dementia risk, and reports of ALS in CTE patients. In addition, we describe other genetic associations between dementia and neuromuscular disease, such as inclusion body myositis with Paget's disease and FTD.