Neuropsychiatric studies in a family with presenile dementia different from Alzheimer and Pick disease

Six generations of CHMP2B-mediated Frontotemporal Dementia: Clinical features, predictive testing, progression, and survival

OBJECTIVES

Chromosome 3-linked frontotemporal dementia (FTD-3) is caused by a c.532-1G > C mutation in the CHMP2B gene. It is extensively studied in a Danish family comprising one of the largest families with an autosomal dominantly inherited frontotemporal dementia (FTD). This retrospective cohort study utilizes demographics to identify risk factors for onset, progression, life expectancy, and death in CHMP2B-mediated FTD. The pedigree of 528 individuals in six generations is provided, and clinical descriptions are presented. Choices of genetic testing are evaluated.

MATERIALS AND METHODS

Demographic and lifestyle factors were assessed in survival analysis in all identified CHMP2B mutation carriers (44 clinically affected FTD-3 patients and 16 presymptomatic CHMP2B mutation carriers). Predictors of onset and progression included sex, parental disease course, education, and vascular risk factors. Life expectancy was established by matching CHMP2B mutation carriers with average life expectancies in Denmark.

RESULTS

Disease course was not correlated to parental disease course and seemed unmodified by lifestyle factors. Diagnosis was recognized at an earlier age in members with higher levels of education, probably reflecting an early dysexecutive syndrome, unmasked earlier in people with higher work-related requirements. Carriers of the CHMP2B mutation had a significant reduction in life expectancy of 13 years. Predictive genetic testing was chosen by 20% of at-risk family members.

CONCLUSIONS

CHMP2B-mediated FTD is substantiated as an autosomal dominantly inherited disease of complete penetrance. The clinical phenotype is a behavioral variant FTD. The disease course is unpredictable, and life expectancy is reduced. The findings may be applicable to other genetic FTD subtypes.

Cortical Frontoparietal Network Dysfunction in CHMP2B-Frontotemporal Dementia

A rare cause of inherited frontotemporal dementia (FTD) is a mutation in the CHMP2B gene on chromosome 3 leading to the autosomal dominantly inherited FTD (CHMP2B-FTD). Since CHMP2B-FTD is clinically well-characterized, and patients show a distinct pattern of executive dysfunction, the condition offers possible insight in the early electroencephalographic (EEG) changes in the cortical networks. Specifically, EEG microstate analysis parses the EEG signals into topographies believed to represent discrete network activations. We investigated the EEG dynamics in patients with symptomatic CHMP2B-FTD (n = 5) as well as pre-symptomatic mutation carriers (n = 5) compared to non-carrier family members (n = 6). The data was parsed into four archetypal microstates and global power was calculated. A trend was found for lower occurrence in microstate D in CHMP2B-FTD (p-value = 0.177, F-value = 2.036). Patients with recent symptom onset (<1 year) showed an increased duration of microstate D, whereas patients who had been symptomatic for longer periods (>2 years) showed decreased duration. Patients with CHMP2B-FTD present with executive dysfunction, and microstate D has previously been shown to be associated with the fronto-parietal network. The biphasic pattern may represent the pathophysiological changes in brain dynamics during neurodegeneration, which may apply to other neurodegenerative diseases.

Lessons learned from CHMP2B, implications for frontotemporal dementia and amyotrophic lateral sclerosis

Frontotemporal dementia (FTD) and Amyotrophic Lateral Sclerosis (ALS) are two neurodegenerative diseases with clinical, genetic and pathological overlap. As such, they are commonly regarded as a single spectrum disorder, with pure FTD and pure ALS representing distinct ends of a continuum. Dysfunctional endo-lysosomal and autophagic trafficking, leading to impaired proteostasis is common across the FTD-ALS spectrum. These pathways are, in part, mediated by CHMP2B, a protein that coordinates membrane scission events as a core component of the ESCRT machinery. Here we review how ALS and FTD disease causing mutations in CHMP2B have greatly contributed to our understanding of how endosomal-lysosomal and autophagic dysfunction contribute to neurodegeneration, and how in vitro and in vivo models have helped elucidate novel candidates for potential therapeutic intervention with implications across the FTD-ALS spectrum.

Frontotemporal lobar degeneration: Pathogenesis, pathology and pathways to phenotype

Frontotemporal Lobar Degeneration (FTLD) is a clinically, pathologically and genetically heterogeneous group of disorders that affect principally the frontal and temporal lobes of the brain. There are three major associated clinical syndromes, behavioral variant frontotemporal dementia (bvFTD), semantic dementia (SD) and progressive non-fluent aphasia (PNFA); three principal histologies, involving tau, TDP-43 and FUS proteins; and mutations in three major genes, MAPT, GRN and C9orf72, along with several other less common gene mutations. All three clinical syndromes can exist separately or in combination with Amyotrophic Lateral Sclerosis (ALS). SD is exclusively a TDP-43 proteinopathy, and PNFA may be so, with both showing tight clinical, histological and genetic inter-relationships. bvFTD is more of a challenge with overlapping histological and genetic features, involvement of any of the three aggregating proteins, and changes in any of the three major genes. However, when ALS is present, all cases show a clear histological phenotype with TDP-43 aggregated proteins, and familial forms are associated with expansions in C9orf72. TDP-43 and FUS are nuclear carrier proteins involved in the regulation of RNA metabolism, whereas tau protein - the product of MAPT - is responsible for the assembly/disassembly of microtubules, which are vital for intracellular transport. Mutations in TDP-43 and FUS genes are linked to clinical ALS rather than FTLD (with or without ALS), suggesting that clinical ALS may be a disorder of RNA metabolism. Conversely, the protein products of GRN and C9orf72, along with those of the other minor genes, appear to form part of the cellular protein degradation machinery. It is possible therefore that FTLD is a reflection of dysfunction within lysosomal/proteasomal systems resulting in failure to remove potentially neurotoxic (TDP-43 and tau) aggregates, which ultimately overwhelm capacity to function. Spread of aggregates along distinct pathways may account for the different clinical phenotypes, and patterns of progression of disease.

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.

Autophagy in dementias

Dementias are a varied group of disorders typically associated with memory loss, impaired judgment and/or language and by symptoms affecting other cognitive and social abilities to a degree that interferes with daily functioning. Alzheimer's disease (AD) is the most common cause of a progressive dementia, followed by dementia with Lewy bodies (DLB), frontotemporal dementia (FTD), (VaD) and HIV-associated neurocognitive disorders (HAND). The pathogenesis of this group of disorders has been linked to the abnormal accumulation of proteins in the brains of affected individuals, which in turn has been related to deficits in protein clearance. Autophagy is a key cellular protein clearance pathway with proteolytic cleavage and degradation via the ubiquitin-proteasome pathway representing another important clearance mechanism. Alterations in the levels of autophagy and the proteins associated with the autophagocytic pathway have been reported in various types of dementias. This review will examine recent literature across these disorders and highlight a common theme of altered autophagy across the spectrum of the dementias.

Clinical aspects of familial forms of frontotemporal dementia associated with parkinsonism

Frontotemporal dementia is the second most common dementia among people under the age of 65. Fifty percent of affected patients have an associated family history. Several pathogenic genes have been identified for frontotemporal dementia associated with parkinsonism, including microtubule-associated protein tau, progranulin, and chromatin modifying protein 2B, and fused in sarcoma. It has also been reported that frontotemporal dementia associated with parkinsonism can be linked to chromosome 9p. In addition, there are families with frontotemporal dementia associated with a parkinsonian phenotype but unknown genetic status. Some of these kindreds have been diagnosed clinically as familial progressive supranuclear palsy, hereditary diffuse leukoencephalopathy with axonal spheroids, "overlap" syndrome, and others. Clinical presentation of frontotemporal dementia associated with parkinsonism is variable at age of symptomatic disease onset, disease duration, symptoms, and their occurrence during the disease course. Clinically, it is often difficult to sort out the different genetic forms of frontotemporal dementia associated with parkinsonism. However, with available clinical genetic testing for known genes, the precise diagnosis can be accomplished in some cases.

Genetic causes of frontotemporal degeneration

The purpose of this review is to provide a comprehensive update on the genetic causes of frontotemporal lobar degeneration (FTLD). Approximately 40% to 50% of patients diagnosed with FTLD have a family history of a ''related disorder,'' whereas 10% to 40% have an autosomal dominant family history for the disease. At this time, mutations occurring in 2 independent genes located on the same chromosome (MAPT and GRN) have been shown to cause the majority of cases of autosomal dominant FTLD. Specific genetic, molecular, pathological, and phenotypic variations associated with each of these gene mutations are discussed, as well as markers that may help differentiate the 2. In addition, 3 relatively rare, additional genes known to cause familial FTLD are examined in brief. Lastly, genetic counseling issues which may be important to the community clinician are discussed.

Frontotemporal dementia linked to chromosome 3 (FTD-3)--current concepts and the detection of a previously unknown branch of the Danish FTD-3 family

BACKGROUND

Among patients with onset of dementia below the age of 65 years, frontotemporal dementia (FTD) is the second most prevalent cause, secondary only to Alzheimer's disease. Recent advances in understanding the heterogeneous genetic background for different clinical and neuropathological entities of FTD have involved identification of several new causative genes.

METHODS AND RESULTS

We report the finding of a truncating mutation in the CHMP2B gene (c.532-1G>C) in a patient with early onset dementia. The patient was previously not known to be related to the single Danish pedigree known to have this specific mutation. Subsequently he has turned out to represent a new branch of the family with several affected individuals.

DISCUSSION

Our findings highlight the need for awareness of the CHMP2B mutation and associated clinical phenotype for neurological assessment in Denmark. Further, we discuss recent advances and current concepts in the understanding of CHMP2B-related dementia.

Sequence analysis of all identified open reading frames on the frontal temporal dementia haplotype on chromosome 3 fails to identify unique coding variants except in CHMP2B

A segregating splice site mutation in the CHMP2B gene has been shown in the single Danish family which has been reported to show linkage between dementia and chromosome 3 markers. Despite extensive analysis, no other segregating mutations have been found in other kindreds, although some point variants have been found both in sporadic cases and in controls. We recently found a premature stop codon in a person without dementia and this led us to investigate whether the splice site mutation in the Danish kindred did not explain the disease, but rather was hitchhiking on the segregating disease haplotype. We determined to test this possibility by sequencing every other gene on the haplotype in a case from the kindred. We did not find any other unique variants. The implications of these findings for the likely mode of pathogenesis of frontal temporal dementia are discussed.

Genetic variability in CHMP2B and frontotemporal dementia

A nonsense/protein chain-terminating mutation in the CHMP2B gene has recently been reported as a cause of frontotemporal dementia (FTD) in the single large family known to show linkage to chromosome 3. Screening for mutations in this gene in a large series of FTD families and individual patients led to the identification of a protein-truncating mutation in 2 unaffected members of an Afrikaner family with FTD, but not in their affected relatives. The putative pathogenicity of CHMP2B mutations for dementia is discussed.

The neuropathology of frontotemporal lobar degeneration with respect to the cytological and biochemical characteristics of tau protein

Pathological examinations, using a panel of tau and other antibodies, were performed on the brains from 55 consecutively acquired cases of frontotemporal lobar degeneration (FTLD). Clinically, these comprised 31 cases of frontotemporal dementia (FTD), 10 cases of motor neurone disease inclusion dementia (MNDID), seven cases of progressive aphasia (PA), four cases of semantic dementia (SD) and three cases of progressive apraxia (PAX). Tau pathology, in the form of neurofibrillary tangles (NFTs) and glial cell tangles, was present in six cases of FTD with parkinsonism linked to chromosome 17, five of these cases resulting from +16 splice-site mutation and one from +13 mutation in the tau gene. The insoluble tau proteins were comprised mostly of four-repeat (4-R) isoforms. Eight other cases of FTD, one of PA and all three cases of PAX showed tau-positive inclusions (Pick bodies) and swollen cells (Pick cells), characteristic of Pick's disease. In these cases, the insoluble tau proteins were present in most instances as three-repeat (3-R) tau isoforms, although two cases with a mixture of 3-R and 4-R isoforms were seen. One other case of FTD showed an unusual pathology characterized by massive extracellular deposition of tau protein, composed of 4-R tau isoforms, within white matter without neuronal or glial cell inclusions. However, 33 (60%) of 55 FTLD cases showed no tau pathology in the brain, except for the rare NFTs, composed of a mix of 3-R and 4-R isoforms, in some of the more elderly cases. Of these 33 cases, 13 had FTD, 10 had MNDID, six had PA and four had SD. The pathological changes present were those of a superficial cortical laminar microvacuolation with mild subpial and subcortical gliosis; the 10 MNDID cases had ubiquitin-positive inclusions in the cerebral cortex and hippocampus. These 33 nontau FTLD cases, along with five Alzheimer's disease (AD) and six Huntington's disease (HD) cases with severe pathology, showed a variable loss of soluble tau proteins, broadly comparable with the extent of neuronal loss from the cortex and loss of the intracortical perikaryal marker, NeuN, but unrelated to proteins within afferent projection fibres such as neurofilament and alpha-synuclein. Levels of tau mRNA were decreased in parallel in the tau-negative FTLD cases and in the severe AD and HD cases. Hence, the loss of tau from these 33 nontau FTLD cases is just one aspect of a neurodegenerative process that destroys many components of the nerve cell machinery and does not represent a specific disordering of the cell's ability to form tau proteins or incorporate these into microtubules.

Tau Protein in Frontotemporal Dementia Linked to Chromosome 3 (FTD-3)

Recent work on frontotemporal dementia (FTD) has revealed the existence of at least 3 genetically distinct groups of inherited FTD: FTDP-17, FTD and motor neuron disease linked to chromosome 9, and FTD linked to chromosome 3 (FTD-3). Tau, on chromosome 17, is the only gene where mutations have been identified and its involvement in FTD has been firmly established. The genes on chromosome 9 and chromosome 3 associated with familial forms of FTD remain to be identified. Abnormal aggregates of tau protein characterize the brain lesions of FTDP-17 patients and ubiquitin inclusions have been found in FTD with motor neuron disease linked to chromosome 9. In this study the frontal cortices of 3 FTD-3 patients from a unique Danish family were examined for characteristic neuropathological features. In these brains tau inclusions were present in neurons and some glial cells in the absence of beta-amyloid deposits. The presence of filamentous tau protein in the frontal cortex of these patients suggests a possible link between tau and the genetic defect present on chromosome 3 and associated with FTD-3, although the limited amount of tau deposits observed makes it difficult to define this as a tauopathy.

Dementia of frontal type and dementias with subcortical gliosis

The group of Frontotemporal dementias (FTD) is composed of non-Alzheimer forms of dementia characterized clinically by behavioural and personality change leading to apathy and mutism. The disorder is associated with a progressive atrophy of the frontal, anterior temporal and anterior parietal lobes of the brain with several types of underlying pathology. One type (frontal lobe degeneration) is characterized by a microvacuolar degeneration of the outer cortical laminae along with a mild and mainly subpial gliosis and a loss of nerve cells, mostly from layers II and III. Another type shows transcortical tissue cavitation and florid gliosis with neuronal degeneration characterized by the presence of tau and ubiquitin positive inclusion bodies and alpha beta-crystallin-positive ballooned neurones: such changes have been termed 'Pick-type histology', and form the basis for the modern definition of 'Pick's disease'. The aetiological relationship between these two histological types is presently unknown. Both histologies can be differently distributed topographically throughout the brain to produce syndromes of progressive language disorder, when affecting bitemporal lobes or the left hemisphere preferentially, or progressive apraxia when parietal and motor regions are involved. Either pathology can be combined with or overlaps with that of classical motor neurone disease to produce motor neurone disease dementia. The underlying cause of FTD is unknown but genetic factors are strongly implicated. About half of cases show a previous family history of a similar disorder. In several families bearing a FTD clinical and pathological phenotype, linkage to chromosome 17 has been established but the pathology of this group appears distinctive and its relation to other forms of FTD awaits further elucidation. It is still possible that the many clinical and pathological variants of FTD may reflect different phenotypic expressions of a particular genetic change(s) at a single locus on this chromosome.

A family with autosomal dominant, non-Alzheimer's presenile dementia

OBJECTIVE

A rare family pedigree is described with a multigenerational history of an early onset, non-Alzheimer's dementia consistent with autosomal dominant inheritance. Information on five generations, with 26 suspected or proven cases of dementia, are presented.

METHOD

Previous work on the family was collated and verified. The pedigree was updated. Thirty-three family members agreed to be interviewed for the present study. Standardised clinical information was obtained using the Cambridge Mental Disorders of the Elderly Examination (CAMDEX) National Adult Reading Test (NART), vocabulary and digit substitution subscales of the Wechster adult intelligence scale-revised edition (WARS-R). Abbot samples were taken for biochemical and genetic analysis.

RESULTS

Fifteen males and 11 females have been affected. The age of onset of dementia in those for whom data were available (n = 12) ranged from 39 to 64 years with a mean of 53 years. The duration of illness ranged from 4 to 14 years and the age at death ranged from 49 to 69 years (mean 62 years). Autopsy data exist for nine cases. In one case the neuropathology was consistent with Alzheimer's disease. In two cases the diagnosis of Pick's disease was made on the basis of frontal or frontal/temporal lobe atrophy without Pick bodies or cells. One case diagnosed as Pick's disease had frontal/temporal lobe atrophy with cells resembling Pick's bodies. In the five remaining cases there were no distinctive neuropathological features to differentiate the type of dementia.

CONCLUSIONS

The importance of recognising familial dementia, collating information on multiple generations and prospectively collecting standardised data is discussed.

Frontotemporal Dementias: A New Clinical Syndrome?

The frontal lobe dementias (FLDs) are a group of disorders that have received considerable attention recently. Diagnosis is based on the presence of behavioral and cognitive disturbances associated pathologically with focal neuronal loss and gliosis without any inclusion bodies. Reports describing FLD differ regarding its clinical features, cognitive disturbances, and neurophysiological and neuropathological characteristics. The authors review the existing literature on FLD and emphasize the similarities and differences between reports. The heterogeneity of this condition as currently described is addressed, and arguments supporting the concept of FLD as a syndrome more appropriately called frontotemporal dementia are discussed. The authors present the development of a more rigid clinical definition of this syndrome using well-defined criteria as the first step toward understanding better this group of disorders.

Genetic characterization of a familial non-specific dementia originating in Jutland, Denmark

Dementias with non-specific pathological changes are a relatively common but under diagnosed form of presenile dementia. A high proportion of reported cases are familial. We report on molecular genetic findings in the largest known pedigree with this syndrome. We have excluded the mutations known to cause familial prion disease, APP-linked familial Alzheimer's disease and candidate regions for Huntington's disease, other forms of Alzheimer's disease and motor neuron disease. We have demonstrated that familial non-specific dementia is a novel genetic dementia.

Genetic characterization of a novel familial dementia

Clinical and neuropathologic findings from a Danish family in which a dementing illness is segregating as an apparent autosomal dominant disorder were previously described (Gydesen et al. 1987). We present here genetic findings from this family in which linkage analysis has excluded Huntington's disease and chromosome 21-encoded Alzheimer's disease. None of the known prion mutations has been detected in affected individuals from this family. However, linkage analysis with the prion gene has been uninformative. This family probably represents a novel genetic dementia.