New developments in frontotemporal dementia and parkinsonism linked to chromosome 17

PURPOSE OF REVIEW: The identification of tau mutations in frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) has revealed invaluable information regarding the role of the tau protein in neurodegenerative disease. Over the past year several new mutations have been identified, and experimental studies have provided further insight into the mechanism of neurodegeneration due to tau mutations and possible interactions with amyloid pathology. RECENT FINDINGS: Extensive clinical and pathological variation is seen in patients with different types of mutation, as well as in patients with the same mutation. Mutations may be found in patients with frontotemporal dementia (FTD), parkinsonism, progressive supranuclear palsy and corticobasal degeneration, justifying mutation analysis in familial cases of these disorders. Genetic heterogeneity exists in frontotemporal dementia, because a number of FTDP-17 families have neither tau mutations nor tau pathology. Genetic linkage has been found in familial FTD (chromosome 3), FTD with amyotrophic lateral sclerosis (9q21-q22), and FTD with inclusion body myopathy (9q13.3-p12). Tau deposits may consist of mainly mutated protein, or of mutated and wild-type protein in equal amounts, depending on the mutation. Recent animal studies show that amyloid-beta deposition may accelerate formation of neurofibrillary tangles. SUMMARY: Hopefully, the identification of responsible genetic defects and associated proteins will be helpful in improving our understanding of the role of the tau protein in the common neurodegenerative process of frontotemporal degeneration.     

Microtubule associated protein (tau) gene variability in patients with frontotemporal dementia

Frontotemporal dementia represents up to 10% of all dementias and is, next to Alzheimer's disease and Lewy body disease, the third most common cause of degenerative dementia. The term "frontotemporal dementia" covers a range of conditions, including Pick's disease, frontal lobe degeneration and dementia associated with motor neurone disease. Neuropathologically FTD is characterised by atrophy of the frontal and temporal lobes of the cerebral cortex, often with additional subcortical changes. Both familial and more frequently sporadic forms of FTD can be recognised. Recently, mutations in the microtubule-associated protein (tau) gene have been found in families with frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17). The identification of mutations in the tau gene indicates that the protein plays a central role in the process of neurodegeneration. Epidemiology of frontotemporal dementias in Poland remains still unknown. A prevalence of tau mutations among Polish patients has not been established yet. Here, we report results of a mutational analysis of the tau gene among Polish FTD patients. No pathogenic mutation was found in the analysed sample. The study confirmed that the frequency of tau mutations is very low and depends strongly on the clinical criteria used to select patients. Mutations in the tau gene account only for a small number of FTD cases with a clear autosomal dominant pattern of disease inheritance. Therefore there should exist additionalgenetic and non-genetic factors contributing to the pathogenesis of both familial (linked and non-linked to chromosome 17) and sporadic forms of FTD.     

The neuropathology of FTD associated With ALS

There is increasing recognition of a clinical overlap between frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). Recent advances in our understanding of the neuropathologic, biochemical, and genetic basis of these conditions provides evidence for a common underlying pathogenesis. The neuropathology in most cases of FTD with ALS is a subtype of frontotemporal lobar degeneration, characterized by neuronal inclusions that are immunoreactive for ubiquitin but not tau (frontotemporal lobar degeneration with ubiquitinated inclusions). These cases show significant pathologic overlap with clinically pure FTD and those with classic ALS. Moreover, the ubiquitinated pathologic protein in all these conditions has recently been identified as TDP-43. A number of families have been reported with autosomal dominant FTD-ALS linked to chromosome 9p and these also have TDP-43-positive frontotemporal lobar degeneration with ubiquitinated inclusions pathology. Together, these findings suggest that FTD-ALS is part of a clinicopathologic spectrum of disease, now identified as TDP-43 proteinopathies.     

Alzheimer disease pathology in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is characterized by degeneration of upper and lower motor neurons. In some ALS patients, dementia or aphasia may be present (ALS-D). The dementia is most commonly a frontotemporal dementia (FTD), and many of these cases have ubiquitin-positive, tau-negative inclusions in neurons of the dentate gyrus and superficial layers of the frontal and temporal lobes. Identical inclusions have been found in cases presenting with FTD and have been designated motor neuron disease (MND)-inclusions. Cases of ALS-D without MND-inclusions have been reported to show neocortical gliosis, neuronal loss, and superficial spongiosis, but there have also been scattered case reports of ALS with Alzheimers disease (AD). To determine whether AD pathology may play a role in the dementia or aphasia syndromes in ALS, we reviewed 30 cases of sporadic ALS diagnosed at the University of Pittsburgh Medical Center. A clinical history of ALS-D was found in 24.1% of the cases, of which 57% had MND-inclusions. Although the ALS-D cases with MND-inclusions typically had amyloid-beta (A) plaques, there were no neuritic plaques. Three cases of ALS-D had no MND-inclusions, and two of these fulfilled pathological criteria for AD. One ALS-D case showed severe amyloid angiopathy but no neuritic plaques or MND-inclusions. MND-inclusions were not found in any ALS case without dementia; however, four patients without dementia or aphasia showed moderate or frequent numbers of neuritic plaques. In conclusion, we found that approximately 30% of ALS cases with dementia have AD and that some ALS cases without frank dementia have significant AD pathology.     

Frontotemporal lobar degeneration with motor neuron disease-type inclusions predominates in 76 cases of frontotemporal degeneration

This report presents the largest series of consecutive, neuropathologically confirmed cases of frontotemporal degeneration (FTD). Prior studies have found dementia lacking distinctive histology (DLDH) to be the most common pathology underlying the clinical diagnosis of FTD. In this series of 76 cases, 29 (38%) were found to have frontotemporal lobar degeneration with motor neuron disease-type inclusions (FTLD-MND-type) or FTLD-MND (with ALS), the most common neuropathological classification in our series. Only eight (11%) were classified as Picks disease. Several cases originally designated as DLDH could be reclassified as FTLD-MND-type based on current recommendations for classification of FTD.     

Neuronal intranuclear inclusions distinguish familial FTD-MND type from sporadic cases

Ubiquitin-immunoreactive (ub-ir) neuronal cytoplasmic inclusions are characteristically found in the extramotor cortex in patients with motor neuron disease (MND) and dementia (MND-dementia) and in a subset of patients with frontotemporal dementia (FTD) without motor symptoms (FTD-MND type). Recently, ub-ir neuronal intranuclear inclusions have been described in a small number of patients with familial FTD-MND type. To better define the sensitivity and specificity of this pathological change, we examined postmortem tissue from 14 patients with FTD-MND type (8 familial, 6 sporadic), 10 cases of MND-dementia (5 familial, 5 sporadic) and 19 cases of MND with no history of cognitive dysfunction (2 familial, 17 sporadic). Numerous intranuclear inclusions were found in multiple anatomic sites in 6/8 cases of familial FTD-MND. Rare intranuclear inclusions were present in the hippocampal dentate granule cells in 1 case of familial MND-dementia. No sporadic cases had intranuclear inclusions. These findings suggest that intranuclear inclusions are specific for familial FTD and may identify a subset of families with a common genetic basis. Although intranuclear inclusions are most characteristic of families with pure FTD, they may also be found in some pedigrees with both FTD and MND, further supporting the hypothesis that FTD-MND type and MND-dementia represent a clinicopathological spectrum of disease.     

Presymptomatic studies in genetic frontotemporal dementia

Approximately 20% of patients with the neurodegenerative disorder frontotemporal dementia (FTD) have an autosomal dominant pattern of inheritance. Genetic FTD is caused by mutations in three genes in most cases (progranulin, microtubule-associated protein tau and chromosome 9 open reading frame 72) although a number of other genes are rare causes. Studies of other neurodegenerative diseases have shown imaging and biomarker evidence of disease onset many years prior to the development of symptoms. Similar studies in genetic FTD are now revealing evidence of a series of presymptomatic changes, initially in plasma biomarkers followed by MR imaging abnormalities of functional and structural connectivity and then grey matter atrophy. Lastly, neuropsychometric tests become abnormal in proximity to the onset of symptoms. Such studies have been relatively small until now but research centres with an expertise in genetic FTD are now forming consortia such as the Genetic Frontotemporal Dementia Initiative (GenFI) to create larger cohorts that can form the basis of future clinical trials.     

Familial frontotemporal dementia with amyotrophic lateral sclerosis and a shared haplotype on chromosome?9p

Families with autosomal dominant frontotemporal dementia and amyotrophic lateral sclerosis (FTD/ALS) have previously been linked to a locus on chromosome 9p21. We describe the clinical phenotype and pathology of a large family with autosomal dominant FTD/ALS with nine affected members originating from Gwent in South Wales, UK. We also further refine the locus on chromosome 9p21 using a haplotype sharing approach and assess heterogeneity in 9p21 linked families. Within this family, affected individuals present with either FTD or ALS or both diseases simultaneously. In addition there was marked phenotypic variation including ataxia, Parkinsonism, psychosis and visuo-spatial cognitive deficits. The pathological features of the three cases described were consistent with type 2 FTD pathology, as previously reported in similar families. However, we also report distinctive cerebellar and glial pathology and a significant proportion of TDP-43 negative inclusions. No mutations in known genes for FTD or ALS were found. We identified a large 4.8-megabase haplotype on chromosome 9p21, which was shared by all affected family members. This haplotype overlaps and limits the previously reported FTD/ALS linkage region on chromosome 9p21. Sequencing of this region did not identify any evidence of a pathogenic exonic mutation. This suggests that the pathogenic change affects non-coding DNA and that the disease is caused by variation in gene or protein expression.     

Neuropsychology of frontal type dementia]

The clinical conceptual change in frontal type dementia is reviewed in discussing its relationships to several related concepts such as Pick's disease, frontotemporal dementia (FTD), semantic dementia (SD) and frontotemporal lobar degeneration. We analyzed frontal type dementia selected from a consecutive series of our outpatients as to the details of neuropsychological symptoms, psychiatric symptoms, and abnormal behaviors. In our series of 143 patients with primary degenerative dementia, there were 16 cases of FTD and 6 cases of SD. Patients with two types of FTD and patients with SD were not distinguishable by neuropsychological examinations, behavioral abnormalities and psychiatric symptoms assessed with the Neuropsychiatric Inventory except for aphasia. The clinical picture of frontal type dementia involves frontal lobe symptoms such as disinhibition, apathy and stereotypy. Semantic memory loss for words, objects or faces suggestive of temporal lobe involvement developed only in patients with SD, and not in patients with FTD. Certain behavioral symptoms seen in frontal type dementia may respond to selective serotonin reuptake inhibitors. In care for patients with frontal type dementia, behavioral disturbances can be diminished and the quality of life can be improved by using their preserved procedural memory, pathological stereotypic behavior and stimulus-bound behavior such as utilization behavior and environmental dependency syndrome.     

Ubiquitin immunohistochemistry suggests classic motor neuron disease, motor neuron disease with dementia, and frontotemporal dementia of the motor neuron disease type represent a clinicopathologic spectrum

One of the characteristic pathologic changes in classic motor neuron disease (MND) is the presence of ubiquitin-immunoreactive (ub-ir) inclusions in the cytoplasm of lower motor neurons. In addition, cases of MND with dementia (MND-d) also have ub-ir neuronal cytoplasmic inclusions and dystrophic neurites in extramotor neocortex and hippocampus. Although this extramotor pathology is a highly sensitive marker for dementia in MND, similar changes are found in a subset of patients with frontotemporal dementia (FTD) with no motor symptoms (FTD-MND type). The purpose of this study is to more fully describe and compare the pattern of ub-ir pathology in these 3 conditions. We performed ubiquitin immunohistochemistry on postmortem tissue, representing a wide range of neuroanatomic structures, in cases of classic MND (n = 20), MND-d (n = 15), and FTD-MND type (n = 15). We found the variety of morphologies and the anatomic distribution of ub-ir pathology to be greater than previously documented. Moreover, the degree of overlap suggests that MND, MND-d, and FTD-MND type represent a spectrum of clinical disease with a common pathologic substrate. The only finding restricted to a specific subgroup of patients was the presence of ub-ir neuronal intranuclear inclusions in some cases of familial FTD.     

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.     

Frontotemporal dementia: therapeutic possibilities

In order to treat frontotemporal dementia (FTD) we must first evaluate the patient's medical condition, as well as his or her social setting (caregiver, financial resources, home characteristics). Primary health-care team must receive information about the patient's disease, and the family should be informed about the disease itself and the social resources they can ask for. It is advisable to formulate a therapeutic scheme including some counsels to improve the suitability of environment, social help measures, behaviour therapy, cognitive stimulation and pharmacological treatment. Atypical antipsychotics have improved "positive symptoms" as logorrhoea, wandering, agitation and aggression, without impairing cognitive function. Selective serotonin reuptake inhibitors improve depressive symptoms, compulsions, food craving and disinhibition. A few reports suggest that idazoxan (alpha 2-noradrenergic antagonist) can improve attention, verbal fluency and planning efficiency. In some cases with "FTD and parkinsonism linked to chromosome 17" it could be justified to perform a genetic analysis to the offspring, in order to know if genetic counseling is necessary. An inflammatory reaction has been observed in brain damaged areas, and therefore antiinflammatory treatment efficacy should be investigated. It would also be interesting to look for neuroprotective agents that lessen the tau protein abnormality. All types of receptors which are involved in FTD should be identified, and then their selective agonists or antagonists could be administered in synergic combinations. We hope that all genetic alterations producing or facilitating FTD are eventually known, and harmless curative means are developed.     

Frontotemporal lobar degeneration: a study in Japan

Frontotemporal lobar degeneration is the most common form of cortical dementia occurring in the presenium after Alzheimer's disease. We analyzed two types of frontotemporal dementia (FTD) and semantic dementia (SD) selected from a consecutive series of outpatients based on neuropsychological symptoms, psychiatric symptoms and abnormal behavior. In our series of 134 patients with primary degenerative dementia, there were 16 cases of FTD and 6 cases of SD. Patients with subgroups of FTD and patients with SD were distinguishable only by the presence of aphasia in the latter group. They were not distinguishable from one another by other neuropsychological examinations, behavioral abnormalities or psychiatric symptoms assessed with the Neuropsychiatric Inventory.     

Neuropathological discrepancy between Japanese Pick’s disease without Pick bodies and frontal lobe degeneration type of frontotemporal dementia proposed by Lund and Manchester Group

The concept of frontotemporal dementia (FTD) proposed by the Lund and Manchester group is useful because it distinguishes dementia with frontal and anterior temporal involvement from Alzheimer‐type dementia. The classification and definition of FTD and related disorders, however, are controversial. One point of controversy is the neuropathology of the frontal lobe degeneration (FLD) type of FTD. The FLD type is described as having mild frontal and anterior temporal atrophy and no accompanying tau or ubiquitin pathology. We investigated cases of Japanese Pick’s disease without Pick bodies (PB), the majority of which are thought to correspond to FLD type, in order to clarify whether the nature of the degeneration in these cases could be distinguishable from that in Japanese Pick’s disease with PB, which corresponds approximately to the Pick type of the Lund and Manchester group. Except for the presence of tau‐pathology, no obvious differences were noted between Pick’s disease without PB (FLD type) and Pick’s disease with PB (Pick type) either on neuropathological examination of own cases or a questionnaire survey of Japanese neuropathologists. The reason for this discrepancy may be based on the role of heredity, namely, most Japanese cases of Pick’s disease are solitary, while the FTD cases of the Lund and Manchester group were reportedly accompanied by extensive familial history. There is a possibility that Japanese, British, and Swedish neuropathologists deal with heterogeneous groups of dementia characterized as FTD without tau or ubiquitin pathology.     

Frontotemporal dementia: Its definition,differential diagnosis,and management

Background: Frontotemporal dementia (FTD) is defined as primary neurodegeneration of the anterior temporal and/or frontal lobes resulting in a group of associated conditions marked by changes in cognition, language, personality, and social functioning. FTD was previously thought to be a rare disease. However, researchers report that FTD is the third most common form of dementia. Because adults with FTD have deficits in language, cognition, and behaviour, familiarity with FTD subtypes, associated deficits, and currently available management strategies is warranted.

Aims: The aims of this tutorial are (a) to define frontotemporal dementia including behavioural and language characteristics of the three clinically distinct FTD subtypes (frontotemporal variant, nonfluent progressive aphasia, semantic dementia); (b) to identify similarities and differences between FTD and Alzheimer's dementia; and (c) to discuss management strategies for patients with FTD.

Main Contribution: Different subtypes and presentations of FTD as well as the neurological, behavioural, and language symptoms that have been consistently identified are reviewed. Behavioural and language symptoms of the two FTD subtypes with primary language disturbances (nonfluent progressive aphasia and semantic dementia) are also reviewed. Patients with FTD are frequently misdiagnosed as presenting with Alzheimer's dementia due to limitations in the literature describing the differing profiles of the two populations. When considering neurological changes, behavioural changes, language and communication behaviours, and disease progression, these patient populations are distinct and easily differentiated. Finally, management strategies are discussed. Although there is no cure for FTD, medical intervention can address some of the associated symptoms, and behavioural techniques may manage the client's environment and prolong communication abilities.

Conclusions: General discussion seeks to differentially diagnose FTD dementia from Alzheimer's dementia as well as to clarify the language and communication symptoms of FTD subtypes. Future research directions are suggested for developing evidence‐based direct and indirect management strategies.     

Polymorphisms in the tau gene in sporadic frontotemporal dementia and other neurodegenerative disorders

The tau gene on chromosome 17 is fundamental in the pathogenesis of a number of neurodegenerative disorders. Mutations in tau are found in familial frontotemporal dementia (FTD) and the A0/A0 genotype associated with progressive supranuclear palsy (PSP). This study investigates the hypothesis that polymorphisms in the tau gene are associated with sporadic FTD. Western Australian populations of patients with sporadic frontotemporal dementia, PSP, Alzheimer's disease (AD), Huntington's disease (HD) and normal controls were studied. A new method was developed using fluorescently labelled probes to determine polymorphisms in the GT repeat region of intron 9. The A0/A0 genotype was found in 95% of PSP patients (n=20), 58.3% of FTD patients (n=48), 60.8% of AD patients (n=52), 75% of HD patients (n=40), and 75% of normal controls (n=40). None of these differences in genotype frequency were found to be significant by the Fisher exact test (P > 0.05). There were no significant differences in the frequencies of A0/A3 and A0/A1 haplotypes. We have not observed a significant increase in the A0/A0 genotype frequency in sporadic frontotemporal dementia suggesting that this polymorphism is unlikely to be related to the development of this condition. Furthermore, we have observed an increase in the A0/A0 genotype in PSP which did not reach statistical significance, suggesting that there may be population differences in the role of genetic factors in conferring risks to neurodegenerative disorders. Our work does not exclude that tau may interact with other genetic factors.     

Clinical and molecular aspects of frontotemporal dementia

Frontotemporal dementia (FTD) is a neurodegenerative disease and next to Alzheimer's disease and vascular dementia, the third most common cause of early-onset progressive dementia. FTD leads to neurodegeneration in the frontal and temporal neocortex and usually encompasses both sides of the frontal and anterior temporal lobes. Psychologically, FTD is characterized by personality changes such as lack of insight, inappropriate behaviour, disinhibition, apathy, executive disabilities and a decline in cognitive functions, with large clinical and neuropathological variations among cases. Neuropathological characteristics include gliosis or microvacuolation of cortical nerve cells. Inclusions staining for tau protein and/or ubiquitin are also common findings. Both sporadic and hereditary forms of FTD have been identified and 30-50% of the FTD cases have a familial background. So far, at least three genetic loci for FTD have been identified, at human chromosomes 3, 9 and 17 in familial forms of the disease. A large number of the familial forms have been linked to chromosome 17q21 and referred to as frontotemporal dementia and Parkinsonism linked to chromosome 17. In the majority of these families, pathogenic mutations in the tau gene were identified. However, tau mutations seem to be a rare cause of disease in the general FTD population. Thus, other genes and/or environmental factors are yet to be identified, which will give further clues to this complex and heterogeneous disorder.     

Tau and neurofilaments in a family with frontotemporal dementia unlinked to chromosome 17q21-22

A Swiss frontotemporal dementia (FTD) kindred with extrapyramidal-like features and without motor neuron disease shows a brain pathology with ubiquitin-positive but tau-negative inclusions. Tau and neurofilament modifications are now studied here in three recently deceased family members. No major and specific decrease of tau was observed as described by others in, e.g., sporadic cases of FTD with absence of tau-positive inclusions. However, a slight decrease of tau, neurofilament, and synaptic proteins, resulting from frontal atrophy was detected. In parallel, polymorphic markers on chromosome 17q21-22, the centromeric region of chromosome 3 and chromosome 9, were tested. Haplotype analysis showed several recombination events for chromosomes 3 and 17, but patients shared a haplotype on chromosome 9q21-22. However as one of the patients exhibited Alzheimer and vascular dementia pathology with uncertain concomitant FTD, this locus is questionable. Altogether, these data indicate principally that the Swiss kindred is unlinked to locus 17q21-22, and that tau is not at the origin of FTD in this family.     

Frontotemporal dementia: Pick type

The status of Pick's disease within the concept of frontotemporal dementia (FTD) is unclear. Some researchers have defined Pick's disease as FTD with Pick bodies. Alternatively, the confusion may be clarified by using the term Pick body dementia (PBD) rather than by using the term Pick's disease in a narrow sense. Pick body dementia is characterized by a prominent frontotemporal lobar atrophy, gliosis, severe neuronal loss, ballooned neurons, and the presence of neuronal inclusions called Pick bodies. In recent years, studies of Pick body dementia have advanced from the standpoint of the tau pathology. Tau-positive glial inclusions as well as neuronal inclusions have been observed in PBD and its related disorders. Various forms of FTD have been proposed based on the presence of neuronal or glial inclusions. We propose a new variant of FTD termed ‘glial tangle-predominant type’. More research is required to understand the tau abnormalities in the various forms of FTD.