A distinct clinical, neuropsychological and radiological phenotype is associated with progranulin gene mutations in a large UK series

Distinct profiles of brain atrophy in frontotemporal lobar degeneration caused by progranulin and tau mutations

Neural network breakdown is a key issue in neurodegenerative disease, but the mechanisms are poorly understood. Here we investigated patterns of brain atrophy produced by defined molecular lesions in the two common forms of genetically mediated frontotemporal lobar degeneration (FTLD). Nine patients with progranulin (GRN) mutations and eleven patients with microtubule-associated protein tau (MAPT) mutations had T1 MR brain imaging. Brain volumetry and grey and white matter voxel-based morphometry (VBM) were used to assess patterns of cross-sectional atrophy in the two groups. In a subset of patients with longitudinal MRI rates of whole-brain atrophy were derived using the brain-boundary-shift integral and a VBM-like analysis of voxel-wise longitudinal volume change was performed. The GRN mutation group showed asymmetrical atrophy whereas the MAPT group showed symmetrical atrophy. Brain volumes were smaller in the GRN group with a faster rate of whole-brain atrophy. VBM delineated a common anterior cingulate–prefrontal–insular pattern of atrophy in both disease groups. Additional disease-specific profiles of grey and white matter loss were identified on both cross-sectional and longitudinal imaging: GRN mutations were associated with asymmetrical inferior frontal, temporal and inferior parietal lobe grey matter atrophy and involvement of long intrahemispheric association white matter tracts, whereas MAPT mutations were associated with symmetrical anteromedial temporal lobe and orbitofrontal grey matter atrophy and fornix involvement. The findings suggest that the effects of GRN and MAPT mutations are expressed in partly overlapping but distinct anatomical networks that link specific molecular dysfunction with clinical phenotype.

Intra-familial clinical heterogeneity due to FTLD-U with TDP-43 proteinopathy caused by a novel deletion in progranulin gene (PGRN)

Frontotemporal dementia (FTD) is one of the commonest forms of early-onset dementia, accounting for up to 20% of all dementia patients. Recently, it has been shown that mutations in progranulin gene (PGRN) cause many familial cases of FTD. Members of a family affected by FTD spectrum disorders were ascertained in Poland and Canada. Clinical, radiological, molecular, genetic, and pathological studies were performed. A sequencing analysis of PGRN exons 1-13 was performed in the proband. Genotyping of the identified PGRN mutation and pathological analysis was carried out in the proband's brother. The onset of symptoms of FTD in the proband included bradykinesia, apathy, and somnolence followed by changes in personality, cognitive deficits, and psychotic features. The proband's clinical diagnosis was FTD and parkinsonism (FTDP). DNA sequence analysis of PGRN revealed a novel, heterozygous mutation in exon 11 (g.2988_2989delCA, P439_R440fsX6). The mutation introduced a premature stop codon at position 444. The proband's brother with the same mutation had a different course first presenting as progressive non-fluent aphasia, and later evolving symptoms of behavioral variant of FTD. He also developed parkinsonism late in the disease course evolving into corticobasal syndrome. Pathological analysis in the brother revealed Frontotemporal Lobar Degeneration-Ubiquitin (FTLD-U)/TDP-43 positive pathology. The novel PGRN mutation is a disease-causing mutation and is associated with substantial intra-familial clinical heterogeneity. Although presenting features were different, rapid and substantial deterioration in the disease course was observed in both family members.

Progressive logopenic/phonological aphasia: erosion of the language network

The primary progressive aphasias (PPA) are paradigmatic disorders of language network breakdown associated with focal degeneration of the left cerebral hemisphere. Here we addressed brain correlates of PPA in a detailed neuroanatomical analysis of the third canonical syndrome of PPA, logopenic/phonological aphasia (LPA), in relation to the more widely studied clinico-anatomical syndromes of semantic dementia (SD) and progressive nonfluent aphasia (PNFA). 32 PPA patients (9 SD, 14 PNFA, 9 LPA) and 18 cognitively normal controls had volumetric brain MRI with regional volumetry, cortical thickness, grey and white matter voxel-based morphometry analyses. Five of nine patients with LPA had cerebrospinal fluid biomarkers consistent with Alzheimer (AD) pathology (AD-PPA) and 2/9 patients had progranulin (GRN) mutations (GRN-PPA). The LPA group had tissue loss in a widespread left hemisphere network. Compared with PNFA and SD, the LPA group had more extensive involvement of grey matter in posterior temporal and parietal cortices and long association white matter tracts. Overlapping but distinct networks were involved in the AD-PPA and GRN-PPA subgroups, with more anterior temporal lobe involvement in GRN-PPA. The importance of these findings is threefold: firstly, the clinico-anatomical entity of LPA has a profile of brain damage that is complementary to the network-based disorders of SD and PNFA; secondly, the core phonological processing deficit in LPA is likely to arise from temporo-parietal junction damage but disease spread occurs through the dorsal language network (and in GRN-PPA, also the ventral language network); and finally, GRN mutations provide a specific molecular substrate for language network dysfunction.

Neurodegenerative dementia and parkinsonism

BACKGROUND

Dementia and Parkinsonism are two major neurodegenerative disorders. Accurate diagnosis can be difficult when patients have both syndromes because of a wide range of etiologies.

OBJECTIVES

To improve clinical diagnosis, we propose a disease classification based on the pathological proteins which are involved in the neuropathological disease process.

DESIGN

Four neuropathological classes are proposed based on four major proteins, tau, A beta, alpha -synuclein and TDP43 : 1/ Tauopathy and amyloidopathy with possible Parkinsonism, 2/ Tauopathy with predominant Parkinsonism, 3/ Synucleinopathies with cognitive impairment/dementia and 4/ The TAR DNA binding protein 43 (TDP-43). This classification raises certain questions in clinical practice due to intriguing overlaps between clinical presentations despite the same pathological protein being involved.

CONCLUSION

The development of molecular and pathological protein research in neurodegenerative disorders can help classify the clinical association of dementia and Parkinsonism and improve therapeutic strategies against proteins involved in the degenerative process.

No evidence of PGRN or MAPT gene dosage alterations in a collection of patients with frontotemporal lobar degeneration

BACKGROUND/AIMS

Alterations in gene dosage have recently been associated with neurodegenerative disorders, such as Alzheimer's disease and Parkinson's disease, and deletions of the progranulin (PGRN) locus were recently described in patients with frontotemporal lobar degeneration (FTLD). FTLD is a genetically complex neurodegenerative disorder with mutations in the PGRN and the microtubule-associated protein tau (MAPT) genes being the most common known causes of familial FTLD. In this study, we investigated 39 patients with FTLD, previously found negative for mutations in PGRN and MAPT, for copy number alterations of these 2 genes.

METHODS

Gene dosage analysis of PGRN and MAPT was performed using multiplex ligation-dependent probe amplification.

RESULTS

We did not identify any PGRN or MAPT gene dosage variations in the 39 FTLD patients investigated.

CONCLUSION

We therefore conclude that alterations in gene copy number of PGRN and MAPT are not a cause of disease in this collection of FTLD patients.

The heritability and genetics of frontotemporal lobar degeneration

BACKGROUND

Frontotemporal lobar degeneration (FTLD) is a genetically and pathologically heterogeneous neurodegenerative disorder.

METHODS

We collected blood samples from a cohort of 225 patients with a diagnosis within the FTLD spectrum and examined the heritability of FTLD by giving each patient a family history score, from 1 (a clear autosomal dominant history of FTLD) through to 4 (no family history of dementia). We also looked for mutations in each of the 5 disease-causing genes (MAPT, GRN, VCP, CHMP2B, and TARDP) and the FUS gene, known to cause motor neuron disease.

RESULTS

A total of 41.8% of patients had some family history (score of 1, 2, 3, or 3.5), although only 10.2% had a clear autosomal dominant history (score of 1). Heritability varied across the different clinical subtypes of FTLD with the behavioral variant being the most heritable and frontotemporal dementia-motor neuron disease and the language syndromes (particularly semantic dementia) the least heritable. Mutations were found in MAPT (8.9% of the cohort) and GRN (8.4%) but not in any of the other genes. Of the remaining patients without mutations but with a strong family history, 7 had pathologic confirmation, falling into 2 groups: type 3 FTLD-TDP without GRN mutations (6) and FTLD-UPS (1).

CONCLUSION

These findings show that frontotemporal lobar degeneration (FTLD) is a highly heritable disorder but heritability varies between the different syndromes. Furthermore, while MAPT and GRN mutations account for a substantial proportion of familial cases, there are other genes yet to be discovered, particularly in patients with type 3 FTLD-TDP without a GRN mutation.

Review: Recent progress in frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) is a highly familial condition and is increasingly being recognized as an important form of dementia. The literature published on this disease is often difficult to collate due to the wide range in nomenclature used. Thankfully, consensus recommendations have now been published to address this issue and hopefully the community will adopt these as intended. Much progress has been made in our understanding of the clinical, pathological and genetic understanding of FTLD in recent years. Progranulin and TDP-43 have recently been identified as new important proteins involved in the pathophysiology of FTLD and this latter protein may have potential as a biomarker of this disease. However, much remains before we have a full picture of the genes that cause FTLD and the biological pathways in which they function. The purpose of this review is to summarize the current concepts and recent advances in our knowledge of this disease.

Frontotemporal lobar degeneration and dementia with Lewy bodies: clinicopathological issues associated with antemortem diagnosis

Currently, the clinical diagnostic criteria of frontotemporal lobar degeneration (FTLD) and dementia with Lewy bodies (DLB) are well known to neurologists and psychiatrists. However, the accuracy of the clinical diagnosis of these diseases in autopsy series is not always adequate. For example, FTLD is a syndrome rather than a clinicopathological disease entity that is comprised of various pathological substrates, including Pick's disease, FTLD with microtubule-associated protein tau gene mutation, FTLD with tau-negative ubiquitin-positive inclusions (FTLD-U), FTLD-U with progranulin gene mutation, corticobasal degeneration, basophilic inclusion body disease, and neuronal intermediate filament inclusion disease. Whether these underlying pathologies can be identified clinically is one of the greatest interests in neuropathological research. The pathophysiological relationship between Lewy pathology and Alzheimer pathology in DLB is explored with interest because it may be associated with the accuracy of clinical diagnoses. For example, although Lewy pathology may progress from the brain stem nuclei to the cerebral cortex in Parkinson's disease, recent studies have demonstrated that the progression pattern in DLB is not always identical to that in Parkinson's disease. It is also considered that the progression pattern of Lewy pathology correlates with the evolution of clinical symptoms and that the progression pattern of Lewy pathology may be altered when Alzheimer pathology coexists. In the present paper, the clinicopathological features of two demented cases are presented, and some pathological issues associated with the clinical diagnosis of FTLD and DLB are discussed.

Clinicopathological characterization of Pick's disease versus frontotemporal lobar degeneration with ubiquitin/TDP-43-positive inclusions

Although frontotemporal lobar degeneration with ubiquitin/TDP-43-positive inclusions (FTLD-TDP) and Pick's disease are common pathological substrates in sporadic FTLD, clinical differentiation of these diseases is difficult. We performed a retrospective review of medical records and semiquantitative examination of neuronal loss of 20 sporadic FTLD-TDP and 19 Pick's disease cases. Semantic dementia as the first syndrome developed only in FTLD-TDP patients. Impaired speech output in the early stage was five times more frequent in Pick's disease than in FTLD-TDP. The total frequency of asymmetric motor disturbances (e.g., parkinsonism, pyramidal signs, and contracture) during the course was significantly more frequent in FTLD-TDP (78%) than in Pick's disease cases (14%). Asymmetric pyramidal signs were found in 7 of 13 FTLD-TDP cases with corticospinal tract degeneration similar to primary lateral sclerosis. Frontotemporal dementia as the first syndrome was noted in both FTLD-TDP (28%) and Pick's disease cases (64%); however, only FTLD-TDP cases subsequently developed asymmetric motor disturbances, and some of the cases further exhibited hemineglect. Concordant with these clinical findings, degeneration in the temporal cortex, caudate nucleus, putamen, globus pallidus, substantia nigra, and corticospinal tract was significantly more severe in FTLD-TDP, and degeneration in the frontal cortex tended to be more severe in Pick's disease. Given these findings, the initial impairment of semantic memory or comprehension and subsequent asymmetric motor disturbances in sporadic FTLD patients predict sporadic FTLD-TDP rather than Pick's disease, while initial behavioral symptoms or non-fluent aphasia without subsequent asymmetric motor disturbances predict Pick's disease rather than sporadic FTLD-TDP.

Voxel-based morphometry patterns of atrophy in FTLD with mutations in MAPT or PGRN

OBJECTIVE

To compare patterns of gray matter loss in subjects with mutations in the progranulin (PGRN) gene to subjects with mutations in the microtubule-associated protein tau (MAPT) gene.

METHODS

We identified all subjects seen at the Mayo Clinic, Rochester, MN, who had screened positive for mutations in PGRN or MAPT and had a head MRI. Twelve cases with mutations in the PGRN gene were matched by time from disease onset to scan to 12 subjects with mutations in the MAPT gene. Voxel-based morphometry was used to assess patterns of gray matter loss in the PGRN and MAPT groups compared to a control cohort, and compared to each other. MAPT subjects were younger than the PGRN subjects; therefore, each group was also compared to a specific age-matched control group.

RESULTS

Both PGRN and MAPT groups showed gray matter loss in frontal, temporal, and parietal lobes compared to controls, although loss was predominantly identified in posterior temporal and parietal lobes in PGRN and anteromedial temporal lobes in MAPT. The MAPT group had greater loss compared to healthy subjects of the same age than the PGRN subjects when compared to healthy subjects of the same age. The MAPT subjects showed greater gray matter loss in the medial temporal lobes, insula, and putamen than the PGRN subjects.

CONCLUSION

These results increase understanding of the biology of these disorders and suggest that patterns of atrophy on MRI may be useful to aid in the differentiation of groups of PGRN and MAPT mutation carriers.

Clinical phenotypes of progressive aphasia

Primary progressive aphasia is defined as an insidious, gradual impairment of language function, which is not accompanied by other cognitive disorders for at least 2 years after onset, and which can be due to a number of neurodegenerative disorders, such as the different varieties of frontotemporal dementia or Alzheimer’s disease. The clinical presentations are heterogeneous, as they faithfully reflect the preferential location of pathological involvement within the language networks. A careful definition of the clinical phenotypes of primary progressive aphasia is contributing to the understanding of language organization in the brain. Moreover, the predictive value of the clinical phenotype as to the underlying pathology has important implications for clinical trials of disease-modifying drugs.

Neologistic jargon aphasia and agraphia in primary progressive aphasia

The terms 'jargon aphasia' and 'jargon agraphia' describe the production of incomprehensible language containing frequent phonological, semantic or neologistic errors in speech and writing, respectively. Here we describe two patients with primary progressive aphasia (PPA) who produced neologistic jargon either in speech or writing. We suggest that involvement of the posterior superior temporal-inferior parietal region may lead to a disconnection between stored lexical representations and language output pathways leading to aberrant activation of phonemes in neologistic jargon. Parietal lobe involvement is relatively unusual in PPA, perhaps accounting for the comparative rarity of jargon early in the course of these diseases.

Apolipoprotein E epsilon4 is associated with disease-specific effects on brain atrophy in Alzheimer's disease and frontotemporal dementia

Apolipoprotein epsilon4 (apoE4) has been strongly linked with Alzheimer's disease (AD) and contributes to several other neurological disorders. We investigated the influence of epsilon4 allele carrier status on the pattern of gray matter atrophy and disease severity in 51 patients with probable AD and 31 patients with behavioral variant frontotemporal dementia (bvFTD), compared with 56 healthy controls. Voxel-based morphometry was performed by using statistical parametric mapping. The epsilon4 allele frequency was higher in the AD group (P < 0.001) than the controls but not in the bvFTD group. No differences in demographic or cognitive profiles were observed between epsilon4 allele carriers and noncarriers within any of the diagnostic groups. However, epsilon4 carrier status was associated with more severe brain atrophy in disease-specific regions compared with noncarriers in both AD and bvFTD. AD epsilon4 carriers showed greater atrophy in the bilateral parietal cortex and right hippocampus, and bvFTD epsilon4 carriers demonstrated greater atrophy in the bilateral medial, dorsolateral, and orbital frontal cortex, anterior insula, and cingulate cortex with right predominance. This regional epsilon4 effect is consistent with the hypothesis that apoE may affect the morphologic expression uniquely in different neurodegenerative diseases. The atrophy patterns in epsilon4 carriers may indicate that they are at greater risk for clinical progression.

Plasma progranulin levels predict progranulin mutation status in frontotemporal dementia patients and asymptomatic family members

Mutations in the progranulin gene (GRN) are an important cause of frontotemporal lobar degeneration (FTLD) with ubiquitin and TAR DNA-binding protein 43 (TDP43)-positive pathology. The clinical presentation associated with GRN mutations is heterogeneous and may include clinical probable Alzheimer's disease. All GRN mutations identified thus far cause disease through a uniform disease mechanism, i.e. the loss of functional GRN or haploinsufficiency. To determine if expression of GRN in plasma could predict GRN mutation status and could be used as a biological marker, we optimized a GRN ELISA and studied plasma samples of a consecutive clinical FTLD series of 219 patients, 70 control individuals, 72 early-onset probable Alzheimer's disease patients and nine symptomatic and 18 asymptomatic relatives of GRN mutation families. All FTLD patients with GRN loss-of-function mutations showed significantly reduced levels of GRN in plasma to about one third of the levels observed in non-GRN carriers and control individuals (P < 0.001). No overlap in distributions of GRN levels was observed between the eight GRN loss-of-function mutation carriers (range: 53-94 ng/ml) and 191 non-GRN mutation carriers (range: 115-386 ng/ml). Similar low levels of GRN were identified in asymptomatic GRN mutation carriers. Importantly, ELISA analyses also identified one probable Alzheimer's disease patient (1.4%) carrying a loss-of-function mutation in GRN. Biochemical analyses further showed that the GRN ELISA only detects full-length GRN, no intermediate granulin fragments. This study demonstrates that using a GRN ELISA in plasma, pathogenic GRN mutations can be accurately detected in symptomatic and asymptomatic carriers. The approximately 75% reduction in full-length GRN, suggests an unbalanced GRN metabolism in loss-of-function mutation carriers whereby more GRN is processed into granulins. We propose that plasma GRN levels could be used as a reliable and inexpensive tool to identify all GRN mutation carriers in early-onset dementia populations and asymptomatic at-risk individuals.

Granulin mutations associated with frontotemporal lobar degeneration and related disorders: an update

Mutations in the gene encoding granulin (HUGO gene symbol GRN, also referred to as progranulin, PGRN), located at chromosome 17q21, were recently linked to tau-negative ubiquitin-positive frontotemporal lobar degeneration (FTLDU). Since then, 63 heterozygous mutations were identified in 163 families worldwide, all leading to loss of functional GRN, implicating a haploinsufficiency mechanism. Together, these mutations explained 5 to 10% of FTLD. The high mutation frequency, however, might still be an underestimation because not all patient samples were examined for all types of loss-of-function mutations and because several variants, including missense mutations, have a yet uncertain pathogenic significance. Although the complete phenotypic spectrum associated with GRN mutations is not yet fully characterized, it was shown that it is highly heterogeneous, suggesting the influence of modifying factors. A role of GRN in neuronal survival was suggested but the exact mechanism by which neurodegeneration and deposition of pathologic brain inclusions occur still has to be clarified.

Challenges and new opportunities in the investigation of new drug therapies to treat frontotemporal dementia

BACKGROUND

Frontotemporal dementia spectrum disorders are a set of neurodegenerative disorders affecting the frontal and anterior temporal lobes. They are often fatal, and currently no medications have been shown to slow their progression. Recent developments in understanding these disorders may aid in developing treatments.

OBJECTIVE

To discuss the development of drug therapies for frontotemporal dementia spectrum disorders, both those under current investigation and those that could be targets for future investigation.

METHODS

This review is divided into four sections: First, a brief review of frontotemporal dementia spectrum disorders; second, a discussion of the challenges in the development of drug therapies third, a review of the current clinical trials; and finally a discussion of some recent discoveries, which have sparked new areas of investigation.

CONCLUSIONS

Hopefully, advances in understanding of frontotemporal dementia spectrum disorders and clinical trial design will aid the development of new treatments.

Frontotemporal dementia in a large Swedish family is caused by a progranulin null mutation

Mutations in the progranulin (PGRN) gene have recently been identified in families with frontotemporal lobar degeneration and ubiquitin-positive brain inclusions linked to chromosome 17q21. We have previously described a Swedish family displaying frontotemporal dementia with rapid progression and linkage to chromosome 17q21. In this study, we performed an extended clinical and neuropathological investigation of affected members of the family and a genetic analysis of the PGRN gene. There was a large variation of the initial presenting symptoms in this family, but common clinical features were non-fluent aphasia and loss of spontaneous speech as well as personality and behavioural changes. Mean age at onset was 54 years with disease duration of close to 4 years. Neuropathological examination revealed frontotemporal neurodegeneration with ubiquitin and TAR DNA binding protein-43 immunoreactive intraneuronal inclusions. Mutation screening of the PGRN gene identified a 1 bp deletion in exon 1 causing a frameshift of the coding sequence and introducing a premature termination codon in exon 2 (Gly35GlufsX19). Analysis of PGRN messenger RNA (mRNA) levels revealed a considerable decrease in lymphoblasts from mutation carriers and fragment size separation, and sequence analysis confirmed that the mutated mRNA allele was almost absent in these samples. In conclusion, the PGRN Gly35fs mutation causes frontotemporal dementia with variable clinical presentation in a large Swedish family, most likely through nonsense-mediated decay of mutant PGRN mRNA and resulting haploinsufficiency.

Phenotypic heterogeneity and genetic modification of P102L inherited prion disease in an international series

The largest kindred with inherited prion disease P102L, historically Gerstmann-Sträussler-Scheinker syndrome, originates from central England, with émigrés now resident in various parts of the English-speaking world. We have collected data from 84 patients in the large UK kindred and numerous small unrelated pedigrees to investigate phenotypic heterogeneity and modifying factors. This collection represents by far the largest series of P102L patients so far reported. Microsatellite and genealogical analyses of eight separate European kindreds support multiple distinct mutational events at a cytosine-phosphate diester-guanidine dinucleotide mutation hot spot. All of the smaller P102L kindreds were linked to polymorphic human prion protein gene codon 129M and were not connected by genealogy or microsatellite haplotype background to the large kindred or each other. While many present with classical Gerstmann-Sträussler-Scheinker syndrome, a slowly progressive cerebellar ataxia with later onset cognitive impairment, there is remarkable heterogeneity. A subset of patients present with prominent cognitive and psychiatric features and some have met diagnostic criteria for sporadic Creutzfeldt-Jakob disease. We show that polymorphic human prion protein gene codon 129 modifies age at onset: the earliest eight clinical onsets were all MM homozygotes and overall age at onset was 7 years earlier for MM compared with MV heterozygotes (P = 0.02). Unexpectedly, apolipoprotein E4 carriers have a delayed age of onset by 10 years (P = 0.02). We found a preponderance of female patients compared with males (54 females versus 30 males, P = 0.01), which probably relates to ascertainment bias. However, these modifiers had no impact on a semi-quantitative pathological phenotype in 10 autopsied patients. These data allow an appreciation of the range of clinical phenotype, modern imaging and molecular investigation and should inform genetic counselling of at-risk individuals, with the identification of two genetic modifiers.

Mutations in progranulin (GRN) within the spectrum of clinical and pathological phenotypes of frontotemporal dementia

BACKGROUND

Frontotemporal dementia (FTD) is predominantly a presenile disorder that is characterised by behavioural changes and cognitive impairment, particularly in language and executive functions, and is associated with neurodegeneration in the frontal or temporal cortices, or both. Research into FTD has made many advances over the past 20 years that have important implications for clinical practice. Different clinical variants (ie, behavioural, aphasic, and motor neuron disease variants) are now recognised as part of the clinical spectrum of FTD. Neuropathologically, the disease can be divided into two main pathological subtypes: frontotemporal lobar degeneration (FTLD) with neuronal and glial tau inclusions (FTLD-tau); and FTLD with neuronal inclusions that are positive for ubiquitin (FTLD-U). 20-30% of cases of FTD follow an autosomal dominant pattern of inheritance, and half of which are caused by defects in MAPT, CHMP2B, and VCP.

RECENT DEVELOPMENTS

Mutations in the gene that encodes progranulin (GRN) on chromosome 17q21-22 have been identified in patients with hereditary FTD who have tau-negative, ubiquitin-positive inclusions. The recognition of the clinical phenotype associated with more than 50 different mutations in GRN has expanded the clinical knowledge of FTD to include presentations that resemble Alzheimer's disease, Lewy body disease, and corticobasal syndrome, with a variable age at onset (35-89 years) within families. Another recent breakthrough is the identification of the TAR DNA-binding protein (TARDBP; also known as TDP-43) as the main constituent of FTLD-U with mutations in GRN and with mutations in VCP, as well as in FTLD with amyotrophic lateral sclerosis. WHERE NEXT?: To develop therapeutic strategies to prevent FTD or delay its progression we must understand whether the loss of progranulin leads to the accumulation of TARDBP. In this Rapid Review, we focus on the clinical and pathological phenotypes associated with mutations in GRN, and distinguish those from other forms of hereditary FTD. In addition, we discuss the potential association of mutations in GRN on the pathophysiology of FTD with the accumulation of TARDBP.

Mapping the progression of progranulin-associated frontotemporal lobar degeneration

BACKGROUND

A 55-year-old woman was followed over a 13-year period as part of a longitudinal study of people at risk for familial dementia. She was a member of a family with an autosomal dominant familial dementia that fulfilled consensus criteria for frontotemporal lobar degeneration. The patient was initially asymptomatic but developed progressive behavioral and cognitive decline characterized by apathy, impaired emotion recognition, mixed aphasia and parietal lobe dysfunction.

INVESTIGATIONS

Clinical assessments, neuropsychometry, volumetric brain MRI, and genetic mutation screening.

DIAGNOSIS

Progranulin-associated frontotemporal lobar degeneration.

MANAGEMENT

Explanation of the patient's condition and genetic counseling for her family.

Lack of TAR-DNA binding protein-43 (TDP-43) pathology in human prion diseases

AIMS

TAR-DNA binding protein-43 (TDP-43) is the major ubiquitinated protein in the aggregates in frontotemporal dementia with ubiquitin-positive, tau-negative inclusions and motor neurone disease. Abnormal TDP-43 immunoreactivity has also been described in Alzheimer's disease, Lewy body diseases and Guam parkinsonism-dementia complex. We therefore aimed to determine whether there is TDP-43 pathology in human prion diseases, which are characterised by variable deposition of prion protein (PrP) aggregates in the brain as amyloid plaques or more diffuse deposits.

MATERIAL AND METHODS

TDP-43, ubiquitin and PrP were analysed by immunohistochemistry and double-labelling immunofluorescence, in sporadic, acquired and inherited forms of human prion disease.

RESULTS

Most PrP plaques contained ubiquitin, while synaptic PrP deposits were not associated with ubiquitin. No abnormal TDP-43 inclusions were identified in any type of prion disease case, and TDP-43 did not co-localize with ubiquitin-positive PrP plaques or with diffuse PrP aggregates.

CONCLUSIONS

These data do not support a role for TDP-43 in prion disease pathogenesis and argue that TDP-43 inclusions define a distinct group of neurodegenerative disorders.

Update on recent molecular and genetic advances in frontotemporal lobar degeneration

Great strides have been made in the last 2 years in the field of frontotemporal lobar degeneration (FTLD), particularly with respect to the genetics and molecular biology of FTLD with ubiquitinated inclusions. It is now clear that most cases of familial FTLD with ubiquitinated inclusions have mutations in the progranulin gene, located on chromosome 17. It is also clear that most ubiquitinated inclusions in FTLD with ubiquitinated inclusions are composed primarily of TAR DNA-binding protein-43. Thus, FTLDs can be separated into 2 major groups (i.e. tauopathies and ubiquitinopathies), and most of the ubiquitinopathies can now be defined as TAR DNA-binding protein-43 proteinopathies. Many of the familial FTLDs are linked to chromosome 17, including both the familial tauopathies and the familial TAR DNA-binding protein-43 proteinopathies with progranulin mutations. This review highlights the neuropathologic features and the most important discoveries of the last 2 years and places these findings into the historical context of FTLD.