Mutations in prion-like domains in hnRNPA2B1 and hnRNPA1 cause multisystem proteinopathy and ALS

Algorithms designed to identify canonical yeast prions predict that around 250 human proteins, including several RNA-binding proteins associated with neurodegenerative disease, harbour a distinctive prion-like domain (PrLD) enriched in uncharged polar amino acids and glycine. PrLDs in RNA-binding proteins are essential for the assembly of ribonucleoprotein granules. However, the interplay between human PrLD function and disease is not understood. Here we define pathogenic mutations in PrLDs of heterogeneous nuclear ribonucleoproteins (hnRNPs) A2B1 and A1 in families with inherited degeneration affecting muscle, brain, motor neuron and bone, and in one case of familial amyotrophic lateral sclerosis. Wild-type hnRNPA2 (the most abundant isoform of hnRNPA2B1) and hnRNPA1 show an intrinsic tendency to assemble into self-seeding fibrils, which is exacerbated by the disease mutations. Indeed, the pathogenic mutations strengthen a 'steric zipper' motif in the PrLD, which accelerates the formation of self-seeding fibrils that cross-seed polymerization of wild-type hnRNP. Notably, the disease mutations promote excess incorporation of hnRNPA2 and hnRNPA1 into stress granules and drive the formation of cytoplasmic inclusions in animal models that recapitulate the human pathology. Thus, dysregulated polymerization caused by a potent mutant steric zipper motif in a PrLD can initiate degenerative disease. Related proteins with PrLDs should therefore be considered candidates for initiating and perhaps propagating proteinopathies of muscle, brain, motor neuron and bone.

C9ORF72 repeat expansion in Australian and Spanish frontotemporal dementia patients

A hexanucleotide repeat expansion in C9ORF72 has been established as a common cause of frontotemporal dementia (FTD). However, the minimum repeat number necessary for disease pathogenesis is not known. The aims of our study were to determine the frequency of the C9ORF72 repeat expansion in two FTD patient collections (one Australian and one Spanish, combined n = 190), to examine C9ORF72 expansion allele length in a subset of FTD patients, and to examine C9ORF72 allele length in ‘non-expansion’ patients (those with <30 repeats). The C9ORF72 repeat expansion was detected in 5–17% of patients (21–41% of familial FTD patients). For one family, the expansion was present in the proband but absent in the mother, who was diagnosed with dementia at age 68. No association was found between C9ORF72 non-expanded allele length and age of onset and in the Spanish sample mean allele length was shorter in cases than in controls. Southern blotting analysis revealed that one of the nine ‘expansion-positive’ patients examined, who had neuropathologically confirmed frontotemporal lobar degeneration with TDP-43 pathology, harboured an ‘intermediate’ allele with a mean size of only ∼65 repeats. Our study indicates that the C9ORF72 repeat expansion accounts for a significant proportion of Australian and Spanish FTD cases. However, C9ORF72 allele length does not influence the age at onset of ‘non-expansion’ FTD patients in the series examined. Expansion of the C9ORF72 allele to as little as ∼65 repeats may be sufficient to cause disease.

The frontotemporal lobar degeneration risk factor, TMEM106B, regulates lysosomal morphology and function

Haploinsufficiency of Progranulin (PGRN), a gene encoding a secreted glycoprotein, is a major cause of frontotemporal lobar degeneration with ubiquitin (FTLD-U) positive inclusions. Single nucleotide polymorphisms in the TMEM106B gene were recently discovered as a risk factor for FTLD-U, especially in patients with PGRN mutations. TMEM106B is also associated with cognitive impairment in amyotrophic lateral sclerosis patients. Despite these studies, little is known about TMEM106B at molecular and cellular levels and how TMEM106B contributes to FTLD. Here, we show that TMEM106B is localized in the late endosome/lysosome compartments and TMEM106B levels are regulated by lysosomal activities. Ectopic expression of TMEM106B induces morphologic changes of lysosome compartments and delays the degradation of endocytic cargoes by the endolysosomal pathway. Furthermore, overexpression of TMEM106B correlates with elevated levels of PGRN, possibly by attenuating lysosomal degradation of PGRN. These results shed light on the cellular functions of TMEM106B and the roles of TMEM106B in the pathogenesis of FTLD-U with PGRN mutations.

Unconventional translation of C9ORF72 GGGGCC expansion generates insoluble polypeptides specific to c9FTD/ALS

Frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) are devastating neurodegenerative disorders with clinical, genetic, and neuropathological overlap. Hexanucleotide (GGGGCC) repeat expansions in a noncoding region of C9ORF72 are the major genetic cause of FTD and ALS (c9FTD/ALS). The RNA structure of GGGGCC repeats renders these transcripts susceptible to an unconventional mechanism of translation-repeat-associated non-ATG (RAN) translation. Antibodies generated against putative GGGGCC repeat RAN-translated peptides (anti-C9RANT) detected high molecular weight, insoluble material in brain homogenates, and neuronal inclusions throughout the CNS of c9FTD/ALS cases. C9RANT immunoreactivity was not found in other neurodegenerative diseases, including CAG repeat disorders, or in peripheral tissues of c9FTD/ALS. The specificity of C9RANT for c9FTD/ALS is a potential biomarker for this most common cause of FTD and ALS. These findings have significant implications for treatment strategies directed at RAN-translated peptides and their aggregation and the RNA structures necessary for their production.

Progress in frontotemporal dementia research

Frontotemporal dementia (FTD) is the second most common type of presenile dementia and is the most common form of dementia with the onset before 60 years of age. Its typical symptoms include behavioral disorders, affective symptoms, and language disorders. The FTD is a genetically and pathologically heterogeneous degenerative disorder. Animal models have provided more insights into the pathogenic mechanisms. There are currently no medications that are specifically approved for the treatment of FTD by the Food and Drug Administration. In this article, we review the recent advances in the molecular pathogenesis, pathology, animal models, and therapy for FTD. Better understanding of the pathogenesis and the use of animal models will help develop novel therapeutic strategies and provide new targets for FTD treatment.

A newly uncovered group of distantly related lysine methyltransferases preferentially interact with molecular chaperones to regulate their activity

Methylation is a post-translational modification that can affect numerous features of proteins, notably cellular localization, turnover, activity, and molecular interactions. Recent genome-wide analyses have considerably extended the list of human genes encoding putative methyltransferases. Studies on protein methyltransferases have revealed that the regulatory function of methylation is not limited to epigenetics, with many non-histone substrates now being discovered. We present here our findings on a novel family of distantly related putative methyltransferases. Affinity purification coupled to mass spectrometry shows a marked preference for these proteins to associate with various chaperones. Based on the spectral data, we were able to identify methylation sites in substrates, notably trimethylation of K135 of KIN/Kin17, K561 of HSPA8/Hsc70 as well as corresponding lysine residues in other Hsp70 isoforms, and K315 of VCP/p97. All modification sites were subsequently confirmed in vitro. In the case of VCP, methylation by METTL21D was stimulated by the addition of the UBX cofactor ASPSCR1, which we show directly interacts with the methyltransferase. This stimulatory effect was lost when we used VCP mutants (R155H, R159G, and R191Q) known to cause Inclusion Body Myopathy with Paget's disease of bone and Fronto-temporal Dementia (IBMPFD) and/or familial Amyotrophic Lateral Sclerosis (ALS). Lysine 315 falls in proximity to the Walker B motif of VCP's first ATPase/D1 domain. Our results indicate that methylation of this site negatively impacts its ATPase activity. Overall, this report uncovers a new role for protein methylation as a regulatory pathway for molecular chaperones and defines a novel regulatory mechanism for the chaperone VCP, whose deregulation is causative of degenerative neuromuscular diseases.

Methylation, or transfer of a single or multiple methyl groups (CH₃), is one of many post-translational modifications that occur on proteins. Such modifications can, in turn, affect numerous aspects of a protein, notably cellular localization, turnover, activity, and molecular interactions. In addition to post-translational modifications, the structural organization of a protein or protein complex can also have a significant impact on its function and stability. A group of factors known as “molecular chaperones” aid newly synthesized proteins in reaching their native conformation or alternating between physiologically relevant states. We present here a new family of factors that promote methylation of chaperones and show that, at least in one case, this modification translates into a modulation in the activity of the substrate chaperone. Our results not only characterize the function of previously unknown gene products, uncover a new role for protein methylation as a regulatory pathway for chaperones, and define a novel regulatory mechanism for the chaperone VCP, whose deregulation is causative of neuromuscular diseases, but also suggest the existence of a post-translational modification code that regulates molecular chaperones. Further decrypting this “chaperone code” will help understanding how the functional organization of the proteome is orchestrated.

Personalized medicine strategies for managing patients with parkinsonism and cognitive deficits

Patients exhibiting the classic manifestations of parkinsonism - tremors, rigidity, postural instability, slowed movements and, sometimes, sleep disturbances and depression - may also display severe cognitive disturbances. All of these particular motoric and behavioral symptoms may arise from Parkinson's disease [PD] per se, but they can also characterize Lewy Body dementia [LBD] or concurrent Parkinson's and Alzheimer's diseases [PD & AD]. Abnormalities of both movement and cognition are also observed in numerous other neurologic diseases, for example Huntington's Disease and the frontotemporal dementia. Distinguishing among these diseases in an individual patient is important in "personalizing" his or her mode of treatment, since an agent that is often highly effective in one of the diagnoses (e.g., L-dopa or muscarinic antagonists in PD) might be ineffective or even damaging in one of the others. That such personalization, based on genetic, biochemical, and imaging-based biomarkers, is feasible is suggested by the numerous genetic abnormalities already discovered in patients with parkinsonism, Alzheimer's disease and Huntington's disease (HD) and by the variety of regional and temporal patterns that these diseases can produce, as shown using imaging techniques.

A novel VCP mutation as the cause of atypical IBMPFD in a Chinese family

INTRODUCTION

Inclusion-body myopathy (IBM) with Paget's disease of bone (PDB) and frontotemporal dementia (FTD), designated as IBMPFD, is a rare, autosomal dominant disorder (MIM 605382). IBMPFD is caused by mutations in the gene that encode valosin-containing protein (VCP). We investigated a Chinese family in which multiple members were diagnosed with PDB and suffered from weakness of the limbs. However, no members of this family were diagnosed with FTD. We made a preliminary diagnosis of PDB, but failed to identify an SQSTM1 mutation in any of the patients. We used whole-exome sequencing to identify the pathogenic gene mutation affecting the Chinese male proband.

MATERIALS AND METHODS

Altogether, 254 subjects, including one 56-year-old male proband, four affected, related individuals and additional nine family members from a non-consanguineous Chinese family, and 240 healthy donors were recruited and genomic DNA was extracted. All eight exons and the exon-intron boundaries of the SQSTM1 gene were amplified by polymerase chain reaction (PCR) and directly sequenced in five patients (II13, II4, II5, II8, II9). Using whole-exome sequencing, we identified a novel mutation in VCP as the disease-causing mutation. We confirmed the result by sequencing a 500-bp region of the promoter and the coding region of VCP in all 254 of the participants using Sanger sequencing.

RESULTS

No mutation in the SQSTM1 gene was identified in the five patients examined using direct Sanger sequencing. However, through whole-exome sequencing we were able to identify a novel missense mutation in exon 3 of the VCP gene (p.Gly97Glu) in the Chinese male proband. This mutation was confirmed using Sanger sequencing. The proband, four affected individuals and three unaffected individuals carried this mutation. We were able to correctly diagnose the patients with atypical IBMPFD. Structural analysis of the p.Gly97Glu mutation in the VCP protein showed that the affected amino-acid is located in the interface of the protein. This abnormality may therefore interfere with protein function.

CONCLUSIONS

This is the first report of a family from China with IBMPFD. A novel VCP mutation was found as the cause of atypical IBMPFD in a Chinese family. Our findings confirm that VCP gene mutations can be a pathogenic cause of IBMPFD.

The C9ORF72 expansion mutation is a common cause of ALS+/-FTD in Europe and has a single founder

A massive hexanucleotide repeat expansion mutation (HREM) in C9ORF72 has recently been linked to amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Here we describe the frequency, origin and stability of this mutation in ALS+/-FTD from five European cohorts (total n=1347). Single-nucleotide polymorphisms defining the risk haplotype in linked kindreds were genotyped in cases (n=434) and controls (n=856). Haplotypes were analysed using PLINK and aged using DMLE+. In a London clinic cohort, the HREM was the most common mutation in familial ALS+/-FTD: C9ORF72 29/112 (26%), SOD1 27/112 (24%), TARDBP 1/112 (1%) and FUS 4/112 (4%) and detected in 13/216 (6%) of unselected sporadic ALS cases but was rare in controls (3/856, 0.3%). HREM prevalence was high for familial ALS+/-FTD throughout Europe: Belgium 19/22 (86%), Sweden 30/41 (73%), the Netherlands 10/27 (37%) and Italy 4/20 (20%). The HREM did not affect the age at onset or survival of ALS patients. Haplotype analysis identified a common founder in all 137 HREM carriers that arose around 6300 years ago. The haplotype from which the HREM arose is intrinsically unstable with an increased number of repeats (average 8, compared with 2 for controls, P<10(-8)). We conclude that the HREM has a single founder and is the most common mutation in familial and sporadic ALS in Europe.

[C9orf72 in Japanese amyotrophic lateral sclerosis (ALS)]

Recently, C9orf72 hexanucleotide (GGGGCC) repeat expansion in intron 1 was reported to be the most common cause of sporadic and familial amyotrophic lateral sclerosis (ALS)/frontotemporal dementia (FTD) in the Caucasian population. The frequency of the intronic repeat expansion is up to 21%-57% in familial ALS and 3%-21% in sporadic ALS.In the Japanese population, the C9orf72 repeat expansion was found to account for 2.8% (3/109) of familial ALS, 0.4% (4/891) of sporadic ALS, and 0% (0/377) of normal healthy controls. Notably, among the Kii peninsula which has recorded a high incidence of ALS or ALS/PDC (parkinsonism-dementia complex), the frequency of the C9orf72 repeat expansion was 20% (3/15) indicating a high prevalence. All patients with the repeat expansion had a common risk haplotype within a narrower region than the Finnish one, suggesting a common founder effect which spread from Europe to East Asia in human migration history.Although Japanese ALS patients with the C9orf72 repeat expansion were rarer than Caucasian patients, we should check family histories of other neurological disorders such as dementia and FTD and should do genetic testing more actively even in sporadic ALS patients. Further studies of C9orf72 will clarify the pathogenesis and find the treatments for familial and sporadic ALS (or ALS/FTD).

[An advanced case of myopathy and dementia with a new mutation in the valosin-containing protein gene]

We report a 51-year-old man with myopathy and dementia probably caused by a novel mutation of the valosin-containing protein (VCP) gene, in the form of a p.Ala439Pro substitution. At 43 years old, he presented at least 2-year history of weakness of right ankle dorsiflexion. Findings from muscle biopsy suggested distal myopathy with rimmed vacuoles. However, no mutation in the GNE gene was identified. He complained of giving way of the knee, and muscle imaging study showed adipose tissue infiltration in the quadriceps. Ten years later, he was confined to a wheelchair and became reticent and antisocial with slightly impaired memory. A muscle CT revealed atrophy or replacement by adipose tissue in the muscles of neck, trunks and extremities muscles with laterality and variation of the degree. The magnetic resonance imaging of the brain showed bilateral frontal and temporal lobe atrophy with left dominance. Findings were compatible with inclusion body myopathy with Paget's disease of bone and frontotemporal dementia.

The homozygote VCP(R¹⁵⁵H/R¹⁵⁵H) mouse model exhibits accelerated human VCP-associated disease pathology

Valosin containing protein (VCP) mutations are the cause of hereditary inclusion body myopathy, Paget's disease of bone, frontotemporal dementia (IBMPFD). VCP gene mutations have also been linked to 2% of isolated familial amyotrophic lateral sclerosis (ALS). VCP is at the intersection of disrupted ubiquitin proteasome and autophagy pathways, mechanisms responsible for the intracellular protein degradation and abnormal pathology seen in muscle, brain and spinal cord. We have developed the homozygous knock-in VCP mouse (VCP(R155H/R155H)) model carrying the common R155H mutations, which develops many clinical features typical of the VCP-associated human diseases. Homozygote VCP(R155H/R155H) mice typically survive less than 21 days, exhibit weakness and myopathic changes on EMG. MicroCT imaging of the bones reveal non-symmetrical radiolucencies of the proximal tibiae and bone, highly suggestive of PDB. The VCP(R155H/R155H) mice manifest prominent muscle, heart, brain and spinal cord pathology, including striking mitochondrial abnormalities, in addition to disrupted autophagy and ubiquitin pathologies. The VCP(R155H/R155H) homozygous mouse thus represents an accelerated model of VCP disease and can be utilized to elucidate the intricate molecular mechanisms involved in the pathogenesis of VCP-associated neurodegenerative diseases and for the development of novel therapeutic strategies.

Epidemiology and genetics of frontotemporal dementia: a door-to-door survey in southern Italy

The objectives of this study were to estimate frontotemporal dementia (FTD) prevalence, identify FTD-related mutations, and correlate FTD phenotype with mutations in a southern Italian population. The study population consisted of subjects ≥ 50 years of age residing in the Community of Biv. on January 1, 2004, and a door-to-door 2-phase design was used. Genetic and biochemical analyses were done on samples collected from 32 patients. Prevalence rates were 0.6 for Alzheimer's disease, 0.4 for vascular dementia (VD), 3.5 for FTD, 0.2 for Parkinson dementia, and 1.2 for unspecified dementia. Three GRN (1 known and 2 novel) mutations with reduced plasma protein levels were found associated to 3 distinct phenotypes (behavioral, affective, and delirious type). We report an unusually high FTD prevalence in the investigated population, but a low prevalence of Alzheimer's disease. We confirm the heterogeneity of FTD phenotype associated with different GRN mutations.

TDP-1/TDP-43 regulates stress signaling and age-dependent proteotoxicity in Caenorhabditis elegans

TDP-43 is a multifunctional nucleic acid binding protein linked to several neurodegenerative diseases including Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia. To learn more about the normal biological and abnormal pathological role of this protein, we turned to Caenorhabditis elegans and its orthologue TDP-1. We report that TDP-1 functions in the Insulin/IGF pathway to regulate longevity and the oxidative stress response downstream from the forkhead transcription factor DAF-16/FOXO3a. However, although tdp-1 mutants are stress-sensitive, chronic upregulation of tdp-1 expression is toxic and decreases lifespan. ALS–associated mutations in TDP-43 or the related RNA binding protein FUS activate the unfolded protein response and generate oxidative stress leading to the daf-16–dependent upregulation of tdp-1 expression with negative effects on neuronal function and lifespan. Consistently, deletion of endogenous tdp-1 rescues mutant TDP-43 and FUS proteotoxicity in C. elegans. These results suggest that chronic induction of wild-type TDP-1/TDP-43 by cellular stress may propagate neurodegeneration and decrease lifespan.

TAR DNA Binding Protein 43 (TDP-43) is implicated in several human age-dependent neurodegenerative disorders, but until now little was known about TDP-43's role in the aging process. Here we used the nematode Caenorhabditis elegans to study the role of the TDP-43 orthologue tdp-1 in aging and neurodegeneration. In this study we discovered that tdp-1 is a stress-responsive gene acting within the Insulin/IGF signaling pathway to regulate lifespan and the response to oxidative stress. We found that, although worms missing tdp-1 were stress-sensitive, elevated expression of tdp-1 was toxic. We asked if tdp-1 also responded to the stress caused by toxic proteins found in Amyotrophic Lateral Sclerosis (ALS). Using worm models for ALS, we discovered that mutant TDP-43 generated oxidative stress and induced tdp-1 expression with negative consequences on neuronal function and lifespan. Consistently, removing tdp-1 rescued toxicity in our worm ALS models. tdp-1's role in the cellular stress response likely reflects an ancient adaptation to deal with unfavorable environmental conditions that is inappropriately activated and maintained by genetic mutations leading to proteotoxic and oxidative stress. We predict that similar mechanisms may exist in humans, helping explain the involvement of TDP-43 in a growing number of neurodegenerative disorders.

TAR DNA Binding Protein 43 (TDP-43) is implicated in several human age-dependent neurodegenerative disorders, but until now little was known about TDP-43's role in the aging process. Here we used the nematode Caenorhabditis elegans to study the role of the TDP-43 orthologue tdp-1 in aging and neurodegeneration. In this study we discovered that tdp-1 is a stress-responsive gene acting within the Insulin/IGF signaling pathway to regulate lifespan and the response to oxidative stress. We found that, although worms missing tdp-1 were stress-sensitive, elevated expression of tdp-1 was toxic. We asked if tdp-1 also responded to the stress caused by toxic proteins found in Amyotrophic Lateral Sclerosis (ALS). Using worm models for ALS, we discovered that mutant TDP-43 generated oxidative stress and induced tdp-1 expression with negative consequences on neuronal function and lifespan. Consistently, removing tdp-1 rescued toxicity in our worm ALS models. tdp-1's role in the cellular stress response likely reflects an ancient adaptation to deal with unfavorable environmental conditions that is inappropriately activated and maintained by genetic mutations leading to proteotoxic and oxidative stress. We predict that similar mechanisms may exist in humans, helping explain the involvement of TDP-43 in a growing number of neurodegenerative disorders.

A clinical approach to early-onset inheritable dementia

Early-onset dementia, presenting before age 65 years, is increasingly recognized. It is often difficult to diagnose, since non-Alzheimer's etiologies and unusual dementias are common. These conditions are more commonly genetic, and important potentially inherited causes of early-onset dementia include early-onset Alzheimer's disease, frontotemporal dementia, Kufs' disease, and Niemann-Pick disease type C. For each of these diseases, this review provides information on common clinical presentations, etiology, pathophysiology, and current and experimental treatments. A discussion of the diagnosis and workup for early-onset dementia is included with an emphasis on conditions that may have other involved family members.

Frequency of the C9orf72 hexanucleotide repeat expansion in patients with amyotrophic lateral sclerosis and frontotemporal dementia: a cross-sectional study

BACKGROUND

We aimed to accurately estimate the frequency of a hexanucleotide repeat expansion in C9orf72 that has been associated with a large proportion of cases of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD).

METHODS

We screened 4448 patients diagnosed with ALS (El Escorial criteria) and 1425 patients with FTD (Lund-Manchester criteria) from 17 regions worldwide for the GGGGCC hexanucleotide expansion using a repeat-primed PCR assay. We assessed familial disease status on the basis of self-reported family history of similar neurodegenerative diseases at the time of sample collection. We compared haplotype data for 262 patients carrying the expansion with the known Finnish founder risk haplotype across the chromosomal locus. We calculated age-related penetrance using the Kaplan-Meier method with data for 603 individuals with the expansion.

FINDINGS

In patients with sporadic ALS, we identified the repeat expansion in 236 (7·0%) of 3377 white individuals from the USA, Europe, and Australia, two (4·1%) of 49 black individuals from the USA, and six (8·3%) of 72 Hispanic individuals from the USA. The mutation was present in 217 (39·3%) of 552 white individuals with familial ALS from Europe and the USA. 59 (6·0%) of 981 white Europeans with sporadic FTD had the mutation, as did 99 (24·8%) of 400 white Europeans with familial FTD. Data for other ethnic groups were sparse, but we identified one Asian patient with familial ALS (from 20 assessed) and two with familial FTD (from three assessed) who carried the mutation. The mutation was not carried by the three Native Americans or 360 patients from Asia or the Pacific Islands with sporadic ALS who were tested, or by 41 Asian patients with sporadic FTD. All patients with the repeat expansion had (partly or fully) the founder haplotype, suggesting a one-off expansion occurring about 1500 years ago. The pathogenic expansion was non-penetrant in individuals younger than 35 years, 50% penetrant by 58 years, and almost fully penetrant by 80 years.

INTERPRETATION

A common Mendelian genetic lesion in C9orf72 is implicated in many cases of sporadic and familial ALS and FTD. Testing for this pathogenic expansion should be considered in the management and genetic counselling of patients with these fatal neurodegenerative diseases.

FUNDING

Full funding sources listed at end of paper (see Acknowledgments).

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

The identification of a hexanucleotide repeat expansion in the C9ORF72 gene as the cause of chromosome 9-linked frontotemporal dementia and motor neuron disease offers the opportunity for greater understanding of the relationship between these disorders and other clinical forms of frontotemporal lobar degeneration. In this study, we screened a cohort of 398 patients with frontotemporal dementia, progressive non-fluent aphasia, semantic dementia or mixture of these syndromes for mutations in the C9ORF72 gene. Motor neuron disease was present in 55 patients (14%). We identified 32 patients with C9ORF72 mutations, representing 8% of the cohort. The patients' clinical phenotype at presentation varied: nine patients had frontotemporal dementia with motor neuron disease, 19 had frontotemporal dementia alone, one had mixed semantic dementia with frontal features and three had progressive non-fluent aphasia. There was, as expected, a significant association between C9ORF72 mutations and presence of motor neuron disease. Nevertheless, 46 patients, including 22 familial, had motor neuron disease but no mutation in C9ORF72. Thirty-eight per cent of the patients with C9ORF72 mutations presented with psychosis, with a further 28% exhibiting paranoid, deluded or irrational thinking, whereas <4% of non-mutation bearers presented similarly. The presence of psychosis dramatically increased the odds that patients carried the mutation. Mutation bearers showed a low incidence of motor stereotypies, and relatively high incidence of complex repetitive behaviours, largely linked to patients' delusions. They also showed a lower incidence of acquired sweet food preference than patients without C9ORF72 mutations. Post-mortem pathology in five patients revealed transactive response DNA-binding protein 43 pathology, type A in one patient and type B in three. However, one patient had corticobasal degeneration pathology. The findings indicate that C9ORF72 mutations cause some but not all cases of frontotemporal dementia with motor neuron disease. Other mutations remain to be discovered. C9ORF72 mutations are associated with variable clinical presentations and pathology. Nevertheless, the findings highlight a powerful association between C9ORF72 mutations and psychosis and suggest that the behavioural characteristics of patients with C9ORF72 mutations are qualitatively distinct. Mutations in the C9ORF72 gene may be a major cause not only of frontotemporal dementia with motor neuron disease but also of late onset psychosis.

[From Pick's disease to frontotemporal dementia]

Frontotemporal dementias (FTD) are defined by a gradual change in social conduct, behavior and language, associated with frontal and anterior temporal lobe degeneration. The clinicalfeatures depend on the location of the degenerative process. In the last 20 years, increasingly specific and sensitive operational criteria have been established. Ongoing neuropathological and genetic studies have highlighted overlaps between FTD, motor neuron disease, and atypical parkinsonian syndromes (supranuclear palsy, corticobasal degeneration). They have also provided a better knowledge of the pathophysiology of FTD, and new specific therapeutic targets. These dementias, which usually occur before the age of 65 years, are now better recognized but are still underdiagnosed and often initially mistaken for psychiatric illnesses. Healthcare professionals managing these patients must therefore be better informed Serotonergic agents provide a symptomatic improvement, but environmental adaptation, prevention of language and swallowing difficulties, and information and support for the family and caregivers remain essential.

Chromosome 9 ALS and FTD locus is probably derived from a single founder

We and others have recently reported an association between amyotrophic lateral sclerosis (ALS) and single nucleotide polymorphisms on chromosome 9p21 in several populations. Here we show that the associated haplotype is the same in all populations and that several families previously shown to have genetic linkage to this region also share this haplotype. The most parsimonious explanation of these data are that there is a single founder for this form of disease.

[FTDP-17 presenting amnestic MCI as an initial symptom: case report]

A 46-year-old woman was admitted to our hospital for examination of her amnesia. Psychiatric examinations revealed that her recent memory was moderately disturbed despite well-preserved general cognitive function. Brain MRI and I-IMP SPECT (eZIS) revealed mild brain atrophy and hypoperfusion localized to the hippocampus, superior parietal lobule, and posterior cingulate gyrus. She was diagnosed with amnestic MCI at that time. However, five years later, she developed personality changes, parkinsonism and dementia. Investigation of her family medical history revealed that the patient's two sisters are demented and under the medical care. DNA analysis revealed an intronic mutation IVS10 C>T in the MAPT gene. Although her two sisters also have the same mutation, her elder sister has typical FTD without parkinsonism. Approximately 10% of patients with amnestic MCI develop Alzheimer's disease each year. Thus, amnestic MCI has been usually considered to be an early stage of Alzheimer's disease. Interestingly our patient having a MAPT gene mutation started to develop amnestic MCI as an initial symptom. Therefore because of the diversity in early clinical features of FTDP-17, aggressive DNA analysis is necessary for accurate diagnosis.

FTD and ALS: genetic ties that bind

Curiously, amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), seemingly disparate neurodegenerative disorders, can be inherited together. Two groups (DeJesus-Hernandez et al. and Renton et al.) show that the long sought after ALS/FTD mutation on chromosomal region 9p is a hexanucleotide expansion in C90RF72. These studies, plus a study on X-linked ALS/FTD, provide molecular starting points for identifying pathways that link ALS and FTD pathogenesis.

Another VCP interactor: NF is enough

Inclusion body myopathy with Paget disease of the bone and frontotemporal dementia (IBMPFD) is a multisystem degenerative disorder caused by mutations in the valosin-containing protein (VCP) gene. How missense mutations in this abundant, ubiquitously expressed, multifunctional protein lead to the degeneration of disparate tissues is unclear. VCP participates in diverse cellular functions by associating with an expanding collection of substrates and cofactors that dictate its functionality. In this issue of the JCI, Wang and colleagues have further expanded the VCP interactome by identifying neurofibromin-1 (NF1) as a novel VCP interactor in the CNS. IBMPFD-associated mutations disrupt binding of VCP to NF1, resulting in reduced synaptogenesis. Thus, aberrant interactions between VCP and NF1 may explain the dementia phenotype and cognitive delay observed in patients with IBMPFD and neurofibromatosis type 1.

Clinical and neuropathologic heterogeneity of c9FTD/ALS associated with hexanucleotide repeat expansion in C9ORF72

Frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) are part of a disease spectrum associated with TDP-43 pathology. Strong evidence supporting this is the existence of kindreds with family members affected by FTD, ALS or mixed features of FTD and ALS, referred to as FTD-MND. Some of these families have linkage to chromosome 9, with hexanucleotide expansion mutation in a noncoding region of C9ORF72. Discovery of the mutation defines c9FTD/ALS. Prior to discovery of mutations in C9ORF72, it was assumed that TDP-43 pathology in c9FTD/ALS was uniform. In this study, we examined the neuropathology and clinical features of 20 cases of c9FTD/ALS from a brain bank for neurodegenerative disorders. Included are six patients clinically diagnosed with ALS, eight FTD, one FTD-MND and four Alzheimer-type dementia. Clinical information was unavailable for one patient. Pathologically, the cases all had TDP-43 pathology, but there were three major pathologic groups: ALS, FTLD-MND and FTLD-TDP. The ALS cases were morphologically similar to typical sporadic ALS with almost no extramotor TDP-43 pathology; all had oligodendroglial cytoplasmic inclusions. The FTLD-MND showed predominantly Mackenzie Type 3 TDP-43 pathology, and all had ALS-like pathology in motor neurons, but more extensive extramotor pathology, with oligodendroglial cytoplasmic inclusions and infrequent hippocampal sclerosis. The FTLD-TDP cases had several features similar to FTLD-TDP due to mutations in the gene for progranulin, including Mackenzie Type 1 TDP-43 pathology with neuronal intranuclear inclusions and hippocampal sclerosis. FTLD-TDP patients were older and some were thought to have Alzheimer-type dementia. In addition to the FTD and ALS clinical presentations, the present study shows that c9FTD/ALS can have other presentations, possibly related to age of onset and the presence of hippocampal sclerosis. Moreover, there is pathologic heterogeneity not only between ALS and FTLD, but also within the FTLD group. Further studies are needed to address the molecular mechanism of clinical and pathological heterogeneity of c9FTD/ALS due to mutations in C9ORF72.

Globular glial tauopathies (GGT) presenting with motor neuron disease or frontotemporal dementia: an emerging group of 4-repeat tauopathies

A number of recent studies have described cases with tau-positive globular oligodendroglial inclusions (GOIs) and such cases have overlapping pathological features with progressive supranuclear palsy (PSP), but present with clinical features of motor neuron disease (MND) and/or frontotemporal dementia (FTD). These two clinical phenotypes have been published independently and as a result, have come to be considered as distinct disease entities. We describe the clinicopathological and biochemical features of two cases with GOIs: one with clinical symptoms suggestive of MND and the other with FTD. Histological changes in our two cases were consistent with their clinical symptoms; the MND case had severe neurodegeneration in the primary motor cortex and corticospinal tract, whereas the FTD case had severe involvement of the frontotemporal cortices and associated white matter. Immunohistochemistry in both cases revealed significant 4-repeat (4R) tau pathology primarily in the form of GOIs, but also in astrocytes and neurons. Astrocytic tau pathology was morphologically similar to that seen in PSP, but in contrast was consistently negative for Gallyas silver staining. Tau-specific western blotting revealed 68, 64 and 35 kDa bands, showing further overlap with PSP. The underlying neuropathological features of these two cases were similar, with the major difference relating to the regional distribution of pathology and resulting clinical symptoms and signs. The globular nature of glial inclusions and the non-fibrillar properties of tau in astrocytes are characteristic features that allow them to be distinguished from PSP and other tauopathies. We, therefore, propose the term globular glial tauopathy as an encompassing term to classify this emerging class of 4R tauopathy.

A novel exon 2 I27V VCP variant is associated with dissimilar clinical syndromes

Mutations in valosin-containing protein (VCP) are associated with a syndromic constellation of inclusion body myositis, Paget's disease of bone and frontotemporal dementia. Here we describe the case reports of two patients with a novel variation (p.I27V) in the VCP gene that was not identified in a healthy control population. One patient presented with a frontotemporal dementia syndrome associated with raised serum alkaline phosphatase and a family history of progressive muscle disease and behavioural decline, while the second patient presented with isolated progressive dysarthria. Together these cases suggest a potential for the same VCP mutation to produce distinct patterns of brain damage, underlining the clinical heterogeneity of VCP-associated disease.

FUS transgenic rats develop the phenotypes of amyotrophic lateral sclerosis and frontotemporal lobar degeneration

Fused in Sarcoma (FUS) proteinopathy is a feature of frontotemporal lobar dementia (FTLD), and mutation of the fus gene segregates with FTLD and amyotrophic lateral sclerosis (ALS). To study the consequences of mutation in the fus gene, we created transgenic rats expressing the human fus gene with or without mutation. Overexpression of a mutant (R521C substitution), but not normal, human FUS induced progressive paralysis resembling ALS. Mutant FUS transgenic rats developed progressive paralysis secondary to degeneration of motor axons and displayed a substantial loss of neurons in the cortex and hippocampus. This neuronal loss was accompanied by ubiquitin aggregation and glial reaction. While transgenic rats that overexpressed the wild-type human FUS were asymptomatic at young ages, they showed a deficit in spatial learning and memory and a significant loss of cortical and hippocampal neurons at advanced ages. These results suggest that mutant FUS is more toxic to neurons than normal FUS and that increased expression of normal FUS is sufficient to induce neuron death. Our FUS transgenic rats reproduced some phenotypes of ALS and FTLD and will provide a useful model for mechanistic studies of FUS–related diseases.

Amyotrophic lateral sclerosis and frontotemporal lobar degeneration are two related diseases characterized by degeneration of selected groups of neuronal cells. Neither of these diseases has a clear cause, and both are incurable at present. Mutation of the fus gene has recently been linked to these two diseases. Here, we describe a novel rat model that expresses a mutated form of the human fus gene and manifests the phenotypes and pathological features of amyotrophic lateral sclerosis and frontotemporal lobar degeneration. Establishment of this FUS transgenic rat model will allow not only for mechanistic study of FUS–related diseases, but also for quick development of therapies for these devastating diseases.

Pathogenic VCP/TER94 alleles are dominant actives and contribute to neurodegeneration by altering cellular ATP level in a Drosophila IBMPFD model

Inclusion body myopathy with Paget's disease of bone and frontotemporal dementia (IBMPFD) is caused by mutations in Valosin-containing protein (VCP), a hexameric AAA ATPase that participates in a variety of cellular processes such as protein degradation, organelle biogenesis, and cell-cycle regulation. To understand how VCP mutations cause IBMPFD, we have established a Drosophila model by overexpressing TER94 (the sole Drosophila VCP ortholog) carrying mutations analogous to those implicated in IBMPFD. Expression of these TER94 mutants in muscle and nervous systems causes tissue degeneration, recapitulating the pathogenic phenotypes in IBMPFD patients. TER94-induced neurodegenerative defects are enhanced by elevated expression of wild-type TER94, suggesting that the pathogenic alleles are dominant active mutations. This conclusion is further supported by the observation that TER94-induced neurodegenerative defects require the formation of hexamer complex, a prerequisite for a functional AAA ATPase. Surprisingly, while disruptions of the ubiquitin-proteasome system (UPS) and the ER-associated degradation (ERAD) have been implicated as causes for VCP-induced tissue degeneration, these processes are not significantly affected in our fly model. Instead, the neurodegenerative defect of TER94 mutants seems sensitive to the level of cellular ATP. We show that increasing cellular ATP by independent mechanisms could suppress the phenotypes of TER94 mutants. Conversely, decreasing cellular ATP would enhance the TER94 mutant phenotypes. Taken together, our analyses have defined the nature of IBMPFD-causing VCP mutations and made an unexpected link between cellular ATP level and IBMPFD pathogenesis.

Compound heterozygosity of 2 novel MAPT mutations in frontotemporal dementia

Intronic MAPT mutations altering exon 10 splicing lead mainly to an increase of 4Rtau. The objective of this study is to report clinical, genetic, and neuropathological data of an apparently sporadic early onset frontotemporal dementia (FTD) case associated with 2 novel intronic MAPT gene mutations IVS10+4A > C and IVS9-15T > C that increase 3Rtau. Methods and subjects used are clinical, neuroradiological, and neuropathological examination; molecular genetics of MAPT, PGRN, and other relevant genes. Exon 10 splicing tested with minigene constructs. Tau deposits detected by immunohistochemistry. Sarkosyl-insoluble and soluble tau investigated by immunoblotting. Two novel MAPT mutations IVS10+4A > C and the IVS9-15T > C transmitted by the unaffected parents were identified. Semiquantitative reverse transcription polymerase chain reaction (RT-PCR) analyses on minigenes and in brain tissue showed that both mutations cause an increase of tau mRNA (messenger ribonucleic acid) transcripts lacking exon 10 only in the patient. Immunohistochemistry and immunoblotting of the patient's brain revealed tau deposits composed mostly of 3Rtau isoforms with a predominance of the shorter 3Rtau isoforms. The compound heterozygosity of the patient increasing 3Rtau seems to be responsible for the disease and furthermore suggests that sporadic cases can be caused by genetic mutations.

[Yuasa-Mitsuyama disease]

Frontotemporal dementia (FTD) is a clinical entity that comprises at least two distinct diseases: Pick's disease with Pick bodies and frontotemporal lobar degeneration with tau-negative and ubiquitin-positive inclusions (FTLD-U). FTLD-U is now usually referred to as FTLD-TAR DNA binding protein 43 (TDP-43). FTLD-TDP-43, but not Pick's disease with tau-positive Pick bodies, is often associated with motor neuron disease (MND). More than 200 cases of this combined form, i.e., FTD-MND, have been reported in Japan. The neuropathological characteristics of MND in patients with FTD are essentially similar to the MND in patients without dementia. However the other characteristics of the combination of FTD and MND are such that the author has considered this disease a unique clinicopathological entity. These characteristics are as follows: (1) frontotemporal lobe-type dementia with insidious onset, usually in the presenile period; (2) neurogenic muscular wasting during the course of the illness [amyotrophic lateral sclerosis (ALS)]-- or [spinal progressive muscular atrophy (SPMA)]-like symptoms); (3) duration from the onset of illness to death is 2-5 years (average duration, 30.6 months); (4) both extrapyramidal symptoms and definite sensory deficiency are less commonly observed; (5) no characteristic abnormalities in the cerebrospinal fluid (CSF) or on the electroencephalogram (EEG) in screening tests; (6) no known parental consanguinity or familial occurrence; and (7) nonspecific mild-to-slight degenerative changes in the frontotemporal cortex, hypoglossal nuclei, spinal cord, and frequently in the substantia nigra. FTD-MND is characterized by ubiquitin-immunoreactive intraneuronal inclusions in cortical layers II and III and the hippocampal dentate granule cells. The occurrence of ubiquitin-positive, tau-negative and ubiquitinated TDP-43 positive inclusions could be the key to determining the pathological background of this disease. Further studies are required clinicopathological differentiation between FTD-MND and ALS-dementia (ALS-D).

Sortilin-mediated endocytosis determines levels of the frontotemporal dementia protein, progranulin

VIDEO ABSTRACT

The most common inherited form of Frontotemporal Lobar Degeneration (FTLD) known stems from Progranulin (GRN) mutation and exhibits TDP-43 plus ubiquitin aggregates. Despite the causative role of GRN haploinsufficiency in FTLD-TDP, the neurobiology of this secreted glycoprotein is unclear. Here, we examined PGRN binding to the cell surface. PGRN binds to cortical neurons via its C terminus, and unbiased expression cloning identifies Sortilin (Sort1) as a binding site. Sort1⁻/⁻ neurons exhibit reduced PGRN binding. In the CNS, Sortilin is expressed by neurons and PGRN is most strongly expressed by activated microglial cells after injury. Sortilin rapidly endocytoses and delivers PGRN to lysosomes. Mice lacking Sortilin have elevations in brain and serum PGRN levels of 2.5- to 5-fold. The 50% PGRN decrease causative in FTLD-TDP cases is mimicked in GRN+/⁻ mice, and is fully normalized by Sort1 ablation. Sortilin-mediated PGRN endocytosis is likely to play a central role in FTLD-TDP pathophysiology.

Contemporary approaches to Alzheimer's disease and frontotemporal dementia

Alzheimer's disease and frontotemporal dementia are two of the most common neurodegenerative dementias. Here, we review the clinical presentation, genetic causes, typical neuropathology, and current treatments for these disorders. We then review molecules involved in their pathogenesis and protocols for working with these species and conclude with a discussion of experimental systems and outcome measures for studying these disorders.

Pathogenic TARDBP mutations in amyotrophic lateral sclerosis and frontotemporal dementia: disease-associated pathways

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are late-onset neurodegenerative disorders that are associated with mutations in the TARDBP gene. The product of this gene, TDP-43, has also been identified as the main component of the intracellular inclusions typical of most cases of ALS and FTD. Recent evidence suggests that TDP-43 is essential for proper development and involved in several fundamental cellular processes, including gene transcription, RNA processing, and the spatial regulation of mRNA translation. Pathogenic TARDBP mutations that impair TDP-43 function could therefore be related to neuronal degeneration in ALS and FTD. Conversely, cellular and animal studies have shown that pathogenic TARDBP mutations induce neuronal toxicity through mislocalization or elevated concentrations of TDP-43, consistent with a gain-of-function mechanism. In this review, we focus on the physiologic functions of TDP-43 within the central nervous system and discuss how these functions may be perturbed or pathologically altered by disease-associated mutations.

Alzheimer's Disease Drug Discovery--11th International Conference--Targeting Pathological Tau. 27-28 September 2010, Jersey City, NJ, USA

The 11th Alzheimer's Disease Drug Discovery International Conference, held in Jersey City, NJ, USA, included topics covering new therapeutic developments in the field of Alzheimer's disease. This conference report highlights selected presentations on targeting pathological tau for the prevention or treatment of Alzheimer's disease. Investigational approaches discussed include aminothienopyridazine inhibitors of tau aggregation, the alternative splicing of tau pre-mRNA, protein phosphatase 2A as a potential therapeutic target, and immunotherapy and macroautophagy approaches for clearing aberrant tau protein from the brain.

TDP-43 and FUS in amyotrophic lateral sclerosis and frontotemporal dementia

Abnormal intracellular protein aggregates comprise a key characteristic in most neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). The seminal discoveries of accumulation of TDP-43 in most cases of ALS and the most frequent form of FTD, frontotemporal lobar degeneration with ubiquitinated inclusions, followed by identification of FUS as the novel pathological protein in a small subset of patients with ALS and various FTD subtypes provide clear evidence that these disorders are related. The creation of a novel molecular classification of ALS and FTD based on the identity of the predominant protein abnormality has, therefore, been possible. The striking functional and structural similarities of TDP-43 and FUS, which are both DNA/RNA binding proteins, imply that abnormal RNA metabolism is a pivotal event, but the mechanisms leading to TDP-43 and FUS accumulation and the resulting neurodegeneration are currently unknown. Nonetheless, TDP-43 and FUS are promising candidates for the development of novel biomarker assays and targeted therapies.

Frontotemporal dementia or frontotemporal lobar degeneration--overview of a group of proteinopathies

Frontotemporal dementia is the second most common early onset dementia after Alzheimer disease. Frontotemporal dementias are a complex group of dementias. The clinical diagnosis can be perplexing because of concurring psychiatric and neurologic syndromes. Frontotemporal lobar degeneration, the underlying pathology, represents an emerging group of proteinopathies. Genetic factors play an important part in the etiologies of dementias. This article overviews current defining characteristics of frontotemporal dementias known also as frontotemporal lobar degenerations.

Frontotemporal dementia, Pick's disease

A significant expansion of knowledge in the last few years, especially in the molecular biology of frontotemporal dementia (FTD) is summarized. This condition, formerly known as Pick's disease and considered rare, is estimated to be 12-15% of all dementias and 30-50% early onset ones. The clinical picture is protean, mainly a behavioural and language impairment, but the extrapyramidal syndromes of CBD and PSP also belong. These seemingly different presentations converge, as one or other areas in the brain are affected. Less than half of the cases are tauopathies, the majority has been discovered to have a TDP-43 and most recently a FUS proteinopathy, shared with ALS, opening potential opportunities for pharmacological approaches to treatment. Tau and progranulin mutations on Ch-17 and some others, point to molecular mechanisms. A glossary is provided to navigate the complex terminology.

[Amyotrophic lateral sclerosis and frontotemporal dementia: overlapping characteristics]

There is an overlap between amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Some 5-10% of ALS patients show changes in their behaviour and personality that are characteristic of FTD and about 10% of FTD patients develop ALS. Mild cognitive impairment occurs in 30% of ALS patients. The progressive decline of muscle strength in ALS patients and social skills in FTD patients places severe demands on the patient and his or her contacts. In some ALS and FTD patients, ubiquitin-positive inclusions have been found in the hippocampus and anterior horn cells. In patients with familial FTD who have ubiquitin-positive inclusions, mutations have been found in the progranulin (PGRN) gene. TAR-DNA-binding protein-43, encoded by the TARDBP gene, has recently been identified as a constituent of the ubiquitin inclusions. TARDBP and PGRN mutations are found in patients with ALS. The overlapping characteristics provide clues for further research into the pathogenesis of ALS and FTD.

Purification, crystallization and preliminary X-ray diffraction analysis of disease-related mutants of p97

The human type II AAA+ protein p97 participates in various cellular activities, presumably through its involvement in the ubiquitin-proteasome degradation pathway. Mutations in p97 have been implicated in patients with inclusion-body myopathy associated with Paget's disease of the bone and frontotemporal dementia (IBMPFD). In this work, three mutant p97 N-D1 fragments, R86A, R95G and R155H, were crystallized in the presence of ATPgammaS with PEG 3350 as a main precipitant, yielding two different crystal forms. The R155H mutant crystal belonged to space group R3, with unit-cell parameters in the hexagonal setting of a = b = 134.2, c = 182.9 angstrom, and was merohedrally twinned, with an estimated twin fraction of 0.34. The crystals of the R86A and R95G mutants belonged to space group P1, with similar unit-cell parameters of a = 90.89, b = 102.6, c = 107.2 angstrom, alpha = 97.5, beta = 90.6, gamma = 91.5 degrees and a = 92.76, b = 103.7, c = 107.7 angstrom , alpha = 97.7, beta = 91.9, gamma = 89.7 degrees, respectively.

[Clinical, pathological, and genetic characteristics of frontotemporal dementia and parkinsonism linked to chromosome 17 with mutations in the MAPT and PGRN]

We reviewed the clinical, neuropathological, and genetic findings in patients with frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) with mutations in microtubule-associated protein tau (MAPT) and progranulin (PGRN). Research on FTDP-17 has greatly progressed over the years. Clinically, FTDP-17 is clinically characterized by autosomal dominant frontotemporal dementia, with or without parkinsonism. Two pathological variants of FTDP-17 are seen: one characterized by tau aggregation in neurons and glial cells, and the other, by ubiquitin-positive inclusions in neurons. Mutations in the MAPT gene have been identified as a cause of familial tau-positive FTDP-17 (MAPT), whereas mutations in the gene encoding PGRN, which is located 1.7 Mb from the MAPT gene on chromosome 17, have been identified in familial ubiquitin-positive FTDP-17 (PGRN). Recent studies have identified 44 different mutations in more than 100 families with FTDP-17 (MAPT), and 66 different mutations in more than 100 families with FTDP-17 (PGRN). Although cases of FTDP-17 have been reported worldwide, FTDP-17 (PGRN) has not yet been seen in Japan. The discovery of monogenic forms of neurodegenerative diseases is important for understanding the pathogenesis of these diseases. The findings of future research may facilitate the understanding of the causes of FTDP, and further improve diagnostic tools and help develop novel preventive methods and treatments for not only the genetic but also the sporadic form of neurodegenerative disorders.

Molecular neuropathology of TDP-43 proteinopathies

The identification of TDP-43 as the major component of the pathologic inclusions in most forms of sporadic and familial frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U) and amyotrophic lateral sclerosis (ALS) resolved a long-standing enigma concerning the nature of the ubiquitinated disease protein under these conditions. Anti-TDP-43 immunohistochemistry and the recent development of novel tools, such as phosphorylation-specific TDP-43 antibodies, have increased our knowledge about the spectrum of pathological changes associated with FTLD-U and ALS and moreover, facilitated the neuropathological routine diagnosis of these conditions. This review summarizes the recent advances in our understanding on the molecular neuropathology and pathobiology of TDP-43 in FTLD and ALS.