"Frontotemporoparietal" dementia: clinical phenotype associated with the c.709-1G>A PGRN mutation

Characterization of Progranulin Gene Mutations in Portuguese Patients with Frontotemporal Dementia

In Portugal, heterozygous loss-of-function mutations in the progranulin (GRN) gene account for approximately half of the genetic mediated forms of frontotemporal dementia (FTD). GRN mutations reported thus far cause FTD through a haploinsufficiency disease mechanism. Herein, we aim to unveil the GRN mutation spectrum, investigated in 257 FTD patients and 19 family members from the central/north region of Portugal using sequencing methods. Seven different pathogenic variants were identified in 46 subjects including 40 patients (16%) and 6 relatives (32%). bvFTD was the most common clinical presentation among the GRN mutation patients, who showed a global pattern of moderate-to-severe frontotemporoparietal deficits in the neuropsychological evaluation. Interestingly, two mutations were novel (p.Thr238Profs*18, p.Leu354Profs*16), and five were previously described, although three of them only in the Portuguese population, suggesting a population-specific GRN mutational spectrum. The subjects harboring a GRN mutation showed a significant reduction in serum PGRN levels, supporting the pathogenic nature of these variants. This work broadens the mutation spectrum of GRN and the identification of the underlying GRN mutations provided an accurate genetic counselling and allowed the enrolment of subjects with GRN mutations (both asymptomatic and symptomatic) in ongoing clinical trials, which is essential to test new drugs for the disease.

Degenerative dementias: A question of syndrome or disease?

BACKGROUND

Neurologists refer to numerous "syndromes,‿ consisting of specific combinations of clinical manifestations, following a specific progression pattern, and with the support of blood analysis (without genomic-proteomic parameters) and neuroimaging findings (MRI, CT, perfusion SPECT, or 18F-FDG-PET scans). Neurodegenerative "diseases,‿ on the other hand, are defined by specific combinations of clinical signs and histopathological findings; these must be confirmed by a clinical examination and a histology study or evidence of markers of a specific disorder for the diagnosis to be made. However, we currently know that most genetic and histopathological alterations can result in diverse syndromes. The genetic or histopathological aetiology of each syndrome is also heterogeneous, and we may encounter situations with pathophysiological alterations characterising more than one neurodegenerative disease. Sometimes, specific biomarkers are detected in the preclinical stage.

DEVELOPMENT

We performed a literature review to identify patients whose histopathological or genetic disorder was discordant with that expected for the clinical syndrome observed, as well as patients presenting multiple neurodegenerative diseases, confirming the heterogeneity and overlap between syndromes and diseases. We also observed that the treatments currently prescribed to patients with neurodegenerative diseases are symptomatic.

CONCLUSIONS

Our findings show that the search for disease biomarkers should be restricted to research centres, given the lack of disease-modifying drugs or treatments improving survival. Moreover, syndromes and specific molecular or histopathological alterations should be managed independently of one another, and new "diseases‿ should be defined and adapted to current knowledge and practice.

Neuropsychological features of progranulin-associated frontotemporal dementia: a nested case-control study

The distinction between sporadic and genetic behavioural-variant frontotemporal dementia (bvFTD) regarding some neuropsychological (NP) features remains challenging. Specifically, progranulin (GRN)-associated bvFTD frequently presents with early episodic memory impairment and some degree of parietal dysfunction which are supporters of Alzheimer's disease (AD) diagnosis. In this context, we aimed to characterize the NP profile of GRN-bvFTD as compared to sporadic-bvFTD and AD in patients with mild dementia (Mini-Mental State Examination score ≥ 17 and Clinical Dementia Rating Scale score ≤ 1. We identified 21 patients at Centro Hospitalar e Universitário de Coimbra, Portugal with GRN mutations belonging to fifteen different families. As our focus was bvFTD variants, FTD-related aphasic forms (3 patients) were excluded. The remaining 18 GRN-bvFTD were further matched with 18 sporadic-bvFTD and 18 AD patients according to disease staging, age and education. All patients completed the Mini-Mental State Examination, Montreal Cognitive Assessment (MoCA) and a comprehensive NP assessment battery. Results were converted into z-scores. Differences between groups in individual NP measures and NP domains were assessed through non-parametric tests (Kruskal-Wallis test analysis) and eta squared (ŋ2) was calculated as a measure of effect size. Group comparisons show that GRN patients have worse performances on verbal retrieval processes (P = 0.039, ŋ2 = 0.110) and visuoconstructive abilities (P = 0.039, ŋ2 = 0.190) than sporadic bvFTD forms. When compared to AD, GRN patients present a higher impairment in frontal (P = 0.001, ŋ2 = 0.211) and parietal (P = 0.041, ŋ2 = 0.129) measures and a better performance in memory tasks (P = 0.020, ŋ2 = 0.120). Sporadic-bvFTD forms are worse than AD in frontal measures (P = 0.032, ŋ2 = 0.200), being better in both memory (P = 0.010, ŋ2 = 0.131) and visuospatial skills (P = 0.023, ŋ2 = 0.231). Considering these results, we conclude that GRN-bvFTD patients present a NP profile that associates the typical patterns of FTD and AD deficits. This is particularly expressive in visuoconstructive abilities, which was the more discriminative feature between groups, followed by episodic verbal memory. This study was approved by the Institutional Ethics Committee of Centro Hospitalar e Universitário de Coimbra, Portugal (CE-029/2019) on June 24, 2019.

Neuroimaging in Frontotemporal Dementia: Heterogeneity and Relationships with Underlying Neuropathology

Frontotemporal dementia encompasses a group of clinical syndromes defined pathologically by degeneration of the frontal and temporal lobes. Historically, these syndromes have been challenging to diagnose, with an average of about three years between the time of symptom onset and the initial evaluation and diagnosis. Research in the field of neuroimaging has revealed numerous biomarkers of the various frontotemporal dementia syndromes, which has provided clinicians with a method of narrowing the differential diagnosis and improving diagnostic accuracy. As such, neuroimaging is considered a core investigative tool in the evaluation of neurodegenerative disorders. Furthermore, patterns of neurodegeneration correlate with the underlying neuropathological substrates of the frontotemporal dementia syndromes, which can aid clinicians in determining the underlying etiology and improve prognostication. This review explores the advancements in neuroimaging and discusses the phenotypic and pathologic features of behavioral variant frontotemporal dementia, semantic variant primary progressive aphasia, and nonfluent variant primary progressive aphasia, as seen on structural magnetic resonance imaging and positron emission tomography.

Development of disease-modifying drugs for frontotemporal dementia spectrum disorders

Frontotemporal dementia (FTD) encompasses a spectrum of clinical syndromes characterized by progressive executive, behavioural and language dysfunction. The various FTD spectrum disorders are associated with brain accumulation of different proteins: tau, the transactive response DNA binding protein of 43 kDa (TDP43), or fused in sarcoma (FUS) protein, Ewing sarcoma protein and TATA-binding protein-associated factor 15 (TAF15) (collectively known as FET proteins). Approximately 60% of patients with FTD have autosomal dominant mutations in C9orf72, GRN or MAPT genes. Currently available treatments are symptomatic and provide limited benefit. However, the increased understanding of FTD pathogenesis is driving the development of potential disease-modifying therapies. Most of these drugs target pathological tau - this category includes tau phosphorylation inhibitors, tau aggregation inhibitors, active and passive anti-tau immunotherapies, and MAPT-targeted antisense oligonucleotides. Some of these therapeutic approaches are being tested in phase II clinical trials. Pharmacological approaches that target the effects of GRN and C9orf72 mutations are also in development. Key results of large clinical trials will be available in a few years. However, clinical trials in FTD pose several challenges, and the development of specific brain imaging and molecular biomarkers could facilitate the recruitment of clinically homogenous groups to improve the chances of positive clinical trial results.

Genotype-phenotype links in frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) represents a group of neurodegenerative brain diseases with highly heterogeneous clinical, neuropathological and genetic characteristics. This high degree of heterogeneity results from the presence of several different underlying molecular disease processes; consequently, it is unlikely that all patients with FTLD will benefit from a single therapy. Therapeutic strategies for FTLD are currently being explored, and tools are urgently needed that enable the selection of patients who are the most likely to benefit from a particular therapy. Definition of the phenotypic characteristics in patients with different FTLD subtypes that share the same underlying disease processes would assist in the stratification of patients into homogeneous groups. The most common subtype of FTLD is characterized by TAR DNA-binding protein 43 (TDP43) pathology (FTLD-TDP). In this group, pathogenic mutations have been identified in four genes: C9orf72, GRN, TBK1 and VCP. Here, we provide a comprehensive overview of the phenotypic characteristics of patients with FTLD-TDP, highlighting shared features and differences among groups of patients who have a pathogenic mutation in one of these four genes.

Promising therapies for the treatment of frontotemporal dementia clinical phenotypes: from symptomatic to disease-modifying drugs

INTRODUCTION

Frontotemporal dementia (FTD) is a heterogeneous clinical entity that includes several disorders characterized by different cellular mechanisms. Distinctive clinical features in FTD include behavioral, affective, and cognitive symptoms. Unfortunately, little progress has been made over the past 20 years in terms of the development of effective disease-modifying drugs with the currently available symptomatic treatments having limited clinical utility.

AREAS COVERED

This article reviews the principal pharmacological intervention studies for FTD. These are predominantly randomized clinical trials and include symptomatic treatments and potential disease-modifying drugs.

EXPERT OPINION

There is insufficient evidence on effective treatments for FTD and studies with better methodological backgrounds are needed. Most studies reporting therapeutic benefits were conducted with selective serotonin reuptake inhibitors, while anti-dementia drugs have been ineffective in FTD. Since the underlying pathology of FTD mostly consists of abnormal tau protein or TDP-43 aggregates, treatments are being developed to interfere with their aggregation process or with the clearance of these proteins. Furthermore, disease-modifying treatments remain years away as demonstrated by the recent negative Phase III findings of a tau aggregation inhibitor (LMTM) for treating the behavioral variant of FTD. The results from current ongoing Phase I/II trials will hopefully give light to future treatment options.

Genetic screen in a large series of patients with primary progressive aphasia

INTRODUCTION

Primary progressive aphasia (PPA) is a neurological syndrome, associated with both frontotemporal dementia and Alzheimer's disease, in which progressive language impairment emerges as the most salient clinical feature during the initial stages of disease.

METHODS

We screened the main genes associated with Alzheimer's disease and frontotemporal dementia for pathogenic and risk variants in a cohort of 403 PPA cases.

RESULTS

In this case series study, 14 (3.5%) cases carried (likely) pathogenic variants: four C9orf72 expansions, nine GRN, and one TARDBP mutation. Rare risk variants, TREM2 R47H and MAPT A152T, were associated with a three- to seven-fold increase in risk for PPA.

DISCUSSION

Our results show that while pathogenic variants within the most common dementia genes were rarely associated with PPA, these were found almost exclusively in GRN and C9orf72, suggesting that PPA is more TDP43- than tau-related in our series. This is consistent with the finding that PPA frequency in dominantly inherited dementias is the highest in kindreds with GRN variants.

Longitudinal Neuropsychological Study of Presymptomatic c.709-1G>A Progranulin Mutation Carriers

OBJECTIVE

The assessment of individuals from families affected by familial frontotemporal dementia (FTD) allows the evaluation of preclinical or pre-diagnosis disease markers. The current work aims to investigate the existence of a cognitive phase in GRN mutation carriers before overt clinical symptoms begin.

METHODS

We performed a longitudinal neuropsychological analysis (three assessments in 4 years) in a group of presymptomatic c.709-1G>A progranulin (GRN) (n=15) mutation carriers and non-carrier relatives (n=25) from seven FTD families.

RESULTS

GRN mutation carriers showed subtle decline over the longitudinal follow-up in several different domains (namely, attention, facial affect recognition, decision-making, language, and memory). The differences between groups were most marked in the facial affect recognition test, with improvement in the non-carrier group and decline in the GRN mutation carrier group, with very large effect sizes.

CONCLUSIONS

Facial affect recognition may decline before clinical diagnosis and makes the adapted version of the Picture of Facial Affect a potential candidate for early detection of GRN-associated FTD. (JINS, 2019, 25, 39-47).

Frontotemporal dementia

Frontotemporal dementia (FTD) is a neurodegenerative disorder characterized by progressive changes in behavior, personality, and language with involvement of the frontal and temporal regions of the brain. About 40% of FTD cases have a positive family history, and about 10% of these cases are inherited in an autosomal-dominant pattern. These gene defects present with distinct clinical phenotypes. As the diagnosis of FTD becomes more recognizable, it will become increasingly important to keep these gene mutations in mind. In this chapter, we review the genes with known associations to FTD. We discuss protein functions, mutation frequencies, clinical phenotypes, imaging characteristics, and pathology associated with these genes.

Frontotemporal dementia: latest evidence and clinical implications

BACKGROUND

Frontotemporal dementia (FTD) describes a cluster of neurocognitive syndromes that present with impairment of executive functioning, changes in behavior, and a decrease in language proficiency. FTD is the second most common form of dementia in those younger than 65 years and is expected to increase in prevalence as the population ages. This goal in our review is to describe advances in the understanding of neurobiological pathology, classification, assessment, and treatment of FTD syndromes.

METHODS

PubMed was searched to obtain reviews and studies that pertain to advancements in genetics, neurobiology, neuroimaging, classification, and treatment of FTD syndromes. Articles were chosen with a predilection to more recent preclinical/clinical trials and systematic reviews.

RESULTS

Recent reviews and trials indicate a significant advancement in the understanding of molecular and neurobiological clinical correlates to variants of FTD. Genetic and histopathologic markers have only recently been discovered in the past decade. Current therapeutic modalities are limited, with most studies reporting improvement in symptoms with nonpharmacological interventions. However, a small number of studies have reported improvement of behavioral symptoms with selective serotonin reuptake inhibitor (SSRI) treatment. Stimulants may help with disinhibition, apathy, and risk-taking behavior. Memantine and cholinesterase inhibitors have not demonstrated efficacy in ameliorating FTD symptoms. Antipsychotics have been used to treat agitation and psychosis, but safety concerns and side effect profiles limit utilization in the general FTD population. Nevertheless, recent breakthroughs in the understanding of FTD pathology have led to developments in pharmacological interventions that focus on producing treatments with autoimmune, genetic, and molecular targets.

CONCLUSION

FTD is an underdiagnosed group of neurological syndromes comprising multiple variants with distinct neurobiological profiles and presentations. Recent advances suggest there is an array of potential novel therapeutic targets, although data concerning their effectiveness are still preliminary or preclinical. Further studies are required to develop pharmacological interventions, as there are currently no US Food and Drug administration approved treatments to manage FTD syndromes.

The unexpected co-occurrence of GRN and MAPT p.A152T in Basque families: Clinical and pathological characteristics

BACKGROUND

The co-occurrence of the c.709-1G>A GRN mutation and the p.A152T MAPT variant has been identified in 18 Basque families affected by frontotemporal dementia (FTD). We aimed to investigate the influence of the p.A152T MAPT variant on the clinical and neuropathological features of these Basque GRN families.

METHODS AND FINDINGS

We compared clinical characteristics of 14 patients who carried the c.709-1G>A GRN mutation (GRN+/A152T-) with 21 patients who carried both the c.709-1G>A GRN mutation and the p.A152T MAPT variant (GRN+/A152T+). Neuropsychological data (n = 17) and plasma progranulin levels (n = 23) were compared between groups, and 7 subjects underwent neuropathological studies. We genotyped six short tandem repeat markers in the two largest families. By the analysis of linkage disequilibrium decay in the haplotype block we estimated the time when the first ancestor to carry both genetic variants emerged. GRN+/A152T+ and GRN+/A152T- patients shared similar clinical and neuropsychological features and plasma progranulin levels. All were diagnosed with an FTD disorder, including behavioral variant FTD or non fluent / agrammatic variant primary progressive aphasia, and shared a similar pattern of neuropsychological deficits, predominantly in executive function, memory, and language. All seven participants with available brain autopsies (6 GRN+/A152T+, 1 GRN+/A152T-) showed frontotemporal lobar degeneration with TDP-43 inclusions (type A classification), which is characteristic of GRN carriers. Additionally, all seven showed mild to moderate tau inclusion burden: five cases lacked β-amyloid pathology and two cases had Alzheimer's pathology. The co-occurrence of both genes within one individual is recent, with the birth of the first GRN+/A152T+ individual estimated to be within the last 50 generations (95% probability).

CONCLUSIONS

In our sample, the p.A152T MAPT variant does not appear to show a discernible influence on the clinical phenotype of GRN carriers. Whether p.A152T confers a greater than expected propensity for tau pathology in these GRN carriers remains an open question.

MAPT H1 Haplotype is Associated with Late-Onset Alzheimer's Disease Risk in APOEɛ4 Noncarriers: Results from the Dementia Genetics Spanish Consortium

The MAPT H1 haplotype has been linked to several disorders, but its relationship with Alzheimer's disease (AD) remains controversial. A rare variant in MAPT (p.A152T) has been linked with frontotemporal dementia (FTD) and AD. We genotyped H1/H2 and p.A152T MAPT in 11,572 subjects from Spain (4,327 AD, 563 FTD, 648 Parkinson's disease (PD), 84 progressive supranuclear palsy (PSP), and 5,950 healthy controls). Additionally, we included 101 individuals from 21 families with genetic FTD. MAPT p.A152T was borderline significantly associated with FTD [odds ratio (OR) = 2.03; p = 0.063], but not with AD. MAPT H1 haplotype was associated with AD risk (OR = 1.12; p = 0.0005). Stratification analysis showed that this association was mainly driven by APOE ɛ4 noncarriers (OR = 1.14; p = 0.0025). MAPT H1 was also associated with risk for PD (OR = 1.30; p = 0.0003) and PSP (OR = 3.18; p = 8.59 × 10-8) but not FTD. Our results suggest that the MAPT H1 haplotype increases the risk of PD, PSP, and non-APOE ɛ4 AD.

Increased Wnt Signaling and Reduced Viability in a Neuronal Model of Progranulin-Deficient Frontotemporal Lobar Degeneration

Progranulin (PGRN) deficiency is considered the major cause of frontotemporal lobar degeneration with TDP-43 protein inclusions (FTLD-TDP). Recent work unveiled a relationship between Wnt signaling and PGRN in cellular models of FTLD and cells of patients carrying loss-of-function GRN mutations. This study was undertaken to explore the relationship between PGRN deficit and Wnt signaling in the regulation of survival of GRN knockdown neuroblastoma SH-SY5Y cells (GRN KD). We report here that both canonical and noncanonical Wnt signaling cascades are overactivated in GRN KD cells. We detected increased expression levels of Wnt1 and Wnt5a ligands of the Frizzled receptors, as well as evidence for increased signaling of the Wnt/β-catenin and Wnt/Ca²⁺ cascades in PGRN deficient cells, such as increased nuclear content of β-catenin and higher levels of cyclin D1, or increased levels of the active form of the NFAT1 transcription factor, respectively. Upregulation of either Wnt/β-catenin or Wnt/Ca²⁺ signaling in GRN KD cells leads to the stimulation of BrdU incorporation into DNA, hyperphosphorylation of the pRb family of proteins and reduced cell viability over time. Blocking the Wnt cascades by specific canonical or noncanonical inhibitors of Wnt-dependent signaling, normalized the rate of DNA synthesis, and what it is more important restored the viability of GRN KD cells. Our results suggest an important role of Wnt activation inducing cell cycle disturbance-mediated neuronal loss in the pathogenesis of PGRN deficiency-linked FTLD-TDP. Therefore, it is plausible that modulation of Wnt signaling could be a promising strategy for developing of new disease-modifying treatments for FTLD-TDP.

Increasing progranulin levels and blockade of the ERK1/2 pathway: upstream and downstream strategies for the treatment of progranulin deficient frontotemporal dementia

Frontotemporal lobar degeneration (FTLD) is a neurodegenerative disorder marked by mild-life onset and progressive changes in behavior, social cognition, and language. Loss-of-function progranulin gene (GRN) mutations are the major cause of FTLD with TDP-43 protein inclusions (FTLD-TDP). Disease-modifying treatments for FTLD-TDP are not available yet. Mounting evidence indicates that cell cycle dysfunction may play a pathogenic role in neurodegenerative disorders including FTLD. Since cell cycle re-entry of posmitotic neurons seems to precede neuronal death, it was hypothesized that strategies aimed at preventing cell cycle progression would have neuroprotective effects. Recent research in our laboratory revealed cell cycle alterations in lymphoblasts from FTLD-TDP patients carrying a null GRN mutation, and in PGRN deficient SH-SY5Y neuroblastoma cells, involving overactivation of the ERK1/2 signaling pathway. In this work, we have investigated the effects of PGRN enhancers drugs and ERK1/2 inhibitors, in these cellular models of PGRN-deficient FTLD. We report here that both restoring the PGRN content, by suberoylanilide hydroxamic acid (SAHA) or chloroquine (CQ), as blocking ERK1/2 activation by selumetinib (AZD6244) or MEK162 (ARRY-162), normalized the CDK6/pRb pathway and the proliferative activity of PGRN deficient cells. Moreover, we found that SAHA and selumetinib prevented the cytosolic TDP-43 accumulation in PGRN-deficient lymphoblasts. Considering that these drugs are able to cross the blood-brain barrier, and assuming that the alterations in cell cycle and signaling observed in lymphoblasts from FTLD patients could be peripheral signs of the disease, our results suggest that these treatments may serve as novel therapeutic drugs for FTLD associated to GRN mutations.

Early neuropsychological characteristics of progranulin mutation carriers

Mutations in the progranulin gene (GRN) are a common cause of familial frontotemporal dementia. We used a comprehensive neuropsychological battery to investigate whether early cognitive changes could be detected in GRN mutation carriers before dementia onset. Twenty-four at-risk members from six families with known GRN mutations underwent detailed neuropsychological testing. Group differences were investigated by domains of attention, language, visuospatial function, verbal memory, non-verbal memory, working memory and executive function. There was a trend for mutation carriers (n=8) to perform more poorly than non-carriers (n=16) across neuropsychological domains, with significant between group differences for visuospatial function (p<.04; d=0.92) and working memory function (p<.02; d=1.10). Measurable cognitive differences exist before the development of frontotemporal dementia in subjects with GRN mutations. The neuropsychological profile of mutation carriers suggests early asymmetric, right hemisphere brain dysfunction that is consistent with recent functional imaging data from our research group and the broader literature.

Parkinsonian syndrome in familial frontotemporal dementia

Parkinsonism in frontotemporal dementia (FTD) was first described in families with mutations in the microtubule-associated protein tau (MAPT) and progranulin (PRGN) genes. Since then, mutations in several other genes have been identified for FTD with parkinsonism, including chromosome 9 open reading frame 72 (C9ORF72), chromatin modifying protein 2B (CHMP2B), valosin-containing protein (VCP), fused in sarcoma (FUS) and transactive DNA-binding protein (TARDBP). The clinical presentation of patients with familial forms of FTD with parkinsonism is highly variable. The parkinsonism seen in FTD patients is usually characterized by akinetic-rigid syndrome and is mostly associated with the behavioral variant of FTD (bvFTD); however, some cases may present with classical Parkinson's disease. In other cases, atypical parkinsonism resembling progressive supranuclear palsy (PSP) or corticobasal syndrome (CBS) has also been described. Although rare, parkinsonism in FTD may coexist with motor neuron disease. Structural neuroimaging, which is crucial for the diagnosis of FTD, shows characteristic patterns of brain atrophy associated with specific mutations. Structural neuroimaging is not helpful in distinguishing among patients with parkinsonian features. Furthermore, dopaminergic imaging that shows nigrostriatal neurodegeneration in FTD with parkinsonism cannot discriminate parkinsonian syndromes that arise from different mutations. Generally, parkinsonism in FTD is levodopa unresponsive, but there have been cases where a temporary benefit has been reported, so dopaminergic treatment is worth trying, especially, when motor and non-motor manifestations can cause significant problems with daily functioning. In this review, we present an update on the clinical and genetic correlations of FTD with parkinsonism.

Understanding phenotype variability in frontotemporal lobar degeneration due to granulin mutation

Phenotype in patients with granulin (GRN) mutations is unpredictable, ranging from behavioral variant frontotemporal dementia (bvFTD) to agrammatic variant of primary progressive aphasia (avPPA). To date the wide clinical variability of FTLD-GRN remains unexplained. The aim of the study was to identify genetic pathways differentiating phenotypic expression in patients carrying GRN mutations. Patients carrying the same GRNT272SfsX10 mutation were enrolled, a careful clinical assessment was carried out, and the diagnosis of either bvFTD (n = 10, age = 63.9 ± 9.4) or avPPA (n = 6, age = 58.8 ± 4.7) was done. Microarray gene expression analysis on leukocytes was performed. Genes differentially expressed between the groups were validated by real time polymerase chain reaction considering an age-matched healthy controls group (n = 16, age = 58.4 ± 10.7). We further considered a group of FTD with no GRN mutations (GRN-) (n = 21, 13 bvFTD, and 8 avPPA) for comparisons. Real-time polymerase chain reaction (PCR) confirmed a significant decrease in leukocytes mRNA messenger RNA (mRNA) levels of RAP1GAP in bvFTD patients as compared with avPPA (p = 0.049). This finding was specific for patients with GRN mutations, as we did not observe this pattern in FTD GRN-patients (p = 0.99). The alteration of RAP1GAP mRNA levels may explain the clinical variability of GRN-FTLD patients. This is the first report linking a molecular pathway to specific phenotype expression in FTLD-GRN. To understand the clinical relevance of our early results it will be mandatory to extend the observation to other clinical and neuropathological series.

Distinctive age-related temporal cortical thinning in asymptomatic granulin gene mutation carriers

Studies in asymptomatic granulin gene (GRN) mutation carriers are essential to improve our understanding of the pattern and timing of early morphologic brain changes in frontotemporal lobar degeneration. The main objectives of this study were to assess the effect of age in cortical thickness changes (CTh) in preclinical GRN mutation carriers and to study the relationship of CTh with cognitive performance in GRN mutation carriers. We calculated CTh maps in 13 asymptomatic carriers of the c.709-1G>A GRN mutation and 13 age- and sex-matched healthy subjects. Asymptomatic GRN mutation carriers presented different patterns of age-related cortical thinning in the right superior temporal and middle temporal gyri and the banks of the superior temporal sulcus bilaterally when compared with controls. Cortical thickness was correlated with neuropsychological test scores: Trail Making Tests A and B, and the Boston Naming Test. Distinctive age-related cortical thinning in asymptomatic GRN mutation carriers in lateral temporal cortices suggests an early and disease-specific effect in these areas.

Neuropsychological features of asymptomatic c.709-1G>A progranulin mutation carriers

Mutations in the progranulin (PGRN) gene have been identified as a cause of frontotemporal dementia (FTD). However, little is known about the neuropsychological abilities of asymptomatic carriers of these mutations. The aim of the study was to assess cognitive functioning in asymptomatic c.709-1G>A PGRN mutation carriers. We hypothesized that poorer neuropsychological performance could be present before the development of clinically significant FTD symptoms. Thirty-two asymptomatic first-degree relatives of FTD patients carrying the c.709-1G>A mutation served as study participants, including 13 PGRN mutation carriers (A-PGRN+) and 19 non-carriers (PGRN-). A neuropsychological battery was administered. We found that the A-PGRN+ participants obtained significantly poorer scores than PGRN- individuals on tests of attention (Trail-Making Test Part A), mental flexibility (Trail-Making Test Part B), and language (Boston Naming Test). Poorer performance on these tests in asymptomatic PGRN mutation carriers may reflect a prodromal phase preceding the onset of clinically significant symptoms of FTD.

Advances in understanding the molecular basis of frontotemporal dementia

Frontotemporal dementia (FTD) is a clinical syndrome with a heterogeneous molecular basis. Until recently, the underlying cause was known in only a minority of cases that were associated with abnormalities of the tau protein or gene. In 2006, however, mutations in the progranulin gene were discovered as another important cause of familial FTD. That same year, TAR DNA-binding protein 43 (TDP-43) was identified as the pathological protein in the most common subtypes of FTD and amyotrophic lateral sclerosis (ALS). Since then, substantial efforts have been made to understand the functions and regulation of progranulin and TDP-43, as well as their roles in neurodegeneration. More recently, other DNA/RNA binding proteins (FET family proteins) have been identified as the pathological proteins in most of the remaining cases of FTD. In 2011, abnormal expansion of a hexanucleotide repeat in the gene C9orf72 was found to be the most common genetic cause of both FTD and ALS. All common FTD-causing genes have seemingly now been discovered and the main pathological proteins identified. In this Review, we highlight recent advances in understanding the molecular aspects of FTD, which will provide the basis for improved patient care through the development of more-targeted diagnostic tests and therapies.

Inactivation of CDK/pRb pathway normalizes survival pattern of lymphoblasts expressing the FTLD-progranulin mutation c.709-1G>A

BACKGROUND

Mutations in the progranulin (PGRN) gene, leading to haploinsufficiency, cause familial frontotemporal lobar degeneration (FTLD-TDP), although the pathogenic mechanism of PGRN deficit is largely unknown. Allelic loss of PGRN was previously shown to increase the activity of cyclin-dependent kinase (CDK) CDK6/pRb pathway in lymphoblasts expressing the c.709-1G>A PGRN mutation. Since members of the CDK family appear to play a role in neurodegenerative disorders and in apoptotic death of neurons subjected to various insults, we investigated the role of CDK6/pRb in cell survival/death mechanisms following serum deprivation.

METHODOLOGY/PRINCIPAL FINDINGS

We performed a comparative study of cell viability after serum withdrawal of established lymphoblastoid cell lines from control and carriers of c.709-1G>A PGRN mutation, asymptomatic and FTLD-TDP diagnosed individuals. Our results suggest that the CDK6/pRb pathway is enhanced in the c.709-1G>A bearing lymphoblasts. Apparently, this feature allows PGRN-deficient cells to escape from serum withdrawal-induced apoptosis by decreasing the activity of executive caspases and lowering the dissipation of mitochondrial membrane potential and the release of cytochrome c from the mitochondria. Inhibitors of CDK6 expression levels like sodium butyrate or the CDK6 activity such as PD332991 were able to restore the vulnerability of lymphoblasts from FTLD-TDP patients to trophic factor withdrawal.

CONCLUSION/SIGNIFICANCE

The use of PGRN-deficient lymphoblasts from FTLD-TDP patients may be a useful model to investigate cell biochemical aspects of this disease. It is suggested that CDK6 could be potentially a therapeutic target for the treatment of the FTLD-TDP.

Prion protein codon 129 polymorphism modifies age at onset of frontotemporal dementia with the C.709-1G>A progranulin mutation

Frontotemporal lobar degeneration because of mutations in the progranulin (PGRN) gene presents a high variability both in the clinical phenotype and age of onset of disease. Factors that influence this variability remain largely unknown. The aim of our study was to determine whether selected genetic variables modify age at onset of disease in our series of 21 patients with a single splicing mutation (c.709-1G>A) in the PGRN gene, all of whom were of Basque descent. In our analysis, we included the following genetic variables: PGRN rs5848 and rs9897526 polymorphisms, APOE and microtubule-associated protein tau genotypes, and PRNP codon 129 polymorphism. We found no association between PGRN polymorphisms, APOE and microtubule-associated protein tau genotypes, and age at onset of the disease; whereas we report evidence for an association between PRNP codon 129 polymorphism and age at onset of disease in frontotemporal dementia-PGRN(+) patients. MM homozygous carriers presented onset of disease on average 8.5 years earlier than patients who carried at least 1 valine on their PRNP codon 129 (MV or VV). The biological justification for this association remains speculative.

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.

Progress in the last decade in our understanding of primary progressive aphasia

Primary progressive aphasia (PPA) is a focal neurodegeneration of the brain affecting the language network. Patients can have isolated language impairment for years without impairment in other areas. PPA is classified as primary progressive nonfluent aphasia (PNFA), semantic dementia (SD), and logopenic aphasia, which have distinct patterns of atrophy on neuroimaging. PNFA and SD are included under frontotemporal lobar degenerations. PNFA patients have effortful speech with agrammatism, which is frequently associated with apraxia of speech and demonstrate atrophy in the left Broca’s area and surrounding region on neuroimaging. Patients with SD have dysnomia with loss of word and object (or face) meaning with asymmetric anterior temporal lobe atrophy. Logopenic aphasics have word finding difficulties with frequent pauses in conversation, intact grammar, and word comprehension but impaired repetition for sentences. The atrophy is predominantly in the left posterior temporal and inferior parietal regions. Recent studies have described several progranulin mutations on chromosome 17 in PNFA. The three clinical syndromes have a less robust relationship to the underlying pathology, which is heterogeneous and includes tauopathy, ubiquitinopathy, Pick’s disease, corticobasal degeneration, progressive supranuclear palsy, and Alzheimer’s disease. Recent studies, however, seem to indicate that a better characterization of the clinical phenotype (apraxic, agrammatic, semantic, logopenic, jargon) increases the predictive value of the underlying pathology. Substantial advances have been made in our understanding of PPAs but developing new biomarkers is essential in making accurate causative diagnoses in individual patients. This is critically important in the development and evaluation of disease-modifying drugs.

Founder effect and estimation of the age of the Progranulin Thr272fs mutation in 14 Italian pedigrees with frontotemporal lobar degeneration

Progranulin (PGRN) mutations have been recognized to be monogenic causes of frontotemporal lobar degeneration (FTLD). PGRN Thr272fs mutation in the Italian population has been previously identified. In the present study, we evaluated the occurrence of a founder effect studying 8 polymorphic microsatellite markers flanking the PGRN gene in 14 apparently unrelated families. We identified a common haplotype associated with PGRN Thr272fs carriers, assuming common ancestry. The inferred age analysis (range between 260 [95% credible set: 227-374] and 295 [95% credible set: 205-397] generations) places the introduction of the mutation back to the Neolithic era when the Celts, the population of that period, settled in Northern Italy. PGRN Thr272fs mutation appears to be as either behavioral frontotemporal dementia (80%) or primary progressive aphasia (20%), it was equally distributed between male and female, and the mean age at onset was 59.6 ± 5.9 (range 53-68). In 14 families, autosomal dominant pattern of inheritance was present in 64.2% of cases. No clinical predictors of disease onset were demonstrated. The identification of a large cohort of frontotemporal lobar degeneration (FTLD) patients with homogeneous genetic background well may be used in the search of disease modulators to elucidate genotype-phenotype correlations of progranulopathies.