Analyses of the MAPT, PGRN, and C9orf72 mutations in Japanese patients with FTLD, PSP, and CBS

Gaps in biomedical research in frontotemporal dementia: A call for diversity and disparities focused research

Frontotemporal dementia (FTD) is one of the leading causes of young-onset dementia before age 65, typically manifesting as abnormal behavior (in behavioral variant FTD) or language impairment (in primary progressive aphasia). Although FTD affects all populations across the globe, knowledge regarding the pathophysiology and genetics derives primarily from studies conducted in North America and Western Europe. Globally, biomedical research for FTD is hindered by variable access to diagnosis, discussed in this group's earlier article, and by reduced access to expertise, funding, and infrastructure. This perspective paper was produced by two professional interest areas of the Alzheimer's Association International Society to Advance Alzheimer's Research and Treatment (ISTAART) and discusses the field's current status on the cross-cultural aspects of basic and translational research in FTD (including that focused on epidemiology, genetics, biomarkers, and treatment). It subsequently provides a summary of gaps and needs to address the disparities and advance global FTD biomedical research.

Identification of Genetic Variants in Progressive Supranuclear Palsy in Southeast Asia

BACKGROUND

Progressive supranuclear palsy (PSP) is largely a sporadic disease with few reported familial cases. Genome-wide association studies (GWAS) in sporadic PSP in Caucasian populations have identified MAPT as the most commonly associated genetic risk locus with the strongest effect size. At present there are limited data on genetic factors associated with PSP in Asian populations.

OBJECTIVES

Our goal was to investigate the genetic factors associated with PSP in Southeast Asian PSP patients.

METHODS

Next-generation sequencing (whole-exome, whole-genome and targeted sequencing) was performed in two Asian cohorts, comprising 177 PSP patients.

RESULTS

We identified 17 pathogenic or likely pathogenic variants in 16 PSP patients (9%), eight of which were novel. The most common relevant genetic variants identified were in MAPT, GBA1, OPTN, SYNJ1, and SQSTM1. Other variants detected were in TBK1, PRNP, and ABCA7-genes that have been implicated in other neurodegenerative diseases. Eighteen patients had a positive family history, of whom two carried pathogenic MAPT variants, and one carried a likely pathogenic GBA1 variant. None of the patients had expanded repeats in C9orf72. Furthermore, we found 16 different variants of uncertain significance in 21 PSP patients in PSEN2, ABCA7, SMPD1, MAPT, ATP13A2, OPTN, SQSTM1, CYLD, and BSN.

CONCLUSIONS

The genetic findings in our PSP cohorts appear to be somewhat distinct from those in Western populations, and also suggest an overlap of the genetic architecture between PSP and other neurodegenerative diseases. Further functional studies and validation in independent Asian cohorts will be useful for improving our understanding of PSP genetics and guiding genetic screening strategies in these populations. © 2024 International Parkinson and Movement Disorder Society.

A scoping review of the unique landscape and challenges associated with dementia in the Western Pacific region

Dementia is a leading public health crisis that is projected to affect 152.8 million individuals by 2050, over half of whom will be living in the Western Pacific region. To determine the challenges and opportunities for capacity building in the region, this scoping review searched databases. Our findings reveal national and ethnoracial differences in the prevalence, literacy and genetic risk factors associated with dementia syndromes, underscoring the need to identify and mitigate relevant risk factors in this region. Importantly, ∼80% of research was derived from higher income countries, where the establishment of patient registries and biobanks reflect increased efforts and allocation of resources towards understanding the pathogenesis of dementia. We discuss the need for increased public awareness through culturally-relevant policies, the potential to support patients and caregivers through digital strategies and development of regional networks to mitigate the growing social impact and economic burden of dementia in this region.

Funding

FightMND Mid-Career Fellowship, NHMRC EL1 Fellowship, NHMRC Practitioner Fellowship (1156093), NHMRC Postgraduate scholarship (2022387).

A novel MAPT variant (E342K) as a cause of familial progressive supranuclear palsy

Background

MAPT variants are a known cause of frontotemporal dementia and Parkinsonian syndrome, of which progressive supranuclear palsy syndrome (PSP) is a rare manifestation.

Objective

To report a novel MAPT variant in a PSP pedigree with autosomal dominant inheritance pattern, and to produce a literature review of PSP patients with MAPT variants.

Methods

A comprehensive clinical, genetic, and molecular neuroimaging investigation was conducted on a 61 years-old female proband diagnosed with PSP. We also collected the clinical presentation data and history of the patient's pedigree, and performed further genetic analysis of 4 relatives, from two generations, with and without symptoms.

Results

The proband exhibited typical clinical manifestation of PSP. A cranial MRI revealed midbrain atrophy, and an FDG-PET scan suggested hypo-metabolic changes in caudate nucleus, left prefrontal lobe, both temporal poles, and midbrain. 18F-florzolo-tau-PET revealed tau-protein deposits in the thalamus and brainstem bilaterally. A gene test by whole-exome sequencing identified a novel MAPT variant [NM_005910.6, exon 11, c.1024G > A (p.E342K)], and the same variant was also identified in one affected relative and one asymptomatic relative, a probable pre-symptomatic carrier.

Conclusion

The PSP pedigree caused by the novel MAPT (E342K) variant, expanded the mutational spectrum of MAPT.

Overlaps and divergences between tauopathies and synucleinopathies: a duet of neurodegeneration

Proteinopathy, defined as the abnormal accumulation of proteins that eventually leads to cell death, is one of the most significant pathological features of neurodegenerative diseases. Tauopathies, represented by Alzheimer's disease (AD), and synucleinopathies, represented by Parkinson's disease (PD), show similarities in multiple aspects. AD manifests extrapyramidal symptoms while dementia is also a major sign of advanced PD. We and other researchers have sequentially shown the cross-seeding phenomenon of α-synuclein (α-syn) and tau, reinforcing pathologies between synucleinopathies and tauopathies. The highly overlapping clinical and pathological features imply shared pathogenic mechanisms between the two groups of disease. The diagnostic and therapeutic strategies seemingly appropriate for one distinct neurodegenerative disease may also apply to a broader spectrum. Therefore, a clear understanding of the overlaps and divergences between tauopathy and synucleinopathy is critical for unraveling the nature of the complicated associations among neurodegenerative diseases. In this review, we discuss the shared and diverse characteristics of tauopathies and synucleinopathies from aspects of genetic causes, clinical manifestations, pathological progression and potential common therapeutic approaches targeting the pathology, in the aim to provide a timely update for setting the scheme of disease classification and provide novel insights into the therapeutic development for neurodegenerative diseases.

Systematic characterization of protein structural features of alternative splicing isoforms using AlphaFold 2

Alternative splicing is an important cellular process in eukaryotes, altering pre-mRNA to yield multiple protein isoforms from a single gene. However, our understanding of the impact of alternative splicing events on protein structures is currently constrained by a lack of sufficient protein structural data. To address this limitation, we employed AlphaFold 2, a cutting-edge protein structure prediction tool, to conduct a comprehensive analysis of alternative splicing for approximately 3,000 human genes, providing valuable insights into its impact on the protein structural. Our investigation employed state of the art high-performance computing infrastructure to systematically characterize structural features in alternatively spliced regions and identified changes in protein structure following alternative splicing events. Notably, we found that alternative splicing tends to alter the structure of residues primarily located in coils and beta-sheets. Our research highlighted a significant enrichment of loops and highly exposed residues within human alternatively spliced regions. Specifically, our examination of the Septin-9 protein revealed potential associations between loops and alternative splicing, providing insights into its evolutionary role. Furthermore, our analysis uncovered two missense mutations in the Tau protein that could influence alternative splicing, potentially contributing to the pathogenesis of Alzheimer's disease. In summary, our work, through a thorough statistical analysis of extensive protein structural data, sheds new light on the intricate relationship between alternative splicing, evolution, and human disease.

Progranulin haploinsufficiency mediates cytoplasmic TDP-43 aggregation with lysosomal abnormalities in human microglia

BACKGROUND

Progranulin (PGRN) haploinsufficiency due to progranulin gene (GRN) variants can cause frontotemporal dementia (FTD) with aberrant TAR DNA-binding protein 43 (TDP-43) accumulation. Despite microglial burden with TDP-43-related pathophysiology, direct microglial TDP-43 pathology has not been clarified yet, only emphasized in neuronal pathology. Thus, the objective of this study was to investigate TDP-43 pathology in microglia of patients with PGRN haploinsufficiency.

METHODS

To design a human microglial cell model with PGRN haploinsufficiency, monocyte-derived microglia (iMGs) were generated from FTD-GRN patients carrying pathogenic or likely pathogenic variants (p.M1? and p.W147*) and three healthy controls.

RESULTS

iMGs from FTD-GRN patients with PGRN deficiency exhibited severe neuroinflammation phenotype and failure to maintain their homeostatic molecular signatures, along with impaired phagocytosis. In FTD-GRN patients-derived iMGs, significant cytoplasmic TDP-43 aggregation and accumulation of lipid droplets with profound lysosomal abnormalities were observed. These pathomechanisms were mediated by complement C1q activation and upregulation of pro-inflammatory cytokines.

CONCLUSIONS

Our study provides considerable cellular and molecular evidence that loss-of-function variants of GRN in human microglia can cause microglial dysfunction with abnormal TDP-43 aggregation induced by inflammatory milieu as well as the impaired lysosome. Elucidating the role of microglial TDP-43 pathology in intensifying neuroinflammation in individuals with FTD due to PGRN deficiency and examining consequential effects on microglial dysfunction might yield novel insights into the mechanisms underlying FTD and neurodegenerative disorders.

Analysis of Genetic and MRI Changes, Blood Markers, and Risk Factors in a Twin Pair Discordant of Progressive Supranuclear Palsy

Background and Objectives: Progressive supranuclear palsy (PSP) is a neurodegenerative disease, a tauopathy, which results in a wide clinical spectrum of neurological symptoms. The diagnosis is mostly based on clinical signs and neuroimaging; however, possible biomarkers for screening have been under investigation, and the role of the gut microbiome is unknown. The aim of our study was to identify potential blood biomarkers and observe variations in the gut microbiome within a PSP discordant monozygotic twin pair. Materials and Methods: Anthropometric measurements, neuropsychological tests, and the neurological state were evaluated. Blood was collected for metabolic profiling and for the detection of neurodegenerative and vascular biomarkers. Both the gut microbiome and brain MRI results were thoroughly examined. Results: We found a relevant difference between alpha-synuclein levels and moderate difference in the levels of MMP-2, MB, Apo-A1, Apo-CIII, and Apo-H. With respect to the ratios, a small difference was observed for ApoA1/SAA and ApoB/ApoA1. Using a microbiome analysis, we also discovered a relative dysbiosis, and the MRI results revealed midbrain and frontoparietal cortical atrophy along with a reduction in overall brain volumes and an increase in white matter lesions in the affected twin. Conclusions: We observed significant differences between the unaffected and affected twins in some risk factors and blood biomarkers, along with disparities in the gut microbiome. Additionally, we detected abnormalities in brain MRI results and alterations in cognitive functions.

Genetics of Multiple System Atrophy and Progressive Supranuclear Palsy: A Systemized Review of the Literature

Multiple system atrophy (MSA) and progressive supranuclear palsy (PSP) are uncommon multifactorial atypical Parkinsonian syndromes, expressed by various clinical features. MSA and PSP are commonly considered sporadic neurodegenerative disorders; however, our understanding is improving of their genetic framework. The purpose of this study was to critically review the genetics of MSA and PSP and their involvement in the pathogenesis. A systemized literature search of PubMed and MEDLINE was performed up to 1 January 2023. Narrative synthesis of the results was undertaken. In total, 43 studies were analyzed. Although familial MSA cases have been reported, the hereditary nature could not be demonstrated. COQ2 mutations were involved in familial and sporadic MSA, without being reproduced in various clinical populations. In terms of the genetics of the cohort, synuclein alpha (SNCA) polymorphisms were correlated with an elevated likelihood of manifesting MSA in Caucasians, but a causal effect relationship could not be demonstrated. Fifteen MAPT mutations were linked with PSP. Leucine-rich repeat kinase 2 (LRRK2) is an infrequent monogenic mutation of PSP. Dynactin subunit 1 (DCTN1) mutations may imitate the PSP phenotype. GWAS have noted many risk loci of PSP (STX6 and EIF2AK3), suggesting pathogenetic mechanisms related to PSP. Despite the limited evidence, it seems that genetics influence the susceptibility to MSA and PSP. MAPT mutations result in the MSA and PSP pathologies. Further studies are crucial to elucidate the pathogeneses of MSA and PSP, which will support efforts to develop novel drug options.

Identification and functional characterization of novel variants of MAPT and GRN in Chinese patients with frontotemporal dementia

Frontotemporal dementia (FTD) is the second most common cause of dementia after Alzheimer's disease, characterized by distinct changes in behavior, personality, and language. Our study performed whole exome sequencing and repeat-primed PCR analysis in 29 unrelated FTD patients. Consequently, 2 known pathogenic variants (MAPT: p.P301L; TBK1: p.I450Kfs), and 4 novel variants (MAPT: p.R406Q, p.D430H, p.A330D; GRN: c.350-2A>G) were identified. The functional analysis results showed that phosphorylated tau levels were higher in cells expressing p.R406Q and p.D430H tau than those expressing wild-type tau, especially at the Thr205, Thr231, and Ser396 phosphorylation epitopes. Besides, the p.R406Q and p.D430H variants of MAPT impaired the ability of tau to bind to the microtubules and increased tau self-aggregation. Furthermore, we found that the c.350-2A>G variant caused exon 5 skipping. Our results showed that p.R406Q, p.D430H, and c.350-2A>G variants were classified as pathogenic. Finally, we summarized the clinical characterization of patients carrying pathogenic variants of MAPT in the East Asia populations. Our results broaden the genetic spectrum of FTD with MAPT and GRN variants.

Progranulin Gene Mutations in Chinese Patients with Frontotemporal Dementia: A Case Report and Literature Review

BACKGROUND

Progranulin (GRN) mutations in frontotemporal dementia (FTD) have been less frequently reported in China than in Western countries.

OBJECTIVE

This study reports a novel GRN mutation and summarizes the genetic and clinical features of patients with GRN mutations in China.

METHODS

Comprehensive clinical, genetic, and neuroimaging examinations were conducted on a 58-year-old female patient diagnosed with semantic variant primary progressive aphasia. A literature review was also conducted and clinical and genetic features of patients with GRN mutations in China were summarized.

RESULTS

Neuroimaging revealed marked lateral atrophy and hypometabolism in the left frontal, temporal, and parietal lobes. The patient was negative for pathologic amyloid and tau deposition by positron emission tomography. A novel heterozygous 45-bp deletion (c.1414-14_1444delCCCTTCCCCGCCAGGCTGTGTGCTGCGAGGATCGCCAGCACTGCT) was detected by whole-exome sequencing of the patient's genomic DNA. Nonsense-mediated mRNA decay was presumed to be involved in the degradation of the mutant gene transcript. The mutation was deemed pathogenic according to American College of Medical Genetics and Genomics criteria. The patient had a reduced plasma GRN level. In the literature, there were reports of 13 Chinese patients - mostly female - with GRN mutations; the prevalence was 1.2% -2.6% and patients mostly had early disease onset.

CONCLUSION

Our findings expand the mutation profile of GRN in China, which can aid the diagnosis and treatment of FTD.

Frequency and Longitudinal Course of Motor Signs in Genetic Frontotemporal Dementia

BACKGROUND AND OBJECTIVES

Frontotemporal dementia (FTD) is a highly heritable disorder. The majority of genetic cases are caused by autosomal dominant pathogenic variants in the chromosome 9 open reading frame 72 (c9orf72), progranulin (GRN), and microtubule-associated protein tau (MAPT) gene. As motor disorders are increasingly recognized as part of the clinical spectrum, the current study aimed to describe motor phenotypes caused by genetic FTD, quantify their temporal association, and investigate their regional association with brain atrophy.

METHODS

We analyzed baseline visit data of known carriers of a pathogenic variant in the c9orf72, GRN, or MAPT gene from the Genetic Frontotemporal Dementia Initiative cohort study. Principal component analysis with varimax rotation was performed to identify motor sign clusters that were compared with respect to frequency and severity between groups. Associations with cross-sectional atrophy patterns were determined using voxel-wise regression. We applied linear mixed effects models to assess whether groups differed in the association between motor signs and estimated time to symptom onset.

RESULTS

A total of 322 pathogenic variant carriers were included in the analysis: 122 c9orf72 (79 presymptomatic), 143 GRN (112 presymptomatic), and 57 MAPT (43 presymptomatic) pathogenic variant carriers. Principal component analysis revealed 5 motor clusters, which we call progressive supranuclear palsy (PSP)-like, bulbar amyotrophic lateral sclerosis (ALS)-like, mixed/ALS-like, Parkinson disease (PD) like, and corticobasal syndrome-like motor phenotypes. There was no significant group difference in the frequency of signs of different motor phenotypes. However, mixed/ALS-like motor signs were most frequent, followed by PD-like motor signs. Although the PSP-like phenotype was associated with mesencephalic atrophy, the mixed/ALS-like phenotype was associated with motor cortex and corticospinal tract atrophy. The PD-like phenotype was associated with widespread cortical and subcortical atrophy. Estimated time to onset, genetic group and their interaction influenced motor signs. In c9orf72 pathogenic variant carriers, motor signs could be detected up to 25 years before expected symptom onset.

DISCUSSION

These results indicate the presence of multiple natural clusters of motor signs in genetic FTD, each correlated with specific atrophy patterns. Their motor severity depends on time and the affected gene. These clinicogenetic associations can guide diagnostic evaluations and the design of clinical trials for new disease-modifying and preventive treatments.

Genetics of progressive supranuclear palsy in a Chinese population

BACKGROUND

Genetics plays an important role in progressive supranuclear palsy (PSP) and remains poorly understood. A detailed literature search identified 19 PSP-associated genes: MAPT, LRRK2, LRP10, DCTN1, GRN, NPC1, PARK, TARDBP, TBK1, BSN, GBA, STX6, EIF2AK3, MOBP, DUSP10, SLCO1A2, RUNX2, CXCR4, and APOE. To date, genetic studies on PSP have focused on Caucasian population. The gaps in PSP genetic study on East Asian populations need to be filled.

METHODS

Exon and flanking regions of the PSP-associated genes were sequenced in 104 patients with PSP and 488 healthy controls. Common variant-based association analysis and gene-based association tests of rare variants were performed using PLINK 1.9 and the sequence kernel association test-optimal, respectively. Additionally, the association of APOE and MAPT genotypes with PSP was evaluated. The above association analyses were repeated among probable PSP patients. Finally, PLINK 1.9 was used to test variants associated with the onset age of PSP.

RESULTS

A rare non-pathogenic variant of MAPT (c.425C > T,p.A142V) was detected in a PSP patient. No common variants were significantly associated with PSP. In both the rare-variant and the rare-damaging-variant groups, the combined effect for GBA reached statistical significance (p = 1.43 × 10^-3, p = 4.98 × 10^-4). The result between APOE, MAPT genotypes and PSP risk were inconsistent across all PSP group and probably PSP group.

CONCLUSIONS

The pathogenic variant in MAPT were uncommon in PSP patients. Moreover, GBA gene was likely to increase the risk of PSP, and GBA-associated diseases were beyond α-synucleinopathies. The association between APOE, MAPT and PSP is still unclear among the non-Caucasian population.

Genotype-Phenotype Correlation in Progressive Supranuclear Palsy Syndromes: Clinical and Radiological Similarities and Specificities

The progressive supranuclear palsy (PSP) syndrome encompasses different entities. PSP disease of sporadic origin is the most frequent presentation, but different genetic mutations can lead either to monogenic variants of PSP disease, or to other conditions with a different pathophysiology that eventually may result in PSP phenotype. PSP syndrome of monogenic origin is poorly understood due to the low prevalence and variable expressivity of some mutations. Through this review, we describe how early age of onset, family history of early dementia, parkinsonism, dystonia, or motor neuron disease among other clinical features, as well as some neuroimaging signatures, may be the important clues to suspect PSP syndrome of monogenic origin. In addition, a diagnostic algorithm is proposed that may be useful to guide the genetic diagnosis once there is clinical suspicion of a monogenic PSP syndrome.

Nomenclature of Genetic Movement Disorders: Recommendations of the International Parkinson and Movement Disorder Society Task Force - An Update

In 2016, the Movement Disorder Society Task Force for the Nomenclature of Genetic Movement Disorders presented a new system for naming genetically determined movement disorders and provided a criterion-based list of confirmed monogenic movement disorders. Since then, a substantial number of novel disease-causing genes have been described, which warrant classification using this system. In addition, with this update, we further refined the system and propose dissolving the imaging-based categories of Primary Familial Brain Calcification and Neurodegeneration with Brain Iron Accumulation and reclassifying these genetic conditions according to their predominant phenotype. We also introduce the novel category of Mixed Movement Disorders (MxMD), which includes conditions linked to multiple equally prominent movement disorder phenotypes. In this article, we present updated lists of newly confirmed monogenic causes of movement disorders. We found a total of 89 different newly identified genes that warrant a prefix based on our criteria; 6 genes for parkinsonism, 21 for dystonia, 38 for dominant and recessive ataxia, 5 for chorea, 7 for myoclonus, 13 for spastic paraplegia, 3 for paroxysmal movement disorders, and 6 for mixed movement disorder phenotypes; 10 genes were linked to combined phenotypes and have been assigned two new prefixes. The updated lists represent a resource for clinicians and researchers alike and they have also been published on the website of the Task Force for the Nomenclature of Genetic Movement Disorders on the homepage of the International Parkinson and Movement Disorder Society (https://www.movementdisorders.org/MDS/About/Committees--Other-Groups/MDS-Task-Forces/Task-Force-on-Nomenclature-in-Movement-Disorders.htm). © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson Movement Disorder Society.

Cognitive Dysfunction in Repeat Expansion Diseases: A Review

With the development of the sequencing technique, more than 40 repeat expansion diseases (REDs) have been identified during the past two decades. Moreover, the clinical features of these diseases show some commonality, and the nervous system, especially the cognitive function was affected in part by these diseases. However, the specific cognitive domains impaired in different diseases were inconsistent. Here, we survey literature on the cognitive consequences of the following disorders presenting cognitive dysfunction and summarizing the pathogenic genes, epidemiology, and different domains affected by these diseases. We found that the cognitive domains affected in neuronal intranuclear inclusion disease (NIID) were widespread including the executive function, memory, information processing speed, attention, visuospatial function, and language. Patients with C9ORF72-frontotemporal dementia (FTD) showed impairment in executive function, memory, language, and visuospatial function. While in Huntington's disease (HD), the executive function, memory, and information processing speed were affected, in the fragile X-associated tremor/ataxia syndrome (FXTAS), executive function, memory, information processing speed, and attention were impaired. Moreover, the spinocerebellar ataxias showed broad damage in almost all the cognitive domains except for the relatively intact language ability. Some other diseases with relatively rare clinical data also indicated cognitive dysfunction, such as myotonic dystrophy type 1 (DM1), progressive myoclonus epilepsy (PME), Friedreich ataxia (FRDA), Huntington disease like-2 (HDL2), and cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS). We drew a cognitive function landscape of the related REDs that might provide an aspect for differential diagnosis through cognitive domains and effective non-specific interventions for these diseases.

Genetic and Epigenetic Constructs of Progressive Supranuclear Palsy

BACKGROUND

Progressive supranuclear palsy (PSP) is a rapidly progressive primary tauopathy characterized by vertical gaze palsy, postural instability, and mild dementia. PSP shows high clinical and pathologic heterogeneity. Although a few risk factors exist, such as advanced age and environmental toxins, the precise etiology remains largely elusive. Compelling evidence now suggests that genetic background plays a pivotal role in the pathogenetic pathways of PSP. Notably, PSP is genetically and phenotypically a complex disorder. Given the tau pathology, several studies in the past have identified microtubule-associated protein tau (MAPT) gene mutations/variations and its haplotype as the major genetic risk factor of PSP, both in the sporadic and the familial forms. Subsequently, genome-wide association studies (GWAS) also identified several novel risk variants. However, these genetic risk determinants fail to explain the pathogenetic basis of PSP and its phenotypic spectrum in majority of the cases. Some genetic variants are known to confer the risk, while others seem to act as modifier genes.

SUMMARY

Besides the complex genetic basis of PSP, the pathobiological mechanisms, differential diagnosis, and management of patients with PSP have further been complicated by genetic conditions that mimic the phenotypes of PSP. This is now becoming increasingly apparent that interactions between genetic and environmental factors significantly contribute to PSP development. Further, the effect of environmental factors seems to be mediated through epigenetic modifications.

KEY MESSAGE

Herein, we provide a comprehensive overview of the genetic and epigenetic constructs of PSP and highlight the relevance of genetic and epigenetic findings in the pathobiology of PSP.

Autosomal Dominant Frontotemporal Lobar Degeneration in a Filipino Family with Progranulin Mutation

BACKGROUND

Compared to Western populations, familial frontotemporal lobar degeneration (FTLD) is rare among Asians. Progranulin (GRN) gene mutation, which is a major cause of FTLD, is likewise rare. We present a family with FTLD from the Philippines with an autosomal dominant pattern of inheritance and GRN mutation and briefly review reports of GRN mutations in Asia.

CASE PRESENTATION

The proband is 66 years old with progressive nonfluent aphasia (PNFA)-corticobasal syndrome . We assessed 3 generations of her pedigree and found 11 affected relatives with heterogenous phenotypes, usually behavioral variant frontotemporal dementia (FTD) and PNFA. Neuroimaging showed atrophy and hypometabolism consistent with FTD syndromes. White matter hyperintensities were seen in affected members even in the absence of vascular risk factors. A GRN mutation R110X was found in 6 members, 3 with symptoms and 3 were asymptomatic. Plasma GRN was low (<112 ng/mL) in all mutation carriers. No mutations were found in microtubule-associated protein tau, APP, PSEN1, and PSEN2 genes, and all were APOE3.

CONCLUSION

This is the first Filipino family with autosomal dominant FTD documented with GRN mutation. Identifying families and cohorts would contribute to therapeutic developments in an area with FTD-GRN.

FTD-PSP is an Unusual Clinical Phenotype in A Frontotemporal Dementia Patient with A Novel Progranulin Mutation

Progranulin (GRN) mutations are a major cause of frontotemporal dementia (FTD); the spectrum of clinical phenotypes of FTD is much more extensive than previously reported. The frequency and locations of GRN mutations in Chinese patients with FTD remain uncertain. We performed cDNA sequencing in one sporadic male patient who initially presented FTD symptoms. Brain magnetic resonance imaging (MRI) and positron emission computed tomography/computed tomography (PET/CT) were applied to further confirm the diagnosis of FTD from this patient. Cellular apoptosis and survival test were performed to identify the function of GRN. We identified one novel missense GRN mutation (c.1498G>A, p.V500I) in this patient, who initially presented typical behavioral-variant frontotemporal dementia (bvFTD) features but then presented progressive supranuclear palsy (PSP) clinical characteristics 5 years after onset. Besides, WT GRN protein showed an adequate trophic stimulus to preserve the survival of SH-SY5Y cells in the medium free of serum, while GRN mutation (c.1498G>A, p.V500I) may impair the ability of supporting cell survival. This study owns significant implications for genetic counseling and clinical heterogeneity. We illustrate the fact that FTD presenting features of bvFTD and PSP in one patient could be considered as a specific phenotype in patients with GRN mutations. GRN p.V500I led to the neuronal degeneration in vitro; this finding provides a significant evidence that this mutation may be a new causative mutation in patients with FTD.

Tau and MAPT genetics in tauopathies and synucleinopathies

MAPT encodes the microtubule-associated protein tau, which is the main component of neurofibrillary tangles (NFTs) and found in other protein aggregates. These aggregates are among the pathological hallmarks of primary tauopathies such as frontotemporal dementia (FTD). Abnormal tau can also be observed in secondary tauopathies such as Alzheimer's disease (AD) and synucleinopathies such as Parkinson's disease (PD). On top of pathological findings, genetic data also links MAPT to these disorders. MAPT variations are a cause or risk factors for many tauopathies and synucleinopathies and are associated with certain clinical and pathological features in affected individuals. In addition to clinical, pathological, and genetic overlap, evidence also suggests that tau and alpha-synuclein may interact on the molecular level, and thus might collaborate in the neurodegenerative process. Understanding the role of MAPT variations in tauopathies and synucleinopathies is therefore essential to elucidate the role of tau in the pathogenesis and phenotype of those disorders, and ultimately to develop targeted therapies. In this review, we describe the role of MAPT genetic variations in tauopathies and synucleinopathies, several genotype-phenotype and pathological features, and discuss their implications for the classification and treatment of those disorders.

The Genetic Landscape of Parkinsonism-Related Dystonias and Atypical Parkinsonism-Related Syndromes

In recent decades, genetic research has nominated promising pathways and biological insights contributing to the etiological landscape of parkinsonism-related dystonias and atypical parkinsonism-related syndromes. Several disease-causing mutations and genetic risk factors have been unraveled, providing a deeper molecular understanding of the complex genetic architecture underlying these conditions. These disorders are difficult to accurately diagnose and categorize, thus making genetics research challenging. On one hand, dystonia is an umbrella term linked to clinically heterogeneous forms of disease including dopa-responsive dystonia, myoclonus-dystonia, rapid-onset dystonia-parkinsonism and dystonia-parkinsonism, often viewed as a precursor to Parkinson’s disease. On the other hand, atypical parkinsonism disorders, such as progressive supranuclear palsy, multiple system atrophy and corticobasal degeneration, are rare in nature and represent a wide range of diverse and overlapping phenotypic variabilities, with genetic research limited by sample size availability. The current review summarizes the plethora of available genetic information for these diseases, outlining limits and future directions.

Systematic Review: Genetic, Neuroimaging, and Fluids Biomarkers for Frontotemporal Dementia Across Latin America Countries

Frontotemporal dementia (FTD) includes a group of clinically, genetically, and pathologically heterogeneous neurodegenerative disorders, affecting the fronto-insular-temporal regions of the brain. Clinically, FTD is characterized by progressive deficits in behavior, executive function, and language and its diagnosis relies mainly on the clinical expertise of the physician/consensus group and the use of neuropsychological tests and/or structural/functional neuroimaging, depending on local availability. The modest correlation between clinical findings and FTD neuropathology makes the diagnosis difficult using clinical criteria and often leads to underdiagnosis or misdiagnosis, primarily due to lack of recognition or awareness of FTD as a disease and symptom overlap with psychiatric disorders. Despite advances in understanding the underlying neuropathology of FTD, accurate and sensitive diagnosis for this disease is still lacking. One of the major challenges is to improve diagnosis in FTD patients as early as possible. In this context, biomarkers have emerged as useful methods to provide and/or complement clinical diagnosis for this complex syndrome, although more evidence is needed to incorporate most of them into clinical practice. However, most biomarker studies have been performed using North American or European populations, with little representation of the Latin American and the Caribbean (LAC) region. In the LAC region, there are additional challenges, particularly the lack of awareness and knowledge about FTD, even in specialists. Also, LAC genetic heritage and cultures are complex, and both likely influence clinical presentations and may modify baseline biomarker levels. Even more, due to diagnostic delay, the clinical presentation might be further complicated by both neurological and psychiatric comorbidity, such as vascular brain damage, substance abuse, mood disorders, among others. This systematic review provides a brief update and an overview of the current knowledge on genetic, neuroimaging, and fluid biomarkers for FTD in LAC countries. Our review highlights the need for extensive research on biomarkers in FTD in LAC to contribute to a more comprehensive understanding of the disease and its associated biomarkers. Dementia research is certainly reduced in the LAC region, highlighting an urgent need for harmonized, innovative, and cross-regional studies with a global perspective across multiple areas of dementia knowledge.

Frequency of frontotemporal dementia-related gene variants in Turkey

Just as its clinical heterogeneity, genetic basis of Frontotemporal dementia (FTD) is also diverse and multiple molecular pathways are thought to be involved in disease pathogenesis. In the present study, FTD- related genes were evaluated in a Turkish cohort of 175 index FTD patients with a gene panel including GRN, MAPT, TARDBP, FUS, CHMP2B and VCP genes. Potential genetic associations were prospected in 16 patients (9.1%); five variants (p.(Gly35Glufs) and p.(Cys253Ter) in GRN; p.(Arg95Cys) in VCP; p.(Met405Val) in TARDBP and p.(Pro636Leu) in MAPT) were classified as pathogenic (P) or likely pathogenic (LP), in four familial and one sporadic patients. Three novel variants in MAPT, CHMP2B and FUS were also identified in familial cases. The most common pathogenic variants were observed in the GRN gene with a frequency of 1.14% (2/175) and this rate was 4.57% (8/175), including variants of uncertain significance (VUS). In this study with the largest cohort of Turkish FTD patients, GRN and MAPT variants were identified as the most common genetic associations; and rare causes like VCP, TARDBP, CHMP2B and FUS variants are recommended to be considered in patients with compatible clinical findings.

The Role of White Matter Dysfunction and Leukoencephalopathy/Leukodystrophy Genes in the Aetiology of Frontotemporal Dementias: Implications for Novel Approaches to Therapeutics

Frontotemporal dementia (FTD) is a common cause of presenile dementia and is characterized by behavioural and/or language changes and progressive cognitive deficits. Genetics is an important component in the aetiology of FTD, with positive family history of dementia reported for 40% of cases. This review synthesizes current knowledge of the known major FTD genes, including C9orf72 (chromosome 9 open reading frame 72), MAPT (microtubule-associated protein tau) and GRN (granulin), and their impact on neuronal and glial pathology. Further, evidence for white matter dysfunction in the aetiology of FTD and the clinical, neuroimaging and genetic overlap between FTD and leukodystrophy/leukoencephalopathy are discussed. The review highlights the role of common variants and mutations in genes such as CSF1R (colony-stimulating factor 1 receptor), CYP27A1 (cytochrome P450 family 27 subfamily A member 1), TREM2 (triggering receptor expressed on myeloid cells 2) and TMEM106B (transmembrane protein 106B) that play an integral role in microglia and oligodendrocyte function. Finally, pharmacological and non-pharmacological approaches for enhancing remyelination are discussed in terms of future treatments of FTD.

Clinical and Neuroimaging Aspects of Familial Frontotemporal Lobar Degeneration Associated with MAPT and GRN Mutations

Numerous kindreds with familial frontotemporal lobar degeneration have been linked to mutations in microtubule-associated protein tau (MAPT) or progranulin (GRN) genes. While there are many similarities in the clinical manifestations and associated neuroimaging findings, there are also distinct differences. In this review, we compare and contrast the demographic/inheritance characteristics, histopathology, pathophysiology, clinical aspects, and key neuroimaging findings between those with MAPT and GRN mutations.

Chinese nutraceuticals and physical activity; their role in neurodegenerative tauopathies

The onset of neurodegenerative disease has not only been a major cause of scientific worry, but of economic burden to the health system. This condition has been further attributed to mis-stability, deletion or mutation of tau protein, causing the onset of Corticobasal degeneration, Pick's diseases, Progressive supranuclear palsy, Argyrophilic grains disease, Alzheimer's diseases etc. as scientifically renowned. This is mainly related to dysregulation of translational machinery, upregulation of proinflammatory cytokines and inhibition of several essential cascades such as ERK signaling cascade, GSK3β, CREB, and PKA/PKB (Akt) signaling cascades that enhances protein processing, normal protein folding, cognitive function, and microtubule associated tau stability. Administration of some nutrients and/or bioactive compounds has a high tendency to impede tau mediated inflammation at neuronal level. Furthermore, prevention and neutralization of protein misfolding through modulation of microtubule tau stability and prevention of protein misfolding is by virtue few of the numerous beneficial effects of physical activity. Of utmost important in this study is the exploration of promising bioactivities of nutraceuticals found in china and the ameliorating potential of physical activity on tauopathies, while highlighting animal and in vitro studies that have been investigated for comprehensive understanding of its potential and an insight into the effects on human highly probable to tau mediated neurodegeneration.

Frontotemporal Dementia: A Cross-Cultural Perspective

It is predictable that syndromes of frontotemporal dementia (FTD) may have a worldwide distribution; however, data available on their incidence and prevalence are variable. This variability most likely reflects disparities across regions in the distribution of the expertise, technology, and resources available for FTD research and care. Important discoveries have been made regarding FTD's phenotypes, genetics, and cultural influences on the expression of symptoms; however, in many countries, there are barriers posed by a dearth of resources. There are pressing needs to further develop research on FTD: including first, population studies designed to fill the gaps in our knowledge about FTD's frequency and risk factors in developing regions and among minority groups in developed countries. It is also necessary to facilitate the psychometric characterization of contemporary diagnostic criteria and their translation to different languages and cultural contexts. Furthermore, much needed is the analysis of differences in the genetic risk factors for FTD, particularly non-Mendelian susceptibility factors. It is hoped that reflections on FTD from an international perspective will spur an extension of the vibrant multicenter collaborations, that exist in North America and Europe, toward new centers to be established and supported in the developing regions of the world.

Progressive Supranuclear Palsy and Corticobasal Degeneration

Progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD) are neurodegenerative tauopathies with neuronal and glial lesions composed of tau that is composed predominantly of isomers with four repeats in the microtubule-binding domain (4R tau). The brain regions vulnerable to pathology in PSP and CBD overlap, but there are differences, particularly with respect to distribution of neuronal loss, the relative abundance of neuronal and glial lesions, the morphologic features of glial lesions, and the frequency of comorbid pathology. Both PSP and CBD have a wide spectrum of clinical manifestations, including disorders of movement and cognition. Recognition of phenotypic diversity in PSP and CBD may improve antemortem diagnostic accuracy, which tends to be very good for the most common presentation of PSP (Richardson syndrome), but poor for the most characteristic presentation of CBD (corticobasal syndrome: CBS). Development of molecular and imaging biomarkers may improve antemortem diagnostic accuracy. Currently, multidisciplinary symptomatic and supportive treatment with pharmacological and non-pharmacological strategies remains the standard of care. In the future, experimental therapeutic trials will be important to slow disease progression.

Genetics of Progressive Supranuclear Palsy: A Review

Progressive supranuclear palsy (PSP) is an atypical parkinsonism with prominent 4R-tau neuropathology, and the classical clinical phenotype is characterized by vertical supranuclear gaze palsy, unprovoked falls, akinetic-rigid syndrome and cognitive decline. Though PSP is generally regarded as sporadic, there is increasing evidence suggesting that a series of common and rare genetic variants impact on sporadic and familial forms of PSP. To date, more than 10 genes have been reported to show a potential association with PSP. Among these genes, the microtubule-associated protein tau (MAPT) is the risk locus with the strongest effect size on sporadic PSP in the case-control genome-wide association studies (GWAS). Additionally, MAPT mutations are the most common cause of familial PSP while the leucine-rich repeat kinase 2 (LRRK2) is a rare monogenic cause of PSP, and several other gene mutations may mimic the PSP phenotype, like the dynactin subunit 1 (DCTN1). In total, 15 MAPT mutations have been identified in cases with PSP, and the mean age at onset is much earlier than in cases carrying LRRK2 or DCTN1 mutations. GWAS have further identified several risk loci of PSP, proposing molecular pathways related to PSP. The present review focused on genetic studies on PSP and summarized genetic factors of PSP, which may help to elucidate the underlying pathogenesis and provide new perspectives for therapeutic strategies.

Japanese Familial Cases of Frontotemporal Dementia and Parkinsonism with N279K Tau Gene Mutation

Background

Mutations in the tau gene linked to chromosome 17 cause frontotemporal dementia and parkinsonism (FTDP-17).

Objective

This study presents 3 Japanese familial cases diagnosed with N279K tau gene mutation, including 1 autopsy-confirmed case.

Methods

We compared the clinical presentations, cognitive functions, and images between the 3 familial cases diagnosed with N279K mutation.

Results

All 3 patients presented symptoms in their early 40s. One patient showed severe cognitive dysfunction and died in his sixth year after onset. The remaining 2 cases presented with parkinsonism-dominant clinical features. Among the 2 cases, 1 presented the characteristic symptoms of progressive supranuclear palsy. The pathological features of the dementia-dominant case showed frontal and temporal lobe-dominant neuronal loss and gliosis. Tau-positive neuronal and glial inclusions were found throughout. Further, tufted astrocytes and globose tangles were present whereas there were no Pick bodies and astrocytic plaques, compatible with pathology-confirmed frontotemporal lobar degeneration (FTLD) -tau subtypes.

Conclusions

Patients with FTDP-17 can be classified into the following 2 major groups: dementia and parkinsonism-plus predominant phenotypes. Among our 3 cases, 1 showed dementia predominance whereas the other 2 showed parkinsonism predominance. Mutations in the microtubule-associated protein tau (MAPT) present with several pathological features. Clinically, our case presented a behavioral variant frontotemporal dementia (bvFTD). However, morphologically, the observed glial and neuronal pathology met the criteria for progressive supranuclear palsy (PSP). This study highlights the clinical heterogeneity within and between families with same MAPT mutation. Few pathologically confirmed PSP cases have been reported with mutations in MAPT.

Genetic Testing for Amyotrophic Lateral Sclerosis and Frontotemporal Dementia: Impact on Clinical Management

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are devastating neurodegenerative disorders that share clinical, pathologic, and genetic features. Persons and families affected by these conditions frequently question why they developed the disease, the expected disease course, treatment options, and the likelihood that family members will be affected. Genetic testing has the potential to answers these important questions. Despite the progress in gene discovery, the offer of genetic testing is not yet "standard of care" in ALS and FTD clinics. The authors review the current genetic landscape and present recommendations for the laboratory genetic evaluation of persons with these conditions.

Arylsulfatase A, a genetic modifier of Parkinson's disease, is an α-synuclein chaperone

Mutations in lysosomal genes increase the risk of neurodegenerative diseases, as is the case for Parkinson's disease. Here, we found that pathogenic and protective mutations in arylsulfatase A (ARSA), a gene responsible for metachromatic leukodystrophy, a lysosomal storage disorder, are linked to Parkinson's disease. Plasma ARSA protein levels were changed in Parkinson's disease patients. ARSA deficiency caused increases in α-synuclein aggregation and secretion, and increases in α-synuclein propagation in cells and nematodes. Despite being a lysosomal protein, ARSA directly interacts with α-synuclein in the cytosol. The interaction was more extensive with protective ARSA variant and less with pathogenic ARSA variant than wild-type. ARSA inhibited the in vitro fibrillation of α-synuclein in a dose-dependent manner. Ectopic expression of ARSA reversed the α-synuclein phenotypes in both cell and fly models of synucleinopathy, the effects correlating with the extent of the physical interaction between these molecules. Collectively, these results suggest that ARSA is a genetic modifier of Parkinson's disease pathogenesis, acting as a molecular chaperone for α-synuclein.

Progressive supranuclear palsy: Advances in diagnosis and management

Progressive supranuclear palsy (PSP) is a complex clinicopathologic disease with no current cure or disease modulating therapies that can only be definitively confirmed at autopsy. Growing understanding of the phenotypic diversity of PSP has led to expanded clinical criteria and new insights into etiopathogenesis that coupled with improved in vivo biomarkers makes increased access to current clinical trials possible. Current standard-of-care treatment of PSP is multidisciplinary, supportive and symptomatic, and several trials of potentially disease modulating agents have already been completed with disappointing results. Current ongoing clinical trials target the abnormal aggregation of tau through a variety of mechanisms including immunotherapy and gene therapy offer a more direct method of treatment. Here we review PSP clinicopathologic correlations, in vivo biomarkers including MRI, PET, and CSF biomarkers. We additionally review current pharmacologic and non-pharmacologic methods of treatment, prior and ongoing clinical trials in PSP. Newly expanded clinical criteria and improved specific biomarkers will aid in identifying patients with PSP earlier and more accurately and expand access to these potentially beneficial clinical trials.

Co-morbidity of progressive supranuclear palsy and amyotrophic lateral sclerosis: a clinical-pathological case report

BACKGROUND

The coexistence of distinct neurodegenerative diseases in single cases has recently attracted greater attention. The phenotypic co-occurrence of progressive supranuclear palsy (PSP) and amyotrophic lateral sclerosis (ALS) has been documented in several cases. That said, the clinicopathological comorbidity of these two diseases has not been demonstrated.

CASE PRESENTATION

A 77-year-old man presented with gait disturbance for 2 years, consistent with PSP with progressive gait freezing. At 79 years old, he developed muscle weakness compatible with ALS. The disease duration was 5 years after the onset of PSP and 5 months after the onset of ALS. Neuropathological findings demonstrated the coexistence of PSP and ALS. Immunohistochemical examination confirmed 4-repeat tauopathy, including globose-type neurofibrillary tangles, tufted astrocytes, and oligodendroglial coiled bodies as well as TAR DNA-binding protein 43 kDa pathology in association with upper and lower motor neuron degeneration. Immunoblotting showed hyperphosphorylated full-length 4-repeat tau bands (64 and 68 kDa) and C-terminal fragments (33 kDa), supporting the diagnosis of PSP and excluding other parkinsonian disorders, such as corticobasal degeneration. Genetic studies showed no abnormalities in genes currently known to be related to ALS or PSP.

CONCLUSIONS

Our case demonstrates the clinicopathological comorbidity of PSP and ALS in a sporadic patient. The possibility of multiple proteinopathies should be considered when distinct symptoms develop during the disease course.

MAPT mutations, tauopathy, and mechanisms of neurodegeneration

In multiple neurodegenerative diseases, including Alzheimer's disease (AD), a prominent pathological feature is the aberrant aggregation and inclusion formation of the microtubule-associated protein tau. Because of the pathological association, these disorders are often referred to as tauopathies. Mutations in the MAPT gene that encodes tau can cause frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17), providing the clearest evidence that tauopathy plays a causal role in neurodegeneration. However, large gaps in our knowledge remain regarding how various FTDP-17-linked tau mutations promote tau aggregation and neurodegeneration, and, more generally, how the tauopathy is linked to neurodegeneration. Herein, we review what is known about how FTDP-17-linked pathogenic MAPT mutations cause disease, with a major focus on the prion-like properties of wild-type and mutant tau proteins. The hypothesized mechanisms by which mutations in the MAPT gene promote tauopathy are quite varied and may not provide definitive insights into how tauopathy arises in the absence of mutation. Further, differences in the ability of tau and mutant tau proteins to support prion-like propagation in various model systems raise questions about the generalizability of this mechanism in various tauopathies. Notably, understanding the mechanisms of tauopathy induction and spread and tau-induced neurodegeneration has important implications for tau-targeting therapeutics.

PSP-Phenotype in SCA8: Case Report and Systemic Review

Spinocerebellar ataxia type 8 (SCA8) is a rare autosomal dominant neurodegenerative disease caused by expanded CTA/CTG repeats in the ATXN8OS gene. Many patients had pure cerebellar ataxia, while some had parkinsonism, both without causal explanation. We analyzed the ATXN8OS gene in 150 Japanese patients with ataxia and 76 patients with Parkinson's disease or related disorders. We systematically reassessed 123 patients with SCA8, both our patients and those reported in other studies. Two patients with progressive supranuclear palsy (PSP) had mutations in the ATXN8OS gene. Systematic analyses revealed that patients with parkinsonism had significantly shorter CTA/CTG repeat expansions and older age at onset than those with predominant ataxia. We show the imaging results of patients with and without parkinsonism. We also found a significant inverse relationship between repeat sizes and age at onset in all patients, which has not been detected previously. Our results may be useful to genetic counseling, improve understanding of the pathomechanism, and extend the clinical phenotype of SCA8.

Clinical heterogeneity of frontotemporal dementia and Parkinsonism linked to chromosome 17 caused by MAPT N279K mutation in relation to tau positron emission tomography features

BACKGROUND

While mechanistic links between tau abnormalities and neurodegeneration have been proven in frontotemporal dementia and parkinsonism linked to chromosome 17 caused by MAPT mutations, variability of the tau pathogenesis and its relation to clinical progressions in the same MAPT mutation carriers are yet to be clarified.

OBJECTIVES

The present study aimed to analyze clinical profiles, tau accumulations, and their correlations in 3 kindreds with frontotemporal dementia and parkinsonism linked to chromosome 17 attributed to the MAPT N279K mutation.

METHODS

Four patients with N279K mutant frontotemporal dementia and parkinsonism linked to chromosome 17/MAPT underwent [¹¹ C]PBB3-PET to estimate regional tau loads.

RESULTS

Haplotype assays revealed that these kindreds originated from a single founder. Despite homogeneity of the disease-causing MAPT allele, clinical progression was more rapid in 2 kindreds than in the other. The kindred with slow progression showed mild tau depositions, mostly confined to the midbrain and medial temporal areas. In contrast, kindreds with rapid progression showed profoundly increased [¹¹ C]PBB3 binding in widespread regions from an early disease stage.

CONCLUSIONS

[¹¹ C]PBB3-PET can capture four-repeat tau pathologies characteristic of N279K mutant frontotemporal dementia and parkinsonism linked to chromosome 17/MAPT. Our findings indicate that, in addition to the mutated MAPT allele, genetic and/or epigenetic modifiers of tau pathologies lead to heterogeneous clinicopathological features. © 2019 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

The role of de novo mutations in adult-onset neurodegenerative disorders

The genetic underpinnings of the most common adult-onset neurodegenerative disorders (AOND) are complex in majority of the cases. In some families, however, the disease can be inherited in a Mendelian fashion as an autosomal-dominant trait. Next to that, patients carrying mutations in the same disease genes have been reported despite a negative family history. Although challenging to demonstrate due to the late onset of the disease in most cases, the occurrence of de novo mutations can explain this sporadic presentation, as demonstrated for severe neurodevelopmental disorders. Exome or genome sequencing of patient-parent trios allows a hypothesis-free study of the role of de novo mutations in AOND and the discovery of novel disease genes. Another hypothesis that may explain a proportion of sporadic AOND cases is the occurrence of a de novo mutation after the fertilization of the oocyte (post-zygotic mutation) or even as a late-somatic mutation, restricted to the brain. Such somatic mutation hypothesis, that can be tested with the use of novel sequencing technologies, is fully compatible with the seeding and spreading mechanisms of the pathological proteins identified in most of these disorders. We review here the current knowledge and future perspectives on de novo mutations in known and novel candidate genes identified in the most common AONDs such as Alzheimer's disease, Parkinson's disease, the frontotemporal lobar degeneration spectrum and Prion disorders. Also, we review the first lessons learned from recent genomic studies of control and diseased brains and the challenges which remain to be addressed.

Coding mutations in NUS1 contribute to Parkinson's disease

Whole-exome sequencing has been successful in identifying genetic factors contributing to familial or sporadic Parkinson's disease (PD). However, this approach has not been applied to explore the impact of de novo mutations on PD pathogenesis. Here, we sequenced the exomes of 39 early onset patients, their parents, and 20 unaffected siblings to investigate the effects of de novo mutations on PD. We identified 12 genes with de novo mutations (MAD1L1, NUP98, PPP2CB, PKMYT1, TRIM24, CEP131, CTTNBP2, NUS1, SMPD3, MGRN1, IFI35, and RUSC2), which could be functionally relevant to PD pathogenesis. Further analyses of two independent case-control cohorts (1,852 patients and 1,565 controls in one cohort and 3,237 patients and 2,858 controls in the other) revealed that NUS1 harbors significantly more rare nonsynonymous variants (P = 1.01E-5, odds ratio = 11.3) in PD patients than in controls. Functional studies in Drosophila demonstrated that the loss of NUS1 could reduce the climbing ability, dopamine level, and number of dopaminergic neurons in 30-day-old flies and could induce apoptosis in fly brain. Together, our data suggest that de novo mutations could contribute to early onset PD pathogenesis and identify NUS1 as a candidate gene for PD.

Marked Reduction in the Striatal Dopamine Transporter Uptake During the Early Stage of Motor Symptoms in Patients with the MAPT N279K Mutation

We herein report two patients harboring the mutation N279K in microtubule-associated protein tau (MAPT), who showed parkinsonism with a disease duration within three years from the onset, evaluated by dopamine transporter (DAT) [¹²³I]N-ω-fluoroprophyl-2β-carbomethoxy-3β-(4-iodophenyl) tropane single-photon emission computed tomography. We performed a quantification analysis, comparing five age- and severity-matched PD patients and six normal controls. The patients with the N279K mutation showed a more marked reduction in their DAT densities, especially in the caudate nucleus and anterior putamen, than the others. An early marked reduction in the DAT densities in the caudate nucleus and anterior putamen may be an early biomarker of patients with MAPT mutations.

Analysis of frontotemporal dementia, amyotrophic lateral sclerosis, and other dementia-related genes in 107 Korean patients with frontotemporal dementia

To identify pathogenic variants in 107 Korean patients with sporadic frontotemporal dementia (FTD), 46 genes related to FTD, amyotrophic lateral sclerosis, and other dementias were screened by next-generation sequencing. Hexanucleotide repeats in C9orf72 gene were also tested by repeat-primed polymerase chain reaction. Next-generation sequencing revealed one known pathogenic variant (c.708+1G>A) in the GRN gene in a patient with behavioral variant FTD (bvFTD). In addition, a novel in-frame deletion (c.2675_2683del) in the CSF1R gene was identified in a patient with bvFTD who had severe bifrontal atrophy with frontal subcortical white matter changes. Novel compound heterozygous variants in the AARS2 gene, c.1040+1G>A and c.636G>A (p.Met212Ile), were found in a patient with bvFTD. Forty-six variants of uncertain significance were detected in other patients. None of the patients had expanded hexanucleotide repeats in C9orf72. These results show that pathogenic variants of known FTD genes are rare in Korean FTD patients but the CSF1R and AARS2 genes should be screened for a genetic diagnosis of FTD or other dementias.

Targeted exome sequencing reveals homozygous TREM2 R47C mutation presenting with behavioral variant frontotemporal dementia without bone involvement

To identify genes associated with frontotemporal dementia (FTD) in South-East Asia, targeted exome sequencing and C9orf72 genotyping was performed in 198 subjects (52 patients with FTD and 146 healthy controls) who were screened for mutations in 12 FTD-associated genes. We detected a homozygous TREM2 R47C mutation in a patient with behavioral variant FTD without bone cysts or bone-associated phenotype. Two novel nonsense GRN mutations in 3 FTD patients from the Philippines were detected, but no known pathogenic mutations in other FTD-associated genes were found. In 45 subjects screened for C9orf72 repeat expansions, no pathogenic expansion (≥30 repeats) was identified, but there was a higher proportion of intermediate length (≥10-29 repeats) alleles in patients compared with controls (8/90 alleles, 8.9% vs. 9/164 alleles, 5.5%). Overall, we detected a mutation rate of 7.7% (4/52 patients) in our cohort. Given recent findings of enrichment of rare TREM2 variants (including R47C) in Alzheimer's disease, it is notable that we detected a homozygous TREM2 R47C carrier presenting with an FTD rather than an Alzheimer's disease phenotype.

Plasma Screening for Progranulin Mutations in Patients with Progressive Supranuclear Palsy and Corticobasal Syndromes

Progranulin gene (GRN) mutations are characterized by heterogeneous presentations. Corticobasal syndrome (CBS) is often associated with GRN mutations, whereas association with progressive supranuclear palsy syndrome (PSPS) is rare. Plasma progranulin levels were evaluated in 34 patients, including 19 with PSPS, 12 with CBS, and 3 with mixed signs, with the purpose to screen for the presence of causal mutations, associated with low levels. We found undetectable levels in a patient with CBS. Sequencing confirmed the presence of the Thr272fs deletion. Progranulin mutation screening is suggested in cases of CBS, even in the absence of positive family history for dementia and/or movement disorders.

The role of MAPT gene in Chinese dementia patients: a P301L pedigree study and brief literature review

BACKGROUND AND PURPOSE

Frontotemporal dementia (FTD) is the second most common presenile dementia characterized by behavioral changes and language impairment. The diagnosis of FTD relies heavily on neuroimaging, and sometimes on genetic screening. However, the genetic components in Chinese FTD patients remain largely unknown. Only a few FTD cases with established mutations have been reported in China. This study reported the detailed clinical and neuroimaging features in a Chinese behavioral variant FTD family. The role of MAPT gene mutation in Chinese dementia patients was also reviewed.

METHODS

By detailed inquiry of all affected individuals in the family, this study summarized the main clinical features of the disease. Four candidate genes (MAPT, PSEN1, PSEN2, and APP) were screened by direct sequencing. Structural magnetic resonance imaging (MRI), functional imaging of cerebral blood flow with arterial spin-labeled MRI (ASL-MRI), and cerebral metabolism with fluorodeoxyglucose positron emission tomography (FDG-PET) were collected in the proband and healthy mutation carriers.

RESULTS

By direct sequencing of candidate genes (MAPT, PSEN1, PSEN2, and APP), this study identified the P301L mutation in the MAPT gene in the proband and three unaffected family members. The phenotype of the affected cases was consistent within the pedigree. In this genetically proven behavioral variant FTD (bvFTD) patient, the maps of hypoperfusion on ASL-MRI look fairly similar to the hypometabolism on FDG-PET. The clinical feature for this bvFTD was in line with the hypoperfusion or hypometabolism pattern on functional neuroimagings. The phenotype of P301L in east Asia seems similar to western countries.

CONCLUSION

For the inherited FTD patients, ASL-MRI and genetic identification were strongly recommended for the final diagnosis. In case of being underestimated, the role of MAPT gene mutation in Chinese FTD patients warrants further investigation.

Progranulin: a new avenue towards the understanding and treatment of neurodegenerative disease

Progranulin, a secreted glycoprotein, is encoded in humans by the single GRN gene. Progranulin consists of seven and a half, tandemly repeated, non-identical copies of the 12 cysteine granulin motif. Many cellular processes and diseases are associated with this unique pleiotropic factor that include, but are not limited to, embryogenesis, tumorigenesis, inflammation, wound repair, neurodegeneration and lysosome function. Haploinsufficiency caused by autosomal dominant mutations within the GRN gene leads to frontotemporal lobar degeneration, a progressive neuronal atrophy that presents in patients as frontotemporal dementia. Frontotemporal dementia is an early onset form of dementia, distinct from Alzheimer's disease. The GRN-related form of frontotemporal lobar dementia is a proteinopathy characterized by the appearance of neuronal inclusions containing ubiquitinated and fragmented TDP-43 (encoded by TARDBP). The neurotrophic and neuro-immunomodulatory properties of progranulin have recently been reported but are still not well understood. Gene delivery of GRN in experimental models of Alzheimer's- and Parkinson's-like diseases inhibits phenotype progression. Here we review what is currently known concerning the molecular function and mechanism of action of progranulin in normal physiological and pathophysiological conditions in both in vitro and in vivo models. The potential therapeutic applications of progranulin in treating neurodegenerative diseases are highlighted.

GRN and MAPT Mutations in 2 Frontotemporal Dementia Research Centers in Brazil

BACKGROUND

Mutations in GRN (progranulin) and MAPT (microtubule-associated protein tau) are among the most frequent causes of monogenic frontotemporal dementia (FTD), but data on the frequency of these mutations in regions such as Latin America are still lacking.

OBJECTIVE

We aimed to investigate the frequencies of GRN and MAPT mutations in FTD cohorts from 2 Brazilian dementia research centers, the University of Sao Paulo and the Federal University of Minas Gerais medical schools.

METHODS

We included 76 probands diagnosed with behavioral-variant FTD (n=55), semantic-variant Primary Progressive Aphasia (PPA) (n=11), or nonfluent-variant PPA (n=10). Twenty-five percent of the cohort had at least 1 relative affected with FTD.

RESULTS

Mutations in GRN were identified in 7 probands, and in MAPT, in 2 probands. We identified 3 novel GRN mutations (p.Q130X, p.317Afs*12, and p.K259Afs*23) in patients diagnosed with nonfluent-variant PPA or behavioral-variant FTD. Plasma progranulin levels were measured and a cutoff value of 70 ng/mL was found, with 100% sensitivity and specificity to detect null GRN mutations.

CONCLUSIONS

The frequency of GRN mutations was 9.6% and that of MAPT mutations was 7.1%. Among familial cases of FTD, the frequency of GRN mutations was 31.5% and that of MAPT mutations was 10.5%.

Frontotemporal lobar degeneration due to P301L tau mutation showing apathy and severe frontal atrophy but lacking other behavioral changes: A case report and literature review

The clinical features in cases that have mutations in the microtubule-associated protein tau gene but lack prominent behavioral changes remain unclear. Here, we describe detailed clinical and pathological features of a case carrying the P301L tau mutation that showed only apathy until the middle stage of the course. The mother of this case was suspected to have mild cognitive decline at age 46. However, before she was fully examined, she had a subarachnoid hemorrhage at age 49 and died at age 53. An autopsy was not done. The proband of this pedigree, a 60-year-old right-handed Japanese man at the time of death, began to make mistakes at work at the age of 51 years. Until age 54, he showed only mild apathy with bradykinesia. Insight was well spared. Parkinsonism and echolalia developed at age 55, and pyramidal signs and oral tendency at age 57. Personality change, disinhibition, stereotypy, or semantic memory impairment was not found throughout the course. The final neurological diagnosis was unspecified dementia. Pathological examination demonstrated numerous round four-repeat tau-positive three-repeat tau-negative or perinuclear ring-like neuronal cytoplasmic inclusions with many ballooned neurons in the frontal and temporal cortices and hippocampus. Genetic analysis using frozen brain tissue demonstrated a P301L tau mutation. Among 31 previously reported cases bearing the P301L tau mutation for which the data regarding initial symptoms are available, one clinical case showed only apathy with depression in the early stage. Given these findings, clinicians should be aware that a clinical course characterized only by apathy for several years, which can be misdiagnosed as a psychiatric disorder, is one of the clinical presentations associated with P301L tau mutation.