TRIM25 mutation (p.C168*), coding for an E3 ubiquitin ligase, is a cause of early-onset autosomal dominant dementia with amyloid load and parkinsonism.

INTRODUCTION: Patients with familial early-onset dementia (EOD) pose a unique opportunity for gene identification studies. METHODS: We present the phenotype and whole-exome sequencing (WES) study of an autosomal dominant EOD family. Candidate genes were examined in a set of dementia cases and controls (n = 3712). Western blotting was conducted of the wild-type and mutant protein of the final candidate. RESULTS: Age at disease onset was 60 years (range 56 to 63). The phenotype comprised mixed amnestic and behavioral features, and parkinsonism. Cerebrospinal fluid and plasma biomarkers, and a positron emission tomography amyloid study suggested Alzheimer's disease. WES and the segregation pattern pointed to a nonsense mutation in the TRIM25 gene (p.C168*), coding for an E3 ubiquitin ligase, which was absent in the cohorts studied. Protein studies supported a loss-of-function mechanism. DISCUSSION: This study supports a new physiopathological mechanism for brain amyloidosis. Furthermore, it extends the role of E3 ubiquitin ligases dysfunction in the development of neurodegenerative diseases. HIGHLIGHTS: A TRIM25 nonsense mutation (p.C168*) is associated with autosomal dominant early-onset dementia and parkinsonism with biomarkers suggestive of Alzheimer's disease. TRIM25 protein studies support that the mutation exerts its effect through loss of function. TRIM25, an E3 ubiquitin ligase, is known for its role in the innate immune response but this is the first report of association with neurodegeneration. The role of TRIM25 dysfunction in development of amyloidosis and neurodegeneration merits a new line of research.

Protein interaction network analysis reveals genetic enrichment of immune system genes in frontotemporal dementia.

Interactors of protein products of known genes for frontotemporal dementia (FTD) are likely to be involved in the molecular pathways towards disease. We therefore applied protein interaction network (PIN) analysis to prioritize candidate genes for rare variant association analysis. We created an FTD-PIN starting from known FTD genes downloading their physical interactors and performed functional enrichment analyses. We identified overrepresented processes in FTD and selected genes (n = 440) belonging to these processes for rare variant analysis in a Belgian cohort of 228 FTD patients and 345 controls. SKAT-O analysis suggested TNFAIP3 as the top gene (p = 0.7 × 10-3) reaching near test-wide significance (p = 2.5 × 10-4). We then analyzed the TNFAIP3-subnetwork within the FTD-PIN which indicated enrichment of several immune signaling networks, suggesting that disrupted immune signaling may be implicated in TNFAIP3-related FTD. Our study demonstrates that integration of PINs with genetic data is a useful approach to increase the power for rare variant association analysis. Furthermore, we present a computational pipeline for identifying potential novel therapeutic targets and risk-modifying variants.

Genetic variation in APOE, GRN, and TP53 are phenotype modifiers in frontotemporal dementia.

Frontotemporal dementia (FTD) is a clinical, genetic, and pathologic heterogeneous group of neurodegenerative diseases. In this study, we investigated the role of APOƐ4, rs5848 in GRN, and rs1042522 in TP53 gene as disease risk factors and/or phenotype modifiers in 440 FTD patients, including 175 C9orf72 expansion carriers. We found that the C9orf72 expansion carriers showing an earlier age at onset (p < 0.001). Among the clinical groups, the FTD-MND (motoneuron disease) showed the lowest survival (hazard ratio [HR] = 4.12), and the progressive nonfluent aphasia group showed the highest onset age (p = 0.03). In our cohort, the rs1042522 in TP53 was associated with disease onset (p = 0.02) and survival (HR = 1.73) and rs5848 GRN with a significantly shorter survival in CC homozygous patients (HR = 1.98). The frequency of APOƐ4 carriers was significantly increased in the C9orf72 noncarriers (p = 0.022). Although validation of our findings is necessary, our results suggest that TP53, GRN, and APOE genes may act as phenotype modifiers in FTD and should be considered in future clinical trials.

Genetic Alzheimer Disease and Sporadic Dementia With Lewy Bodies: A Comorbidity Presenting as Primary Progressive Aphasia.

We report a 44-year-old woman, with a family history of early-onset dementia, presenting with primary progressive aphasia. This clinically variable syndrome has multiple underlying pathologies, and correlations between clinical manifestations and postmortem neuropathologic findings are controversial. Our patient suffered worsening language impairment with major word-finding difficulties but preserved comprehension. She also developed episodic memory impairment. Her condition progressed to dementia with behavioral changes. Magnetic resonance imaging showed early left perisylvian and bitemporal atrophy. The patient died shortly afterward from colon cancer. Neuropathologic examination revealed advanced early-onset Alzheimer and Lewy body disease, plus a clinically nonrelevant metastasis of her colon cancer in her left parietal lobe. Genetic examination revealed a p.Glu184Asp mutation in the presenilin1 gene. Our findings confirm the importance of a thorough appreciation for the clinical and neuropathologic correlations in patients with atypical neurodegenerative dementias.

Clinicopathological description of two cases with SQSTM1 gene mutation associated with frontotemporal dementia.

There is a strong genetic influence on the clinicopathological phenotypes associated with frontotemporal lobar degeneration (FTLD) and frontotemporal dementia (FTD). Intracellular deposition of TDP-43 is the phenotypical hallmark of a frequent subgroup of cases. Mutations in the sequestosome 1 (SQSTM1) gene have rarely been found in individuals with FTD. Here we provide a comprehensive clinicopathological description of two cases with a SQSTM1 mutation. The clinical phenotype of patient 1 (mutation p.Glu396*) was compatible with the behavioural variant (bv) of FTD. TDP-43 pathology was consistent with the features of type B of FTLD-TDP pathology. However, prominent neuronal granular cytoplasmic TDP-43 immunoreactivity and abundant oligodendroglial inclusions, proven by colocalization with the oligodendroglial-marker TPPP/p25, were also seen. The clinical phenotype of patient 2 was compatible with bvFTD associated with parkinsonism and bulbar symptoms in the later stage. Genetic testing of patient 2 identified a C9orf72 repeat expansion mutation together with a missense mutation (p.Arg212Cys) in SQSTM1. TDP-43 pathology was characterized by neuritic profiles compatible mostly with type A. In contrast to patient 1, p62 pathology was seen to a greater extent as TDP-43 immunoreactivity in neurons. Using an antibody that detects poly(GP) peptides produced via repeat associated non-ATG translation associated with expanded hexanucleotide repeat in the C9orf72 gene, we confirmed the presence of pathognomonic inclusions. The present study supports previous observations on amyotrophic lateral sclerosis (ALS) that SQSTM1 mutations consistently associate with TDP-43 pathology. The co-presence of C9orf72 mutation may influence the phenotype, thus finding one FTLD (or ALS) related mutation does not exclude the presence of further influential genetic alterations. Oligodendroglial TDP-43 pathology is considerable in some forms of FTLD-TDP, thus their evaluation might be considered to be included in classification systems.

The molecular basis of the frontotemporal lobar degeneration-amyotrophic lateral sclerosis spectrum.

There is increasing evidence that frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS) represent a continuum of neurodegenerative diseases. FTLD is complicated by ALS in a significant proportion of patients, and neuropsychological studies have demonstrated frontotemporal dysfunction in up to 50% of ALS patients. More recently, advances in neuropathology and molecular genetics have started to disclose the biological basis for the observed clinical concurrence. TDP-43 and FUS have been discovered as key pathological proteins in both FTLD and ALS. The most recent discovery of a pathological hexanucleotide repeat expansion in the gene C9orf72 as a frequent cause of both FTLD and ALS has eventually confirmed the association of these two at first sight distinct neurodegenerative diseases. Mutations in the TARDBP, FUS, and VCP genes had previously been associated with different phenotypes of the FTLD-ALS spectrum, although in these cases one end of the spectrum predominates. Whilst on the one hand providing evidence for overlap, these discoveries have also highlighted that FTLD and ALS are etiologically diverse. In this review, we review the recent advances that support the existence of an FTLD-ALS spectrum, with particular emphasis on the molecular genetic aspect.

Mutations in DNAJC5, encoding cysteine-string protein alpha, cause autosomal-dominant adult-onset neuronal ceroid lipofuscinosis.

Autosomal-dominant adult-onset neuronal ceroid lipofuscinosis (ANCL) is characterized by accumulation of autofluorescent storage material in neural tissues and neurodegeneration and has an age of onset in the third decade of life or later. The genetic and molecular basis of the disease has remained unknown for many years. We carried out linkage mapping, gene-expression analysis, exome sequencing, and candidate-gene sequencing in affected individuals from 20 families and/or individuals with simplex cases; we identified in five individuals one of two disease-causing mutations, c.346_348delCTC and c.344T>G, in DNAJC5 encoding cysteine-string protein alpha (CSPα). These mutations-causing a deletion, p.Leu116del, and an amino acid exchange, p.Leu115Arg, respectively-are located within the cysteine-string domain of the protein and affect both palmitoylation-dependent sorting and the amount of CSPα in neuronal cells. The resulting depletion of functional CSPα might cause in parallel the presynaptic dysfunction and the progressive neurodegeneration observed in affected individuals and lysosomal accumulation of misfolded and proteolysis-resistant proteins in the form of characteristic ceroid deposits in neurons. Our work represents an important step in the genetic dissection of a genetically heterogeneous group of ANCLs. It also confirms a neuroprotective role for CSPα in humans and demonstrates the need for detailed investigation of CSPα in the neuronal ceroid lipofuscinoses and other neurodegenerative diseases presenting with neuronal protein aggregation.

FUS pathology defines the majority of tau- and TDP-43-negative frontotemporal lobar degeneration.

Through an international consortium, we have collected 37 tau- and TAR DNA-binding protein 43 (TDP-43)-negative frontotemporal lobar degeneration (FTLD) cases, and present here the first comprehensive analysis of these cases in terms of neuropathology, genetics, demographics and clinical data. 92% (34/37) had fused in sarcoma (FUS) protein pathology, indicating that FTLD-FUS is an important FTLD subtype. This FTLD-FUS collection specifically focussed on aFTLD-U cases, one of three recently defined subtypes of FTLD-FUS. The aFTLD-U subtype of FTLD-FUS is characterised clinically by behavioural variant frontotemporal dementia (bvFTD) and has a particularly young age of onset with a mean of 41 years. Further, this subtype had a high prevalence of psychotic symptoms (36% of cases) and low prevalence of motor symptoms (3% of cases). We did not find FUS mutations in any aFTLD-U case. To date, the only subtype of cases reported to have ubiquitin-positive but tau-, TDP-43- and FUS-negative pathology, termed FTLD-UPS, is the result of charged multivesicular body protein 2B gene (CHMP2B) mutation. We identified three FTLD-UPS cases, which are negative for CHMP2B mutation, suggesting that the full complement of FTLD pathologies is yet to be elucidated.

Serum biomarker for progranulin-associated frontotemporal lobar degeneration.

OBJECTIVE: Mutations that lead to a loss of progranulin (PGRN) explain a considerable portion of the occurrence of frontotemporal lobar degeneration. We tested a biomarker allowing rapid detection of a loss of PGRN. METHODS: We used an enzyme-linked immunosorbent assay to measure in serum the PGRN protein levels of six affected and eight unaffected carriers from within an extended Belgian founder family segregating the null mutation IVS1+5G>C. Further, we measured serum PGRN levels in 2 patients with another null mutation (a Met1 and a frameshift mutation), in 4 patients carrying a predicted pathogenic missense mutation and in 5 patients carrying a benign missense polymorphism, in 9 unaffected noncarrier relatives, and in 22 community controls. RESULTS: Serum PGRN levels were reduced in both affected and unaffected null mutation carriers compared with noncarrier relatives (p(exact) < 0.0001), and allowed perfect discrimination between carriers and noncarriers (sensitivity: 1.0; 1 - specificity: 0.0). Serum PGRN levels in Cys139Arg and Arg564Cys mutation carriers were significantly lower than in controls, but greater than in null mutation carriers, fitting the hypothesis of partial loss of function caused by these missense mutations. As expected, levels for carriers of benign missense polymorphisms were not significantly different from controls. INTERPRETATION: Our results indicate that the serum PGRN level is a reliable biomarker for diagnosing and early detection of frontotemporal lobar degeneration caused by PGRN null mutations, and provided the first in vivo evidence that at least some missense mutations in PGRN may lead to a (partial) loss of PGRN.

CHMP2B C-truncating mutations in frontotemporal lobar degeneration are associated with an aberrant endosomal phenotype in vitro.

The charged multivesicular body protein 2B gene (CHMP2B) was recently associated with frontotemporal lobar degeneration (FTLD) linked to chromosome 3 in a Danish FTLD family (FTD-3). In this family, a mutation in the acceptor splice site of exon 6 produced two aberrant transcripts predicting two C-truncated CHMP2B proteins due to a read through of intron 5 (p.Met178ValfsX2) and a cryptic splicing event within exon 6 (p.Met178LeufsX30). Extensive mutation analysis of CHMP2B in Belgian patients (N = 146) identified one nonsense mutation in exon 5 (c.493C>T) in a familial FTLD patient, predicting a C-truncated protein p.Gln165X analogous to the Danish mutant proteins. Overexpression of Belgian p.Gln165X in human neuroblastoma SK-N-SH cells showed the formation of large, aberrant endosomal structures that were highly similar to those observed for Danish p.Met178ValfsX2. Together, these data suggest that C-truncating mutations in CHMP2B might underlie the pathogenic mechanism in FTLD by disturbing endosome function. We also describe a missense mutation in exon 5 of CHMP2B (p.Asn143Ser) in a familial patient with cortical basal degeneration. However, the pathogenic character of this mutation remains elusive.

Frontotemporal lobar degeneration with ubiquitin-positive inclusions: a molecular genetic update.

Frontotemporal lobar degeneration (FTLD) is a clinically, pathologically and genetically highly complex disorder. In the last few years enormous progress has been made in dissecting the genetic etiology of FTLD. Mutations have been identified in the progranulin gene (PGRN), the charged multivesicular body protein 2B gene (CHMP2B) and the valosin-containing protein gene (VCP). Mutations in these genes all lead to FTLD pathology characterized by ubiquitin-immunoreactive neuronal cytoplasmic and intranuclear lentiform inclusions (FTLD-U). The similar pathology suggests that these genes may be connected trough a common disease pathway leading to neurodegeneration and the formation of these pathognomic inclusions. This review focuses on the molecular genetic processes underlying FTLD-U pathology.

Null mutations in progranulin cause ubiquitin-positive frontotemporal dementia linked to chromosome 17q21.

Frontotemporal dementia (FTD) with ubiquitin-immunoreactive neuronal inclusions (both cytoplasmic and nuclear) of unknown nature has been linked to a chromosome 17q21 region (FTDU-17) containing MAPT (microtubule-associated protein tau). FTDU-17 patients have consistently been shown to lack a tau-immunoreactive pathology, a feature characteristic of FTD with parkinsonism linked to mutations in MAPT (FTDP-17). Furthermore, in FTDU-17 patients, mutations in MAPT and genomic rearrangements in the MAPT region have been excluded by both genomic sequencing and fluorescence in situ hybridization on mechanically stretched chromosomes. Here we demonstrate that FTDU-17 is caused by mutations in the gene coding for progranulin (PGRN), a growth factor involved in multiple physiological and pathological processes including tumorigenesis. Besides the production of truncated PGRN proteins due to premature stop codons, we identified a mutation within the splice donor site of intron 0 (IVS0 + 5G > C), indicating loss of the mutant transcript by nuclear degradation. The finding was made within an extensively documented Belgian FTDU-17 founder family. Transcript and protein analyses confirmed the absence of the mutant allele and a reduction in the expression of PGRN. We also identified a mutation (c.3G > A) in the Met1 translation initiation codon, indicating loss of PGRN due to lack of translation of the mutant allele. Our data provide evidence that PGRN haploinsufficiency leads to neurodegeneration because of reduced PGRN-mediated neuronal survival. Furthermore, in a Belgian series of familial FTD patients, PGRN mutations were 3.5 times more frequent than mutations in MAPT, underscoring a principal involvement of PGRN in FTD pathogenesis.