Frontotemporal dementia (FTD) is a complex disorder characterised by a broad range of clinical manifestations, differential pathological signatures, and genetic variability. Mutations in three genes—MAPT, GRN, and C9orf72—have been associated with FTD. We sought to identify novel genetic risk loci associated with the disorder.
We did a two-stage genome-wide association study on clinical FTD, analysing samples from 3526 patients with FTD and 9402 healthy controls. All participants had European ancestry. In the discovery phase (samples from 2154 patients with FTD and 4308 controls), we did separate association analyses for each FTD subtype (behavioural variant FTD, semantic dementia, progressive non-fluent aphasia, and FTD overlapping with motor neuron disease [FTD-MND]), followed by a meta-analysis of the entire dataset. We carried forward replication of the novel suggestive loci in an independent sample series (samples from 1372 patients and 5094 controls) and then did joint phase and brain expression and methylation quantitative trait loci analyses for the associated (p<5 × 10−8) and suggestive single-nucleotide polymorphisms.
We identified novel associations exceeding the genome-wide significance threshold (p<5 × 10−8) that encompassed the HLA locus at 6p21.3 in the entire cohort. We also identified a potential novel locus at 11q14, encompassing RAB38/CTSC, for the behavioural FTD subtype. Analysis of expression and methylation quantitative trait loci data suggested that these loci might affect expression and methylation incis.
Our findings suggest that immune system processes (link to 6p21.3) and possibly lysosomal and autophagy pathways (link to 11q14) are potentially involved in FTD. Our findings need to be replicated to better define the association of the newly identified loci with disease and possibly to shed light on the pathomechanisms contributing to FTD.
The National Institute of Neurological Disorders and Stroke and National Institute on Aging, the Wellcome/ MRC Centre on Parkinson’s disease, Alzheimer’s Research UK, and Texas Tech University Health Sciences Center.
Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are complex neurodegenerative disorders that can be either sporadic or familial and can overlap clinically and pathologically. We present the first Central-Eastern European family with ALS-FTD syndrome due to a C9ORF72 repeat expansion.
We studied a family consisting of 37 family members, and six of these family members were genetically evaluated for C9ORF72 expansions. Family members were evaluated clinically, by history, and by chart review.
Five generations of the family were studied, and six affected family members were identified. All affected members were females and had a different clinical presentation, which was either ALS, FTD, or both. Among genetically evaluated subjects, five carried a C9ORF72 expansion; four of these individuals remain clinically unaffected.
Our report reveals that the hexanucleotide repeat expansion of C9ORF72, which is the most common genetic cause of ALS-FTD complex disorder, is also present in Central-Eastern Europe. Further studies are needed to assess the frequency of this expansion in the Polish population with familial as well as sporadic ALS, FTD, and the ALS-FTD complex disorder.
ALS-FTD complex disorder; familial ALS-FTD; C9ORF72 gene mutation; phenotype
Understanding of frontotemporal lobar degeneration (FTLD), the underlying pathology that is most often linked to the clinical diagnosis of frontotemporal dementia (FTD), is rapidly increasing. Mutations in 7 known genes (MAPT, GRN, C9orf72, VCP, CHMP2B, and rarely TARDBP and FUS) are associated with FTD and the pathologic classification of FTLD has recently been modified to reflect these discoveries. Mutations in one of these genes (GRN), which encodes progranulin, have been implicated in up to one quarter of FTLD cases with TAR DNA-binding protein 43-positive inclusions (FTLD-TDP); there currently are more than 60 known pathogenic mutations of the gene. We present the clinical, pathologic, and genetic findings of 6 cases from 4 families, 5 of which were shown to have a novel GRN c.708+6_+9delTGAG mutation.
Dementia; Familial FTD; FTLD-TDP; GRN; Mutation; Progranulin
Idiopathic Basal Ganglia Calcification (IBGC) is characterized by bilateral calcification of the basal ganglia associated with a spectrum of neuropsychiatric and motor syndromes. In this study, we set out to determine the frequency of the recently identified IBGC gene SLC20A2 in 27 IBGC cases from the Mayo Clinic Florida Brain Bank using both Sanger sequencing and Taqman copy number analysis to cover the complete spectrum of possible mutations. We identified SLC20A2 pathogenic mutations in 2 of the 27 cases of IBGC (7%). Sequencing analysis identified a p.S113* nonsense mutation in SLC20A2 in one case. Taqman copy-number analysis of SLC20A2 further revealed a genomic deletion in a second case, which was part of a large previously reported Canadian IBGC family with dystonia. Subsequent whole-genome sequencing in this family revealed a 563,256 bp genomic deletion with precise breakpoints on chromosome 8 affecting multiple genes including SLC20A2 and the known dystonia related gene THAP1. The deletion co-segregated with disease in all family members. The deletion of THAP1 in addition to SLC20A2 in the Canadian IBGC family may contribute to the severe and early-onset dystonia in this family. The identification of a SLC20A2 genomic deletion in a familial form of IBGC demonstrates that reduced SLC20A2 in the absence of mutant protein is sufficient to cause neurodegeneration and that previously reported SLC20A2 mutation frequencies may be underestimated.
basal ganglia calcification; dystonia; SLC20A2; THAP1; genomic deletion; mutation
The most common cause of familial frontotemporal lobar degeneration with TAR DNA-binding protein-43 pathology (FTLD-TDP) has been found to be an expansion of a hexanucleotide repeat (GGGGCC) in a noncoding region of the gene C9ORF72. Hippocampal sclerosis (HpScl) is a common finding in FTLD-TDP. Our objective was to screen for the presence of C9ORF72 hexanucleotide repeat expansions in a pathologically-confirmed cohort of “pure” hippocampal sclerosis cases (n=33), outside the setting of FTLD-TDP and Alzheimer’s disease (AD). Using a recently described repeat-associated non-ATG (RAN) translation (C9RANT) antibody that was found to be highly specific for c9FTD/ALS, we identified a single “pure” HpScl autopsy case with a repeat expansion in C9ORF72 (c9HpScl). Mutation screening was also performed with repeat-primed polymerase chain reaction and further confirmed with southern blotting. The c9HpScl patient had a 14-year history of a slowly progressive amnestic syndrome and a clinical diagnosis of probable AD. Neuropsychological testing revealed memory impairment, but no deficits in other cognitive domains. Autopsy showed hippocampal sclerosis with TDP-43 immunoreactive neuronal inclusions relatively limited to limbic lobe structures. Neuritic pathology immunoreactive for p62 was more frequent than TDP-43 in amygdala and hippocampus. Frequent p62 positive neuronal inclusions were present in cerebellar granule neurons as is typical of C9ORF72 mutation carriers. There was no significant FTLD or motor neuron disease. C9RANT was found to be sensitive and specific in this autopsy-confirmed series of HpScl cases. The findings in this patient suggest that the clinical and pathologic spectrum of C9ORF72 repeat expansion is wider than frontotemporal dementia and motor neuron disease, including cases of progressive amnestic dementia with restricted TDP-43 pathology associated with HpScl.
Hippocampus; C9ORF72; memory; neuropathology; frontotemporal lobar degeneration; C9RANT
Atypical Parkinsonism associated with white matter pathology has been described in cerebrovascular diseases, mitochondrial cytopathies, osmotic demyelinating disorders, leukoencephalopathies including leukodystrophies, and others. Hereditary diffuse leukoencephalopathy with spheroids (HDLS) is an autosomal dominant disorder with symptomatic onset in midlife and death within a few years after symptom onset. Neuroimaging reveals cerebral white matter lesions that are pathologically characterized by non-inflammatory myelin loss, reactive astrocytosis, and axonal spheroids. Most cases are caused by mutations in the colony-stimulating factor 1 receptor (CSF1R) gene.
We studied neuropathologically verified HDLS patients with CSF1R mutations to assess Parkinsonian features. Ten families were evaluated with 16 affected individuals. During the course of the illness, all patients had at least some degree of bradykinesia. Fifteen patients had postural instability, and seven had rigidity. Two patients initially presented with Parkinsonian gait and asymmetrical bradykinesia. These two patients and two others exhibited bradykinesia, rigidity, postural instability, and tremor (two with resting) early in the course of the illness. Levodopa/carbidopa therapy in these four patients provided no benefit, and the remaining 12 patients were not treated. The mean age of onset for all patients was about 45 years (range, 18-71) and the mean disease duration was approximately six years (range, 3-11).
We also reviewed HDLS patients published prior to the CSF1R discovery for the presence of Parkinsonian features. Out of 50 patients, 37 had gait impairments, 8 rigidity, 7 bradykinesia, and 5 resting tremor. Our report emphasizes the presence of atypical Parkinsonism in HDLS due to CSF1R mutations.
HDLS; CSF1R mutation; Parkinsonism; Autosomal dominant; White matter disorders
To describe in detail the presenting symptoms and clinical course of a cohort of patients with Frontotemporal dementia and the recently described C9ORF72 repeat expansion.
Recent discovery of the C9ORF72 repeat expansion linked to familial frontotemporal dementia and ALS has permitted retrospective evaluation of potential defining clinical characteristics that may distinguish C9ORF72 mutation carriers from other patients with FTD. Prior reports have identified a subset of patients with an increased incidence of psychosis, specifically delusions, though the detailed nature of these symptoms is not yet well described.
We conducted a retrospective chart review of to report the detailed case histories of 7 patients with C9ORF72 mutations from a cohort of 61 patients with FTD.
Detailed histories available from these patients reveal an increased incidence of psychosis, including visual and auditory hallucinations and delusions compared to sporadic FTD patients in our cohort.
This cohort confirms and adds symptom-related details to prior reports of increased incidence of psychotic phenomenon in FTD and ALS patients with C9ORF72 mutations, to enhance future clinical identification and diagnosis of patients presenting with these symptoms.
frontotemporal dementia; psychosis; C9ORF72 mutation; motor neuron disease
The nuclear protein fused in sarcoma (FUS) is found in cytoplasmic inclusions in a subset of patients with the neurodegenerative disorder frontotemporal lobar degeneration (FTLD-FUS). FUS contains a methylated arginine-glycine-glycine domain which is required for transport into the nucleus. Recent findings have shown that this domain is hypomethylated in patients with FTLD-FUS. To determine if the cause of hypomethylation is the result of mutations in protein N-arginine methyltransferases (PRMTs), we selected 3 candidate genes (PRMT1, PRMT3 and PRMT8) and performed complete sequencing analysis and real-time PCR mRNA expression analysis in 20 FTLD-FUS cases. No mutations or statistically significant changes in expression were observed in our patient samples, suggesting that defects in PRMTs are not the cause of FTLD-FUS.
Frontotemporal lobar degeneration (FTLD) is the second leading cause of dementia in individuals under age 65. In many patients, the predominant pathology includes neuronal cytoplasmic or intranuclear inclusions of ubiquitinated TAR DNA binding protein 43 (FTLDTDP). Recently, a genome-wide association study identified the first FTLD-TDP genetic risk factor, in which variants in and around the TMEM106B gene (top SNP rs1990622) were significantly associated with FTLD-TDP risk. Intriguingly, the most significant association was in FTLD-TDP patients carrying progranulin (GRN) mutations. Here we investigated to what extent the coding variant, rs3173615 (p.T185S) in linkage disequilibrium with rs1990622, affects progranulin protein (PGRN) biology and TMEM106B protein regulation.
First, we confirmed the association of TMEM106B variants with FTLD-TDP in a new cohort of GRN mutation carriers. We next generated and characterized a TMEM106B-specific antibody for investigation of this protein. Enzyme-linked immunoassay analysis of PGRN levels showed similar effects upon T185 and S185 TMEM106B overexpression. However, overexpression of T185 consistently led to higher TMEM106B protein levels than S185. Cycloheximide treatment experiments revealed that S185 degrades faster than T185 TMEM106B, potentially due to differences in N-glycosylation at residue N183. Together, our results provide a potential mechanism by which TMEM106B variants lead to differences in FTLD-TDP risk.
TMEM106B; frontotemporal dementia; progranulin; glycosylation
To evaluate the proton MR spectroscopy (1H MRS) changes in carriers of a novel octapeptide repeat insertion in the Prion Protein Gene (PRNP) and family history of frontotemporal dementia with ataxia. Four at-risk mutation carriers and 13 controls were compared using single voxel, short TE, 1H MRS from the posterior cingulate gyrus. The mutation carriers had an increased choline/creatine, p=0.003 and increased myoinositol/creatine ratio, p=0.003. 1H MRS identified differences in markers of glial activity and choline metabolism in pre- and early symptomatic carriers of a novel PRNP gene octapeptide insertion. These findings expand the possible diagnostic utility of 1H MRS in familial prion disorders.
MRS; MRI; familial prion disorders; frontotemporal dementia
Mutations in C9ORF72 resulting in expanded hexanucleotide repeats were recently reported to be the underlying genetic abnormality in chromosome 9p-linked frontotemporal lobar degeneration with TAR DNA-binding protein of 43 kD (TDP-43) proteinopathy (FTLD-TDP), amyotrophic lateral sclerosis (ALS), and frontotemporal lobar degeneration with motor neuron disease (FTLD-MND). Several subsequent publications described the neuropathology as being similar to that seen in cases of FTLD-TDP and ALS without C9ORF72 mutations, except that cases with mutations have p62 and ubiquitin positive, TDP-43 negative inclusions in cerebellum, hippocampus, neocortex, and basal ganglia. The identity of this protein is as yet unknown, and its significance is unclear. With the goal of potentially uncovering the significance of these TDP-43 negative inclusions, we compared the clinical, pathologic, and genetic characteristics in 5 cases of FTLD-TDP and FTLD-MND with C9ORF72 mutations to 20 cases without mutations. We confirmed the apparent specificity of p62 positive, TDP-43 negative inclusions in cerebellum, hippocampus, cortex, and basal ganglia to FTLD with C9ORF72 mutations. p62 positive, TDP-43 negative inclusions in hippocampus correlated with hippocampal atrophy, but no additional correlations were uncovered. However, although ambiguity of TDP sub-typing has previously been reported in cases with C9ORF72 mutations, this is the first report to show that although most FTLD cases with C9ORF72 mutations were TDP type B, some of the pathologic characteristics in these cases were more similar to TDP types A and C than to TDP type B FTLD cases without mutations. These features include greater cortical and hippocampal atrophy, greater ventricular dilatation, more neuronal loss and gliosis in temporal lobe and striatum, and TDP-43 positive fine neuritic profiles in the hippocampus in FTLD cases with C9ORF72 mutations compared to FTLD-TDP type B cases without mutations, implying that the C9ORF72 mutation modifies the pathologic phenotype of FTLD-TDP type B.
C9ORF72; repeat expansion; p62; ubiquitin; TDP-43; FTLD; ALS
Pigmented orthochromatic leukodystrophy (POLD) and hereditary diffuse leukoencephalopathy with axonal spheroids (HDLS) are rare neurodegenerative disorders characterized by cerebral white matter abnormalities, myelin loss, and axonal swellings. The striking overlap of clinical and pathologic features of these disorders suggested a common pathogenesis; however, no genetic or mechanistic link between POLD and HDLS has been established. Recently, we reported that mutations in the colony-stimulating factor 1 receptor (CSF1R) gene cause HDLS. In this study, we determined whether CSF1R mutations are also a cause of POLD.
We performed sequencing of CSF1R in 2 pathologically confirmed POLD families. For the largest family (FTD368), a detailed case report was provided and brain samples from 2 affected family members previously diagnosed with POLD were re-evaluated to determine whether they had HDLS features. In vitro functional characterization of wild-type and mutant CSF1R was also performed.
We identified CSF1R mutations in both POLD families: in family 5901, we found c.2297T>C (p.M766T), previously reported by us in HDLS family CA1, and in family FTD368, we identified c.2345G>A (p.R782H), recently reported in a biopsy-proven HDLS case. Immunohistochemical examination in family FTD368 showed the typical neuronal and glial findings of HDLS. Functional analyses of CSF1R mutant p.R782H (identified in this study) and p.M875T (previously observed in HDLS), showed a similar loss of CSF1R autophosphorylation of selected tyrosine residues in the kinase domain for both mutations when compared with wild-type CSF1R.
We provide the first genetic and mechanistic evidence that POLD and HDLS are a single clinicopathologic entity.
Patients with frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) may be agraphic. The study aimed at characterizing agraphia in individuals with a P301L MAPT mutation.
Two pairs of siblings with FTDP-17 were longitudinally examined for agraphia in relation to language and cognitive deficits.
All patients presented with dysexecutive agraphia. In addition, in the first pair of siblings one sibling demonstrated spatial agraphia with less pronounced allographic agraphia and the other sibling had aphasic agraphia. Aphasic agraphia was also present in one sibling from the second pair.
Agraphia associated with FTDP-17 is very heterogeneous.
frontotemporal dementia; writing; neuropsychological assessment; dysexecutive agraphia; spatial agraphia; aphasic agraphia
Expansions of the non-coding GGGGCC hexanucleotide repeat in the chromosome 9 open reading frame 72 (C9ORF72) gene were recently identified as the long sought-after cause of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) on chromosome 9p. In this study we aimed to determine whether the length of the normal - unexpanded - allele of the GGGGCC repeat in C9ORF72 plays a role in the presentation of disease or affects age at onset in C9ORF72 mutation carriers. We also studied whether the GGGGCC repeat length confers risk or affects age at onset in FTD and ALS patients without C9ORF72 repeat expansions. C9ORF72 genotyping was performed in 580 FTD, 995 ALS and 160 FTD-ALS patients and 1444 controls, leading to the identification of 211 patients with pathogenic C9ORF72 repeat expansions and an accurate quantification of the length of the normal alleles in all patients and controls. No meaningful association between the repeat length of the normal alleles of the GGGGCC repeat in C9ORF72 and disease phenotype or age at onset was observed in C9ORF72 mutation carriers or non-mutation carriers.
Amyotrophic lateral sclerosis; Frontotemporal Dementia; C9ORF72; Repeat-expansion disease; Association study
To describe the phenotype of patients with C9FTD/ALS (C9ORF72) hexanucleotide repeat expansion.
A total of 648 patients with frontotemporal dementia (FTD)–related clinical diagnoses and Alzheimer disease (AD) dementia were tested for C9ORF72 expansion and 31 carried expanded repeats (C9+). Clinical and neuroimaging data were compared between C9+ (15 behavioral variant FTD [bvFTD], 11 FTD–motor neuron disease [MND], 5 amyotrophic lateral sclerosis [ALS]) and sporadic noncarriers (48 bvFTD, 19 FTD-MND, 6 ALS).
All C9+ patients displayed clinical syndromes of bvFTD, ALS, or FTD-MND. At first evaluation, C9+ bvFTD patients had more delusions and greater impairment of working memory, but milder eating dysregulation compared to bvFTD noncarriers. C9+FTD-MND patients had a trend for longer survival and had an earlier age at onset than FTD-MND noncarriers. Voxel-based morphometry demonstrated more thalamic atrophy in FTD and FTD-MND carriers than in noncarriers.
Patients with the C9ORF72 hexanucleotide repeat expansion develop bvFTD, ALS, or FTD-MND with similar clinical and imaging features to sporadic cases. Other FTD spectrum diagnoses and AD dementia appear rare or absent among C9+ individuals. Longer survival in C9+ FTD-MND suggests slower disease progression and thalamic atrophy represents a novel and unexpected feature.
To describe the brain MRI characteristics of hereditary diffuse leukoencephalopathy with spheroids (HDLS) with known mutations in the colony-stimulating factor 1 receptor gene (CSF1R) on chromosome 5.
We reviewed 20 brain MRI scans of 15 patients with autopsy- or biopsy-verified HDLS and CSF1R mutations. We assessed sagittal T1-, axial T1-, T2-, proton density-weighted and axial fluid-attenuated inversion recovery images for distribution of white matter lesions (WMLs), gray matter involvement, and atrophy. We calculated a severity score based on a point system (0−57) for each MRI scan.
Of the patients, 93% (14 of 15) demonstrated localized WMLs with deep and subcortical involvement, whereas one patient revealed generalized WMLs. All WMLs were bilateral but asymmetric and predominantly frontal. Fourteen patients had a rapidly progressive clinical course with an initial MRI mean total severity score of 16.7 points (range 10−33.5). Gray matter pathology and brainstem atrophy were absent, and the corticospinal tracts were involved late in the disease course. There was no enhancement, and there was minimal cerebellar pathology.
Recognition of the typical MRI patterns of HDLS and the use of an MRI severity score might help during the diagnostic evaluation to characterize the natural history and to monitor potential future treatments. Indicators of rapid disease progression were symptomatic disease onset before 45 years, female sex, WMLs extending beyond the frontal regions, a MRI severity score greater than 15 points, and mutation type of deletion.
Rare mutations in the gene encoding for tau (MAPT, microtubule-associated protein tau) cause frontotemporal dementia-spectrum (FTD-s) disorders, including FTD, progressive supranuclear palsy (PSP) and corticobasal syndrome, and a common extended haplotype spanning across the MAPT locus is associated with increased risk of PSP and Parkinson's disease. We identified a rare tau variant (p.A152T) in a patient with a clinical diagnosis of PSP and assessed its frequency in multiple independent series of patients with neurodegenerative conditions and controls, in a total of 15 369 subjects.
Tau p.A152T significantly increases the risk for both FTD-s (n = 2139, OR = 3.0, CI: 1.6–5.6, P = 0.0005) and Alzheimer's disease (AD) (n = 3345, OR = 2.3, CI: 1.3–4.2, P = 0.004) compared with 9047 controls. Functionally, p.A152T (i) decreases the binding of tau to microtubules and therefore promotes microtubule assembly less efficiently; and (ii) reduces the tendency to form abnormal fibers. However, there is a pronounced increase in the formation of tau oligomers. Importantly, these findings suggest that other regions of the tau protein may be crucial in regulating normal function, as the p.A152 residue is distal to the domains considered responsible for microtubule interactions or aggregation. These data provide both the first genetic evidence and functional studies supporting the role of MAPT p.A152T as a rare risk factor for both FTD-s and AD and the concept that rare variants can increase the risk for relatively common, complex neurodegenerative diseases, but since no clear significance threshold for rare genetic variation has been established, some caution is warranted until the findings are further replicated.
A rare variant in the Triggering Receptor Expressed on Myeloid cells 2 (TREM2) gene has been reported to be a genetic risk factor for Alzheimer’s disease by two independent groups (Odds ratio between 2.9-4.5). Given the key role of TREM2 in the effective phagocytosis of apoptotic neuronal cells by microglia, we hypothesized that dysfunction of TREM2 may play a more generalized role in neurodegeneration. With this in mind we set out to assess the genetic association of the Alzheimer’s disease-related risk variant in TREM2 (rs75932628, p.R47H) with other related neurodegenerative disorders.
The study included 609 patients with frontotemporal dementia, 765 with amyotrophic lateral sclerosis, 1493 with Parkinson’s disease, 772 with progressive supranuclear palsy, 448 with ischemic stroke and 1957 controls subjects free of neurodegenerative disease. A significant association was observed for the TREM2 p.R47H substitution in susceptibility to frontotemporal dementia (OR = 5.06; p-value = 0.001) and Parkinson’s disease (OR = 2.67; p-value = 0.026), while no evidence of association with risk of amyotrophic lateral sclerosis, progressive supranuclear palsy or ischemic stroke was observed.
Our results suggest that the TREM2 p.R47H substitution is a risk factor for frontotemporal dementia and Parkinson’s disease in addition to Alzheimer’s disease. These findings suggest a more general role for TREM2 dysfunction in neurodegeneration, which could be related to its role in the immune response.
TREM2; Frontotemporal dementia; Parkinson disease; Genetic association
Frontotemporal dementia and amyotrophic lateral sclerosis are closely related clinical syndromes with overlapping molecular pathogenesis. Several families have been reported with members affected by frontotemporal dementia, amyotrophic lateral sclerosis or both, which show genetic linkage to a region on chromosome 9p21. Recently, two studies identified the FTD/ALS gene defect on chromosome 9p as an expanded GGGGCC hexanucleotide repeat in a non-coding region of the chromosome 9 open reading frame 72 gene (C9ORF72). In the present study, we provide detailed analysis of the clinical features and neuropathology for 16 unrelated families with frontotemporal dementia caused by the C9ORF72 mutation. All had an autosomal dominant pattern of inheritance. Eight families had a combination of frontotemporal dementia and amyotrophic lateral sclerosis while the other eight had a pure frontotemporal dementia phenotype. Clinical information was available for 30 affected members of the 16 families. There was wide variation in age of onset (mean = 54.3, range = 34–74 years) and disease duration (mean = 5.3, range = 1–16 years). Early diagnoses included behavioural variant frontotemporal dementia (n = 15), progressive non-fluent aphasia (n = 5), amyotrophic lateral sclerosis (n = 9) and progressive non-fluent aphasia–amyotrophic lateral sclerosis (n = 1). Heterogeneity in clinical presentation was also common within families. However, there was a tendency for the phenotypes to converge with disease progression; seven subjects had final clinical diagnoses of both frontotemporal dementia and amyotrophic lateral sclerosis and all of those with an initial progressive non-fluent aphasia diagnosis subsequently developed significant behavioural abnormalities. Twenty-one affected family members came to autopsy and all were found to have transactive response DNA binding protein with Mr 43 kD (TDP-43) pathology in a wide neuroanatomical distribution. All had involvement of the extramotor neocortex and hippocampus (frontotemporal lobar degeneration-TDP) and all but one case (clinically pure frontotemporal dementia) had involvement of lower motor neurons, characteristic of amyotrophic lateral sclerosis. In addition, a consistent and relatively specific pathological finding was the presence of neuronal inclusions in the cerebellar cortex that were ubiquitin/p62-positive but TDP-43-negative. Our findings indicate that the C9ORF72 mutation is a major cause of familial frontotemporal dementia with TDP-43 pathology, that likely accounts for the majority of families with combined frontotemporal dementia/amyotrophic lateral sclerosis presentation, and further support the concept that frontotemporal dementia and amyotrophic lateral sclerosis represent a clinicopathological spectrum of disease with overlapping molecular pathogenesis.
frontotemporal dementia; frontotemporal lobar degeneration; amyotrophic lateral sclerosis; C9ORF72, TDP-43
Two studies recently identified a GGGGCC hexanucleotide repeat expansion in a non-coding region of the chromosome 9 open reading frame 72 gene (C9ORF72) as the cause of chromosome 9p-linked amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). In a cohort of 231 probands with ALS, we identified the C9ORF72 mutation in 17 familial (27.4 %) and six sporadic (3.6%) cases. Patients with the mutation presented with typical motor features of ALS, although subjects with the C9ORF72 mutation had more frequent bulbar onset, compared to those without this mutation. Dementia was significantly more common in ALS patients and families with the C9ORF72 mutation and was usually early-onset FTD. There was striking clinical heterogeneity among the members of individual families with the mutation. The associated neuropathology was a combination of ALS with TDP-ir inclusions and FTLD-TDP. In addition to TDP-43-immunoreactive pathology, a consistent and specific feature of cases with the C9ORF72 mutation was the presence of ubiquitin-positive, TDP-43-negative inclusions in a variety of neuroanatomical regions, such as the cerebellar cortex. These findings support the C9ORF72 mutation as an important newly-recognized cause of ALS, provide a more detailed characterization of the associated clinical and pathological features and further demonstrate the clinical and molecular overlap between ALS and FTD.
amyotrophic lateral sclerosis; frontotemporal dementia; frontotemporal lobar degeneration; C9ORF72; TDP-43; chromosome 9p
Frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) are part of a disease spectrum associated with TDP-43 pathology. Strong evidence supporting this is the existence of kindreds with family members affected by FTD, ALS or mixed features of FTD and ALS, referred to as FTD-MND. Some of these families have linkage to chromosome 9, with hexanucleotide expansion mutation in a noncoding region of C9ORF72. Discovery of the mutation defines c9FTD/ALS. Prior to discovery of mutations in C9ORF72, it was assumed that TDP-43 pathology in c9FTD/ALS was uniform. In this study, we examined the neuropathology and clinical features of 20 cases of c9FTD/ALS from a brain bank for neurodegenerative disorders. Included are six patients clinically diagnosed with ALS, eight FTD, one FTD-MND and four Alzheimer type dementia. Clinical information was unavailable for one patient. Pathologically, the cases all had TDP-43 pathology, but there were three major pathologic groups: ALS, FTLD-MND and FTLD-TDP. The ALS cases were morphologically similar to typical sporadic ALS with almost no extramotor TDP-43 pathology; all had oligodendroglial cytoplasmic inclusions. The FTLD-MND showed predominantly Mackenzie Type 3 TDP-43 pathology, and all had ALS-like pathology in motor neurons, but more extensive extramotor pathology, with oligodendroglial cytoplasmic inclusions and infrequent hippocampal sclerosis. The FTLD-TDP cases had several features similar to FTLD-TDP due to mutations in the gene for progranulin, including Mackenzie Type 1 TDP-43 pathology with neuronal intranuclear inclusions and hippocampal sclerosis. FTLD-TDP patients were older and some were thought to have Alzheimer type dementia. In addition to the FTD and ALS clinical presentations, the present study shows that c9FTD/ALS can have other presentations, possibly related to age of onset and presence of hippocampal sclerosis. Moreover, there is pathologic heterogeneity not only between ALS and FTLD, but within the FTLD group. Further studies are needed to address the molecular mechanism of clinical and pathological heterogeneity of c9FTD/ALS due to mutations in C9ORF72.
Several families have been reported with autosomal dominant frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS), genetically linked to chromosome 9p21. Here we report an expansion of a non-coding GGGGCC hexanucleotide repeat in the gene C9ORF72 that is strongly associated with disease in a large FTD/ALS kindred, previously reported to be conclusively linked to chromosome 9p. This same repeat expansion was identified in the majority of our families with a combined FTD/ALS phenotype and TDP-43 based pathology. Analysis of extended clinical series found the C9ORF72 repeat expansion to be the most common genetic abnormality in both familial FTD (11.7%) and familial ALS (22.5%). The repeat expansion leads to the loss of one alternatively spliced C9ORF72 transcript and to formation of nuclear RNA foci, suggesting multiple disease mechanisms. Our findings indicate that repeat expansion in C9ORF72 is a major cause of both FTD and ALS.
Expanded glutamine repeats of the ataxin-2 (ATXN2) protein cause spinocerebellar ataxia type 2 (SCA2), a rare neurodegenerative disorder. More recent studies have suggested that expanded ATXN2 repeats are a genetic risk factor for amyotrophic lateral sclerosis (ALS) via an RNA-dependent interaction with TDP-43. Given the phenotypic diversity observed in SCA2 patients, we set out to determine the polymorphic nature of the ATXN2 repeat length across a spectrum of neurodegenerative disorders. In this study, we genotyped the ATXN2 repeat in 3919 neurodegenerative disease patients and 4877 healthy controls and performed logistic regression analysis to determine the association of repeat length with the risk of disease. We confirmed the presence of a significantly higher number of expanded ATXN2 repeat carriers in ALS patients compared with healthy controls (OR = 5.57; P= 0.001; repeat length >30 units). Furthermore, we observed significant association of expanded ATXN2 repeats with the development of progressive supranuclear palsy (OR = 5.83; P= 0.004; repeat length >30 units). Although expanded repeat carriers were also identified in frontotemporal lobar degeneration, Alzheimer's and Parkinson's disease patients, these were not significantly more frequent than in controls. Of note, our study identified a number of healthy control individuals who harbor expanded repeat alleles (31–33 units), which suggests caution should be taken when attributing specific disease phenotypes to these repeat lengths. In conclusion, our findings confirm the role of ATXN2 as an important risk factor for ALS and support the hypothesis that expanded ATXN2 repeats may predispose to other neurodegenerative diseases, including progressive supranuclear palsy.
Hereditary diffuse leukoencephalopathy with spheroids (HDLS) is an autosomal dominantly inherited central nervous system white matter disease with variable clinical presentations including personality and behavioral changes, dementia, depression, parkinsonism, seizures, and others1,2. We combined genome-wide linkage analysis with exome sequencing and identified 14 different mutations affecting the tyrosine kinase domain of the colony stimulating factor receptor 1 (encoded by CSF1R) in 14 families affected by HDLS. In one kindred, the de novo occurrence of the mutation was confirmed. Follow-up sequencing analyses identified an additional CSF1R mutation in a patient clinically diagnosed with corticobasal syndrome (CBS). In vitro, CSF-1 stimulation resulted in the rapid autophosphorylation of selected tyrosine-residues in the kinase domain of wild-type but not mutant CSF1R, suggesting that HDLS may result from a partial loss of CSF1R function. Since CSF1R is a critical mediator of microglial proliferation and differentiation in the brain, our findings suggest an important role for microglial dysfunction in HDLS pathogenesis.