Genetic studies are transforming the way we diagnose, evaluate and treat patients. The era of genome-wide association studies promised to discover common risk variants in heterogeneous disorders where previous small-scale association studies had on the whole failed. However, as we enter the post-association era a degree of disappoint is felt regarding the lack of risk factors with large effect for a number of disorders including vascular disease. Vascular disorders are sporadic by nature, though a familial component has been observed. This review will focus on vascular dementia, the genetic risk factors for vascular disorders and highlight how new technologies may overcome the limitations of genome-wide association and nominate those genes that influence disease risk.
Microtubule-associated protein tau encoded by the MAPT gene binds to microtubules and is important for maintaining neuronal morphology and function. Alternative splicing of MAPT pre-mRNA generates six major tau isoforms in the adult central nervous system resulting in tau proteins with three or four microtubule-binding repeat domains. In a group of neurodegenerative disorders called tauopathies, tau becomes aberrantly hyperphosphorylated and dissociates from microtubules, resulting in a progressive accumulation of intracellular tau aggregates. The spectrum of sporadic frontotemporal lobar degeneration associated with tau pathology includes progressive supranuclear palsy, corticobasal degeneration, and Pick’s disease. Alzheimer’s disease is considered the most prevalent tauopathy. This review is divided into two broad sections. In the first section we discuss the molecular classification of sporadic tauopathies, with a focus on describing clinicopathologic relationships. In the second section we discuss the neuroimaging methodologies that are available for measuring tau pathology (directly using tau positron emission tomography ligands) and tau-mediated neuronal injury (magnetic resonance imaging and fluorodeoxyglucose positron emission tomography). Both sections have detailed descriptions of the following neurodegenerative dementias – Alzheimer’s disease, progressive supranuclear palsy, corticobasal degeneration and Pick’s disease.
Excessive daytime sleepiness is a commonly reported problem in dementia with Lewy bodies (DLB). We examined the relationship between nighttime sleep continuity and the propensity to fall asleep during the day in clinically probable DLB compared to Alzheimer’s disease (AD) dementia.
A full-night polysomnography was carried out in 61 participants with DLB and 26 with AD dementia. Among this group, 32 participants with DLB and 18 with AD dementia underwent a daytime Multiple Sleep Latency Test (MSLT). Neuropathologic examinations of 20 participants with DLB were carried out.
Although nighttime sleep efficiency did not differentiate diagnostic groups, the mean MSLT initial sleep latency was significantly shorter in participants with DLB than in those with AD dementia (mean 6.4 ± 5 minutes vs 11 ± 5 minutes, P <0.01). In the DLB group, 81% fell asleep within 10 minutes compared to 39% of the AD dementia group (P <0.01), and 56% in the DLB group fell asleep within 5 minutes compared to 17% in the AD dementia group (P <0.01). Daytime sleepiness in AD dementia was associated with greater dementia severity, but mean MSLT latency in DLB was not related to dementia severity, sleep efficiency the night before, or to visual hallucinations, fluctuations, parkinsonism or rapid eye movement sleep behavior disorder. These data suggest that abnormal daytime sleepiness is a unique feature of DLB that does not depend on nighttime sleep fragmentation or the presence of the four cardinal DLB features. Of the 20 DLB participants who underwent autopsy, those with transitional Lewy body disease (brainstem and limbic) did not differ from those with added cortical pathology (diffuse Lewy body disease) in dementia severity, DLB core features or sleep variables.
Daytime sleepiness is more likely to occur in persons with DLB than in those with AD dementia. Daytime sleepiness in DLB may be attributed to disrupted brainstem and limbic sleep–wake physiology, and further work is needed to better understand the underlying mechanisms.
Abnormal cytoplasmic accumulation of Fused in Sarcoma (FUS) in neurons defines subtypes of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). FUS is a member of the FET protein family that includes Ewing's sarcoma (EWS) and TATA-binding protein-associated factor 2N (TAF15). FET proteins are predominantly localized to the nucleus, where they bind RNA and DNA to modulate transcription, mRNA splicing, and DNA repair. In ALS cases with FUS inclusions (ALS-FUS), mutations in the FUS gene cause disease, whereas FTLD cases with FUS inclusions (FTLD-FUS) do not harbor FUS mutations. Notably, in FTLD-FUS, all FET proteins accumulate with their nuclear import receptor Transportin 1 (TRN1), in contrast ALS-FUS inclusions are exclusively positive for FUS. In the present study, we show that induction of DNA damage replicates several pathologic hallmarks of FTLD-FUS in immortalized human cells and primary human neurons and astrocytes. Treatment with the antibiotic calicheamicin γ1, which causes DNA double-strand breaks, leads to the cytoplasmic accumulation of FUS, TAF15, EWS, and TRN1. Moreover, cytoplasmic translocation of FUS is mediated by phosphorylation of its N terminus by the DNA-dependent protein kinase. Finally, we observed elevated levels of phospho-H2AX in FTLD-FUS brains, indicating that DNA damage occurs in patients. Together, our data reveal a novel regulatory mechanism for FUS localization in cells and suggest that DNA damage may contribute to the accumulation of FET proteins observed in human FTLD-FUS cases, but not in ALS-FUS.
amyotrophic lateral sclerosis (ALS); cytoplasmic translocation; DNA damage; frontotemporal lobar degeneration (FTLD); Fused in Sarcoma (FUS); phosphorylation
To determine the rate of progression of mild cognitive impairment (MCI) to dementia with Lewy bodies (DLB).
We followed 337 patients with MCI in the Mayo Alzheimer's Disease Research Center (range 2–12 years). Competing risks survival models were used to examine the rates of progression to clinically probable DLB and Alzheimer disease (AD). A subset of patients underwent neuropathologic examination.
In this clinical cohort, 116 remained as MCI, while 49 progressed to probable DLB, 162 progressed to clinically probable AD, and 10 progressed to other dementias. Among nonamnestic MCI, progression rate to probable DLB was 20 events per 100 person-years and to probable AD was 1.6 per 100 person-years. Among amnestic MCI, progression rate to probable AD was 17 events per 100 person-years, and to DLB was 1.5 events per 100 person-years. In 88% of those who developed probable DLB, the baseline MCI diagnosis included attention and/or visuospatial deficits. Those who developed probable DLB were more likely to have baseline daytime sleepiness and subtle parkinsonism. In 99% of the clinically probable AD group, the baseline MCI diagnosis included memory impairment. Neuropathologic confirmation was obtained in 24 of 30 of those with clinically probable AD, and in 14 of 18 of those with clinically probable DLB.
In a clinical sample, patients with nonamnestic MCI were more likely to develop DLB, and those with amnestic MCI were more likely to develop probable AD.
Mitochondria and the ER form tight structural associations and these facilitate a number of cellular functions. However, the mechanisms by which regions of the ER become tethered to mitochondria are not properly known. Understanding these mechanisms is not just important for comprehending fundamental physiological processes but also for understanding pathogenic processes in some disease states. In particular, disruption to ER-mitochondria associations is linked to some neurodegenerative diseases. Here we show that the ER-resident protein VAPB interacts with the mitochondrial protein PTPIP51 to regulate ER-mitochondria associations. Moreover, we demonstrate that TDP-43, a protein pathologically linked to ALS and FTD perturbs ER-mitochondria interactions and that this is associated with disruption to the VAPB-PTPIP51 interaction and cellular Ca2+ homeostasis. Finally, we show that overexpression of TDP-43 leads to activation of glycogen synthase kinase-3β (GSK-3β) and that GSK-3β regulates the VAPB-PTPIP51 interaction. Our results describe a new pathogenic mechanism for TDP-43.
Mutations in TDP-43 lead to familial ALS. Expanding evidence suggests that impaired mitochondrial dynamics likely contribute to the selective degeneration of motor neurons in SOD1-associated ALS. In this study, we investigated whether and how TDP-43 mutations might impact mitochondrial dynamics and function. We demonstrated that overexpression of wild-type TDP-43 resulted in reduced mitochondrial length and density in neurites of primary motor neurons, features further exacerbated by ALS-associated TDP-43 mutants Q331K and M337V. In contrast, suppression of TDP-43 resulted in significantly increased mitochondrial length and density in neurites, suggesting a specific role of TDP-43 in regulating mitochondrial dynamics. Surprisingly, both TDP-43 overexpression and suppression impaired mitochondrial movement. We further showed that abnormal localization of TDP-43 in cytoplasm induced substantial and widespread abnormal mitochondrial dynamics. TDP-43 co-localized with mitochondria in motor neurons and their colocalization was enhanced by ALS associated mutant. Importantly, co-expression of mitochondrial fusion protein mitofusin 2 (Mfn2) could abolish TDP-43 induced mitochondrial dynamics abnormalities and mitochondrial dysfunction. Taken together, these data suggest that mutant TDP-43 impairs mitochondrial dynamics through enhanced localization on mitochondria, which causes mitochondrial dysfunction. Therefore, abnormal mitochondrial dynamics is likely a common feature of ALS which could be potential new therapeutic targets to treat ALS.
Frontotemporal lobar degeneration (FTLD) is pathologically heterogeneous with TAR DNA binding protein 43 kDa (TDP-43) proteinopathy the most common substrate. Previous work has identified atrophy patterns across TDP-43 subtypes with Type A showing greater frontotemporal and parietal atrophy, Type C predominantly anterior temporal, and Type B predominantly posterior frontal. Despite neuroanatomical correlates of involvement, neuropsychological findings have been inconsistent. The current study utilized broader neurocognitive domains based on aggregated neuropsychological measures to distinguish between subtypes. We hypothesized that patterns of neurocognitive domain impairments would predict FTLD–TDP-43 subtype. Fifty-one patients, aged 38–87, were identified post mortem with pathologically confirmed FTLD with TDP-43. Participants were classified into subtypes A, B, or C. Patients had completed neuropsychological assessments as part of their clinical evaluation. Six cognitive domains were created: Language; Cognitive Speed; Memory; Learning; Visuoperception; and Fluency. Binary logistic regression was conducted. All but three patients could be classified as FTLD–TDP Types A, B, or C: 26 as Type A; nine as Type B; and 13 as Type C. Cognitive Speed scores were associated with Types A and C (p < 0.001 and p = 0.003, respectively). Impaired performances on the Trail Making Test differentiated Types A and C. Worse Boston Naming Test and Logical Memory (Immediate) (p < 0.05) scores also increased the likelihood of Type C phenotype. Findings suggest Cognitive Speed associates with TDP-43 subtypes. Type C also demonstrated language-specific involvement. Differences between TDP-43 subtypes further supports the notion of differences in pathophysiology or topography across these types.
Cognitive speed; Dementia; Frontotemporal lobar degeneration; Neuropathology; Neuropsychology; TDP-43
Clinical and neuropathological similarities between dementia with Lewy bodies (DLB), Parkinson’s and Alzheimer’s diseases (PD and AD, respectively) suggest that these disorders may share etiology. To test this hypothesis, we have performed an association study of 54 genomic regions, previously implicated in PD or AD, in a large cohort of DLB cases and controls. The cohort comprised 788 DLB cases and 2624 controls. To minimize the issue of potential misdiagnosis, we have also performed the analysis including only neuropathologically proven DLB cases (667 cases). The results show that the APOE is a strong genetic risk factor for DLB, confirming previous findings, and that the SNCA and SCARB2 loci are also associated after a study-wise Bonferroni correction, although these have a different association profile than the associations reported for the same loci in PD. We have previously shown that the p.N370S variant in GBA is associated with DLB, which, together with the findings at the SCARB2 locus, suggests a role for lysosomal dysfunction in this disease. These results indicate that DLB has a unique genetic risk profile when compared with the two most common neurodegenerative diseases and that the lysosome may play an important role in the etiology of this disorder. We make all these data available.
To determine structural MRI and digital microscopic characteristics of REM sleep behavior disorder in individuals with low-, intermediate-, and high-likelihood dementia with Lewy bodies (DLB) at autopsy.
Patients with autopsy-confirmed low-, intermediate-, and high-likelihood DLB, according to the probability statement recommended by the third report of the DLB Consortium, and antemortem MRI, were identified (n = 75). The clinical history was assessed for presence (n = 35) and absence (n = 40) of probable REM sleep behavior disorder (pRBD), and patients' antemortem MRIs were compared using voxel-based morphometry. Pathologic burdens of phospho-tau, β-amyloid, and α-synuclein were measured in regions associated with early neuropathologic involvement, the hippocampus and amygdala.
pRBD was present in 21 patients (60%) with high-likelihood, 12 patients (34%) with intermediate-likelihood, and 2 patients (6%) with low-likelihood DLB. Patients with pRBD were younger, more likely to be male (p ≤ 0.001), and had a more frequent neuropathologic diagnosis of diffuse (neocortical) Lewy body disease. In the hippocampus and amygdala, phospho-tau and β-amyloid burden were lower in patients with pRBD compared with those without pRBD (p < 0.01). α-Synuclein burden did not differ in the hippocampus, but trended in the amygdala. Patients without pRBD had greater atrophy of temporoparietal cortices, hippocampus, and amygdala (p < 0.001) than those with pRBD; atrophy of the hippocampus (p = 0.005) and amygdala (p = 0.02) were associated with greater phospho-tau burdens in these regions.
Presence of pRBD is associated with a higher likelihood of DLB and less severe Alzheimer-related pathology in the medial temporal lobes, whereas absence of pRBD is characterized by Alzheimer-like atrophy patterns on MRI and increased phospho-tau burden.
Loss of function COQ2 mutations results in primary CoQ10 deficiency. Recently, recessive mutations of the COQ2 gene have been identified in two unrelated Japanese families with multiple system atrophy (MSA). It has also been proposed that specific heterozygous variants in the COQ2 gene may confer susceptibility to sporadic MSA. To assess the frequency of COQ2 variants in patients with MSA, we sequenced the entire coding region and investigated all exonic copy number variants of the COQ2 gene in 97 pathologically-confirmed and 58 clinically-diagnosed MSA patients from the United States.
We did not find any homozygous or compound heterozygous pathogenic COQ2 mutations including deletion or multiplication within our series of MSA patients. In two patients, we identified two heterozygous COQ2 variants (p.S54W and c.403 + 10G > T) of unknown significance, which were not observed in 360 control subjects. We also identified one heterozygous carrier of a known loss of function p.S146N substitution in a severe MSA-C pathologically-confirmed patient.
The COQ2 p.S146N substitution has been previously reported as a pathogenic mutation in primary CoQ10 deficiency (including infantile multisystem disorder) in a recessive manner. This variant is the third primary CoQ10 deficiency mutation observed in an MSA case (p.R387X and p.R197H). Therefore it is possible that in the heterozygous state it may increase susceptibility to MSA. Further studies, including reassessing family history in patients of primary CoQ10 deficiency for the possible occurrence of MSA, are now warranted to resolve the role of COQ2 variation in MSA.
Electronic supplementary material
The online version of this article (doi:10.1186/1750-1326-9-44) contains supplementary material, which is available to authorized users.
COQ2; Multiple system atrophy; Genetics; CoQ10 deficiency
Neurofibrillary tangles (NFTs) are one of the key histological lesions of Alzheimer’s disease (AD) and are associated with brain atrophy. We assessed regional NFT density in 30 patients with AD, 10 of which presented as the logopenic variant of primary progressive aphasia (lvPPA) and 20 that presented as dementia of the Alzheimer’s type (DAT). Regional grey matter volumes were measured using antemortem MRI. NFT density was significantly higher in left temporoparietal cortices in lvPPA compared to DAT, with no differences observed in hippocampus. There was a trend for the ratio of temporoparietal-to-hippocampal NFT density to be higher in lvPPA. The imaging findings mirrored the pathological findings, with smaller left temporoparietal volumes observed in lvPPA compared to DAT, and no differences observed in hippocampal volume. This study demonstrates that lvPPA is associated with a phenomenon of enhanced temporoparietal neurodegeneration, a finding that improves our understanding of the biological basis of lvPPA.
Primary progressive aphasia; Logopenic variant of primary progressive aphasia; Alzheimer’s disease; Neurofibrillary tangles; Hippocampus; MRI; Apolipoprotein E; TDP-43; Voxel-based morphometry; Alzheimer’s dementia
Mutations in the α-synuclein-encoding gene SNCA are considered as a rare cause of Parkinson's disease (PD). Our objective was to examine the frequency of the SNCA point mutations among PD patients of Polish origin.
Detection of the known SNCA point mutations A30P (c.88G>C), E46K (c.136G>A) and A53T (c.157A>T) was performed either using the Sequenom MassArray iPLEX platform or by direct sequencing of the SNCA exons 2 and 3. As the two novel substitutions A18T (c.52G>A) and A29S (c.85G>T) were identified, their frequency in a control population of Polish origin was assessed and in silico analysis performed to investigate the potential impact on protein structure and function.
We did not observe the previously reported point mutations in the SNCA gene in our 629 PD patients; however, two novel potentially pathogenic substitutions A18T and A29S were identified. Each variant was observed in a single patient presenting with a typical late-onset sporadic PD phenotype. Although neither variant was observed in control subjects and in silico protein analysis predicts a damaging effect for A18T and pA29S substitutions, the lack of family history brings into question the true pathogenicity of these rare variants.
Larger population based studies are needed to determine the pathogenicity of the A18T and A29S substitutions. Our findings highlight the possible role of rare variants contributing to disease risk and may support further screening of the SNCA gene in sporadic PD patients from different populations.
α-synuclein; SNCA gene; Parkinson's disease; Genetic etiology; Missense mutations
Expanded hexanucleotide repeats in C9ORF72 are a common genetic cause of frontotemporal dementia and amyotrophic lateral sclerosis. Repeat expansions have also been detected infrequently in other disorders, including Alzheimer’s disease, dementia with Lewy bodies and Parkinsonian disorders.
To assess the incidence of the expanded C9ORF72 repeat in cases of depressive pseudodementia.
An immunohistochemical screen of autopsied brains collected between 1998 and 2013.
Brain bank at Mayo Clinic Florida, a large tertiary care research institution.
Thirty one neuropathologically normal individuals (no atrophy, neuronal loss, or gliosis beyond what would be expected for age) with an antemortem clinical history or diagnosis of depression and/or dementia.
Main Outcome Measures
Presence of the hexanucleotide repeat was established using immunohistochemistry with a highly disease-specific antibody (C9RANT), and was further validated in carriers using repeat-primed polymerase chain reaction and Southern blotting.
Of the 31 cases studied, 2 (6.45%) individuals harbored the C9ORF72 repeat expansion. Both patients were men with refractory depression. One patient experienced drug-induced Parkinsonism and sudden-onset dementia, while the other patient had a more insidious disease course suspected to be Alzheimer’s disease. Clinical and neuropathologic features are described.
Conclusions and Relevance
This report expands the range of clinicopathologic presentations of C9ORF72 expanded hexanucleotide repeat to include psychiatric disorders such as depressive pseudodementia.
Midbrain atrophy is a characteristic feature of progressive supranuclear palsy (PSP), although it is unclear whether it is associated with the PSP syndrome (PSPS) or PSP pathology. We aimed to determine whether midbrain atrophy is a useful biomarker of PSP pathology, or whether it is only associated with typical PSPS.
We identified all autopsy-confirmed subjects with the PSP clinical phenotype (i.e. PSPS) or PSP pathology and a volumetric MRI. Of 24 subjects with PSP pathology, 11 had a clinical diagnosis of PSPS (PSP-PSPS), and 13 had a non-PSPS clinical diagnosis (PSP-other). Three subjects had PSPS and corticobasal degeneration pathology (CBD-PSPS). Healthy control and disease control groups (i.e. a group without PSPS or PSP pathology) and a group with CBD pathology and corticobasal syndrome (CBD-CBS) were selected. Midbrain area was measured in all subjects.
Midbrain area was reduced in each group with clinical PSPS (with and without PSP pathology). The group with PSP pathology and non-PSPS clinical syndromes did not show reduced midbrain area. Midbrain area was smaller in the subjects with PSPS compared to those without PSPS (p<0.0001), with an area under the receiver-operator-curve of 0.99 (0.88,0.99). A midbrain area cut-point of 92 mm2 provided optimum sensitivity (93%) and specificity (89%) for differentiation.
Midbrain atrophy is associated with the clinical presentation of PSPS, but not with the pathological diagnosis of PSP in the absence of the PSPS clinical syndrome. This finding has important implications for the utility of midbrain measurements as diagnostic biomarkers for PSP pathology.
Progressive supranuclear palsy; tau; neuropathology; MRI; midbrain
Hexanucleotide repeat expansions in chromosome 9 open reading frame 72 (C9ORF72) are currently the major genetic cause of frontotemporal dementia (FTD) and motor neuron disease (MND). Presently, it is unknown whether expansion size affects disease severity or phenotypes.
We performed a cross-sectional Southern blot characterization study (Xpansize-72) in a cohort of subjects obtained at the Mayo Clinic and Banner Sun Health Research Institute. All subjects carried GGGGCC repeat expansions in C9ORF72, and high quality DNA was available from the frontal cortex, cerebellum and/or blood. Southern blotting techniques and densitometry were employed to estimate the repeat size of the most abundant expansion species. Comparisons of repeat sizes between tissues were made using Wilcoxon rank sum and Wilcoxon signed rank tests, and between disease subgroups using Kruskal-Wallis rank sum tests. The association of repeat size with age at onset and age at collection was evaluated using a Spearman’s test of correlation; whereas the association between repeat size and survival after disease onset was examined using Cox proportional hazards regression models.
Our cohort consisted of 84 C9ORF72 expansion carriers, including FTD patients (n=35), FTD/MND patients (n=16), MND patients (n=30), and unaffected subjects (n=3). We focused our analysis on three major tissue subgroups: frontal cortex (41 subjects [21 FTD, 11 FTD/MND, 9 MND]), cerebellum (40 subjects [20 FTD, 12 FTD/MND, 8 MND]), and blood (50 subjects [15 FTD, 9 FTD/MND, 23 MND, 3 unaffected expansion carriers]). Repeat lengths in the cerebellum were significantly smaller (median 12·3 kb [~1667 repeat units], IQR 11·1–14·3) than in the frontal cortex (median 33·8 kb [~5250 repeat units], IQR 23·5–44·9, p<0·0001), or in blood (median 18·6 kb [~2717 repeat units], IQR 13·9–28·1, p=0·0002). Within these tissues, there was no significant difference in repeat length between disease subgroups (cerebellum p=0·96, frontal cortex p=0·27, blood p=0·10). In the frontal cortex of FTD patients, repeat length correlated with age at onset (r=0·63, p=0·003) and age at collection (r=0·58, p=0·006); this correlation was not detected in the cerebellum or blood. Finally, only in the cerebellum, survival after disease onset was poorer in patients from our overall cohort with repeat lengths greater than 1467 repeat units (25th percentile, HR 3·27, 95% CI 1·34–7·95, p=0·009): the median survival was 4·8 years (IQR 3·0–7·4) in the group with longer expansions versus 7·4 years (IQR 6·3–10·9) in the group with smaller expansions.
Substantial variation in repeat size is observed between cerebellum, frontal cortex, and blood; relatively long repeat sizes in the cerebellum confer an important survival disadvantage. Our findings indicate that expansion size does affect disease severity, which could be relevant for genetic counseling.
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
Variants within the leucine-rich repeat kinase 2 gene are recognized as the most frequent genetic cause of Parkinson’s disease. Leucine-rich repeat kinase 2 variation related to susceptibility to disease displays many features that reflect the nature of complex late-onset sporadic disorders, such as Parkinson’s disease. The Genetic Epidemiology of Parkinson’s disease consortium recently performed the largest genetic association study for variants in the leucine-rich repeat kinase 2 gene across 23 different sites in 15 countries. Herein we detail the allele frequencies for the novel risk factors (p.A419V and p.M1646T) and the protective haplotype (p.N551K-R1398H-K1423K) reported in the original publication. Simple population allele frequencies can not only provide an insight into the clinical relevance of specific variants but also help genetically define patient groups. Establishing individual patient-based genomic susceptibility profiles incorporating both risk and protective factors will determine future diagnostic and treatment strategies.
Parkinson disease; LRRK2; genetics; association study
Hexanucleotide repeat expansions in chromosome 9 open reading frame 72 (C9ORF72) are causative for frontotemporal dementia (FTD) and motor neuron disease (MND). Substantial phenotypic heterogeneity has been described in patients with these expansions. We set out to identify genetic modifiers of disease risk, age at onset, and survival after onset that may contribute to this clinical variability.
We examined a cohort of 330 C9ORF72 expansion carriers and 374 controls. In these individuals, we assessed variants previously implicated in FTD and/or MND; 36 variants were included in our analysis. After adjustment for multiple testing, our analysis revealed three variants significantly associated with age at onset (rs7018487 [UBAP1; p-value = 0.003], rs6052771 [PRNP; p-value = 0.003], and rs7403881 [MT-Ie; p-value = 0.003]), and six variants significantly associated with survival after onset (rs5848 [GRN; p-value = 0.001], rs7403881 [MT-Ie; p-value = 0.001], rs13268953 [ELP3; p-value = 0.003], the epsilon 4 allele [APOE; p-value = 0.004], rs12608932 [UNC13A; p-value = 0.003], and rs1800435 [ALAD; p-value = 0.003]).
Variants identified through this study were previously reported to be involved in FTD and/or MND, but we are the first to describe their effects as potential disease modifiers in the presence of a clear pathogenic mutation (i.e. C9ORF72 repeat expansion). Although validation of our findings is necessary, these variants highlight the importance of protein degradation, antioxidant defense and RNA-processing pathways, and additionally, they are promising targets for the development of therapeutic strategies and prognostic tests.
Electronic supplementary material
The online version of this article (doi:10.1186/1750-1326-9-38) contains supplementary material, which is available to authorized users.
C9ORF72; Frontotemporal dementia; Motor neuron disease; Genetic modifier; Repeat expansion
Optineurin (OPTN) is a multifunctional protein involved in cellular morphogenesis, vesicle trafficking, maintenance of the Golgi complex, and transcription activation through its interactions with the Rab8, myosin 6 (MYO6), huntingtin. Recently, OPTN immunoreactivity has been reported in intranuclear inclusions in patients with neuronal intranuclear inclusions disease (NIID). Other studies have shown that the RNA-binding protein, fused in sarcoma (FUS), is a component of intranuclear inclusions in NIID. We aimed to investigate the relationship between OPTN, its binding protein MYO6 and FUS in this study. In control subjects, OPTN (C-terminal) (OPTN-C) and MYO6 immunoreactivity was mainly demonstrated in the cytoplasm of neurons. In NIID patients, both neuronal intranuclear inclusions (NII) and glial intranuclear inclusions (GII) were immunopositive for MYO6 as well as OPTN-C. However, the intensity of OPTN-C immunostaining of the neuronal cytoplasm with and without NII was less than that of the control subjects. Double immunofluorescence staining for OPTN-C, ubiquitin (Ub), p62 and FUS revealed co-localization of these proteins within NII. Moreover, Ub positive inclusions were co-localized with MYO6. The percentage of co-localization of Ub with OPTN-C, FUS or MYO6 in NII was 100%, 52% and 92%, respectively. Ultrastructurally, the inclusions consisted of thin and thick filaments. Both filaments were immunopositive for Ub and OPTN-C. These findings suggest that OPTN plays a central role in the disease pathogenesis, and that OPTN may be a major component of NII.
Optineurin; Myosin-6; neuronal intranuclear inclusion disease; FUS; intranuclear inclusion
Alzheimer's disease (AD) and related dementias are a major public health challenge and present a therapeutic imperative for which we need additional insight into molecular pathogenesis. We performed a genome-wide association study and analysis of known genetic risk loci for AD dementia using neuropathologic data from 4,914 brain autopsies. Neuropathologic data were used to define clinico-pathologic AD dementia or controls, assess core neuropathologic features of AD (neuritic plaques, NPs; neurofibrillary tangles, NFTs), and evaluate commonly co-morbid neuropathologic changes: cerebral amyloid angiopathy (CAA), Lewy body disease (LBD), hippocampal sclerosis of the elderly (HS), and vascular brain injury (VBI). Genome-wide significance was observed for clinico-pathologic AD dementia, NPs, NFTs, CAA, and LBD with a number of variants in and around the apolipoprotein E gene (APOE). GalNAc transferase 7 (GALNT7), ATP-Binding Cassette, Sub-Family G (WHITE), Member 1 (ABCG1), and an intergenic region on chromosome 9 were associated with NP score; and Potassium Large Conductance Calcium-Activated Channel, Subfamily M, Beta Member 2 (KCNMB2) was strongly associated with HS. Twelve of the 21 non-APOE genetic risk loci for clinically-defined AD dementia were confirmed in our clinico-pathologic sample: CR1, BIN1, CLU, MS4A6A, PICALM, ABCA7, CD33, PTK2B, SORL1, MEF2C, ZCWPW1, and CASS4 with 9 of these 12 loci showing larger odds ratio in the clinico-pathologic sample. Correlation of effect sizes for risk of AD dementia with effect size for NFTs or NPs showed positive correlation, while those for risk of VBI showed a moderate negative correlation. The other co-morbid neuropathologic features showed only nominal association with the known AD loci. Our results discovered new genetic associations with specific neuropathologic features and aligned known genetic risk for AD dementia with specific neuropathologic changes in the largest brain autopsy study of AD and related dementias.
Alzheimer's disease (AD) and related dementias are a major public health challenge and present a therapeutic imperative for which we need additional insight into molecular pathogenesis. We performed a genome-wide association study (GWAS), as well as an analysis of known genetic risk loci for AD dementia, using data from 4,914 brain autopsies. Genome-wide significance was observed for 7 genes and pathologic features of AD and related diseases. Twelve of the 22 genetic risk loci for clinically-defined AD dementia were confirmed in our pathologic sample. Correlation of effect sizes for risk of AD dementia with effect size for hallmark pathologic features of AD were strongly positive and linear. Our study discovered new genetic associations with specific pathologic features and aligned known genetic risk for AD dementia with specific pathologic changes in a large brain autopsy study of AD and related dementias.
Mutations in profilin-1 (PFN1) have recently been
identified in patients with amyotrophic lateral sclerosis (ALS). Because of
the considerable overlap between ALS and the common subtype of
frontotemporal dementia, which is characterized by transactive response
DNA-binding protein 43 pathology (FTLD-TDP), we tested cohorts of ALS and
FTLD-TDP patients for PFN1 mutations.
DNA was obtained from 342 ALS patients and 141 FTLD-TDP patients at
our outpatient clinic and brain bank for neurodegenerative diseases at the
Mayo Clinic Florida, Jacksonville, USA. We screened these patients for
mutations in coding regions of PFN1 by Sanger sequencing.
Subsequently, we used TaqMan genotyping assays to investigate the identified
variant in 1167 control subjects.
One variant, p.E117G, was detected in 1 ALS patient, 1 FTLD-TDP
patient, and 2 control subjects. The mutation frequency of patients versus
control subjects was not significantly different (p-value
= 0.36). Moreover, PFN1 and TDP-43 staining of autopsy material did
not differ between patients with or without this variant.
The p.E117G variant appears to represent a benign polymorphism.
PFN1 mutations, in general, are rare in ALS and
Amyotrophic lateral sclerosis; frontotemporal dementia; profilin-1; TDP-43; genetics
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