An NIA-sponsored workgroup on preclinical Alzheimer’s disease (AD) articulated the need to characterize cognitive differences between normal aging and preclinical AD.
71 apolipoprotein E (APOE) e4 homozygotes (HMZ), 194 e3/4 heterozygotes (HTZ), and 356 e4 noncarriers (NC) aged 21–87 years who were cognitively healthy underwent neuropsychological testing every two years. Longitudinal trajectories of test scores were compared between APOE subgroups.
There was a significant effect of age on all cognitive domains in both APOE e4 carriers and NC. A significant effect of APOE e4 gene dose was confined to the memory domain and the Dementia Rating Scale. Cross sectional comparisons did not discriminate the groups.
While cognitive aging patterns are similar in APOE e4 carriers and NC, preclinical AD is characterized by a significant e4 gene dose effect that impacts memory and is detectable longitudinally. Preclinical neuropsychological testing strategies should emphasize memory sensitive measures and longitudinal design.
preclinical Alzheimer’s disease; cognitive aging; age-related memory loss; mild cognitive impairment; apolipoprotein E; longitudinal testing
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
Here, we describe a nonsense haplotype in PRNP associated with clinical Alzheimer's disease. The patient presented an early-onset of cognitive decline with memory loss as the primary cognitive problem. Whole-exome sequencing revealed a nonsense mutation in PRNP (NM_000311, c.C478T; p.Q160*; rs80356711) associated with homozygosity for the V allele at position 129 of the protein, further highlighting how very similar genotypes in PRNP result in strikingly different phenotypes.
Alzheimer's disease; Prion; PRNP; Nonsense mutation; Exome sequencing
Here, we describe a nonsense haplotype in PRNP associated with clinical Alzheimer’s disease. The patient presented an early-onset of cognitive decline with memory loss as the primary cognitive problem. Whole-exome sequencing revealed a nonsense mutation in PRNP (NM_000311, c.C478T; p.Q160*; rs80356711) associated with homozygosity for the V allele at position 129 of the protein, further highlighting how very similar genotypes in PRNP result in strikingly different phenotypes.
Alzheimer’s disease; Prion; PRNP; Nonsense mutation; Exome sequencing
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.
Recently, Coppola and colleagues demonstrated that a rare MAPT sequence variant, c.454G>A (p.A152T), significantly increases the risk of frontotemporal dementia (FTD) spectrum disorders and Alzheimer's disease (AD) in a screen of 15,369 subjects1. We describe clinical features of 9 patients with neurodegenerative disease (4 women) harboring p.A152T, aged 51 to 79 years at symptom onset. Seven developed FTD spectrum clinical syndromes, including progressive supranuclear palsy syndrome (PSP, n=2), behavioral variant FTD (bvFTD, n=1), nonfluent variant primary progressive aphasia (nfvPPA, n=2), and corticobasal syndrome (CBS, n=2); two patients were diagnosed with clinical AD. Thus, MAPT p.A152T is associated with a variety of FTD spectrum clinical presentations, although patients with clinical AD are also identified. These data warrant larger studies with clinicopathological correlation to elucidate the influence of this genetic variant on neurodegenerative disease.
All Cognitive Disorders/Dementia; Alzheimer's disease; Frontotemporal Dementia; Corticobasal degeneration; Progressive Supranuclear Palsy
adult-onset leukoencephalopathy with axonal spheroids and pigmented glia; CSF1R; calcification; computed tomography; white matter; differential diagnosis
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
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
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
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.
The aetiology and pathogenesis of non-genetic forms of frontotemporal dementia (FTD) is unknown and even with the genetic forms of FTD, pathogenesis remains elusive. Given the association between systemic inflammation and other neurodegenerative processes, links between autoimmunity and FTD need to be explored.
To describe the prevalence of systemic autoimmune disease in semantic variant primary progressive aphasia (svPPA), a clinical cohort, and in progranulin (PGRN) mutation carriers compared to neurologically healthy normal controls (NC) and Alzheimer’s disease (AD) as dementia controls.
Academic medical centres.
129 svPPA, 39 PGRN, 186 NC, and 158 AD patients underwent chart review for autoimmune conditions. A large subset of svPPA, PGRN, and NC cohorts underwent serum analysis for tumor necrosis factor α (TNF-α) levels.
Chi-square comparison of autoimmune prevalence and follow up logistic regression.
There was a significantly increased risk of autoimmune disorders clustered around inflammatory arthritides, cutaneous disorders, and gastrointestinal conditions in the svPPA and PGRN cohorts. Elevated TNF-α levels were observed in svPPA and PGRN compared to NC.
svPPA and PGRN are associated with increased prevalence of specific and related autoimmune diseases compared to NC and AD. These findings suggest a unique pattern of systemic inflammation in svPPA and PGRN and open new research avenues for understanding and treating disorders associated with underlying transactive response DNA-binding protein 43 (TDP-43) aggregation.
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
The occurrence of repeat-associated non-ATG (RAN) translation, an atypical form of translation of expanded repeats that results in the synthesis of homopolymeric expansion proteins, is becoming more widely appreciated among microsatellite expansion disorders. Such disorders include amyotrophic lateral sclerosis and frontotemporal dementia caused by a hexanucleotide repeat expansion in the C9ORF72 gene (c9FTD/ALS). We and others have recently shown that this bidirectionally transcribed repeat is RAN translated, and the “c9RAN proteins” thusly produced form neuronal inclusions throughout the central nervous system of c9FTD/ALS patients. Nonetheless, the potential contribution of c9RAN proteins to disease pathogenesis remains poorly understood. In the present study, we demonstrate that poly(GA) c9RAN proteins are neurotoxic and may be implicated in the neurodegenerative processes of c9FTD/ALS. Specifically, we show that expression of poly(GA) proteins in cultured cells and primary neurons leads to the formation of soluble and insoluble high molecular weight species, as well as inclusions composed of filaments similar to those observed in c9FTD/ALS brain tissues. The expression of poly(GA) proteins is accompanied by caspase-3 activation, impaired neurite outgrowth, inhibition of proteasome activity, and evidence of endoplasmic reticulum (ER) stress. Of importance, ER stress inhibitors, salubrinal and TUDCA, provide protection against poly(GA)-induced toxicity. Taken together, our data provide compelling evidence towards establishing RAN translation as a pathogenic mechanism of c9FTD/ALS, and suggest that targeting the ER using small molecules may be a promising therapeutic approach for these devastating diseases.
Electronic supplementary material
The online version of this article (doi:10.1007/s00401-014-1336-5) contains supplementary material, which is available to authorized users.
Amyotrophic lateral sclerosis; C9ORF72; Expanded repeat; Frontotemporal dementia; Repeat-associated non-ATG translation; Poly(GA) proteins; Proteasome activity; ER stress
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
Progressive supranuclear palsy (PSP) is a relatively common neurodegenerative tauopathy clinically characterized by parkinsonism, axial rigidity, and supranuclear gaze palsy. Pathologic findings of PSP are neuronal loss, gliosis, and neurofibrillary tangles in basal ganglia, diencephalon, and brainstem; there is increasing recognition of clinicopathologic variants of PSP.1
We examined the clinical and pathologic phenotypes of GRN mutation carriers with the pathogenic A9D (g.26C>A) missense mutation.
Three patients with GRN A9D mutations were evaluated clinically and came to autopsy with subsequent neuropathologic examination.
The clinical diagnoses of patients with GRN A9D mutations were amyotrophic lateral sclerosis, atypical extrapyramidal disorder, and behavioral variant frontotemporal dementia. Immunohistochemistry for TAR DNA-binding protein 43 (TDP-43) revealed variability in morphology and distribution of pathology. One patient had notable involvement of motor neurons in the spinal cord as well as type B TDP-43, whereas 2 other patients had type A TDP-43.
The clinical presentation of the GRN A9D missense mutation is not restricted to behavioral variant frontotemporal dementia and may include aphasia, extrapyramidal features, and, notably, amyotrophic lateral sclerosis.
In this prospective cohort study, we investigated cerebral glucose metabolism reductions on [18F]-fluorodeoxyglucose (FDG)-PET in progranulin (GRN) mutation carriers prior to frontotemporal dementia (FTD) onset.
Nine mutation carriers (age 51.5 ± 13.5 years) and 11 noncarriers (age 52.7 ± 9.5 years) from 5 families with FTD due to GRN mutations underwent brain scanning with FDG-PET and MRI and clinical evaluation. Normalized FDG uptake values were calculated with reference to the pons. PET images were analyzed with regions of interest (ROI) and statistical parametric mapping (SPM) approaches.
Compared with noncarriers, GRN mutation carriers had a lowered anterior-to-posterior (AP) ratio of FDG uptake (0.86 ± 0.09 vs 0.92 ± 0.05) and less left-right asymmetry, consistent with an overall pattern of right anterior cerebral hypometabolism. This pattern was observed regardless of whether they were deemed clinically symptomatic no dementia or asymptomatic. Individual ROIs with lowered FDG uptake included right anterior cingulate, insula, and gyrus rectus. SPM analysis supported and extended these findings, demonstrating abnormalities in the right and left medial frontal regions, right insular cortex, right precentral and middle frontal gyri, and right cerebellum. Right AP ratio was correlated with cognitive and clinical scores (modified Mini-Mental State Examination r = 0.74; Functional Rating Scale r = −0.73) but not age and years to estimated onset in mutation carriers.
The frontotemporal lobar degenerative process associated with GRN mutations appears to begin many years prior to the average age at FTD onset (late 50s–early 60s). Right medial and ventral frontal cortex and insula may be affected in this process but the specific regional patterns associated with specific clinical variants remain to be elucidated.
To identify potential genetic modifiers contributing to the phenotypic variability that is detected in patients with repeat expansions in chromosome 9 open reading frame 72 (C9ORF72), we investigated the frequency of these expansions in a cohort of 334 subjects previously found to carry mutations in genes known to be associated with a spectrum of neurodegenerative diseases.
A 2-step protocol, with a fluorescent PCR and a repeat-primed PCR, was used to determine the presence of hexanucleotide expansions in C9ORF72. For one double mutant, we performed Southern blots to assess expansion sizes, and immunohistochemistry to characterize neuropathology.
We detected C9ORF72 repeat expansions in 4 of 334 subjects (1.2% [or 1.8% of 217 families]). All these subjects had behavioral phenotypes and also harbored well-known pathogenic mutations in either progranulin (GRN: p.C466LfsX46, p.R493X, p.C31LfsX35) or microtubule-associated protein tau (MAPT: p.P301L). Southern blotting of one double mutant with a p.C466LfsX46 GRN mutation demonstrated a long repeat expansion in brain (>3,000 repeats), and immunohistochemistry showed mixed neuropathology with characteristics of both C9ORF72 expansions and GRN mutations.
Our findings indicate that co-occurrence of 2 evidently pathogenic mutations could contribute to the pleiotropy that is detected in patients with C9ORF72 repeat expansions. These findings suggest that patients with known mutations should not be excluded from further studies, and that genetic counselors should be aware of this phenomenon when advising patients and their family members.
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.