Investigation of C9orf72 repeat expansions in Parkinson's disease

Large repeat expansions in the C9orf72 gene were recently reported to be a major cause of familial amyotrophic lateral sclerosis and frontotemporal dementia. Given some of the clinical and pathologic overlap between these 2 diseases and Parkinson's disease, we sought to evaluate the presence of these expansions in a cohort of French-Canadian patients with Parkinson's disease. No pathologic expansion was found in our cohort of patients suggesting that C9orf72 repeat expansions do not play a major role in the pathogenesis of Parkinson's disease.     

Screening for C9orf72 repeat expansions in Chinese amyotrophic lateral sclerosis patients

An intronic GGGGCC hexanucleotide repeat expansion in the C9orf72 gene was recently identified as a major cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia in white populations. To determine if the C9orf72 repeat expansion was present in ALS patients in Chinese populations, we studied the size of the hexanucleotide repeat expansion in a cohort of familial and sporadic ALS patients of Chinese origin. No expanded hexanucleotide repeats were identified. This indicates that C9orf72 mutations are not a common cause of familial or sporadic ALS in Chinese mainland.     

C9orf72 repeat expansions are restricted to the ALS-FTD spectrum

Expansion of a GGGGCC repeat (RE) in the C9orf72 gene has been recently reported as the main genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Given the growing evidence of genetic and clinicopathologic overlap among ALS, FTD, and other neurodegenerative diseases, we investigated the occurrence of RE in a subset of 9 patients with ALS-plus syndromes, including Parkinson's disease (PD), progressive supranuclear palsy (PSP), corticobasal syndrome (CBS), and multiple system atrophy. We identified RE in 2 ALS-plus individuals (22.2%) displaying PSP and CBS features. On the basis of this finding, we extended our analysis to a cohort composed of 190 PD, 103 CBS, 107 PSP, and 177 Alzheimer's disease cases. We did not identify any RE in these patients, indicating that C9orf72 is in all probability not involved in the pathogenesis of these disorders. However, the high frequency of C9orf72 RE in patients with ALS-plus syndromes suggests that, similar to ALS-FTD patients, individuals with combined motor neuron and extrapyramidal features should be screened for RE, independent of their family history.     

Screening for C9orf72 repeat expansions in parkinsonian syndromes

Parkinsonism might precede, coincide, or follow the behavioral or language-predominant cognitive impairments characteristic of frontotemporal dementia (FTD). In this study, we analyze the hexanucleotide repeat expansions within C9orf72 gene in various parkinsonian syndromes because it is a recently identified important genetic cause of FTD. The expanded hexanucleotide repeat is only identified in our familial FTD patients but not in patients with predominant parkinsonism. The lack of association between abnormal C9orf72 repeat expansion and parkinsonian syndromes might imply pathogenic mechanisms other than tau or Lewy body pathology.     

Analysis of the C9orf72 hexanucleotide repeat expansion in Korean patients with familial and sporadic amyotrophic lateral sclerosis

The expansion of a noncoding hexanucleotide repeat (GGGGCC) in the chromosome 9 open reading frame (C9orf72) gene has been identified as the most common cause of familial and sporadic amyotrophic lateral sclerosis (ALS) in Caucasian populations. The role of the C9orf72 repeat expansion in Korean ALS patients, however, has not been reported. We therefore investigated the frequency of the C9orf72 repeat expansion in 254 Korean patients with familial (n = 8) and sporadic (n = 246) ALS and found that none of the patients had the expansion. The number of hexanucleotide repeats ranged from 2 to 11 in the 254 ALS patients without the expansion. Our results suggest that the C9orf72 repeat expansion is not the main cause of ALS in the Korean population.     

A familial frontotemporal dementia associated with C9orf72 repeat expansion and dysplastic gangliocytoma

A hexanucleotide repeat expansion in the chromosome 9 open reading frame 72 gene (C9orf72) was recently identified as the most common genetic cause of frontotemporal dementia/amyotrophic lateral sclerosis. Here we describe the clinical, pathologic, and genetic features of a Finnish C9orf72 expansion carrier, who developed a dysplastic gangliocytoma (Lhermitte-Duclos disease), a rare hamartoma/overgrowth syndrome of cerebellar granule cells associated with mutations in the phosphatase and tensin homolog gene. In addition to the dysplastic gangliocytoma, the patient showed typical transactive response DNA-binding protein with M_r 43 kD (TDP-43) pathology mainly in the cortex and the substantia nigra and numerous p62-positive/TDP-43-negative inclusions in the cerebellar granule cells. His sister carried the same gene defect and showed a similar type of TDP-43/p62 pathology in her brain. Our findings confirm that the clinical and pathologic picture of C9orf72 mutation carriers is more heterogeneous than originally thought and warrants further studies on the possible involvement of phosphatase and tensin homolog gene pathway in the specific cerebellar granule cell pathology associated with C9orf72 expansion.     

Identification of C9orf72 repeat expansions in patients with amyotrophic lateral sclerosis and frontotemporal dementia in mainland China

The GGGGCC repeat expansion in the C9orf72 gene was recently identified as a major cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) in white populations. To estimate the frequency of hexanucleotide repeats in patients with ALS and FTD from mainland China, we screened for C9orf72 in a cohort of 128 patients and 150 control subjects using the repeat-primed polymerase chain reaction method. We observed pathogenic repeat expansions in a family with ALS-FTD and in a patient with sporadic FTD. In the family with ALS-FTD, the proband and the 2 asymptomatic siblings exhibited C9orf72 repeat expansions, and the clinical feature of the proband was characterized by pure motor syndrome with no cognitive impairment. The patient with sporadic FTD presented primarily with deteriorating behavior and mental status. Genotype analysis revealed that the proband shared the previously reported 20-single nucleotide polymorphism risk haplotype, whereas the patient with sporadic FTD carried all single nucleotide polymorphisms except rs2814707-A. To our knowledge, this study is the first to report 2 C9orf72 mutation patients in mainland China, and they shared the similar risk haplotype identified in white populations, suggesting that ALS and FTD associated with C9orf72 mutation was probably derived from a single founder.     

C9ORF72 repeat expansion not detected in patients with multiple sclerosis

A hexanucleotide repeat expansion in the chromosome 9 Open Reading Frame 72 gene (C9ORF72) has recently been reported to be cause of familial amyotrophic lateral sclerosis and frontotemporal lobar degeneration. Nevertheless, in the last few years this mutation has been found to be associated with heterogeneous phenotypes, including multiple sclerosis (MS) in concurrence with amyotrophic lateral sclerosis. In this study, we sought to evaluate the presence of the C9ORF72 repeat expansion in a cohort consisting of 314 patients with MS and 222 control subjects. No pathogenic expansion was found in MS and control populations, suggesting that C9ORF72 does not play a major role in MS pathogenesis.     

C9ORF72 repeat expansions not detected in a group of patients with schizophrenia

A hexanucleotide repeat expansion in C9ORF72 was recently found to cause some cases of frontotemporal lobar degeneration, frontotemporal dementia (FTD)-amyotrophic lateral sclerosis, and amyotrophic lateral sclerosis. Patients with frontotemporal lobar degeneration with the C9ORF72 repeat expansion are more likely than those without to present with psychosis. In this study, we screened DNA samples from 192 unrelated subjects with schizophrenia for the C9ORF72 repeat expansion. None of the subjects with schizophrenia had the pathogenic expansion. C9ORF72 repeat expansions either do not cause schizophrenia, or do so rarely (less than 1% of cases).     

Polymerase chain reaction and Southern blot-based analysis of the C9orf72 hexanucleotide repeat in different motor neuron diseases

The GGGGCC-hexanucleotide repeat expansion in C9orf72 is the most common genetic cause of familial amyotrophic lateral sclerosis and frontotemporal dementia. This study determined the frequency of C9orf72 repeat expansions in different motor neuron diseases (amyotrophic lateral sclerosis (ALS), motor neuron diseases affecting primarily the first or the second motor neuron and hereditary spastic paraplegia). Whereas most studies on C9orf72 repeat expansions published so far rely on a polymerase chain reaction-based screening, we applied both polymerase chain reaction-based techniques and Southern blotting. Furthermore, we determined the sensitivity and specificity of Southern blotting of the C9orf72 hexanucleotide repeat in DNA derived from lymphoblastoid cell lines. C9orf72 repeat expansions were found in 27.1% out of 166 familial ALS patients, only once in 68 sporadic ALS patients, and not in 61 hereditary spastic paraplegia patients or 52 patients with motor neuron diseases affecting clinically primarily either the first or the second motor neuron. We found hints for a correlation between C9orf72 repeat length and the age of onset. Somatic instability of the C9orf72 repeat was observed in lymphoblastoid cell lines compared with DNA derived from whole blood from the same patient and therefore caution is warranted for repeat length determination in immortalized cell lines.     

Lack of C9ORF72 coding mutations supports a gain of function for repeat expansions in amyotrophic lateral sclerosis

Hexanucleotide repeat expansions in C9ORF72 are a common cause of familial and apparently sporadic amyotrophic lateral sclerosis (ALS) and frontal temporal dementia (FTD). The mechanism by which expansions cause neurodegeneration is unknown, but current evidence supports both loss-of-function and gain-of-function mechanisms. We used pooled next-generation sequencing of the C9ORF72 gene in 389 ALS patients to look for traditional loss-of-function mutations. Although rare variants were identified, none were likely to be pathogenic, suggesting that mutations other than the repeat expansion are not a common cause of ALS, and providing supportive evidence for a gain-of-function mechanism. We also show by repeat-primed PCR genotyping that the C9ORF72 expansion frequency varies by geographical region within the United States, with an unexpectedly high frequency in the Mid-West. Finally we also show evidence of somatic instability of the expansion size by Southern blot, with the largest expansions occurring in brain tissue.     

Large C9orf72 repeat expansions are not a common cause of Parkinson's disease

The concept of a pathological overlap between neurodegenerative disorders is gaining momentum. We sought to determine the contribution of C9orf72 repeat expansions, recently discovered as a cause of frontotemporal dementia and amyotrophic lateral sclerosis, in a large number of Parkinson's disease patients. No large expansions were identified in our cohort.     

Clinical and genetic analysis of MAPT, GRN, and C9orf72 genes in Korean patients with frontotemporal dementia

The hexanucleotide repeat expansion (GGGGCC) in chromosome 9 open-reading frame 72 (C9orf72) and mutations in the microtubule-associated protein tau (MAPT) and progranulin (GRN) genes are known to be associated with the main causes of familial or sporadic amyotrophic lateral sclerosis and frontotemporal dementia (FTD) in Western populations. These genetic abnormalities have rarely been studied in Asian FTD populations. We investigated the frequencies of mutations in MAPT and GRN and the C9orf72 abnormal expansion in 75 Korean FTD patients. Two novel missense variants of unknown significance in the MAPT and GRN were detected in each gene. However, neither abnormal C9orf72 expansion nor pathogenic MAPT or GRN mutation was found. Our findings indicate that MAPT, GRN, and C9orf72 mutations are rare causes of FTD in Korean patients.     

The C9ORF72 hexanucleotide repeat expansion is a rare cause of schizophrenia

A hexanucleotide repeat expansions in the first intron of C9ORF72 has been shown to be responsible for a high number of familial cases of amyotrophic lateral sclerosis and/or frontotemporal lobar degeneration. The same mutation has been described in a patient with bipolar disorder, but up to now, not in patients suffering from schizophrenia. We determined the frequency of the C9ORF72 hexanucleotide repeat expansions in a population of 298 patients with schizophrenia or schizoaffective disorder. The pathogenic repeat expansion was detected in 2 patients (0.67%). Both of them presented with auditory hallucinations and had comorbid alcohol abuse. In addition, a positive family history for psychiatric and/or neurodegenerative diseases was present. The repeat expansion in the C9ORF72 gene is a rare, but possible, cause of schizophrenic spectrum disorders. We cannot rule out however whether the number of repeats influence the phenotype.     

Length of normal alleles of C9ORF72 GGGGCC repeat do not influence disease phenotype

Expansions of the noncoding GGGGCC hexanucleotide repeat in the Chromosome 9 open reading frame 72 (C9ORF72) gene cause frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). 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. 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 nonmutation carriers.     

VAPB and C9orf72 mutations in 1 familial amyotrophic lateral sclerosis patient

Previously, we have reported amyotrophic lateral sclerosis (ALS) families with multiple mutations in major ALS-associated genes. These findings provided evidence for an oligogenic basis of ALS. In our present study, we screened a cohort of 755 sporadic ALS patients, 111 familial ALS patients (97 families), and 765 control subjects of Dutch descent for mutations in vesicle-associated membrane protein B (VAPB). We have identified 1 novel VAPB mutation (p.V234I) in a familial ALS patient known to have a chromosome 9 open reading frame 72 (C9orf72) repeat expansion. This p.V234I mutation was absent in control subjects, located in a region with high evolutionary conservation, and predicted to have damaging effects. Taken together, these findings provide additional evidence for an oligogenic basis of ALS.     

The C9ORF72 expansion does not affect the phenotype in Nasu-Hakola disease with the DAP12 mutation

Nasu-Hakola disease (NHD) is a rare autosomal recessive disease that is characterized by cyst-like bone lesions and pathologic fractures combined with an early-onset frontal type of dementia. Mutations in DNAX-activation protein 12 (DAP12) and triggering receptor expressed on myeloid cells 2 (TREM2) are the known genetic causes of NHD. However, the role of both these genes in the neurodegenerative process is still partly unclear, and the input of other modifying factors has been postulated. Frontotemporal lobar degeneration (FTLD) is a neuropathologically and genetically heterogeneous neurodegenerative disease. A hexanucleotide repeat expansion in the chromosome 9–associated open reading frame 72 (C9ORF72) gene is the most common cause of familial FTLD in Finland. Here, we describe a family with 3 siblings with a clinical diagnosis of NHD. All patients had an equivalent age of onset of the behavioral/cognitive symptoms, and brain imaging revealed a similar pattern of brain atrophy and calcification in putamen and caudate nucleus. Case II-3 had the most severe phenotype with epilepsy and a rapid cognitive decline. Genetic analyses were performed in 2 patients (cases II-2 and II-3), and both had a homozygous DAP12 deletion. Because the role of DAP12 and TREM2 in neurodegeneration in NHD is partly unclear, our aim was to evaluate the role of other genetic variations as modifiers. The C9ORF72 expansion was found in case II-2. Exome sequencing did not reveal any other mutations that could be involved in FTLD. Case II-3 had a novel predictably deleterious mutation in the progressive myoclonic epilepsy type 2 (EPM2), which may have influenced his epilepsy as the EPM2 has been implicated in Lafora progressive myoclonic epilepsy. We conclude that the C9ORF72 expansion is probably an incidental finding because it did not have any apparent influence on the phenotype. Exome sequencing identified several rare missense variants and indels. Additional analyses in other NHD patients will be needed to elucidate their clinical relevance.     

Analysis of the hexanucleotide repeat in C9ORF72 in Alzheimer's disease

Frontotemporal lobar degeneration (FTLD) is a highly familial neurodegenerative disease. It has recently been shown that the most common genetic cause of FTLD and amyotrophic lateral sclerosis (ALS) is a hexanucleotide repeat expansion in C9ORF72. To investigate whether this expansion was specific to the FTLD/ALS disease spectrum, we genotyped the hexanucleotide repeat region of C9ORF72 in a large cohort of patients with Alzheimer's disease (AD). A normal range of repeats was found in all cases. We conclude that the hexanucleotide repeat expansion is specific to the FTLD/ALS disease spectrum.