Genetic reports abstractFrequency of C9orf72 repeat expansions in amyotrophic lateral sclerosis: a Belgian cohort study
Introduction
Recently, a hexanucleotide repeat expansion (GGGGCC)n upstream of the coding region of the C9orf72 gene, was identified to be responsible for chromosome 9p21-linked amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) (DeJesus-Hernandez et al., 2011, Renton et al., 2011). ALS is a devastating adult-onset motor neuron disease that has a familial cause in approximately 10% of the patients. It is characterized by upper and lower motor neuron degeneration, resulting in progressive muscle weakness, muscle wasting, fasciculations, hyperreflexia, and spasticity. Disease onset is usually in the fifth to sixth decade of life and symptoms start in the spinal region in most patients (limb onset). The bulbar region is affected first in 20%–30% of patients. Eventually, respiratory failure leads to death, usually 2–5 years after disease onset (Rowland and Shneider, 2001). FTLD is a dementia syndrome that encompasses different clinical subtypes, including behavioral variant frontotemporal dementia, semantic dementia, and primary nonfluent aphasia (Neary et al., 2005). It is characterized by progressive changes in behavior, executive dysfunction, and/or language impairment. FTLD is the second most common cause of dementia in individuals younger than 65 years of age and accounts for 5%–15% of all cases of dementia. It has a familial cause in up to 40% of the cases. The most important genes associated with FTLD are microtubule-associated protein tau, progranulin (GRN), and C9orf72, responsible for 5%–15%, 10%–25%, and 10%–25%, respectively (Baker et al., 2006, Cruts et al., 2006, DeJesus-Hernandez et al., 2011, Gijselinck et al., 2012, Hutton et al., 1998, Renton et al., 2011). Mutations in valosin-containing protein (VCP) and charged multivesicular body protein 2B are much less common (Rademakers et al., 2012, Sieben et al., 2012). Altogether, these mutations account for approximately 40%–50% of the familial FTLD.
In ALS, mutations are found in the superoxide dismutase gene (SOD1), responsible for approximately 20% of the ALS pedigrees (Rosen et al., 1993). Mutations in TARDBP and fused in sarcoma (FUS) each account for 2%–5% of familial ALS (fALS) (Kabashi et al., 2008, Kwiatkowski et al., 2009, Sreedharan et al., 2008, Vance et al., 2009). Mutations in other genes, such as vesicle-associated membrane protein B, angiogenin (ANG), VCP, ataxin-2 (ATXN2), ubiquilin-2, profilin 1, and optineurin, are much rarer and most likely each represent only a small proportion of ALS (Al-Chalabi et al., 2012). The recently identified C9orf72 repeat expansion has been observed in approximately 34% of fALS cases and in approximately 6% of sporadic cases, varying strongly between the different populations studied (van Blitterswijk et al., 2012).
The objective of our study was to determine the presence of C9orf72 repeat expansions in Belgian patients with familial and sporadic ALS. We also investigated genotype-phenotype correlations in our cohort.
Section snippets
Patients and control subjects
Patients diagnosed with ALS at the neuromuscular center in Leuven between 1992 and 2011 could participate in the study. Blood samples from patients were obtained after written informed consent. In total, 119 patients with fALS from 62 kindreds, and 471 patients with sporadic ALS (sALS) were screened for a C9orf72 repeat expansion. This study was approved by the local ethical committee of the University Hospitals Leuven. Patients without family history of ALS were considered as sporadic ALS.
Results
Screening for C9orf72 repeat expansion was performed in patients with previously unexplained fALS. In our cohort of 119 consecutive patients with fALS (belonging to 62 different pedigrees), 50 patients were previously explained by mutations in SOD1 (from 14 different pedigrees, corresponding to 22.6% of the families), FUS (7 patients from 2 pedigrees or 3.2%), TARDBP mutations (1 patient of 1 pedigree or 1.6%), or ATXN2 (2 patients from 1 pedigree or 1.6%) (Lemmens et al., 2009, Van Damme
Discussion
Our study assessed the presence of C9orf72 hexanucleotide repeat expansions in a large cohort of Belgian ALS patients. C9orf72 repeat expansions were found in 51.6% of the fALS pedigrees, being the highest reported frequency after Sweden (63%) (Smith et al., 2013, van Blitterswijk et al., 2012). Previous studies in smaller Belgian cohorts reported a frequency of 47% and 84% (Gijselinck et al., 2012, Smith et al., 2013). In our cohort, this mutation was associated with a higher proportion of
Disclosure statement
The authors have no conflicts of interest.
Blood samples from patients and control subjects were obtained after written informed consent. This study was approved by the local ethical committee of the University Hospitals Leuven.
Acknowledgements
The authors thank the patients and control subjects for participating in this study, and L. Cosemans for assistance with sample management.
This work was supported by the University of Leuven (GOA 11/014) and the Belgian government (Interuniversity Attraction Poles, program P7/16 of the Belgian Federal Science Policy Office), and the European Community's Health Seventh Framework Programme (FP7/2007-2013 [259867]). P.V.D., B.D., and V.T. hold a clinical investigatorship of FWO-Vlaanderen. A.G.
References (36)
- et al.
Cognitive and clinical characteristics of patients with amyotrophic lateral sclerosis carrying a C9orf72 repeat expansion: a population-based cohort study
Lancet Neurol.
(2012) - et al.
Expanded GGGGCC hexanucleotide repeat in noncoding region of C9ORF72 causes chromosome 9p-linked FTD and ALS
Neuron
(2011) - et al.
A C9orf72 promoter repeat expansion in a Flanders-Belgian cohort with disorders of the frontotemporal lobar degeneration-amyotrophic lateral sclerosis spectrum: a gene identification study
Lancet Neurol.
(2012) - et al.
Frequency of the C9orf72 hexanucleotide repeat expansion in patients with amyotrophic lateral sclerosis and frontotemporal dementia: a cross-sectional study
Lancet Neurol.
(2012) - et al.
Frontotemporal dementia
Lancet Neurol.
(2005) - et al.
A hexanucleotide repeat expansion in C9ORF72 is the cause of chromosome 9p21-linked ALS-FTD
Neuron
(2011) - et al.
Length of normal alleles of C9ORF72 GGGGCC repeat do not influence disease phenotype
Neurobiol. Aging
(2012) - et al.
The genetics and neuropathology of amyotrophic lateral sclerosis
Acta Neuropathol.
(2012) - et al.
p62 positive, TDP-43 negative, neuronal cytoplasmic and intranuclear inclusions in the cerebellum and hippocampus define the pathology of C9orf72-linked FTLD and MND/ALS
Acta Neuropathol.
(2011) - et al.
Mutations in progranulin cause tau-negative frontotemporal dementia linked to chromosome 17
Nature
(2006)
El Escorial revisited: revised criteria for the diagnosis of amyotrophic lateral sclerosis
Amyotroph. Lateral Scler. Other Motor Neuron Disord.
Clinical characteristics of patients with familial amyotrophic lateral sclerosis carrying the pathogenic GGGGCC hexanucleotide repeat expansion of C9ORF72
Brain
Extensive genetics of ALS: a population-based study in Italy
Neurology
Clinico-pathological features in amyotrophic lateral sclerosis with expansions in C9ORF72
Brain
Null mutations in progranulin cause ubiquitin-positive frontotemporal dementia linked to chromosome 17q21
Nature
C9ORF72 hexanucleotide expansions of 20-22 repeats are associated with frontotemporal deterioration
Neurology
Whole-genome sequencing reveals a coding non-pathogenic variant tagging a non-coding pathogenic hexanucleotide repeat expansion in C9orf72 as cause of amyotrophic lateral sclerosis
Hum. Mol. Genet.
Familial frontotemporal dementia and amyotrophic lateral sclerosis associated with the C9ORF72 hexanucleotide repeat
Brain
Cited by (35)
Initial Identification of a Blood-Based Chromosome Conformation Signature for Aiding in the Diagnosis of Amyotrophic Lateral Sclerosis
2018, EBioMedicineCitation Excerpt :Other studies suggest common pathogenic mechanisms for both the non-genetic and the genetic forms of ALS, as well as, similar clinical courses and dysfunctional features [2, 25]. A hexanucleotide expansion in the C9orf72 gene is the most common genetic mutation [26, 27]. The discovery of the repeat expansion of the C9orf72 hexanucleotide provides bridge between familial ALS and sporadic ALS [27–29].
Identification of a novel loss-of-function C9orf72 splice site mutation in a patient with amyotrophic lateral sclerosis
2016, Neurobiology of AgingCitation Excerpt :It is possible that the patients with a small expansion in blood (e.g., 38 and 63 repeats) could have a large pathologic expansion in the central nervous system as a result of somatic instability (Fratta et al., 2015). The frequencies of C9orf72 repeat expansions have been shown to vary substantially in ALS cohorts from different geographic regions worldwide (Alavi et al., 2014; Debray et al., 2013; Fahey et al., 2014; Ratti et al., 2012). Among Caucasian populations, high frequencies of expanded repeats have been reported, ranging from 25% to 50% for FALS and 4% to 7% for SALS (Corrado et al., 2011; Ratti et al., 2012), although several studies have excluded a founder effect (Fratta et al., 2015; Xi et al., 2015).
Improved PCR based methods for detecting C9orf72 hexanucleotide repeat expansions
2016, Molecular and Cellular ProbesCitation Excerpt :We detected a relatively higher degree of variation than has been reported in studies based on Southern UK populations, with a 10 bp deletion being reported commonly in Northern England [11]. The prevalence of C9orf72 expansions in the Scottish ALS population is similar to that reported in other population based series of ALS internationally [3,18]. The admixture experiments which were carried out, where expansions can be detected even when diluted to 1% in a normal background, suggest that these assays are not severely affected by preferential amplification, and the conditions seem to be optimal for PCR of longer fragments.
ALS: A bucket of genes, environment, metabolism and unknown ingredients
2016, Progress in NeurobiologyCitation Excerpt :The bulk of works during the last 2 years have made such an enormous contribution to the understanding of the toxicity mechanisms of C9ORF72 mutation to motor neurons that the involvement of C9ORF72 in the pathogenesis of ALS merits special attention in this review. Although the repeat size among patients, or even among different tissues within the same individual, shows a heterogeneous pattern, and the correlation between the number of repeats and the severity of clinical phenotypes is not clear, it has been demonstrated that carriers of C9ORF72 expansions have a higher incidence of ALS, in particular the bulbar onset ALS (Debray et al., 2013; Ratti et al., 2012 Ratti et al., 2012). It was first reported that expansions cause haploinsufficiency of C9ORF72.
"Preconditioning" with latrepirdine, an adenosine 5'-monophosphate-activated protein kinase activator, delays amyotrophic lateral sclerosis progression in SOD1<sup>G93A</sup> mice
2015, Neurobiology of AgingCitation Excerpt :Genetic testing for mutations associated with ALS to identify subjects at risk is becoming increasingly important. For example, genetic screening for C9orf72 repeat expansions identified 51.6% of cases of fALS and 9.6% of sALS cases (Debray et al., 2013). Therefore, with the increased identification of genes conferring significant risks for the development of ALS or other neurodegenerative disorders, the use of “preconditioning” treatment paradigms may become tangible in the near future.
Evidence-based consensus guidelines for ALS genetic testing and counseling
2023, Annals of Clinical and Translational Neurology