Elsevier

Neurobiology of Aging

Volume 34, Issue 12, December 2013, Pages 2890.e7-2890.e12
Neurobiology of Aging

Genetic reports abstract
Frequency of C9orf72 repeat expansions in amyotrophic lateral sclerosis: a Belgian cohort study

https://doi.org/10.1016/j.neurobiolaging.2013.06.009Get rights and content

Abstract

We determined the frequency of C9orf72 repeat expansions in a large cohort of Belgian patients with familial (fALS) and sporadic (sALS) amyotrophic lateral sclerosis (ALS). In total, 119 patients with fALS from 62 kindreds, 471 patients with sALS, and 384 control subjects were included. A C9orf72 repeat expansion was found in 32 of 62 fALS pedigrees (51.6%), in 45 of 471 patients with sALS (9.6%), but in none of the control subjects. Compared with fALS of unknown etiology or fALS caused by mutations in other ALS-causing genes, C9orf72 repeat expansion carriers had a later age at onset (57.3 vs. 51.4 years; p = 0.0061), a higher proportion of bulbar onset (31.9% vs. 12.5%, p < 0.0001), and a reduced survival (29.4 vs. 67.7 months, p = 0.0003). In the sALS cohort, there were no significant differences in these disease characteristics between the C9orf72 repeat expansion carriers and the noncarriers. C9orf72 repeat expansions are a frequent cause of ALS in Belgium, and also in sALS patients. These results might justify genetic testing of C9orf72 in all ALS patients.

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.

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