The C9orf72 repeat size correlates with onset age of disease, DNA methylation and transcriptional downregulation of the promoter.
Pathological expansion of a G4C2 repeat, located in the 5' regulatory region of C9orf72, is the most common genetic cause of frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS). C9orf72 patients have highly variable onset ages suggesting the presence of modifying factors and/or anticipation. We studied 72 Belgian index patients with FTLD, FTLD-ALS or ALS and 61 relatives with a C9orf72 repeat expansion. We assessed the effect of G4C2 expansion size on onset age, the role of anticipation and the effect of repeat size on methylation and C9orf72 promoter activity. G4C2 expansion sizes varied in blood between 45 and over 2100 repeat units with short expansions (45-78 units) present in 5.6% of 72 index patients with an expansion. Short expansions co-segregated with disease in two families. The subject with a short expansion in blood but an indication of mosaicism in brain showed the same pathology as those with a long expansion. Further, we provided evidence for an association of G4C2 expansion size with onset age (P<0.05) most likely explained by an association of methylation state of the 5' flanking CpG island and expansion size in blood (P<0.0001) and brain (P<0.05). In several informative C9orf72 parent-child transmissions, we identified earlier onset ages, increasing expansion sizes and/or increasing methylation states (P=0.0034) of the 5' CpG island, reminiscent of disease anticipation. Also, intermediate repeats (7-24 units) showed a slightly higher methylation degree (P<0.0001) and a decrease of C9orf72 promoter activity (P<0.0001) compared with normal short repeats (2-6 units). Decrease of transcriptional activity was even more prominent in the presence of small deletions flanking G4C2 (P<0.0001). Here we showed that increased methylation of CpGs in the C9orf72 promoter may explain how an increasing G4C2 size lead to loss-of-function without excluding repeat length-dependent toxic gain-of-function. These data provide insights into disease mechanisms and have important implications for diagnostic counseling and potential therapeutic approaches.
Neurodegenerative Brain Diseases Group VIB Department of Molecular Genetics, Antwerp, Belgium.|Institute Born-Bunge, University of Antwerp, Antwerp, Belgium.
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Gijselinck
Neurodegenerative Brain Diseases Group VIB Department of Molecular Genetics, Antwerp, Belgium.|Institute Born-Bunge, University of Antwerp, Antwerp, Belgium.
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Van Mossevelde
Neurodegenerative Brain Diseases Group VIB Department of Molecular Genetics, Antwerp, Belgium.|Institute Born-Bunge, University of Antwerp, Antwerp, Belgium.
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van der Zee
Neurodegenerative Brain Diseases Group VIB Department of Molecular Genetics, Antwerp, Belgium.|Institute Born-Bunge, University of Antwerp, Antwerp, Belgium.|Department of Neurology, University Hospital Ghent and University of Ghent, Ghent, Belgium.
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Sieben
Institute Born-Bunge, University of Antwerp, Antwerp, Belgium.|Department of Neurology and Memory Clinic, Hospital Network Antwerp Middelheim and Hoge Beuken, Antwerp, Belgium.
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Engelborghs
Department of Neurology, University Hospital Ghent and University of Ghent, Ghent, Belgium.
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De Bleecker
Department of Neurology, Saint-Luc University Hospital and Institute of Neuroscience, Université Catholique de Louvain, Brussels, Belgium.
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Ivanoiu
Department of Neurology, General Hospital Sint-Jan Brugge-Oostende, Bruges, Belgium.
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Deryck
German Center for Neurodegenerative Diseases (DZNE), Munich, Germany.|Adolf Butenandt Institute, Biochemistry and Munich Cluster of Systems Neurology (SyNergy), Ludwig-Maximilians University Munich, Munich, Germany.
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Edbauer
Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, Ontario, Canada.
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Zhang
Neurodegenerative Brain Diseases Group VIB Department of Molecular Genetics, Antwerp, Belgium.|Institute Born-Bunge, University of Antwerp, Antwerp, Belgium.
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Heeman
Neurodegenerative Brain Diseases Group VIB Department of Molecular Genetics, Antwerp, Belgium.|Institute Born-Bunge, University of Antwerp, Antwerp, Belgium.
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Bäumer
Neurodegenerative Brain Diseases Group VIB Department of Molecular Genetics, Antwerp, Belgium.|Institute Born-Bunge, University of Antwerp, Antwerp, Belgium.
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Van den Broeck
Neurodegenerative Brain Diseases Group VIB Department of Molecular Genetics, Antwerp, Belgium.|Institute Born-Bunge, University of Antwerp, Antwerp, Belgium.
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Mattheijssens
Neurodegenerative Brain Diseases Group VIB Department of Molecular Genetics, Antwerp, Belgium.|Institute Born-Bunge, University of Antwerp, Antwerp, Belgium.
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Peeters
Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, Ontario, Canada.|Division of Neurology, Department of Medicine, University of Toronto, Toronto, Ontario, Canada.
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Rogaeva
Neurodegenerative Brain Diseases Group VIB Department of Molecular Genetics, Antwerp, Belgium.|Institute Born-Bunge, University of Antwerp, Antwerp, Belgium.|Department of Neurology, Antwerp University Hospital, Edegem, Belgium.
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De Jonghe
Institute Born-Bunge, University of Antwerp, Antwerp, Belgium.|Department of Neurology, Antwerp University Hospital, Edegem, Belgium.
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Cras
Institute Born-Bunge, University of Antwerp, Antwerp, Belgium.
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Martin
Institute Born-Bunge, University of Antwerp, Antwerp, Belgium.|Department of Neurology and Memory Clinic, Hospital Network Antwerp Middelheim and Hoge Beuken, Antwerp, Belgium.
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de Deyn
Neurodegenerative Brain Diseases Group VIB Department of Molecular Genetics, Antwerp, Belgium.|Institute Born-Bunge, University of Antwerp, Antwerp, Belgium.
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Cruts
Neurodegenerative Brain Diseases Group VIB Department of Molecular Genetics, Antwerp, Belgium.|Institute Born-Bunge, University of Antwerp, Antwerp, Belgium.
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Van Broeckhoven
D000328:Adult; D017668:Age of Onset; D000690:Amyotrophic Lateral Sclerosis / Q000235:genetics* / Q000378:metabolism; D001530:Belgium; D000073885:C9orf72 Protein; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation / Q000235:genetics; D015536:Down-Regulation; D044127:Epigenesis, Genetic / Q000235:genetics; D057890:Epigenomics / Q000379:methods; D005260:Female; D057174:Frontotemporal Lobar Degeneration / Q000235:genetics / Q000378:metabolism; D020022:Genetic Predisposition to Disease / Q000235:genetics; D006801:Humans; D008297:Male; D008875:Middle Aged; D011401:Promoter Regions, Genetic / Q000235:genetics; D011506:Proteins / Q000235:genetics* / Q000378:metabolism
D000073885:C9orf72 Protein; C568651:C9orf72 protein, human; D011506:Proteins