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. 2025 Feb;26(1-2):132-140.
doi: 10.1080/21678421.2024.2405118. Epub 2024 Sep 24.

Amyotrophic lateral sclerosis caused by the C9orf72 expansion in Norway - prevalence, ancestry, clinical characteristics and sociodemographic status

Cathrine Goberg Olsen  1   2 , Vetle Nilsen Malmberg  2   3 , Maria Fahlström  1 , Karl Bjørnar Alstadhaug  4 , Ingrid Kristine Bjørnå  5 , Geir Julius Braathen  1 , Geir Bråthen  6   7 , Natasha Demic  8 , Erika Hallerstig  9 , Ineke Hogenesch  10 , Morten Andreas Horn  11 , Margitta T Kampman  12 , Grethe Kleveland  13 , Unn Ljøstad  14   15 , Angelina Maniaol  11 , Åse Hagen Morsund  16 , Ola Nakken  17 , Katrin Schlüter  18 , Stephan Schuler  19 , Elin Seim  20 , Heidi Øyen Flemmen  3 , Ole-Bjørn Tysnes  15   21 , Trygve Holmøy  2   17 , Helle Høyer  1   2
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Free article

Amyotrophic lateral sclerosis caused by the C9orf72 expansion in Norway - prevalence, ancestry, clinical characteristics and sociodemographic status

Cathrine Goberg Olsen et al. Amyotroph Lateral Scler Frontotemporal Degener. 2025 Feb.
Free article

Abstract

Objective: The most common genetic cause of amyotrophic lateral sclerosis (ALS) is the C9orf72 expansion. A high incidence of this expansion has been detected in Sweden and Finland. This Norwegian population-based study aimed to identify the prevalence, geographic distribution, ancestry, and relatedness of ALS patients with a C9orf72 expansion (C9pos). Further, we compared C9pos and C9neg patients' clinical presentation, family history of ALS and other neurodegenerative disorders, and sociodemographic status.

Methods: We recruited ALS patients from all 17 Departments of neurology in Norway. Blood samples and questionnaires regarding clinical characteristics, sociodemographic status and family history of ALS, and other neurodegenerative disorders were collected. The C9orf72 expansion was examined for all patients.

Results: The study enrolled 500 ALS patients, 8.8% of whom were C9pos, with half being sporadic ALS cases. The proportion of C9pos cases differed between regions, ranging from 17.9% in the Northern region to 1.9% in the Western region. The majority of C9pos patients had non-Finnish European descent and were not closely related. C9pos patients exhibited a significantly shorter mean survival time, had a higher frequency of relatives with ALS or dementia, and were more often unmarried/single and childless than C9neg patients.

Conclusion: C9pos patients constitute a large portion of the Norwegian ALS population. Ancestry and relatedness do not adequately explain regional differences. Relying on clinical information to identify C9pos patients has proven to be challenging. Half of C9pos patients were reported as having sporadic ALS, underlining the importance of carefully assessing family history and the need for genetic testing.

Keywords: Amyotrophic lateral sclerosis; C9orf72; Norway; clinical and sociodemographic data.

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