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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 (C9 pos ). Further, we compared C9 pos and C9 neg 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 C9 pos , with half being sporadic ALS cases. The proportion of C9 pos cases differed between regions, ranging from 17.9% in the Northern region to 1.9% in the Western region. The majority of C9 pos patients had non-Finnish European descent and were not closely related. C9 pos 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 C9 neg patients., Conclusion: C9 pos 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 C9 pos patients has proven to be challenging. Half of C9 pos patients were reported as having sporadic ALS, underlining the importance of carefully assessing family history and the need for genetic testing.

Genetic repeat expansions cause neuronal degeneration in amyotrophic lateral sclerosis as well as other neurodegenerative disorders such as spinocerebellar ataxia, Huntington's disease and Kennedy's disease. Repeat expansions in the same gene can cause multiple clinical phenotypes. We aimed to characterize repeat expansions in a Norwegian amyotrophic lateral sclerosis cohort. Norwegian amyotrophic lateral sclerosis patients ( n = 414) and neurologically healthy controls adjusted for age and gender ( n = 713) were investigated for repeat expansions in AR , ATXN1 , ATXN2 and HTT using short read exome sequencing and the ExpansionHunter software. Five amyotrophic lateral sclerosis patients (1.2%) and two controls (0.3%) carried ≥36 repeats in HTT ( P = 0.032), and seven amyotrophic lateral sclerosis patients (1.7%) and three controls (0.4%) carried ≥29 repeats in ATXN2 ( P = 0.038). One male diagnosed with amyotrophic lateral sclerosis carried a pathogenic repeat expansion in AR , and his diagnosis was revised to Kennedy's disease. In ATXN1 , 50 amyotrophic lateral sclerosis patients (12.1%) and 96 controls (13.5%) carried ≥33 repeats ( P = 0.753). None of the patients with repeat expansions in ATXN2 or HTT had signs of Huntington's disease or spinocerebellar ataxia type 2, based on a re-evaluation of medical records. The diagnosis of amyotrophic lateral sclerosis was confirmed in all patients, with the exception of one patient who had primary lateral sclerosis. Our findings indicate that repeat expansions in HTT and ATXN2 are associated with increased likelihood of developing amyotrophic lateral sclerosis. Further studies are required to investigate the potential relationship between HTT repeat expansions and amyotrophic lateral sclerosis., Competing Interests: The authors report no competing interests., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Guarantors of Brain.)

Background: Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that affects motor neurons. In Europe, disease-causing genetic variants have been identified in 40-70% of familial ALS patients and approximately 5% of sporadic ALS patients. In Norway, the contribution of genetic variants to ALS has not yet been studied. In light of the potential development of personalized medicine, knowledge of the genetic causes of ALS in a population is becoming increasingly important. The present study provides clinical and genetic data on familial and sporadic ALS patients in a Norwegian population-based cohort., Methods: Blood samples and clinical information from ALS patients were obtained at all 17 neurological departments throughout Norway during a 2-year period. Genetic analysis of the samples involved expansion analysis of C9orf72 and exome sequencing targeting 30 known ALS-linked genes. The variants were classified using genotype-phenotype correlations and bioinformatics tools., Results: A total of 279 ALS patients were included in the study. Of these, 11.5% had one or several family members affected by ALS, whereas 88.5% had no known family history of ALS. A genetic cause of ALS was identified in 31 individuals (11.1%), among which 18 (58.1%) were familial and 13 (41.9%) were sporadic. The most common genetic cause was the C9orf72 expansion (6.8%), which was identified in 8 familial and 11 sporadic ALS patients. Pathogenic or likely pathogenic variants of SOD1 and TBK1 were identified in 10 familial and 2 sporadic cases. C9orf72 expansions dominated in patients from the Northern and Central regions, whereas SOD1 variants dominated in patients from the South-Eastern region., Conclusion: In the present study, we identified several pathogenic gene variants in both familial and sporadic ALS patients. Restricting genetic analysis to only familial cases would miss more than 40 percent of those with a disease-causing genetic variant, indicating the need for genetic analysis in sporadic cases as well., (© 2022 The Author(s). Published by S. Karger AG, Basel.)