Genetic testing and counselling of patients with monogenic amyotrophic lateral sclerosis in Northern Finland: a retrospective, single-centre study.

Amyotrophic lateral sclerosis (ALS) is a common neurodegenerative disease. Its aetiology is complex, but a subset is caused by single-gene pathogenic variants (monogenic ALS). The most common ALS-associated genes are SOD1 and C9orf72. We evaluated the implementation of genetic testing and associated genetic counselling for ALS at a Finnish tertiary-level university hospital. We used the electronic patient records of Oulu University Hospital (Oulu, Finland) to identify patients diagnosed with ALS between 2000 and 2023. Medical records were reviewed for neurological diagnosis and completion of genetic testing and counselling. We identified a total of 387 patients diagnosed with ALS. Of these, 225 patients (58%) were offered genetic testing, and 186 (83%) accepted. The offer for genetic counselling was given to 60 patients, of whom 46 (77%) attended counselling, whilst 13 did not. The proportion of patients who declined counselling did not differ between those with SOD1 and C9orf72 variants. Among the 143 patients tested for SOD1 variants, 36 (25%) were confirmed to harbor the ALS-associated p.Asp91Ala variant in SOD1; 31 were homozygous and 5 were heterozygous. In the 96 analyses of the C9orf72 hexanucleotide expansion, the diagnostic yield was 27 (28%) patients. A positive family history was more common in SOD1-ALS than in C9orf72-ALS (53% vs 33%). Nearly one fifth of patients declined testing and over one fifth of those with genetic ALS did not attend genetic counselling. The reasons for this warrant further investigation.