Epidemiology and clinical picture of amyotrophic lateral sclerosis (ALS) in Southwest Finland

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease of motor neurons with unclear etiology in the majority of patients. The disease onset can be bulbar, spinal, respiratory or a combination of these. Irrespective of the onset region, the disease progresses to every voluntary muscle except ocular and sphincter muscles causing death approximately in 3-4 years from the first symptoms. The incidence of ALS worldwide is approximately 1-2,6/100’000 people annually and prevalence is 5-6/100’000 people. The rate of familial amyotrophic lateral sclerosis is reported to be 5-10% of all cases. The most common gene variant worldwide causing ALS is C9orf72 repeat expansion. It has been claimed that this repeat expansion may originate from Finland because of its high incidence in the Finnish population. However, there are no up-to-date epidemiological figures to support this claim. To identify patients with ALS, we searched the hospital discharge register in Southwest Finland for patients with motor neuron disease-related ICD-10 codes G12.1-G12.9. The time frame was between January 1st, 2010 and December 31th, 2018. During the years 2010-2018 the mean incidence in Southwest Finland was 4,2/100’000 people and prevalence on December 31, 2018 was 11,9/100’000 people. Our results confirm that ALS is very prevalent in the Finnish population. This study covered only Southwest Finland, so more research is needed to find out the incidence and prevalence of ALS in whole Finland. In our study we noted a higher prevalence for the SOD1 mutation partly due to limited testing of C9orf72 mutation