The Epidemiology of Huntington's Disease in Iceland

Introduction: Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder characterized by involuntary movements, psychiatric symptoms and cognitive decline. Its prevalence is highest in individuals of European descent. However, a previous study in 2007 in Iceland showed an unusually low incidence and prevalence. The aim of this study was to investigate the incidence and prevalence of HD in Iceland between 2008 and 2022 as well as age, sex, symptoms, number of cytidine-adenosine-guanosine (CAG) repeats, treatment, and prognosis. Methods: A retrospective epidemiological study was conducted with clinical information obtained from medical records of individuals diagnosed with HD 2008-2022. Information was also obtained from the Department of Genetics at University Hospital of Iceland and neurologists managing HD patients. Results: Among the 22 diagnosed individuals (11 men) identified, the point prevalence on December 31, 2022, was 4.38 per 100,000 inhabitants, with an average annual incidence rate of 0.314 per 100,000 person-years. The average age at symptom onset was 46.3 years. A total of 21 out of 22 individuals had confirmed HD through genetic testing, with an average CAG repeat length of 42.3 (range 40-45). Five individuals died during the study period, with the most common cause of death being aspiration pneumonia. The average age at death was 70.4 years. Conclusion: The prevalence and incidence of HD in Iceland have increased compared to the 2007 study but remain lower than in other European populations. Results showed a lower number of CAG repeats in the Icelandic HD population, potentially explaining the higher age at symptom onset and death compared to global averages. The prevalence of Huntington's disease (HD) in Iceland has increased since 2007 but remains lower than in other European populations. A possible explanation for this is the founder effect and genetic drift which occurs by chance when a population is created from people settling in isolated communities. The higher age at symptom onset and death compared to the rest of the world could be a reflection of a relatively low number of cytidine-adenosine-guanosine repeats in the Icelandic HD cohort.