title: The prevalence and causes of dementia in people under the age of 65 years.
abstract: OBJECTIVE
  To determine the prevalence of dementia in people under the age of 65 in a large catchment area, and use these figures to estimate the number of younger people affected by dementia in the UK.
  
  
  METHODS
  Epidemiological catchment area prevalence survey.
  
  
  METHODS
  The London boroughs of Kensington and Chelsea, Westminster, and Hillingdon with a total population of 567500 people.
  
  
  METHODS
  All residents of the catchment area with dementia, where the illness began before the age of 65 years. Participants were notified to the study by medical and care professionals. The diagnosis and age of onset was established from all available health and social care records. In total, 227 people were identified, of whom 185 fulfilled the inclusion criteria of having a dementia which started before their 65th birthday.
  
  
  METHODS
  Diagnosis of dementia and differential diagnosis of the cause of the dementia.
  
  
  RESULTS
  The prevalence of dementia in those aged 30-64 was 54.0 per 100000 (95% CI 45.1 to 64.1 per 100000). For those aged 45-64 years, the prevalence was 98.1 per 100000 (95% CI 81.1 to 118.0 per 100000). From the age of 35 onwards, the prevalence of dementia approximately doubled with each 5 year increase in age. Extrapolating these figures nationally suggests that there are 18319 (15296-21758) people with dementia under the age of 65 in the UK.
  
  
  CONCLUSIONS
  The study confirms previous "guestimates" of the number of younger people affected by dementia in UK. The prevalence figures generated are robust, and are supported by other smaller and targeted prevalence surveys. The prevalence figures provided by this study will allow health planners to accurately estimate need and plan services.
authors.affiliation: Imperial College London and the Institute of Neurology (UCL), London, UK. rj.harvey@virgin.net
authors.forename: R J
authors.initials: RJ
authors.lastname: Harvey
authors.forename: M
authors.initials: M
authors.lastname: Skelton-Robinson
authors.forename: M N
authors.initials: MN
authors.lastname: Rossor
mesh_terms: D000328:Adult; D017668:Age of Onset; D003704:Dementia / Q000453:epidemiology* / Q000209:etiology*; D003937:Diagnosis, Differential; D005260:Female; D006306:Health Surveys; D006801:Humans; D008297:Male; D008875:Middle Aged; D020380:Needs Assessment; D015995:Prevalence; D006113:United Kingdom / Q000453:epidemiology