The prevalence of dementia in Down syndrome.

The prevalence of clinical dementia was assessed in three age groups of patients with Down syndrome in the county of Aarhus, Denmark: Group I: 14-16 years (n = 13), group 2: 23-29 years (n = 34), group 3: 50-60 years (n = 25). Seventy-two (85%) of 85 patients participated. Caregivers were interviewed and a neurological examination was performed. An EEG was recorded in 50 patients. Definite clinical dementia was defined as an acquired and progressive decline in 4 or more out of 17 items that are considered to indicate dementia in Down syndrome. Possible dementia was considered when 1-3 items were affected. Six (24%) in group 3 had definite clinical dementia. A further 6 patients in group 3 and 2 (6%) in group 2 had possible dementia. This is the first population-based study with a clinical assessment of the prevalence of dementia in Down syndrome.