BACKGROUND The reported prevalence rates of dementia in people with Down's syndrome have varied considerably across studies. The aim of this study was to investigate the extent of clinical change with age using an established diagnostic instrument in an unbiased, population-based sample of older people with Down's syndrome.
METHOD Changes in memory, personality, general mental functioning and daily living skills were assessed using a modified version of the informant interview of the Cambridge Examination for Mental Disorders of the Elderly (CAMDEX).
RESULTS Age-specific prevalence rates of dementia varied according to the diagnostic criteria used. Using CAMDEX criteria for Alzheimer's disease, prevalence rates increased from 3.4 to 10.3 to 40% in the 30-39, 40-49 and 50-59 age group, respectively.
CONCLUSIONS Overall, the age-related pattern of presentation and dementia diagnoses differs from that seen in the general elderly population. However, age-specific prevalence rates of Alzheimer's disease were similar but 30-40 years earlier in life.