How prevalent is Alzheimer disease (pre-senile dementia) in adults with Down syndrome?
In the 1960’s, autopsies of adults with DS showed that after about age 30 years, they all have the characteristic plaques and neurofibrillary tangles associated with Alzheimer disease. From that finding, it was assumed that all adults with DS would eventually get Alzheimer dementia if they lived long enough. However, population studies in the 1980s and ’90s showed that the percentage of adults with DS who actually get dementia range from 16% to 50%, depending on the criteria used to diagnose dementia. (The rate of Alzhemier disease in the general population is 5 to 10%.) The diagnosis of Alzheimer-type dementia in adults with mental retardation is very difficult, and has been complicated by the fact that many medical conditions seen in adults with DS may mimic cognitive deterioration. So the true prevalence of Alzheimer’s dementia in DS may not yet be known.
