Rubenstein E, et al. - Between 2008 and 2018, researchers report prevalence and incidence of dementia and Alzheimer disease (AD) in Down syndrome (DS) in a full Medicaid population of adults with DS in Wisconsin. For individuals with DS, the life span has profoundly improved, leading to a large, understudied population of middle-aged and older adults with DS. Clinical researches reveal individuals with DS are at higher risk and have an earlier onset of dementia. Down syndrome is characterized by the trisomy of chromosome 21, the site of the amyloid precursor protein gene. In individuals with DS, overexpression of amyloid precursor protein–produced β-amyloid is predicted to increase the risk for AD dementia. Autopsy and neuroimaging examinations show that by age 40 years, virtually all adults with DS exhibit AD neuropathology. Population-based epidemiological work is required to define the extent of dementia in DS and demonstrate the public health results for the DS population, their families, and health service systems.