Furthermore, Down syndrome (DS), the most common genetic cause of mental disability, has been used to support Aβ as a therapeutic target because of the notably high prevalence of dementia with Alzheimer-type pathology in DS patients (greater than 50% after the age of 60) and the fact that the amyloid precursor protein gene, which gives rise to Aβ, is present on chromosome 21, which is triplicated in DS (65). This evidence concerns the gene APP and dementia.