Because of the ubiquity of Alzheimer disease-type pathology in persons with Down syndrome, the preclinical findings consistent with dysregulation of NMDAR activity in mouse models of Down syndrome, the safety profile of memantine (which is superior to the AChE inhibitors that are already being tested in persons with Down syndrome), and the possibility that memantine may indeed delay the onset of Alzheimer disease-type pathology in young adults with Down syndrome, all the professionals involved with this project decided that a small-scale randomized controlled clinical trial was warranted at present.