BIROn-Birkbeck Institutional Research Online Wiseman, F. and Fisher, E. and Al_Janabi, T. and Hardy, J. and Karmiloff- Smith, Annette and Nizetic, D. and Tybulewicz, V. and Strydom, A. (2015) A genetic cause of Alzheimer disease: mechanistic insights from Down

Down syndrome, caused by an extra copy of chromosome 21, is associated with a greatly increased risk of early onset Alzheimer disease. It is thought that this risk is conferred by the presence of three copies of the gene encoding amyloid precursor protein (APP), an Alzheimer risk factor, although the possession of extra copies of other chromosome 21 genes may also play a role. Further study of the mechanisms underlying the development of Alzheimer disease in Down syndrome could provide insights into the mechanisms that cause dementia in the general population. Down syndrome (DS) is a complex, highly variable disorder that arises from trisomy of chromosome 21. It was one of the first chromosomal disorders to be identified and occurs with an incidence of approximately 1 in 800 births. Its prevalence within a given population is also influenced by infant mortality rates, access to healthcare, termination rates, average maternal age and life expectancy.