APP and Alzheimer disease: In this regard, numerous studies, including ours, have focused on soluble Aβ oligomers made from synthetic Aβ40/42 peptides, secreted by FAD-mutant APP-expressing cells, or isolated directly from human (AD) cortex as to their effects on the hippocampal LTP and long-term synaptic depression (LTD), but the results have been variable and difficult to distil into a central conclusion.