APP and Alzheimer disease: The first study to suggest a link between ACE and AD in Drosophila was a modifier screen aimed to identify genes that either enhanced or suppressed phenotypes resulting from over-expression of Psn followed by a secondary screen to determine if any of the Psn modifiers could also suppress phenotypes generated from expression of the truncated form of APP, called C99 (van de Hoef et al., 2009).