The present invention relates to a transgenic non-human animal embryo lacking native presenilin 1 and a transgenic non-human animal having only a non-native presenilin 1. The transgenic animals and cells derived therefrom can be used in the study of the expression pattern, activity and modulators of presenilin 1, in the study of the role of presenilin 1 in Alzheimer's Disease and in the study of disorders of the central nervous system.