APP and Alzheimer disease: Furthermore, evidence for loss of function of ATM was detected in three different AD transgenic mouse models; R1.40, which expresses a single (full-length) APP transgene, PS/APP, expressing transgenes for both APP and presenilin-1 (PSEN1) and triple-transgenic animals (3xTg), which bear APP, PSEN1, and MAPT transgenes, together implying that defective repair of DSBs is present in AD (Shen et al., 2016).