APP and Alzheimer disease: Although dysregulated circRNAs in the senescence-accelerated mouse-prone 8 (SAMP8) mice and the precursor protein (APP) and presenilin 1 (PS1) double transgenic mice have been revealed in several investigations using RNA sequencing or microarrays (Zhang et al., 2017; Ma et al., 2019; Zhang Y. et al., 2021), circRNA expression profiles have not been determined in the brain of 5 × FAD mice, the transgenic mice that co-express a total of five familial AD mutations (Oakley et al., 2006).