SummarySpontaneous lateâonset Alzheimer's disease (LOAD) accounts for more than 95% of all human AD. As mice do not normally develop AD and as understanding on molecular processes leading to spontaneous LOAD has been insufficient to successfully model LOAD in mouse, no mouse model for LOAD has been available. Existing mouse AD models are all earlyâonset AD (EOAD) models that rely on forcible expression of ADâassociated protein(s), which may not recapitulate prerequisites for spontaneous LOAD. This limitation in AD modeling may contribute to the high failure rate of AD drugs in clinical trials. In this study, we hypothesized that genomic instability facilitates development of LOAD and tested two genomic instability mice models in the brain pathology at the old age. Shugoshinâ1 (Sgo1) haploinsufficient (â) mice, a model of chromosome instability (CIN) with chromosomal and centrosomal cohesinopathy, spontaneously exhibited a major feature of AD pathology; amyloid beta accumulation that colocalized with phosphorylated Tau, betaâsecretase 1 (BACE), and mitotic marker phosphoâHistone H3 (pâH3) in the brain. Another CIN model, spindle checkpointâdefective BubR1â/+ haploinsufficient mice, did not exhibit the pathology at the same age, suggesting the prolonged mitosisâorigin of the AD pathology. RNAâseq identified ten differentially expressed genes, among which seven genes have indicated association with AD pathology or neuronal functions (e.g., ARC, EBF3). Thus, the model represents a novel model that recapitulates spontaneous LOAD pathology in mouse. The Sgo1â/+ mouse may serve as a novel tool for investigating mechanisms of spontaneous progression of LOAD pathology, for early diagnosis markers, and for drug development.