PLK2 and Alzheimer disease: Moreover, it may be that even under basal conditions there is a high level of hyperactivity and therefore endogenous Plk2 in 5xFAD mice, consistent with the overproduction of exogenous Aβ in these animals and the known Aβ-dependent neuronal hyperexcitation in 5xFAD and other AD models [18,54,56].