To confirm the DNA damage and Chk1 activation in AD brains, we detected the protein levels of DNA damage markers (γH2A.X and 53BP1) and Chk1 and active forms of Chk1 (Chk1 phosphorylated at S345, S317, and S296), as well as CIP2A levels in brains of AD patients and APP/PS1 transgenic mice. Here, CHEK1 is linked to Alzheimer disease.