APEX1 and Alzheimer disease: However, our study differed in several ways from that study: assays were performed on peripheral blood cells; APE1 is associated with a different aspect of the DDR than the DDR factors of the above study, namely BER; the AD patients were of a later stage of disease (diagnosed as mild to moderate AD) where AD pathology may impede with the ability of cells to produce a vigorous DDR (such as impairing the APE1 enzyme activity).