APOE and Alzheimer disease: The AD and MCI groups showed a greater frequency of the APOE ε4 allele compared with healthy controls (23.6% for AD and 21.4% for MCI vs. 7.3% for control; AD vs. control, χ2 = 18.86, p<0.01; MCI vs. control, χ2 = 11.01, p = 0.001).