An interaction effect with APOE ɛ4 was observed for anti– HSV-1 IgG and anti– HSV IgM carriage, separately, in association with worse performance on the TMT-A in our sample, suggesting that these factors have a synergistic effect on executive dysfunction, as previously seen for declines in episodic memory and MMSE scores, and for the risk of AD [7, 8, 27–29]. The gene discussed is APOE; the disease is Alzheimer disease.