Because APOE4 is the most common genetic risk marker for sporadic AD and other age-related changes such as neuroinflammation and increased blood–brain barrier permeability [70], it was surprising to see that 35% of the nLongC cohort may already be at risk for age-related neurodegeneration simply based on APOE4, even though they were middle-aged at the time of infection. Here, APOE is linked to infection.