And subgroup analysis stratified by ethnicity and APOE ε4 was performed and showed no obvious difference (Ethnicity: p = 0.11; APOE ε4: p = 0.40), implying that the ethnicity and APOE ε4 exerted no influence on the association between the 5HTTLPR (L/S) polymorphism and risk of AD. Here, APOE is linked to Alzheimer disease.