Given the difficulty finding age-matched APOE ε4/ε4 control subjects (low prevalence of this genotype in the general and healthy population), we could not compare AD APOE ε4/ε4 with control ε4/ε4 cases, and the analysis within the APOE ε3/ε4 genotype exhibited less statistical power because the size of the control group was small. This evidence concerns the gene APOE and Alzheimer disease.