When performing stratified analyses by APOE-ε4 to test the association between insomnia and cognitive performance in those domains where a trend for an interaction was found, we found a detrimental effect of insomnia on MBT-TDFR performance (p = 0.036) exclusively in APOE-ε4 homozygous, and a detrimental effect of insomnia only in APOE-ε4 non-carriers on WAIS-IV Digit Span performance (p < 0.001) (Additional file 1: Figure S1). This evidence concerns the gene APOE and insomnia measurement.