APOE and Alzheimer disease: Likewise, clinical trials suggested that different types of KDs significantly improved the quality of life and daily function [166] and eased AD-related cognitive impairment [167,168], especially in subjects without the epsilon 4 allele of the apolipoprotein E gene (APOE ɛ4), suggesting that KB metabolism is related to APOE ɛ4 status [169-171].