Low BDNF levels were demonstrated in patients with Alzheimer’s disease, which decrease in BDNF level correlates with loss of cognitive functions [353,354], suggesting that ketosis (elevated blood βHB levels) can exert its beneficial effects on Alzheimer’s disease and cognitive functions, among others, through HDAC/BDNF system leading to enhancement of alleviating BDNF effects (e.g., by stimulation of hippocampal neurogenesis) [355]. Here, HDAC9 is linked to early-onset autosomal dominant Alzheimer disease.