BDNF and Alzheimer disease: Additionally, our results complement previous reports of significant interaction between COMT Val158Met and APOEε4 on risk for AD [48], additive effects of BDNF Val66Met and APOEε4 on hippocampal activity in healthy older adults [49], and interaction between BDNF Val66Met and APOEε4 on episodic memory in cognitively healthy older adults [50].