Taken together, our findings suggest that episodic memory performance may be partially explained by pathologies that co-occur in the AD process (e.g., synaptic dysfunction), implicating CSF GAP-43 as a biomarker that may complement well-established predictors of episodic memory performance (e.g., hippocampal volume) in older adults even after adjusting for ATN group status. This evidence concerns the gene GAP43 and Alzheimer disease.