Despite documented associations between hippocampal volume and episodic memory functions (O’Shea et al., 2022; Zammit et al., 2017; Zilioli et al., 2024) and between hippocampal volume and CSF GAP-43 (Lu, 2022; Qiang et al., 2022), few studies have examined whether CSF GAP-43 and hippocampal atrophy have additive and/or interactive effects on episodic memory performance. This evidence concerns the gene GAP43 and hippocampal atrophy.