GAP43 and Alzheimer disease: To examine whether the observed CSF GAP-43 × Hippocampal ROI interaction was a general mechanism of neurodegeneration or present in specific ATN groups, exploratory analyses examined the associations between CSF GAP-43, hippocampal ROI volumes, and episodic memory in ATN classified no AD pathology participants (n = 182) and AD continuum participants (n = 312).