Synaptic loss and dysfunction is another early feature of Alzheimer’s disease pathology closely related to cognitive impairment.3,19-22 One marker of pre-synaptic degeneration and dysfunction is growth-associated protein 43 (GAP-43), an intra-cellular membrane-bound protein encoded by the GAP-43 gene. Here, GAP43 is linked to early-onset autosomal dominant Alzheimer disease.