The Amyloid beta 4 (A4) precursor protein-binding family A member 1 (APBA1) is a member of the X11 protein family and a neuronal adapter protein that interacts with the Alzheimer's disease amyloid precursor protein (APP). APBA1 stabilizes APP and inhibits production of proteolytic APP fragments including the Aβ peptide that is deposited in the brains of Alzheimer's disease patients. It is thoμght to be involved in signal transduction processes and is a putative vesicular trafficking protein in the brain that can form a complex with the potential to couple synaptic vesicle exocytosis to neuronal cell adhesion. APBA1 can also bind to CASK, a multidomain scaffolding protein involved in brain development and synapse formation.