APBA2, a member of the X11 protein family, is a phosphotyrosine-binding domain protein and is a neuronal adapter protein that interacts with amyloid precursor protein (APP) and neuritic plaques in the brains of patients with Alzheimer's disease. It stabilizes APP and inhibits production of proteolytic APP fragments including the A beta peptide that is deposited in the brains of Alzheimer's disease patients. APBA2 is believed to be involved in signal transduction processes and is also regarded as 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. Recent reports suggest that it may also be a candidate gene for autism.