APP and Alzheimer disease: Familial AD patients with mutations in the Aβ precursor protein (APP) gene tested negative for the amyloid-specific positron emission tomography (PET) probe, Pittsburgh compound B (PiB), which is commonly used to detect Aβ deposits in sporadic AD (sAD) cases [22], despite showing a severe cerebral amyloid burden in postmortem analysis [23], suggesting the presence of a structural difference between Aβ deposits in these subjects when compared to sporadic patients [24,25].