In 2009, the discovery that PrPC acts as a receptor for the amyloid Aβ peptide [4], which is produced from the amyloid precursor protein APP following endoproteolytic cleavage and whose accumulation is a central event in Alzheimer’s disease (AD) [5], sparked renewed interest in the signalling function of PrPC. The gene discussed is APP; the disease is early-onset autosomal dominant Alzheimer disease.