DKK1 and Alzheimer disease: Notably, amyloid-β (Aβ) oligomers, the pathogenic molecule in AD, rapidly increase Dkk1 expression as synapses degenerate (Purro et al., 2012) and knockdown or blockade of Dkk1 protects synapses against Aβ (Purro et al., 2012; Sellers et al., 2018).