Receptor for Dickkopf proteins. Cooperates with DKK1/2 to inhibit Wnt/beta-catenin signaling by promoting the endocytosis of Wnt receptors LRP5 and LRP6. Plays a role in limb development; attenuates Wnt signaling in the developing limb to allow normal limb patterning and can also negatively regulate bone formation. Interacts with ERLEC1. Forms a ternary complex with DKK1 and LRP6. Binding to ERLEC1 is mediated by the oligosaccharides linked to the kringle domain.