DKK1: A gene that inhibits the activity of osteoblasts, the cells that build bone. DKK1 acts by inhibiting Wnt signaling, which is essential for the growth and development of osteoblasts.

DKK1 is overexpressed in the plasma cells in multiple myeloma. The DKK1 produced by the myeloma cells tips the balance between osteoblasts and osteoclasts in favor of bone resorption. This contributes to the maintenance of the lytic ("punched-out") lesions in bone characteristic of multiple myeloma. DKK1 stands for Dickkopf1.