Dickkopf related protein 1 (Dkk-1) is a secreted protein that contains two cysteine rich regions that participate in embryonic development by inhibiting the Wnt signaling pathway. All Dkk-1 knockout homozygous mice have died at birth due to defects in the structure of the skull and neural crest, such as the inability to develop the eyes, olfactory basal plate, frontal nose, mandible, etc., as well as incomplete development of the forebrain and midbrain, as well as toe to toe fusion of the forelimbs. The increased expression of Dkk-1 in bone marrow, plasma, and peripheral blood is associated with osteolytic lesions in patients with multiple myeloma.