A viable Dkk1 knockout (KO) mouse strain in which embryonic lethality is rescued by developmental Wnt3 heterozygosity (Dkk1<sup>-/-</sup>:Wnt3<sup>+/-</sup>) exhibits increased bone formation and a high bone mass phenotype.
Dynamic histomorphometry identified increased bone formation as the mechanism underlying the high bone mass phenotype in Dkk1 KO mice, with no changes in bone resorption.