Craniometaphyseal dysplasia (CMD) is a rare craniotubular bone disorder, characterized by life-long mineralization and bone deposition in craniofacial bones, while decreased bone deposition and flaring is seen in the metaphyses of long bones. Recently, we discovered mutations in a transmembrane protein, ANK, which is responsible for the autosomal dominant form of CMD. ANK is likely to be involved in pyrophosphate transport and the loss of ANK protein in mice causes progressive ankylosis with increased cartilage calcification. However, ANK's molecular properties, its interaction with other proteins, and its mode of action are unknown. The clustering of the mutations in the ANK gene of CMD patients and the bone matrix phenotype caused by mutant ANK protein suggests that CMD is not solely caused by a quantitative effect of pyrophosphate transport, but by a more complex mechanism. The goal of this proposal is to provide tools and to perform experiments that will eventually lead to the discovery of 1) the role of ANK in bone homeostasis and 2) the mechanism of mutant ANK causing the CMD phenotype.