Endocrinologists may be challenged not only by the great diversity of rare heritable metabolic bone diseases, but also by an unusual array of genetically transmitted skeletal dysplasias. The striking impact that many such skeletal dysplasias have on bone leads physicians naturally to question whether there is a metabolic component that might respond to mineral or hormonal therapy. Indeed, overt derangements in mineral or hormonal therapy. Indeed, overt derangements in mineral homeostasis occur, and a few do respond to medical treatment. Accordingly, some skeletal dysplasias do "bridge the gap" with the disorders that are traditionally regarded as metabolic in origin. The skills of the endocrinologist may be called on for either group of patients.