The idea of bone dysplasia "families" emerged in the mid 1980s [Spranger, 19881. As put forth by its principal proponent, J. Spranger, the concept was simple: similar bone dysplasias are pathogenetically related. He suggested that the concept would have two uses. The first was theoretical; it would guide investigators searching for pathogenetic mechanisms. If a mechanism were discovered in one member of a family, a similar mechanism should be sought in other members of the bone dysplasia family. The second was practical; if a certain radiographic pattern were recognized in a patient, it should suggest family-specific radiographic and biochemical tests to be performed which might lead to a diagnosis. Even if such testing were uninformative, knowledge about the family might be useful for management and counseling.
One of the first publications regarding bone dysplasia families listed seven families: dysostosis multiplex, osteogenesis imperfecta, achondroplasia, spondyloepiphyseal dysplasia (SED) congenita, Larsen-otopalatodigital dysplasia (OPD), Stickler-Kniest dysplasia, and diastrophic dysplasia [Spranger, 19881. At the time relatively little was known about the pathogenesis of the members of the last five of these families; the basis of the classification was radiographic.
By the early 1990s the family concept had a major impact on the nomenclature of the disorders. Indeed, the number of named chondrodysplasias had steadily grown through the 1970s and 1980s to an almost unmanageable number. At a meeting of the international working group on bone dysplasias held in Bad Honnef, Germany in 1991, this upward trend was reversed by grouping disorders of qualitatively similar radiographic findings [International Working Group on Constitutional Diseases of Bone, 19921. This classification listed 24 major groups of bone dysplasias. Many previously used clinical and genetic criteria, such as age of onset and inheritance pattern, were no longer considered allowing greater flexibility in grouping together disorders exhibiting different degrees of severity. For example, the achondroplasia family included