Abstract
The point prevalence at birth of generalised bone dysplasias was estimated by a study of all children born between 1 January 1970 and 31 December 1983 in the county of Fyn (Denmark). Additionally the population prevalence on 31 December 1983 of all patients with generalised bone dysplasias in this county was determined. The county is a well defined, representative subregion of Denmark which demographically comprises a cross section of about 9% of the Danish population. In total, bone dysplasias were found to be more frequent than generally assumed. Achondroplasia was, however, less common with a point prevalence at birth of 1.3 per 100,000, while osteogenesis imperfecta (21.8), multiple epiphyseal dysplasia tarda (9.0), achondrogenesis (6.4), osteopetrosis (5.1), and thanatophoric dysplasia (3.8) were found more frequently. It is striking how many bone dysplasias are still erroneously classified as achondroplasia. Correct diagnosis is important for a valid prognosis, for treatment, and for genetic counselling. The diagnosis relies almost exclusively on the radiographical findings.