Variation of quantitative and qualitative changes of enchondral ossification in heterozygous achondroplasia.

Whereas the radiologic features of achondroplasia--the most common type of skeletal dysplasia in adults--are clearly defined there is still some debate about the severity and the type of histologic changes. Earlier descriptions reported severe disturbance of enchondral ossification to be typical of achondroplasia: They are, however, misleading by dealing mostly with cases of lethal neonatal dwarfism (e.g. thanatophoric dysplasia). Newer findings confirmed that only minor, quantitative lesions are typical of heterozygous achondroplasia. But even in recent years some observers noted more severe changes of enchondral ossification. An extensive histologic skeletal survey in a newborn achondroplastic male revealed remarkable findings: It clearly showed that in addition to a generalized, but moderate narrowing of the zones of enchondral ossification focal severe changes were present in various epiphyseal plates including clusterlike arrangement of enlarged chondrocytes, vacuolization, premature calcification and important fibrosis of cartilagineous matrix with membranous ossification. Our findings thus enable us to reconcile the seemingly divergent statements made before.