SLC26A2 and diastrophic dysplasia: ,10 Mutations of the DTDST gene are responsible for four clinical manifestations of chondrodysplasia: “classic” diastrophic dysplasia (DTD), multiple epiphyseal dysplasia 4 (MED 4), atelosteogenesis type II (AO-II) and achondroplasia type 1B (ACG-1B).2