Atypical or variant forms of well-known chondrodysplasias may pose diagnostic problems. We report on a girl with clinical features suggesting diastrophic dysplasia but with unusual radiographic features including severe platyspondyly, wide metaphyses, and fibular overgrowth, which are partially reminiscent of metatropic dysplasia. The diagnosis was clarified by molecular analysis of the DTDST gene, which revealed homozygosity for a previously undescribed mutation leading to a Q454P substitution in the 10th transmembrane domain of the DTDST sulfate transporter. Molecular analysis may be of particular value in such atypical cases.