Bone dysplasia series - Achondroplasia, hypochondroplasia and thanatophoric dysplasia: review and update

The authors summarize the clinical, genetic and histopathologic features, a s well as the complications, and radiological diagnosis of 3 related genera lized short-limb skeletal dysplasias: achondroplasia, hypochondroplasia and thanatophoric dysplasia. In all of these dysplasias, there is abnormal end ochondral ossification, but periosteal ossification is not affected. These 3 relatively common entities are known to be allelic to the same gene: the fibroblast growth factor receptor 3 gene on chromosome 4p. Heterozygous ach ondroplasia is the most common nonlethal skeletal dysplasia. The distinctiv e clinical and radiological features allow a precise diagnosis, as there is little variability in the appearance of affected patients. There is also a very evident molecular homogeneity. On histopathology of the growth plate, there is a quantitative decrease in endochondral ossification. Precise pre natal ultrasonographic diagnosis is possible in the third trimester, and so metimes even in the second. Hypochondroplasia is a relatively common, milde r form of achondroplasia, which varies within and between families and lack s the neurological complications often seen in achondroplasia of this group . An accurate prenatal ultrasonographic diagnosis is rare. There are milder changes on histology of the growth plate. Thanatophoric dysplasia is the l ethal and most severe dysplasia. It has distinct features - mainly short tu bular bones and short ribs with platyspondyly - allowing a precise radiolog ic and prenatal ultrasonographic diagnosis. On histopathology of the growth plate, there is disruption of endochondral ossification.