IHH and thanatophoric dysplasia: In TD, the HDAC4 protein was highly expressed in tibial growth plate chondrocytes, and the expression level was significantly higher than that in the normal and treatment groups; however, the expression levels of BMP2/Runx2, the key factor in the intramembrane osteogenic signal pathway, and IHH/PTHrP, the target factor of endochondral osteogenesis, were low, and even the hypertrophy marker proteins COMP and Col-X of growth plate chondrocytes were almost not expressed.