Mutations in the FGFR3 gene can also cause other types of skeletal dysplasia,, which need to be identified and classified from mild to severe: hypochondroplasia (HCH), achondroplasia, thanodermal dysplasia type I (TD I), severe achondroplasia with developmental delay and nigroschisis (SADDN), and thanodermal dysplasia type II (TD II). This evidence concerns the gene FGFR3 and skeletal dysplasia.