Achondroplasia (ACH) and hypochondroplasia (HCH) are among the most common forms of skeletal dysplasia, both caused by gain-of-function pathogenic variants in the fibroblast growth factor receptor 3 (FGFR3) gene, which lead to increased FGFR3 signaling. The gene discussed is FGFR3; the disease is hypochondroplasia.