FGF4 and skeletal dysplasia: The exact mechanism linking FGF4 retrogene expression and skeletal dysplasia is not defined; limited data are available relating to temporal and spatial expression of FGF4 retrogenes and although FGF4 protein overexpression acting through FGFR3 is an intriguing comparative model, FGF ligands are known to bind to multiple receptors [1,2,5].