FGFR4 (fibroblast growth factor receptor 4) is part of a family of fibroblast growth factor receptors that mediate the biological functions of specific growth factors. There are four members of the FGF receptor family: FGFR-1 (flg), FGFR-2 (bek, KGFR), FGFR-3 and FGFR-4. Each receptor contains an extracellular ligand binding domain, a transmembrane domain and a cytoplasmic kinase domain. Following ligand binding and dimerization, the receptors are phosphorylated at specific tyrosine residues. These receptor proteins play a role in important processes such as cell division, regulating cell growth and maturation, formation of blood vessels, wound healing, and embryo development. Although specific functions of FGFR4 remain unclear, studies indicate that the gene is involved in muscle development and the maturation of bone cells in the skull. FGFR4 may also play a role in the development and maintenance of specialized cells (called foveal cones) in the light-sensitive layer (the retina) at the back of the eye.