Fibroblast growth factor receptor 1 (FGFR1), also known as basic fibroblast growth factor receptor 1, fms-related tyrosine kinase-2 / Pfeiffer syndrome, and CD331, is a receptor tyrosine kinase whose ligands are specific members of the fibroblast growth factor family. FGFR1 has been shown to be associated with Pfeiffer syndrome. Mice genetically engineered to lack a functional Fgfr1 gene (ortholog of the human FGFR1 gene) die in utero before 10.5 days of gestation. Embryos exhibit extensive deficiencies in the development and organization of mesoderm-derived tissues and the musculoskeletal system. The Fgfr1 gene appears critical for the truncation of embryonic structures and formation of muscle and bone tissues and thereby the normal formation of limbs, skull, outer, middle, and inner ear, neural tube, tail, and lower spine as well as normal hearing.