FGFR3: Abbreviation for fibroblast growth factor receptor 3. Mutations in the FGFR3 gene are known to cause three different syndromes -- hypochondroplasia, achondroplasia, and thanatophoric dysplasia. These syndromes represent variations in severity. Hypochondroplasia is the mildest and thanatophoric dysplasia (also called thanatophoric dwarfism) is the most severe. In fact, thanatophoric dysplasia is a type of dwarfism in which death usually occurs in the first hours of life. FGF3 is an example of how different syndromes can result from mutations in a single gene.