FGFR3 and achondroplasia: Gain-of-function mutations in both human and mice FGFR3 result in achondroplasia characterized by a short limb phenotype (Iwata et al., 2000, 2001; Lee et al., 2017; Segev et al., 2000), while knockout of FGFR3 in mice produces a long limb phenotype (Eswarakumar and Schlessinger, 2007; Toydemir et al., 2006; Tseng et al., 2010; Wen et al., 2016) (Table 1).