FGFR3 and Osteopenia: Total deletion of Fgfr3 results in osteopenia and thinner cortical bone in adult mice (Eswarakumar and Schlessinger, 2007; Valverde-Franco et al., 2004), and the absence of Fgfr3 increases early OB differentiation but interferes with the cells' normal activity, thus leading to defective mineralization.