FGF23 signals via a complex of anFGF receptor (FGFR1(IIIc)) and Klotho [41]; mice with a loss-of-functionmutation in Klotho develop osteoporosis amongst otherabnormalities, and modest evidence of association of Klotho withBMD has been reported in several studies [42], [43], [44], [45]. The gene discussed is FGFR1; the disease is osteoporosis.