PHEX and X-linked hypophosphatemia: Mineralization defects and paradoxical mineralization of entheses are the hallmarks of X-linked hypophosphatemia (XLH) (Polisson et al., 1985; Reid et al., 1989), a rare skeletal disease caused by inactivating mutations in the phosphate-regulating endopeptidase homolog X-linked (PHEX) gene (Sabbagh et al., 2000; Gaucher et al., 2009).