FGF23 and hypophosphatemia: Cutaneous skeletal hypophosphatemia syndrome (CSHS) is characterized by the association of dysplastic skeletal lesions, congenital skin nevi of epidermal and/or melanocytic origin (including epidermal nevi [EN], giant congenital melanocytic nevi [GCMN], and phacomatosis pigmentokeratotica [PPK]), and FGF23-mediated hypophosphatemia (1).