In 1989, scientists from Marquette University in Milwaukee, using animal models of parabiosis, postulated that a humoral factor was involved in the genesis of X-linked hypophosphatemia (XLH) [12] and, in 1994, a group from the Mayo Clinic, culturing cells from a tumor which caused hypophosphatemic OM, obtained a supernatant that inhibited tubular reabsorption of Pi, without increasing intracellular cAMP (i.e., it was not related to PTH) [13]. Here, PTH is linked to X-linked hypophosphatemia.