In the following years, FGF23 turned out to be the long-sought “phosphatonin” that had already been postulated in the 1980s, when parabiosis experiments in hypophosphatemic Hyp mice had shown that the renal phosphate wasting and the hypophosphatemia in these mice were caused by a factor circulating in the blood (2). This evidence concerns the gene FGF23 and hypophosphatemia.