Also, hyperphosphatemia and increased PTH and calcitriol activity increase the production of fibroblast growth factor 23 (FGF23) from osteocystic cells in bone, which is responsible for the decrease in P renal reabsorption (Haussler et al., 2012; Fukumoto, 2014). The gene discussed is FGF23; the disease is hyperphosphatemia.