Serum levels of FGF23, a phosphaturic hormone that suppresses 1,25(OH)2-vitamin D3 production in kidneys [24], increase early in the course of CKD and reach levels that are several hundred times the normal range in patients with advanced CKD and end-stage renal disease (ESRD) [2]. The gene discussed is FGF23; the disease is stage 5 chronic kidney disease.