Fibroblast growth factor 23 (FGF23) is considered a causative gene in tumor-induced osteomalacia (TIO), including low-phosphorus (P) rickets/osteomalacia with P reabsorption failure in the renal tubules and autosomal dominant hypophosphatemic rickets/osteomalacia (ADHR) [1,2]. The gene discussed is FGF23; the disease is rickets.