The gain of function (GoF) mutation of the cleavage site of FGF23 (R176Q/W and R179Q/W) produces FGF23 elevation and is the cause of autosomal dominant hypophosphatemic rickets (ADHR) (MIM 193100), featured by vitamin D-resistant rickets, hypophosphatemia, renal phosphate wasting with low or normal levels of 1,25(OH)2D3, high alkaline phosphatase (ALP) and osteomalacia. The gene discussed is FGF23; the disease is osteomalacia.