The absence of this proteolytic activity in humans through the FGF23 gene mutations R176Q, R176W, R179Q, and R179W are causative for autosomal dominant hypophosphatemic rickets (ADHR), characterized by elevated intact FGF23 and hypophosphatemia (21) (Figure 2). The gene discussed is FGF23; the disease is autosomal dominant hypophosphatemic rickets.