CREB1 and hypophosphatemia: Several OGD patients caused by activating mutations of FGFR1 present hypophosphatemia and increased serum level of FGF23.132 Inhibition of FGFR1 decreased FGF23 mRNA expression in the bone.590 Integrative nuclear FGFR1 promotes FGF23 transcription by activating the transcription factor CREB.591 HMW isoform of FGF2 (HMWFGF2), the ligand for nuclear FGFR1, stimulates FGF23 expression.592 Transgenic mice with overexpression of HMW FGF2 in immature and mature osteoblasts display increased FGF23 level, hypophosphatemia, and rickets.592