DMP1 and hypophosphatemia: Even though DMP-1 is weakly expressed in chondrocytes (Fig. 1D),(26) the Dmp1 null rickets phenotype is likely attributable to hypophosphatemia.(6) Here we show that the hypertrophic chondrocyte zone in Dmp1 null mice is remarkably expanded with few changes in other growth plate zones at the age of 10 days, as revealed by Safranin O staining (Fig. 4C, upper middle panel).