"Results show that urine pyrophosphate (PPI) levels are increased in Npt2a-/- mice when compared to WT possibly to protect from renal mineralization in the setting of hyperphosphaturia. However the presence of two hypomorphic Enpp1asj/asj alleles decreases urine PPi and worsens renal calcium phosphate deposit formation in Npt2a-/- mice."xsd:string