Interestingly, urine PPi in 10 weeks old Npt2a-/- mice is higher than in 4 weeks old weanlings (1257±272 micromole/l vs. 149.4 ± 28.8 micromole/l). This may be a developmental change of urine PPi over the first 10 weeks of life and could be a contributing factor explaining the initial observation in Npt2a-/- mice reported by the Tenenhouse lab , that renal calcifications peak with weaning age and subsequently decrease during adult life in these mice.