PTH and Hypercalciuria: However, homozygous ablation of Npt2a in mice (Npt2a-/-) results in increased urinary phosphate excretion, hypophosphatemia, an appropriate elevation in the serum levels of 1,25-dihydroxyvitamin D, hypercalcemia, decreased serum parathyroid hormone levels, increased serum alkaline phosphatase activity and hypercalciuria (see below) [66].