Mice that are homozygous for the targeted mutation are viable and fertile, and do not display any gross physical or behavioral abnormalities. No gene product (mRNA or protein) is detected by Northern blot analysis of bone, kidney, liver or lung, or by Western blot analysis of kidney. Homozygotes are smaller in size and have reduced weight compared to wildtype littermates. Secondary ossification defects revealed at weaning are followed by compensatory bone development. Mutant mice exhibit increased urinary excretion of inorganic phosphate and calcium, diet dependent hypercalciuria and hypercalcemia, as well as decreased serum parathyroid hormone levels, increased serum alkaline phosphatase activity, and elevated serum 1,25-dihyudroxyvitamin D. Homozygous mice do not respond to dietary challenges of low inorganic phosphate or parathyroid hormone content. Calcium and inorganic phosphate containing renal stones, nephrocalcinosis, are found in homozygotes at all ages. This mutant mouse strain may be useful in studies of hereditary hypophosphatemic rickets with hypercalciuria, HHRH, and familial hypercalciuria.
