INTESTINAL MALABSORPTION OF 2ND CA-45 IN YOUNG GY MICE, A 2ND MODEL FOR X-LINKED HYPOPHOSPHATEMIA

X-linked hypophosphatemia, a common metabolic bone disease in humans a nd mice (the Hyp and Gy mutations), is characterized by decreased plas ma phosphate, decreased renal tubular reabsorption of phosphate, ricke ts, and osteomalacia. The question of whether intestinal malabsorption of calcium contributes to the bone disease is controversial. Intestin al absorption of Ca-45 was studied in three different mouse colonies: Gy on B6C3H background, Hyp on B6C3H background, and Hyp on C57BL/6J b ackground, all at 4 weeks of age. The duodenum was isolated by sutures , and Ca-45 in a 150 mM NaCl and 2 mM CaCl2 solution at pH 7.2 was inj ected into the lumen. Absorption was measured by the amount of Ca-45 r emaining in the lumen and by the plasma isotope level. The Gy and Hyp mice of both sexes significantly malabsorbed Ca-45 at 4 weeks of age c ompared to normal littermates. Following the 4 week study, intestinal absorption was measured at 2, 7-8, and 12 weeks of age in normal and G y mice on the B6C3H background. At 2 and 7-8 weeks of age, the Gy male s significantly malabsorbed Ca-45 compared to their normal littermates . Serum 1,25-dihydroxyvitamin D was not significantly altered in Gy ma les at 4 weeks of age. This suggests the possibility of resistance of the intestine to stimulation. Malabsorption of calcium in young Gy and Hyp mice may exacerbate the low mineralization in their rachitic bone disease.