Increased metaphyseal bone mass in the young X-linked hypophosphatemic (Hyp) mouse

A study of skeletal development in X-linked hypophosphatemic (Hyp) mice revealed that radiographic characteristics of the disease appear as early as seven days after birth and that an unexpected transitory metaphyseal radio-opacity occurs in the long bones of the Hyp mice. Hyperostotic osteomalacia appears at the first week, peaks at the third week, and starts to fade by the fourth week. Undecalcified bone sections of three-week-old mice revealed an increased amount of trabecular bone in the metaphysis of the Hyp mice accounting for the increased radio-opacity. Blood chemistry data in three-week-old mice showed a low plasma phosphate, a slight hypocalcemia and elevated alkaline phosphatase. Three-week-old Hyp mice had a reduced percentage of magnesium in their bone ash compared to normal. The blood chemistry data resembled those of adult Hyp mice and did not explain the increased metaphyseal bone mass. The mechanism underlying this genetic abnormality of bone is unclear.