Rearing and step climbing behavior of X-linked hypophosphatemic (Hyp) mice

Hyp mice are a model for X-linked hypophosphatemia, the most common form of vitamin D-resistant rickets. Previous reports indicate alterations in the nervous system of these mice. The present study examined rearing and step climbing behavior in Hyp mice in the staircase test. We found that male Hyp mice have large reductions in both the number of rears and steps climbed when compared to normal male mice. When compared to normal female mice, female Hyp mice have a small reduction in the number of steps climbed but no significant reduction in the number of rears. However, they have greater rearing and climbing activity than male Hyp mice. These reductions in activity are not correlated with the severity of bone disease. Gonadectomy had no effect on activity in male mice but reduced activity comparably in both Hyp and normal female mice. We conclude that Hyp mice have altered behavior in the staircase test and that the magnitude and type of the alteration is influenced by the sex of the animal.