To determine if the deleterious effect of FVIII deficiency is unique or persists in the setting of a different genetic form of hemophilia, we examined the skeletal consequences of FIX deficiency in one group of juvenile male mice (10-week-old) and another group of adult (20-week-old) male mice. This evidence concerns the gene F8 and hyperinsulinemic hypoglycemia, familial, 4.