These high levels of 1,25(OH)2D3 are suggestive of end-organ resistance [189,190] and have been demonstrated to be caused by the overexpression of a VDR-independent VDRE-binding protein which interferes with vitamin D-regulated transactivation [191], making this species a useful model for hereditary vitamin D resistant rickets (HVDRR). The gene discussed is VDR; the disease is vitamin D-dependent rickets, type 2.