(B) Radiographs of 20-mo-old male wt, XpdTTD/†XPCS, and XpdTTD/TTD mice. Ageing XpdTTD/TTD mice develop kyphosis (curvature of the spinal column) and reduction of bone mineral density as shown in the 6–8 segment of the tail vertebrae counted from the pelvis (see close-up at right). Note the absence of these features in the XpdTTD / † XPCS mouse.