The objective of this study is to compare the length and density of bones in transgenic mice overexpressing S-100B with control mice, at different ages, in order to see if significant differences exist and if these differences change throughout the life of the mouse. The transgenic mouse used in this study is an animal model of Down Syndrome. In humans, Down Syndrome is known to effect bone development, including craniofacial bones, bones in the limbs, and digits in the hands and feet. In addition, people with Down Syndrome generally have a significantly lower BMD (bone mineral density) than individuals unaffected by the disorder, making them more prone to Osteoporosis. In this study, three age groups of mice were used, 28 days old, four to five months old and nine months old. Each group consisted of a total of six animals, three control and three experimental. The youngest and oldest groups were both comprised of all females and the middle-aged group was comprised of all males. The animals were each x-rayed in full body positions so that almost the entire skeleton was visible. Then, three separate experimenters each took nineteen different bone measurements using a very accurate, digital caliber (measuring to the nearest hundredth of a millimeter). As preliminary results, differences can be seen between the experimental and control groups for several of the bone measurements and for the different age groups. In addition to the x-rays, a second bone scan will be performed within the next few months. In preparation for the scan, six animals were sacrificed, 3 from the experimental group and three from the control group. The femur bones and a portion of the spinal columns from each are currently being refrigerated and stored in alcohol. The scan will be performed on a machine that uses two separate x-ray beams in order to produce images. These images will achieve extremely high resolution and will allow us to examine the bones more closely, including a measurement of bone density.