Histomorphometric analyses [50] of the long bones (Table 3) corroborated the radiologic evidence of age-related bone loss. Bone volume (BV/TV), newly formed osteoid (OV/TV), and mineral apposition rate (MAR) were all significantly reduced in 12-month-old Sam68+/+ mice compared with 4-month-old Sam68+/+ mice. These reductions were associated with a significant increase in marrow fat (FV/TV) and decreased numbers of osteoblasts (nOB/TV) and osteoclasts (nOC/TV) per tissue volume (Table 3). These results were in contrast to those of the 12-month-old Sam68−/− mice in which all histomorphometric parameters, including marrow fat, resembled those of young mice of either genotype (Table 3). When cells were expressed as a function of the bone perimeter (nOB/BP, nOC/BP), there were no statistical differences and the ratio of osteoblasts to osteoclasts was similar in all groups of mice (Table 3).