A2M and osteoporosis: These data, together with studies showing that A2M plasma levels and BM-MSC A2M promoter methylation levels are negatively and positively correlated, respectively, with age in humans (Birkenmeier et al., 2003) and that genetic deletion of A2m results in deleterious skeletal alterations in mature mice, identify A2M as a putative disease modifying protein in senile osteoporosis.