If systemic calcium levels drop, CASR signaling decreases, allowing PTH and PTHrP secretion, which induces renal retention of Ca+2, increased gut Ca+2 absorption, and eventually elevated bone resorption.108,109 Lorentzon et al. found that different CASR alleles are related to bone mineral density (BMD),110 and healthy adolescent girls with the S allele have lower BMD than individuals lacking the S allele, and Di et al.20 also verified that the CASR A986S polymorphism increased the risk of osteoporosis in aging males. This evidence concerns the gene CASR and osteoporosis.