Osteoporotic fractures can be catastrophic. There are 1.7 million hip fractures per year worldwide. About 25 percent of the people who suffer hip fractures die in six months, and many require permanent institutional care. Humpback posturing in women is a visible sign of osteoporosis and signifies the crush of life's passage. Bone density achieved in early adulthood is the major determinant of risk of osteoporotic fracture.
Bone density depends on complex interactions between the osteoclast and osteoblast.
It is controlled by multiple systemic hormones, local cytokines, and growth regulation factors. It has previously been shown that osteoporotic fracture as a result of low bone density is under strong genetic control. It has been known for 20 years that bone density varies less in monozygotic twins than in dizygotic twins. They showed that common allelic variants in the gene encoding for the vitamin D receptor can predict the bone mineral density and account for up to 75 percent of the total genetic effect on bone density in healthy individuals. There are two versions of the specific gene that direct construction of the receptor, called B and b. The B allele predicts the weaker skeleton apparently because a mutation of the receptor gene encodes a dysfunctional receptor.