The −844 A > G polymorphism (rs2227631) is located in the promotor region of the PAI-1 gene, leads to increased PAI-1 protein levels, and is associated with osteonecrosis of the femoral head, osteoporotic vertebral compression fracture [17], and acute coronary syndrome [18,19]. The gene discussed is SERPINE1; the disease is familial avascular necrosis of femoral head.