Apolipoprotein E polymorphism: A new genetic marker of hip fracture risk--The Study of Osteoporotic Fractures.

Hip fractures are common and devastating events. The apolipoprotein E*4 (APOE) allele, associated with Alzheimer's disease, has also been associated with osteoporosis in hemodialysis patients. We prospectively studied 1750 women, age >/=65 years, who underwent measurements of hip and calcaneal bone mineral density (BMD), were typed for APOE and followed for approximately 7.0 years for the occurrence of fractures and falls. Women with at least one APOE*4 allele had an increased risk of hip fracture, relative hazard (RH) (95% confidence interval) = 1.90 (1.05-3.41) and wrist fracture, RH = 1.67 (1.01-2.77) compared with women without APOE*4, even after adjusting for age, cognitive function, falling, and BMD. The effect of APOE*4 on hip fracture was greatest among women with additional (>/=3) other risk factors. Women with an APOE*4 allele were also likely to report a maternal history of fracture. The average number of falls per year did not differ by APOE*4: 0.46 for APOE*4 women and 0.41 for women without an APOE*4 allele. Women with an APOE*4 allele experienced greater weight loss which contributed to faster rates of bone loss. We conclude that women with the APOE*4 polymorphism are at substantially increased risk of hip and wrist fracture that is not explained by bone density, impaired cognitive function, or falling. Possible alternate explanations include an effect of APOE on vitamin K, bone turnover, or weight loss. The APOE polymorphism may be a candidate gene for hip fractures among community dwelling nondemented women.