Association between androgen receptor gene polymorphism and bone density in older women using hormone replacement therapy.

Objective: The objective of this study was to investigate the relationship between bone mineral density (BMD) and both CAG repeat polymorphism of the androgen receptor (AR) gene and skewed X chromosome inactivation (SI) in postmenopausal women.

Methods: BMD was measured by DEXA. Both the number and the X-weighted biallelic mean of the CAG repeats of AR were analysed by PCR, before and after DNA digestion with methylation-sensitive HpaII in 192 healthy Caucasian postmenopausal women.

Results: The number of CAG repeats ranged from 10 to 34, with a median value of 22. CAG)(n< or =22) and CAG)(n> or =23) alleles were designated as short and long alleles, respectively. In women using hormone replacement therapy (HRT) (n=81), lumbar spine BMD was significantly lower, and femoral neck and total body BMD marginally lower in those with long-long alleles when compared with those with other genotypes. SI (> or =80%) was observed in 24% of the women and was not associated with BMD. In women using HRT, femoral neck BMD was significantly lower, and lumbar spine and total body BMD marginally lower in those whose X-weighted CAG repeat biallelic was greater than 22.59 (median value) when compared to other genotypes. These results were not found in women not using HRT.

Conclusion: In conclusion, our results suggest that BMD may be associated with AR gene polymorphism in postmenopausal women using HRT but not with SI. Further studies are needed to investigate the mechanisms of the interaction between HRT, BMD and AR found in the present study.