Bone mass, bone turnover, vitamin D, and estrogen receptor gene polymorphisms in male to female transsexuals: effects of estrogenic treatment on bone metabolism of the male.

The effect of chronic administration of estrogens on bone and mineral metabolism in men is not known. We have studied the effect of chronic administration of estrogens on bone mineral metabolism in a group of transsexual (TS) Canarian men, who were taking estrogens for a minimum of 3 years. This is a cross-sectional study of cases and controls and we studied biochemical markers of bone remodeling, bone mineral density (BMD), and selected biochemical and hormonal features. TS subjects had shorter stature than controls, and after adjusting for height and weight, we found that they had lower values for serum-free testosterone and higher values for BMD, both in the lumbar spine and in femoral neck. Biochemistry, bone remodeling markers, and calcitropic hormone values were similar in both groups. Finally, the distributions of vitamin D receptor (BsmI) and estrogen receptor (ER-Pvu and ER-Xba) polymorphisms were also similar in both groups. We conclude that the chronic administration of estrogens in men may produce an increase in serum estradiol, a decrease in free testosterone levels, and an increase in BMD-both in lumbar spine and in femoral neck. We found no association between the transsexual phenotype and the distribution of vitamin D receptor (BsmI) and estrogen receptor (ER-Pvu and ER-Xba).