Skeletal effects of long-term estrogen and testosterone replacement treatment in a man with congenital aromatase deficiency: evidences of a priming effect of estrogen for sex steroids action on bone.

The relative contribution of each sex steroid (i.e. estrogen and androgen) on bone in men and the relationships among sex steroids and changes in BMD and bone strength are still unknown. A defective BMD of bone tissue is constantly present in men with aromatase deficiency. This study evaluates the effects of different regimens of treatment with sex steroids over 7.3 years follow-up on BMD in an adult man affected by aromatase deficiency and by a concomitant mild hypogonadism, as previously described. The aim of the study is to provide additional data on the relative roles of androgens and estrogens in male bone metabolism. The effects of testosterone (T) treatment alone and estrogen (tE2) treatment alone as well as the effects of the combined treatment with testosterone and estradiol (T plus tE2) on areal BMD (aBMD) at dual-energy X-ray absorptiometry (DXA) and the effects of T plus tE2 on volumetric BMD (vBMD), particular at cortical site, measured by peripheral quantitative computed tomography (pQCT), are investigated. Hormones and markers of bone turnover were monitored during all phases of the study. Treatment with tE2 normalized serum estradiol, but only the combined treatment with T plus tE2 normalized both serum estradiol and testosterone. Markers of bone turnover reached a pattern close to normality during T plus tE2. The aBMD was little modified by T, but increased more during tE2. T plus tE2 resulted in a further increase in both aBMD at DXA and vBMD at pQCT. Cortical thickness increased during T plus tE2 both in radius and tibia. Only the combined treatment led to optimal parameters of aBMD suggesting that testosterone needs estrogens as a permissive factor for a direct androgen anabolic action on bone in men.