The contribution of testosterone to skeletal development and maintenance: lessons from the androgen insensitivity...

Although androgen status affects bone mass in women and men, an androgen requirement for skeletal normalcy has not been established. Women with androgen insensitivity syndrome (AIS) have 46,XY genotypes with androgen receptor abnormalities rendering them partially or completely refractory to androgen. Twenty-eight women with AIS (22 complete and 6 high grade partial), aged 11-65 yr, responded to questionnaires about health history, gonadal surgery, and exogenous estrogen use and underwent bone mineral density (BMD) assessment by dual energy x-ray absortiometry. BMD values at the lumbar spine and proximal femur were compared to age-specific female normative values and listed as z-scores. Average height for adults in this cohort, 174 cm (68.5 in.), was moderately increased compared with the average height of adult American women of 162.3 cm, with skewing toward higher values: 5 women exceeded 6 ft in height, and 30% of the 18 adult women with complete AIS exceeded 5 ft, 11 in. in height. The average lumbar spine and hip BMD z-scores of the 6 women with partial AIS did not differ from population norms. In contrast, the average lumbar spine BMD z-score of women with complete AIS was significantly reduced at -1.08 (P = 0.0003), whereas the average value for hip BMD did not differ from normal. When BMD was compared between women who reported good estrogen replacement therapy compliance and those who reported poor compliance, there was a significantly greater deficit at the spine for women with poor compliance (z = -2.15 +/- 0.15 vs. -0.75 +/- 0.28; P < .0001). Furthermore, hip BMD was also significantly reduced in the noncompliant group (z = -0.95 +/- .40). Comparison of BMD values to normative male standards gave z-score reductions (z = -1.81 +/- 0.36) greater than those observed with female standards. Because of the high prevalence of tall stature in this study sample, we calculated bone mineral apparent density, a variable that adjusts for differences in bone size. Even for the estrogen-compliant group, bone mineral apparent density z-scores were subnormal at both the spine (z = -1.3 +/- 0.43; P < 0.01) and the hip (z = -1.38 +/- 0.28; P = 0.017). Six women with complete AIS had sustained cortical bone fractures, of whom 3 reported multiple (>3) fractures. We conclude that even when compliance to exogenous estrogen use is excellent, women with complete AIS show moderate deficits in spine BMD, averaging close to 1 SD from normative means, and that with correction of BMD for bone size, skeletal deficits are magnified and include the proximal femur. The results suggest that severe osteopenia in some women with AIS probably reflects a component of inadequate estrogen replacement rather than androgen lack alone.