Estrogen-specific action on bone geometry and volumetric bone density: longitudinal observations in an adult with complete androgen insensitivity.
BACKGROUND
Sex steroids have distinct effects on bone growth and maintenance in men and women, mediated through their respective steroid receptors. Though most evidence is derived from animal studies, several concepts have been confirmed in humans by detection of specific mutations. In this report we describe changes in bone size and volumetric bone density in a complete androgen insensitive subject (CAIS) due to a mutation in the androgen receptor during 5 years of estrogen treatment.


METHODS
We present a case report of a 31 year old XY female with CAIS with a longitudinal follow-up for 5 years of areal and volumetric bone parameters. Areal and volumetric bone parameters were determined using dual-energy X-ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT). Sex steroids, LH, FSH and IGF-I were determined by immunoassay.


RESULTS
Complete androgen insensitivity syndrome was genetically confirmed by detection of the mutation Asp767Tyr in the androgen receptor gene. Bone size at presentation was found to be intermediate between male and female reference values. Low areal and volumetric bone density (both trabecular and cortical) was observed at baseline and improved gradually with estrogen treatment (+2% to 6.5%). Upon estrogen treatment, endosteal contraction (-1%) was demonstrated, with increasing cortical thickness (+3%), cortical area (+5%) and unchanged periosteal circumference.


CONCLUSIONS
During adult life, estrogens mediate endosteal bone apposition and volumetric bone density, without marked influence on periosteal bone apposition. The finding of a bone size intermediate between male and female supports testosterone as an essential mediator for periosteal bone expansion, but not as the sole stimulus for bone expansion during growth.
Department of Endocrinology, Ghent University Hospital, De Pintelaan 185, 9000 Ghent, Belgium. Youri.Taes@ugent.be
Youri
Y
Taes
Bruno
B
Lapauw
Sara
S
Vandewalle
Hans
H
Zmierczak
Stefan
S
Goemaere
Dirk
D
Vanderschueren
Jean-Marc
JM
Kaufman
Guy
G
T'Sjoen
D000279:Administration, Cutaneous; D000293:Adolescent; D000328:Adult; D013734:Androgen-Insensitivity Syndrome / Q000473:pathology*; D015415:Biomarkers / Q000378:metabolism; D015519:Bone Density / Q000187:drug effects*; D001842:Bone and Bones / Q000187:drug effects* / Q000473:pathology*; D004967:Estrogens / Q000008:administration & dosage / Q000494:pharmacology*; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D009929:Organ Size; D010521:Periosteum / Q000187:drug effects / Q000473:pathology
D015415:Biomarkers; D004967:Estrogens