Bone Abstracts

Introduction: We describe a monozygotic twin pair, of which one boy was diagnosed with anorchia. Both were followed-up till age 17.

Case report: At birth, in one twin 46 XY boy (A), testes were not palpable while his brother (B) was unaffected. Stimulation with human chorionic gonadotrophin (hCG) and orchidopexia were unsuccessful at age 3. A second hCG-stimulation test was performed at age 8, where serum testosterone response failed to increase. No testicular tissue was detected by abdominal laparoscopy. At the age of 10.5, when the bone age was 11.6 years both in A and B, low dose testosterone substitution therapy (25 mg/2 weeks) was started. Before puberty induction, A and B had similar weight and height. During puberty, a slightly faster increase in weight (A/B 11–19%) and height (A/B 3–7%) was observed in A. A and B ended up with a similar and normal final height, weight, arm span and sitting height. Secondary sexual characteristics developed normally in both brothers. At the age of 17, bone mineral density, body composition (dual X-ray absorptiometry, DXA-scan), volumetric bone parameters at forearm and calf (peripheral quantitative CT-scan) were evaluated. We observed similar bone mineral density at the lumbar spine, total hip, distal radius and whole body (DXA, A and B<5%). Fat percentage was 14% in A vs 11% in B. Trabecular (distal radius) and cortical volumetric bone parameters (mid and proximal tibia) were comparable (A and B <0.5%). However, at one cortical site (proximal radius), A had a smaller cortical bone size with a thicker cortex (all 10–20%).

Conclusion: Low dose testosterone substitution in bilateral anorchia, guided by the pubertal evolution in the healthy twin, led to a comparable pubertal development, final height and bone mineral density. Moreover, testosterone did not seem to be necessary for normal increase in length before puberty.