Abstract
Objective: Turner syndrome (TS) is caused by partial or complete loss of an X chromosome and characterized by short stature an amenorrhea. This condition is also associated with osteoporosis and frequent fractures.
The aims were to determine volumetric bone mineral density and bone strength, to measure muscle function, to evaluate their relationships and differences from healthy controls, and to test associations with the duration of hormone replacement therapy and the incidence of fractures. Patients, material and methods: Included in the study were 67 (39) girls with Turner syndrome.
Volumetric bone mineral density (vBMD) and bone strength parameters at the radius were determined by peripheral quantitative computed tomography (pQCT) and compared with the published reference norms. For measurements at the tibia/fibula, a control group of 67 healthy girls was included.
Trabecular BMD and bone strength were measured at the metaphysis (bone strength index, BSI) and diaphysis (strength strain index, SSI) of the tibia using pQCT. The impact of TS on the muscle-bone unit was tested by multiple linear regression.
Results: Trabecular vBMD at the radius was significantly reduced in TS (mean Z-score 0.7 +- 1.3; p < 0.001) compared to the normal values; cortical vBMD adjusted for cortical thickness was increased (Z-score 1.1 +- 1.0; p < 0.001). TS was not significantly associated with Fmax after adjustment for age, height and weight; however, there were negative associations with trabecular vBMD (coefficient -0.22 +- 0.045, p < 0.001) and both bone strength indices at the tibia (coefficients -0.24 +- 0.07, p < 0.001 for BSI and -0.096 +- 0.035, p < 0.01 for SSI).
With identical Fmax, BSI and SSI were reduced by 18 % (p < 0.01) and 7 % (p = 0.027), respectively, in TS patients as compared with healthy girls. Neither therapy nor the incidence of fractures had significant effects on the tested muscle and bone parameters.
Conclusion: In girls with TS, the same muscle strength is associated with lower bone strength as compared with their healthy counterparts. This is probably due to changes in the sensitivity of bones to mechanical loading.