Background: Turner syndrome (TS) associates with decreased bone mineral density and altered bone geometry, a risk factors leading to increased fracture rate. Although hypogonadism or SHOX gene haploinsufficiency are the probable causes, the exact mechanism remains unclarified. Particularly, the muscle function as an important determinant of bone strength has yet not been widely studied in TS patients.
Objective and hypotheses: We hypothesised there is muscle dysfunction leading to increased fracture rate in TS patients. Secondary aim was to describe the influence of pubertal stage, hormone therapy, fracture history, and genotype.
Patients and methods: All TS patients consenting to the study and having no other chronic disease were included (60 patients, age 13.7±4.5 years). Age- and weight-specific Z-scores of muscle parameters were calculated based on control group of 432 healthy girls. A Leonardo Mechanograph® Ground Reaction Force Platform was used to assess muscle force (Fmax) by the multiple one-legged hoping test and muscle power (Pmax) by the single two-legged jump test. Muscle function parameters were related to body weight (Fmax/BW) and body mass (Pmax/mass), respectively.
Results: While Fmax and Fmax/BW were normal (mean weight-specific Z-scores 0.11±0.77, P=0.27, and 0.046±0.62, P=0.55), Pmax and Pmax/mass were decreased in TS patients (Z-scores −0.93±1.5, P<0.001, and −0.45±0.58, P<0.001) compared to healthy controls. The muscle function parameters were not significantly influenced by menarcheal stage, hormone therapy duration, fracture history or genotype (linear regression adjusted for age, weight and height; P>0.05 for all).
Conclusion: Fmax, a principal determinant of bone strength, is normal in TS. The changes in bone quality and structure in TS are thus not likely related to inadequate mechanical loading but rather represent a primary bone deficit. A decreased Pmax represents a novel indicator of impaired muscle coordination in TS.
18 Sep 2014 - 20 Sep 2014