Muscle Morphology, Function and Bone Mineralization in Girls with Turner's Syndrome

Abstract

The purposes of this research were i) to compare skeletal muscle development, function and bone mineralization in girls with Turner's syndrome (TS) (n=7) and healthy control girls (n=13), and ii) to examine the effects of growth hormone (GH) and estrogen (E2) therapy on musculoskeletal variables using a case study approach in two TS girls and one healthy control. Anthropometric measurements included: height, body mass, percent fat, and muscle and bone cross-sectional areas and muscle density from computed axial tomography. Evoked peak twitch torque (TT), maximal voluntary strength (MVC), contractile properties and motor unit activation (MUA) were determined for the elbow flexors (EF), plantar flexors (PF) and the knee extensors (KE). Total body and segmental bone mineral content (BMC) and density (BMD) were measured with dual photon absorptiometry. Dietary intake and participation in physical activity were assessed from questionnaires. Absolute strength (TT and MVC) for the TS patients was lower than that of the control girls' for EF, PF and KE and could not be accounted for by differences in muscle density, contractile properties, MUA, diet or level of physical activity. There were no significant differences in evoked and voluntary strength corrected for muscle area and lever length between the TS and control girls. Total body, leg and trunk BMC were lower in the TS girls compared to the controls; however, when normalized for body mass and bone width, total body BMC (g/kg) and BMD respectively were comparable between the TS and control girls. Growth hormone therapy increased height and lean mass, and reduced adiposity. All measures of arm strength increased but leg strength (PF & KE) was reduced. These may reflect the lack of GH effects on the leg muscle or possibly a detraining effect from the subject's withdraw! from a skating program. Growth hormone therapy resulted in increased leg BMC which may reflect a lag time between bone growth and subsequent mineralization. Estrogen therapy resulted in increased muscle area, fat mass and strength at all 3 muscle groups. The latter may be due to the laying down of muscle proteins as a result of estrogen therapy. The lack of major changes in BMC or BMD probably reflects the short duration of the follow-up period. Further studies are required with larger numbers for longer treatment periods in order to make conclusive statements about the effects of hormonal therapy on muscle function and bone mineralization in Turner's patients.