ABSTRACT
Down syndrome (DS), the most common genetic cause of developmental disability, is characterized by intellectual disability and musculoskeletal disorders (Sago et al., 2000). Clinically, children with DS are described as having low tone which may affect muscle strength and motor skills. Many studies show that individuals with DS, particularly the males, have lower than normal bone mineral density (Angelopoulou et al., 1999; Sepulveda et al., 1995). It may be a cause of early onset osteoporosis. The significant increase in the life expectancy of individuals with Down syndrome (Englund et al., 2013) could increase the prevalence of this disease. The amount of bone mass in adolescence is a key determinant of the amount of bone mass in adulthood. The ultimate target population for osteoporosis prophylaxis may indeed be the young, rather than the elderly. The clinical assessment of osteoporosis relies mainly on bone mineral density (BMD) measurements using dual-energy X-ray absorptiometry (DXA). DXA does not provide any information on bone structure and matrix factors. QUS variables, in addition to bone density (Brunader and Shelton, 2002), measure some characteristics of bone quality such as micro architecture, elasticity and density (Njeh et al., 1997). The link existing between muscle and bone (“functional muscle-bone unit”) is well described today (Schoenau and Fricke, 2006). The key idea is the analysis of bone parameters under consideration of muscle function. The muscle contraction places the greatest physiological load on bone, and so the strength of bone must adapt to muscle strength (Schoenau, 2006). It can be argued that a deficit of muscle contraction represents the major cause of bone weakness (secondary bone disease). Therefore, if muscle hypotonia is reported in subjects with Down syndrome, a resulting osteopenia would be observed. The purpose of this study was to assess the bone status of children with DS as well as their body stability as surrogate of muscle tonicity.
