The relationship between serum ghrelin and body composition with bone mineral density and QUS parameters in subjects with Rett syndrome.

Several studies have reported that females with Rett's syndrome frequently have marked decreases in bone mineral density (BMD). However, the pathogenesis of impaired bone status in RTT girls remains controversial. This study aimed to investigate whether ghrelin, an orexigenic peptide secreted by the stomach, was associated with body composition parameters, bone mineral density and quantitative ultrasound (QUS) in girls with Rett's syndrome. In 123 Rett girls (13.6±8.2 years) and in 55 similar age range controls we evaluated ghrelin serum levels, 25OHD, quantitative ultrasound parameters at phalanxes by Bone Profiler-IGEA (amplitude dependent speed of sound: AD-SoS and bone transmission time: BTT), total body bone mineral density (BMD-WB) by Hologic QDR 4500. Whole body mineral content (BMC-WB), BMC-WB/height, fat mass (FM), fat percentage and lean mass (LM) were determined by using the same DXA device. We found that serum ghrelin levels were significantly higher in the Rett patients with respect to the control group (p<0.05). In Rett girls ghrelin serum levels were inversely correlated with both age (R(2)=0.17, p<0.001) and BMI (R(2)=0.14, p<0.001). Moreover, in Rett subjects the values of BMD-WB, BMC-WB, BMC-WB/height and QUS parameters were significantly lower than in control subjects. Fat mass and lean mass were lower in Rett subjects than in controls, but the difference reached the statistical significance only for lean mass. In Rett girls ghrelin serum levels were not predictors of bone status. Instead, we found that in Rett subjects, lean mass, age and 25OHD were significant independent predictors of BMC-WB/h, whereas both age and height were independent predictors of BMD-WB. Moreover, AD-SoS was predicted by age, fat percentage and height; while BTT was predicted only by height. In conclusion, our findings indicate that ghrelin levels were higher in Rett girls with respect to healthy controls, and negatively associated with both DXA and QUS parameters. However, in our study ghrelin was not found to be an independent predictor of bone mass, so supporting the hypothesis that ghrelin is elevated in Rett subjects in a compensatory manner.