The aim of this study was to determine the body composition and resting metabolic rate (RMR) of girls with Rett syndrome (RS) (n=15) and to compare them with an equally handicapped group of girls with developmental disabilities (DD) (n=13). Body composition was measured by bioelectrical impedance analysis and RMR  -  the amount of energy expended while at rest  -  by indirect calorimetry. Weight, height, body mass index (BMI), BMI percentiles and food intake were all measured and calculated by standardized procedures. Feeding time, ambulatory status and ability to self-feed were also assessed. Due to the sampling, there were no significant differences in age, height, weight, BMI, BMI percentiles and ambulatory status. Significant differences between groups were found for lower percentage lean body mass (LBM) (64.2±14.6 vs. 84.4±24.6) and higher absolute and relative fat mass (FM) in RS. RMR values adjusted for LBM were significantly higher in the group of girls with RS (approximately 160 kcal/day), indicating that higher energy expenditure is a component of increased risk of severely low body weight.

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