Free and bound leptin in prepubertal children with Down's syndrome and different degrees of adiposity

Objective: To evaluate plasma total, free (FL) and protein-bound (BL) leptin in children with Down's syndrome (DS) and different degrees of adiposity and its relationship with thyroid stimulating hormone (TSH), free thyroxine (FT4), and free triiodothyronine (FT3). Subjects: A total of 24 prepubertal clinically euthyroid DS children. Methods: Plasma leptin, TSH, FT4, and FT3 concentrations were determined by immunometric /radioimmunologic assays. FL and BL were evaluated by fast protein liquid chromatography. Results: In DS children, leptin circulates in two fractions corresponding to BL and FL. The amount of BL and FL is negatively and positively correlated to body mass index (BMI), respectively. Plasma leptin concentrations correlate with BMI, but not with TSH, FT4, and FT3. Conclusions: In prepubertal DS children, leptin circulates as both BL and FL, correlates with adiposity and its concentration appears independent of thyroid function.