Thyroid hormones influences sex steroid binding protein levels in infancy: study in congenital hypothyroidism.

In order to test the hypothesis of a role of thyroid hormones on the circulating levels of sex steroid binding protein (SHBG) in children, SHBG levels were determined in 15 infants with congenital hypothyroidism at diagnosis and during the first 18 months of T4 therapy and in a separate group of 13 children with congenital hypothyroidism (7.1 +/- 0.5 yr, mean +/- SD), treated before 1 month of age, both during adequate L-T4 therapy and 4 weeks after withdrawing therapy. SHBG levels were significantly lower in hypothyroid infants than in controls (48.2 +/- 6.5 vs. 77.8 +/- 7.9 nmol/L; P less than 0.01), and significantly lower in infants with athyreosis compared to those with ectopic or eutopic glands (P less than 0.05). In patients with low values at diagnosis, SHBG increased rapidly and remained normal during LT4 therapy. After 1.5-18 months of treatment, a positive correlation (P less than 0.01) was found between SHBG, FT4, and FT3 levels. In older hypothyroid children, 4 weeks after withdrawal of therapy a significant (P less than 0.05) decrease in SHBG concentrations was observed. Analysis of these results as well as previous reports in adults, indicates that thyroid hormones influence SHBG concentrations in infants and children. This study also indicates that thyroid hormones may play a role in the physiological postnatal increase of SHBG.