Endocrine involvement in children with beta-thalassaemia major. Transverse and longitudinal studies. I. Pituitary-thyroidal axis function and its correlation with serum ferritin levels.
Thyroid function was investigated by a TRH test in 24 clinically prepubertal children, 3-15 years old with beta-thalassaemia major; in 7 of them the test was repeated once and in 2 twice at intervals of at least 12 months. Basal T4, T3, TBG and TSH levels and the TSH levels during a TRH test were determined and correlated with age and serum ferritin levels. Basal serum T4, T3 and TBG levels were lower and serum TSH levels were higher during the test and in the basal state in thalassaemia major children than in control children. These results show a compensated sub-clinical primary hypothyroidism. The transversal study did not show any significant correlation between the hormonal parameters studied and chronological age or serum ferritin levels. In contrast, the longitudinal study showed a significant correlation between pituitary-thyroidal axis function and siderosis (positive correlations between the variations of TSH levels as delta, peak, 30 and 45 min values and the variations of serum ferritin levels). The thyroid impairment seems not to be correlated with serum ferritin levels in the transversal study because of the presence of an individual different sensitivity of the gland to the iron overload. The ferritin dependence of this impairment is shown only by longitudinal studies where individual differences in sensitivity of the gland are absent.(ABSTRACT TRUNCATED AT 250 WORDS)