ESPE Abstracts

Background: Fibroblast growth factor 21 (FGF-21) is a complex molecule involved in lipid and glucose metabolism. FGF-21 shares biochemical pathways and sites of action with thyroid hormones. Current data correlate FGF-21 levels to thyroid function. The aim of the present study was to investigate possible associations among FGF-21 levels, resting metabolic rate (RMR), lipidemic profile and L-thyroxin replacement therapy treatment in children and adolescents with Hashimoto’s thyroiditis and hypothyroidism.

Methods: Sixty children and adolescents (age range 5-18 year old), with newly diagnosed Hashimoto’s thyroiditis (30 in hypothyroidism, 30 in euthyroidism) and 30 age and gender matched healthy participants (control group) were enrolled. Anthropometric data were recorded; biochemical parameters RMR and serum FGF-21 levels were assessed in all participants. Participants with Hashimoto’s thyroiditis and hypothyroidism were thereafter administered L-thyroxin replacement therapy. Six months after initiation of L-thyroxin medication, serum FGF-21 levels were re-evaluated.

Results: At baseline, serum FGF-21 levels were measured lower in the hypothyroidism group compared to the control group, but this difference was not statistically significant (P > 0.05). Despite the increase in serum FGF-21 levels after 6 months of L-thyroxin treatment, this augmentation did not reach significance (P > 0.05). Free thyroxin levels correlated positively to FGF-21 levels in both the total study population (r = 0.399, P < 0.01) and in the group with hypothyroidism at baseline (r = 0.385, P < 0.05). Participants with hypothyroidism and euthyroidism presented elevated triglyceride levels (P < 0.05). L-thyroxin treatment had no impact on RMR, lipid concentrations or glycemic parameters. An increase in fat mass and free fat mass was reported in the hypothyroidism group after L-thyroxin administration, independently of serum FGF-21 levels.

Conclusions: In the present novel study of FGF21 levels in youngsters with hypothyroidism due to Hashimoto’s thyroiditis, serum FGF21 levels are measured lower than in healthy individuals and increased after treatment with L-thyroxin, although without statistical significance. Further studies with a large number of young patients with severe hypothyroidism due to Hashimoto’s thyroiditis are needed to confirm the association between FGF-21 levels and thyroid function.