Finally, several genes involved in TGF-β signalling were differentially expressed in HT thyroid tissue, including higher expression of TGFB1 itself, but also higher expression of inhibitory SMAD7 and lower expression of ligand binding TGFBR2 and the coreceptor TGFBR3. TGF-β is known to play an important role in restricting thyroid epithelial cell proliferation indicating that, despite higher expression of TGFB1, sensitivity to TGF-β is reduced in FHT, as has been observed for thyroid tumours in humans43,44. This evidence concerns the gene SMAD7 and thyroid tumor.