New pathophysiological mechanisms for hyperthyroidism.

From the analysis of accumulated data about adrenergic receptors, it was hypothesized that some mutations within the thyroid-stimulating hormone (TSH) receptor would activate it constitutively. As TSH positively controls the function, differentiation and growth of thyrocytes by cyclic AMP-dependent mechanisms, such somatic or germline mutations would cause readily identifiable phenotypes in the form of monoclonal hyperfunctional benign tumours or hereditary dominant hyperthyroidism, respectively. This hypothesis turned out to be correct: of 29 hyperfunctioning adenomas, 23 were found to have a mutation at various positions of the serpentine portion of the TSH receptor. In five families with autosomal dominant hyperthyroidism and one sporadic case, five additional different mutations were identified. Altogether, 20 different residues have been found mutated in toxic adenomas or toxic thyroid hyperplasia. It is tempting to speculate that as the TSH receptor is already 'noisy' in its wild-type state, it would be more readily activated by mutations than others.