In iodine deficiency areas, activating mutations in the TSH receptor and Gs-alpha gene are found in the majority of toxic thyroid adenomas and in some toxic goiter nodules. Since TSH receptor and Gs-alpha gene mutations are very rare in areas with high iodine supply, iodine deficiency has been suspected to favor the occurrence of these mutations by yet unknown pathways. However, TSH receptor and Gs-alpha gene mutations alone are not sufficient to cause toxic adenomas and nodules. There is compelling evidence that other secondary and cAMP-independent mechanisms, including enhanced expression of various growth factors, their corresponding receptors and of signaling proteins, may affect the mutated cell and thus promote cell proliferation and in turn generation of the tumor.