Thyrotropin receptor mutations in hyperfunctioning thyroid adenomas from Brazil

Constitutively activating mutations in the thyrotropin (TSH) receptor have been identified as a major molecular cause of hyperfunctioning thyroid aden omas. A smaller subset of these benign tumors is caused by constitutive act ivation of the adenylyl cyclase cascade by somatic mutations in the Gs alph a gene. In this study, we analyzed hyperfunctioning thyroid adenomas from s even Brazilian patients for TSH receptor and G(s alpha) gene mutations. Sol itary autonomous thyroid adenomas were identified by ultrasound and scintig raphy, and DNA was extracted from adenomatous and periadenomatous tissue. E xons 9 and 10 of the TSH receptor gene, and exons 8 and 9 of the Gs alpha g ene, were amplified by polymerase chain reaction (PCR) and subjected to dir ect sequence analysis. Six of seven adenomas harbored heterozygous mutation s known to confer constitutive activity to the TSH receptor. In one case, a spartate 619 was substituted by glycine (D619G). In four adenomas, alanine 623 was replaced by valine (A623V). Both residues are located in the third intracellular loop. In one instance, aspartate 633 located in the sixth tra nsmembrane domain was replaced by tyrosine (D633Y). In this patient, one al lele also contained a change of aspartate 727 to glutamate (D727E). This su bstitution is thought to be a polymorphic variant of the wild-type but it h as also been associated with toxic multinodular goiters. Functional compari son of D727 with E727 did not reveal differences in basal or TSH-stimulated cyclic adenosine monophosphate (cAMP)-dependent luciferase activity in tra nsiently transfected cells. These results demonstrate a high prevalence of activating TSH receptor mutations in toxic adenomas in this small series fr om Brazil (similar to 86%). These findings are in agreement with reports fr om other countries with a marginal iodine intake but contrast with studies from regions with a high iodine intake where these mutations appear to be l ess prevalent.