Prevalence of mutations in TSHR, GNAS, PRKAR1A and RAS genes in a large series of toxic thyroid adenomas from Galicia, an iodine-deficient area in NW Spain

doi:10.1530/EJE-08-0313

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Prevalence of mutations in TSHR, GNAS, PRKAR1A and RAS genes in a large series of toxic thyroid adenomas from Galicia, an iodine-deficient area in NW Spain

F Palos-Paz¹, O Perez-Guerra¹, J Cameselle-Teijeiro³, C Rueda-Chimeno⁵, F Barreiro-Morandeira⁴, J Lado-Abeal¹^,2, the Galician Group for the Study of Toxic Multinodular Goitre, D Araujo Vilar¹^,2, R Argueso⁷, O Barca¹, M Botana⁷, J M Cabezas-Agrícola², P Catalina⁶, L Dominguez Gerpe¹, T Fernandez⁹, A Mato⁸, A Nuño¹¹, M Penin¹⁰ and B Victoria¹

^¹ Unidade de Enfermedades Tiroideas e Metabólicas (UETeM)^² Endocrinology Section, Department of Medicine^³ , Pathology Department^⁴ Surgery Department, Complexo Hospitalario Universitary de Santiago (CHUS), University of Santiago de Compostela, Santiago de Compostela, 15705, Spain^⁵ , General Surgery Section^⁶ Endocrinology Section, Complexo Hospitalario de Pontevedra, Pontevedra, Spain^⁷ Endocrinology Section, Complexo Hospitalario Xeral-Calde, Lugo, Spain^⁸ Endocrinology Section, Complexo Hospitalario de Ourense, Ourense, Spain^⁹ Endocrinology Section, Complexo Hospitalario Universitario Juan-Canalejo, A Coruña, Spain^¹⁰ Endocrinology Section, Hospital Arquitecto Marcide, Ferrol, Spain^¹¹ General Surgery Section, Hospital do Meixoeiro, Complexo Hospitalario Universitario de Vigo, Vigo, Spain

(Correspondence should be addressed to J Lado-Abeal who is now at UETeM, Department of Medicine, School of Medicine, University of Santiago de Compostela, C/San Francisco sn 15705, Santiago de Compostela, Spain; Email: joaquin.lado{at}usc.es)

Objective: Toxic thyroid adenoma (TA) is a common cause of hyperthyroidism.Mutations in the TSH receptor (TSHR) gene, and less frequentlyin the adenylate cyclase-stimulating G alpha protein (GNAS)gene, are well established causes of TA in Europe. However,genetic causes of TA remain unknown in a small percentage ofcases. We report the first study to investigate mutations inTSHR, GNAS, protein kinase, cAMP-dependent, regulatory, typeI alpha (PRKAR1A) and RAS genes, in a large series of TA fromGalicia, an iodine-deficient region in NW Spain.

Design and methods: Eighty-five TA samples were obtained surgically from 77 hyperthyroidpatients, operated on for treatment of non-autoimmune toxicnodular goitre. After DNA extraction, all coding exons of TSHR,GNAS and PRKAR1A genes, and exons 2 and 3 of HRAS, KRAS andNRAS were amplified by PCR and sequenced. Previously unreportedmutants were cloned in expression vectors and their basal constitutiveactivities were determined by quantification of cAMP responseelement (CRE)-luciferase activity in CO7 cells transfected withwild-type and mutant plasmids.

Results: TSHR gene mutations were found in 52 (61.2%) samples, GNAS genemutations in 4 (4.71%) samples and no PRKAR1A or RAS mutationswere found. Only three previously unreported mutations werefound, two affecting the TSHR, A623F and I635V, and one affectingthe G-protein ${alpha}$ -subunit (Gs ${alpha}$ ), L203P. All mutant proteins showedhigher CRE-luciferase activity than their wild-type counterparts.

Conclusions: TA in a hyperthyroid population living in Galicia, a Spanishiodine-deficient region, harbours elevated frequencies of TSHRand GNAS mutations activating the cAMP pathway. However, thegenetic cause of TA was undetermined in 34% of the TA samples.