title: The W520X mutation in the TSHR gene brings on subclinical hypothyroidism through an haploinsufficiency mechanism.
abstract: BACKGROUND
  TSHR is a G-protein-coupled seven transmembrane domain receptor that activates the two major signal transduction pathways: the Gαs/adenylate cyclase and the Gαq/11/phospholipase C pathways. Inactivating mutations in the TSHR gene have been demonstrated to be responsible for subclinical hypothyroidism, a disorder characterized by elevated serum TSH concentrations despite normal thyroid hormones levels.
  
  
  OBJECTIVE
  We identified in a child a nonsense mutation (W520X) in the third transmembrane domain of the TSHR that causes the lack of the C-terminus portion of the receptor. The functional significance of this variation was assessed in vitro.
  The W520X mutation was introduced into the pSVL vector containing the wild-type sequence of TSHR gene. Wild-type and mutated vectors were expressed in Chinese Hamster Ovary (CHO) cells, and cAMP, inositol phosphate (IP), immunofluorescence and FACS analyses were performed.
  
  
  RESULTS
  Transfection with pSVL-TSHR vector induced basal cAMP and IP production in the absence of TSH stimulation, indicating a constitutive activity for the TSHR. An impairment of receptor function was demonstrated by the observation that cells expressing the mutant TSHR exhibited a lower second messenger production with respect to the wild-type, despite a normal expression of the receptor at the cell surface.
  
  
  CONCLUSIONS
  The mechanism through which the W520X mutation exerts its effect is more likely haploinsufficiency rather than a dominant-negative effect. This could explain the phenotype of our patient, who has a hormonal pattern in the range of a mild subclinical hypothyroidism, without an overt disease phenotype.
authors.affiliation: Division of Pediatrics, Department of Health Sciences, University of Piemonte Orientale, Via Solaroli 17, 28100 Novara, Italy. stefania.moia@med.unipmn.it.
authors.forename: S
authors.initials: S
authors.lastname: Moia
authors.forename: M
authors.initials: M
authors.lastname: Godi
authors.forename: G E
authors.initials: GE
authors.lastname: Walker
authors.forename: M
authors.initials: M
authors.lastname: Roccio
authors.forename: P
authors.initials: P
authors.lastname: Agretti
authors.forename: M
authors.initials: M
authors.lastname: Tonacchera
authors.forename: R
authors.initials: R
authors.lastname: Berardi
authors.forename: S
authors.initials: S
authors.lastname: Bellone
authors.forename: F
authors.initials: F
authors.lastname: Prodam
authors.forename: M
authors.initials: M
authors.lastname: Giordano
authors.forename: G
authors.initials: G
authors.lastname: Bona
mesh_terms: D000818:Animals; D016466:CHO Cells; D002648:Child; D006224:Cricetinae; D003412:Cricetulus; D005260:Female; D057895:Haploinsufficiency; D006801:Humans; D007037:Hypothyroidism / Q000235:genetics*; D008297:Male; D011989:Receptors, Thyrotropin / Q000235:genetics* / Q000502:physiology
chemical_list: D011989:Receptors, Thyrotropin
references.citation: Trends Endocrinol Metab. 1998 May-Jun;9(4):133-40
references.pmid: 18406256
references.citation: PLoS One. 2010 Feb 26;5(2):e9449
references.pmid: 20195479
references.citation: Clin Endocrinol (Oxf). 2007 Nov;67(5):712-8
references.pmid: 17697008
references.citation: J Clin Invest. 2007 Sep;117(9):2399-407
references.pmid: 17694176
references.citation: Hum Mol Genet. 2005 Oct 15;14(20):2991-3002
references.pmid: 16135555
references.citation: Cell Mol Life Sci. 2001 Aug;58(9):1301-22
references.pmid: 11577986
references.citation: Naunyn Schmiedebergs Arch Pharmacol. 2002 Nov;366(5):381-416
references.pmid: 12382069
references.citation: Biochem J. 1987 Nov 1;247(3):519-24
references.pmid: 2827631
references.citation: Methods Mol Biol. 2008;448:109-37
references.pmid: 18370233
references.citation: Arch Dis Child. 1996 Sep;75(3):245-6
references.pmid: 8976668
references.citation: PLoS One. 2012;7(8):e42358
references.pmid: 22916127
references.citation: N Engl J Med. 1995 Jan 19;332(3):155-60
references.pmid: 7528344
references.citation: J Biol Chem. 1982 Dec 10;257(23):14035-40
references.pmid: 6128341
references.citation: J Clin Endocrinol Metab. 1997 Apr;82(4):1094-100
references.pmid: 9100579
references.citation: Thyroid. 2009 Jul;19(7):765-73
references.pmid: 19583488
references.citation: Clin Endocrinol (Oxf). 2004 Feb;60(2):220-7
references.pmid: 14725684
references.citation: J Clin Endocrinol Metab. 2002 Jun;87(6):2549-55
references.pmid: 12050212
references.citation: J Clin Invest. 2005 Aug;115(8):1972-83
references.pmid: 16075037
references.citation: Biochemistry. 1984 Sep 25;23(20):4519-25
references.pmid: 6149763
references.citation: Mol Endocrinol. 1994 Apr;8(4):498-509
references.pmid: 7914349
references.citation: J Clin Endocrinol Metab. 2009 May;94(5):1706-12
references.pmid: 19240155
references.citation: J Pediatr (Rio J). 2007 Nov;83(5 Suppl):S209-16
references.pmid: 18000629
references.citation: J Clin Endocrinol Metab. 1996 Dec;81(12):4229-35
references.pmid: 8954020
references.citation: J Clin Endocrinol Metab. 2012 Feb;97(2):E228-32
references.pmid: 22112806
references.citation: Clin Endocrinol (Oxf). 2009 Feb;70(2):335-8
references.pmid: 18727713
references.citation: J Clin Endocrinol Metab. 2009 Jul;94(7):2414-20
references.pmid: 19417038
references.citation: J Biol Chem. 1990 Dec 5;265(34):20970-5
references.pmid: 2250002
references.citation: Endocr Rev. 2000 Feb;21(1):90-113
references.pmid: 10696571
references.citation: JAMA. 2004 Jan 14;291(2):228-38
references.pmid: 14722150
references.citation: EMBO J. 2001 Sep 3;20(17):4987-97
references.pmid: 11532962
references.citation: Cell Mol Life Sci. 2010 Mar;67(5):677-700
references.pmid: 19859661
references.citation: Cell Mol Life Sci. 2011 Jan;68(1):159-67
references.pmid: 20652618
references.citation: Endocrinology. 2009 Feb;150(2):1043-50
references.pmid: 18927215
references.citation: Endocr Rev. 1992 Aug;13(3):596-611
references.pmid: 1425489
references.citation: J Clin Endocrinol Metab. 2007 Jul;92(7):2816-20
references.pmid: 17456567
references.citation: Mol Cell Endocrinol. 1987 Aug;52(3):273-8
references.pmid: 2820816
references.citation: J Clin Endocrinol Metab. 2009 Nov;94(11):4187-94
references.pmid: 19820021
references.citation: Clin Endocrinol (Oxf). 2005 Aug;63(2):146-51
references.pmid: 16060907